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Table S1 to S4; Figures S1 to S12

Numerous studies have implicated changes in the Y chromosome in male cancers, yet few have investigated the biological importance of Y chromosome noncoding RNA. Here we identify a group of Y chromosome–expressed long noncoding RNA (lncRNA) that are involved in male non–small cell lung cancer (NSCLC) radiation sensitivity. Radiosensitive male NSCLC cell lines demonstrated a dose-dependent induction of linc-SPRY3-2/3/4 following irradiation, which was not observed in radioresistant male NSCLC cell lines. Cytogenetics revealed the loss of chromosome Y (LOY) in the radioresistant male NSCLC cell lines. Gain- and loss-of-function experiments indicated that linc-SPRY3-2/3/4 transcripts affect cell viability and apoptosis. Computational prediction of RNA binding proteins (RBP) motifs and UV-cross-linking and immunoprecipitation (CLIP) assays identified IGF2BP3, an RBP involved in mRNA stability, as a binding partner for linc-SPRY3-2/3/4 RNA. The presence of linc-SPRY3-2/3/4 reduced the half-life of known IGF2BP3 binding mRNA, such as the antiapoptotic HMGA2 mRNA, as well as the oncogenic c-MYC mRNA. Assessment of Y chromosome in NSCLC tissue microarrays and expression of linc-SPRY3-2/3/4 in NSCLC RNA-seq and microarray data revealed a negative correlation between the loss of the Y chromosome or linc-SPRY3-2/3/4 and overall survival. Thus, linc-SPRY3-2/3/4 expression and LOY could represent an important marker of radiotherapy in NSCLC.Significance:This study describes previously unknown Y chromosome–expressed lncRNA regulators of radiation response in male NSCLC and show a correlation between loss of chromosome Y and radioresistance.

Numerous studies have implicated changes in the Y chromosome in male cancers, yet few have investigated the biological importance of Y chromosome noncoding RNA. Here we identify a group of Y chromosome–expressed long noncoding RNA (lncRNA) that are involved in male non–small cell lung cancer (NSCLC) radiation sensitivity. Radiosensitive male NSCLC cell lines demonstrated a dose-dependent induction of linc-SPRY3-2/3/4 following irradiation, which was not observed in radioresistant male NSCLC cell lines. Cytogenetics revealed the loss of chromosome Y (LOY) in the radioresistant male NSCLC cell lines. Gain- and loss-of-function experiments indicated that linc-SPRY3-2/3/4 transcripts affect cell viability and apoptosis. Computational prediction of RNA binding proteins (RBP) motifs and UV-cross-linking and immunoprecipitation (CLIP) assays identified IGF2BP3, an RBP involved in mRNA stability, as a binding partner for linc-SPRY3-2/3/4 RNA. The presence of linc-SPRY3-2/3/4 reduced the half-life of known IGF2BP3 binding mRNA, such as the antiapoptotic HMGA2 mRNA, as well as the oncogenic c-MYC mRNA. Assessment of Y chromosome in NSCLC tissue microarrays and expression of linc-SPRY3-2/3/4 in NSCLC RNA-seq and microarray data revealed a negative correlation between the loss of the Y chromosome or linc-SPRY3-2/3/4 and overall survival. Thus, linc-SPRY3-2/3/4 expression and LOY could represent an important marker of radiotherapy in NSCLC.Significance:This study describes previously unknown Y chromosome–expressed lncRNA regulators of radiation response in male NSCLC and show a correlation between loss of chromosome Y and radioresistance.

Chloroethylagelastatin A (CEAA) is an analogue of agelastatin A (AA), a natural alkaloid derived from a marine sponge. It is under development for therapeutic use against brain tumors as it has excellent central nervous system (CNS) penetration and pre-clinical therapeutic activity against brain tumors. Recently, AA was shown to inhibit protein synthesis by binding to the ribosomal A-site. In this study, we developed a novel virtual screening platform to perform a comprehensive screening of various AA analogues showing that AA analogues with proven therapeutic activity including CEAA have significant ribosomal binding capacity whereas therapeutically inactive analogues show poor ribosomal binding and revealing structural fingerprint features essential for drug-ribosome interactions. In particular, CEAA was found to have greater ribosomal binding capacity than AA. Biological tests showed that CEAA binds the ribosome and contributes to protein synthesis inhibition. Our findings suggest that CEAA may possess ribosomal inhibitor activity and that our virtual screening platform may be a useful tool in discovery and development of novel ribosomal inhibitors.

High-risk human papillomavirus (HPV) infection is one of the first events in the process of carcinogenesis in cervical and head and neck cancers. The expression of the viral oncoproteins E6 and E7 are essential in this process by inactivating the tumor suppressor proteins p53 and Rb, respectively, in addition to their interactions with other host proteins. Non-coding RNAs, such as long non-coding RNAs (lncRNAs) have been found to be dysregulated in several cancers, suggesting an important role in tumorigenesis. In order to identify host lncRNAs affected by HPV infection, we expressed the high-risk HPV-16 E6 oncoprotein in primary human keratinocytes and measured the global lncRNA expression profile by high-throughput sequencing (RNA-seq). We found several host lncRNAs differentially expressed by E6 including GAS5, H19, and FAM83H-AS1. Interestingly, FAM83H-AS1 was found overexpressed in HPV-16 positive cervical cancer cell lines in an HPV-16 E6-dependent manner but independently of p53 regulation. Furthermore, FAM83H-AS1 was found to be regulated through the E6-p300 pathway. Knockdown of FAM83H-AS1 by siRNAs decreased cellular proliferation, migration and increased apoptosis. FAM83H-AS1 was also found to be altered in human cervical cancer tissues and high expression of this lncRNA was associated with worse overall survival, suggesting an important role in cervical carcinogenesis.

Multiple myeloma (MM) cells demonstrate high basal endoplasmic reticulum (ER) stress and are typically exquisitely sensitive to agents such as proteasome inhibitors that activate the unfolded protein response. The flavin adenosine dinucleotide (FAD) containing endoplasmic reticulum oxidoreductin enzyme (Ero1L) catalyzes de-novo disulfide bridge formation of ER resident proteins and contributes to proper protein folding. Here we show that increased Ero1L expression is prognostic of poor outcomes for MM patients relapsing on therapy. We propose that targeting protein folding via inhibition of Ero1L may represent a novel therapeutic strategy for the treatment of MM. In this report we show that treatment of MM cells with EN-460, a known inhibitor of ERO1L, was sufficient to inhibit cell proliferation and induce apoptosis. Furthermore, we show that cell death correlated in part with induction of ER stress. We also show that EN460 inhibited the enzyme activity of Ero1L, with an IC50 of 22.13 μM, consistent with previous reports. However, EN-460 was also found to inhibit other FAD-containing enzymes including MAO-A (IC50 = 7.91 μM), MAO-B (IC50 = 30.59 μM) and LSD1 (IC50 = 4.16 μM), suggesting overlap in inhibitor activity and the potential need to develop more specific inhibitors to enable pharmacological validation of ERO1L as a target for the treatment of MM. We additionally prepared and characterized azide-tagged derivatives of EN-460 as possible functional probe compounds (e.g., for photo-affinity labeling) for future target-engagement studies and further development of structure-activity relationships.

Introduction: Multiple Myeloma (MM) is a hematologic cancer characterized by neoplastic proliferation of the plasma cells in the bone marrow. Newly diagnosed MM patients typically respond to currently available treatments. However, the disease is not curable and unfortunately all patients eventually will relapse with drug resistant disease. Clinical data continues to indicate that novel treatment strategies are required to improve patient outcomes. Our group has developed a novel agent cyclic peptide called MTI-101 for the treatment of MM. MTI-101 was optimized form the D-amino acid linear peptide HYD-1 (1). HYD-1 and the more potent MTI-101 were discovered to induce necroptotic cell death by disrupting Ca2+ homeostasis in MM cell lines. Our laboratory previously reported that acquisition towards resistance to MTI-101 correlated with repression of genes predicted to activate SOCE including decreased PLCβ, SERCA, ITPR3, and TRPC1 expression (2). Moreover, our data showed that pharmacological inhibition of SOCE or reducing the expression of TRPC1 blocks MTI-101 induced cell death (2). Activation of SOCE is dependent on STIM1-ORAI1 recruitment to endoplasmic reticulum- plasma membrane junction (ER-PM junction), allowing an oscillatory Ca2+ flux via activation of ICRAC (Calcium Release Activated Calcium channel) (3). Kaczmarek et al showed that TRPC5 (TRPC1 heterodimer) activity can be positively regulated by calpain truncation (4). In this study, we sought to determine the role of TRPC1 in MTI-101 Ca2+ induced necrosis, as we hypothesize that MTI-101 induced prolonged SOCE activation is due to TRPC1 truncation by calpains activation, leading to disruption of Ca2+ homeostasis and cell death Methods: To evaluate determinants of activity of MTI-101, we developed an assay to measure intracellular Ca2+ levels and cell death by using the Ca2+ indicator Fluo-4 AM and DAPI as a marker for cell death. Further, to evaluate the role of MTI-101 on TRPC1 activation, MTI-101 treated cells were lysed using RIPA detergent, and the detergent resistant component was lysed using RIPA and 2% SDS, followed by sonication with an ultrasonic homogenizer. Both compartments were analyzed via western blot. Results: Our data showed that MTI-101-induced robust, delayed calcium flux is causative for cell death due to irreversible activation of SOCE, while thapsigargin causes rapid, transient, reversible activation. Further, the data indicated that MTI-101 treatment induces TRPC1 truncation and translocation to a detergent-resistant compartment of the cell. Moreover, inhibiting the Ca2+ activated proteases calpain1 and calpain2 abrogated MTI-101 induced Ca2+ flux and cell death, and interferes with TRPC1 truncation following MTI-101 treatment in a time dependent manner. Conclusions: MTI-101 induces a robust, and sustained activation of SOCE causative for cell death. Increased intracellular Ca2+ levels following MTI-101 treatment induces calpains activation, furthering TRPC1 truncation and activation leading to necroptotic cell death. Our future studies will focus on evaluating the role of mutants TRPC1 on MTI-101 activity, identify calpains consensus sites on TRPC1, and determine the role of ORAI1 in MTI-101 Ca2+ induced cell death. Citation Format: Osama M Elzamzamy, Karen Hayes, Werner Geldenhuys, Lori A Hazlehurst. Role of MTI-101 in disrupting calcium homeostasis leading to cell death in multiple myeloma [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference on Molecular Targets and Cancer Therapeutics; 2019 Oct 26-30; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2019;18(12 Suppl):Abstract nr A019. doi:10.1158/1535-7163.TARG-19-A019

Cellular quiescence (also known as G0 arrest) is characterized by reduced DNA replication, increased autophagy, and increased expression of cyclin-dependent kinase p27Kip1. Quiescence is essential for wound healing, organ regeneration, and preventing neoplasia. Previous findings indicate that microRNAs (miRNAs) play an important role in regulating cellular quiescence. Our recent publication demonstrated the existence of an alternative miRNA biogenesis pathway in primary human foreskin fibroblast (HFF) cells during quiescence. Indeed, we have identified a group of pri-miRNAs (whose mature miRNAs were found induced during quiescence) modified with a 2,2,7-trimethylguanosine (TMG)-cap by the trimethylguanosine synthase 1 (TGS1) protein and transported to the cytoplasm by the Exportin-1 (XPO1) protein. We used an antibody against (TMG)-caps (which does not cross-react with the (m7G)-caps that most pri-miRNAs or mRNAs contain [Luhrmann et al., 1982]) to perform RNA immunoprecipitations from total RNA extracts of proliferating or quiescent HFFs. The novelty of this assay is the specific isolation of pri-miRNAs as well as other non-coding RNAs containing a TMG-cap modification.

The reversible state of proliferative arrest known as “cellular quiescence” plays an important role in tissue homeostasis and stem cell biology. By analyzing the expression of miRNAs and miRNA-processing factors during quiescence in primary human fibroblasts, we identified a group of miRNAs that are induced during quiescence despite markedly reduced expression of Exportin-5, a protein required for canonical miRNA biogenesis. The biogenesis of these quiescence-induced miRNAs is independent of Exportin-5 and depends instead on Exportin-1. Moreover, these quiescence-induced primary miRNAs (pri-miRNAs) are modified with a 2,2,7-trimethylguanosine (TMG)-cap, which is known to bind Exportin-1, and knockdown of Exportin-1 or trimethylguanosine synthase 1, responsible for (TMG)-capping, inhibits their biogenesis. Surprisingly, in quiescent cells Exportin-1–dependent pri-miR-34a is present in the cytoplasm together with a small isoform of Drosha, implying the existence of a different miRNA processing pathway in these cells. Our findings suggest that during quiescence the canonical miRNA biogenesis pathway is down-regulated and specific miRNAs are generated by an alternative pathway to regulate genes involved in cellular growth arrest.

Head and neck squamous cell carcinoma (HNSCC) has a proclivity for locoregional invasion. HNSCC mediates invasion in part through invadopodia-based proteolysis of the extracellular matrix (ECM). Activation of Src, Erk1/2, Abl and Arg downstream of epidermal growth factor receptor (EGFR) modulates invadopodia activity through phosphorylation of the actin regulatory protein cortactin. In MDA-MB-231 breast cancer cells, Abl and Arg function downstream of Src to phosphorylate cortactin, promoting invadopodia ECM degradation activity and thus assigning a pro-invasive role for Ableson kinases. We report that Abl kinases have an opposite, negative regulatory role in HNSCC where they suppress invadopodia and tumor invasion. Impairment of Abl expression or Abl kinase activity with imatinib mesylate enhanced HNSCC matrix degradation and 3D collagen invasion, functions that were impaired in MDA-MB-231. HNSCC lines with elevated EGFR and Src activation did not contain increased Abl or Arg kinase activity, suggesting that Src could bypass Abl/Arg to phosphorylate cortactin and promote invadopodia ECM degradation. Src-transformed Abl(-/-)/Arg(-/-) fibroblasts produced ECM degrading invadopodia containing pY421 cortactin, indicating that Abl/Arg are dispensable for invadopodia function in this system. Imatinib-treated HNSCC cells had increased EGFR, Erk1/2 and Src activation, enhancing cortactin pY421 and pS405/418 required for invadopodia function. Imatinib stimulated shedding of the EGFR ligand heparin-binding EGF-like growth factor (HB-EGF) from HNSCC cells, where soluble HB-EGF enhanced invadopodia ECM degradation in HNSCC but not in MDA-MB-231. HNSCC cells treated with inhibitors of the EGFR-invadopodia pathway indicated that EGFR and Src are required for invadopodia function. Collectively, our results indicate that Abl kinases negatively regulate HNSCC invasive processes through suppression of an HB-EGF autocrine loop responsible for activating a EGFR-Src-cortactin cascade, in contrast to the invasion promoting functions of Abl kinases in breast and other cancer types. Our results provide mechanistic support for recent failed HNSCC clinical trials utilizing imatinib.

The filamentous (F)-actin regulatory protein cortactin plays an important role in tumor cell movement and invasion by promoting and stabilizing actin related protein (Arp)2/3-mediated actin networks necessary for plasma membrane protrusion. Cortactin is a substrate for ERK1/2 and Src family kinases, with previous in vitro findings demonstrating ERK1/2 phosphorylation of cortactin as a positive and Src phosphorylation as a negative regulatory event in promoting Arp2/3 activation through neuronal Wiskott Aldrich Syndrome protein (N-WASp). Evidence for this regulatory cortactin "switch" in cells has been hampered due to the lack of phosphorylation-specific antibodies that recognize ERK1/2-phosphorylated cortactin. Our findings with phosphorylation-specific antibodies against these ERK1/2 sites (pS405 and pS418) indicate that cortactin can be co-phosphorylated at 405/418 and tyrosine residues targeted by Src family tyrosine kinases. These results indicate that the ERK/Src cortactin switch is not the sole mechanism by which ERK1/2 and tyrosine phosphorylation events regulate cortactin function in cell systems.

Recently, two independent research teams discovered thousands of conserved non-coding human circular RNAs (circRNAs), however, there are no studies suggesting the existence of circRNAs produced by human viruses. The objective of this study is to explore our hypothesis that human papillomavirus (HPV)-16 creates viral circRNAs that may alter host activity in order to promote viral replication and induction of carcinogenesis. CircRNAs are non-coding RNAs generated by the alternative splicing of a 5' acceptor and 2' or 3' donor sites, creating a “head” to “tail” covalent junction of exonic and/or intronic regions. Although the role of circRNAs is largely unknown, studies have demonstrated several functions for circRNAs including sequestering microRNAs (miRNAs) and regulation of transcription. Recently, circRNAs have also been associated with several cancers such as colorectal, breast, and gastric cancers. Infections with high-risk HPVs, such as types 16 and 18, are responsible for the majority of cervical cancers and a subset of head and neck squamous cell carcinomas (HNSCC). HPV is a small double-stranded circular DNA encoding six early proteins (E-1, -2, -4, -5, -6, and -7) and two late proteins (L-1, -2). HPV DNA is tightly regulated and undergoes extensive and complex splicing to achieve the expression of these proteins. Our preliminary data suggest that HPV-16 extensive splicing generates at least two viral circRNAs (hpv-circRNAs) that could potentially regulate host cellular processes promoting tumorigenesis. We demonstrated the existence of the “head” to “tail” junctions of hpv-circRNAs in HPV-16 viral RNA with reverse transcription polymerase chain reaction (RT-PCR) amplification using divergent primers in RNA extracted from cervical tumor cell lines. Quantitative RT-PCR (qRT-PCR) analysis showed the retention of the hpv-circRNAs in RNase R treated samples suggesting the absence of free RNA ends in these hpv-circRNAs. Moreover, these viral circRNAs persisted even after the cervical tumor cells were exposed to Actinomycin D for 48 hrs (to inhibit RNA synthesis), confirming the stability of these hpv-circRNAs in comparison to the short-lived lariat structures that also can occur during splicing. Together, our data suggest the existence of viral circRNAs produced in HPV-16. To the best of our knowledge, these are the first described human viral generated circRNAs. Currently, we are characterizing these hpv-circRNAs by conducting knockdown and rescue experiments followed by behavior assays (e.g. invasion, angiogenesis, and proliferation). We believe this project will be significant in that it will identify and show the importance of viral circRNAs in HPV-related cancers as well as give us new information about a novel mechanism by which high-risk HPV infection contributes to cervical and HNSCC carcinogenesis. Citation Format: Karen E. Hayes, Jamie A. Barr, Jeremy E. Wilusz, Ivan Martinez. The discovery of novel noncoding circular RNAs generated by high-risk human papillomavirus type 16. [abstract]. In: Proceedings of the AACR Special Conference on Noncoding RNAs and Cancer: Mechanisms to Medicines ; 2015 Dec 4-7; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2016;76(6 Suppl):Abstract nr A34.

The objective of this study is to identify the importance of long non-coding RNAs (lncRNAs) in the induction of carcinogenesis by high-risk human papillomavirus (HPV)-16 oncoprotein E6 in HPV-related cancers. Dysregulation of long non-coding RNAs (lncRNAs) occurs in most human cancers, however, there are only a few studies showing dysregulation of specific lncRNAs in human papillomavirus (HPV)-related cancers. High-risk HPV infection (e.g. HPV-16 and HPV-18) is one the most common causes of cervical cancer, as well as a subset of head and neck squamous cell carcinoma (HNSCC). It is well known that one of the main factors contributing to HPV-related carcinogenesis is the expression of high-risk HPV E6 viral oncoprotein and its interaction with several human proteins, such as the tumor suppressor p53 and the anti-apoptotic protein Bak. It is hypothesized that HPV-16 E6 changes the expression of host lncRNAs to regulate downstream processes important in the induction of carcinogenesis. To test this hypothesis, we stably express high-risk HPV-16 E6 in primary human keratinocytes and conducted high-throughput RNA sequencing analysis to identify HPV-16 E6-mediated changes in lncRNAs expression. Our preliminary data shows over 500 lncRNAs up- or down- regulated by greater than 2-fold with the expression of HPV-16 E6 compared to control. We validated the expression changes of many individual lncRNAs after the expression of HPV-16E6, via q-RT-PCR and Northern blots. In addition we observe similar expression patterns when comparing normal cells to HPV+ cervical cancer cell lines. Currently, we are characterizing specific lncRNAs of interest that are altered with expression of HPV-16 E6 by using 5' and 3' rapid amplification of cDNA ends (RACE) experiments as well as determining certain lncRNA's mechanism of action contributing to cancer by conducting knockdown and rescue experiments followed by behavior assays (e.g. invasion, angiogenesis, and proliferation). To aid in the determination of the function of the lncRNAs, we plan to use Fluorescence in situ Hybridization (FISH) assays to identify their localization. We believe this project will be significant in that it will identify and show the importance of lncRNAs in HPV-related cancers as well as give us new information about a novel mechanism by which high-risk HPV infection contributes to cervical and HNSCC carcinogenesis. Citation Format: Jamie A. Barr, Karen E. Hayes, Ivan Martinez. Importance of long noncoding RNAs in human papillomavirus-related cancers. [abstract]. In: Proceedings of the AACR Special Conference on Noncoding RNAs and Cancer: Mechanisms to Medicines ; 2015 Dec 4-7; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2016;76(6 Suppl):Abstract nr A26.

Cellular invasion into local tissues is a process important in development and homeostasis. Malregulated invasion and subsequent cell movement is characteristic of multiple pathological processes, including inflammation, cardiovascular disease and tumor cell metastasis. Focalized proteolytic degradation of extracellular matrix (ECM) components in the epithelial or endothelial basement membrane is a critical step in initiating cellular invasion. In tumor cells, extensive in vitro analysis has determined that ECM degradation is accomplished by ventral actin-rich membrane protrusive structures termed invadopodia. Invadopodia form in close apposition to the ECM, where they moderate ECM breakdown through the action of matrix metalloproteinases (MMPs). The ability of tumor cells to form invadopodia directly correlates with the ability to invade into local stroma and associated vascular components. Visualization of invadopodia-mediated ECM degradation of cells by fluorescent microscopy using dye-labeled matrix proteins coated onto glass coverslips has emerged as the most prevalent technique for evaluating the degree of matrix proteolysis and cellular invasive potential. Here we describe a version of the standard method for generating fluorescently-labeled glass coverslips utilizing a commercially available Oregon Green-488 gelatin conjugate. This method is easily scaled to rapidly produce large numbers of coated coverslips. We show some of the common microscopic artifacts that are often encountered during this procedure and how these can be avoided. Finally, we describe standardized methods using readily available computer software to allow quantification of labeled gelatin matrix degradation mediated by individual cells and by entire cellular populations. The described procedures provide the ability to accurately and reproducibly monitor invadopodia activity, and can also serve as a platform for evaluating the efficacy of modulating protein expression or testing of anti-invasive compounds on extracellular matrix degradation in single and multicellular settings.

Loco-regional invasion of head and neck cancer is linked to metastatic risk and presents a difficult challenge in designing and implementing patient management strategies. Orthotopic mouse models of oral cancer have been developed to facilitate the study of factors that impact invasion and serve as model system for evaluating anti-tumor therapeutics. In these systems, visualization of disseminated tumor cells within oral cavity tissues has typically been conducted by either conventional histology or with in vivo bioluminescent methods. A primary drawback of these techniques is the inherent inability to accurately visualize and quantify early tumor cell invasion arising from the primary site in three dimensions. Here we describe a protocol that combines an established model for squamous cell carcinoma of the tongue (SCOT) with two-photon imaging to allow multi-vectorial visualization of lingual tumor spread. The OSC-19 head and neck tumor cell line was stably engineered to express the F-actin binding peptide LifeAct fused to the mCherry fluorescent protein (LifeAct-mCherry). Fox1(nu/nu) mice injected with these cells reliably form tumors that allow the tongue to be visualized by ex-vivo application of two-photon microscopy. This technique allows for the orthotopic visualization of the tumor mass and locally invading cells in excised tongues without disruption of the regional tumor microenvironment. In addition, this system allows for the quantification of tumor cell invasion by calculating distances that invaded cells move from the primary tumor site. Overall this procedure provides an enhanced model system for analyzing factors that contribute to SCOT invasion and therapeutic treatments tailored to prevent local invasion and distant metastatic spread. This method also has the potential to be ultimately combined with other imaging modalities in an in vivo setting.

The actin regulatory protein cortactin is involved in multiple signaling pathways impinging on the cortical actin cytoskeleton. Cortactin is phosphorylated by ERK1/2 and Src family tyrosine kinases, resulting in neuronal Wiskott Aldrich Syndrome protein (N-WASp) activation and enhanced actin related protein (Arp)2/3-mediated actin nucleation. Cortactin migrates as an 80/85 kDa doublet when analyzed by SDS-PAGE. Phosphorylation by ERK1/2 is associated with conversion of the 80 kDa to the 85 kDa form, postulated to occur by inducing a conformational alteration that releases the carboxyl-terminal SH3 domain from autoinhibition. Our recent analysis of the 80–85 kDa cortactin “shift” in tumor cells indicates that while ERK1/2 phosphorylation is associated with the 85 kDa shift, this phosphorylation event is not required for the shift to occur, nor does ERK1/2 phosphorylation appreciably alter global cortactin confirmation. These data indicate that additional factors besides ERK1/2 phosphorylation contribute to generating and/or maintaining the activated 85 kDa cortactin form in stimulated cells.

Background Tumor cell motility and invasion is governed by dynamic regulation of the cortical actin cytoskeleton. The actin-binding protein cortactin is commonly upregulated in multiple cancer types and is associated with increased cell migration. Cortactin regulates actin nucleation through the actin related protein (Arp)2/3 complex and stabilizes the cortical actin cytoskeleton. Cortactin is regulated by multiple phosphorylation events, including phosphorylation of S405 and S418 by extracellular regulated kinases (ERK)1/2. ERK1/2 phosphorylation of cortactin has emerged as an important positive regulatory modification, enabling cortactin to bind and activate the Arp2/3 regulator neuronal Wiskott-Aldrich syndrome protein (N-WASp), promoting actin polymerization and enhancing tumor cell movement. Methodology/Principal Findings In this report we have developed phosphorylation-specific antibodies against phosphorylated cortactin S405 and S418 to analyze the subcellular localization of this cortactin form in tumor cells and patient samples by microscopy. We evaluated the interplay between cortactin S405 and S418 phosphorylation with cortactin tyrosine phosphorylation in regulating cortactin conformational forms by Western blotting. Cortactin is simultaneously phosphorylated at S405/418 and Y421 in tumor cells, and through the use of point mutant constructs we determined that serine and tyrosine phosphorylation events lack any co-dependency. Expression of S405/418 phosphorylation-null constructs impaired carcinoma motility and adhesion, and also inhibited lamellipodia persistence monitored by live cell imaging. Conclusions/Significance Cortactin phosphorylated at S405/418 is localized to sites of dynamic actin assembly in tumor cells. Concurrent phosphorylation of cortactin by ERK1/2 and tyrosine kinases enables cells with the ability to regulate actin dynamics through N-WASp and other effector proteins by synchronizing upstream regulatory pathways, confirming cortactin as an important integration point in actin-based signal transduction. Reduced lamellipodia persistence in cells with S405/418A expression identifies an essential motility-based process reliant on ERK1/2 signaling, providing additional understanding as to how this pathway impacts tumor cell migration.

The proto-oncogene Src tyrosine kinase (Src) is overexpressed in human cancers and is currently a target of anti-invasive therapies. Activation of Src is an essential catalyst of invadopodia production. Invadopodia are cellular structures that mediate extracellular matrix (ECM) proteolysis, allowing invasive cell types to breach confining tissue barriers. Invadopodia assembly and maturation is a multistep process, first requiring the targeting of actin-associated proteins to form pre-invadopodia, which subsequently mature by recruitment and activation of matrix metalloproteases (MMPs) that facilitate ECM degradation. We demonstrate that active, oncogenic Src alleles require the presence of a wild-type counterpart to induce ECM degradation at invadopodia sites. In addition, we identify the phosphorylation of the invadopodia regulatory protein cortactin as an important mediator of invadopodia maturation downstream of wild-type Src. Distinct phosphotyrosine-based protein-binding profiles in cells forming pre-invadopodia and mature invadopodia were identified by SH2-domain array analysis. These results indicate that although elevated Src kinase activity is required to target actin-associated proteins to pre-invadopodia, regulated Src activity is required for invadopodia maturation and matrix degradation activity. Our findings describe a previously unappreciated role for proto-oncogenic Src in enabling the invasive activity of constitutively active Src alleles.

Elevated Src kinase activity is linked to the progression of solid tumors, including head and neck squamous cell carcinoma (HNSCC). Src regulates HNSCC proliferation and tumor invasion, with the Src-targeted small molecule inhibitor saracatinib displaying potent anti-invasive effects in preclinical studies. However, the pro-invasive cellular mechanism(s) perturbed by saracatinib are unclear. The anti-proliferative and anti-invasive effects of saracatinib on HNSCC cell lines were therefore investigated in pre-clinical cell and mouse model systems. Saracatinib treatment inhibited growth, cell cycle progression and transwell Matrigel invasion in HNSCC cell lines. Dose-dependent decreases in Src activation and phosphorylation of the invasion-associated substrates focal adhesion kinase, p130 CAS and cortactin were also observed. While saracatinib did not significantly impact HNSCC tumor growth in a mouse orthotopic model of tongue squamous cell carcinoma, impaired perineural invasion and cervical lymph node metastasis was observed. Accordingly, saracatinib treatment displayed a dose-dependent inhibitory effect on invadopodia formation, extracellular matrix degradation and matrix metalloprotease 9 activation. These results suggest that inhibition of Src kinase by saracatinib impairs the pro-invasive activity of HNSCC by inhibiting Src substrate phosphorylation important for invadopodia formation and associated matrix metalloprotease activity.

Head and neck squamous cell carcinoma (HNSCC) has a proclivity for locoregional invasion. HNSCC mediates invasion in part through invadopodia-based proteolysis of the extracellular matrix (ECM). Activation of Src, Erk1/2, Abl and Arg downstream of epidermal growth factor receptor (EGFR) modulates invadopodia activity through phosphorylation of the actin regulatory protein cortactin. In MDA-MB-231 breast cancer cells, Abl and Arg function downstream of Src to phosphorylate cortactin, promoting invadopodia ECM degradation activity and thus assigning a pro-invasive role for Ableson kinases. We report that Abl kinases have an opposite, negative regulatory role in HNSCC where they suppress invadopodia and tumor invasion. Impairment of Abl expression or Abl kinase activity with imatinib mesylate enhanced HNSCC matrix degradation and 3D collagen invasion, functions that were impaired in MDA-MB-231. HNSCC lines with elevated EGFR and Src activation did not contain increased Abl or Arg kinase activity, suggesting Src could bypass Abl/Arg to phosphorylate cortactin and promote invadopodia ECM degradation. Src transformed Abl-/-/Arg-/- fibroblasts produced ECM degrading invadopodia containing pY421 cortactin, indicating that Abl/Arg are dispensable for invadopodia function in this system. Imatinib treated HNSCC cells had increased EGFR, Erk1/2 and Src activation, enhancing cortactin pY421 and pS405/418 required for invadopodia function. Imatinib stimulated shedding of the EGFR ligand heparin-binding EGF-like growth factor (HB-EGF) from HNSCC cells, where soluble HB-EGF enhanced invadopodia ECM degradation in HNSCC but not in MDA-MB-231. HNSCC cells treated with therapeutic inhibitors of the EGFR invadopodia pathway indicated that EGFR and Src are required for invadopodia function. Collectively our results indicate that Abl kinases negatively regulate HNSCC invasive processes through suppression of an HB-EGF autocrine loop responsible for activating an EGFR-Src-cortactin cascade, in contrast to the invasion promoting functions of Abl kinases in breast and other cancer types. Our results provide mechanistic support for recent failed HNSCC clinical trials utilizing imatinib. Citation Format: Karen E. Hayes, Elyse L. Walk, Amanda G. Ammer, Laura C. Kelley, Karen H. Martin, Scott A. Weed. Ableson kinases negatively regulate invadopodia function and invasion in head and neck squamous cell carcinoma by inhibiting an HB-EGF autocrine loop. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 4936. doi:10.1158/1538-7445.AM2013-4936