46 research outputs found
The PBAF chromatin remodeling complex represses transcription and promotes rapid repair at DNA double-strand breaks
No full text© 2015, © 2015 The Author(s). Published with license by Taylor & Francis Group, LLC. © 2015, © Andreas Kakarougkas, Jessica A Downs, and Penny A Jeggo. Transcription in the vicinity of DNA double-strand breaks (DSBs) is suppressed via a process involving ataxia telangiectasia mutated protein (ATM) and H2AK119 ubiquitylation.1 We discuss recent findings that components of the Polybromo and Brahma-related gene 1 (BRG1)-associated factor (PBAF) remodeling complex and the polycomb repressive complex (PRC1/2) are also required.2 Failure to activate transcriptional suppression impedes a rapid DSB repair process
DNA repair: PARP – another guardian angel?
No full textAbstractCell lines and mice defective in poly(ADP-ribose) polymerase (PARP) have elevated spontaneous genetic rearrangements and abnormal responses to stresses. These results may be explained by an altered response to damage induced by free radicals, and suggest that PARP limits genomic instability from such damage
Impaired lymphocyte development and antibody class switching and increased malignancy in a murine model of DNA ligase IV syndrome
No full textHypomorphic mutations in DNA ligase IV (LIG4) cause a human syndrome of immunodeficiency, radiosensitivity, and growth retardation due to defective DNA repair by the nonhomologous end-joining (NHEJ) pathway. Lig4-null mice are embryonic lethal, and better mouse models are needed to study human LigIV syndrome. We recently identified a viable mouse strain with a Y288C hypomorphic mutation in the Lig4 gene. Lig4Y288C mice exhibit a greater than 10-fold reduction of LigIV activity in vivo and recapitulate the immunodeficiency and growth retardation seen in human patients. Here, we have demonstrated that the Lig4Y288C mutation leads to multiple defects in lymphocyte development and function, including impaired V(D)J recombination, peripheral lymphocyte survival and proliferation, and B cell class switch recombination. We also highlight a high incidence of thymic tumors in the Lig4Y288C mice, suggesting that wild-type LigIV protects against malignant transformation. These findings provide explanations for the complex lymphoid phenotype of human LigIV syndrome.This work was funded by the Wellcome Trust and the NIHR Biomedical Research Centre Programme. A. Nijnik was supported by a Wellcome Trust Prize Studentship. P.A. Jeggo is supported by the Medical Research Council, the Association for International Cancer Research, an Integrated Project EU grant, DNA Repair (LSHG-CT-2005-512113), and the United Kingdom Department of Health
Mutations in pericentrin cause Seckel syndrome with defective ATR-dependent DNA damage signaling.
No full textContains fulltext :
70806.pdf (Publisher’s version ) (Closed access)Large brain size is one of the defining characteristics of modern humans. Seckel syndrome (MIM 210600), a disorder of markedly reduced brain and body size, is associated with defective ATR-dependent DNA damage signaling. Only a single hypomorphic mutation of ATR has been identified in this genetically heterogeneous condition. We now report that mutations in the gene encoding pericentrin (PCNT)--resulting in the loss of pericentrin from the centrosome, where it has key functions anchoring both structural and regulatory proteins--also cause Seckel syndrome. Furthermore, we find that cells of individuals with Seckel syndrome due to mutations in PCNT (PCNT-Seckel) have defects in ATR-dependent checkpoint signaling, providing the first evidence linking a structural centrosomal protein with DNA damage signaling. These findings also suggest that other known microcephaly genes implicated in either DNA repair responses or centrosomal function may act in common developmental pathways determining human brain and body size
Nbs1 promotes ATM dependent phosphorylation events including those required for G1/S arrest.
No full textCell lines from Nijmegen Breakage Syndrome (NBS) and ataxia telangiectasia (A-T) patients show defective S phase checkpoint arrest. In contrast, only A-T but not NBS cells are significantly defective in radiation-induced G1/S arrest. Phosphorylation of some ATM substrates has been shown to occur in NBS cells. It has, therefore, been concluded that Nbs1 checkpoint function is S phase specific. Here, we have compared NBS with A-T cell lines (AT-5762ins137) that express a low level of normal ATM protein to evaluate the impact of residual Nbs1 function in NBS cells. The radiation-induced cell cycle response of these NBS and 'leaky' A-T cells is almost identical; normal G2/M arrest after 2 Gy, intermediate G1/S arrest depending on the dose and an A-T-like S phase checkpoint defect. Thus, the checkpoint assays differ in their sensitivity to low ATM activity. Radiation-induced phosphorylation of the ATM-dependent substrates Chk2, RPAp34 and p53-Ser15 are similarly impaired in AT-5762ins137 and NBS cells in a dose dependent manner. In contrast, NBS cells show normal ability to activate ATM kinase following irradiation in vitro and in vivo. We propose that Nbs1 facilitates ATM-dependent phosphorylation of multiple downstream substrates, including those required for G1/S arrest
The contribution of dormant origins to genome stability:from cell biology to human genetics
No full textThe ability of a eukaryotic cell to precisely and accurately replicate its DNA is crucial to maintain genome stability. Here we describe our current understanding of the process by which origins are licensed for DNA replication and review recent work suggesting that fork stalling has exerted a strong selective pressure on the positioning of licensed origins. In light of this, we discuss the complex and disparate phenotypes observed in mouse models and humans patients that arise due to defects in replication licensing proteins
Regulation of protein kinase B (PKB/Akt) by DNA-dependent protein kinase (DNA-PK) under physiological conditions
No full textThe serine/threonine protein kinase B (PKB/Akt) is a downstream effector of phosphatidylinositol 3-kinase (PI3K) and a major regulator of a variety of cellular processes, including metabolism, transcription, survival, proliferation, and growth. PKB is activated by several stimuli, including hormones, growth factors, cytokines and, as recently reported, also by DNA damage. Activation of PKB requires phosphorylation at two key regulatory sites: Thr308 and Ser473 (of PKBa). Phosphorylation by 3-phosphoinositide-dependent kinase-1 (PDK1) occurs on Thr308 in the activation loop of PKB. The phosphorylation on Ser473 within a C-terminal hydrophobic motif leads to full activation of PKB and mediated by two members of the PI3K-related kinase (PIKK) family, mTOR/rictor complex (mTORC2) or DNA-dependent protein kinase (DNA-PK) in a stimulus specific manner. Insulin or growth factor induced PKB Ser473 phosphorylation is regulated by mTORC2. In contrast, DNA damage-induced phosphorylation of PKB Ser473 is mediated by DNA-PK.
The present study made use of genetically modified mouse models to investigate PKB regulation by DNA-PK, as phosphorylation of Ser473 may be stimulus-, signalling pathway- and/or cell type-specific. In this study, we investigated the role of DNA-PK in basal, insulin-induced, and DNA damage-induced phosphorylation of PKB Ser473 under physiological conditions. We report that DNA-PK phosphorylated PKB on Ser473 upon DNA damage induced by γ-irradiation in vivo. In contrast, DNA-PK was dispensable for insulin and growth factor-induced PKB activation. Interestingly, analysis of basal PKB Ser473 phosphorylation in DNA-PKcs−/− mice showed tissue-specific deregulation of the PKB/FoxO pathway. In particular, we provide evidence that persistent PKB hyperactivity in the thymus apparently contributes to spontaneous tumourigenesis in DNA-PKcs−/− mice. Lymphomagenesis could be prevented by the deletion of PKBa and implies deregulation of PKB in DNA-PKcs−/− thymi.
Deregulation of PKB is implicated in various types of cancer and PI3K/PKB pathway is one of the most deregulated pathways in human malignancies. Therefore PI3K/PKB pathway is a major focus of current efforts for the treatment of cancer. In the second part of the study we made use of differential activation of PKB by upstream kinases in response to specific stimuli as a tool to dissect the mode of action of a small molecule inhibitor BBD130
