The Experts below are selected from a list of 1671 Experts worldwide ranked by ideXlab platform
Lixiao Che - One of the best experts on this subject based on the ideXlab platform.
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RESEARCH ARTICLE The UBC Domain Is Required for BRUCE to Promote BRIT1/MCPH1 Function in DSB Signaling and Repair Post Formation of BRUCE-USP8-BRIT1 Complex
2016Co-Authors: Lixiao CheAbstract:BRUCE is implicated in the regulation of DNA double-strand break response to preserve genome stability. It acts as a scaffold to tether USP8 and BRIT1, together they form a nuclear BRUCE-USP8-BRIT1 complex, where BRUCE holds K63-ubiquitinated BRIT1 from access to DSB in unstressed cells. Following DSB induction, BRUCE promotes USP8 mediated deubiquitination of BRIT1, a prerequisite for BRIT1 to be released from the com-plex and recruited to DSB by binding to γ-H2AX. BRUCE contains UBC and BIR domains, but neither is required for the scaffolding function of BRUCE mentioned above. Therefore, it remains to be determined whether they are required for BRUCE in DSB response. Here we show that the UBC domain, not the BIR domain, is required for BRUCE to promote DNA repair at a step post the formation of BRUCE-USP8-BRIT1 complex. Mutation or deletion of the BRUCE UBC domain did not disrupt the BRUCE-USP8-BRIT1 complex, but impaired deubiquitination and consequent recruitment of BRIT1 to DSB. This leads to impaired chro-matin relaxation, decreased accumulation of MDC1, NBS1, pATM and RAD51 at DSB, and compromised homologous recombination repair of DNA DSB. These results demonstrate that in addition to the scaffolding function in complex formation, BRUCE has an E3 ligase function to promote BRIT1 deubiquitination by USP8 leading to accumulation of BRIT1 at DNA double-strand break. These data support a crucial role for BRUCE UBC activity in the early stage of DSB response
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The UBC Domain Is Required for BRUCE to Promote BRIT1/MCPH1 Function in DSB Signaling and Repair Post Formation of BRUCE-USP8-BRIT1 Complex
PLOS ONE, 2015Co-Authors: Lixiao CheAbstract:BRUCE is implicated in the regulation of DNA double-strand break response to preserve genome stability. It acts as a scaffold to tether USP8 and BRIT1, together they form a nuclear BRUCE-USP8-BRIT1 complex, where BRUCE holds K63-ubiquitinated BRIT1 from access to DSB in unstressed cells. Following DSB induction, BRUCE promotes USP8 mediated deubiquitination of BRIT1, a prerequisite for BRIT1 to be released from the complex and recruited to DSB by binding to γ-H2AX. BRUCE contains UBC and BIR domains, but neither is required for the scaffolding function of BRUCE mentioned above. Therefore, it remains to be determined whether they are required for BRUCE in DSB response. Here we show that the UBC domain, not the BIR domain, is required for BRUCE to promote DNA repair at a step post the formation of BRUCE-USP8-BRIT1 complex. Mutation or deletion of the BRUCE UBC domain did not disrupt the BRUCE-USP8-BRIT1 complex, but impaired deubiquitination and consequent recruitment of BRIT1 to DSB. This leads to impaired chromatin relaxation, decreased accumulation of MDC1, NBS1, pATM and RAD51 at DSB, and compromised homologous recombination repair of DNA DSB. These results demonstrate that in addition to the scaffolding function in complex formation, BRUCE has an E3 ligase function to promote BRIT1 deubiquitination by USP8 leading to accumulation of BRIT1 at DNA double-strand break. These data support a crucial role for BRUCE UBC activity in the early stage of DSB response.
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the ubc domain is required for bruce to promote brit1 mcph1 function in dsb signaling and repair post formation of bruce usp8 brit1 complex
PLOS ONE, 2015Co-Authors: Lixiao CheAbstract:BRUCE is implicated in the regulation of DNA double-strand break response to preserve genome stability. It acts as a scaffold to tether USP8 and BRIT1, together they form a nuclear BRUCE-USP8-BRIT1 complex, where BRUCE holds K63-ubiquitinated BRIT1 from access to DSB in unstressed cells. Following DSB induction, BRUCE promotes USP8 mediated deubiquitination of BRIT1, a prerequisite for BRIT1 to be released from the complex and recruited to DSB by binding to γ-H2AX. BRUCE contains UBC and BIR domains, but neither is required for the scaffolding function of BRUCE mentioned above. Therefore, it remains to be determined whether they are required for BRUCE in DSB response. Here we show that the UBC domain, not the BIR domain, is required for BRUCE to promote DNA repair at a step post the formation of BRUCE-USP8-BRIT1 complex. Mutation or deletion of the BRUCE UBC domain did not disrupt the BRUCE-USP8-BRIT1 complex, but impaired deubiquitination and consequent recruitment of BRIT1 to DSB. This leads to impaired chromatin relaxation, decreased accumulation of MDC1, NBS1, pATM and RAD51 at DSB, and compromised homologous recombination repair of DNA DSB. These results demonstrate that in addition to the scaffolding function in complex formation, BRUCE has an E3 ligase function to promote BRIT1 deubiquitination by USP8 leading to accumulation of BRIT1 at DNA double-strand break. These data support a crucial role for BRUCE UBC activity in the early stage of DSB response.
Yoko Aoki - One of the best experts on this subject based on the ideXlab platform.
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new noonan syndrome model mice with rit1 mutation exhibit cardiac hypertrophy and susceptibility to β adrenergic stimulation induced cardiac fibrosis
EBioMedicine, 2019Co-Authors: Shingo Takahara, Tetsuya Niihori, Shinichi Inoue, Sachiko Miyagawatomita, Katsuhisa Matsuura, Yasumi Nakashima, Yoichi Matsubara, Yoshikatsu Saiki, Yoko AokiAbstract:Abstract Background Noonan syndrome (NS) is a genetic disorder characterized by short stature, a distinctive facial appearance, and heart defects. We recently discovered a novel NS gene, RIT1, which is a member of the RAS subfamily of small GTPases. NS patients with RIT1 mutations have a high incidence of hypertrophic cardiomyopathy and edematous phenotype, but the specific role of RIT1 remains unclear. Methods To investigate how germline RIT1 mutations cause NS, we generated knock-in mice that carried a NS-associated Rit1 A57G mutation (Rit1A57G/+). We investigated the phenotypes of Rit1A57G/+ mice in fetal and adult stages as well as the effects of isoproterenol on cardiac function in Rit1A57G/+ mice. Findings Rit1A57G/+ embryos exhibited decreased viability, edema, subcutaneous hemorrhage and AKT activation. Surviving Rit1A57G/+ mice had a short stature, craniofacial abnormalities and splenomegaly. Cardiac hypertrophy and cardiac fibrosis with increased expression of S100A4, vimentin and periostin were observed in Rit1A57G/+ mice compared to Rit1+/+ mice. Upon isoproterenol stimulation, cardiac fibrosis was drastically increased in Rit1A57G/+ mice. Phosphorylated (at Thr308) AKT levels were also elevated in isoproterenol-treated Rit1A57G/+ hearts. Interpretation The A57G mutation in Rit1 causes cardiac hypertrophy, fibrosis and other NS-associated features. Biochemical analysis indicates that the AKT signaling pathway might be related to downstream signaling in the RIT1 A57G mutant at a developmental stage and under β-adrenergic stimulation in the heart. Fund The Grants-in-Aid were provided by the Practical Research Project for Rare/Intractable Diseases from the Japan Agency for Medical Research and Development, the Japan Society for the Promotion of Science KAKENHI Grant.
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New Noonan syndrome model mice with RIT1 mutation exhibit cardiac hypertrophy and susceptibility to β-adrenergic stimulation-induced cardiac fibrosisResearch in context
'Elsevier BV', 2019Co-Authors: Shingo Takahara, Tetsuya Niihori, Shinichi Inoue, Katsuhisa Matsuura, Yasumi Nakashima, Yoichi Matsubara, Yoshikatsu Saiki, Sachiko Miyagawa-tomita, Yoko AokiAbstract:Background: Noonan syndrome (NS) is a genetic disorder characterized by short stature, a distinctive facial appearance, and heart defects. We recently discovered a novel NS gene, RIT1, which is a member of the RAS subfamily of small GTPases. NS patients with RIT1 mutations have a high incidence of hypertrophic cardiomyopathy and edematous phenotype, but the specific role of RIT1 remains unclear. Methods: To investigate how germline RIT1 mutations cause NS, we generated knock-in mice that carried a NS-associated Rit1 A57G mutation (Rit1A57G/+). We investigated the phenotypes of Rit1A57G/+ mice in fetal and adult stages as well as the effects of isoproterenol on cardiac function in Rit1A57G/+ mice. Findings: Rit1A57G/+ embryos exhibited decreased viability, edema, subcutaneous hemorrhage and AKT activation. Surviving Rit1A57G/+ mice had a short stature, craniofacial abnormalities and splenomegaly. Cardiac hypertrophy and cardiac fibrosis with increased expression of S100A4, vimentin and periostin were observed in Rit1A57G/+ mice compared to Rit1+/+ mice. Upon isoproterenol stimulation, cardiac fibrosis was drastically increased in Rit1A57G/+ mice. Phosphorylated (at Thr308) AKT levels were also elevated in isoproterenol-treated Rit1A57G/+ hearts. Interpretation: The A57G mutation in Rit1 causes cardiac hypertrophy, fibrosis and other NS-associated features. Biochemical analysis indicates that the AKT signaling pathway might be related to downstream signaling in the RIT1 A57G mutant at a developmental stage and under β-adrenergic stimulation in the heart. Fund: The Grants-in-Aid were provided by the Practical Research Project for Rare/Intractable Diseases from the Japan Agency for Medical Research and Development, the Japan Society for the Promotion of Science KAKENHI Grant. Keywords: Noonan syndrome, RIT1, Cardiac hypertrophy, Cardiac fibrosis, AK
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gain of function mutations in rit1 cause noonan syndrome a ras mapk pathway syndrome
American Journal of Human Genetics, 2013Co-Authors: Yoko Aoki, Tsutomu Ogata, Tetsuya Niihori, Toshihiro Banjo, Nobuhiko Okamoto, Seiji Mizuno, Kenji Kurosawa, Fumio Takada, Michihiro Yano, Toru AndoAbstract:RAS GTPases mediate a wide variety of cellular functions, including cell proliferation, survival, and differentiation. Recent studies have revealed that germline mutations and mosaicism for classical RAS mutations, including those in HRAS, KRAS, and NRAS, cause a wide spectrum of genetic disorders. These include Noonan syndrome and related disorders (RAS/mitogen-activated protein kinase [RAS/MAPK] pathway syndromes, or RASopathies), nevus sebaceous, and Schimmelpenning syndrome. In the present study, we identified a total of nine missense, nonsynonymous mutations in RIT1, encoding a member of the RAS subfamily, in 17 of 180 individuals (9%) with Noonan syndrome or a related condition but with no detectable mutations in known Noonan-related genes. Clinical manifestations in the RIT1-mutation-positive individuals are consistent with those of Noonan syndrome, which is characterized by distinctive facial features, short stature, and congenital heart defects. Seventy percent of mutation-positive individuals presented with hypertrophic cardiomyopathy; this frequency is high relative to the overall 20% incidence in individuals with Noonan syndrome. Luciferase assays in NIH 3T3 cells showed that five RIT1 alterations identified in children with Noonan syndrome enhanced ELK1 transactivation. The introduction of mRNAs of mutant RIT1 into 1-cell-stage zebrafish embryos was found to result in a significant increase of embryos with craniofacial abnormalities, incomplete looping, a hypoplastic chamber in the heart, and an elongated yolk sac. These results demonstrate that gain-of-function mutations in RIT1 cause Noonan syndrome and show a similar biological effect to mutations in other RASopathy-related genes.
Tetsuya Niihori - One of the best experts on this subject based on the ideXlab platform.
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new noonan syndrome model mice with rit1 mutation exhibit cardiac hypertrophy and susceptibility to β adrenergic stimulation induced cardiac fibrosis
EBioMedicine, 2019Co-Authors: Shingo Takahara, Tetsuya Niihori, Shinichi Inoue, Sachiko Miyagawatomita, Katsuhisa Matsuura, Yasumi Nakashima, Yoichi Matsubara, Yoshikatsu Saiki, Yoko AokiAbstract:Abstract Background Noonan syndrome (NS) is a genetic disorder characterized by short stature, a distinctive facial appearance, and heart defects. We recently discovered a novel NS gene, RIT1, which is a member of the RAS subfamily of small GTPases. NS patients with RIT1 mutations have a high incidence of hypertrophic cardiomyopathy and edematous phenotype, but the specific role of RIT1 remains unclear. Methods To investigate how germline RIT1 mutations cause NS, we generated knock-in mice that carried a NS-associated Rit1 A57G mutation (Rit1A57G/+). We investigated the phenotypes of Rit1A57G/+ mice in fetal and adult stages as well as the effects of isoproterenol on cardiac function in Rit1A57G/+ mice. Findings Rit1A57G/+ embryos exhibited decreased viability, edema, subcutaneous hemorrhage and AKT activation. Surviving Rit1A57G/+ mice had a short stature, craniofacial abnormalities and splenomegaly. Cardiac hypertrophy and cardiac fibrosis with increased expression of S100A4, vimentin and periostin were observed in Rit1A57G/+ mice compared to Rit1+/+ mice. Upon isoproterenol stimulation, cardiac fibrosis was drastically increased in Rit1A57G/+ mice. Phosphorylated (at Thr308) AKT levels were also elevated in isoproterenol-treated Rit1A57G/+ hearts. Interpretation The A57G mutation in Rit1 causes cardiac hypertrophy, fibrosis and other NS-associated features. Biochemical analysis indicates that the AKT signaling pathway might be related to downstream signaling in the RIT1 A57G mutant at a developmental stage and under β-adrenergic stimulation in the heart. Fund The Grants-in-Aid were provided by the Practical Research Project for Rare/Intractable Diseases from the Japan Agency for Medical Research and Development, the Japan Society for the Promotion of Science KAKENHI Grant.
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New Noonan syndrome model mice with RIT1 mutation exhibit cardiac hypertrophy and susceptibility to β-adrenergic stimulation-induced cardiac fibrosisResearch in context
'Elsevier BV', 2019Co-Authors: Shingo Takahara, Tetsuya Niihori, Shinichi Inoue, Katsuhisa Matsuura, Yasumi Nakashima, Yoichi Matsubara, Yoshikatsu Saiki, Sachiko Miyagawa-tomita, Yoko AokiAbstract:Background: Noonan syndrome (NS) is a genetic disorder characterized by short stature, a distinctive facial appearance, and heart defects. We recently discovered a novel NS gene, RIT1, which is a member of the RAS subfamily of small GTPases. NS patients with RIT1 mutations have a high incidence of hypertrophic cardiomyopathy and edematous phenotype, but the specific role of RIT1 remains unclear. Methods: To investigate how germline RIT1 mutations cause NS, we generated knock-in mice that carried a NS-associated Rit1 A57G mutation (Rit1A57G/+). We investigated the phenotypes of Rit1A57G/+ mice in fetal and adult stages as well as the effects of isoproterenol on cardiac function in Rit1A57G/+ mice. Findings: Rit1A57G/+ embryos exhibited decreased viability, edema, subcutaneous hemorrhage and AKT activation. Surviving Rit1A57G/+ mice had a short stature, craniofacial abnormalities and splenomegaly. Cardiac hypertrophy and cardiac fibrosis with increased expression of S100A4, vimentin and periostin were observed in Rit1A57G/+ mice compared to Rit1+/+ mice. Upon isoproterenol stimulation, cardiac fibrosis was drastically increased in Rit1A57G/+ mice. Phosphorylated (at Thr308) AKT levels were also elevated in isoproterenol-treated Rit1A57G/+ hearts. Interpretation: The A57G mutation in Rit1 causes cardiac hypertrophy, fibrosis and other NS-associated features. Biochemical analysis indicates that the AKT signaling pathway might be related to downstream signaling in the RIT1 A57G mutant at a developmental stage and under β-adrenergic stimulation in the heart. Fund: The Grants-in-Aid were provided by the Practical Research Project for Rare/Intractable Diseases from the Japan Agency for Medical Research and Development, the Japan Society for the Promotion of Science KAKENHI Grant. Keywords: Noonan syndrome, RIT1, Cardiac hypertrophy, Cardiac fibrosis, AK
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spectrum of mutations and genotype phenotype analysis in noonan syndrome patients with rit1 mutations
Human Genetics, 2016Co-Authors: Masako Yaoita, Tetsuya Niihori, Nobuhiko Okamoto, Seiji Mizuno, Shion Hayashi, Atsushi Watanabe, Masato Yokozawa, Hiroshi Suzumura, Akihiko Nakahara, Yusuke NakanoAbstract:RASopathies are autosomal dominant disorders caused by mutations in more than 10 known genes that regulate the RAS/MAPK pathway. Noonan syndrome (NS) is a RASopathy characterized by a distinctive facial appearance, musculoskeletal abnormalities, and congenital heart defects. We have recently identified mutations in RIT1 in patients with NS. To delineate the clinical manifestations in RIT1 mutation-positive patients, we further performed a RIT1 analysis in RASopathy patients and identified 7 RIT1 mutations, including two novel mutations, p.A77S and p.A77T, in 14 of 186 patients. Perinatal abnormalities, including nuchal translucency, fetal hydrops, pleural effusion, or chylothorax and congenital heart defects, are observed in all RIT1 mutation-positive patients. Luciferase assays in NIH 3T3 cells demonstrated that the newly identified RIT1 mutants, including p.A77S and p.A77T, and the previously identified p.F82V, p.T83P, p.Y89H, and p.M90I, enhanced Elk1 transactivation. Genotype-phenotype correlation analyses of previously reported NS patients harboring RIT1, PTPN11, SOS1, RAF1, and KRAS revealed that hypertrophic cardiomyopathy (56 %) was more frequent in patients harboring a RIT1 mutation than in patients harboring PTPN11 (9 %) and SOS1 mutations (10 %). The rates of hypertrophic cardiomyopathy were similar between patients harboring RIT1 mutations and patients harboring RAF1 mutations (75 %). Short stature (52 %) was less prevalent in patients harboring RIT1 mutations than in patients harboring PTPN11 (71 %) and RAF1 (83 %) mutations. These results delineate the clinical manifestations of RIT1 mutation-positive NS patients: high frequencies of hypertrophic cardiomyopathy, atrial septal defects, and pulmonary stenosis; and lower frequencies of ptosis and short stature.
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gain of function mutations in rit1 cause noonan syndrome a ras mapk pathway syndrome
American Journal of Human Genetics, 2013Co-Authors: Yoko Aoki, Tsutomu Ogata, Tetsuya Niihori, Toshihiro Banjo, Nobuhiko Okamoto, Seiji Mizuno, Kenji Kurosawa, Fumio Takada, Michihiro Yano, Toru AndoAbstract:RAS GTPases mediate a wide variety of cellular functions, including cell proliferation, survival, and differentiation. Recent studies have revealed that germline mutations and mosaicism for classical RAS mutations, including those in HRAS, KRAS, and NRAS, cause a wide spectrum of genetic disorders. These include Noonan syndrome and related disorders (RAS/mitogen-activated protein kinase [RAS/MAPK] pathway syndromes, or RASopathies), nevus sebaceous, and Schimmelpenning syndrome. In the present study, we identified a total of nine missense, nonsynonymous mutations in RIT1, encoding a member of the RAS subfamily, in 17 of 180 individuals (9%) with Noonan syndrome or a related condition but with no detectable mutations in known Noonan-related genes. Clinical manifestations in the RIT1-mutation-positive individuals are consistent with those of Noonan syndrome, which is characterized by distinctive facial features, short stature, and congenital heart defects. Seventy percent of mutation-positive individuals presented with hypertrophic cardiomyopathy; this frequency is high relative to the overall 20% incidence in individuals with Noonan syndrome. Luciferase assays in NIH 3T3 cells showed that five RIT1 alterations identified in children with Noonan syndrome enhanced ELK1 transactivation. The introduction of mRNAs of mutant RIT1 into 1-cell-stage zebrafish embryos was found to result in a significant increase of embryos with craniofacial abnormalities, incomplete looping, a hypoplastic chamber in the heart, and an elongated yolk sac. These results demonstrate that gain-of-function mutations in RIT1 cause Noonan syndrome and show a similar biological effect to mutations in other RASopathy-related genes.
Shiaw-yih Lin - One of the best experts on this subject based on the ideXlab platform.
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chromodomain helicase dna binding protein 4 chd4 regulates homologous recombination dna repair and its deficiency sensitizes cells to poly adp ribose polymerase parp inhibitor treatment
Journal of Biological Chemistry, 2012Co-Authors: Mei-ren Pan, Hui Ju Hsieh, Guang Peng, Hui Dai, Wen-chun Hung, Shiaw-yih LinAbstract:To ensure genome stability, cells have evolved a robust defense mechanism to detect, signal, and repair damaged DNA that is generated by exogenous stressors such as ionizing radiation, endogenous stressors such as free radicals, or normal physiological processes such as DNA replication. Homologous recombination (HR) repair is a critical pathway of repairing DNA double strand breaks, and it plays an essential role in maintaining genomic integrity. Previous studies have shown that BRIT1, also known as MCPH1, is a key regulator of HR repair. Here, we report that chromodomain helicase DNA-binding protein 4 (CHD4) is a novel BRIT1 binding partner that regulates the HR repair process. The BRCA1 C-terminal domains of BRIT1 are required for its interaction with CHD4. Depletion of CHD4 and overexpression of the ATPase-dead form of CHD4 impairs the recruitment of BRIT1 to the DNA damage lesions. As a functional consequence, CHD4 deficiency sensitizes cells to double strand break-inducing agents, reduces the recruitment of HR repair factor BRCA1, and impairs HR repair efficiency. We further demonstrate that CHD4-depleted cells are more sensitive to poly(ADP-ribose) polymerase inhibitor treatment. In response to DNA damage induced by poly(ADP-ribose) polymerase inhibitors, CHD4 deficiency impairs the recruitment of DNA repair proteins BRIT1, BRCA1, and replication protein A at early steps of HR repair. Taken together, our findings identify an important role of CHD4 in controlling HR repair to maintain genome stability and establish the potential therapeutic implications of targeting CHD4 deficiency in tumors.
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brit1 mcph1 is essential for mitotic and meiotic recombination dna repair and maintaining genomic stability in mice
PLOS Genetics, 2010Co-Authors: Yulong Liang, Guang Peng, Shiaw-yih Lin, Hongfang Gao, Xingxu Huang, Pumin Zhang, John A Goss, F C Brunicardi, Asha S MultaniAbstract:BRIT1 protein (also known as MCPH1) contains 3 BRCT domains which are conserved in BRCA1, BRCA2, and other important molecules involved in DNA damage signaling, DNA repair, and tumor suppression. BRIT1 mutations or aberrant expression are found in primary microcephaly patients as well as in cancer patients. Recent in vitro studies suggest that BRIT1/MCPH1 functions as a novel key regulator in the DNA damage response pathways. To investigate its physiological role and dissect the underlying mechanisms, we generated BRIT1(-/-) mice and identified its essential roles in mitotic and meiotic recombination DNA repair and in maintaining genomic stability. Both BRIT1(-/-) mice and mouse embryonic fibroblasts (MEFs) were hypersensitive to gamma-irradiation. BRIT1(-/-) MEFs and T lymphocytes exhibited severe chromatid breaks and reduced RAD51 foci formation after irradiation. Notably, BRIT1(-/-) mice were infertile and meiotic homologous recombination was impaired. BRIT1-deficient spermatocytes exhibited a failure of chromosomal synapsis, and meiosis was arrested at late zygotene of prophase I accompanied by apoptosis. In mutant spermatocytes, DNA double-strand breaks (DSBs) were formed, but localization of RAD51 or BRCA2 to meiotic chromosomes was severely impaired. In addition, we found that BRIT1 could bind to RAD51/BRCA2 complexes and that, in the absence of BRIT1, recruitment of RAD51 and BRCA2 to chromatin was reduced while their protein levels were not altered, indicating that BRIT1 is involved in mediating recruitment of RAD51/BRCA2 to the damage site. Collectively, our BRIT1-null mouse model demonstrates that BRIT1 is essential for maintaining genomic stability in vivo to protect the hosts from both programmed and irradiation-induced DNA damages, and its depletion causes a failure in both mitotic and meiotic recombination DNA repair via impairing RAD51/BRCA2's function and as a result leads to infertility and genomic instability in mice.
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brit1 mcph1 is a dna damage responsive protein that regulates the brca1 chk1 pathway implicating checkpoint dysfunction in microcephaly
Proceedings of the National Academy of Sciences of the United States of America, 2005Co-Authors: Shiaw-yih Lin, Rekha Rai, Stephen J ElledgeAbstract:BRIT1 [BRCT-repeat inhibitor of hTERT expression], a repressor of human telomerase function, is implicated in cellular immortalization. Here, we find that BRIT1 acts as a regulator of both the intra-S and G2/M checkpoints. When BRIT1 expression is depleted, cells lose the ionizing radiation (IR)-induced cell cycle arrest and become IR sensitive. BRIT1 is a chromatin-associated protein that forms irradiation-induced nuclear foci that colocalize with γ-H2AX foci. BRIT1 is also required for the expression of both BRCA1 and the checkpoint kinase Chk1 and phosphorylation of Nbs1. Thus, the checkpoint defects in the absence of BRIT1 are likely to result from its regulation of Nbs1, BRCA1, and Chk1. BRIT1 is identical to the recently discovered MCPH1 gene, found mutant in patients with primary microcephaly. The ataxia telangiectasia mutated-Rad3 related (ATR)–Chk1 pathway is defective in Seckel syndrome, another microcephaly disorder. We propose that the microcephaly observed in patients with MCPH1 deficiencies is due to disruption of the ATR–BRCA1–Chk1 signaling pathway that is also disrupted in Seckel syndrome patients.
Titus J. Boggon - One of the best experts on this subject based on the ideXlab platform.
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Structural basis for the disruption of the Cerebral Cavernous Malformations 2 (CCM2) interaction with Krev Interaction Trapped 1 (KRIT1) by disease-associated mutations
Journal of Biological Chemistry, 2014Co-Authors: Oriana S. Fisher, Rong Zhang, Weizhi Liu, Amy L. Stiegler, Sondhya Ghedia, James L. Weber, Titus J. BoggonAbstract:Familial cerebral cavernous malformations (CCMs) are predominantly neurovascular lesions and are associated with mutations within the KRIT1, CCM2, and PDCD10 genes. The protein products of KRIT1 and CCM2 (Krev interaction trapped 1 (KRIT1) and cerebral cavernous malformations 2 (CCM2), respectively) directly interact with each other. Disease-associated mutations in KRIT1 and CCM2 mostly result in loss of their protein products, although rare missense point mutations can also occur. From gene sequencing of patients known or suspected to have one or more CCMs, we discover a series of missense point mutations in KRIT1 and CCM2 that result in missense mutations in the CCM2 and KRIT1 proteins. To place these mutations in the context of the molecular level interactions of CCM2 and KRIT1, we map the interaction of KRIT1 and CCM2 and find that the CCM2 phosphotyrosine binding (PTB) domain displays a preference toward the third of the three KRIT1 NPX(Y/F) motifs. We determine the 2.75 A co-crystal structure of the CCM2 PTB domain with a peptide corresponding to KRIT1(NPX(Y/F)3), revealing a Dab-like PTB fold for CCM2 and its interaction with KRIT1(NPX(Y/F)3). We find that several disease-associated missense mutations in CCM2 have the potential to interrupt the KRIT1-CCM2 interaction by destabilizing the CCM2 PTB domain and that a KRIT1 mutation also disrupts this interaction. We therefore provide new insights into the architecture of CCM2 and how the CCM complex is disrupted in CCM disease.
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structural determinants for binding of sorting nexin 17 snx17 to the cytoplasmic adaptor protein krev interaction trapped 1 KRIT1
Journal of Biological Chemistry, 2014Co-Authors: Amy L. Stiegler, Rong Zhang, Weizhi Liu, Titus J. BoggonAbstract:Sorting nexin 17 (SNX17) is a member of the family of cytoplasmic sorting nexin adaptor proteins that regulate endosomal trafficking of cell surface proteins. SNX17 localizes to early endosomes where it directly binds NPX(Y/F) motifs in the cytoplasmic tails of its target receptors to mediate their rates of endocytic internalization, recycling, and/or degradation. SNX17 has also been implicated in mediating cell signaling and can interact with cytoplasmic proteins. KRIT1 (Krev interaction trapped 1), a cytoplasmic adaptor protein associated with cerebral cavernous malformations, has previously been shown to interact with SNX17. Here, we demonstrate that SNX17 indeed binds directly to KRIT1 and map the binding to the second Asn-Pro-Xaa-Tyr/Phe (NPX(Y/F)) motif in KRIT1. We further characterize the interaction as being mediated by the FERM domain of SNX17. We present the co-crystal structure of SNX17-FERM with the KRIT1-NPXF2 peptide to 3.0 A resolution and demonstrate that the interaction is highly similar in structure and binding affinity to that between SNX17 and P-selectin. We verify the molecular details of the interaction by site-directed mutagenesis and pulldown assay and thereby confirm that the major binding site for SNX17 is confined to the NPXF2 motif in KRIT1. Taken together, our results verify a direct interaction between SNX17 and KRIT1 and classify KRIT1 as a SNX17 binding partner.
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structural basis for small g protein effector interaction of ras related protein 1 rap1 and adaptor protein krev interaction trapped 1 KRIT1
Journal of Biological Chemistry, 2012Co-Authors: Rong Zhang, Weizhi Liu, Kyle M Draheim, David A Calderwood, Titus J. BoggonAbstract:Abstract Cerebral cavernous malformations (CCMs) affect 0.1–0.5% of the population resulting in leaky vasculature and severe neurological defects. KRIT1 (Krev interaction trapped-1) mutations associate with ∼40% of familial CCMs. KRIT1 is an effector of Ras-related protein 1 (Rap1) GTPase. Rap1 relocalizes KRIT1 from microtubules to cell membranes to impact integrin activation, potentially important for CCM pathology. We report the 1.95 A co-crystal structure of KRIT1 FERM domain in complex with Rap1. Rap1-KRIT1 interaction encompasses an extended surface, including Rap1 Switch I and II and KRIT1 FERM F1 and F2 lobes. Rap1 binds KRIT1-F1 lobe using a GTPase-ubiquitin-like fold interaction but binds KRIT1-F2 lobe by a novel interaction. Point mutagenesis confirms the interaction. High similarity between KRIT1-F2/F3 and talin is revealed. Additionally, the mechanism for FERM domains acting as GTPase effectors is suggested. Finally, structure-based alignment of each lobe suggests classification of FERM domains as ERM-like and TMFK-like (talin-myosin-FAK-KRIT-like) and that FERM lobes resemble domain “modules.”
