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BRIT1/MCPH1 links chromatin remodelling to DNA damage response.

ABSTRACT: To detect and repair damaged DNA, DNA-damage-response proteins need to overcome the barrier of condensed chromatin to gain access to DNA lesions. ATP-dependent chromatin remodelling is one of the fundamental mechanisms used by cells to relax chromatin in DNA repair. However, the mechanism mediating their recruitment to DNA lesions remains largely unknown. BRIT1 (also known as MCPH1) is an early DNA-damage-response protein that is mutated in human primary microcephaly. Here we report a previously unknown function of BRIT1 as a regulator of the ATP-dependent chromatin remodelling complex SWI-SNF in DNA repair. After damage to DNA, BRIT1 increases its interaction with SWI-SNF through ATM/ATR-dependent phosphorylation on the BAF170 subunit. This increase in binding affinity provides a means by which SWI-SNF can be specifically recruited to and maintained at DNA lesions. Loss of BRIT1 causes impaired chromatin relaxation as a result of decreased association of SWI-SNF with chromatin. This explains the decreased recruitment of repair proteins to DNA lesions and the reduced efficiency of repair in BRIT1-deficient cells, resulting in impaired cell survival after DNA damage. Our findings therefore identify BRIT1 as a key molecule that links chromatin remodelling with response to DNA damage in the control of DNA repair, and its dysfunction contributes to human disease.

SUBMITTER: Peng G

PROVIDER: S-EPMC2714531 | biostudies-literature | 2009 Jul

REPOSITORIES: biostudies-literature

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BRIT1/MCPH1 links chromatin remodelling to DNA damage response.

Peng Guang G Yim Eun-Kyoung EK Dai Hui H Jackson Andrew P AP Burgt Ineke van der Iv Pan Mei-Ren MR Hu Ruozhen R Li Kaiyi K Lin Shiaw-Yih SY

Nature cell biology 20090614 7

To detect and repair damaged DNA, DNA-damage-response proteins need to overcome the barrier of condensed chromatin to gain access to DNA lesions. ATP-dependent chromatin remodelling is one of the fundamental mechanisms used by cells to relax chromatin in DNA repair. However, the mechanism mediating their recruitment to DNA lesions remains largely unknown. BRIT1 (also known as MCPH1) is an early DNA-damage-response protein that is mutated in human primary microcephaly. Here we report a previously ...[more]

PMID: 19525936

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Project description:Rationale: SUMOylation regulates a plethora of biological processes, and its inhibitors are currently under investigation in clinical trials as anticancer agents. Thus, identifying new targets with site-specific SUMOylation and defining their biological functions will not only provide new mechanistic insights into the SUMOylation signaling but also open an avenue for developing new strategy for cancer therapy. MORC family CW-type zinc finger 2 (MORC2) is a newly identified chromatin-remodeling enzyme with an emerging role in the DNA damage response (DDR), but its regulatory mechanism remains enigmatic. Methods: In vivo and in vitro SUMOylation assays were used to determine the SUMOylation levels of MORC2. Overexpression and knockdown of SUMO-associated enzymes were used to detect their effects on MORC2 SUMOylation. The effect of dynamic MORC2 SUMOylation on the sensitivity of breast cancer cells to chemotherapeutic drugs was examined through in vitro and in vivo functional assays. Immunoprecipitation, GST pull-down, MNase, and chromatin segregation assays were used to explore the underlying mechanisms. Results: Here, we report that MORC2 is modified by small ubiquitin-like modifier 1 (SUMO1) and SUMO2/3 at lysine 767 (K767) in a SUMO-interacting motif dependent manner. MORC2 SUMOylation is induced by SUMO E3 ligase tripartite motif containing 28 (TRIM28) and reversed by deSUMOylase sentrin-specific protease 1 (SENP1). Intriguingly, SUMOylation of MORC2 is decreased at the early stage of DNA damage induced by chemotherapeutic drugs that attenuate the interaction of MORC2 with TRIM28. MORC2 deSUMOylation induces transient chromatin relaxation to enable efficient DNA repair. At the relatively late stage of DNA damage, MORC2 SUMOylation is restored, and SUMOylated MORC2 interacts with protein kinase CSK21 (casein kinase II subunit alpha), which in turn phosphorylates DNA-PKcs (DNA-dependent protein kinase catalytic subunit), thus promoting DNA repair. Notably, expression of a SUMOylation-deficient mutant MORC2 or administration of SUMO inhibitor enhances the sensitivity of breast cancer cells to DNA-damaging chemotherapeutic drugs. Conclusions: Collectively, these findings uncover a novel regulatory mechanism of MORC2 by SUMOylation and reveal the intricate dynamics of MORC2 SUMOylation important for proper DDR. We also propose a promising strategy to sensitize MORC2-driven breast tumors to chemotherapeutic drugs by inhibition of the SUMO pathway.

Project description:MCPH1, also known as BRIT1, has recently been identified as a novel key regulatory gene of the DNA damage response pathway. MCPH1 is located on human chromosome 8p23.1, where human cancers frequently show loss of heterozygosity. As such, MCPH1 is aberrantly expressed in many malignancies, including breast and ovarian cancers, and the function of MCPH1 has been implicated in tumor suppression. However, it remains poorly understood whether MCPH1 deficiency leads to tumorigenesis. Here we generated and studied both Mcph1(-/-) and Mcph1(-/-)p53(-/-) mice; we showed that Mcph1(-/-) mice developed tumors with long latency, and that primary lymphoma developed significantly earlier in Mcph1(-/-)p53(-/-) mice than in Mcph11(+/+)p53(-/-) and Mcph1(+/-)p53(-/-) mice. The Mcph1(-/-)p53(-/-) lymphomas and derived murine embryonic fibroblasts (MEFs) were both more sensitive to irradiation. Mcph1 deficiency resulted in remarkably increased chromosome and chromatid breaks in Mcph1(-/-)p53(-/-) lymphomas and MEFs, as determined by metaphase spread assay and spectral karyotyping analysis. In addition, Mcph1 deficiency significantly enhanced aneuploidy as well as abnormal centrosome multiplication in Mcph1(-/-)p53(-/-) cells. Meanwhile, Mcph1 deficiency impaired double strand break (DSB) repair in Mcph1(-/-)p53(-/-) MEFs as demonstrated by neutral Comet assay. Compared with Mcph1(+/+)p53(-/-) MEFs, homologous recombination and non-homologous end-joining activities were significantly decreased in Mcph1(-/-)p53(-/-) MEFs. Notably, reconstituted MCPH1 rescued the defects of DSB repair and alleviated chromosomal aberrations in Mcph1(-/-)p53(-/-) MEFs. Taken together, our data demonstrate MCPH1 deficiency promotes genomic instability and increases cancer susceptibility. Our study using knockout mouse models provides convincing genetic evidence that MCPH1 is a bona fide tumor suppressor gene. Its deficiency leading to defective DNA repair in tumors can be used to develop novel targeted cancer therapies in the future.

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BRIT1/MCPH1 links chromatin remodelling to DNA damage response.

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BRIT1/MCPH1 links chromatin remodelling to DNA damage response.

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