BRCA1 promotes homologous recombination repair and antagonizes 53BP1-dependent nonhomologous end joining (NHEJ) pathway. However, the molecular basis of the competition between BRCA1 and 53BP1 ...pathways remains elusive. Here we report that RIF1 protein translocates to damage sites via ATM-dependent 53BP1 phosphorylation. Strikingly, loss of RIF1 rescues initial DNA end resection and checkpoint activation in BRCA1-depleted cells. Interestingly RIF1 accumulation at damage sites is antagonized by BRCA1 in S and G2 phases. Conversely, the translocation of BRCA1 to damage sites is inhibited by RIF1 in G1 phase. However, loss of RIF1 differs from that of 53BP1 deficiency, as it cannot fully rescue RAD51 foci formation, homologous recombination defect, and radio-hypersensitivity in BRCA1-deficient cells. This is likely because RIF1, but not 53BP1, also regulates the foci formation and chromatin loading of BLM (the Bloom syndrome helicase). Thus, RIF1 not only acts downstream of 53BP1 and counteracts BRCA1-mediated end resection but also has a secondary role in promoting BLM function in DNA repair.
Background: 53BP1 counteracts BRCA1 in DNA repair.
Results: RIF1 acts downstream of 53BP1 and counteracts BRCA1 in DNA end resection. It also has a 53BP1-independent role in regulating BLM chromatin association.
Conclusion: RIF1 is the major downstream effector of 53BP1.
Significance: These results reveal that RIF1 antagonizes BRCA1, functions in DNA end protection, and prevents homologous recombination repair.
Enhancer of Zeste 2 (EZH2) is the enzymatic subunit of Polycomb Repressive Complex 2 (PRC2), which catalyzes histone H3 lysine 27 trimethylation (H3K27me3) at target promoters for gene silencing. ...Here, we report that EZH2 activates androgen receptor (AR) gene transcription through direct occupancy at its promoter. Importantly, this activating role of EZH2 is independent of PRC2 and its methyltransferase activities. Genome-wide assays revealed extensive EZH2 occupancy at promoters marked by either H3K27ac or H3K27me3, leading to gene activation or repression, respectively. Last, we demonstrate enhanced efficacy of enzymatic EZH2 inhibitors when used in combination with AR antagonists in blocking the dual roles of EZH2 and suppressing prostate cancer progression in vitro and in vivo. Taken together, our study reports EZH2 as a transcriptional activator, a key target of which is AR, and suggests a drug-combinatory approach to treat advanced prostate cancer.
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•EZH2 directly activates androgen receptor (AR) gene transcription•EZH2 induces AR through Polycomb- and methylation-independent mechanisms•Local chromatin environment dictates the roles of EZH2 as an activator or repressor•Prostate cancer depends on both catalytic and non-catalytic activities of EZH2
Kim et al. report EZH2 as a transcriptional activator that directly induces AR gene expression in a Polycomb- and methylation-independent manner, providing a mechanism to escape enzymatic EZH2 inhibitors. Combination of inhibitors with AR-targeted therapies showed a strong synergy in blocking the EZH2 downstream pathways and suppressing prostate cancer progression.
The Polycomb group (PcG) protein Enhancer of Zeste Homolog 2 (EZH2) is one of the three core subunits of the Polycomb Repressive Complex 2 (PRC2). It harbors histone methyltransferase activity ...(MTase) that specifically catalyze histone 3 lysine 27 (H3K27) methylation on target gene promoters. As such, PRC2 are epigenetic silencers that play important roles in cellular identity and embryonic stem cell maintenance. In the past two decades, mounting evidence supports EZH2 mutations and/or over-expression in a wide array of hematological cancers and solid tumors, including prostate cancer. Further, EZH2 is among the most upregulated genes in neuroendocrine prostate cancers, which become abundant due to the clinical use of high-affinity androgen receptor pathway inhibitors. While numerous studies have reported epigenetic functions of EZH2 that inhibit tumor suppressor genes and promote tumorigenesis, discordance between EZH2 and H3K27 methylation has been reported. Further, enzymatic EZH2 inhibitors have shown limited efficacy in prostate cancer, warranting a more comprehensive understanding of EZH2 functions. Here we first review how canonical functions of EZH2 as a histone MTase are regulated and describe the various mechanisms of PRC2 recruitment to the chromatin. We further outline non-histone substrates of EZH2 and discuss post-translational modifications to EZH2 itself that may affect substrate preference. Lastly, we summarize non-canonical functions of EZH2, beyond its MTase activity and/or PRC2, as a transcriptional cofactor and discuss prospects of its therapeutic targeting in prostate cancer.
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.
Understanding the mechanisms of androgen receptor (AR) activation in the milieu of low androgen is critical to effective treatment of castration-resistant prostate cancer (CRPC). Here, we report ...HOTAIR as an androgen-repressed lncRNA, and, as such, it is markedly upregulated following androgen deprivation therapies and in CRPC. We further demonstrate a distinct mode of lncRNA-mediated gene regulation, wherein HOTAIR binds to the AR protein to block its interaction with the E3 ubiquitin ligase MDM2, thereby preventing AR ubiquitination and protein degradation. Consequently, HOTAIR expression is sufficient to induce androgen-independent AR activation and drive the AR-mediated transcriptional program in the absence of androgen. Functionally, HOTAIR overexpression increases, whereas HOTAIR knockdown decreases, prostate cancer cell growth and invasion. Taken together, our results provide compelling evidence of lncRNAs as drivers of androgen-independent AR activity and CRPC progression, and they support the potential of lncRNAs as therapeutic targets.
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•The lncRNA HOTAIR is repressed by androgen and, thus, upregulated in CRPC•HOTAIR inhibits AR degradation by blocking its binding to E3 ubiquitin ligase MDM2•HOTAIR increases AR chromatin targeting and enhances the AR-mediated gene program•HOTAIR drives androgen-independent AR activation and promotes CRPC
Castration-resistant prostate cancer (CRPC) is a lethal disease. Zhang et al. show that HOTAIR is an AR-repressed lncRNA that is upregulated in CRPC. HOTAIR binds to AR and reduces AR degradation by blocking its interaction with E3 ubiquitin ligase MDM2, thereby enhancing AR transcriptional activity and potentiating CRPC cell growth.
A biotinylated glutathione (GSH)-responsive zinc(II) phthalocyanine has been prepared and characterized. With a 2,4-dinitrobenzenesulfonyl moiety, its fluorescence emission and singlet oxygen ...generation were silenced in its intact state. Upon exposure to high concentration of GSH, its photosensitizing properties were restored in phosphate buffered saline and inside tumor cells. It also showed preferential uptake on HepG2 human hepatocarcinoma cells (with higher biotin receptor expression) rather than Chinese hamster ovary (CHO) cells (with lower biotin receptor expression). Upon irradiation, it caused photocytotoxicity with an IC
value down to 0.1 μm on HepG2 cells. Moreover, it can localize in the endoplasmic reticulum (ER), causing ER stress after light irradiation.
Castration-resistant prostate cancer (CRPC) that has developed resistance to the new-generation androgen receptor (AR) antagonist enzalutamide is a lethal disease. Transcriptome analysis of multiple ...prostate cancer models identified CXCR7, an atypical chemokine receptor, as one of the most upregulated genes in enzalutamide-resistant cells. AR directly repressed
by binding to an enhancer 110 kb downstream of the gene and expression was restored upon androgen deprivation. We demonstrate that CXCR7 is a critical regulator of prostate cancer sensitivity to enzalutamide and is required for CRPC growth
and
. Elevated CXCR7 activated MAPK/ERK signaling through ligand-independent, but β-arrestin 2-dependent mechanisms. Examination of patient specimens showed that CXCR7 and pERK levels increased significantly from localized prostate cancer to CRPC and further upon enzalutamide resistance. Preclinical studies revealed remarkable efficacies of MAPK/ERK inhibitors in suppressing enzalutamide-resistant prostate cancer. Overall, these results indicate that CXCR7 may serve as a biomarker of resistant disease in patients with prostate cancer and that disruption of CXCR7 signaling may be an effective strategy to overcome resistance. SIGNIFICANCE: These findings identify CXCR7-mediated MAPK activation as a mechanism of resistance to second-generation antiandrogen therapy, highlighting the therapeutic potential of MAPK/ERK inhibitors in CRPC.
PALI1 is a newly identified accessory protein of the Polycomb repressive complex 2 (PRC2) that catalyzes H3K27 methylation. However, the roles of PALI1 in cancer are yet to be defined. Here, we ...report that PALI1 is upregulated in advanced prostate cancer (PCa) and competes with JARID2 for binding to the PRC2 core subunit SUZ12. PALI1 further interacts with the H3K9 methyltransferase G9A, bridging the formation of a unique G9A-PALI1-PRC2 super-complex that occupies a subset of G9A-target genes to mediate dual H3K9/K27 methylation and gene repression. Many of these genes are developmental regulators required for cell differentiation, and their loss in PCa predicts poor prognosis. Accordingly, PALI1 and G9A drive PCa cell proliferation and invasion in vitro and xenograft tumor growth in vivo. Collectively, our study shows that PALI1 harnesses two central epigenetic mechanisms to suppress cellular differentiation and promote tumorigenesis, which can be targeted by dual EZH2 and G9A inhibition.
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•PALI1 is upregulated in prostate cancer and competes with JARID2 for SUZ12 binding•PALI1 bridges PRC2 and G9A interaction to catalyze dual H3K9/K27 methylation•PALI1 represses cell differentiation regulators and promotes tumor growth•Combinatorial PRC2 and G9A inhibition shows synergistic anti-tumor effects
Very little is known about the role of PRC2-accessory protein PALI1 in cancer. Fong et al. reveal that PALI1 competes with JARID2 for PRC2 binding. Furthermore, it bridges a unique interaction between PRC2 and G9A to catalyze dual H3K9/K27 methylation, suppress developmental regulators, and drive cancer progression.
DNA damage-induced proliferating cell nuclear antigen (PCNA) ubiquitination serves as the key event mediating post-replication repair. Post-replication repair involves either translesion synthesis ...(TLS) or damage avoidance via template switching. In this study, we have identified and characterized C1orf124 as a regulator of TLS. C1orf124 co-localizes and interacts with unmodified and mono-ubiquitinated PCNA at UV light-induced damage sites, which require the PIP box and UBZ domain of C1orf124. C1orf124 also binds to the AAA-ATPase valosin-containing protein via its SHP domain, and cellular resistance to UV radiation mediated by C1orf124 requires its interactions with valosin-containing protein and PCNA. Interestingly, C1orf124 binds to replicative DNA polymerase POLD3 and PDIP1 under normal conditions but preferentially associates with TLS polymerase η (POLH) upon UV damage. Depletion of C1orf124 compromises PCNA monoubiquitination, RAD18 chromatin association, and RAD18 localization to UV damage sites. Thus, C1orf124 acts at multiple steps in TLS, stabilizes RAD18 and ubiquitinated PCNA at damage sites, and facilitates the switch from replicative to TLS polymerase to bypass DNA lesion.
Background: Translesion synthesis involves proliferating cell nuclear antigen (PCNA) monoubiquitination and polymerase switching.
Results: C1orf124 is required for cell survival following UV damage. It binds to monoubiquitinated PCNA and participates in polymerase switching.
Conclusion: C1orf124 serves as a central platform that facilitates translesion synthesis.
Significance: This study provides a mechanism for translesion synthesis.
The nucleus is a unique organelle that contains essential genetic materials in chromosome territories. The interchromatin space is composed of nuclear subcompartments, which are defined by several ...distinctive nuclear bodies believed to be factories of DNA or RNA processing and sites of transcriptional and/or posttranscriptional regulation. In this paper, we performed a genome-wide microscopy-based screening for proteins that form nuclear foci and characterized their localizations using markers of known nuclear bodies. In total, we identified 325 proteins localized to distinct nuclear bodies, including nucleoli (148), promyelocytic leukemia nuclear bodies (38), nuclear speckles (27), paraspeckles (24), Cajal bodies (17), Sam68 nuclear bodies (5), Polycomb bodies (2), and uncharacterized nuclear bodies (64). Functional validation revealed several proteins potentially involved in the assembly of Cajal bodies and paraspeckles. Together, these data establish the first atlas of human proteins in different nuclear bodies and provide key information for research on nuclear bodies.
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