SPOP promotes transcriptional expression of DNA repair and replication factors to prevent replication stress and genomic instability

Increased frequency of CHD1 deletions in prostate cancers of African American men is associated with rapid disease progression without inducing homologous recombination deficiency

We analyzed genomic data derived from the prostate cancer of African and European American men in order to identify differences that may contribute to racial disparity of outcome and that could also define novel therapeutic strategies. In addition to analyzing patient derived next generation sequencing data, we performed FISH based confirmatory studies of Chromodomain helicase DNA-binding protein 1 (CHD1) loss on prostate cancer tissue microarrays. We created CRISPR edited, CHD1 deficient prostate cancer cell lines for genomic, drug sensitivity and functional homologous recombination (HR) activity analysis. We found that subclonal deletion of CHD1 is nearly three times as frequent in prostate tumors of African American men than in men of European ancestry and it associates with rapid disease progression. We further showed that CHD1 deletion is not associated with homologous recombination deficiency associated mutational signatures in prostate cancer. In prostate cancer cell line models CHD1 deletion did not induce HR deficiency as detected by RAD51 foci formation assay or mutational signatures, which was consistent with the moderate increase of olaparib sensitivity. CHD1 deficient prostate cancer cells, however, showed higher sensitivity to talazoparib. CHD1 loss may contribute to worse outcome of prostate cancer in African American men. A deeper understanding of the interaction between CHD1 loss and PARP inhibitor sensitivity will be needed to determine the optimal use of targeted agents such as talazoparib in the context of castration resistant prostate cancer.

Effect of ubiquitin protease system on DNA damage response in prostate cancer (Review)

Genomic instability is an essential hallmark of cancer, and cellular DNA damage response (DDR) defects drive tumorigenesis by disrupting genomic stability. Several studies have identified abnormalities in DDR-associated genes, and a dysfunctional ubiquitin-proteasome system (UPS) is the most common molecular event in metastatic castration-resistant prostate cancer (PCa). For example, mutations in Speckle-type BTB/POZ protein-Ser119 result in DDR downstream target activation deficiency. Skp2 excessive upregulation inhibits homologous recombination repair and promotes cell growth and migration. Abnormally high expression of a deubiquitination enzyme, ubiquitin-specific protease 12, stabilizes E3 ligase MDM2, which further leads to p53 degradation, causing DDR interruption and genomic instability. In the present review, the basic pathways of DDR, UPS dysfunction, and its induced DDR alterations mediated by genomic instability, and especially the potential application of UPS and DDR alterations as biomarkers and therapeutic targets in PCa treatment, were described.

SPOP Mutations Target STING1 Signaling in Prostate Cancer and Create Therapeutic Vulnerabilities to PARP Inhibitor-Induced Growth Suppression

PURPOSE

Speckle-type POZ protein (SPOP) is important in DNA damage response (DDR) and maintenance of genomic stability. Somatic heterozygous missense mutations in the SPOP substrate-binding cleft are found in up to 15% of prostate cancers. While mutations in SPOP predict for benefit from androgen receptor signaling inhibition (ARSi) therapy, outcomes for patients with SPOP-mutant (SPOPmut) prostate cancer are heterogeneous and targeted treatments for SPOPmut castrate-resistant prostate cancer (CRPC) are lacking.

EXPERIMENTAL DESIGN

Using in silico genomic and transcriptomic tumor data, proteomics analysis, and genetically modified cell line models, we demonstrate mechanistic links between SPOP mutations, STING signaling alterations, and PARP inhibitor vulnerabilities.

RESULTS

We demonstrate that SPOP mutations are associated with upregulation of a 29-gene noncanonical (NC) STING (NC-STING) signature in a subset of SPOPmut, treatment-refractory CRPC patients. We show in preclinical CRPC models that SPOP targets and destabilizes STING1 protein, and prostate cancer-associated SPOP mutations result in upregulated NC-STING-NF-κB signaling and macrophage- and tumor microenvironment (TME)-facilitated reprogramming, leading to tumor cell growth. Importantly, we provide in vitro and in vivo mechanism-based evidence that PARP inhibitor (PARPi) treatment results in a shift from immunosuppressive NC-STING-NF-κB signaling to antitumor, canonical cGAS-STING-IFNβ signaling in SPOPmut CRPC and results in enhanced tumor growth inhibition.

CONCLUSIONS

We provide evidence that SPOP is critical in regulating immunosuppressive versus antitumor activity downstream of DNA damage-induced STING1 activation in prostate cancer. PARPi treatment of SPOPmut CRPC alters this NC-STING signaling toward canonical, antitumor cGAS-STING-IFNβ signaling, highlighting a novel biomarker-informed treatment strategy for prostate cancer.

Genomic alterations related to HPV infection status in a cohort of Chinese prostate cancer patients

BACKGROUND

Human papillomavirus (HPV) has been proposed as a potential pathogenetic organism involved in prostate cancer (PCa), but the association between HPV infection and relevant genomic changes in PCa is poorly understood.

METHODS

To evaluate the relationship between HPV genotypes and genomic alterations in PCa, HPV capture sequencing of DNA isolated from 59 Han Chinese PCa patients was performed using an Illumina HiSeq2500. Additionally, whole-exome sequencing of DNA from these 59 PCa tissue samples and matched normal tissues was carried out using the BGI DNBSEQ platform. HPV infection status and genotyping were determined, and the genetic disparities between HPV-positive and HPV-negative PCa were evaluated.

RESULTS

The presence of the high-risk HPV genome was identified in 16.9% of our cohort, and HPV16 was the most frequent genotype detected. The overall mutational burden in HPV-positive and HPV-negative PCa was similar, with an average of 2.68/Mb versus 2.58/Mb, respectively, in the targeted whole-exome region. HPV-negative tumors showed a mutational spectrum concordant with published PCa analyses with enrichment for mutations in SPOP, FOXA1, and MED12. HPV-positive tumors showed more mutations in KMT2C, KMT2D and ERCC2. Copy number alterations per sample were comparable between the two groups. However, the significantly amplified or deleted regions of the two groups only partially overlapped. We identified amplifications in oncogenes, including FCGR2B and CCND1, and deletions of tumor suppressors, such as CCNC and RB1, only in HPV-negative tumors. HPV-positive tumors showed unique deletions of tumor suppressors such as NTRK1 and JAK1.

CONCLUSIONS

The genomic mutational landscape of PCa differs based on HPV infection status. This work adds evidence for the direct involvement of HPV in PCa etiology. Different genomic features render HPV-positive PCa a unique subpopulation that might benefit from virus-targeted therapy.

Cul3 substrate adaptor SPOP targets Nup153 for degradation

SPOP is a Cul3 substrate adaptor responsible for degradation of many proteins related to cell growth and proliferation. Because mutation or misregulation of SPOP drives cancer progression, understanding the suite of SPOP substrates is important to understanding regulation of cell proliferation. Here, we identify Nup153, a component of the nuclear basket of the nuclear pore complex, as a novel substrate of SPOP. SPOP and Nup153 bind to each other and colocalize at the nuclear envelope and some nuclear foci in cells. The binding interaction between SPOP and Nup153 is complex and multivalent. Nup153 is ubiquitylated and degraded upon expression of SPOPWT but not its substrate binding-deficient mutant SPOPF102C. Depletion of SPOP via RNAi leads to Nup153 stabilization. Upon loss of SPOP, the nuclear envelope localization of spindle assembly checkpoint protein Mad1, which is tethered to the nuclear envelope by Nup153, is stronger. Altogether, our results demonstrate SPOP regulates Nup153 levels and expands our understanding of the role of SPOP in protein and cellular homeostasis.

SPOP is essential for DNA replication licensing through maintaining translation of CDT1 and CDC6 in HaCaT cells

Speckle-type pox virus and zinc finger (POZ) protein (SPOP), a substrate recognition receptor for the cullin-3/RING ubiquitin E3 complex, leads to the ubiquitination of >40 of its target substrates. Since a variety of point mutations in the substrate-binding domain of SPOP have been identified in cancers, including prostate and endometrial cancers, the pathological roles of those cancer-associated SPOP mutants have been extensively elucidated. In this study, we evaluated the cellular functions of wild-type SPOP in non-cancerous human keratinocyte-derived HaCaT cells expressing wild-type SPOP gene. SPOP knockdown using siRNA in HaCaT cells dramatically reduced cell growth and arrested their cell cycles at G1/S phase. The expression of DNA replication licensing factors CDT1 and CDC6 in HaCaT cells drastically decreased on SPOP knockdown as their translation was inhibited. CDT1 and CDC6 downregulation induced p21 expression without p53 activation. Our results suggest that SPOP is essential for DNA replication licensing in non-cancerous keratinocyte HaCaT cells.

CHD1, a multifaceted epigenetic remodeler in prostate cancer

Chromatin remodeling proteins contribute to DNA replication, transcription, repair, and recombination. The chromodomain helicase DNA-binding (CHD) family of remodelers plays crucial roles in embryonic development, hematopoiesis, and neurogenesis. As the founding member, CHD1 is capable of assembling nucleosomes, remodeling chromatin structure, and regulating gene transcription. Dysregulation of CHD1 at genetic, epigenetic, and post-translational levels is common in malignancies and other human diseases. Through interacting with different genetic alterations, CHD1 possesses the capabilities to exert oncogenic or tumor-suppressive functions in context-dependent manners. In this Review, we summarize the biochemical properties and dysregulation of CHD1 in cancer cells, and then discuss CHD1's roles in different contexts of prostate cancer, with an emphasis on its crosstalk with diverse signaling pathways. Furthermore, we highlight the potential therapeutic strategies for cancers with dysregulated CHD1. At last, we discuss current research gaps in understanding CHD1's biological functions and molecular basis during disease progression, as well as the modeling systems for biology study and therapeutic development.

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.

HELQ suppresses migration and proliferation of non-small cell lung cancer cells by repairing DNA damage and inducing necrosis

HELQ plays a key role in DNA damage response and cell-cycle checkpoint regulation. It has been implicated in ovarian and pituitary tumors and may play a role in germ cell maintenance. This study investigated the role of HELQ in lung cancer. The expression of HELQ in patients with non-small-cell lung cancer (NSCLC) was downregulated compared with normal human lungs. Clinical prognostic analysis of Kaplan-Meier plots revealed that patients with NSCLC with low HELQ levels had a reduced overall survival. Further, we found that HELQ depletion enhanced lung cancer cell malignancy. Furthermore, overexpression of HELQ in lung cancer cells reduced cell migration in vitro, while DNA damage repair was inhibited. Both in vitro and in vivo studies have shown that HELQ induces cell death. Mechanistically, we found that cells overexpressing HELQ showed a tendency to induce necrosis. After analyzing the database of HELQ interactors. we found that RIPK3 may interact with it and proved this conclusion by immunoprecipitation. Our findings identified the tumor suppressive role of HELQ in malignant human lung cancer and unraveled a potential therapeutic strategy for cancer treatment through HELQ activation. Moreover, HELQ may also be a predictive biomarker for the clinical predisposition, progression, and prognosis of lung cancer.

Comprehensive analysis of TP53 and SPOP mutations and their impact on survival in metastatic prostate cancer

Background

Although TP53 and SPOP are frequently mutated in metastatic prostate cancer (PCa), their prognostic value is ambiguous, and large sample studies are lacking, especially when they co-occur with other genetic alterations.

Methods

Genomic data and patients’ clinical characteristics in PCa were downloaded from the cBioPortal database. We extensively analyzed other gene alterations in different mutation status of TP53 and SPOP. We further subdivided TP53 and SPOP mutation into subgroups based on different mutation status, and then evaluated the prognostic value. Two classification systems for TP53 survival analysis were used.

Results

A total of 2,172 patients with PCa were analyzed in our study, of which 1,799 were metastatic PCa patients. The mutual exclusivity analysis showed that TP53 and SPOP mutation has a strong mutual exclusion (p<0.001). In multivariable analysis, truncating TP53 mutations (HR=1.773, 95%CI:1.403-2.239, p<0.001) and other TP53 mutations(HR=1.555, 95%CI:1.267-1.908, p<0.001) were independent negative prognostic markers in metastatic PCa, whereas SPOP mutations(HR=0.592, 95%CI:0.427-0.819, p<0.001) were an independent prognostic factor for better prognosis. Mutations in TP53 were significantly associated with wild-type status for SPOP and CDK12, structural variants/fusions for TMPRSS2 and ERG, AR amplification and PTEN deletion (p<0.001). And truncating TP53 mutations have higher AR amplification rates than other TP53 mutations (p=0.022). Consistently, truncating TP53 mutations had a worse prognosis than other TP53 mutations (p<0.05). Then Kaplan-Meier survival curve showed that Co-occurring TP53 mutations in AR amplification or PTEN deletion tumors significantly reduced survival (p<0.05). Furthermore, those with SPOP-mutant tumors with co-occurring TP53 truncating mutations had shorter overall survival than those with SPOP-mutant tumors with wild-type or other TP53 mutations.

Conclusions

This study found that TP53 and SPOP mutations were mutually exclusive and both were independent prognostic markers for metastatic PCa. Genomic alteration and survival analysis revealed that TP53 and SPOP mutations represented distinct molecular subtypes. Our data suggest that molecular stratification on the basis of TP53 and SPOP mutation status should be implemented for metastatic PCa to optimize and modify clinical decision-making.

The functions and effects of CUL3-E3 ligases mediated non-degradative ubiquitination

Ubiquitination of substrates usually have two fates: one is degraded by 26S proteasome, and the other is non-degradative ubiquitination modification which is associated with cell cycle regulation, chromosome inactivation, protein transportation, tumorigenesis, achondroplasia, and neurological diseases. Cullin3 (CUL3), a scaffold protein, binding with the Bric-a-Brac-Tramtrack-Broad-complex (BTB) domain of substrates recognition adaptor and RING-finger protein 1 (RBX1) form ubiquitin ligases (E3). Based on the current researches, this review has summarized the functions and effects of CUL3-E3 ligases mediated non-degradative ubiquitination.

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.

SPOP Inhibition of Endometrial Carcinoma and Its Clinicopathological Relationship

Objective

Endometrial carcinoma (EC) ranks first in the incidence of female genital malignancies in developed countries. SPOP (speckle-type POZ protein) has changed in EC with a statistically high frequency. This research may play a crucial role in the initiation and progression of EC, ultimately leading to fresh therapeutic targets. Explore the expression of SPOP in EC; observe its effect on the proliferation, invasion, and migration of EC cells after upregulating the expression of SPOP through RNA activation.

Methods

The expression levels of SPOP protein in 150 EC tissues and 45 normal endometrial tissues were detected by immunohistochemistry and Western blotting. Analyze the relationship between SPOP expression and clinicopathological characteristics. The differences of the proliferation, migration, and invasion abilities between before and after transfection were analyzed using CCK-8 and Transwell assays.

Results

The results of immunohistochemistry and Western blotting showed the expression level of SPOP in EC tissue significantly reduced or even missed compared with normal endometrial tissue. The results of CCK-8 showed that the growth of EC significantly slowed down after the upregulating of SPOP expression. The results of the Transwell assay showed the migration and invasion abilities of EC cells were weakened after the level of SPOP was upregulated.

Conclusions

The expression level of SPOP in EC tissues is lower and related to the clinicopathological features compared with normal endometrial tissues. After upregulating the SPOP expression by RNA activation in EC cell lines, the abilities of proliferation, migration, and invasion of cells were significantly inhibited.

Clinical and genomic features of SPOP-mutant prostate cancer

BACKGROUND

Inactivating missense mutations in the SPOP gene, encoding speckle-type poxvirus and zinc-finger protein, are one of the most common genetic alterations in prostate cancer.

METHODS

We retrospectively identified 72 consecutive prostate cancer patients with somatic SPOP mutations, through next-generation sequencing analysis, who were treated at the Johns Hopkins Hospital. We evaluated clinical and genomic characteristics of this SPOP-mutant subset.

RESULTS

SPOP alterations were clustered in the MATH domain, with hotspot mutations involving the F133 and F102 residues. The most frequent concurrent genetic alterations were in APC (16/72 [22%]), PTEN (13/72 [18%]), and TP53 (11/72 [15%]). SPOP-mutant cancers appeared to be mutually exclusive with tumors harboring the TMPRSS2-ERG fusion, and were significantly enriched for Wnt pathway (APC, CTNNB1) mutations and de-enriched for TP53/PTEN/RB1 alterations. Patients with mtSPOP had durable responses to androgen deprivation therapy (ADT) with a median time-to-castration-resistance of 42.0 (95% confidence interval [CI], 25.7-60.8) months. However, time-to-castration-resistance was significantly shorter in SPOP-mutant patients with concurrent TP53 mutations (hazard ratio [HR] 4.53; p = 0.002), HRD pathway (ATM, BRCA1/2, and CHEK2) mutations (HR 3.19; p = 0.003), and PI3K pathway (PTEN, PIK3CA, and AKT1) alterations (HR 2.69; p = 0.004). In the castration-resistant prostate cancer setting, median progression-free survival was 8.9 (95% CI, 6.7-NR) months on abiraterone and 7.3 (95% CI, 3.2-NR) months on enzalutamide. There were no responses to PARP inhibitor treatment.

CONCLUSIONS

SPOP-mutant prostate cancers represent a unique subset with absent ERG fusions and frequent Wnt pathway alterations, with potentially greater dependency on androgen signaling and enhanced responsiveness to ADT. Outcomes are best for SPOP-altered patients without other concurrent mutations.

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.

Exploration of Redox-Related Molecular Patterns and the Redox Score for Prostate Cancer

Redox homeostasis is the key to cell survival, and its imbalance can promote the occurrence and progression of tumors. However, it remains unclear whether these redox-related genes (RRGs) have potential roles in the tumor microenvironment, immunotherapy, and drug sensitivity. Here, we performed a systematic and comprehensive analysis of 489 prostate cancer (PC) samples from The Cancer Genome Atlas database and 214 PC samples from 8 datasets in the Gene Expression Omnibus database to determine redox modification patterns and the redox scoring system for PC. We identified two modification patterns (Redox_A and Redox_B) in PC using unsupervised consensus clustering based on 1410 differential expression RRGs. We then compared the prognostic value, tumor microenvironment characteristics, immune cell infiltration, and molecular characteristics of the two patterns. The Redox_A pattern was significantly enriched in the carcinogenic activation signaling pathways and had a poor prognosis, while the Redox_B pattern was mainly enriched in a variety of metabolic and redox pathways and had a good prognosis. Next, redox-related characteristic genes were extracted from these two patterns, and a scoring system (Redox_score) was constructed to evaluate PC patients. Further analysis indicated that lower Redox_score patients had a better prognosis, while higher Redox_score patients had a higher tumor mutation burden, driver gene mutation rate, and immune checkpoint inhibitor gene expression. We also found that higher Redox_score patients were more responsive to anti-PD-1 immunotherapy. Moreover, Redox_score was determined to be significantly correlated with anticancer drug sensitivity and resistance. Our study provides a comprehensive analysis of redox modifications in PC and reveals new patterns of PC based on RRGs, which will provide insights into the complex mechanisms of PC and develop more effective individualized therapeutic strategies.

SPOP mutation induces replication over-firing by impairing Geminin ubiquitination and triggers replication catastrophe upon ATR inhibition

Geminin and its binding partner Cdt1 are essential for the regulation of DNA replication. Here we show that the CULLIN3 E3 ubiquitin ligase adaptor protein SPOP binds Geminin at endogenous level and regulates DNA replication. SPOP promotes K27-linked non-degradative poly-ubiquitination of Geminin at lysine residues 100 and 127. This poly-ubiquitination of Geminin prevents DNA replication over-firing by indirectly blocking the association of Cdt1 with the MCM protein complex, an interaction required for DNA unwinding and replication. SPOP is frequently mutated in certain human cancer types and implicated in tumorigenesis. We show that cancer-associated SPOP mutations impair Geminin K27-linked poly-ubiquitination and induce replication origin over-firing and re-replication. The replication stress caused by SPOP mutations triggers replication catastrophe and cell death upon ATR inhibition. Our results reveal a tumor suppressor role of SPOP in preventing DNA replication over-firing and genome instability and suggest that SPOP-mutated tumors may be susceptible to ATR inhibitor therapy.

Geminin-Cdt1 plays essential roles in the regulation of DNA replication. Here the authors reveal that the CULLIN3 E3 ubiquitin ligase adaptor protein SPOP prevents DNA replication over-firing and genome instability by affecting Geminin ubiquitination.

Molecular features of exceptional response to neoadjuvant anti-androgen therapy in high-risk localized prostate cancer

High-risk localized prostate cancer (HRLPC) is associated with a substantial risk of recurrence and disease mortality. Recent clinical trials have shown that intensifying anti-androgen therapies administered before prostatectomy can induce pathologic complete responses or minimal residual disease, called exceptional response, although the molecular determinants of these clinical outcomes are largely unknown. Here, we perform whole-exome and transcriptome sequencing on pre-treatment multi-regional tumor biopsies from exceptional responders (ERs) and non-responders (NRs, pathologic T3 or lymph node-positive disease) to intensive neoadjuvant anti-androgen therapies. Clonal SPOP mutation and SPOPL copy-number loss are exclusively observed in ERs, while clonal TP53 mutation and PTEN copy-number loss are exclusively observed in NRs. Transcriptional programs involving androgen signaling and TGF-β signaling are enriched in ERs and NRs, respectively. These findings may guide prospective validation studies of these molecular features in large HRLPC clinical cohorts treated with neoadjuvant anti-androgens to improve patient stratification.

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.

ATM-phosphorylated SPOP contributes to 53BP1 exclusion from chromatin during DNA replication

53BP1 activates nonhomologous end joining (NHEJ) and inhibits homologous recombination (HR) repair of DNA double-strand breaks (DSBs). Dissociation of 53BP1 from DSBs and consequent activation of HR, a less error-prone pathway than NHEJ, helps maintain genome integrity during DNA replication; however, the underlying mechanisms are not fully understood. Here, we demonstrate that E3 ubiquitin ligase SPOP promotes HR during S phase of the cell cycle by excluding 53BP1 from DSBs. In response to DNA damage, ATM kinase-catalyzed phosphorylation of SPOP causes a conformational change in SPOP, revealed by x-ray crystal structures, that stabilizes its interaction with 53BP1. 53BP1-bound SPOP induces polyubiquitination of 53BP1, eliciting 53BP1 extraction from chromatin by a valosin-containing protein/p97 segregase complex. Our work shows that SPOP facilitates HR repair over NHEJ during DNA replication by contributing to 53BP1 removal from chromatin. Cancer-derived SPOP mutations block SPOP interaction with 53BP1, inducing HR defects and chromosomal instability.

Gene polymorphism-related differences in the outcomes of abiraterone for prostate cancer: a systematic overview

Numerous prostate cancer (PC) associated genes have been reported in previous genome-wide association studies. Elucidation of prostate cancer pharmacogenomics have enhanced studies into the impact of germline genetic changes on treatment, in addition to evaluating related genomic alterations and biomarkers in prostate tumor tissues. Currently, Abiraterone (Abi) is used as one of the therapeutic options for PC. In this article, germline variants that have been associated with responses to Abi in patients with advanced PC are summarized. These include biomarker genes such as CYP17A1, AR-V7, HSD3B1, SLCO2B1, SULT1E1, and SRD5A2 that are involved in homologous recombination, as well as in gene expression mutations in important signaling pathways, such as WNT and Abi metabolic pathways.

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.

CHD1 and SPOP synergistically protect prostate epithelial cells from DNA damage

BACKGROUND

Recent genomic profiling has identified a subtype of prostate cancer (PCa) characterized by two key genetic alterations: missense mutation of speckle-type POZ protein (SPOP) and homozygous deletion of chromodomain helicase DNA-binding protein 1 (CHD1). Mutually exclusive with E26 transformation-specific (ETS) rearrangements, this subtype displays high genomic instability. Previous studies indicate that deficient SPOP or CHD1 alone leads to feeble prostate abnormalities and each protein is involved in DNA damage response (DDR). It remains to be determined whether CHD1 and SPOP cooperate to suppress prostate tumorigenesis and DDR.

METHODS

Prostate-specific single or double knockout of Spop and Chd1 was generated with the Cre/loxP system in mice. Wild-type or mutant SPOP (F102C, F133V) overexpression and CHD1 knockdown with short hairpin RNA were created in human benign prostatic hyperplasia cell line BPH1. The levels of DNA damage and homologous recombination repair were measured by immunofluorescence staining of γH2AX and RAD51, respectively.

RESULTS

Spop/Chd1 double-knockout mice displayed prostatic intraepithelial neoplasia at both young (3 months) and old (12 months) ages and failed to generate prostate adenocarcinoma. Compared with wild-type or single-knockout mice, the double-knockout prostate harbored moderately higher proliferating cells and dramatically augmented the level of γH2AX staining, although androgen receptor-positive cells and apoptotic cells remained at a similar level. In BPH1 cell line, SPOP mutant overexpression and CHD1 silencing synergistically sensitized the cells to DNA damage by camptothecin, an inducer of double-strand breaks.

CONCLUSIONS

Our results indicate that SPOP and CHD1 can synergistically promote repair of naturally occurring or chemically induced DNA damages in prostate epithelial cells. Regarding the progression of the SPOP/CHD1 subtype of PCa, other functionally complementary drivers warrant further identification. The clinical implication is that this subtype of PCa may be particularly sensitive to poly(ADP-ribose) polymerase inhibitors or DNA-damaging agents.

The Roles of SPOP in DNA Damage Response and DNA Replication

Speckle-type BTB/POZ protein (SPOP) is a substrate recognition receptor of the cullin-3 (CUL3)/RING type ubiquitin E3 complex. To date, approximately 30 proteins have been identified as ubiquitinated substrates of the CUL3/SPOP complex. Pathologically, missense mutations in the substrate-binding domain of SPOP have been found in prostate and endometrial cancers. Prostate and endometrial cancer-associated SPOP mutations lose and increase substrate-binding ability, respectively. Expression of these SPOP mutants, thus, causes aberrant turnovers of the substrate proteins, leading to tumor formation. Although the molecular properties of SPOP and its cancer-associated mutants have been intensively elucidated, their cellular functions remain unclear. Recently, a number of studies have uncovered the critical role of SPOP and its mutants in DNA damage response and DNA replication. In this review article, we summarize the physiological functions of SPOP as a “gatekeeper” of genome stability.

SPOP Deregulation Improves the Radiation Response of Prostate Cancer Models by Impairing DNA Damage Repair

Speckle-type POZ (pox virus and zinc finger protein) protein (SPOP) is the most commonly mutated gene in prostate cancer (PCa). Recent evidence reports a role of SPOP in DNA damage response (DDR), indicating a possible impact of SPOP deregulation on PCa radiosensitivity. This study aimed to define the role of SPOP deregulation (by gene mutation or knockdown) as a radiosensitizing factor in PCa preclinical models. To express WT or mutant (Y87N, K129E and F133V) SPOP, DU145 and PC-3 cells were transfected with pMCV6 vectors. Sensitivity profiles were assessed using clonogenic assay and immunofluorescent staining of γH2AX and RAD51 foci. SCID xenografts were treated with 5 Gy single dose irradiation using an image-guided small animal irradiator. siRNA and miRNA mimics were used to silence SPOP or express the SPOP negative regulator miR-145, respectively. SPOP deregulation, by either gene mutation or knockdown, consistently enhanced the radiation response of PCa models by impairing DDR, as indicated by transcriptome analysis and functionally confirmed by decreased RAD51 foci. SPOP silencing also resulted in a significant downregulation of RAD51 and CHK1 expression, consistent with the impairment of homologous recombination. Our results indicate that SPOP deregulation plays a radiosensitizing role in PCa by impairing DDR via downregulation of RAD51 and CHK1.

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.

Detection of Molecular Signatures of Homologous Recombination Deficiency in Prostate Cancer with or without BRCA1/2 Mutations

PURPOSE

Prostate cancers with mutations in genes involved in homologous recombination (HR), most commonly BRCA2, respond favorably to PARP inhibition and platinum-based chemotherapy. We investigated whether other prostate tumors that do not harbor deleterious mutations in these particular genes can similarly be deficient in HR, likely rendering those sensitive to HR-directed therapies.

EXPERIMENTAL DESIGN

Homologous recombination deficiency (HRD) levels can be estimated using various mutational signatures derived from next-generation sequencing data. We used this approach on whole-genome sequencing (WGS; n = 311) and whole-exome sequencing (WES) data (n = 498) of both primary and metastatic prostate adenocarcinomas to determine whether prostate cancer cases display clear signs of HRD in somatic tumor biopsies.

RESULTS

Known BRCA-deficient samples showed all previously described HRD-associated mutational signatures in the WGS data. HRD-associated mutational signatures were also detected in a subset of patients who did not harbor germline or somatic mutations in BRCA1/2 or other HR-related genes. Similar results, albeit with lower sensitivity and accuracy, were also obtained from WES data.

CONCLUSIONS

These findings may expand the number of cases likely to respond to PARP inhibitor treatment. On the basis of the HR-associated mutational signatures, 5% to 8% of localized prostate cancer cases may be good candidates for PARP-inhibitor treatment (including those with BRCA1/2 mutations).

SPOP is essential for DNA-protein cross-link repair in prostate cancer cells: SPOP-dependent removal of topoisomerase 2A from the topoisomerase 2A-DNA cleavage complex

SPOP, speckle-type POZ protein is a substrate adaptor protein of the Cullin-3/RING ubiquitin E3 complex. The spop gene is the most commonly point mutated in human primary prostate cancers, but the pathological contribution of the SPOP mutations remains unclear. In this study, we investigated several known factors that are critical in the DNA–­protein cross-link repair process. The depletion of SPOP or overexpression of a prostate cancer–associated SPOP mutant, F133V, in androgen receptor-positive prostate cancer cells increased the amount of topoisomerase 2A (TOP2A) in the nuclei together with the increased amount of γH2AX, an indication of DNA breaks. Tyrosyl–DNA phosphodiesterases (TDPs) and an endo/exonuclease MRE11 are enzymes that liberate TOP2A from the TOP2A–DNA cleavage complex, and thus is essential for the completion of the DNA repair process. We found that the amount of TDP1 and TDP2 was decreased in SPOP-depleted cells, and that of TDP2 and MRE11 was decreased in F133V-overexpressing cells. These results suggest that the F133V mutant exerts dominant-negative and gain-of-function effects in down-regulation of TDP2 and MRE11, respectively. We conclude that SPOP is involved in the DNA–protein cross-link repair process through the elimination of TOP2A from the TOP2A cleavage complex, which may contribute to the genome stability.

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.