Suppression of DNA-damage checkpoint signaling by Rsk-mediated phosphorylation of Mre11.
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2013-12-17
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Ataxia telangiectasia mutant (ATM) is an S/T-Q-directed kinase that is critical for the cellular response to double-stranded breaks (DSBs) in DNA. Following DNA damage, ATM is activated and recruited by the MRN protein complex [meiotic recombination 11 (Mre11)/DNA repair protein Rad50/Nijmegen breakage syndrome 1 proteins] to sites of DNA damage where ATM phosphorylates multiple substrates to trigger cell-cycle arrest. In cancer cells, this regulation may be faulty, and cell division may proceed even in the presence of damaged DNA. We show here that the ribosomal s6 kinase (Rsk), often elevated in cancers, can suppress DSB-induced ATM activation in both Xenopus egg extracts and human tumor cell lines. In analyzing each step in ATM activation, we have found that Rsk targets loading of MRN complex components onto DNA at DSB sites. Rsk can phosphorylate the Mre11 protein directly at S676 both in vitro and in intact cells and thereby can inhibit the binding of Mre11 to DNA with DSBs. Accordingly, mutation of S676 to Ala can reverse inhibition of the response to DSBs by Rsk. Collectively, these data point to Mre11 as an important locus of Rsk-mediated checkpoint inhibition acting upstream of ATM activation.
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Chen, Chen, Liguo Zhang, Nai-Jia Huang, Bofu Huang and Sally Kornbluth (2013). Suppression of DNA-damage checkpoint signaling by Rsk-mediated phosphorylation of Mre11. Proc Natl Acad Sci U S A, 110(51). pp. 20605–20610. 10.1073/pnas.1306328110 Retrieved from https://hdl.handle.net/10161/8387.
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Scholars@Duke
Liguo Zhang
Sally A. Kornbluth
Our lab studies the regulation of complex cellular processes, including cell cycle progression and programmed cell death (apoptosis). These tightly orchestrated processes are critical for appropriate cell proliferation and cell death, and when they go awry can result in cancer and degenerative disorders. Within these larger fields, we have focused on understanding the cellular mechanisms that prevent the onset of mitosis prior to the completion of DNA replication, the processes that prevent cell division when the mitotic spindle is disrupted, the signaling pathways that prevent apoptotic cell death in cancer cells and the mechanisms that link cell metabolism to cell death and survival.
In our quest to answer these important cell biological and biochemical questions, we are varied in our use of experimental systems. Traditionally, we have used cell-free extracts prepared from eggs of the frog Xenopus laevis which can recapitulate cell cycle events and apoptotic processes in vitro. For the study of cell cycle events, extracts are prepared which can undergo multiple rounds of DNA replication and mitosis in vitro. Progression through the cell cycle can be monitored by microscopic observation of nuclear morphology and by biochemically assaying the activity of serine/threonine kinases which control cell cycle transitions.
For the study of apoptosis, modifications in extract preparation have allowed us to produce extracts which can apoptotically fragment nuclei and can accurately reproduce the biochemical events of apoptosis, including internucleosomal DNA cleavage and activation of apoptotic proteases, the caspases.
More recently, we have focused on studying apoptosis and cell cycle progression in mammalian models, both tissue culture cells and mouse models of cancer. In these studies, we are trying to determine the precise signaling mechanisms used by cancer cells to accelerate proliferation and evade apoptotic cell death mechanisms. We also endeavor to subvert these mechanisms to therapeutic advantage. We are particularly interested in links between metabolism and cell death, as high metabolic rates in cancer cells appear to suppress apoptosis to evade chemotherapy-induced cell death.
Finally, we also have several projects using the facile genetics of Drosophila melanogaster to further understand links between metabolism and cell death and also the ways in which mitochondrial dynamics are linked to apoptotic pathways.
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