SPOP E3 Ubiquitin Ligase Adaptor Promotes Cellular Senescence by Degrading the SENP7 deSUMOylase

SPOP/NOLC1/B4GALT1 signaling axis enhances paclitaxel resistance in endometrial cancer by inducing O-dysglycosylation

The effective treatment of paclitaxel-resistant patients remains a major challenge. We found that nucleolar and coiled body phosphoprotein 1 (NOLC1) was highly expressed in the paclitaxel-resistant endometrial cancer (ECa) cells and pathological tissue of ECa patients, which could promote the occurrence and progression of ECa cells. Mechanistically, we confirmed that the E3 ubiquitin ligase substrate-binding adaptor SPOP mediates the ubiquitination and degradation of NOLC1, thereby maintaining normal protein levels. However, ECa-associated SPOP mutants abrogated the binding and ubiquitination of NOLC1, resulting in the accumulation of NOLC1, and ultimately promoting the proliferation, migration, and invasion of ECa cells. In addition, we demonstrated that NOLC1 could act as a transcriptional factor to activate the transcriptional expression of B4GALT1, ultimately leading to abnormal glycosylation metabolism. Moreover, knockdown of B4GALT1 can partly counteract the cancer-promoting effect caused by the overexpression of NOLC1 in vitro and in vivo. Based on these findings, an O-glycosylation inhibitor combined with paclitaxel could effectively improve the sensitivity of paclitaxel-resistant cells. In summary, we found that SPOP can negatively regulate the NOLC1-B4GALT1 signaling axis in ECa, whereas ECa-associated SPOP mutants lead to abnormal activation of this signaling axis, leading to glycosylation metabolism disorders. In addition, paclitaxel combined with B4GALT1-KD or glycosylation inhibitors can significantly inhibit the growth of paclitaxel-resistant endometrial cancer cells.

The impact of dysregulation SUMOylation on prostate cancer

Prostate cancer (PCa) remains one of the most common malignancies in men, with its development and progression being governed by complex molecular pathways. SUMOylation, a post-translational modification (PTM) that involves the covalent attachment of small ubiquitin-like modifier (SUMO) proteins to target substrates, has emerged as a critical regulator of various cellular processes such as transcription, DNA repair, cell cycle progression, and apoptosis. Emerging evidence reveals that abnormal SUMOylation may contribute to PCa pathogenesis, and notably, SUMO-associated enzymes are commonly dysregulated in PCa. This review explores the mechanisms by which SUMOylation is implicated in the regulation of key pathways, and summary aberrant expression of SUMO-related enzymes or SUMOylation sites mutations of substrtes in PCa, as well as the therapeutic implications of targeting the SUMO-related enzymes in PCa treatment.

SUMO-specific proteases: SENPs in oxidative stress-related signaling and diseases

Oxidative stress is employed to depict a series of responses detrimental to normal cellular functions resulting from an imbalance between intracellular oxidants, mainly reactive oxygen species and antioxidant defenses. Oxidative stress often contributes to the development of various diseases, including cancer, cardiovascular diseases, and neurodegenerative diseases. In this process, the relationship between small ubiquitin-like modifier (SUMO) and oxidative stress has garnered significant attention, with its posttranslational modification (PTM) frequently serving as a marker of oxidative stress status. Sentrin/SUMO-specific proteases (SENPs), affected by alternative splicing, PTMs such as phosphorylation and ubiquitination, and various protein interactions, are crucial molecules in the SUMO process. The human SENP family has six members (SENP1-3, SENP5-7), which are classified into two categories based on sequence similarity, substrate specificity, and subcellular location. They have two core functions in the human body: first, by cleaving the precursor SUMO and exposing the C-terminal glycine, they initiate the SUMO process; second, they can specifically recognize and dissociate SUMO proteins bound to substrates, a process known as deSUMOylation. However, the connection between deSUMOylation and oxidative stress remains a relatively unexplored area despite their strong association with oxidative diseases such as cancer and cardiovascular disease. This article aims to illustrate the significant contribution of SENPs to the oxidative stress pathway through deSUMOylation by reviewing their structure and classification, their roles in oxidative stress, and the changes in their expression and activity in several typical oxidative stress-related diseases.

Androgen receptor post-translational modifications and their implications for pathology

A major mechanism to modulate the biological activities of the androgen receptor (AR) involves a growing number of post-translational modifications (PTMs). In this review we summarise the current knowledge on the structural and functional impact of PTMs that affect this major transcription factor. Next, we discuss the cross-talk between these different PTMs and the presence of clusters of modified residues in the AR protein. Finally, we discuss the implications of these covalent modifications for the aetiology of diseases such as spinal and bulbar muscular atrophy (Kennedy's disease) and prostate cancer, and the perspectives for pharmacological intervention.

The SUMOylation and ubiquitination crosstalk in cancer

BACKGROUND

The cancer occurrence and progression are largely affected by the post-translational modifications (PTMs) of proteins. Currently, it has been shown that the relationship between ubiquitination and SUMOylation is highly complex and interactive. SUMOylation affects the process of ubiquitination and degradation of substrates. Contrarily, SUMOylation-related proteins are also regulated by the ubiquitination process thus altering their protein levels or activity. Emerging evidence suggests that the abnormal regulation between this crosstalk may lead to tumorigenesis.

PURPOSE

In this review, we have discussed the study of the relationship between ubiquitination and SUMOylation, as well as the possibility of a corresponding application in tumor therapy.

METHODS

The relevant literatures from PubMed have been reviewed for this article.

CONCLUSION

The interaction between ubiquitination and SUMOylation is crucial for the occurrence and development of cancer. A greater understanding of the crosstalk of SUMOylation and ubiquitination may be more conducive to the development of more selective and effective SUMOylation inhibitors, as well as a promotion of synergy with other tumor treatment strategies.

Substrate-dependent interaction of SPOP and RACK1 aggravates cardiac fibrosis following myocardial infarction

Speckle-type pox virus and zinc finger (POZ) protein (SPOP), a substrate recognition adaptor of cullin-3 (CUL3)/RING-type E3 ligase complex, is investigated for its role in cardiac fibrosis in our study. Cardiac fibroblasts (CFs) activation was achieved with TGF-β1 (20 ng/mL) and MI mouse model was established by ligation of the left anterior descending coronary, and lentivirus was employed to mediate interference of SPOP expression. SPOP was increased both in fibrotic post-MI mouse hearts and TGF-β1-treated CFs. The gain-of-function of SPOP promoted myofibroblast transformation in CFs, and exacerbated cardiac fibrosis and cardiac dysfunction in MI mice, while the loss-of-function of SPOP exhibited the opposite effects. Mechanistically, SPOP bound to the receptor of activated protein C kinase 1 (RACK1) and induced its ubiquitination and degradation by recognizing Ser/Thr-rich motifs on RACK1, leading to Smad3-mediated activation of CFs. Forced RACK1 expression canceled the effects of SPOP on cardiac fibrosis. The study reveals therapeutic targets for fibrosis-related cardiac diseases.

SPOP mutations promote tumor immune escape in endometrial cancer via the IRF1-PD-L1 axis

Blockade of programmed cell death 1 (PD-1)/programmed cell death 1 ligand (PD-L1) has evolved into one of the most promising immunotherapy strategies for cancer patients. Tumor cells frequently overexpress PD-L1 to evade T cell-mediated immune surveillance. However, the specific genetic alterations that drive aberrant overexpression of PD-L1 in cancer cells remain poorly understood. The gene encoding the E3 ubiquitin ligase substrate-binding adaptor SPOP is frequently mutated in endometrial cancer (EC). Here, we report that SPOP negatively regulates PD-L1 expression at the transcriptional level. Wild-type SPOP binds to IRF1, a primary transcription factor responsible for the inducible expression of PD-L1, and subsequently triggers its ubiquitin- proteasomal degradation to suppress IRF1-mediated transcriptional upregulation of PD-L1. In contrast, EC-associated SPOP mutants lose their capacity to degrade IRF1 but stabilize IRF1, and upregulate PD-L1 expression. EC-associated SPOP mutations accelerate xenograft tumor growth partially by increasing IRF1 and PD-L1 expression. Together, we identify SPOP as a negative regulator of the IRF1-PD-L1 axis and characterize the critical roles of IRF1 and PD-L1 in SPOP mutation-driven tumor immune evasion in EC.

SPOP in Cancer: Phenomena, Mechanisms and Its Role in Therapeutic Implications

Speckle-type POZ (pox virus and zinc finger protein) protein (SPOP) is a cullin 3-based E3 ubiquitin ligase adaptor protein that plays a crucial role in ubiquitin-mediated protein degradation. Recently, SPOP has attracted major research attention as it is frequently mutated in a range of cancers, highlighting pleiotropic tumorigenic effects and associations with treatment resistance. Structurally, SPOP contains a functionally critical N-terminal meprin and TRAF homology (MATH) domain for many SPOP substrates. SPOP has two other domains, including the internal Bric-a-brac-Tramtrack/Broad (BTB) domain, which is linked with SPOP dimerization and binding to cullin3, and a C-terminal nuclear localization sequence (NLS). The dysregulation of SPOP-mediated proteolysis is associated with the development and progression of different cancers since abnormalities in SPOP function dysregulate cellular signaling pathways by targeting oncoproteins or tumor suppressors in a tumor-specific manner. SPOP is also involved in genome stability through its role in the DNA damage response and DNA replication. More recently, studies have shown that the expression of SPOP can be modulated in various ways. In this review, we summarize the current understanding of SPOP's functions in cancer and discuss how to design a rational therapeutic target.

Cancer-Associated Dysregulation of Sumo Regulators: Proteases and Ligases

SUMOylation is a post-translational modification that has emerged in recent decades as a mechanism involved in controlling diverse physiological processes and that is essential in vertebrates. The SUMO pathway is regulated by several enzymes, proteases and ligases being the main actors involved in the control of sumoylation of specific targets. Dysregulation of the expression, localization and function of these enzymes produces physiological changes that can lead to the appearance of different types of cancer, depending on the enzymes and target proteins involved. Among the most studied proteases and ligases, those of the SENP and PIAS families stand out, respectively. While the proteases involved in this pathway have specific SUMO activity, the ligases may have additional functions unrelated to sumoylation, which makes it more difficult to study their SUMO-associated role in cancer process. In this review we update the knowledge and advances in relation to the impact of dysregulation of SUMO proteases and ligases in cancer initiation and progression.

Novel insights into the SPOP E3 ubiquitin ligase: From the regulation of molecular mechanisms to tumorigenesis

Ubiquitin-mediated protein degradation is the primary biological process by which protein abundance is regulated and protein homeostasis is maintained in eukaryotic cells. Speckle-type pox virus and zinc finger (POZ) protein (SPOP) is a typical substrate adaptor of the Cullin 3-RING ligase (CRL3) family; it serves as a bridge between the Cullin 3 (Cul3) scaffold protein and its substrates. In recent years, SPOP has received increasing attention because of its versatility in its regulatory pathways and the diversity of tumor types involved. Mechanistically, SPOP substrates are involved in a wide range of biological processes, and abnormalities in SPOP function perturb downstream biological processes and promote tumorigenesis. Additionally, liquid-liquid phase separation (LLPS), a potential mechanism of membraneless organelle formation, was recently found to mediate the self-triggered colocalization of substrates with higher-order oligomers of SPOP. Herein, we summarize the structure of SPOP and the specific mechanisms by which it mediates the efficient ubiquitination of substrates. Additionally, we review the biological functions of SPOP, the regulation of SPOP expression, the role of SPOP in tumorigenesis and its therapeutic value.

SENP7 senses oxidative stress to sustain metabolic fitness and antitumor functions of CD8+ T cells

The functional integrity of CD8⁺ T cells is tightly coupled to metabolic reprogramming, but how oxidative stress directs CD8⁺ T cell metabolic fitness in the tumor microenvironment (TME) remains elusive. Here, we report that SUMO-specific protease 7 (SENP7) senses oxidative stress to maintain the CD8⁺ T cell metabolic state and antitumor functions. SENP7-deficient CD8⁺ T cells exhibited decreased glycolysis and oxidative phosphorylation, resulting in attenuated proliferation in vitro and dampened antitumor functions in vivo. Mechanistically, CD8⁺ T cell–derived ROS triggered cytosolic SENP7–mediated PTEN deSUMOylation, thereby promoting PTEN degradation and preventing PTEN-dependent metabolic defects. Importantly, lowering T cell–intrinsic ROS restricted SENP7 cytosolic translocation and repressed CD8⁺ T cell metabolic and functional activity in human colorectal cancer samples. Our findings reveal that SENP7, as an oxidative stress sensor, sustains CD8⁺ T cell metabolic fitness and effector functions and unveil an oxidative stress–sensing machinery in tumor-infiltrating CD8⁺ T cells.

SPOP-mutant prostate cancer: Translating fundamental biology into patient care

Comprehensive cancer genome studies have revealed genetically-defined subtypes of prostate cancer with distinct truncal driver mutations. Because prostate cancer has been largely seen as a rather uniform disease, the clinical significance of this discovery remained largely obscure. However, recent findings imply distinct biological features and therapeutic vulnerabilities linked to specific truncal mutations. Here we review our current understanding of prostate cancers harboring recurrent point mutations in the ubiquitin ligase adaptor protein SPOP and discuss opportunities for future clinical translation. More specifically, activation of the androgen receptor (AR) signaling emerges as the key oncogenic pathway. SPOP-mutant prostate cancer patients respond to AR inhibition in various clinical settings. Molecular insights on how mutant SPOP promotes tumorigenesis may open more specific therapeutic avenues which, in combination with conventional AR-targeting agents, could improve the outcome of patients with SPOP-mutant prostate cancer.

Dissecting multiple roles of SUMOylation in prostate cancer

Protein modification with small ubiquitin-like modifiers (SUMOs) plays dual roles in prostate cancer (PCa) tumorigenesis and development. Any intermediary of the SUMO conjugation cycle going awry may forfeit the balance between tumorigenic potential and anticancer effects. Deregulated SUMOylation on the androgen receptor and oncoproteins also takes part in this pathological process, as exemplified by STAT3/NF-κB and tumor suppressors such as PTEN and p53. Here, we outline recent developments and discoveries of SUMOylation in PCa and present an overview of its multiple roles in PCa tumorigenesis/promotion and suppression, while elucidating its potential as a therapeutic target for PCa.

Prostate cancer-associated SPOP mutations lead to genomic instability through disruption of the SPOP-HIPK2 axis

Speckle-type Poz protein (SPOP), an E3 ubiquitin ligase adaptor, is the most frequently mutated gene in prostate cancer. The SPOP-mutated subtype of prostate cancer shows high genomic instability, but the underlying mechanisms causing this phenotype are still largely unknown. Here, we report that upon DNA damage, SPOP is phosphorylated at Ser119 by the ATM serine/threonine kinase, which potentiates the binding of SPOP to homeodomain-interacting protein kinase 2 (HIPK2), resulting in a nondegradative ubiquitination of HIPK2. This modification subsequently increases the phosphorylation activity of HIPK2 toward HP1γ, and then promotes the dissociation of HP1γ from trimethylated (Lys9) histone H3 (H3K9me3) to initiate DNA damage repair. Moreover, the effect of SPOP on the HIPK2-HP1γ axis is abrogated by prostate cancer-associated SPOP mutations. Our findings provide new insights into the molecular mechanism of SPOP mutations-driven genomic instability in prostate cancer.

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.

Phosphorylation-dependent regulation of SPOP by LIMK2 promotes castration-resistant prostate cancer

BACKGROUND

SPOP, an E3 ubiquitin ligase adaptor, can act either as a tumour suppressor or a tumour promoter. In prostate cancer (PCa), it inhibits tumorigenesis by degrading several oncogenic substrates. SPOP is the most altered gene in PCa (~15%), which renders it ineffective, promoting cancer. The remaining PCa tumours, which retain WT-SPOP, still progress to castration-resistant (CRPC) stage, indicating that other critical mechanisms exist for downregulating SPOP. SPOP is reduced in ~94% of WT-SPOP-bearing prostate tumours; however, no molecular mechanism is known for its downregulation.

METHODS

SPOP was identified as a direct target of LIMK2 using an innovative technique. The reciprocal relationship between SPOP and LIMK2 and its consequences on oncogenicity were analysed using a variety of biochemical assays. To probe this relationship in vivo, xenograft studies were conducted.

RESULTS

LIMK2 degrades SPOP by direct phosphorylation at three sites. SPOP promotes LIMK2's ubiquitylation, creating a feedback loop. SPOP's degradation stabilises AR, ARv7 and c-Myc promoting oncogenicity. Phospho-resistant SPOP completely suppresses tumorigenesis in vivo, indicating that LIMK2-mediated SPOP degradation is a key event in PCa progression.

CONCLUSIONS

While genomically altered SPOP-bearing tumours require gene therapy, uncovering LIMK2-SPOP relationship provides a powerful opportunity to retain WT-SPOP by inhibiting LIMK2, thereby halting disease progression.

Post-Translational Modifications That Drive Prostate Cancer Progression

While a protein primary structure is determined by genetic code, its specific functional form is mostly achieved in a dynamic interplay that includes actions of many enzymes involved in post-translational modifications. This versatile repertoire is widely used by cells to direct their response to external stimuli, regulate transcription and protein localization and to keep proteostasis. Herein, post-translational modifications with evident potency to drive prostate cancer are explored. A comprehensive list of proteome-wide and single protein post-translational modifications and their involvement in phenotypic outcomes is presented. Specifically, the data on phosphorylation, glycosylation, ubiquitination, SUMOylation, acetylation, and lipidation in prostate cancer and the enzymes involved are collected. This type of knowledge is especially valuable in cases when cancer cells do not differ in the expression or mutational status of a protein, but its differential activity is regulated on the level of post-translational modifications. Since their driving roles in prostate cancer, post-translational modifications are widely studied in attempts to advance prostate cancer treatment. Current strategies that exploit the potential of post-translational modifications in prostate cancer therapy are presented.

Kidney Allograft Fibrosis: Diagnostic and Therapeutic Strategies

Interstitial fibrosis with tubule atrophy (IF/TA) is the response to virtually any sustained kidney injury and correlates inversely with kidney function and allograft survival. IF/TA is driven by various pathways that include hypoxia, renin-angiotensin-aldosterone system, transforming growth factor (TGF)-β signaling, cellular rejection, inflammation and others. In this review we will focus on key pathways in the progress of renal fibrosis, diagnosis and therapy of allograft fibrosis. This review discusses the role and origin of myofibroblasts as matrix producing cells and therapeutic targets in renal fibrosis with a particular focus on renal allografts. We summarize current trends to use multi-omic approaches to identify new biomarkers for IF/TA detection and to predict allograft survival. Furthermore, we review current imaging strategies that might help to identify and follow-up IF/TA complementary or as alternative to invasive biopsies. We further discuss current clinical trials and therapeutic strategies to treat kidney fibrosis.Supplemental Visual Abstract; http://links.lww.com/TP/C141.

Hypoxia-induced SPOP attenuates the mobility of trophoblast cells through inhibition of the PI3K/AKT/GSK3β pathway

Placental hypoxia has been implicated in pregnancy pathologies such as pre-eclampsia and intrauterine growth restriction. However, the underlying mechanism by which the trophoblasts respond to hypoxia remains unclear. Speckle-type POZ protein (SPOP), an E3 ubiquitin ligase adapter, was previously reported to play important roles in various physiological and pathological processes. This study aims to investigate the expression and biological functions of SPOP after exposure to cobalt chloride (CoCl₂ )-mimicked hypoxia conditions using human trophoblast-derived choriocarcinoma cell lines and extravillous cytotrophoblast. These data showed that SPOP protein was directly induced by CoCl₂ -mimicked hypoxia and regulated by HIF-1α at the posttranscription level. CoCl₂ treatment could dramatically influence the localization of SPOP in trophoblasts, especially the accumulation of SPOP into the nucleus. In addition, both CoCl₂ -mimicked hypoxia and induction of endogenous SPOP expression by lentivirus transfection attenuated the migration and invasion abilities of trophoblasts. Furthermore, we demonstrated that SPOP was involved in CoCl₂ -induced the inhibition of the PI3K/AKT/GSK3β pathway in placental trophoblasts. Taken together, these data indicate that accumulation of HIF-1α augments the expression of SPOP in trophoblasts, which impairs trophoblastic mobility by targeting the PI3K/AKT/GSK3β pathway. This potentially leads to insufficient uterine spiral artery remodeling and suboptimal placental perfusion, and thus the development of pregnancy-related complication.

Cellular Senescence and Anti-Cancer Therapy

BACKGROUND

Cellular senescence is generally understood as a permanent cell cycle arrest stemming from different causes. The mechanism of cellular senescence-induced cell cycle arrest is complex, involving interactions between telomere shortening, inflammations and cellular stresses. In recent years, a growing number of studies have revealed that cellular senescence could mediate the cancer progression of neighboring cells, but this idea is controversial and contradictory evidence argues that cellular senescence also contributes to tumor suppression.

OBJECTIVE

Given that the complicated role of senescence in various physiological and pathological scenarios, we try to clarify the precise contribution role of cellular senescence to tumor progression.

METHODS

Search for the information in a large array of relevant articles to support our opinion.

RESULTS

We discuss the relatively widespread occurrence of cellular senescence in cancer treatment and identify the positive and negative side of senescence contributed to tumor progression.

CONCLUSION

We argue that the availability of pro-senescence therapy could represent as a promising regimen for managing cancer disease, particularly with regard to the poor clinical outcome obtained with other anticancer therapies.

SPOP promotes ubiquitination and degradation of MyD88 to suppress the innate immune response

As a canonical adaptor for the Toll-like receptor (TLR) family, myeloid differentiation primary response protein 88 (MyD88) has crucial roles in host defense against infection by microbial pathogens, and its dysregulation might induce autoimmune diseases. Here, we demonstrate that the chicken Cullin 3-based ubiquitin ligase adaptor Speckle-type BTB-POZ protein (chSPOP) recognizes the intermediate domain of chicken MyD88 (chMyD88) and degrades it through the proteasome pathway. Knockdown or genetic ablation of chSPOP leads to aberrant elevation of chMyD88 protein. Through this interaction, chSPOP negatively regulates NF-κB pathway activity and thus the production of IL-1β upon LPS challenge in chicken macrophages. Furthermore, Spop-deficient mice are more susceptible to infection with Salmonella typhimurium. Collectively, these findings demonstrate MyD88 as a bona fide substrate of SPOP and uncover a mechanism by which SPOP regulates MyD88 abundance and disease susceptibility.

The diverse roles of SPOP in prostate cancer and kidney cancer

Multiple studies have confirmed that speckle-type pox virus and zinc finger (POZ) protein (SPOP) functions as a substrate adaptor of cullin 3-based E3 ligase and has a crucial role in various cellular processes via specific targeting of proteins for ubiquitination and subsequent proteasomal degradation. Dysregulation of SPOP-mediated proteolysis might be involved in the development and progression of human prostate and kidney cancers. In prostate cancer, SPOP seems to function as a tumour suppressor by targeting several proteins, including androgen receptor (AR), steroid receptor coactivator 3 (SRC3) and BRD4, for degradation, whereas it might function as an oncoprotein in kidney cancer, for example, by targeting phosphatase and tensin homologue (PTEN) for proteasomal degradation. In addition, nuclear SPOP targets AR for degradation and has a role as a tumour suppressor in prostate cancer; however, in kidney cancer, SPOP largely accumulates in the cytoplasm and fails to promote degradation of AR located in the nucleus, resulting in activation of AR-driven pathways and cancer progression. Owing to the context-dependent function of SPOP in human malignancies, further assessment of the molecular mechanisms involving SPOP in prostate and kidney cancers is needed to improve our understanding of its role in the development of these cancer types. Treatments that target SPOP might become therapeutic strategies in these malignancies in the future.

SPOP and cancer: a systematic review

The initiation and progression of cancer is dependent on the acquisition of mutations in oncogenes or tumor suppressor genes that ultimately leads to the dysregulation of key regulatory pathways. Though these mutations often occur in direct regulators of such pathways, some may confer tumorigenic potential by indirectly targeting several pathways congruently thereby exerting pleiotropic effects. In recent years, the tumor suppressor gene Speckle Type POZ Protein (SPOP) has gained a lot of attention as it has been found to be altered in a variety of different cancers. SPOP appears to exert pleiotropic tumorigenic effects as multiple different regulatory pathways become dysregulated upon SPOP alterations. SPOP has been identified as an E3 ubiquitin ligase substrate binding subunit of the proteasome complex. Since protein degradation is critical in regulating proper cellular function it is not surprising that the proteasome pathway is often found to be disrupted in cancer. Many studies have now indicated that mutations or changes in the expression of SPOP are one of several underlying reasons of proteasome pathway disruption in different cancers. Ultimately, either SPOP downregulation or mutation promotes stabilization of direct SPOP targets which subsequently promotes cancer through the dysregulation of key regulatory pathways. In this review, we will discuss the current literature on cancer-specific SPOP alterations as well the SPOP targets that are stabilized, and the pathways that are dysregulated, as a result.

The role of ubiquitination in tumorigenesis and targeted drug discovery

Ubiquitination, an important type of protein posttranslational modification (PTM), plays a crucial role in controlling substrate degradation and subsequently mediates the "quantity" and "quality" of various proteins, serving to ensure cell homeostasis and guarantee life activities. The regulation of ubiquitination is multifaceted and works not only at the transcriptional and posttranslational levels (phosphorylation, acetylation, methylation, etc.) but also at the protein level (activators or repressors). When regulatory mechanisms are aberrant, the altered biological processes may subsequently induce serious human diseases, especially various types of cancer. In tumorigenesis, the altered biological processes involve tumor metabolism, the immunological tumor microenvironment (TME), cancer stem cell (CSC) stemness and so on. With regard to tumor metabolism, the ubiquitination of some key proteins such as RagA, mTOR, PTEN, AKT, c-Myc and P53 significantly regulates the activity of the mTORC1, AMPK and PTEN-AKT signaling pathways. In addition, ubiquitination in the TLR, RLR and STING-dependent signaling pathways also modulates the TME. Moreover, the ubiquitination of core stem cell regulator triplets (Nanog, Oct4 and Sox2) and members of the Wnt and Hippo-YAP signaling pathways participates in the maintenance of CSC stemness. Based on the altered components, including the proteasome, E3 ligases, E1, E2 and deubiquitinases (DUBs), many molecular targeted drugs have been developed to combat cancer. Among them, small molecule inhibitors targeting the proteasome, such as bortezomib, carfilzomib, oprozomib and ixazomib, have achieved tangible success. In addition, MLN7243 and MLN4924 (targeting the E1 enzyme), Leucettamol A and CC0651 (targeting the E2 enzyme), nutlin and MI-219 (targeting the E3 enzyme), and compounds G5 and F6 (targeting DUB activity) have also shown potential in preclinical cancer treatment. In this review, we summarize the latest progress in understanding the substrates for ubiquitination and their special functions in tumor metabolism regulation, TME modulation and CSC stemness maintenance. Moreover, potential therapeutic targets for cancer are reviewed, as are the therapeutic effects of targeted drugs.

The emerging role of SPOP protein in tumorigenesis and cancer therapy

The nuclear speckle-type pox virus and zinc finger (POZ) protein (SPOP), a representative substrate-recognition subunit of the cullin-RING E3 ligase, has been characterized to play a dual role in tumorigenesis and cancer progression. Numerous studies have determined that SPOP suppresses tumorigenesis in a variety of human malignancies such as prostate, lung, colon, gastric, and liver cancers. However, several studies revealed that SPOP exhibited oncogenic function in kidney cancer, suggesting that SPOP could exert its biological function in a cancer type-specific manner. The role of SPOP in thyroid, cervical, ovarian, bone and neurologic cancers has yet to be determined. In this review article, we describe the structure and regulation of SPOP in human cancer. Moreover, we highlight the critical role of SPOP in tumorigenesis based on three major categories: physiological evidence (animal models), pathological evidence (human cancer specimens) and biochemical evidence (downstream ubiquitin substrates). Furthermore, we note that SPOP could be a promising therapeutic target for cancer treatment.

The emerging role of SPOP protein in tumorigenesis and cancer therapy

The nuclear speckle-type pox virus and zinc finger (POZ) protein (SPOP), a representative substrate-recognition subunit of the cullin-RING E3 ligase, has been characterized to play a dual role in tumorigenesis and cancer progression. Numerous studies have determined that SPOP suppresses tumorigenesis in a variety of human malignancies such as prostate, lung, colon, gastric, and liver cancers. However, several studies revealed that SPOP exhibited oncogenic function in kidney cancer, suggesting that SPOP could exert its biological function in a cancer type-specific manner. The role of SPOP in thyroid, cervical, ovarian, bone and neurologic cancers has yet to be determined. In this review article, we describe the structure and regulation of SPOP in human cancer. Moreover, we highlight the critical role of SPOP in tumorigenesis based on three major categories: physiological evidence (animal models), pathological evidence (human cancer specimens) and biochemical evidence (downstream ubiquitin substrates). Furthermore, we note that SPOP could be a promising therapeutic target for cancer treatment.

Cullin 3 and Its Role in Tumorigenesis

Cullin 3 (Cul3) family of ubiquitin ligases comprises three components, the RING finger protein RBX1, the Cul3 scaffold, and a Bric-a-brac/Tramtrack/Broad complex (BTB) protein. The BTB protein serves as a bridge to connect Cul3 to substrate and is functionally equivalent to the combination of substrate adaptor and linker in other Cullin complexes. Human genome encodes for ~180 BTB proteins, implying a broad spectrum of ubiquitination signals and substrate repertoire. Accordingly, Cul3 ubiquitin ligases are involved in diverse cellular processes, including cell division, differentiation, cytoskeleton remodeling, stress responses, and nerve cell functions. Emerging evidence has pointed to the prominent role of Cul3 ubiquitin ligases in cancer. This chapter will describe recent advances on the roles of Cul3 E3 ligase complexes in regulating various cancer hallmarks and therapeutic responses and the mutation/dysregulation of Cul3 substrate adaptors in cancer. In particular, we will focus on several extensively studied substrate adaptors, such as Keap1, SPOP, KLHL20, and LZTR1, and will also discuss other recently identified Cul3 adaptors with oncogenic or tumor-suppressive functions. We conclude that Cul3 ubiquitin ligases represent master regulators of human malignancies and highlight the importance of developing modulating agents for oncogenic/tumor-suppressive Cul3 E3 ligase complexes to prevent or intervene tumorigenesis.

Divergent Modulation of Proteostasis in Prostate Cancer

Proteostasis regulates key cellular processes such as cell proliferation, differentiation, transcription, and apoptosis. The mechanisms by which proteostasis is regulated are crucial and the deterioration of cellular proteostasis has been significantly associated with tumorigenesis since it specifically targets key oncoproteins and tumor suppressors. Prostate cancer (PCa) is the second most common cause of cancer death in men worldwide. Androgens mediate one of the most central signaling pathways in all stages of PCa via the androgen receptor (AR). In addition to their regulation by hormones, PCa cells are also known to be highly secretory and are particularly prone to ER stress as proper ER function is essential. Alterations in various complex signaling pathways and cellular processes including cell cycle control, transcription, DNA repair, apoptosis, cell adhesion, epithelial-mesenchymal transition (EMT), and angiogenesis are critical factors influencing PCa development through key molecular changes mainly by posttranslational modifications in PCa-related proteins, including AR, NKX3.1, PTEN, p53, cyclin D1, and p27. Several ubiquitin ligases like MDM2, Siah2, RNF6, CHIP, and substrate-binding adaptor SPOP; deubiquitinases such as USP7, USP10, USP26, and USP12 are just some of the modifiers involved in the regulation of these key proteins via ubiquitin-proteasome system (UPS). Some ubiquitin-like modifiers, especially SUMOs, have been also closely associated with PCa. On the other hand, the proteotoxicity resulting from misfolded proteins and failure of ER adaptive capacity induce unfolded protein response (UPR) that is an indispensable signaling mechanism for PCa development. Lastly, ER-associated degradation (ERAD) also plays a crucial role in prostate tumorigenesis. In this section, the relationship between prostate cancer and proteostasis will be discussed in terms of UPS, UPR, SUMOylation, ERAD, and autophagy.

DeSUMOylase SENP7-Mediated Epithelial Signaling Triggers Intestinal Inflammation via Expansion of Gamma-Delta T Cells

Inflammatory bowel disease (IBD) is a complex autoimmune disorder recently shown to be associated with SUMOylation, a post-translational modification mechanism. Here, we have identified a link between epithelial deSUMOylases and inflammation in IBD. DeSUMOylase SENP7 was seen to be upregulated specifically in intestinal epithelial cells in both human IBD and a mouse model. In steady state, but not IBD, SENP7 expression was negatively regulated by a direct interaction and ubiquitination by SIAH2. Upregulated SENP7 in inflamed tissue displayed a distinct interactome. These changes led to an expansion of localized proinflammatory γδ T cells. Furthermore, in vivo knockdown of SENP7 or depletion of γδ T cells abrogated dextran sulfate sodium (DSS)-induced gut inflammation. Strong statistical correlations between upregulated SENP7 and high clinical disease indices were observed in IBD patients. Overall, our data reveal that epithelial SENP7 is necessary and sufficient for controlling gut inflammation, thus highlighting its importance as a potential drug target.

Prostate Cancer-associated SPOP mutations enhance cancer cell survival and docetaxel resistance by upregulating Caprin1-dependent stress granule assembly

BACKGROUND

The gene encoding the E3 ubiquitin ligase substrate-binding adaptor SPOP is frequently mutated in primary prostate cancer, but how SPOP mutations contribute to prostate cancer pathogenesis remains poorly understood. Stress granules (SG) assembly is an evolutionarily conserved strategy for survival of cells under stress, and often upregulated in human cancers. We investigated the role of SPOP mutations in aberrant activation of the SG in prostate cancer and explored the relevanve of the mechanism in therapy resistance.

METHODS

We identified SG nucleating protein Caprin1 as a SPOP interactor by using the yeast two hybrid methods. A series of functional analyses in cell lines, patient samples, and xenograft models were performed to investigate the biological significance and clinical relevance of SPOP regulation of SG signaling in prostate cancer.

RESULTS

The cytoplasmic form of wild-type (WT) SPOP recognizes and triggers ubiquitin-dependent degradation of Caprin1. Caprin1 abundance is elevated in SPOP-mutant expressing prostate cancer cell lines and patient specimens. SPOP WT suppresses SG assembly, while the prostate cancer-associated mutants enhance SG assembly in a Caprin1-dependent manner. Knockout of SPOP or expression of prostate cancer-associated SPOP mutants conferred resistance to death caused by SG inducers (e.g. docetaxel, sodium arsenite and H2O2) in prostate cancer cells.

CONCLUSIONS

SG assembly is aberrantly elevated in SPOP-mutated prostate cancer. SPOP mutations cause resistance to cellular stress induced by chemtherapeutic drug such as docetaxel in prostate cancer.

Uterine function in the mouse requires speckle-type poz protein

Speckle-type poz protein (SPOP) is an E3-ubiquitin ligase adaptor for turnover of a diverse number of proteins involved in key cellular processes such as chromatin remodeling, transcriptional regulation, and cell signaling. Genomic analysis revealed that SPOP somatic mutations are found in a subset of endometrial cancers, suggesting that these mutations act as oncogenic drivers of this gynecologic malignancy. These studies also raise the question as to the role of wild-type SPOP in normal uterine function. To address this question, we generated a mouse model (Spopd/d) in which SPOP is ablated in uterine cells that express the PGR. Fertility studies demonstrated that SPOP is required for embryo implantation and for endometrial decidualization. Molecular analysis revealed that expression levels of the PGR at the protein and transcript level are significantly reduced in the Spopd/d uterus. While this result was unexpected, this finding explains in part the dysfunctional phenotype of the Spopd/d uterus. Moderate increased levels of the ESR1, GATA2, and SRC2 were detected in the Spopd/d uterus, suggesting that SPOP is required to maintain the proteome for normal uterine function. With age, the Spopd/d endometrium exhibits large glandular cysts with foci of epithelial proliferation, further supporting a role for SPOP in maintaining a healthy uterus. Collectively, studies on the Spopd/d mouse support an important role for SPOP in normal uterine function and suggest that this mouse model may prove useful to study the role of SPOP-loss-of-function mutations in the etiopathogenesis of endometrial cancer.

SPOP-mediated degradation of BRD4 dictates cellular sensitivity to BET inhibitors

Bromodomain and extra-terminal (BET) proteins are frequently overexpressed in various human cancers, therefore have been clinically pursed as attractive therapeutic anti-cancer targets. However, relatively little is known about the mechanism(s) underlying aberrant BET overexpression in human cancers. Recently, we reported that prostate cancer-derived SPOP mutants fail to interact with and promote BRD4 degradation, leading to accumulation of BRD4 in prostate cancer cells. As a result, prostate cancer cells harboring SPOP mutations are more resistant to BET inhibitors. Therefore, our results help to elucidate the tumor suppressor role of SPOP in the prostate cancer setting by negatively controlling BET proteins stability. More importantly, our results also provide a molecular basis for using combination with BET inhibitors and other inhibitors to treat prostate cancer patients with SPOP mutations.

TRIM28 protects TRIM24 from SPOP-mediated degradation and promotes prostate cancer progression

TRIM24 is an effector substrate of the E3 ubiquitin ligase adaptor SPOP and becomes stabilized in prostate cancer (PCa) with SPOP mutations. However, how TRIM24 protein is regulated in the vast majority of SPOP-wildtype PCa is unknown. Here we report TRIM28 as a critical upstream regulator of TRIM24. TRIM28 protein interacts with TRIM24 to prevent its ubiquitination and degradation by SPOP. Further, TRIM28 facilitates TRIM24 occupancy on the chromatin and, like TRIM24, augments AR signaling. TRIM28 promotes PCa cell proliferation in vitro and xenograft tumor growth in vivo. Importantly, TRIM28 is upregulated in aggressive PCa and associated with elevated levels of TRIM24 and worse clinical outcome. TRIM24 and AR coactivated gene signature of SPOP-mutant PCa is similarly activated in human PCa with high TRIM28 expression. Taken together, this study provides a novel mechanism to broad TRIM24 protein stabilization and establishes TRIM28 as a promising therapeutic target.

TRIM24 is stabilized in SPOP-mutated prostate cancers, but the regulation of TRIM24 in wild-type prostate cancers is unknown. Here, the authors show that TRIM28 interacts with TRIM24 to prevent SPOP-mediated ubiquitination of TRIM24 and enhances TRIM24 and AR signaling to induce prostate cancer tumorigenesis.

Functional roles of Speckle-Type Poz (SPOP) Protein in Genomic stability

Understanding the functional significance of the essential elements in maintaining genomic stability provides insights into the process of tumor initiation and progression, and predicts therapeutic responses. One such element that has recently attracted significant attention is the Speckle-Type Poz Protein (SPOP), an E3 ubiquitin ligase adaptor protein. SPOP is frequently mutated or has altered expression in various cancers, including prostate, renal and endometrial. SPOP is involved in the regulation of proteasome-mediated degradation of several oncoproteins. Moreover, recent data also indicate SPOP's direct involvement in the DNA damage response. SPOP mutants induce alternations in the DNA damage repair pathway by promoting the error-prone Non-homologous end joining (NHEJ) pathway. SPOP has been linked with significant functions in cellular signaling pathways and cancer suppression. This mini-review will discuss recent findings regarding SPOP's role in genomic stability in the pathological setting.

SPOP promotes ATF2 ubiquitination and degradation to suppress prostate cancer progression

Background

Next-generation sequencing of the exome and genome of prostate cancers has identified numerous genetic alterations. SPOP (Speckle-type POZ Protein) is one of the most frequently mutated genes in primary prostate cancer, suggesting that SPOP may be a potential driver of prostate cancer. The aim of this work was to investigate how SPOP mutations contribute to prostate cancer development and progression.

Methods

To identify molecular mediators of the tumor suppressive function of SPOP, we performed a yeast two-hybrid screen in a HeLa cDNA library using the full-length SPOP as bait. Immunoprecipitation and Western Blotting were used to analyze the interaction between SPOP and ATF2. Cell migration and invasion were determined by Transwell assays. Immunohistochemistry were used to analyze protein levels in patients’ tumor samples.

Results

Here we identified ATF2 as a bona fide substrate of the SPOP-CUL3-RBX1 E3 ubiquitin ligase complex. SPOP recognizes multiple Ser/Thr (S/T)-rich degrons in ATF2 and triggers ATF2 degradation via the ubiquitin-proteasome pathway. Strikingly, prostate cancer-associated mutants of SPOP are defective in promoting ATF2 degradation in prostate cancer cells and contribute to facilitating prostate cancer cell proliferation, migration and invasion.

Conclusion

SPOP promotes ATF2 ubiquitination and degradation, and ATF2 is an important mediator of SPOP inactivation-induced cell proliferation, migration and invasion.

Electronic supplementary material

The online version of this article (10.1186/s13046-018-0809-0) contains supplementary material, which is available to authorized users.

Ubiquitination: Friend and foe in cancer

Dynamic modulation and posttranslational modification of proteins are tightly controlled biological processes that occur in response to physiological cues. One such dynamic modulation is ubiquitination, which marks proteins for degradation via the proteasome, altering their localization, affecting their activity, and promoting or interfering with protein interactions. Hence, ubiquitination is crucial for a plethora of physiological processes, including cell survival, differentiation and innate and adaptive immunity. Similar to kinases, components of the ubiquitination system are often deregulated, leading to a variety of diseases, such as cancer and neurodegenerative disorders. In a context-dependent manner, ubiquitination can regulate both tumor-suppressing and tumor-promoting pathways in cancer. This review outlines how components of the ubiquitination systems (e.g. E3 ligases and deubiquitinases) act as oncogenes or tumor suppressors according to the nature of their substrates. Furthermore, I interrogate how the current knowledge of the differential roles of ubiquitination in cancer lead to technical advances to inhibit or reactivate the components of the ubiquitination system accordingly.

Speckle-type POZ protein suppresses hepatocellular carcinoma cell migration and invasion via ubiquitin-dependent proteolysis of SUMO1/sentrin specific peptidase 7

Hepatocellular carcinoma (HCC) is associated with high metastatic potential and high mortality. Accumulating evidence has demonstrated that speckle-type POZ protein (SPOP) is a key adaptor molecule of ubiquitination. However, the molecular mechanism of SPOP-mediated ubiquitination in HCC metastasis remains obscure. In the present study, our results indicated that SPOP expression was significantly downregulated in HCC and was associated with tumor size, differentiation and metastasis. Cox regression model showed that low SPOP expression was a risk factor related to the prognosis of HCC patients. Loss- and gain-of-function assays demonstrated that SPOP inhibited HCC cell migration and invasion in vitro. Mechanisitically, co-immunoprecipitation and ubiquitination assays revealed that SPOP recognized and bound SENP7 and promoted its degradation via ubiquitin-dependent proteolysis. Analysis of immunohistochemistry showed that vimentin expression was correlated negatively with SPOP and positively with SENP7. These results implied that increased degradation of SENP7 by overexpression of SPOP decreased vimentin levels, which in turn attenuated HCC cell metastasis. Moreover, in vivo assays showed that SPOP overexpression also significantly suppressed liver and lung metastases. In summary, SPOP inhibits HCC cell metastasis via ubiquitin-dependent SENP7 proteolysis and may thus serve as a new opinion for the prevention of HCC metastasis.

SUMO-specific proteases and isopeptidases of the SENP family at a glance

The ubiquitin-related SUMO system controls many cellular signaling networks. In mammalian cells, three SUMO forms (SUMO1, SUMO2 and SUMO3) act as covalent modifiers of up to thousands of cellular proteins. SUMO conjugation affects cell function mainly by regulating the plasticity of protein networks. Importantly, the modification is reversible and highly dynamic. Cysteine proteases of the sentrin-specific protease (SENP) family reverse SUMO conjugation in mammalian cells. In this Cell Science at a Glance article and the accompanying poster, we will summarize how the six members of the mammalian SENP family orchestrate multifaceted deconjugation events to coordinate cell processes, such as gene expression, the DNA damage response and inflammation.

The Immortal Senescence

Activation of oncogenic signaling paradoxically results in the permanent withdrawal from cell cycle and induction of senescence (oncogene-induced senescence (OIS)). OIS is a fail-safe mechanism used by the cells to prevent uncontrolled tumor growth, and, as such, it is considered as the first barrier against cancer. In order to progress, tumor cells thus need to first overcome the senescent phenotype. Despite the increasing attention gained by OIS in the past 20 years, this field is still rather young due to continuous emergence of novel pathways and processes involved in OIS. Among the many factors contributing to incomplete understanding of OIS are the lack of unequivocal markers for senescence and the complexity of the phenotypes revealed by senescent cells in vivo and in vitro. OIS has been shown to play major roles at both the cellular and organismal levels in biological processes ranging from embryonic development to barrier to cancer progression. Here we will briefly outline major advances in methodologies that are being utilized for induction, identification, and characterization of molecular processes in cells undergoing oncogene-induced senescence. The full description of such methodologies is provided in the corresponding chapters of the book.

Functional analysis of Cullin 3 E3 ligases in tumorigenesis

Cullin 3-RING ligases (CRL3) play pivotal roles in the regulation of various physiological and pathological processes, including neoplastic events. The substrate adaptors of CRL3 typically contain a BTB domain that mediates the interaction between Cullin 3 and target substrates to promote their ubiquitination and subsequent degradation. The biological implications of CRL3 adaptor proteins have been well described where they have been found to play a role as either an oncogene, tumor suppressor, or can mediate either of these effects in a context-dependent manner. Among the extensively studied CRL3-based E3 ligases, the role of the adaptor protein SPOP (speckle type BTB/POZ protein) in tumorigenesis appears to be tissue or cellular context dependent. Specifically, SPOP acts as a tumor suppressor via destabilizing downstream oncoproteins in many malignancies, especially in prostate cancer. However, SPOP has largely an oncogenic role in kidney cancer. Keap1, another well-characterized CRL3 adaptor protein, likely serves as a tumor suppressor within diverse malignancies, mainly due to its specific turnover of its downstream oncogenic substrate, NRF2 (nuclear factor erythroid 2-related factor 2). In accordance with the physiological role the various CRL3 adaptors exhibit, several pharmacological agents have been developed to disrupt its E3 ligase activity, therefore blocking its potential oncogenic activity to mitigate tumorigenesis.

SPOP regulates prostate epithelial cell proliferation and promotes ubiquitination and turnover of c-MYC oncoprotein

The E3 ubiquitin ligase adaptor speckle-type POZ protein (SPOP) is frequently dysregulated in prostate adenocarcinoma (PC), via either somatic mutations or mRNA downregulation, suggesting an important tumour suppressor function. To examine its physiologic role in the prostate epithelium in vivo, we generated mice with prostate-specific biallelic ablation of Spop. These mice exhibited increased prostate mass, prostate epithelial cell proliferation, and expression of c-MYC protein compared to littermate controls, and eventually developed prostatic intraepithelial neoplasia (PIN). We found that SPOPWT can physically interact with c-MYC protein and, upon exogenous expression in vitro, can promote c-MYC ubiquitination and degradation. This effect was attenuated in PC cells by introducing PC-associated SPOP mutants or upon knockdown of SPOP via short-hairpin-RNA, suggesting that SPOP inactivation directly increases c-MYC protein levels. Gene Set Enrichment Analysis revealed enrichment of Myc-induced genes in transcriptomic signatures associated with SPOPMT. Likewise, we observed strong inverse correlation between c-MYC activity and SPOP mRNA levels in two independent PC patient cohorts. The core SPOPMT;MYCHigh transcriptomic response, defined by the overlap between the SPOPMT and c-MYC transcriptomic programmes, was also associated with inferior clinical outcome in human PCs. Finally, the organoid-forming capacity of Spop-null murine prostate cells was more sensitive to c-MYC inhibition than that of Spop-WT cells, suggesting that c-MYC upregulation functionally contributes to the proliferative phenotype of Spop knock-out prostates. Taken together, our data highlight SPOP as an important regulator of luminal epithelial cell proliferation and c-MYC expression in prostate physiology, identify c-MYC as a novel bona fide SPOP substrate, and help explain the frequent inactivation of SPOP in human PC. We propose SPOPMT-induced stabilization of c-MYC protein as a novel mechanism that can increase total c-MYC levels in PC cells, in addition to amplification of c-MYC locus.

Melatonin regulates PARP1 to control the senescence-associated secretory phenotype (SASP) in human fetal lung fibroblast cells

Cellular senescence is an important tumor-suppressive mechanism. However, acquisition of a senescence-associated secretory phenotype (SASP) in senescent cells has deleterious effects on the tissue microenvironment and, paradoxically, promotes tumor progression. In a drug screen, we identified melatonin as a novel SASP suppressor in human cells. Strikingly, melatonin blunts global SASP gene expression upon oncogene-induced senescence (OIS). Moreover, poly(ADP-ribose) polymerase-1 (PARP-1), a sensor of DNA damage, was identified as a new melatonin-dependent regulator of SASP gene induction upon OIS. Here, we report two different but potentially coherent epigenetic strategies for melatonin regulation of SASP. The interaction between the telomeric repeat-containing RNA (TERRA) and PARP-1 stimulates the SASP, which was attenuated by 67.9% (illustrated by the case of IL8) by treatment with melatonin. Through binding to macroH2A1.1, PARP-1 recruits CREB-binding protein (CBP) to mediate acetylation of H2BK120, which positively regulates the expression of target SASP genes, and this process is interrupted by melatonin. Consequently, the findings provide novel insight into melatonin's epigenetic role via modulating PARP-1 in suppression of SASP gene expression in OIS-induced senescent cells. Our studies identify melatonin as a novel anti-SASP molecule, define PARP-1 as a new target by which melatonin regulates SASP, and establish a new epigenetic paradigm for a pharmacological mechanism by which melatonin interrupts PARP-1 interaction with the telomeric long noncoding RNA(lncRNA) or chromatin.

Dysregulation of INF2-mediated mitochondrial fission in SPOP-mutated prostate cancer

Next-generation sequencing of the exome and genome of prostate cancers has identified numerous genetic alternations. SPOP (Speckle-type POZ Protein) was one of the most frequently mutated genes in primary prostate cancer, suggesting SPOP is a potential driver of prostate cancer development and progression. However, how SPOP mutations contribute to prostate cancer pathogenesis remains poorly understood. SPOP acts as an adaptor protein of the CUL3-RBX1 E3 ubiquitin ligase complex that generally recruits substrates for ubiquitination and subsequent degradation. ER-localized isoform of the formin protein inverted formin 2 (INF2) mediates actin polymerization at ER-mitochondria intersections and facilitates DRP1 recruitment to mitochondria, which is a critical step in mitochondrial fission. Here, we revealed that SPOP recognizes a Ser/Thr (S/T)-rich motif in the C-terminal region of INF2 and triggers atypical polyubiquitination of INF2. These ubiquitination modifications do not lead to INF2 instability, but rather reduces INF2 localization in ER and mitochondrially associated DRP1 puncta formation, therefore abrogates its ability to facilitate mitochondrial fission. INF2 mutant escaping from SPOP-mediated ubiquitination is more potent in prompting mitochondrial fission. Moreover, prostate cancer-associated SPOP mutants increase INF2 localization in ER and promote mitochondrial fission, probably through a dominant-negative effect to inhibit endogenous SPOP. Moreover, INF2 is important for SPOP inactivation-induced prostate cancer cell migration and invasion. These findings reveal novel molecular events underlying the regulation of INF2 function and localization, and provided insights in understanding the relationship between SPOP mutations and dysregulation of mitochondrial dynamics in prostate cancer.

Prostate cancer is the leading cause of global cancer-related death. The development of improved diagnoses and novel therapies has been confounded by significant patient heterogeneity. During recent years, significant progress has been made in identifying the molecular alterations in prostate cancer using next-generation sequencing. SPOP gene was frequently altered by somatic point mutations in a distinct molecular subclass of prostate cancer, although the precise role that SPOP mutation plays in the development of prostate cancer is unclear. Mitochondria are highly motile organelles that undergo constant fission and fusion. Unbalanced mitochondrial fission and fusion events are associated with mitochondrial dysfunction and frequently linked to human cancer. Here, we are the first to report that SPOP mutations are associated with dysregulation of mitochondrial dynamics in prostate cancer and this finding may have potential clinical implications in prostate cancer treatment.

Detection of the Ubiquitinome in Cells Undergoing Oncogene-Induced Senescence

Senescent cells exhibit dramatic changes in protein post-translational modifications. Here, we describe a method, stable isotope labeling with amino acids in cell culture (SILAC) coupled to liquid chromatography tandem mass spectrometry (LC-MS/MS), to identify changes in the ubiquitinome in cells that have undergone oncogene-induced senescence.

Prostate cancer-associated mutation in SPOP impairs its ability to target Cdc20 for poly-ubiquitination and degradation

Recent studies revealed that mutations in SPOP (Speckle-type POZ protein) occur in up to 15% of patients with prostate cancer. However, the physiological role of SPOP in regulating prostate tumorigenesis remains elusive. Here, we identified the Cdc20 oncoprotein as a novel ubiquitin substrate of SPOP. As such, pharmacological inhibition of Cullin-based E3 ligases by MLN4924 could stabilize endogenous Cdc20 in cells. Furthermore, we found that Cullin 3, and, to a less extent, Cullin 1, specifically interacted with Cdc20. Depletion of Cullin 3, but not Cullin 1, could upregulate the abudance of Cdc20 largely via prolonging Cdc20 half-life. Moreover, SPOP, the adaptor protein of Cullin 3 family E3 ligase, specifically interacted with Cdc20, and promoted the poly-ubiquitination and subsequent degradation of Cdc20 in a degron-dependent manner. Importantly, prostate cancer-derived SPOP mutants failed to interact with Cdc20 to promote its degradation. As a result, SPOP-deficient prostate cancer cells with elevated Cdc20 expression became resistant to a pharmacological Cdc20 inhibitor. Therefore, our results revealed a novel role of SPOP in tumorigenesis in part by promoting the degradation of the Cdc20 oncoprotein.

Old cells, new tricks: chromatin structure in senescence

Cellular senescence is a stable form of cell cycle arrest with roles in many pathophysiological processes including development, tissue repair, cancer, and aging. Senescence does not represent a single entity but rather a heterogeneous phenotype that depends on the trigger and cell type of origin. Such heterogeneous features include alterations to chromatin structure and epigenetic states. New technologies are beginning to unravel the distinct mechanisms regulating chromatin structure during senescence. Here, we describe the multiple levels of chromatin organization associated with senescence: global and focal, linear, and higher order.