Search

Proteolytic targeting chimaeras (PROTACs) have been developed as an effective technology for targeted protein degradation. PROTACs are heterobifunctional molecules that can trigger the polyubiquitination of proteins of interest (POIs) by recruiting the ubiquitin-proteasome system, thereby inhibiting the intracellular level of POIs. To date, a variety of small-molecule PROTACs (CRBN, VHL, IAP, and MDM2-based PROTACs) have been developed. IAP-based PROTACs, also known as specific and nongenetic IAP-dependent protein erasers (SNIPERs), are used to degrade the target proteins closely related to diseases. Their structures consist of three parts, including target protein ligand, E3 ligase ligand, and the linker between them. So far, many SNIPERs have been extensively studied worldwide and have performed well in multiple diseases, especially cancer. In this review, we will present the most relevant advances in the field of SNIPERs and provide our perspective on the opportunities and challenges for SNIPERs to become therapeutic agents.

How organisms control organ size is not fully understood. We found that Syd/JIP3 is required for proper wing size in Drosophila. JIP3 mutations are associated with organ size defects in mammals. The underlying mechanisms are not well understood. We discovered that Syd/JIP3 inhibition results in a downregulation of the inhibitor of apoptosis protein 1 (Diap1) in the Drosophila wing. Correspondingly, Syd/JIP3 deficient tissues exhibit ectopic cell death and yield smaller wings. Syd/JIP3 inhibition generated similar effects in mammalian cells, indicating a conserved mechanism. We found that Yorkie/YAP stimulates Syd/JIP3 in Drosophila and mammalian cells. Notably, Syd/JIP3 is required for the full effect of Yorkie-mediated tissue growth. Thus Syd/JIP3 regulation of Diap1 functions downstream of Yorkie/YAP to control growth. This study provides mechanistic insights into the recent and perplexing link between JIP3 mutations and organ size defects in mammals, including in humans where de novo JIP3 variants are associated with microcephaly., Competing Interests: Declaration of competing interest None., (Copyright © 2020 Elsevier Inc. All rights reserved.)

Over the last decade, the E3-ubiquitine ligases from IAP (Inhibitor of Apoptosis) family have emerged as potent regulators of immune response. In immune cells, they control signaling pathways driving differentiation and inflammation in response to stimulation of tumor necrosis factor receptor (TNFR) family, pattern-recognition receptors (PRRs), and some cytokine receptors. They are able to control the activity, the cellular fate, or the stability of actors of signaling pathways, acting at different levels from components of receptor-associated multiprotein complexes to signaling effectors and transcription factors, as well as cytoskeleton regulators. Much less is known about ubiquitination substrates involved in non-immune signaling pathways. This review aimed to present IAP ubiquitination substrates and the role of IAP-mediated ubiquitination in regulating signaling pathways.

Patients with urothelial carcinoma frequently fail to respond to first‑line chemotherapy using cisplatin and gemcitabine due to development of resistant tumor cells. The aim of the present study was to investigate whether an alternative treatment with tumor necrosis factor‑related apoptosis‑inducing ligand (TRAIL) that induces tumor cell death via the extrinsic apoptotic pathway may be effective against chemotherapy‑resistant urothelial cancer cell lines. The viability of the urothelial cancer cell line RT112 and its chemotherapy‑adapted sublines was investigated by MTT assay. The expression of anti‑apoptotic proteins was determined by western blotting and the individual roles of cellular inhibitor of apoptosis protein (cIAP)1, cIAP2, x‑linked inhibitor of apoptosis protein (XIAP) and induced myeloid leukemia cell differentiation protein (Mcl‑1) were investigated by siRNA‑mediated depletion. In particular, the bladder cancer sublines that were resistant to gemcitabine and cisplatin were cross‑resistant to TRAIL. Resistant cells displayed upregulation of anti‑apoptotic molecules compared with the parental cell line. Treatment with the second mitochondrial activator of caspases (SMAC) mimetic LCL‑161 that antagonizes cIAP1, cIAP2 and XIAP resensitized chemoresistant cells to TRAIL. The resensitization of tumor cells to TRAIL was confirmed by depletion of antiapoptotic proteins with siRNA. Collectively, the findings of the present study demonstrated that SMAC mimetic LCL‑161 increased the sensitivity of the parental cell line RT112 and chemotherapy‑resistant sublines to TRAIL, suggesting that inhibiting anti‑apoptotic molecules renders TRAIL therapy highly effective for chemotherapy‑sensitive and ‑resistant urothelial cancer cells.

X-linked inhibitor of apoptosis protein (XIAP), survivin, and BRUCE are members of the inhibitor-of-apoptosis protein (IAP) family known for their inhibitory effects on caspase activity and dysregulation of these molecules has widely been shown to cause embryonic defects and to promote tumorigenesis in human. Besides the anti-apoptotic functions, recent discoveries have revealed that XIAP, survivin, and BRUCE also exhibit regulatory functions for autophagy in cells. As the role of autophagy in human diseases has already been discussed extensively in different reviews; in this review, we will discuss the emerging autophagic role of XIAP, survivin, and BRUCE in cancer cells. We also provide an update on the anti-apoptotic functions and the roles in maintaining DNA integrity of these molecules. Second mitochondria-derived activator of caspases (Smac) is a pro-apoptotic protein and IAPs are the molecular targets of various Smac mimetics currently under clinical trials. Better understanding on the functions of XIAP, survivin, and BRUCE can enable us to predict possible side effects of these drugs and to design a more "patient-specific" clinical trial for Smac mimetics in the future.

Inhibitors of Apoptosis Protein (IAP) genes participate in processes like apoptosis, proliferation, innate immunity, inflammation, cell motility, differentiation and in malignancies. Here we reveal 25 IAP genes in the tunicate Botryllus schlosseri's genome and their functions in two developmental biology phenomena, a new mode of whole body regeneration (WBR) induced by budectomy, and blastogenesis, the four-staged cycles of botryllid ascidian astogeny. IAP genes that were specifically upregulated during these developmental phenomena were identified, and protein expression patterns of one of these genes, IAP28, were followed. Most of the IAP genes upregulation recorded at blastogenetic stages C/D was in concert with the upregulation at 100 μM H 2 O 2 apoptotic-induced treatment and in parallel to expressions of AIF1, Bax, Mcl1, caspase 2 and two orthologues of caspase 7. Wnt agonist altered the takeover duration along with reduced IAP expressions, and displacement of IAP28 + phagocytes. WBR was initiated solely at blastogenetic stage D, where zooidal absorption was attenuated and regeneration centers were formed either from remains of partially absorbed zooids or from deformed ampullae. Subsequently, bud-bearing zooids developed, in concert with a massive IAP28-dependent phagocytic wave that eliminated the old zooids, then proceeded with the establishment of morphologically normal-looking colonies. IAP4, IAP14 and IAP28 were also involved in WBR, in conjunction with the expression of the pro-survival PI3K-Akt pathway. IAPs function deregulation by Smac mimetics resulted in severe morphological damages, attenuation in bud growth and differentiation, and in destabilization of colonial coordination. Longtime knockdown of IAP functions prior to the budectomy, resulted in colonial death., (Copyright © 2018 Elsevier Inc. All rights reserved.)

Protein- and cell-based immunotherapeutic agents have revolutionized cancer treatment. However, small-molecule immunomodulators with favorable pharmacological properties for reaching intracellular targets remain to be developed. To explore the vast chemical space, a robust method that recapitulates the complex cancer-immune microenvironment in a high-throughput format is essential. To address this critical gap, we developed a high-throughput immunomodulator phenotypic screening platform, HTiP, which integrates the immune and cancer cell co-culture system with imaging- and biochemical-based multiplexed readouts. Using the HTiP platform, we have demonstrated its capability in modeling an oncogenic KRAS mutation-driven immunosuppressive phenotype. From a bioactive chemical library, multiple structurally distinct compounds were identified, all of which target the same class of proteins, inhibitor of apoptosis protein (IAP). IAP has demonstrated roles in cancer immunity. Identification of IAP antagonists as potent anti-tumor immune enhancers provides strong validating evidence for the use of the HTiP platform to discover small-molecule immunomodulators., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

The inhibitor of apoptosis proteins (IAPs) are a family of proteins that were chiefly known for their ability to inhibit apoptosis by blocking caspase activation or activity. Recent research has shown that cellular IAP1 (cIAP1), cIAP2, and X-linked IAP (XIAP) also regulate signaling by receptors of the innate immune system by ubiquitylating their substrates. These IAPs thereby act at the intersection of pathways leading to cell death and inflammation. Mutation of IAP genes can impair tissue homeostasis and is linked to several human diseases. Small-molecule IAP antagonists have been developed to treat certain malignant, infectious, and inflammatory diseases. Here, we will discuss recent advances in our understanding of the functions of cIAP1, cIAP2, and XIAP; the consequences of their mutation or dysregulation; and the therapeutic potential of IAP antagonist drugs., Competing Interests: Competing interests: DLV was on the scientific advisory board of TetraLogic, and he and NL have patent applications related to birinapant.No competing interests were disclosed.No competing interests were disclosed.

Purpose: Evading apoptosis is one of the major hallmarks of cancer cells. Inhibitors of apoptosis (IAPs) proteins are considered as a most important gene families involved in apoptosis. BRUCE protein, a member of IAPs, is able to quench apoptosis as well as playing role in cell division. Our aim in this study was to analyze BRUCE protein expression in gastric carcinoma (GC) and its correlation with the clinicopathological features., Methods: Using immunohistochemistry, 52 GC specimens were studied for BRUCE protein expression. A validated scoring method was applied., Results: BRUCE protein expression was detected in majority of tumor tissues (98.07 %). A significant correlation between gender and BRUCE expression (p = 0.024) was detected. Indeed, females showed higher level of BRUCE expression than male patients., Conclusion: Since specific expression of BRUCE protein was revealed in majority of GC tissues, BRUCE protein may be a useful therapeutic target for cancer therapy. Furthermore, based on the native role of BRUCE protein in inhibition of apoptosis, using this protein in targeted therapy of tumor cells may help to inhibit tumor cells growth and survival leading to rapid elimination of tumor mass.

Background: The inhibitor of apoptosis protein (IAP) family are reported to play important roles in cancer cells evading apoptosis. However, the significance of their expression in human esophageal squamous cell carcinoma (ESCC) cells remains uncertain., Aims: The present study aimed to investigate the role of the IAP family members in tumor necrosis factor-α (TNF-α)-induced apoptosis of human ESCC cells., Methods: Five human ESCC cell lines were pretreated with TNF-α, cycloheximide (CHX, protein synthesis inhibitor), epoxomicin (proteasome inhibitor). Apoptosis assay and protein study with Western blot testing were conducted. Knockdown experiments with IAP siRNA were conducted, and the effect on cell apoptosis was analyzed., Results: Significant apoptosis was induced in five ESCC cell lines by TNF-α plus CHX stimulation, but not when treated with TNF-α or CHX alone. The protein expression levels of cIAP1 and XIAP were decreased by treatment with TNF-α in the presence of CHX, and the degree of cIAP1 and XIAP expression decrease was correlated with sensitivity to TNF-α plus CHX-induced apoptosis. Epoxomicin suppressed TNF-α plus CHX-induced degradation of survivin, cIAP1, and XIAP, in addition to apoptosis. A caspase inhibitor (z-VAD-fmk) suppressed TNF-α plus CHX-induced apoptosis, but did not suppress degradation of survivin, cIAP1, and XIAP. Furthermore, cIAP1 or XIAP siRNA transfected cells underwent apoptosis in response to treatment with TNF-α alone. Double knockdown of both genes resulted in further increased apoptosis., Conclusion: cIAP1 and XIAP play an essential role in the resistance of ESCC cells against apoptosis.

Recent advances in genome-wide surveys have revealed a number of lepidopteran insect homologs of mammalian and Drosophila genes that are responsible for apoptosis regulation. However, the underlying molecular mechanisms for apoptosis regulation in lepidopteran insect cells remain poorly understood. In the present study, we demonstrated that the transfection of Bombyx mori BM-N cells with dsRNA against the B. mori cellular iap1 gene (cbm-iap1) induces severe apoptosis that is accompanied by an increase of caspase-3-like protease activity. In these apoptotic cells, the cleaved form of the endogenous initiator caspase Dronc (Bm-Dronc) was detected, indicating that cBm-IAP1 protein depletion by RNAi silencing resulted in the activation of Bm-Dronc. In transient expression assays in BM-N cells, cBm-IAP1 suppressed the apoptosis triggered by Bm-Dronc overexpression and depressed the elevation of caspase-3-like protease activity, but also increased the cleaved form of Bm-Dronc protein. cBm-IAP1 also suppressed the caspase-3-like protease activity stimulated by Bm-caspase-1 overexpression. Co-immunoprecipitation experiments demonstrated that cBm-IAP1 strongly interacts with Bm-Dronc, but only has weak affinity for Bm-caspase-1. Transient expression analyses showed that truncated cBm-IAP1 proteins defective in the BIR1, BIR2 or RING domain were unable to suppress Bm-Dronc-induced apoptosis. In addition, BM-N cells expressing truncated cBm-IAP1 proteins underwent apoptosis, suggesting that intact cBm-IAP1, which has anti-apoptotic activity, was replaced or displaced by the overexpressed truncated cBm-IAP1 proteins, which are incapable of interfering with the apoptotic caspase cascade. Taken together, the present results demonstrate that cBm-IAP1 is a vital negative regulator of apoptosis in BM-N cells and functions by preventing the activation and/or activity of Bm-Dronc and Bm-caspase-1., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

A key to successfully generate the penaeid shrimp cell line is to find out how primary cells died. The most suitable period to culture Penaeus monodon haemocytes was in the first 48 h of culture because cells had normal morphology, high percent of viable cells (65.29 ± 5.43%), low percent of early (11.75 ± 1.30%) and late apoptotic cells (15.47 ± 11.71%) determined by Annexin V and TUNEL including constant IAP (0.06 ± 0.01-0.07 ± 0.01) and caspase-3 expression (0.30 ± 0.06-0.39 ± 0.10) by real-time PCR throughout the experiment. Moreover, adding 50 and 250 μM of the cell permeable pan caspase inhibitor Z-VAD-FMK produced some melanised cells since the 48(th) hour, while percent of viable cells was decreased since the 24(th) hour with no difference in percent of early and late apoptotic cells compared to control at each time point. No difference of IAP and caspase-3 expression level in both Z-VAD-FMK groups was found compared to control and vehicle groups at each time point, excluding caspase-3 in 250 μM Z-VAD-FMK at the 24(th) hour was higher than control and vehicle. Supplementing sodium fluoride (NaF) induced cell membrane damage and cellular shrinkage of primary haemocytes within 2 h. Even percent of viable cells was reduced down to zero and percent of late apoptotic cells was increased by 2 h of incubation in 25 and 50 mM NaF, IAP and caspase-3 in all NaF groups was not different from control. These results indicate that a number of primary haemocytes derived in this study die through the apoptotic process., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

Apoptosis is a form of cell death in response to diverse stressful physiological or pathological stimuli. One of the most important gene families involved in apoptosis is inhibitors of apoptosis. As a member of inhibitors of apoptosis, BRUCE can suppress apoptosis and promote cell division. Because esophageal squamous cell carcinoma (ESCC) cells, as well as other cancer cells, are immortal, our aim in this study was to analyze BRUCE protein expression in ESCC and evaluate its correlation with tumoral clinicopathologic features. Fifty ESCC specimens were examined for BRUCE protein expression using immunohistochemistry. A defined scoring method was applied. BRUCE protein was detected in 82% of tumors. Tumor progression stage and invasion depth correlated significantly with BRUCE protein expression (P=.019 and .005, respectively). Furthermore, association of BRUCE expression with tumor location was near significant (P=.058). The correlation of BRUCE overexpression in ESCC and disease aggressiveness may confirm the importance of BRUCE in ESCC progression and invasiveness. Therefore, BRUCE protein may be a molecular marker for aggressive ESCC and, thus, a potential therapeutic target to inhibit tumor cell progression and invasion., (Copyright © 2016 Elsevier Inc. All rights reserved.)

Outcomes for patients diagnosed with the bone cancer osteosarcoma have not improved significantly in the last four decades. Only around 60% of patients and about a quarter of those with metastatic disease survive for more than five years. Although DNA-damaging chemotherapy drugs can be effective, they can provoke serious or fatal adverse effects including cardiotoxicity and therapy-related cancers. Better and safer treatments are therefore needed. We investigated the anti-osteosarcoma activity of IAP antagonists (also known as Smac mimetics) using cells from primary and metastatic osteosarcomas that arose spontaneously in mice engineered to lack p53 and Rb expression in osteoblast-derived cells. The IAP antagonists SM-164, GDC-0152 and LCL161, which efficiently target XIAP and cIAPs, sensitized cells from most osteosarcomas to killing by low levels of TNFα but not TRAIL. RIPK1 expression levels and activity correlated with sensitivity. RIPK3 levels varied considerably between tumors and RIPK3 was not required for IAP antagonism to sensitize osteosarcoma cells to TNFα. IAP antagonists, including SM-164, lacked mutagenic activity. These data suggest that drugs targeting XIAP and cIAP1/2 may be effective for osteosarcoma patients whose tumors express abundant RIPK1 and contain high levels of TNFα, and would be unlikely to provoke therapy-induced cancers in osteosarcoma survivors., Competing Interests: The authors have no conflicts of interest.

It is now well established that the mitochondrion is a central regulator of mammalian cell apoptosis. However, the importance of this organelle in non-mammalian apoptosis has long been regarded as minor, mainly because of the absence of a crucial role for cytochrome c in caspase activation. Recent results indicate that the control of caspase activation and cell death in Drosophila occurs at the mitochondrial level. Numerous proteins, including RHG proteins and proteins of the Bcl-2 family that are key regulators of Drosophila apoptosis, constitutively or transiently localize in mitochondria. These proteins participate in the cell death process at different levels such as degradation of Diap1, a Drosophila IAP, production of mitochondrial reactive oxygen species or stimulation of the mitochondrial fission machinery. Here, we review these mitochondrial events that might have their counterpart in human.

PTEN loss is prognostic for patient relapse post-radiotherapy in prostate cancer (CaP). Infiltration of tumor-associated macrophages (TAMs) is associated with reduced disease-free survival following radical prostatectomy. However, the association between PTEN loss, TAM infiltration and radiotherapy response of CaP cells remains to be evaluated. Immunohistochemical and molecular analysis of surgically-resected Gleason 7 tumors confirmed that PTEN loss correlated with increased CXCL8 expression and macrophage infiltration. However PTEN status had no discernable correlation with expression of other inflammatory markers by CaP cells, including TNF-α. In vitro, exposure to conditioned media harvested from irradiated PTEN null CaP cells induced chemotaxis of macrophage-like THP-1 cells, a response partially attenuated by CXCL8 inhibition. Co-culture with THP-1 cells resulted in a modest reduction in the radio-sensitivity of DU145 cells. Cytokine profiling revealed constitutive secretion of TNF-α from CaP cells irrespective of PTEN status and IR-induced TNF-α secretion from THP-1 cells. THP-1-derived TNF-α increased NFκB pro-survival activity and elevated expression of anti-apoptotic proteins including cellular inhibitor of apoptosis protein-1 (cIAP-1) in CaP cells, which could be attenuated by pre-treatment with a TNF-α neutralizing antibody. Treatment with a novel IAP antagonist, AT-IAP, decreased basal and TNF-α-induced cIAP-1 expression in CaP cells, switched TNF-α signaling from pro-survival to pro-apoptotic and increased radiation sensitivity of CaP cells in co-culture with THP-1 cells. We conclude that targeting cIAP-1 can overcome apoptosis resistance of CaP cells and is an ideal approach to exploit high TNF-α signals within the TAM-rich microenvironment of PTEN-deficient CaP cells to enhance response to radiotherapy.

The inhibitor of apoptosis (IAP) proteins maintain a balance between cell proliferation and cell death by inhibiting caspase activity and facilitating immune responses. In this study, phylogenetic analysis revealed lineage-specific expansion and tandem duplication of IAPs in the Pacific oyster Crassostrea gigas. We then investigated a representative oyster-specific XIAP-like gene (CgIAP2) to understand how it regulates initiator caspase. Cloning of full-length CgIAP2 from oyster cDNA uncovered a deduced protein containing two BIR domains and a RING domain. Homolog comparison demonstrated that CgIAP2 clustered into the invertebrate branch. We found that CgIAP2 was likely involved in apoptosis inhibition and immune defense, based on high mRNA expression in the gills and labial palps, as well as increased mRNA expression after bacterial challenge. A yeast two-hybrid assay revealed that the BIR2 domain was necessary and sufficient to mediate interaction between CgIAP2 and Cgcaspase-2, providing direct evidence that CgIAP2 participates in apoptosis inhibition., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

Chemotherapy and radiotherapy can cause permanent damage to the genomes of surviving cells, provoking severe side effects such as second malignancies in some cancer survivors. Drugs that mimic the activity of death ligands, or antagonise pro-survival proteins of the Bcl-2 or IAP families have yielded encouraging results in animal experiments and early phase clinical trials. Because these agents directly engage apoptosis pathways, rather than damaging DNA to indirectly provoke tumour cell death, we reasoned that they may offer another important advantage over conventional therapies: minimisation or elimination of side effects such as second cancers that result from mutation of surviving normal cells. Disappointingly, however, we previously found that concentrations of death receptor agonists like TRAIL that would be present in vivo in clinical settings provoked DNA damage in surviving cells. In this study, we used cell line model systems to investigate the mutagenic capacity of drugs from two other classes of direct apoptosis-inducing agents: the BH3-mimetic ABT-737 and the IAP antagonists LCL161 and AT-406. Encouragingly, our data suggest that IAP antagonists possess negligible genotoxic activity. Doses of ABT-737 that were required to damage DNA stimulated Bax/Bak-independent signalling and exceeded concentrations detected in the plasma of animals treated with this drug. These findings provide hope that cancer patients treated by BH3-mimetics or IAP antagonists may avoid mutation-related illnesses that afflict some cancer survivors treated with conventional DNA-damaging anti-cancer therapies., (Copyright © 2015 Elsevier B.V. All rights reserved.)

Although technically a member of the Inhibitor of Apoptosis (IAP) gene family, survivin has consistently defied assumptions, refuted predictions and challenged paradigms. Despite its more than 5500 citations currently in Medline, the biology of survivin has remained fascinatingly complex, its exploitation in human disease, most notably cancer, tantalizing, and its regulation of cellular homeostasis unexpectedly far-reaching. An inconvenient outsider that resists schemes and dogmas, survivin continues to hold great promise to unlock fundamental circuitries of cellular functions in health and disease., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

Gene deletion studies have helped reveal the unique and overlapping roles played by IAP proteins. Crossing IAP mutant mice has helped unravel the complex feed-back regulatory circuits in which cIAP1, cIAP2 and XIAP allow innate defensive responses to microbial pathogens, without the development of auto-inflammatory syndromes. Deletion of genes for Survivin and its homologs in yeasts, invertebrates and mammals has shown that it functions differently, as it is not a regulator of innate immunity or apoptosis, but acts together with INCENP, aurora kinase B and Borealin to allow chromosome segregation during mitosis., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

As indicated by their name, members of the Inhibitor of APoptosis (IAP) family were first believed to be functionally restricted to apoptosis inhibition. It is now clear that IAPs have a much wider spectrum of action, and recent studies even suggest that some of its members primarily regulate inflammatory responses. Inflammation, the first response of the immune system to infection or tissue injury, is highly regulated by ubiquitylation - a posttranslational modification of proteins with various consequences. In this review, we focus on the recently reported functions of XIAP, cIAP1 and cIAP2 as ubiquitin ligases regulating innate immunity and inflammation., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

Members of the inhibitor of apoptosis (IAP) family are characterised by the presence of at least one baculoviral IAP repeat (BIR) domain. However, during the course of evolution, other globular modules have been adopted to perform distinct functions. Consequently, the IAP family is now recognised as consisting of members that perform critical functions in different aspects of cellular regulation. In this review, the structural diversity present within the IAP protein family is presented. Known structures of individual domains are discussed and their properties are described in light of recent data. In particular the plasticity of BIR domains and their ability to accommodate different binding partners is highlighted, as well as the importance of communication between the domains in regulating the covalent attachment of ubiquitin., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

The identification, now more than 20 years ago, of the first iap genes in baculoviruses subsequently led to many important discoveries concerning the regulation of apoptosis and other important biological processes in insects and mammals. Currently there are more than 200 known viral IAP homologs in baculoviruses and other families of invertebrate DNA viruses. This review begins with a personal account of the events leading up to the discovery of the first iap genes, followed by a summary of what is currently known about the different types of viral IAPs and their functions in regulating apoptosis, and possibly other cellular processes., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

The inhibitor of apoptosis protein (IAP) family acts as an inhibitor of apoptosis pathways. The potential prognostic value of the expression of selected IAP family members, XIAP, cIAP-1, cIAP-2 and survivin protein, was evaluated with regard to treatment response and survival of 56 newly diagnosed adult patients with acute myeloid leukemia (AML). The presence of these IAP members influenced the achievement of a complete response (CR). In addition, overall survival (OS) was influenced by low survivin expression in univariate and multivariate analysis (p = 0.014 and p = 0.013, respectively). A strong correlation was observed between members of the IAP family (XIAP and cIAP-1, XIAP and cIAP-2, cIAP-1 and cIAP-2, p < 0.001 for all comparisons), while Smac/DIABLO demonstrated an inverse correlation with XIAP, cIAP-1 and cIAP-2 (p < 0.001 for all comparisons). Further studies should be undertaken to better demonstrate the mode of action of IAP members, as well as their prognostic and therapeutic potentials.

Interferon Regulatory Factor (IRF)-1, originally identified as a transcription factor of the human interferon (IFN)-β gene, mediates tumor suppression and may inhibit oncogenesis. We have shown that IRF-1 in human breast cancer cells results in the down-regulation of survivin, tumor cell death, and the inhibition of tumor growth in vivo in xenogeneic mouse models. In this current report, we initiate studies comparing the effect of IRF-1 in human nonmalignant breast cell and breast cancer cell lines. While IRF-1 in breast cancer cells results in growth inhibition and cell death, profound growth inhibition and cell death are not observed in nonmalignant human breast cells. We show that TNF-α or IFN-γ induces IRF-1 in breast cancer cells and results in enhanced cell death. Abrogation of IRF-1 diminishes TNF-α and IFN-γ-induced apoptosis. We test the hypothesis that IRF-1 augments TNF-α-induced apoptosis in breast cancer cells. Potential signaling networks elicited by IRF-1 are investigated by evaluating the NF-κB pathway. TNF-α and/or IFN-γ results in decreased presence of NF-κB p65 in the nucleus of breast cancer cells. While TNF-α and/or IFN-γ can induce IRF-1 in nonmalignant breast cells, a marked change in NF-κB p65 is not observed. Moreover, the ectopic expression of IRF-1 in breast cancer cells results in caspase-3, -7, -8 cleavage, inhibits NF-κB activity, and suppresses the expression of molecules involved in the NF-κB pathway. These data show that IRF-1 in human breast cancer cells elicits multiple signaling networks including intrinsic and extrinsic cell death and down-regulates molecules involved in the NF-κB pathway.

The baculovirus Bombyx mori nucleopolyhedrovirus (BmNPV) possesses two genes, iap1 and iap2, which encode inhibitor of apoptosis (IAP) proteins. We previously showed that although both genes are dispensable for viral propagation, iap2 is required for efficient viral propagation in cultured cells. BmNPV IAP2 contains three putative functional domains: a baculovirus IAP repeat (BIR), a BIR-like (BIRL) domain, and a RING finger domain. To identify the domain affecting viral growth, we generated a series of BmNPV bacmids expressing iap2 derivatives lacking one or two domains, or possessing a single amino acid substitution to abolish IAP2 ubiquitin ligase activity. We examined their properties in both cultured cells and B. mori larvae. We found that either the BIR or BIRL domain of IAP2 plays an important role in BmNPV infection, and that the RING finger domain, which is required for ubiquitin ligase activity, does not greatly contribute to BmNPV propagation. This is the first study to identify functional domains of the baculovirus IAP2 protein., (Copyright © 2014 Elsevier Inc. All rights reserved.)

Bivalent heterodimeric IAP antagonists that incorporate (R)-tetrahydroisoquinoline in the P3' subunit show high affinity for the BIR2 domain and demonstrated potent IAP inhibitory activities in biochemical and cellular assays. Potent in vivo efficacy was observed in a variety of human tumor xenograft models. The bivalent heterodimeric molecule 3 with a P3-P3' benzamide linker induced pharmacodynamic markers of apoptosis and was efficacious when administered intravenously at a dose of 1mg/kg to mice harboring A875 human melanoma tumors. Analog 5, with a polyamine group incorporated at the P2' thiovaline side chain exhibited antiproliferative activity against the P-gp expressing HCT116/VM46 cell line., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

Mitogen-activated protein kinases (MAPKs) are highly conserved protein kinase modules, and they control fundamental cellular processes. While the activation of MAPKs has been well studied, little is known on the mechanisms driving their inactivation. Here we uncover a role for ubiquitination in the inactivation of a MAPK module. Extracellular-signal-regulated kinase 5 (ERK5) is a unique, conserved member of the MAPK family and is activated in response to various stimuli through a three-tier cascade constituting MEK5 and MEKK2/3. We reveal an unexpected role for Inhibitors of Apoptosis Proteins (IAPs) in the inactivation of ERK5 pathway in a bimodal manner involving direct interaction and ubiquitination. XIAP directly interacts with MEKK2/3 and competes with PB1 domain-mediated binding to MEK5. XIAP and cIAP1 conjugate predominantly K63-linked ubiquitin chains to MEKK2 and MEKK3 which directly impede MEK5-ERK5 interaction in a trimeric complex leading to ERK5 inactivation. Consistently, loss of XIAP or cIAP1 by various strategies leads to hyperactivation of ERK5 in normal and tumorigenic cells. Loss of XIAP promotes differentiation of human primary skeletal myoblasts to myocytes in a MEKK2/3-ERK5-dependent manner. Our results reveal a novel, obligatory role for IAPs and ubiquitination in the physical and functional disassembly of ERK5-MAPK module and human muscle cell differentiation., (© 2014 The Authors.)

The mechanisms for regulation of the Inhibitor of Apoptosis (IAP) Survivin in cells undergoing stress associated with tumor development and the tumor microenvironment are not well understood. The stress response transcription factors HIF-1α and Yin Yang 1 (YY1) were hypothesized to contribute to the upregulation of Survivin in tumor cells. As expected, U2OS cells overexpressing HIF-1α showed a 2- to 3-fold transactivation when transfected. Surprisingly, when YY1 was overexpressed in this survivin promoter reporter system, luciferase expression was repressed 30- to 40-fold. YY1 involvement in survivin promoter repression was confirmed using siRNA directed against YY1. These studies showed that knockdown of YY1 releases the survivin promoter from the observed repression and leads to a 3- to 5-fold increase in promoter activity above basal levels. A U2OS cell line containing a stable YY1 Tet-off system was used to determine whether a temporal increase in YY1 expression affects Survivin protein levels. A low to moderate decrease in Survivin protein was observed 24h and 48h after Tet removal. Studies also confirmed that YY1 is capable of directly binding to the survivin promoter. Collectively, these findings identify novel basal transcriptional requirements of survivin gene expression which are likely to play important roles in the development of cancer and resistance to its treatment., (Copyright © 2014 Elsevier Inc. All rights reserved.)

Objective: The objective of this study is to chemosensitize ovarian cancer (OVCa) cells to cisplatin (CDDP) using an inhibitor of Survivin, YM155. The efficacy of YM155 in combination with CDDP was determined in vitro, ex vivo and in vivo., Methods: Human OVCa cell lines A2780p and their cisplatin-resistant derivative A2780cis, were treated with CDDP, YM155, and the combined treatment (YM155+CDDP), and cell viability, mRNA and protein expression levels, cell-cycle distribution, and DNA damage were then evaluated. Furthermore, the efficacy of YM155 combined with CDDP was further examined in established primary cell cultures and xenograft models., Results: The combination of YM155 with CDDP induced G2/M cell cycle arrest and apoptosis, increased DNA damage, and decreased Survivin levels, especially in A2780cis CDDP-resistant cells. Additionally, YM155 in combination with CDDP sensitized primary cell cultures to CDDP. Studies in vivo showed how this combination significantly decreased the tumor size of OVCa xenografts., Conclusions: Our results demonstrate that in OVCa cells the expression of Survivin did not affect their sensitivity to YM155, suggesting that Survivin was not the only target of YM155. The combination of YM155 with CDDP could be a good option for therapy of CDDP-resistant OVCa, independently of p53 status., (Copyright © 2013 Elsevier Inc. All rights reserved.)

Inhibitor of apoptosis (IAP) proteins interface with, and regulate a large number of, cell signaling pathways. If there is a common theme to these pathways, it is that they are involved in the development of the immune system, immune responses, and unsurprisingly, given their name, cell death. Beyond that it is difficult to discover an underlying logic because sometimes IAPs are required to inhibit or prevent signaling, whereas in other cases they are required for signaling to take place. In whatever role they play, they are recruited into signaling complexes and function as ubiquitin E3 ligases, via their RING domains. This review discusses IAP regulation of signaling pathways and focuses on the mammalian IAPs, XIAP, c-IAP1, and c-IAP2, with a particular emphasis on techniques and methods that were used to uncover their roles. We also provide a perspective on targeting IAP proteins for therapeutic intervention and methods used to define the clinical relevance of IAP proteins., (© 2014 Elsevier Inc. All rights reserved.)

Survivin is a member of the inhibitor of apoptosis protein (IAP) family with crucial roles in apoptosis and cell cycle regulation. Post-translational modifications (PTMs) have a ubiquitous role in the regulation of a diverse range of proteins' cellular functions and survivin is not an exception. Phosphorylation, acetylation and ubiquitination seem to regulate survivin anti-apoptotic and mitotic roles and also its nuclear localization. In the present review we explore the role of PTMs on protein-protein interactions focused on survivin to provide new insights into the functions and cell localization of this IAP in pathophysiological conditions, which might help the envisioning of novel targeted therapies for diseases characterized by impaired survivin activity. Protein-protein interaction analysis was performed with bioinformatics tools based on published data aiming to give an integrated perspective of this IAP's role in the cell., (Copyright © 2013 Elsevier Inc. All rights reserved.)

Chronic hepatitis B virus (HBV) infection remains a global health threat and affects hundreds of millions worldwide. Small molecule compounds that mimic natural antagonists of inhibitor of apoptosis (IAP) proteins, known as Smac-mimetics (second mitochondria-derived activator of caspases-mimetics), can promote the death of HBV-replicating liver cells and promote clearance of infection in preclinical models of HBV infection. The Smac-mimetic birinapant is a substrate of the multidrug resistance protein 1 (MDR1) efflux pump, and therefore inhibitors of MDR1 increase intracellular concentration of birinapant in MDR1 expressing cells. Liver cells are known to express MDR1 and other drug pump proteins. In this study, we investigated whether combining the clinical drugs, birinapant and the MDR1 inhibitor zosuquidar, increases the efficacy of birinapant in killing HBV expressing liver cells. We showed that this combination treatment is well tolerated and, compared to birinapant single agent, was more efficient at inducing death of HBV-positive liver cells and improving HBV-DNA and HBV surface antigen (HBsAg) control kinetics in an immunocompetent mouse model of HBV infection. Thus, this study identifies a novel and safe combinatorial treatment strategy to potentiate substantial reduction of HBV replication using an IAP antagonist.

Chronic hepatitis B virus (HBV) infection remains a global health threat and affects hundreds of millions worldwide. Small molecule compounds that mimic natural antagonists of inhibitor of apoptosis (IAP) proteins, known as Smac-mimetics (second mitochondria-derived activator of caspases-mimetics), can promote the death of HBV-replicating liver cells and promote clearance of infection in preclinical models of HBV infection. The Smac-mimetic birinapant is a substrate of the multidrug resistance protein 1 (MDR1) efflux pump, and therefore inhibitors of MDR1 increase intracellular concentration of birinapant in MDR1 expressing cells. Liver cells are known to express MDR1 and other drug pump proteins. In this study, we investigated whether combining the clinical drugs, birinapant and the MDR1 inhibitor zosuquidar, increases the efficacy of birinapant in killing HBV expressing liver cells. We showed that this combination treatment is well tolerated and, compared to birinapant single agent, was more efficient at inducing death of HBV-positive liver cells and improving HBV-DNA and HBV surface antigen (HBsAg) control kinetics in an immunocompetent mouse model of HBV infection. Thus, this study identifies a novel and safe combinatorial treatment strategy to potentiate substantial reduction of HBV replication using an IAP antagonist. [ABSTRACT FROM AUTHOR]