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There have been tremendous strides in the development of therapies for the treatment of NSCLC over the past decade. Nevertheless, the most common recurrent mutation driving the growth of NSCLC, mutant KRAS, accounting for ~25% of patients with advanced NSCLC, remains without an effective therapy. Thus, novel therapies are critically needed to improve the lives of patients suffering from KRAS-driven lung cancers. Protein phosphatase 2A (PP2A) is a serine threonine-directed tumor-suppressive phosphatase that is dysregulated and deactivated in cancer by multiple mechanisms including somatic mutation, suppression of individual subunits, increased expression of endogenous PP2A inhibitors and changes in post-translational modifications to the catalytic C subunit. Given its central role in regulating many key cellular processes and its role in human disease pathogenesis, many efforts have been developed to therapeutically target PP2A. Our group has developed first-in-class direct small-molecule activators of PP2A (SMAPs) by using the chemical scaffold of the FDA-approved tricyclic neuroleptics. We have used molecular modeling, hydroxyl radical footprinting and cryo-electron microscopy to structurally resolve the mechanism of action of SMAP-mediated growth suppression. Specifically, SMAPs protect the regulatory c-terminal tail of the catalytic subunit through changes in the methylation of the terminal leucine (L309) that induces the holoenzyme heterotrimerization and increased substrate-directed catalysis. SMAP treatment of KRAS-mutant lung cancer cells induced apoptosis and decreased the phosphorylation of PP2A targets including AKT and ERK. We found that treatment of xenograft, PDX, and GEMM mouse models of KRAS-mutant lung cancer cells with SMAPs resulted in marked tumor growth inhibition. Taken together, these studies demonstrate the potential of using SMAPs as an approach to treat KRAS-mutant NSCLC. We also established that PP2A activity defines the response of KRAS-mutant lung cancer cells across library of over 200 kinase inhibitors. In vivo studies using xenograft mouse models of KRAS-mutant lung adenocarcinoma demonstrated that SMAP in combination with MEK inhibitor resulted in tumor regression. Our studies have identified a combination of drugs that is effective in vivo for the treatment of KRAS-mutant lung cancer. Our strategy of reactivating endogenous PP2A may be applicable to the treatment of other KRAS-driven cancers and represents a first step into a new territory of developing small-molecule activators of tumor-suppressor proteins. Citation Format: Jaya Sangodkar, Jukka Westermarck, Derek Taylor, Goutham Narla. Therapeutic reactivation of the protein phosphatase 2A (PP2A) for the treatment of KRAS-driven cancers [abstract]. In: Proceedings of the AACR Special Conference on Targeting RAS-Driven Cancers; 2018 Dec 9-12; San Diego, CA. Philadelphia (PA): AACR; Mol Cancer Res 2020;18(5_Suppl):Abstract nr A48.

Raf/mitogen-activated protein/extracellular signal-regulated kinase kinase (MEK)1,2/extracellular signal-regulated kinase1,2 and MKK3,6/p38 mitogen-activated protein kinase pathways play an important role in cellular survival and apoptosis. The results of this study identify novel mechanisms to explain the opposing effects of these pathways in the regulation of apoptosis induction. Our results show that activation of p38 by adenoviral expression of MKK3b or arsenite treatment was followed by rapid dephosphorylation of MEK1,2 and subsequent apoptosis in human skin fibroblasts. Inhibition of p38 activity by SB203580 and adenoviral expression of dominant-negative forms of p38 potently inhibited MEK1,2 dephosphorylation and apoptosis. Strikingly, p38-mediated dephosphorylation of MEK1,2, was not detected in a series of transformed human cell lines. Taken together, we provide evidence for mechanisms unidentified previously that negatively regulates survival signaling during apoptosis induction. In addition, we show that in all transformed cell lines we have studied thus far, the function of this pathway is impaired.

Disease relapse from standard chemotherapy in acute myeloid leukemia (AML) is poorly understood. The importance of protein phosphatase 2A (PP2A) as an AML tumor suppressor is emerging. Therefore, here, we examined the potential role of endogenous PP2A inhibitor proteins as biomarkers predicting AML relapse in a standard patient population by using three independent patient materials: cohort1 (n = 80), cohort2 (n = 48) and The Cancer Genome Atlas Acute Myeloid Leukemia (TCGA LAML) dataset (n = 160). Out of the examined PP2A inhibitors (CIP2A, SET, PME1, ARPP19 and TIPRL), expression of ARPP19 mRNA was found to be independent of the current AML risk classification. Functionally, ARPP19 promoted AML cell viability and expression of oncoproteins MYC, CDK1, and CIP2A. Clinically, ARPP19 mRNA expression was significantly lower at diagnosis (p = 0.035) in patients whose disease did not relapse after standard chemotherapy. ARPP19 was an independent predictor for relapse both in univariable (p = 0.007) and in multivariable analyses (p = 0.0001) and gave additive information to EVI1 expression and risk group status (additive effect, p = 0.005). Low ARPP19 expression was also associated with better patient outcome in the TCGA LAML cohort (p = 0.019). In addition, in matched patient samples from diagnosis, remission and relapse phases, ARPP19 expression was associated with disease activity (p = 0.034), indicating its potential usefulness as a minimal residual disease (MRD) marker. Together, these data demonstrate the oncogenic function of ARPP19 in AML and its risk group independent role in predicting AML patient relapse tendency.

Neuroblastoma is a neural crest-derived childhood tumor of the peripheral nervous system in which MycN amplification is a hallmark of poor prognosis. Here we show that MycN is expressed together with phosphorylation-stabilizing factor CIP2A in regions of the neural plate destined to form the CNS, but MycN is excluded from the neighboring neural crest stem cell domain. Interestingly, ectopic expression of MycN or CIP2A in the neural crest domain biases cells toward CNS-like neural stem cells that express Sox2. Consistent with this, some forms of neuroblastoma have been shown to share transcriptional resemblance with CNS neural stem cells. As high MycN/CIP2A levels correlate with poor prognosis, we posit that a MycN/CIP2A-mediated cell-fate bias may reflect a possible mechanism underlying early priming of some aggressive forms of neuroblastoma. In contrast to MycN, its paralogue cMyc is normally expressed in the neural crest stem cell domain and typically is associated with better overall survival in clinical neuroblastoma, perhaps reflecting a more “normal” neural crest-like state. These data suggest that priming for some forms of aggressive neuroblastoma may occur before neural crest emigration from the CNS and well before sympathoadrenal specification.

Kinase inhibitor resistance constitutes a major unresolved clinical challenge in cancer. Furthermore, the role of serine/threonine phosphatase deregulation as a potential cause for resistance to kinase inhibitors has not been thoroughly addressed. We characterize protein phosphatase 2A (PP2A) activity as a global determinant of KRAS-mutant lung cancer cell resistance across a library of >200 kinase inhibitors. The results show that PP2A activity modulation alters cancer cell sensitivities to a large number of kinase inhibitors. Specifically, PP2A inhibition ablated mitogen-activated protein kinase kinase (MEK) inhibitor response through the collateral activation of AKT/mammalian target of rapamycin (mTOR) signaling. Combination of mTOR and MEK inhibitors induced cytotoxicity in PP2A-inhibited cells, but even this drug combination could not abrogate MYC up-regulation in PP2A-inhibited cells. Treatment with an orally bioavailable small-molecule activator of PP2A DT-061, in combination with the MEK inhibitor AZD6244, resulted in suppression of both p-AKT and MYC, as well as tumor regression in two KRAS-driven lung cancer mouse models. DT-061 therapy also abrogated MYC-driven tumorigenesis. These data demonstrate that PP2A deregulation drives MEK inhibitor resistance in KRAS-mutant cells. These results emphasize the need for better understanding of phosphatases as key modulators of cancer therapy responses.

Reactive astrogliosis and early synaptic degeneration are 2 characteristic hallmarks in Alzheimer's disease (AD) brains, but a direct link between the 2 events has not been established. Here, we show that cancerous inhibitor of PP2A (CIP2A), a cancerous protein with high expression level in astrocytes, is upregulated in patients with AD and 3xTg-AD transgenic mice. Overexpression of CIP2A in astrocytes through adeno-associated virus infection both in cultured cells and in mice brains results in activation of astrocytes, increased production of cytokines and Aβ, and synaptic degeneration indicated by decreased levels of synaptic proteins, spine loss, and impairment in long-term potentiation. As a result of synaptic degeneration, CIP2A overexpression in astrocytes in vivo induces significant deficits in visual episodic memory detected by novel objective recognition test and spatial memory detected by Morris water maze. We conclude that CIP2A-promoted astrogliosis induces synaptic degeneration and cognitive deficits in AD.

Therapies targeting tyrosine and serine/threonine kinases have raised enormous interest as potential cure for cancer patients in many common cancer types. However, except for the success story with BCR/ABL tyrosine kinase inhibitors in chronic myeloid leukemia (CML), critical review of results of a large number of clinical trials indicates that the clinical success with kinase inhibitors has been overall disappointing. These alarming results call for critical assessment of whether there is some fundamental flaw in the design of strategies to target phosphorylation-dependent oncogenic signaling for cancer therapy. This viewpoint debates on one potential, but thus far largely neglected, molecular explanation why inhibition of protein kinases is not sufficient for cancer cure. We note that the phosphorylation status, and thus the oncogenic potential of any given protein, is not regulated only by kinases, but rather by an intimate balance between kinases and their antagonist phosphatases. We further review the supporting functional evidence that for oncogenic transformation of human cells it is not enough to activate kinase signaling by activated kinases, if a group of counteracting tumor suppressor phosphatases is not inactivated. Based on these considerations, and a very recently emerged role of oncogenic function of a group of phosphatase inhibitor proteins as human oncoproteins, we propose that in order to efficiently inhibit phosphorylation-dependent signaling in cancer cells, and thus provide better therapeutic index, the kinase inhibitors should be combined with strategies to reactivate tumor suppressor phosphatases such as Protein Phosphatase 2A (PP2A).

High MYC expression is linked to proliferative activity in most normal tissues and in cancer. MYC also supports self-renewal and proliferation of many types of tissue progenitor cells. Cancerous inhibitor of PP2A (CIP2A) promotes MYC phosphorylation and activity during intestinal crypt regeneration in vivo and in various cancers. CIP2A also supports male germ cell proliferation in vivo. However, the role of MYC in normal germ cell proliferation and spermatogonial progenitor self-renewal is currently unclear. Here, we demonstrate that male germ cells are CIP2A-positive but lack detectable levels of MYC protein; whereas MYC is highly expressed in Leydig cells and peritubular myoid cells contributing thereby to the testicular stem cell niche. On the other hand, MYC was co-expressed with CIP2A in testicular cancers. These results demonstrate that CIP2A and MYC are spatially uncoupled in the regulation of spermatogenesis, but functional relationship between these two human oncoproteins is established during testicular cancer transformation. We propose that further analysis of mechanisms of MYC silencing in spermatogonial progenitors may reveal novel fundamental information relevant to understanding of MYC expression in cancer.

Systemic understanding of protein phosphatase 2A (PP2A)-regulated cellular processes is still at infancy. Here, we present mass-spectrometry analysis of phospho-targets (dephosphorylome) regulated by PP2A modulation. In addition to PP2A-regulated processes and targets, the data reveal important general concepts and rules related to PP2A-mediated phosphoregulation. These include the unidirectionality paradigm of regulation of phosphorylation, and differential spatial distribution of kinase-and phosphatase-dominated phosphotargets. Data also present first systemic analysis of targets of PP2A-modulating oncoproteins, CIP2A, PME-1, and SET; including targets via which PP2A may coordinately regulate activities of cancer drivers and tumor suppressors such as MYC or TP53. To validate functional utility of this dataset, PP2A dephosphorylome activity was correlated with cancer cell responses to over 300 drugs. Notably, we find that cancer therapy responses can be broadly classified based on PP2A dephosphorylome activity, both in quantitative and qualitative manner. In summary, our data characterize rules by which PP2A coordinate cancer cell phosphosignaling and drug responses. The results also may also direct the use of emerging pharmacological approaches for PP2A activity modulation in human diseases.

Glioblastoma multiforme (GBM) has a poor prognosis with an overall survival of 14-15 months after surgery, radiation and chemotherapy using temozolomide (TMZ). A major problem is that the tumors acquire resistance to therapy. In an effort to improve the therapeutic efficacy of TMZ, we performed a genome-wide RNA interference (RNAi) synthetic lethality screen to establish a functional gene signature for TMZ sensitivity in human GBM cells. We then queried the Connectivity Map database to search for drugs that would induce corresponding changes in gene expression. By this approach we identified several potential pharmacological sensitizers to TMZ, where the most potent drug was the established antipsychotic agent Thioridazine, which significantly improved TMZ sensitivity while not demonstrating any significant toxicity alone. Mechanistically, we show that the specific chemosensitizing effect of Thioridazine is mediated by impairing autophagy, thereby preventing adaptive metabolic alterations associated with TMZ resistance. Moreover, we demonstrate that Thioridazine inhibits late-stage autophagy by impairing fusion between autophagosomes and lysosomes. Finally, Thioridazine in combination with TMZ significantly inhibits brain tumor growth in vivo, demonstrating the potential clinical benefits of compounds targeting the autophagy-lysosome pathway. Our study emphasizes the feasibility of exploiting drug repurposing for the design of novel therapeutic strategies for GBM.

The aetiology and pathogenesis of salivary gland malignancies remain unknown. To reveal novel molecular factors behind the development of salivary gland cancer, we performed gene expression analyses from Smgb-Tag mouse salivary gland samples. The overall purpose was to apply these results for clinical use to find new approaches for both possible therapeutic targets and more accurate diagnostic tools. Smgb-Tag mouse strain, in which salivary neoplasms arise through a dysplastic phase in submandibular glands, was investigated using genome-wide microarray expression analysis, ingenuity pathway analysis, RT-PCR, and immunohistochemistry. Thirty-eight human salivary gland adenoid cystic carcinoma samples were investigated using immunohistochemistry for validation purposes. Our genome-wide study showed that Ppp2r1b, a PP2A subunit encoding tumor suppressor gene, is underexpressed in submandibular gland tumors of Smgb-Tag mice. mTOR signaling pathway was significantly enriched and mTOR linked PP2A subunit gene B55 gamma was significantly underexpressed in the analyses. Furthermore, parallel immunohistochemical analysis of three PP2A inhibitors demonstrated that two PP2A inhibitors, CIP2A and SET, are highly expressed in both dysplastic and adenocarcinomatous tumors of the Smgb-Tag mice. In addition, all 38 investigated human salivary adenoid cystic carcinoma samples stained positively for CIP2A and most for SET. Finally, p-S6 staining showed activation of mTOR pathway in human adenoid cystic carcinoma samples. Our results suggest that PP2A inhibition either via PP2A subunit underexpression or PP2A inhibitor overexpression play an important role in the formation of salivary gland malignancy, potentially due to mTOR signaling activation.

Radiotherapy is a mainstay for treatment of many human cancer types, including head and neck squamous cell carcinoma (HNSCC). Thereby, it is clinically very relevant to understand the mechanisms determining radioresistance. Here, we identify CIP2A as an Oct4 target gene and provide evidence that they co-operate in radioresistance. Oct4 positively regulates CIP2A expression both in testicular cancer cell lines as well as in embryonic stem cells. To expand the relevance of these findings we show that Oct4 and CIP2A are co-expressed in CD24 positive side-population of patient-derived HNSCC cell lines. Most importantly, all Oct4 positive HNSCC patient samples were CIP2A positive and this double positivity was linked to poor differentiation level, and predicted for decreased patient survival among radiotherapy treated HNSCC patients. Oct4 and CIP2A expression was also linked with increased aggressiveness and radioresistancy in HNSCC cell lines. Together we demonstrate that CIP2A is a novel Oct4 target gene in stem cells and in human cancer cell lines. Clinically these results suggest that diagnostic evaluation of HNSCC tumors for Oct4 or Oct4/CIP2A positivity might help to predict HNSCC tumor radioresistancy. These results also identify both Oct4 and CIP2A as potential targets for radiosensitation.

Preoperative (chemo)radiotherapy, (C)RT, is an essential part of the treatment of rectal cancer patients, but tumor response to this therapy among patients is variable. Thus far, there are no clinical biomarkers that could be used to predict response to (C)RT or to stratify patients into different preoperative treatment groups according to their prognosis. Overexpression of cancerous inhibitor of protein phosphatase 2A (CIP2A) has been demonstrated in several cancers and is frequently associated with reduced survival. Recently, high CIP2A expression has also been indicated to contribute to radioresistance in head and neck squamous cell carcinoma, but few studies have examined the connection between CIP2A and radiation response regarding other malignancies. We have evaluated CIP2A protein expression levels in relation to tumor regression after preoperative (C)RT and survival of rectal adenocarcinoma patients. The effects of CIP2A knockdown by siRNA on cell survival were further investigated in colorectal cancer cells exposed to radiation. Patients with low‐CIP2A‐expressing tumors had more frequently moderate or excellent response to long‐course (C)RT than patients with high‐CIP2A‐expressing tumors. They also had higher 36‐month disease‐specific survival (DSS) rate in categorical analysis. In the multivariate analysis, low CIP2A expression level remained as an independent predictive factor for increased DSS. Suppression of CIP2A transcription by siRNA was found to sensitize colorectal cancer cells to irradiation and decrease their survival in vitro. In conclusion, these results suggest that by contributing to radiosensitivity of cancer cells, low CIP2A protein expression level associates with a favorable response to long‐course (C)RT in rectal cancer patients.

Propagation of transient signals requires coordinated suppression of antagonistic phosphatase activity. Protein phosphatase 2A (PP2A) is a broad specificity serine/threonine phosphatase that functions as an antagonist of many signaling pathways associated with growth and proliferation, and endogenous inhibitory mechanisms suppress PP2A activity in response to mitogenic stimuli. These inhibitory mechanisms, including expression and activation of endogenous inhibitor proteins and phosphoregulation of PP2A subunits, are also engaged by aberrant constitutive activation of mitogenic pathways in cancer. Inhibition of PP2A activity has been shown to promote malignant transformation and endogenous inhibitory mechanisms of PP2A have been associated with malignant progression and prognosis in a wide range of cancers. Despite existence of recurrent mutations and other genetic and gene regulatory alterationsin PP2A genes, they collectively appear at relatively low frequency, and in only some cancer types. The non-genomic inhibition of PP2A activity by increased expression of endogenous PP2A inhibitor proteins greatly exceeds the frequency of genetic mutations of PP2A genes in human cancers. This feature makes PP2A an untypical tumor suppressor, and may have influenced its recognition as one of the critical human cell transformation mechanisms. We propose that non-genetic inhibition is the dominant mechanism causing loss of PP2A tumor suppressor function in cancer cells, possibly because these mechanisms do not elicit genomic instability associated with genetic loss of function of specific PP2A subunits.

Kaposi's sarcoma herpesvirus (KSHV)-encoded v-cyclin, a homolog of cellular cyclin D2, activates cellular CDK6, promotes G1-S transition of the cell cycle, induces DNA damage, apoptosis, autophagy and is reported to have oncogenic potential. Here we show that in vivo expression of v-cyclin in the B- and T-cell lymphocyte compartments results in a markedly low survival due to high penetrance of early-onset T-cell lymphoma and pancarditis. The v-cyclin transgenic mice have smaller pre-tumorigenic lymphoid organs, showing decreased cellularity, and increased proliferation and apoptosis. Furthermore, v-cyclin expression resulted in decreased amounts of CD3-expressing mature T-cells in the secondary lymphoid organs concurrent with alterations in the T-cell subpopulations of the thymus. This suggests that v-cyclin interferes with normal T-cell development. As the Notch pathway is recognized for its role in both T-cell development and lymphoma initiation, we addressed the role of Notch in the v-cyclin-induced alterations. Fittingly, we demonstrate induction of Notch3 and Hes1 in the pre-tumorigenic thymi and lymphomas of v-cyclin expressing mice, and show that lymphoma growth and viability are dependent on activated Notch signaling. Notch3 transcription and growth of the lymphomas was dependent on CDK6, as determined by silencing of CDK6 expression or chemical inhibition, respectively. Our work here reveals a viral cyclin-CDK6 complex as an upstream regulator of Notch receptor, suggesting that cyclins can play a role in the initiation of Notch-dependent lymphomagenesis.

Induction of terminal proliferation arrest, senescence, is important for in vivo tumor-suppressive function of p53. Moreover, p53-mutant cells are highly resistant to senescence induction by either oncogenic signaling during cellular transformation or in response to different therapies. Senescence resistance in p53-mutant cells has been attributed mostly to inhibition of the checkpoint function of p53 in response to senescence-inducing stress signals. Here, we review very recent evidence that offers an alternative explanation for senescence resistance in p53-defective cancer cells: p21-mediated E2F1 expression. We discuss the potential relevance of these findings for senescence-inducing therapies and highlight cyclin-dependent kinases (CDK) and mechanisms downstream of retinoblastoma protein (RB) as prospective prosenescence therapeutic targets. In particular, we discuss recent findings indicating an important role for the E2F1–CIP2A feedback loop in causing senescence resistance in p53-compromised cancer cells. We further propose that targeting of the E2F1–CIP2A feedback loop could provide a prosenescence therapeutic approach that is effective in both p53-deficient and RB-deficient cancer cells, which together constitute the great majority of all cancer cells. Diagnostic evaluation of the described senescence resistance mechanisms in human tumors might also be informative for patient stratification for already existing therapies. Clin Cancer Res; 20(14); 3644–50. ©2014 AACR.

Neeraj Prabhakar,1,2 Jixi Zhang,3 Diti Desai,1 Eudald Casals,1 Tina Gulin-Sarfraz,1 Tuomas Näreoja,2,4 Jukka Westermarck,5,6 Jessica M Rosenholm1 1Pharmaceutical Sciences Laboratory, Faculty of Science and Engineering, Åbo Akademi University, 2Laboratory of Biophysics, Faculty of Medicine, University of Turku, Turku, Finland; 3College of Bioengineering, ChongqingUniversity, Chongqing, People’s Republic of China; 4Department of Neuroscience, Karolinska Institute, Stockholm, Sweden; 5Centre for Biotechnology, University of Turku and Åbo Akademi, 6Department of Pathology, University of Turku, Turku, Finland Abstract: Small interfering RNA (siRNA) is a highly potent drug in gene-based therapy with the challenge being to deliver it in a sustained manner. The combination of mesoporous silica nanoparticles (MSNs) and polycations in the confined pore space allows for incorporation and controlled release of therapeutic siRNA payloads. We hereby constructed MSNs with expanded mesopores and pore-surface-hyperbranched poly(ethyleneimine) (PEI) tethered with redox-cleavable linkers that could carry a high payload of siRNA (120mg·g-1). The developed nanocarriers were efficiently taken up by cancer cells and were subsequently able to escape to the cytoplasm from the endosomes, most likely owing to the integrated PEI. Triggered by the intracellular redox conditions, the siRNA was sustainably released inside the cells over a period of several days. Functionality of siRNAs was demonstrated by using cell-killing siRNA as cargo. Despite not being the aim of the developed system, in vitro experiments using cell-killing siRNAs showed that the efficacy of siRNA transfection was comparable to the commercial in vitro transfection agent Lipofectamine. Consequently, the developed MSN-based delivery system offers a potential approach to hybrid nanocarriers for more efficient and long-term siRNA delivery and, in a longer perspective, in vivo gene silencing for RNA interference (RNAi) therapy. Keywords: mesoporous silica nanoparticles, RNAi therapy, siRNA delivery, stimuli-responsive drug release, hybrid nanocarriers

Reactivation of tumor suppressor phosphatases may provide entirely novel opportunities for cancer therapy. Here, we discover clinically relevant functional co-operation between loss of activities of two human tumor suppressor phosphatases, PTEN, and PP2A. Analysis of prostate cancer tissue microarray material consisting of 358 patients treated primarily with radical prostatectomy revealed that overexpression of PP2A inhibitor protein PME-1 associates with significantly shorter time to therapy relapse in patients with PTEN-deficient PrCa. Further, PP2A inhibition by PME-1 overexpression in PTEN-deficient cell models inhibits apoptosis induction in anchorage-independent conditions (anoikis). PP2A reactivation by small molecules (SMAPs) was also found to inhibit viability of PTEN-deficient PrCa cells. Importantly, rather than regulating the well-known PP2A target pathways, PME-1 was found to physically associate with, and to regulate deformability of the nuclear lamina in PrCa cells. Mass spectrometry phosphoproteomics analysis identified several PME-1-regulated nuclear lamina constituents, and PME-1 deficient cells with compromised nuclear lamina were particularly vulnerable to apoptosis induction by mechanical stress. As a direct molecular target, Lamin A/C phosphorylation was found to be protected by PME-1-mediated PP2A inhibition under anoikis-inducing conditions. PME-1 inhibition in PrCa cells resulted in increased apoptosis in an in ovo tumor model, and PME-1-depleted cells had compromised long-term survival in zebrafish circulation. In summary we discover that PP2A reactivation by PME-1 targeting sensitizes PTEN-deficient PrCa cells to anoikis. Clinically, the results identify PME-1 as a novel candidate biomarker for increased relapse risk in PTEN-deficient PrCa, and indicate pharmacological PP2A activation as a novel potential therapeutic approach against circulating prostate cancer cells. At the general level, the results clearly emphasize the need for better understanding of phosphatases as key modulators of cancer progression. Citation Format: Christian Rupp, Aleksi Isomursu, Anna Aakula, Andrew Erickson, Song-Ping Li, Amanpreet Kaur, Pragya Shah, Yuba R. Pokharel, Lloyd Trottman, Jan Lammerding, Antti Rannikko, Pekka Taimen, Tuomas Mirtti, Ilkka Paatero, Johanna Ivaska, Jukka K. Westermarck. Combined inhibition of tumor suppressors PTEN and PP2A drives anoikis resistance and is associated with therapy relapse in prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 3486.

Background. Cancer clinical trials seek to determine the safety and efficacy of new treatment modalities. Due to the impact of cancer clinical trials on health care, economic activity and cancer research, many large-scale efforts have been undertaken around the world to create clinical trial-facilitating environments. The Nordic countries (Norway, Sweden, Denmark, Iceland and Finland) are among the countries with the highest 5-year net survival for cancer patients, which is a testimony to their high standard of early diagnosis, cancer care and functional public health care system. However, the contribution of the Nordic countries to the international cancer clinical trial landscape has remained largely unexplored. Methods. We mined www.clinicaltrials.gov for cancer clinical trials starting between the 1st of January 2000 and the 31st of December 2017. Trials were designated Cancer Clinical Trials if the trial indication contained one of 17 cancer-specific words (e.g. “cancer”, “neoplasia”, “malignancy”). The trial databases of all European Free Trade Association (EFTA; the EU, Switzerland, Norway, Iceland and Liechtenstein) countries was downloaded and subsequently mined for specific terms, i.e. cancer indication, study location and intervention type. A trial was counted for every country with a study center and thus the same trial can be counted for multiple countries. Results. Here, we present an analysis of the cancer clinical trial landscape in the EFTA and the Nordic countries. While in the EFTA the number of cancer clinical trials strongly increased from 2000-2014, that number has not grown between 2014 and 2017, unlike in the USA or China. Comparison of the number of cancer clinical trials in different EFTA countries showed strong variation, and indicated that Sweden, Finland and Norway have been involved in far fewer cancer clinical trials than expected for countries of their economic size or socio-economic status. Denmark is the only Nordic country to perform much better than the EFTA average. Discussion. We show that despite a high standard of care, most Nordic countries are lagging behind in cancer clinical trials compared to countries of similar socio-economic stature. This low number of cancer clinical trials may slow down uptake of new cancer drugs to routine care, prevent patients from receiving state-of-the-art therapies, increase health care costs, and inhibit scientific progress and commercial activity. We provide recommended actions to increase the number of cancer clinical trials, with special focus on Finland as part of the national growth strategy in the health sector. Note: This abstract was not presented at the meeting. Citation Format: Jeroen Pouwels, Sebastian Soidinsalo, Heidi Haikala, Panu Jaakola, Tarja Jalava, Heikki Joensuu, Mika Mustonen, Pasi Korhonen, Panu Kovanen, Anne Lehtonen, Johanna Mattson, Outi Monni, Jukka Westermarck, Juha Klefström. The cancer clinical trial landscape in the EU and the Nordic countries [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr LB-251.

Protein phosphatase 2A (PP2A) complexes function as tumor suppressors by inhibiting the activity of several critical oncogenic signaling pathways. Consequently, inhibition of the PP2A phosphatase activity is one of many prerequisites for the transformation of normal human cells into cancerous cells. However, mechanisms for PP2A inactivation in human cancers are poorly understood. The aberrant expression of cancerous inhibitor of protein phosphatase 2A (CIP2A), a recently identified endogenous PP2A inhibitor in malignant cells, is one such mechanism. Various independent studies have validated CIP2A's role in promoting tumor growth and resistance to apoptosis and senescence-inducing therapies. Notably, high CIP2A expression predicts poor patient prognosis in several human cancer types. Among the oncogenic proteins dephosphorylated by PP2A, the MYC oncoprotein, which is phosphorylated at serine 62, has surfaced as a marker for the oncogenic activity of CIP2A. The positive-feedback loop between CIP2A and MYC augments the activity of MYC in cancer cells. In addition, CIP2A promotes the phosphorylation and activity of additional oncoproteins, including E2F1 and AKT. However, CIP2A is not essential for normal mouse growth and development. These findings indicate that CIP2A is a novel anticancer target based on PP2A reactivation and inhibition of the oncogenic activity of its downstream effectors. The potential approaches and feasibility of targeting CIP2A are discussed here. Cancer Res; 73(22); 6548–53. ©2013 AACR.

Checkpoint kinase Chk1 is constitutively active in many cancer cell types and new generation Chk1 inhibitors show marked antitumor activity as single agents. Here we present a hitherto unrecognized mechanism that contributes to the response of cancer cells to Chk1-targeted therapy. Inhibiting chronic Chk1 activity in cancer cells induced the tumor suppressor activity of protein phosphatase protein phosphatase 2A (PP2A), which by dephosphorylating MYC serine 62, inhibited MYC activity and impaired cancer cell survival. Mechanistic investigations revealed that Chk1 inhibition activated PP2A by decreasing the transcription of cancerous inhibitor of PP2A (CIP2A), a chief inhibitor of PP2A activity. Inhibition of cancer cell clonogenicity by Chk1 inhibition could be rescued in vitro either by exogenous expression of CIP2A or by blocking the CIP2A-regulated PP2A complex. Chk1-mediated CIP2A regulation was extended in tumor models dependent on either Chk1 or CIP2A. The clinical relevance of CIP2A as a Chk1 effector protein was validated in several human cancer types, including neuroblastoma, where CIP2A was identified as an NMYC-independent prognostic factor. Because the Chk1–CIP2A–PP2A pathway is driven by DNA-PK activity, functioning regardless of p53 or ATM/ATR status, our results offer explanative power for understanding how Chk1 inhibitors mediate single-agent anticancer efficacy. Furthermore, they define CIP2A-PP2A status in cancer cells as a pharmacodynamic marker for their response to Chk1-targeted therapy. Cancer Res; 73(22); 6757–69. ©2013 AACR.

Senescence induction contributes to cancer therapy responses and is crucial for p53-mediated tumor suppression. However, whether p53 inactivation actively suppresses senescence induction has been unclear. Here, we show that E2F1 overexpression, due to p53 or p21 inactivation, promotes expression of human oncoprotein CIP2A, which in turn, by inhibiting PP2A activity, increases stabilizing serine 364 phosphorylation of E2F1. Several lines of evidence show that increased activity of E2F1-CIP2A feedback renders breast cancer cells resistant to senescence induction. Importantly, mammary tumorigenesis is impaired in a CIP2A-deficient mouse model, and CIP2A-deficient tumors display markers of senescence induction. Moreover, high CIP2A expression predicts for poor prognosis in a subgroup of patients with breast cancer treated with senescence-inducing chemotherapy. Together, these results implicate the E2F1-CIP2A feedback loop as a key determinant of breast cancer cell sensitivity to senescence induction. This feedback loop also constitutes a promising prosenescence target for therapy of cancers with an inactivated p53–p21 pathway. Significance: It has been recently realized that most currently used chemotherapies exert their therapeutic effect at least partly by induction of terminal cell arrest, senescence. However, the mechanisms by which cell-intrinsic senescence sensitivity is determined are poorly understood. Results of this study identify the E2F1-CIP2A positive feedback loop as a key determinant of breast cancer cell sensitivity to senescence and growth arrest induction. Our data also indicate that this newly characterized interplay between 2 frequently overexpressed oncoproteins constitutes a promising prosenescence target for therapy of cancers with inactivated p53 and p21. Finally, these results may also facilitate novel stratification strategies for selection of patients to receive senescence-inducing cancer therapies. Cancer Discov; 3(2); 182–97. ©2013 AACR. This article is highlighted in the In This Issue feature, p. 125

Protein-protein interactions drive biological processes. They are critical for all intra- and extracellular functions, and the technologies to analyze them are widely applied throughout the various fields of biological sciences. This study takes an in-depth view of some common principles of cellular regulation and provides a detailed account of approaches required to comprehensively map signaling protein-protein interactions in any particular cellular system or condition. We provide a critical review of the benefits and disadvantages of the yeast two-hybrid method and affinity purification coupled with mass spectrometric procedures for identification of signaling protein-protein interactions. In particular, we emphasize the quantitative and qualitative differences between tandem affinity and one-step purification (such as FLAG and Strep tag) methods. Although applicable to all types of interaction studies, a special section is devoted in this review to aspects that should be considered when attempting to identify signaling protein interactions that often are transient and weak by nature. Finally, we discuss shotgun and quantitative information that can be gleaned by MS-coupled methods for analysis of multiprotein complexes.

The AP-1 transcription factor c-Jun is essential for stress-induced apoptosis in several models. The apoptosis-antagonizing transcription factor is a novel nucleolar stress sensor, which is required as a cofactor for c-Jun–mediated apoptosis., The AP-1 transcription factor c-Jun has been shown to be essential for stress-induced apoptosis in several models. However, the molecular mechanisms underlying the proapoptotic activity of c-Jun are poorly understood. We identify the apoptosis-antagonizing transcription factor (AATF) as a novel nucleolar stress sensor, which is required as a cofactor for c-Jun–mediated apoptosis. Overexpression or down-regulation of AATF expression levels led to a respective increase or decrease in the amount of activated and phosphorylated c-Jun with a proportional alteration in the induction levels of the proapoptotic c-Jun target genes FasL and TNF-α. Accordingly, AATF promoted commitment of ultraviolet (UV)-irradiated cells to c-Jun-dependent apoptosis. Whereas AATF overexpression potentiated UV-induced apoptosis in wild-type cells, c-Jun–deficient mouse embryonic fibroblasts were resistant to AATF-mediated apoptosis induction. Furthermore, AATF mutants defective in c-Jun binding were also defective in inducing AP-1 activity and c-Jun–mediated apoptosis. UV irradiation induced a translocation of AATF from the nucleolus to the nucleus, thereby enabling its physical association to c-Jun. Analysis of AATF deletion mutants revealed that the AATF domains required for compartmentalization, c-Jun binding, and enhancement of c-Jun transcriptional activity were all also required to induce c-Jun–dependent apoptosis. These results identify AATF as a nucleolar-confined c-Jun cofactor whose expression levels and spatial distribution determine the stress-induced activity of c-Jun and the levels of c-Jun–mediated apoptosis.

Protein phosphatase 2A (PP2A) complexes counteract many oncogenic kinase pathways. In cancer cells, PP2A function can be compromised by several mechanisms, including sporadic mutations in its scaffolding A and regulatory B subunits or more frequently through overexpression of cellular PP2A inhibitors. Here, we identify a novel genetic mechanism by which PP2A function is recurrently affected in human cancer, involving haploinsufficiency of

Ribosome biogenesis regulates animal growth and is controlled by nutrient-responsive mTOR signaling. How ribosome biogenesis is regulated during the developmental growth of animals and how nutrient-responsive signaling adjusts ribosome biogenesis in this setting have remained insufficiently understood. We uncover PWP1 as a chromatin-associated regulator of developmental growth with a conserved role in RNA polymerase I (Pol I)-mediated rRNA transcription. We further observed that PWP1 epigenetically maintains the rDNA loci in a transcription-competent state. PWP1 responds to nutrition in Drosophila larvae via mTOR signaling through gene expression and phosphorylation, which controls the nucleolar localization of dPWP1. Our data further imply that dPWP1 acts synergistically with mTOR signaling to regulate the nucleolar localization of TFIIH, a known elongation factor of Pol I. Ribosome biogenesis is often deregulated in cancer, and we demonstrate that high PWP1 levels in human head and neck squamous cell carcinoma tumors are associated with poor prognosis.

Protein phosphatase 2A (PP2A) plays a major role in maintaining cellular signaling homeostasis by dephosphorylation of a variety of signaling proteins and acts as a tumor suppressor. Protein phosphatase methylesterase-1 (PME-1) negatively regulates PP2A activity by highly complex mechanisms that are reviewed here. Importantly, recent studies have shown that PME-1 promotes oncogenic MAPK/ERK and AKT pathway activities in various cancer types. In human glioma, high PME-1 expression correlates with tumor progression and kinase inhibitor resistance. We discuss the emerging cancer-associated function of PME-1 and its potential clinical relevance.

Glioblastoma multiforme lacks effective therapy options. Although deregulated kinase pathways are drivers of malignant progression in glioblastoma multiforme, glioma cells exhibit intrinsic resistance toward many kinase inhibitors, and the molecular basis of this resistance remains poorly understood. Here, we show that overexpression of the protein phosphatase 2A (PP2A) inhibitor protein PME-1 drives resistance of glioma cells to various multikinase inhibitors. The PME-1–elicited resistance was dependent on specific PP2A complexes and was mediated by a decrease in cytoplasmic HDAC4 activity. Importantly, both PME-1 and HDAC4 associated with human glioma progression, supporting clinical relevance of the identified mechanism. Synthetic lethality induced by both PME-1 and HDAC4 inhibition was dependent on the coexpression of proapoptotic protein BAD. Thus, PME-1–mediated PP2A inhibition is a novel mechanistic explanation for multikinase inhibitor resistance in glioma cells. Clinically, these results may inform patient stratification strategies for future clinical trials with selected kinase inhibitors in glioblastoma multiforme. Cancer Res; 76(23); 7001–11. ©2016 AACR.

High MYC expression is linked to proliferative activity in most normal tissues and in cancer. MYC also supports self-renewal and proliferation of many types of tissue progenitor cells. Cancerous inhibitor of PP2A (CIP2A) promotes MYC phosphorylation and activity during intestinal crypt regeneration in vivo and in various cancers. CIP2A also supports male germ cell proliferation in vivo. However, the role of MYC in normal germ cell proliferation and spermatogonial progenitor self-renewal is currently unclear. Here, we demonstrate that male germ cells are CIP2A-positive but lack detectable levels of MYC protein; whereas MYC is highly expressed in Leydig cells and peritubular myoid cells contributing thereby to the testicular stem cell niche. On the other hand, MYC was co-expressed with CIP2A in testicular cancers. These results demonstrate that CIP2A and MYC are spatially uncoupled in the regulation of spermatogenesis, but functional relationship between these two human oncoproteins is established during testicular cancer transformation. We propose that further analysis of mechanisms of MYC silencing in spermatogonial progenitors may reveal novel fundamental information relevant to understanding of MYC expression in cancer.

The oncoprotein Cancerous Inhibitor of Protein Phosphatase 2A ( CIP2A) is overexpressed in most malignancies and is an obvious candidate target protein for future cancer therapies. However, the physiological importance of CIP2A-mediated PP2A inhibition is largely unknown. As PP2A regulates immune responses, we investigated the role of CIP2A in normal immune system development and during immune response in vivo. We show that CIP2A-deficient mice (CIP2A(HOZ)) present a normal immune system development and function in unchallenged conditions. However when challenged with Listeria monocytogenes, CIP2A(HOZ) mice display an impaired adaptive immune response that is combined with decreased frequency of both CD4(+) T-cells and CD8(+) effector T-cells. Importantly, the cell autonomous effect of CIP2A deficiency for T-cell activation was confirmed. Induction of CIP2A expression during T-cell activation was dependent on Zap70 activity. Thus, we reveal CIP2A as a hitherto unrecognized mediator of T-cell activation during adaptive immune response. These results also reveal CIP2A(HOZ) as a possible novel mouse model for studying the role of PP2A activity in immune regulation. On the other hand, the results also indicate that CIP2A targeting cancer therapies would not cause serious immunological side-effects.

Recent reports have called into question the reproducibility, validity and translatability of the preclinical animal studies due to limitations in their experimental design and statistical analysis. To this end, we implemented a matching-based modelling approach for optimal intervention group allocation, randomization and power calculations, which takes full account of the complex animal characteristics at baseline prior to interventions. In prostate cancer xenograft studies, the method effectively normalized the confounding baseline variability, and resulted in animal allocations which were supported by RNA-seq profiling of the individual tumours. The matching information increased the statistical power to detect true treatment effects at smaller sample sizes in two castration-resistant prostate cancer models, thereby leading to saving of both animal lives and research costs. The novel modelling approach and its open-source and web-based software implementations enable the researchers to conduct adequately-powered and fully-blinded preclinical intervention studies, with the aim to accelerate the discovery of new therapeutic interventions.

Protein phosphatase 2A (PP2A) is a critical human tumor-suppressor complex. A recently characterized PP2A inhibitor protein, namely cancerous inhibitor of PP2A (CIP2A), has been found to be overexpressed at a high frequency in most of the human cancer types. However, our understanding of gene expression programs regulated by CIP2A is almost absent. Moreover, clinical relevance of the CIP2A-regulated transcriptome has not been addressed thus far. Here, we report a high-confidence transcriptional signature regulated by CIP2A. Bioinformatic pathway analysis of the CIP2A signature revealed that CIP2A regulates several MYC-dependent and MYC-independent gene programs. With regard to MYC-independent signaling, JNK2 expression and transwell migration were inhibited by CIP2A depletion, whereas MYC depletion did not affect either of these phenotypes. Instead, depletion of either CIP2A or MYC inhibited cancer cell colony growth with statistically indistinguishable efficiency. Moreover, CIP2A depletion was shown to regulate the expression of several established MYC target genes, out of which most were MYC-repressed genes. CIP2A small-interfering RNA-elicited inhibition of colony growth or activation of MYC-repressed genes was reversed at large by concomitant PP2A inhibition. Finally, the CIP2A signature was shown to cluster with basal-type and human epidermal growth factor receptor (HER)2-positive (HER2+) breast cancer signatures. Accordingly, CIP2A protein expression was significantly associated with basal-like (P=0.0014) and HER2+ (P0.0001) breast cancers. CIP2A expression also associated with MYC gene amplification (P0.001). Taken together, identification of CIP2A-driven transcriptional signature, and especially novel MYC-independent signaling programs regulated by CIP2A, provides important resource for understanding CIP2A's role as a clinically relevant human oncoprotein. With regard to MYC, these results both validate CIP2A's role in regulating MYC-mediated gene expression and provide a plausible novel explanation for the high MYC activity in basal-like and HER2+ breast cancers.

Ovarian cancer is the sixth most common cancer in women and the second most common gynaecological malignancy in the world. Incidence rates have increased slowly in developed countries, with an incidence rate of 9 per 100 000 (Parkin et al, 2005). Five-year survival is less than 50% for ovarian cancer patients, as most cases are found at an advanced stage (Jemal et al, 2008). The standard treatment is extensive surgery usually followed by chemotherapy. Ovarian surface epithelium and tubal tissue have been proposed to represent the origins of ovarian cancer, of which the most frequent subtype is serous carcinoma (Dubeau, 2008). Ovarian cancer can be divided into two subgroups: type I tumours that are slowly developing low-grade serous, mucinous, endometriod, and clear-cell carcinomas, whereas type II tumours are rapidly progressing high-grade serous or undifferentiated carcinomas (Levanon et al, 2008). Precursor lesions of the type II ovarian cancers are poorly understood and prognosis is poor. This type of ovarian tumours also more commonly harbour mutations in the p53 gene and show a high proliferation index (Shih and Kurman, 2004; Landen et al, 2008). Cancerous inhibitor of protein phosphatase 2A (CIP2A) is a human oncoprotein overexpressed in head and neck squamous cell carcinoma and in colon cancer (Junttila and Westermarck, 2007; Junttila et al, 2007; Mumby, 2007). CIP2A interacts with PP2A and prevents PP2A-mediated dephosphorylation of the oncogene c-Myc (Junttila et al, 2007). CIP2A is a marker of reduced overall survival in certain subgroups of gastric cancer (Khanna et al, 2009), and its expression associates with high grade and lymph node metastasis in breast cancer (Come et al, 2009). Its role in ovarian carcinogenesis is, however, unknown. To address the role of CIP2A in ovarian cancer, we investigated the association of CIP2A protein expression to clinicopathological variables and molecular markers in serous ovarian cancer.

Introduction Basal-like breast cancer (BLBC) is an aggressive breast cancer molecular subtype, and it lacks efficient therapy options. Expression levels of oncoprotein CIP2A are increased in BLBC as compared to other breast cancer subtypes. Our results demonstrate that high CIP2A expression significantly predicts poor patient survival in triple negative breast cancer, that constitutes a major subset of BLBC. CIP2A inhibition also significantly impairs tumour growth of human BLBC xenografts. Previously, we have shown that CIP2A promotes breast cancer by inhibiting senescent growth arrest (Laine et al. Cancer Discov 2013). Induction of senescence and senescence associated secretome (SASP) has been shown to alter function of tumour infiltrating immune cells. Based on this we hypothesise that in addition to effects of CIP2A-mediated senescence inhibition to tumour cell-intrinsic mechanisms, it may impact infiltrating immune cells and thus therapy response. Material and methods To investigate the role of CIP2A in BLBC a carcinogen DMBA-induced tumour formation approach in Cip2a-/- mouse model was applied. In order to test our hypothesis about the effect of CIP2A-targeted senescence in immune cells we have set up mouse mammary tumour cell and organoid cultures from a spontaneous BLBC genetically engineered mouse model K14Cre;Brca1fl/fl;Tp53fl/fl. These cultures are genetically manipulated by CRISPR/Cas9 system to knock out CIP2A both prior to transplantation into recipient mice and in established tumours. To validate the in vivo findings we are using several different human breast cancer patient cohorts. Results and discussions Our results demonstrate that CIP2A-deficient mice are severely impaired in a formation of DMBA-induced basal-like mammary tumours. Together with the clinical data, these results suggest that CIP2A is a novel driver oncoprotein, and a potential therapeutic target, in human BLBC. In addition, we have validated the tumour cell-intrinsic role of CIP2A in K14Cre;Brca1fl/fl;Tp53fl/fl BLBC mouse model as loss of CIP2A induces senescent growth arrest in mammary gland tumour cells in vitro. Currently, we are studying the interplay between the immune system and CIP2A-inhibited tumours in vitro and in vivo. Conclusion Overall, this study will address feasibility of CIP2A targeting as a novel approach to combat basal-like breast cancer. Results of this project will also enhance our general understanding of cross-talk between senescent cancer cells and the tumour environment in this clinically challenging human cancer type.

The transforming growth factor-beta (TGF-beta) maintains epithelial homeostasis and suppresses early tumor formation, but paradoxically at later stages of tumor progression, TGF-beta promotes malignancy. TGF-beta activates phosphorylation of Smad2 and -3 effectors. Smad2 and -3 are known to have different functions, but differential regulation of their phosphorylation has not been described. Here we show that upon hypoxia, the TGF-beta-induced phosphorylation of Smad3 was inhibited, although Smad2 remained phosphorylated. The inhibition of Smad3 phosphorylation was not due to TGF-beta receptor inactivation. We show that Smad3 was dephosphorylated by PP2A (protein phosphatase 2A) specifically under hypoxic conditions. The hypoxic Smad3 dephosphorylation required intact expression of the essential scaffold component PR65 of PP2A. PP2A physically interacted with Smad3 that occurred only in hypoxia. Accordingly, Smad3-associated PP2A activity was found under hypoxic conditions. Hypoxia attenuated the nuclear accumulation of TGF-beta-induced Smad3 but did not affect Smad2. Moreover, the influence of TGF-beta on a set of Smad3-activated genes was attenuated by hypoxia, and this was reversed by chemical PP2A inhibition. Our data demonstrate the existence of a Smad3-specific phosphatase and identify a novel role for PP2A. Moreover, our data implicate a novel mechanism by which hypoxia regulates growth factor responses.

The identification of novel factors regulating human T helper (Th)–cell differentiation into functionally distinct Th1 and Th2 subsets is important for understanding the mechanisms behind human autoimmune and allergic diseases. We have identified a protein of relevant evolutionary and lymphoid interest (PRELI), a novel protein that induces oxidative stress and a mitochondrial apoptosis pathway in human primary Th cells. We also demonstrated that PRELI inhibits Th2-cell development and down-regulates signal transducer and activator of transcription 6 (STAT6), a key transcription factor driving Th2 differentiation. Our data suggest that calpain, an oxidative stress–induced cysteine protease, is involved in the PRELI-induced down-regulation of STAT6. Moreover, we observed that a strong T-cell receptor (TCR) stimulus induces expression of PRELI and inhibits Th2 development. Our results suggest that PRELI is involved in a mechanism wherein the strength of the TCR stimulus influences the polarization of Th cells. This study identifies PRELI as a novel factor influencing the human primary Th-cell death and differentiation.

Purpose: To investigate the clinical relevance of the recently characterized human oncoprotein cancerous inhibitor of protein phosphatase 2A (CIP2A) in human breast cancer. Experimental Design: CIP2A expression (mRNA and protein) was measured in three different sets of human mammary tumors and compared with clinicopathologic variables. The functional role of CIP2A in breast cancer cells was evaluated by small interfering RNA–mediated depletion of the protein followed by an analysis of cell proliferation, migration, anchorage-independent growth, and xenograft growth. Results: CIP2A mRNA is overexpressed (n = 159) and correlates with higher Scarff-Bloom-Richardson grades (n = 251) in samples from two independent human breast cancer patients. CIP2A protein was found to be overexpressed in 39% of 33 human breast cancer samples. Furthermore, CIP2A mRNA expression positively correlated with lymph node positivity of the patients and with the expression of proliferation markers and p53 mutations in the tumor samples. Moreover, CIP2A protein expression was induced in breast cancer mouse models presenting mammary gland–specific depletion of p53 and either BRCA1 or BRCA2. Functionally, CIP2A depletion was shown to inhibit the expression of its target protein c-Myc. Loss of CIP2A also inhibited anchorage-independent growth in breast cancer cells. Finally, CIP2A was shown to support MDA-MB-231 xenograft growth in nude mice. Conclusions: Our data show that CIP2A is associated with clinical aggressivity in human breast cancer and promotes the malignant growth of breast cancer cells. Thus, these results validate the role of CIP2A as a clinically relevant human oncoprotein and warrant further investigation of CIP2A as a therapeutic target in breast cancer treatment. (Clin Cancer Res 2009;15(16):5092–100)

Loss-of-function mutations in the IKBKAP gene, which encodes IKAP (ELP1), cause familial dysautonomia (FD), with defective neuronal development and maintenance. Molecular mechanisms leading to FD are poorly understood. We demonstrate that various RNA-interference-based depletions of IKAP lead to defective adhesion and migration in several cell types, including rat primary neurons. The defects could be rescued by reintroduction of wild-type IKAP but not by FD-IKAP, a truncated form of IKAP constructed according to the mutation found in the majority of FD patients. Cytosolic IKAP co-purified with proteins involved in cell migration, including filamin A, which is also involved in neuronal migration. Immunostaining of IKAP and filamin A revealed a distinct co-localization of these two proteins in membrane ruffles. Depletion of IKAP resulted in a significant decrease in filamin A localization in membrane ruffles and defective actin cytoskeleton organization, which both could be rescued by the expression of wild-type IKAP but not by FD-IKAP. No downregulation in the protein levels of paxillin or beclin 1, which were recently described as specific transcriptional targets of IKAP, was detected. These results provide evidence for the role of the cytosolic interactions of IKAP in cell adhesion and migration, and support the notion that cell-motility deficiencies could contribute to FD.

MYC is a pleiotropic transcription factor that has been linked to a diverse range of cellular functions, such as cell cycle regulation, proliferation, growth, differentiation and metabolism. Not surprisingly, aberrant MYC signaling has been observed in human cancers and MYC has been demonstrated to promote cell transformation and tumor progression. Here we discuss recent discoveries that have expanded our knowledge of MYC protein stability. In particular we focus on mechanisms that might explain the increased stability of MYC often observed in human cancers and cell lines. We also summarize our recent characterization of Cancerous inhibitor of PP2A (CIP2A(/KIAA1524)) as a protein that inhibits PP2A-mediated MYC dephosphorylation and proteolytic degradation. Finally, we discuss the potential relevance of mechanisms that regulate MYC stability for tumor formation in the context of cancer therapy.

Recent studies indicate that the specificity of p38 mitogen-activated protein kinase (MAPK)-mediated cellular stress responses is determined by the expression pattern of the distinct p38 isoforms. Here, we have analysed the function of distinct p38 isoforms in the growth and invasion of head and neck squamous cell carcinomas (HNSCCs). Activation of p38 MAPK by arsenite resulted in inactivation of the ERK1,2 signaling pathway by dephosphorylation of MEK1,2 in primary human epidermal keratinocytes (HEKs), whereas in HNSCC cells this p38-mediated inhibition of the ERK1,2 pathway was absent. Quantitation of p38 pathway component mRNA expression in HNSCC cell lines (n=42) compared to HEKs (n=8) revealed that p38alpha and p38delta isoforms are predominantly expressed in both cell types and that MKK3 is the primary upstream activator expressed. Inhibition of endogenous p38alpha or p38delta activity by adenoviral delivery of corresponding dominant-negative p38 isoforms potently reduced MMP-13 and MMP-1 expressions, and suppressed the invasion of HNSCC cells through collagen. Dominant-negative p38alpha and p38delta inhibited squamous cell carcinoma (SCC) cell proliferation and inhibition of p38alpha activity also compromised survival of SCC cells. p38alpha and p38delta were predominantly expressed in HNSCCs (n=24) and nonneoplastic epithelium in vivo (n=6), with MKK3 being the primary upstream activator. Activation and expression of p38alpha and p38delta by tumor cells was detected in HNSCCs in vivo (n=16). Adenoviral expression of dominant-negative p38alpha or p38delta in cutaneous SCC cells potently inhibited their implantation in skin of severe combined immunodeficiency mice and growth of xenografts in vivo. Our results indicate that p38alpha and p38delta specifically promote the malignant phenotype of SCC cells by regulating cell survival, proliferation and invasion, suggesting these p38 MAPK isoforms as potential therapeutic targets in HNSCCs.

Colorectal cancer (CRC) accounts for high mortality. So far, there is lack of markers capable of predicting which patients are at risk of aggressive course of the disease. Protein phosphatase‐2A (PP2A) inhibitor proteins have recently gained interest as markers of more aggressive disease in certain cancers. Here, we report the role of PP2A inhibitor PME‐1 in CRC. PME‐1 expression was assessed from a rectal cancer patient cohort by immunohistochemistry, and correlations were performed for various clinicopathological variables and patient survival. Rectal cancer patients with higher cytoplasmic PME‐1 protein expression (above median) had less recurrences (P = 0.003, n = 195) and better disease‐free survival (DFS) than the patients with low cytoplasmic PME‐1 protein expression (below median). Analysis of PPME‐1 mRNA expression from TCGA dataset of colon and rectal adenocarcinoma (COADREAD) patient cohort confirmed high PPME1 expression as an independent protective factor predicting favorable overall survival (OS) (P = 0.005, n = 396) compared to patients with low PPME1 expression. CRC cell lines were used to study the effect of PME‐1 knockdown by siRNA on cell survival. Contrary to other cancer types, PME‐1 inhibition in CRC cell lines did not reduce the viability of cells or the expression of active phosphorylated AKT and ERK proteins. In conclusion, PME‐1 expression predicts for a favorable outcome of CRC patients. The unexpected role of PME‐1 in CRC in contrast with the oncogenic role of PP2A inhibitor proteins in other malignancies warrants further studies of cancer‐specific function for each of these proteins.

High content protein interaction screens have revolutionized our understanding of protein complex assembly. However, one of the major challenges in translation of high content protein interaction data is identification of those interactions that are functionally relevant for a particular biological question. To address this challenge, we developed a relevance ranking platform (RRP), which consist of modular functional and bioinformatic filters to provide relevance rank among the interactome proteins. We demonstrate the versatility of RRP to enable a systematic prioritization of the most relevant interaction partners from high content data, highlighted by the analysis of cancer relevant protein interactions for oncoproteins Pin1 and PME-1. We validated the importance of selected interactions by demonstration of PTOV1 and CSKN2B as novel regulators of Pin1 target c-Jun phosphorylation and reveal previously unknown interacting proteins that may mediate PME-1 effects via PP2A-inhibition. The RRP framework is modular and can be modified to answer versatile research problems depending on the nature of the biological question under study. Based on comparison of RRP to other existing filtering tools, the presented data indicate that RRP offers added value especially for the analysis of interacting proteins for which there is no sufficient prior knowledge available. Finally, we encourage the use of RRP in combination with either SAINT or CRAPome computational tools for selecting the candidate interactors that fulfill the both important requirements, functional relevance, and high confidence interaction detection.

Hyperactivated RAS drives progression of many human malignancies. However, oncogenic activity of RAS is dependent on simultaneous inactivation of protein phosphatase 2A (PP2A) activity. Although PP2A is known to regulate some of the RAS effector pathways, it has not been systematically assessed how these proteins functionally interact. Here we have analyzed phosphoproteomes regulated by either RAS or PP2A, by phosphopeptide enrichment followed by mass-spectrometry-based label-free quantification. To allow data normalization in situations where depletion of RAS or PP2A inhibitor CIP2A causes a large uni-directional change in the phosphopeptide abundance, we developed a novel normalization strategy, named pairwise normalization. This normalization is based on adjusting phosphopeptide abundances measured before and after the enrichment. The superior performance of the pairwise normalization was verified by various independent methods. Additionally, we demonstrate how the selected normalization method influences the downstream analyses and interpretation of pathway activities. Consequently, bioinformatics analysis of RAS and CIP2A regulated phosphoproteomes revealed a significant overlap in their functional pathways. This is most likely biologically meaningful as we observed a synergistic survival effect between CIP2A and RAS expression as well as KRAS activating mutations in TCGA pan-cancer data set and synergistic relationship between CIP2A and KRAS depletion in colony growth assays.

DNA damaging therapies such as irradiation therapy and chemotherapy are used in the treatment of numerous cancer types both definitively and in combination with surgery. However, many cancer types show intrinsic resistance to DNA damaging therapies resulting in failure in tumor eradication and relapse after therapy. Thus it would be very useful to identify novel diagnostic strategies to predict for tumor radio tolerance. Head and neck squamous cell carcinoma (HNSCC) is a common cancer type characterized with great heterogeneity and lack of predictive markers for tumor radio resistance. Recent literature has revealed Cancerous inhibitor of PP2A, CIP2A, as a novel potential diagnostic marker for HNSCC, and other tumors, that show high radio resistance. In particular, we recently identified a functional link between stem cell factor Oct4 and CIP2A in HNSCC cells and demonstrated their potential role in predicting for HNSCC tumor response to radiotherapy. CIP2A´s role in mediating radio resistance in vivo has also been recently confirmed by using genetic mouse model. This raises an interesting possibility that diagnostic evaluation of CIP2A in combination with other factors indicative for cancer cell stemness, could be a novel useful diagnostic approach for stratification of HNSCC patients based on their tumor radio resistance. CIP2A could also serve as a target protein for therapeutic radiosensitation.

// Anchit Khanna 1,2 , Jayant K. Rane 3 , Kati K. Kivinummi 1,4 , Alfonso Urbanucci 1,5,6 , Merja A. Helenius 1 , Teemu T. Tolonen 1 , Outi R. Saramaki 1 , Leena Latonen 1 , Visa Manni 1 , John E. Pimanda 2 , Norman J. Maitland 3 , Jukka Westermarck 7,8 and Tapio Visakorpi 1 1 Prostate Cancer Research Center (PCRC), Institute of Biosciences and Medical Technology (BioMediTech), University of Tampere and Tampere University Hospital, Tampere, Finland 2 Adult Cancer Program, The Prince of Wales Clinical School, Lowy Cancer Research Centre, UNSW Medicine, University of New South Wales, Sydney, Australia 3 YCR Cancer Research Unit, Department of Biology, The University of York, Heslington, United Kingdom 4 Department of Signal Processing, Tampere University of Technology, Tampere, Finland 5 Centre for Molecular Medicine Norway (NCMM), Nordic EMBL Partnership, University of Oslo and Oslo University Hospital, Oslo, Norway 6 Department of Cancer Prevention, Institute for Cancer Research, Oslo University Hospital, Oslo, Norway 7 Turku Centre for Biotechnology, University of Turku and Abo Akademi University, Turku, Finland 8 Department of Pathology, University of Turku, Turku, Finland Correspondence to: Tapio Visakorpi, email: // Anchit Khanna, email: // Keywords : CIP2A, androgen receptor, castration-resistant prostate cancer, cancer stem-like cells Received : December 30, 2014 Accepted : April 03, 2015 Published : April 19, 2015 Abstract Residual androgen receptor (AR)-signaling and presence of cancer stem-like cells (SCs) are the two emerging paradigms for clinically challenging castration-resistant prostate cancer (CRPC). Therefore, identification of AR-target proteins that are also overexpressed in the cancer SC population would be an attractive therapeutic approach. Our analysis of over three hundred clinical samples and patient-derived prostate epithelial cultures (PPECs), revealed Cancerous inhibitor of protein phosphatase 2A (CIP2A) as one such target. CIP2A is significantly overexpressed in both hormone-naive prostate cancer (HN-PC) and CRPC patients . CIP2A is also overexpressed, by 3- and 30-fold, in HN-PC and CRPC SCs respectively. In vivo binding of the AR to the intronic region of CIP2A and its functionality in the AR-moderate and AR-high expressing LNCaP cell-model systems is also demonstrated. Further, we show that AR positively regulates CIP2A expression, both at the mRNA and protein level. Finally, CIP2A depletion reduced cell viability and colony forming efficiency of AR-independent PPECs as well as AR-responsive LNCaP cells, in which anchorage-independent growth is also impaired. These findings identify CIP2A as a common denominator for AR-signaling and cancer SC functionality, highlighting its potential therapeutic significance in the most clinically challenging prostate pathology: castration-resistant prostate cancer.

DNA topoisomerase I (Topo I) is a molecular target for the anticancer agent topotecan in the treatment of small cell lung cancer and ovarian carcinomas. However, the molecular mechanisms by which topotecan treatment inhibits cancer cell proliferation are unclear. We describe here the identification of Topo I as a novel endogenous interaction partner for transcription factor c-Jun. Reciprocal coimmunoprecipitation analysis showed that Topo I and c-Jun interact in transformed human cells in a manner that is dependent on JNK activity. c-Jun target gene epidermal growth factor receptor (EGFR) was identified as a novel gene whose expression was specifically inhibited by topotecan. Moreover, Topo I overexpression supported c-Jun-mediated reporter gene activation and both genetic and chemical inhibition of c-Jun converted cells resistant to topotecan-elicited EGFR downregulation. Topotecan-elicited suppression of proliferation was rescued by exogenously expressed EGFR. Furthermore, we demonstrate the cooperation of the JNK-c-Jun pathway, Topo I, and EGFR in the positive regulation of HT-1080 cell proliferation. Together, these results have identified transcriptional coactivator Topo I as a first endogenous cofactor for c-Jun in the regulation of cell proliferation. In addition, the results of the present study strongly suggest that inhibition of EGFR expression is a novel mechanism by which topotecan inhibits cell proliferation in cancer therapy.