Project description:The human RecQ helicase BLM is involved in the DNA damage response, DNA metabolism, and genetic stability. Loss of function mutations in BLM cause the genetic instability/cancer predisposition syndrome Bloom syndrome. However, the molecular mechanism underlying the regulation of BLM in cancers remains largely elusive. Here, we demonstrate that the deubiquitinating enzyme USP37 interacts with BLM and that USP37 deubiquitinates and stabilizes BLM, thereby sustaining the DNA damage response (DDR). Mechanistically, DNA double-strand breaks (DSB) promotes ATM phosphorylation of USP37 and enhances the binding between USP37 and BLM. Moreover, knockdown of USP37 increases BLM polyubiquitination, accelerates its proteolysis, and impairs its function in DNA damage response. This leads to enhanced DNA damage and sensitizes breast cancer cells to DNA-damaging agents in both cell culture and in vivo mouse models. Collectively, our results establish a novel molecular mechanism for the USP37-BLM axis in regulating DSB repair with an important role in chemotherapy and radiotherapy response in human cancers.
Project description:The chromatin-remodeling enzyme SMARCA5 plays a key role in DNA-templated events including transcription, DNA replication, and DNA repair. Loss of function of the SMARCA5 can cause neurodevelopmental disorder and Williams syndrome. However, the molecular mechanism underlying the regulation of SMARCA5 in prostate cancer remains largely elusive. Here, we report that the deubiquitinating enzyme USP3 directly interacts with SMARCA5 and removes K63-linked polyubiquitination of SMARCA5 to maintain its stability, which promotes DNA damage repair and chemotherapy resistance. Depletion of USP3 or SMARCA5 promoted PCa cells sensitive to docetaxel and overexpression of USP3 restored the cells resistance to docetaxel treatment in SMARCA5 silenced cells in vitro and vivo. Clinically, USP3 was significantly up-regulated in prostate cancer tissues and positively associated with SMARCA5 expression. Collectively, our findings uncover a novel molecular mechanism for the USP3-SMARCA5 axis in regulating DSB repair with an important role in chemotherapy response in human prostate cancers, highlighting that targeting USP3-SMARCA5 axis could be a valuable strategy to treat USP3/SMARCA5-overexpressing chemotherapy-resistant patients and improve drug treatment.
Project description:Abraxas brother 1 (ABRO1) has been reported to be a component of the BRISC complex, a multiprotein complex that specifically cleaves 'Lys-63'-linked ubiquitin. However, current knowledge of the functions of ABRO1 is limited. Here we report that ABRO1 is frequently downregulated in human liver, kidney, breast and thyroid gland tumour tissues. Depletion of ABRO1 in cancer cells reduces p53 levels and enhances clone formation and cellular transformation. Conversely, overexpression of ABRO1 suppresses cell proliferation and tumour formation in a p53-dependent manner. We further show that ABRO1 stabilizes p53 by facilitating the interaction of p53 with USP7. DNA-damage induced accumulation of endogenous ABRO1 as well as translocation of ABRO1 to the nucleus, and the induction of p53 by DNA damage is almost completely attenuated by ABRO1 depletion. Our study shows that ABRO1 is a novel p53 regulator that plays an important role in tumour suppression and the DNA damage response.
Project description:Mediator of IRF3 activation (MITA, also known as stimulator of interferon genes, STING) senses the second messenger cyclic GMP-AMP (cGAMP) which is synthesized upon DNA virus infection and activates innate antiviral immune response. It has been demonstrated that the activity of MITA is delicately regulated by various post-translational modifications including polyubiquitination. In this study, we identified the deubiquitinating enzyme USP44 as a positive regulator of MITA. USP44 is recruited to MITA following DNA virus infection and removes K48-linked polyubiquitin moieties from MITA at K236, therefore prevents MITA from proteasome mediated degradation. USP44-deficiency results in acceleration of HSV-1-induced degradation of MITA and reduced induction of type I interferons (IFNs) and proinflammatory cytokines. Consistently, Usp44-/- mice are more susceptible to HSV-1 infection as indicated by higher tissue viral titers, greater tissue damage and lower survival rate. These findings suggest that USP44 plays a specific and critical role in the regulation of innate immune response against DNA viruses.
Project description:Upon exposure to ionizing irradiation, the MRE11-RAD50-NBS1 complex potentiates the recruitment of ATM (ataxia-telangiectasia mutated) kinase to the double-strand breaks. We show that the lack of BLM causes a decrease in the autophosphorylation of ATM in mice mammary glands, which have lost one or both copies of BLM. In isogenic human cells, the DNA damage response (DDR) pathway was dampened in the absence of BLM, which negatively affected the recruitment of DDR factors onto the chromatin, thereby indicating a direct role of BLM in augmenting DDR. Mechanistically, this was due to the BLM-dependent dissociation of inactive ATM dimers into active monomers. Fragmentation analysis of BLM followed by kinase assays revealed a 20-mer BLM peptide (91-110 aa), sufficient to enhance ATM-dependent p53 phosphorylation. ATM-mediated phosphorylation of BLM at Thr99 within BLM (91-110) peptide enhanced ATM kinase activity due to its interaction with NBS1 and causing ATM monomerization. Delivery of phosphomimetic T99E counterpart of BLM (91-110 aa) peptide led to ATM activation followed by restoration of the DDR even in the absence of ionizing irradiation (both in cells and in BLM knockout mice), indicating its role as a DDR agonist, which can be potentially used to prevent the initiation of neoplastic transformation.
Project description:Microrchidia family CW-type zinc finger 2 (MORC2) is a newly identified chromatin remodeling enzyme with an emerging role in DNA damage response (DDR), but the underlying mechanism remains largely unknown. Here, we show that poly(ADP-ribose) polymerase 1 (PARP1), a key chromatin-associated enzyme responsible for the synthesis of poly(ADP-ribose) (PAR) polymers in mammalian cells, interacts with and PARylates MORC2 at two residues within its conserved CW-type zinc finger domain. Following DNA damage, PARP1 recruits MORC2 to DNA damage sites and catalyzes MORC2 PARylation, which stimulates its ATPase and chromatin remodeling activities. Mutation of PARylation residues in MORC2 results in reduced cell survival after DNA damage. MORC2, in turn, stabilizes PARP1 through enhancing acetyltransferase NAT10-mediated acetylation of PARP1 at lysine 949, which blocks its ubiquitination at the same residue and subsequent degradation by E3 ubiquitin ligase CHFR. Consequently, depletion of MORC2 or expression of an acetylation-defective PARP1 mutant impairs DNA damage-induced PAR production and PAR-dependent recruitment of DNA repair proteins to DNA lesions, leading to enhanced sensitivity to genotoxic stress. Collectively, these findings uncover a previously unrecognized mechanistic link between MORC2 and PARP1 in the regulation of cellular response to DNA damage.
Project description:Hepatocellular carcinoma (HCC) has emerged as one of the most prevalent life-threatening cancers, and the high mortality rate is largely due to the metastasis. The sustained activation of Smad4 and transforming growth factor-β (TGF-β) is closely associated with advanced HCC metastasis. However, the regulatory mechanism underlying the aberrant activation of Smad4 and TGF-β pathway remains elusive. In this study, using a functional screen of USPs siRNA library, we identified ubiquitin-specific proteases USP10 as a deubiquitinating enzyme (DUB) that sustains the protein level of Smad4 and activates TGF-β signaling. Further analysis showed that USP10 directly interacts with Smad4 and stabilizes it through the cleavage of its proteolytic ubiquitination, thus promoting HCC metastasis. The suppression of USP10 by either shRNAs or catalytic inhibitor Spautin-1 significantly inhibited the migration of HCC cells, whereas the reconstitution of Smad4 was able to efficiently rescue this defect. Overall, our study not only uncovers the regulatory effect of USP10 on the protein abundance of Smad4, but also indicates that USP10 could be regarded as a potential intervention target for the metastatic HCC in Smad4-positive patients.
Project description:The deubiquitinating enzyme USP37 is known to contribute to timely onset of S phase and progression of mitosis. However, it is not clear if USP37 is required beyond S-phase entry despite expression and activity of USP37 peaking within S phase. We have utilized flow cytometry and microscopy to analyze populations of replicating cells labeled with thymidine analogs and monitored mitotic entry in synchronized cells to determine that USP37-depleted cells exhibited altered S-phase kinetics. Further analysis revealed that cells depleted of USP37 harbored increased levels of the replication stress and DNA damage markers γH2AX and 53BP1 in response to perturbed replication. Depletion of USP37 also reduced cellular proliferation and led to increased sensitivity to agents that induce replication stress. Underlying the increased sensitivity, we found that the checkpoint kinase 1 is destabilized in the absence of USP37, attenuating its function. We further demonstrated that USP37 deubiquitinates checkpoint kinase 1, promoting its stability. Together, our results establish that USP37 is required beyond S-phase entry to promote the efficiency and fidelity of replication. These data further define the role of USP37 in the regulation of cell proliferation and contribute to an evolving understanding of USP37 as a multifaceted regulator of genome stability.
Project description:The amplitude of transforming growth factor-β (TGF-β) signal is tightly regulated to ensure appropriate physiological responses. As part of negative feedback loop SMAD7, a direct transcriptional target of downstream TGF-β signaling acts as a scaffold to recruit the E3 ligase SMURF2 to target the TGF-β receptor complex for ubiquitin-mediated degradation. Here, we identify the deubiquitinating enzyme USP26 as a novel integral component of this negative feedback loop. We demonstrate that TGF-β rapidly enhances the expression of USP26 and reinforces SMAD7 stability by limiting the ubiquitin-mediated turnover of SMAD7. Conversely, knockdown of USP26 rapidly degrades SMAD7 resulting in TGF-β receptor stabilization and enhanced levels of p-SMAD2. Clinically, loss of USP26 correlates with high TGF-β activity and confers poor prognosis in glioblastoma. Our data identify USP26 as a novel negative regulator of the TGF-β pathway and suggest that loss of USP26 expression may be an important factor in glioblastoma pathogenesis.