Conservation of the Chk1 Checkpoint Pathway in Mammals: Linkage of DNA Damage to Cdk Regulation Through Cdc25

Abstract

In response to DNA damage, mammalian cells prevent cell cycle progression through the control of critical cell cycle regulators. A human gene was identified that encodes the protein Chk1, a homolog of the Schizosaccharomyces pombe Chk1 protein kinase, which is required for the DNA damage checkpoint. Human Chk1 protein was modified in response to DNA damage. In vitro Chk1 bound to and phosphorylated the dual-specificity protein phosphatases Cdc25A, Cdc25B, and Cdc25C, which control cell cycle transitions by dephosphorylating cyclin-dependent kinases. Chk1 phosphorylates Cdc25C on serine-216. As shown in an accompanying paper by Peng et al. in this issue, serine-216 phosphorylation creates a binding site for 14-3-3 protein and inhibits function of the phosphatase. These results suggest a model whereby in response to DNA damage, Chk1 phosphorylates and inhibits Cdc25C, thus preventing activation of the Cdc2-cyclin B complex and mitotic entry.

The Candida albicans 14‐3‐3 gene, BMH1, is essential for growth

“…UV damage, 14-3-3 proteins bind to the phosphatase, Cdc25p, thereby inhibiting its ability to dephosphorylate Cdc2, leading to G 1 or G 2 arrest (Peng et al, 1997). A similar mechanism was demonstrated in mammalian cells (Sanchez et al, 1997). Although RAD24 and RAD25 appear to be functionally redundant, Rad25p has only marginal effects on resistance to UV resistance (Ford et al, 1994).…”

An ATM- and ATR-dependent checkpoint inactivates spindle assembly by targeting CEP63

“…Mitosis onset is prevented in response to DNA damage through the stabilisation of the inhibitory phosphorylation on Cdk1-Cyclin B (Dasso and Newpot, 1990;Jin et al, 1996). Activated ATM and ATR induce Chk1 and Chk2, which initiates Cdc25 inhibition and/or degradation (Matsuoka et al, 1998;Sanchez et al, 1997;Kastan and Bartek, 2004). For example, in fission yeast, Chk1 kinase phosphorylation of Cdc25C at Ser216 enables 14-3-3 proteins to bind, which leads to nuclear displacement of Cdc25C, preventing dephosphorylation of Cdk1-Cyclin B1 (Peng et al, 1997).…”

Hsp90-inhibitor geldanamycin abrogates G2 arrest in p53-negative leukemia cell lines through the depletion of Chk1

“…Appearance of phosphorylated upper bands of Cdc25C, Myt 1 and Bcl-2 are hallmarks of the presence of mitotic cells (Sanchez et al, 1997;Ling et al, 1998). Although nocodazole treatment for 12 h gave rise to the retarded upper bands of Cdc25C, Myt 1 and Bcl-2 in rapidly growing Jurkat cells, pre-and simultaneous treatment with 50 nM doxorubicin completely eliminated their upper retardation.…”

“…Chk1 plays the central role in DNA damage-induced G 2 arrest by maintaining Cdc25C in the phosphorylated inactive form, which suppresses Cdc2 activation (Elledge, 1996;Peng et al, 1997;Sanchez et al, 1997;Weinert, 1997;Bulavin et al, 2003). Caffeine has been shown to abrogate DNA damage-induced G 2 arrest by inhibiting Ataxia telangiectasia mutated (ATM) and ATM-related (ATR) kinases, which situated upstream of Chk1 in the DNA damage checkpoint pathway (Fan et al, 1995;Powell et al, 1995;Russell et al, 1995;Yao et al, 1996;Sarkaria et al, 1999).…”