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Many cancers harbor homologous recombination defects (HRDs). A HRD is a therapeutic target that is being successfully utilized in treatment of breast/ovarian cancer via synthetic lethality. However, canonical HRD caused by BRCAness mutations do not prevail in liver cancer. Here we report a subtype of HRD caused by the perturbation of a proteasome variant (CDW19S) in hepatitis B virus-bearing (HBV-bearing) cells. This amalgamate protein complex contained the 19S proteasome decorated with [CRL4.sup.WDR70] ubiquitin ligase, and assembled at broken chromatin in a [PSMD4.sup.Rpn10]-and ATM-MDC1-RNF8-dependent manner. CDW19S promoted DNA end processing via segregated modules that promote nuclease activities of MRE11 and EXO1. Contrarily, a proteasomal component, [ADRM1.sup.Rpn13], inhibited resection and was removed by [CRL4WDR.sup.70]-catalyzed ubiquitination upon commitment of extensive resection. HBx interfered with [ADRM1.sup.Rpn13] degradation, leading to the imposition of [ADRM1.sup.Rpn13]- dependent resection barrier and consequent viral HRD subtype distinguishable from that caused by BRCA1 defect. Finally, we demonstrated that viral HRD in HBV-associated hepatocellular carcinoma can be exploited to restrict tumor progression. Our work clarifies the underlying mechanism of a virus-induced HRD subtype., Introduction Long-term liver infection with hepatitis B virus (HBV) predisposes carriers to hepatocellular carcinoma (1). Therapy for late-stage HBV-associated hepatocellular carcinoma remains a major challenge, with poor therapy responses and [...]

Impairment of genome instability drives the development of cancer by disrupting anti-cancer barriers. Upon genotoxic insults, DNA damage responsive factors, notably ATM kinase, is crucial to protect genomic integrity while promoting cell death. Meanwhile, cytotoxic therapy-inducing DNA lesions is double-edged sword by causing cancer metastasis based on animal models and clinical observations. The underlying mechanisms for the procancer effect of cytotoxic therapies are poorly understood. Here, we report that cancer cells subjected to cytotoxic treatments elicit dramatic alteration of gene expression controlling the potential of epithelium-mesenchyme transition (EMT). Resultantly, EMT-dependent cell mobility is potently induced upon DNA damage. This stimulation of EMT is mainly Ataxia-Telangiectasia-mutated (ATM)-dependent, as the chemical inhibitor specifically inhibiting ATM kinase activity can suppress the EMT gene expression and thus cell mobility. At last, we show that cancer cells with ATM activation display increased metastatic potential in ovarian cancer tissues. Taken together, we reveal a novel role of ATM in promoting metastatic potential of cancer cells by favoring EMT gene expression. [ABSTRACT FROM AUTHOR]

Eukaryotic genomes are packaged into highly condensed chromatin and this repressive chromatin barrier can be overcome by altering the chromatin structure via histone modification enzymes. Here, we report Wdr70 in Schizosaccharomyces pombe (sp Wdr70) plays important roles in multiple cellular processes including cell cycle progression, chromatin structure and DNA repair. Depletion of Wdr70 gene causes cell cycle delay, hypersensitivity to DNA damage reagents and quick phenotypic changes. Moreover, we observed strong genetic interaction between Wdr70 and genes regulating checkpoint and homologous recombination (HR), pinpointing the function of Wdr70 to DNA end resection. Finally, we show that the function of Wdr70 could be attributed to monoubiquitination of histone H2B (uH2B) in the vicinity of DNA double strand breaks (DSBs). Taken together, our data reveal that Wdr70 and H2B monoubiquitination-dependent chromatin modulation is required for chromatin homeostasis and genetic stability. • Wdr70 plays roles in cell cycle progression, chromatin structure and DNA repair. • Wdr70 ablation results in quick phenotypic changes. • Wdr70 regulates DNA end resection in parallel with MRN complex. • Increased dNTP supply mitigates HR defect of Wdr70 -depleted cells without improving DSB-associated H2B monoubiquitination. [ABSTRACT FROM AUTHOR]

Malignancies including ovarian cancer (OvCa) are genetically unstable. Genomic integrity is maintained by tumor suppressor p53 and DNA damage response network, which crosstalk to each other via not well characterized mechanisms. In this work, we characterize features of damage-related signals in cultured epithelial OvCa cells and tumor biopsies. We found that endogenous burden of DNA damage in OvCa tissues were ubiquitously accumulated in high-grade malignancies than lower grade of cancer that cannot be obviously explained by disturbed function of in DNA damage response (DDR). In contrast, CHK1 phosphorylation (CHK1-pS345) marking the checkpoint activation in nucleolar compartments are prevalent in high-grade OvCa, coincident to the elevated DNA damage in nucleoplasm. Generation of CHK1-pS345 requires the presence of p53 protein in addition to the well-known activities of ATM/ATR kinases. Apparently, mutant forms of p53 possess higher activity in triggering CHK1 phosphorylation than wild type, implying a potential role of p53 in maintaining rDNA integrity. Loss of p53 function would cause replication stress in nucleoli. Altogether, our study reveals endogenous nucleoli stress in OvCa that is coupled to perturbed function of p53 in DNA repair. [ABSTRACT FROM AUTHOR]

Hepatitis B virus (HBV) infection is a major public health problem by affecting 350 million people worldwide. The mechanisms that regulate HBV gene expression and viral replication remain poorly understood. HBx is known as the central regulator for HBV replication and is associated with the CUL4–DDB1 ubiquitin ligase through H-box motif. Here, we show that blocking the activity of DDB1 by RNA interfering inhibited viral production and gene expression of HBV, and direct association of HBx with DDB1 promoted viral activities, indicating that DDB1 function is required for viral production. On the other hand, HBx interfered with DDB1-dependent polyubiquitination of PRMT1, arginine methyltransferase 1, suggesting that HBx can also block the function of a subset of CUL4–DDB1 E3 ligases. Thus, we conclude that HBx regulates the function of DDB1 in both positive and negative manners in the context of distinct CUL4–DDB1 complexes and plays different roles in HBV replication cycle. [ABSTRACT FROM AUTHOR]

Double-strand breaks repaired by homologous recombination (HR) are first resected to form single-stranded DNA, which binds replication protein A (RPA). RPA attracts mediators that load the Rad51 filament to promote strand invasion, the defining feature of HR. How the resection machinery navigates nucleosome-packaged DNA is poorly understood. Here we report that in Schizosaccharomyces pombe a conserved DDB1-CUL4-associated factor (DCAF), Wdr70, is recruited to DSBs as part of the Cullin4-DDB1 ubiquitin ligase (CRL4(Wdr70)) and stimulates distal H2B lysine 119 mono-ubiquitination (uH2B). Wdr70 deletion, or uH2B loss, results in increased loading of the checkpoint adaptor and resection inhibitor Crb2(53BP1), decreased Exo1 association and delayed resection. Wdr70 is dispensable for resection upon Crb2(53BP1) loss, or when the Set9 methyltransferase that creates docking sites for Crb2 is deleted. Finally, we establish that this histone regulatory cascade similarly controls DSB resection in human cells.