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DNA damage is a common event and probably leads to mutation or deletion within chromosomal DNA, which may cause cancer or premature aging. DNA damage induces several cellular responses including DNA repair, checkpoint activity and the triggering of apoptotic pathways. DNA damage checkpoints are associated with biochemical pathways that end delay or arrest of cell-cycle progression. These checkpoints engage damage sensor proteins, such as the RAD9-RAD1-HUS1 (9-1-1) complex, and the RAD17–RFC complex, in the detection of DNA damage and transduction of signals to ATM, ATR, CHK1 and CHK2 kinases. CHK1 and CHK2 kinases regulate CDC25, p21 and p53 that ultimately inactivate cyclin-dependent kinases (CDKs) which inhibit cell-cycle progression.
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