XIAP facilitates breast and colon carcinoma growth via promotion of p62 depletion through ubiquitination-dependent proteasomal degradation

Moracin D suppresses cell growth and induces apoptosis via targeting the XIAP/PARP1 axis in pancreatic cancer

BACKGROUND

Pancreatic cancer, a tumor with a high metastasis rate and poor prognosis, is among the deadliest human malignancies. Investigating effective drugs for their treatment is imperative. Moracin D, a natural benzofuran compound isolated from Morus alba L., shows anti-inflammation and anti-breast cancer properties and is effective against Alzheimer's disease. However, the effect and mechanism of Moracin D action in pancreatic cancer remain obscure.

PURPOSE

To investigate the function and molecular mechanism of Moracin D action in repressing the malignant progression of pancreatic cancer.

METHODS

Pancreatic cancer cells were treated with Moracin D, and cell proliferation was evaluated by cell counting kit-8 (CCK-8) and immunofluorescence assays. The clonogenicity of pancreatic cancer cells was assessed based on plate colony formation and soft agar assay. Flow cytometry was used to detect cell apoptosis. The expression of proteins related to the apoptosis pathway was determined by Western blot analysis. Moracin D and XIAP were subjected to docking by auto-dock molecular docking analysis. Ubiquitination levels of XIAP and the interaction of XIAP and PARP1 were assessed by co-immunoprecipitation analysis. Moracin D's effects on tumorigenicity were assessed by a tumor xenograft assay.

RESULTS

Moracin D inhibited cell proliferation, induced cell apoptosis, and regulated the protein expression of molecules involved in caspase-dependent apoptosis pathways. Moracin D suppressed clonogenicity and tumorigenesis of pancreatic cancer cells. Mechanistically, XIAP could interact with PARP1 and stabilize PARP1 by controlling its ubiquitination levels. Moracin D diminished the stability of XIAP and decreased the expression of XIAP by promoting proteasome-dependent XIAP degradation, further blocking the XIAP/PARP1 axis and repressing the progression of pancreatic cancer. Moracin D could dramatically improve the chemosensitivity of gemcitabine in pancreatic cancer cells.

CONCLUSION

Moracin D repressed cell growth and tumorigenesis, induced cell apoptosis, and enhanced the chemosensitivity of gemcitabine through the XIAP/PARP1 axis in pancreatic cancer. Moracin D is a potential therapeutic agent or adjuvant for pancreatic cancer.

Role of protein degradation systems in colorectal cancer

Protein degradation is essential for maintaining protein homeostasis. The ubiquitin‒proteasome system (UPS) and autophagy-lysosome system are the two primary pathways responsible for protein degradation and directly related to cell survival. In malignant tumors, the UPS plays a critical role in managing the excessive protein load caused by cancer cells hyperproliferation. In this review, we provide a comprehensive overview of the dual roles played by the UPS and autolysosome system in colorectal cancer (CRC), elucidating their impact on the initiation and progression of this disease while also highlighting their compensatory relationship. Simultaneously targeting both protein degradation pathways offers new promise for enhancing treatment efficacy against CRC. Additionally, apoptosis is closely linked to ubiquitination and autophagy, and caspases degrade proteins. A thorough comprehension of the interplay between various protein degradation pathways is highly important for clarifying the mechanism underlying the onset and progression of CRC.

The involvement of E3 ubiquitin ligases in the development and progression of colorectal cancer

To date, colorectal cancer (CRC) still has limited therapeutic efficacy and poor prognosis and there is an urgent need for novel targets to improve the outcome of CRC patients. The highly conserved ubiquitination modification mediated by E3 ubiquitin ligases is an important mechanism to regulate the expression and function of tumor promoters or suppressors in CRC. In this review, we provide an overview of E3 ligases in modulating various biological processes in CRC, including proliferation, migration, stemness, metabolism, cell death, differentiation and immune response of CRC cells, emphasizing the pluripotency of E3 ubiquitin ligases. We further focus on the role of E3 ligases in regulating vital cellular signal pathways in CRC, such as Wnt/β-catenin pathway and NF-κB pathway. Additionally, considering the potential of E3 ligases as novel targets in the treatment of CRC, we discuss what aspects of E3 ligases can be utilized and exploited for efficient therapeutic strategies.

Molecular basis for nuclear accumulation and targeting of the inhibitor of apoptosis BIRC2

The inhibitor of apoptosis protein BIRC2 regulates fundamental cell death and survival signaling pathways. Here we show that BIRC2 accumulates in the nucleus via binding of its second and third BIR domains, BIRC2BIR2 and BIRC2BIR3, to the histone H3 tail and report the structure of the BIRC2BIR3-H3 complex. RNA-seq analysis reveals that the genes involved in interferon and defense response signaling and cell-cycle regulation are most affected by depletion of BIRC2. Overexpression of BIRC2 delays DNA damage repair and recovery of the cell-cycle progression. We describe the structural mechanism for targeting of BIRC2BIR3 by a potent but biochemically uncharacterized small molecule inhibitor LCL161 and demonstrate that LCL161 disrupts the association of endogenous BIRC2 with H3 and stimulates cell death in cancer cells. We further show that LCL161 mediates degradation of BIRC2 in human immunodeficiency virus type 1-infected human CD4+ T cells. Our findings provide mechanistic insights into the nuclear accumulation of and blocking BIRC2.

Exploration of Phaeanthine: A Bisbenzylisoquinoline Alkaloid Induces Anticancer Effect in Cervical Cancer Cells Involving Mitochondria-Mediated Apoptosis

Natural-product-based pharmacophores possess considerably more structural diversity, attractive physicochemical features, and relatively less toxicity than synthesized drug entities. In this context, our studies on phaeanthine, a bisbenzylisoquinoline alkaloid isolated from the rhizomes of Cyclea peltata (Lam) Hook.f & Thoms., showed selective cytotoxicity toward cervical cancer cells (HeLa) with an IC₅₀ of 8.11 ± 0.04 μM. Subsequent investigation with in silico molecular docking of phaeanthine displayed preferential binding to the antiapoptotic protein Akt as reflected by a docking score of -5.023. Interestingly, the follow-up in vitro assessment of the compound correlated with mitochondria-mediated apoptosis specifically by downregulating the expression of Akt and p-Akt, including other antiapoptotic proteins MCl-1, IGF-2, and XIAP. In the complementary in vitro assessment, mitochondrial membrane polarization and dynamics of intercellular cytochrome c validated the intrinsic mechanism of the apoptotic phenomenon. To the best of our knowledge, this is the first comprehensive anticancer profiling study of phaeanthine against HeLa cells.

Lentiviral Gene Transfer Corrects Immune Abnormalities in XIAP Deficiency

BACKGROUND

X-linked inhibitor of apoptosis protein (XIAP) deficiency is a severe immunodeficiency with clinical features including hemophagocytic lymphohistiocytosis (HLH) and inflammatory bowel disease (IBD) due to defective NOD2 responses. Management includes immunomodulatory therapies and hematopoietic stem cell transplant (HSCT). However, this cohort is particularly susceptible to the chemotherapeutic regimens and acutely affected by graft-vs-host disease (GvHD), driving poor long-term survival in transplanted patients. Autologous HSC gene therapy could offer an alternative treatment option and would abrogate the risks of alloreactivity.

METHODS

Hematopoietic progenitor (Lin-ve) cells from XIAPy/- mice were transduced with a lentiviral vector encoding human XIAP cDNA before transplantation into irradiated XIAP y/- recipients. After 12 weeks animals were challenged with the dectin-1 ligand curdlan and recovery of innate immune function was evaluated though analysis of inflammatory cytokines, body weight, and splenomegaly. XIAP patient-derived CD14+ monocytes were transduced with the same vector and functional recovery was demonstrated using in vitro L18-MDP/NOD2 assays.

RESULTS

In treated XIAPy/- mice, ~40% engraftment of gene-corrected Lin-ve cells led to significant recovery of weight loss, splenomegaly, and inflammatory cytokine responses to curdlan, comparable to wild-type mice. Serum IL-6, IL-10, MCP-1, and TNF were significantly reduced 2-h post-curdlan administration in non-corrected XIAPy/- mice compared to wild-type and gene-corrected animals. Appropriate reduction of inflammatory responses was observed in gene-corrected mice, whereas non-corrected mice developed an inflammatory profile 9 days post-curdlan challenge. In gene-corrected patient CD14+ monocytes, TNF responses were restored following NOD2 activation with L18-MDP.

CONCLUSION

Gene correction of HSCs recovers XIAP-dependent immune defects and could offer a treatment option for patients with XIAP deficiency.

XIAP and PHB1 Regulate Anoikis through Competitive Binding to TRAF6

Anoikis resistance is a prerequisite for circulating tumor cells to survive. However, the mechanism underlying anoikis resistance is poorly understood. In the current study, the effect of TNF receptor-associated factor 6 (TRAF6)-induced NF-kB activation on anoikis susceptibility in tumor cells was evaluated. Differential TRAF6-binding proteins in anoikis-sensitive versus anoikis-resistant tumor cells were screened by LC/MS-MS analysis. The effects of TRAF6-binding proteins on the stability of TRAF6, the activation of NF-kB signaling and anoikis susceptibility in tumor cells were detected. We found that the loss of TRAF6 expression is an important molecular event linked to anoikis. X-linked inhibitor of apoptosis protein (XIAP), an E3 ligase, can bind, ubiquitinate, and degrade TRAF6 and may lead to inactivation of NF-κB signaling and anoikis sensitivity. High expression of prohibitin 1 (PHB1) competes with XIAP for binding to TRAF6 and confers anoikis resistance to tumor cells. PHB1 and TRAF6 knockdown eliminated tumor cells from the circulation in vivo. Significant correlations between elevated PHB1 and TRAF6 expression and distant metastasis were observed in patients with oral cancer. Collectively, we elucidated a novel mechanism governing anoikis. Our data also indicated that TRAF6 and PHB1 are potential therapeutic targets for tumor cells disseminating in the circulation.

IMPLICATIONS

Our data implicate that PHB1 competes with XIAP for binding to TRAF6 and confers anoikis resistance to tumor cells.

The cross-talk of autophagy and apoptosis in breast carcinoma: implications for novel therapies?

Breast cancer is still the most common cancer in women worldwide. Resistance to drugs and recurrence of the disease are two leading causes of failure in treatment. For a more efficient treatment of patients, the development of novel therapeutic regimes is needed. Recent studies indicate that modulation of autophagy in concert with apoptosis induction may provide a promising novel strategy in breast cancer treatment. Apoptosis and autophagy are two tightly regulated distinct cellular processes. To maintain tissue homeostasis abnormal cells are disposed largely by means of apoptosis. Autophagy, however, contributes to tissue homeostasis and cell fitness by scavenging of damaged organelles, lipids, proteins, and DNA. Defects in autophagy promote tumorigenesis, whereas upon tumor formation rapidly proliferating cancer cells may rely on autophagy to survive. Given that evasion of apoptosis is one of the characteristic hallmarks of cancer cells, inhibiting autophagy and promoting apoptosis can negatively influence cancer cell survival and increase cell death. Hence, combination of antiautophagic agents with the enhancement of apoptosis may restore apoptosis and provide a therapeutic advantage against breast cancer. In this review, we discuss the cross-talk of autophagy and apoptosis and the diverse facets of autophagy in breast cancer cells leading to novel models for more effective therapeutic strategies.

Cell-penetrating peptide-mediated delivery of therapeutic peptides/proteins to manage the diseases involving oxidative stress, inflammatory response and apoptosis

OBJECTIVES

Peptides and proteins represent great potential for modulating various cellular processes including oxidative stress, inflammatory response, apoptosis and consequently the treatment of related diseases. However, their therapeutic effects are limited by their inability to cross cellular barriers. Cell-penetrating peptides (CPPs), which can transport cargoes into the cell, could resolve this issue, as would be discussed in this review.

KEY FINDINGS

CPPs have been successfully exploited in vitro and in vivo for peptide/protein delivery to treat a wide range of diseases involving oxidative stress, inflammatory processes and apoptosis. Their in vivo applications are still limited due to some fundamental issues of CPPs, including nonspecificity, proteolytic instability, potential toxicity and immunogenicity.

SUMMARY

Totally, CPPs could potentially help to manage the diseases involving oxidative stress, inflammatory response and apoptosis by delivering peptides/proteins that could selectively reach proper intracellular targets. More studies to overcome related CPP limitations and confirm the efficacy and safety of this strategy are needed before their clinical usage.

Subcellular localization of X-linked inhibitor of apoptosis protein (XIAP) in cancer: does that matter?

X-linked inhibitor of apoptosis protein (XIAP) finely tunes the balance between survival and death to control homeostasis. XIAP is found aberrantly expressed in cancer, which has been shown to promote resistance to therapy-induced apoptosis and confer poor outcome. Despite its predominant cytoplasmic localization in human tissues, growing evidence implicates the expression of XIAP in other subcellular compartments in sustaining cancer hallmarks. Herein, we review our current knowledge on the prognostic role of XIAP localization and discuss molecular mechanisms underlying differential biological functions played in each compartment. The comprehension of XIAP subcellular shuttling and functional dynamics might provide the rationale for future anticancer therapeutics.

The complexity of biological control systems: An autophagy case study

Autophagy and YAP1-WWTR1/TAZ signalling are tightly linked in a complex control system of forward and feedback pathways which determine different cellular outcomes in differing cell types at different time-points after perturbations. Here we extend our previous experimental and modelling approaches to consider two possibilities. First, we have performed additional mathematical modelling to explore how the autophagy-YAP1 crosstalk may be controlled by posttranslational modifications of components of the pathways. Second, since analogous contrasting results have also been reported for autophagy as a regulator of other transduction pathways engaged in tumorigenesis (Wnt/β-catenin, TGF-β/Smads, NF-kB or XIAP/cIAPs), we have considered if such discrepancies may be explicable through situations involving competing pathways and feedback loops in different cell types, analogous to the autophagy-YAP/TAZ situation. Since distinct posttranslational modifications dominate those pathways in distinct cells, these need to be understood to enable appropriate cell type-specific therapeutic strategies for cancers and other diseases.

Autophagy and Ubiquitination as Two Major Players in Colorectal Cancer: A Review on Recent Patents

BACKGROUND

As one of the most commonly diagnosed cancers among men and women, Colorectal Cancer (CRC) leads to high rates of morbidity and mortality across the globe. Recent anti- CRC therapies are now targeting specific signaling pathways involved in colorectal carcinogenesis. Ubiquitin Proteasome System (UPS) and autophagy are two main protein quality control systems, which play major roles in the carcinogenesis of colorectal cancer. A balanced function of these two pathways is necessary for the regulation of cell proliferation and cell death.

OBJECTIVE

In this systematic review, we discuss the available evidence regarding the roles of autophagy and ubiquitination in progression and inhibition of CRC.

METHODS

The search terms "colorectal cancer" or "colon cancer" or "colorectal carcinoma" or "colon carcinoma" in combination with "ubiquitin proteasome" and "autophagy" were searched in PubMed, Web of Science, and Scopus databases, and also Google Patents (https://patents.google .com) from January 2000 to Feb 2020.

RESULTS

The most important factors involved in UPS and autophagy have been investigated. There are many important factors involved in UPS and autophagy but this systematic review shows the studies that have mostly focused on the role of ATG, 20s proteasome and mTOR in CRC, and the more important factors such as ATG8, FIP200, and TIGAR factors that are effective in the regulation of autophagy in CRC cells have not been yet investigated.

CONCLUSION

The most important factors involved in UPS and autophagy such as ATG, 20s proteasome and mTOR, ATG8, FIP200, and TIGAR can be considered in drug therapy for controlling or activating autophagy.

Killing HIV-infected resting central memory CD4+ T cells by targeting inhibitor of apoptosis proteins-inhibited autophagy

Dysfunction of CD4⁺ T cells by HIV infection can cause serious immune defects. Recently, Campbell and colleagues described an intriguing and simple therapeutic method for HIV-infected resting central memory CD4⁺ T cells (HIV-T_CM), dependently on inhibitor of apoptosis (IAP) family proteins-targeted and second mitochondria-derived activator of caspases (SMAC) mimetics-mediated apoptosis, which is only triggered in HIV-T_CM and not uninfected ones. Autophagy induction and subsequent formation of a ripoptosome-like death signaling complex were observed after such treatment, which may partially explain the potential mechanism. However, the direct intracellular inhibitory effects of IAPs on autophagy, as well as the critical roles of autophagy in activating extracellular anti-infection immune responses, warrant further investigation. Thus, this pointer aims to provide potential alternative mechanisms and to suggest important avenues for follow-up study.

CUL5-ASB6 Complex Promotes p62/SQSTM1 Ubiquitination and Degradation to Regulate Cell Proliferation and Autophagy

p62/SQSTM1 (sequestosome-1) is a key protein involved in multiple cellular bioprocesses including autophagy, nutrient sensing, cell growth, cell death, and survival. Therefore, it is implicated in human diseases such as obesity and cancer. Here, we show that the CUL5–ASB6 complex is a ubiquitin E3 ligase complex mediating p62 ubiquitination and degradation. Depletion of CUL5 or ASB6 induced p62 accumulation, and overexpression of ASB6 promoted ubiquitination and degradation of p62. Functionally, ASB6 overexpression can inhibit the proliferation of MEF and hepatocellular carcinoma cells by reducing p62 protein level, and impair the occurrence of autophagy. Overall, our study identified a new molecular mechanism regulating p62 stability, which may provide additional insights for understanding the delicate control of p62 and cell proliferation–autophagy control in physiological and pathological settings.

Hsa-miR-125b Therapeutic Role in Colon Cancer Is Dependent on the Mutation Status of the TP53 Gene

Colon cancer is the third most common cancer type worldwide and is highly dependent on DNA mutations that progressively appear and accumulate in the normal colon epithelium. Mutations in the TP53 gene appear in approximately half of these patients and have significant implications in disease progression and response to therapy. miR-125b-5p is a controversial microRNA with a dual role in cancer that has been reported to target specifically TP53 in colon adenocarcinomas. Our study investigated the differential therapeutic effect of miR-125b-5p replacement in colon cancer based on the TP53 mutation status of colon cancer cell lines. In TP53 mutated models, miR-125b-5p overexpression slows cancer cells’ malignant behavior by inhibiting the invasion/migration and colony formation capacity via direct downregulation of mutated TP53. In TP53 wild type cells, the exogenous modulation of miR-125b-5p did not significantly affect the molecular and phenotypic profile. In conclusion, our data show that miR-125b-5p has an anti-cancer effect only in TP53 mutated colon cancer cells, explaining partially the dual behavior of this microRNA in malignant pathologies.

Ubiquitin-proteasome system and the role of its inhibitors in cancer therapy

Despite all the other cells that have the potential to prevent cancer development and metastasis through tumour suppressor proteins, cancer cells can upregulate the ubiquitin–proteasome system (UPS) by which they can degrade tumour suppressor proteins and avoid apoptosis. This system plays an extensive role in cell regulation organized in two steps. Each step has an important role in controlling cancer. This demonstrates the importance of understanding UPS inhibitors and improving these inhibitors to foster a new hope in cancer therapy. UPS inhibitors, as less invasive chemotherapy drugs, are increasingly used to alleviate symptoms of various cancers in malignant states. Despite their success in reducing the development of cancer with the lowest side effects, thus far, an appropriate inhibitor that can effectively inactivate this system with the least drug resistance has not yet been fully investigated. A fundamental understanding of the system is necessary to fully elucidate its role in causing/controlling cancer. In this review, we first comprehensively investigate this system, and then each step containing ubiquitination and protein degradation as well as their inhibitors are discussed. Ultimately, its advantages and disadvantages and some perspectives for improving the efficiency of these inhibitors are discussed.

Endoplasmic Reticulum Stress-Mediated p62 Downregulation Inhibits Apoptosis via c-Jun Upregulation

Cereblon (CRBN), a substrate receptor of cullin 4-RING E3 ligase (CRL4) regulates the ubiquitination and degradation of c-Jun, mediating the lipopolysaccharide-induced cellular response. However, the upstream signaling pathway that regulates this process is unknown. In this study, we describe how endoplasmic reticulum (ER) stress reversely regulates sequestosome-1 (p62)and c-Jun protein levels. Furthermore, our study reveals that expression of p62 attenuates c-Jun protein levels through the ubiquitin-proteasome system. Conversely, siRNA knockdown of p62 elevates c-Jun protein levels. Immunoprecipitation and immunoblotting experiments demonstrate that p62 interacts with c-Jun and CRBN to form a ternary protein complex. Moreover, we find that CRBN knockdown completely abolishes the inhibitory effect of p62 on c-Jun. Using brefeldin A as an inducer of ER stress, we demonstrate that the p62/c-Jun axis participates in the regulation of ER stress-induced apoptosis, and that CRBN is required for this regulation. In summary, we have identified an upstream signaling pathway, which regulates p62-mediated c-Jun degradation. Our findings elucidate the underlying molecular mechanism by which p62/c-Jun axis regulates the ER stress-induced apoptosis, and provide a new molecular connection between ER stress and apoptosis.

Guidelines for the use and interpretation of assays for monitoring autophagy (4th edition)(1)

In 2008, we published the first set of guidelines for standardizing research in autophagy. Since then, this topic has received increasing attention, and many scientists have entered the field. Our knowledge base and relevant new technologies have also been expanding. Thus, it is important to formulate on a regular basis updated guidelines for monitoring autophagy in different organisms. Despite numerous reviews, there continues to be confusion regarding acceptable methods to evaluate autophagy, especially in multicellular eukaryotes. Here, we present a set of guidelines for investigators to select and interpret methods to examine autophagy and related processes, and for reviewers to provide realistic and reasonable critiques of reports that are focused on these processes. These guidelines are not meant to be a dogmatic set of rules, because the appropriateness of any assay largely depends on the question being asked and the system being used. Moreover, no individual assay is perfect for every situation, calling for the use of multiple techniques to properly monitor autophagy in each experimental setting. Finally, several core components of the autophagy machinery have been implicated in distinct autophagic processes (canonical and noncanonical autophagy), implying that genetic approaches to block autophagy should rely on targeting two or more autophagy-related genes that ideally participate in distinct steps of the pathway. Along similar lines, because multiple proteins involved in autophagy also regulate other cellular pathways including apoptosis, not all of them can be used as a specific marker for bona fide autophagic responses. Here, we critically discuss current methods of assessing autophagy and the information they can, or cannot, provide. Our ultimate goal is to encourage intellectual and technical innovation in the field.

XIAP's Profile in Human Cancer

XIAP, the X-linked inhibitor of apoptosis protein, regulates cell death signaling pathways through binding and inhibiting caspases. Mounting experimental research associated with XIAP has shown it to be a master regulator of cell death not only in apoptosis, but also in autophagy and necroptosis. As a vital decider on cell survival, XIAP is involved in the regulation of cancer initiation, promotion and progression. XIAP up-regulation occurs in many human diseases, resulting in a series of undesired effects such as raising the cellular tolerance to genetic lesions, inflammation and cytotoxicity. Hence, anti-tumor drugs targeting XIAP have become an important focus for cancer therapy research. RNA-XIAP interaction is a focus, which has enriched the general profile of XIAP regulation in human cancer. In this review, the basic functions of XIAP, its regulatory role in cancer, anti-XIAP drugs and recent findings about RNA-XIAP interactions are discussed.

PCBP2 Posttranscriptional Modifications Induce Breast Cancer Progression via Upregulation of UFD1 and NT5E

It is commonly accepted that cellular protein levels are primarily determined by mRNA levels. However, discordance between protein and mRNA expression has been implicated in many pathologic conditions including oncogenesis. The mechanisms involved in this discordance are complicated and far from understood. In this study, it was observed that the expression levels of poly(C) binding protein 2 (PCBP2) mRNA and protein were diametric in breast normal and cancer cell lines, paraffin-embedded and fresh tissue specimens, consistent with data from The Cancer Genome Atlas and the Clinical Proteomic Tumor Analysis Consortium. Moreover, PCBP2 protein expression was significantly associated with disease progression and poor outcome in patients with breast cancer. Depletion of PCBP2 protein inhibited cell proliferation, colony formation, migration, invasion, and in vivo tumor growth and metastasis. Forced expression of PCBP2 exhibited the opposite effect. Mechanistically, it was demonstrated that PCBP2 3' untranslated region (3'UTR) was subject to alternative splicing and polyadenylation (APA) in breast cancer tissues and cell lines. Non-full-length 3'UTR PCBP2 transcripts yielded more protein than the full-length 3'UTR transcripts and enhanced the oncogenic and metastatic capacities of human breast cancer cells. Furthermore, UFD1 and NT5E were identified as genes downstream of PCBP2. PCBP2 promoted oncogenicity of breast cancer cells via upregulation of the expression of UFD1 and NT5E by direct binding to their 3'UTR-B portions. IMPLICATIONS: Findings demonstrate that APA of PCBP2 3'UTR contributes to its increased expression with subsequent promotion of breast cancer progression by regulating UFD1 and NT5E. VISUAL OVERVIEW: http://mcr.aacrjournals.org/content/molcanres/19/1/86/F1.large.jpg.

miR-431-5p regulates cell proliferation and apoptosis in fibroblast-like synoviocytes in rheumatoid arthritis by targeting XIAP

BACKGROUND

miR-431-5p is dysregulated in various cancers and plays an important function in the development of cancer. However, its role in fibroblast-like synoviocytes (FLSs) in patients with rheumatoid arthritis (RA) remains to be understood.

METHODS

Quantitative real-time polymerase chain reaction was used to detect the relative expression of miR-431-5p in synovial tissues and FLSs. Cell proliferation assays helped examine RA FLS proliferation. Flow cytometry was performed to determine apoptosis and cell cycle progression in RA FLSs. We used dual-luciferase assays to determine the correlation between miR-431-5p and its putative target, X-linked inhibitor of apoptosis (XIAP). Quantitative real-time PCR and western blotting were used to measure XIAP levels in synovial tissues and transfected RA FLSs.

RESULTS

miR-431-5p was downregulated in synovial tissues and FLSs of patients with RA. Upregulation of miR-431-5p prohibited cell proliferation and the G0/G1-to-S phase transition but promoted apoptosis in RA FLSs, while miR-431-5p inhibition showed the opposite results. miR-431-5p directly targeted XIAP in RA FLSs and reversely correlated with XIAP levels in synovial tissues. Notably, XIAP silencing partially restored the effects of miR-431-5p inhibition in RA FLSs.

CONCLUSION

miR-431-5p regulates cell proliferation, apoptosis, and cell cycle of RA FLSs by targeting XIAP, suggesting its potential in the treatment of RA.

The anti-apoptotic proteins Bcl-2 and Bcl-xL suppress Beclin 1/Atg6-mediated lethal autophagy in polyploid cells

Inhibition of Aurora-B kinase is a synthetic lethal therapy for tumors that overexpress the MYC oncoprotein. It is currently unclear whether co-occurring oncogenic alterations might influence this synthetic lethality by conferring more or less potency in the killing of tumor cells. To identify such modifiers, isogenic cell lines were utilized to test a variety of cancer genes that have been previously demonstrated to promote survival under conditions of cellular stress, contribute to chemoresistance and/or suppress MYC-primed apoptosis. It was found that Bcl-2 and Bcl-xL, two antiapoptotic members of the Bcl-2 family, can partially suppress the synthetic lethality, but not multinucleation, elicited by a pan-aurora kinase inhibitor, VX-680. Suppression was show to stem from the inhibition of autophagy, specifically in multinucleated cells, rather than a general inhibition of apoptosis. The anti-autophagic activity of Bcl-2 also impacted polyploid cell recovery in colony-forming assays, suggesting a route of escape from MYC-VX-680 synthetic lethality that may have clinical consequences. These findings expand on previous conclusions that autophagic death of VX-680-induced polyploid cells is mediated by Atg6. Bcl-2 and Bcl-xL negatively modulate MYC-VX-680 synthetic lethality and it is the anti-autophagic activity of these two Bcl-2 family proteins, specifically in multinucleate cells, that contributes to resistance to Aurora kinase-targeting drugs.

IAP-Mediated Protein Ubiquitination in Regulating Cell Signaling

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.

Cadmium induces mitochondrial ROS inactivation of XIAP pathway leading to apoptosis in neuronal cells

Cadmium (Cd), a heavy metal pollutant, contributes to neurodegenerative disorders. Recently, we have demonstrated that Cd induction of reactive oxygen species (ROS) causes apoptosis in neuronal cells. Whether X-linked inhibitor of apoptosis protein (XIAP) is involved in Cd-induced ROS-dependent neuronal apoptosis remains unclear. Here, we show that Cd-induced ROS reduced the expression of XIAP, which resulted in up-regulation of murine double minute 2 homolog (MDM2) and down-regulation of p53, leading to apoptosis in PC12 cells and primary neurons. Inhibition of MDM2 with Nutlin-3a reversed Cd-induced reduction of p53 and substantially rescued cells from excess ROS-dependent death. Overexpression of XIAP protected against Cd induction of ROS-dependent neuronal apoptosis. Inhibition of XIAP by Embelin strengthened Cd-induced ROS and apoptosis in the cells. Furthermore, we found that Cd inactivation of XIAP pathway was attributed to Cd induction of mitochondrial ROS, as evidenced by using a mitochondrial superoxide indicator MitoSOX and a mitochondria-targeted antioxidant Mito-TEMPO. Taken together, these results indicate that Cd induces mitochondrial ROS inactivation of XIAP-MDM2-p53 pathway leading to apoptosis in neuronal cells. Our findings suggest that activators of XIAP or modulation of XIAP-MDM2-p53 pathway by antioxidants may be exploited for the prevention of Cd-induced oxidative stress and neurodegenerative diseases.

Ubiquitin, SUMO, and Nedd8 as Therapeutic Targets in Cancer

Ubiquitin defines a family of approximately 20 peptidic posttranslational modifiers collectively called the Ubiquitin-like (UbLs). They are conjugated to thousands of proteins, modifying their function and fate in many ways. Dysregulation of these modifications has been implicated in a variety of pathologies, in particular cancer. Ubiquitin, SUMO (-1 to -3), and Nedd8 are the best-characterized UbLs. They have been involved in the regulation of the activity and/or the stability of diverse components of various oncogenic or tumor suppressor pathways. Moreover, the dysregulation of enzymes responsible for their conjugation/deconjugation has also been associated with tumorigenesis and cancer resistance to therapies. The UbL system therefore constitutes an attractive target for developing novel anticancer therapeutic strategies. Here, we review the roles and dysregulations of Ubiquitin, SUMO, and Nedd8 pathways in tumorigenesis, as well as recent advances in the identification of small molecules targeting their conjugating machineries for potential application in the fight against cancer.

Piwi-Interacting RNA1037 Enhances Chemoresistance and Motility in Human Oral Squamous Cell Carcinoma Cells

Background

Piwi-interacting RNAs (piRNAs) are thought to silence transposable genetic elements. However, the functional roles of piRNAs in oral squamous cell carcinoma (OSCC) remain unelucidated. In the present study, we aimed to investigate the role of Piwi-interacting RNA 1037 (piR-1037) in chemoresistance to cisplatin (CDDP)-based chemotherapy and the oncogenic role of piR-1037 in OSCC cells.

Methods

RT-PCR was used to evaluate the levels of piR-1037 and X-linked Inhibitor of apoptosis protein (XIAP) mRNA in OSCC cell lines or tumor xenografts. Transfection of piR-1037 DNA antisense and piR-1037 RNA oligonucleotides was performed to suppress and overexpress piR-1037 in OSCC cells, respectively. A CCK8 assay was used to measure the viability or proliferation of OSCC cells. Apoptosis in OSCC cells and xenografts was determined using a TUNEL assay kit. The activity of caspase-3, caspase-8 and caspase-1 in OSCC cells was measured with colorimetric caspase assay kits. Western blot analysis was conducted to analyze XIAP expression in OSCC cells and xenograft samples. Immunoprecipitation (IP) and RNA pull-down assays were utilized to analyze the piR-1037 - XIAP interaction. Transwell assays were performed to evaluate migration and invasion of OSCC cells.

Results

CDDP treatment upregulated piR-1037 expression in OSCC cells and OSCC xenografts. Suppression of the CDDP-induced upregulation of piR-1037 expression enhanced the sensitivity of OSCC cells to CDDP. piR-1037 promoted protein expression and directly bound XIAP, a key apoptotic inhibitor that is implicated in chemoresistance. The relationship between piR-1037 and XIAP suggested that piR-1037 enhanced OSCC cell chemoresistance to CDDP at least partially through XIAP. Moreover, targeting the basal expression of piR-1037 inhibited cell motility by affecting epithelial–mesenchymal transition (EMT).

Conclusion

piR-1037 enhances the chemoresistance and motility of OSCC cells. piR-1037 promotes chemoresistance by interacting with XIAP and regulates the motility of OSCC cells by driving EMT.

Circular RNA circ0005276 promotes the proliferation and migration of prostate cancer cells by interacting with FUS to transcriptionally activate XIAP

Prostate cancer (PCa) is one of the major men's malignancies with high mortality worldwide. Circular RNAs (circRNAs) have been shown to serve as essential regulators in human cancers. CircRNA can exert their functions by cooperating with their host genes. In the present study, microarray analysis revealed an upregulated mRNA in PCa samples. X-linked inhibitor of apoptosis protein (XIAP), a key regulator in the progression of human cancers. Through bioinformatics analysis, we determined that XIAP is a host gene for circRNA0005276. Therefore, this study focused on the interaction between circ0005276 and XIAP as well as their functions in PCa progression. The upregulation of XIAP and circ0005276 was determined in PCa tissues and cell lines. Moreover, we confirmed the positive regulation of circ0005276 on XIAP expression. Functionally, we validated that circ0005276 and XIAP promoted cell proliferation, migration and epithelial-mesenchymal transition. Mechanistically, we verified that circ0005276 interacted with FUS binding protein (FUS) so as to activate the transcription of XIAP. Rescue assays were conducted to determine the crucial role of XIAP in circ0005276 and FUS-mediated PCa cellular processes. Collectively, our study revealed the mechanism and function of circ0005276 and its host gene XIAP in PCa progression.

miR-146a-5p enhances hepatitis B virus replication through autophagy to promote aggravation of chronic hepatitis B

The objective of this study was to investigate the mechanism by which miR-146a-5p mediated autophagy and hepatitis B virus (HBV) replication. Quantitative real-time polymerase chain reaction (qRT-PCR) was used to determine the mRNA expression levels of miR-146a-5p and X-linked inhibitor of apoptosis (XIAP) and HBV DNA and RNA. The protein expression levels of XIAP, IκB-α, murine double minute 2 oncoprotein (MDM2) and p53, the phosphorylation of p65, and the conversion of light chain 3 (LC3)-I to LC3-II were detected by Western blotting. The expression levels of XIAP, HBV-related pro-inflammatory cytokines, and serum markers were detected by enzyme-linked immunosorbent assay (ELISA). miR-146a-5p was highly expressed in patients with chronic hepatitis B (CHB) and HBV-expressing hepatocytes. HBV core protein (HBc) and HBV X protein (HBx) were responsible for its effects on miR-146a-5p expression through the nuclear factor-κB pathway. Furthermore, the miR-146a-5p inhibitor suppressed autophagic response and HBV replication as well as MDM2/p53 expression. Luciferase reporter assay confirmed that XIAP was a direct target of miR-146a-5p. We therefore demonstrated that miR-146a-5p mediated positive feedback loop by regulating autophagy-induced HBV replication via targeting the XIAP-mediated MDM2/p53 axis. © 2019 IUBMB Life, 71(9):1336-1346, 2019.