Differential Mode of Regulation of the Checkpoint Kinases CHK1 and CHK2 by Their Regulatory Domains

Chuen-Pei Ng, Hung Chiu Lee, Chung Wai Ho, Talha Arooz, Wai Yi Siu, Anita Lau, Randy Y. C. Poon
2003 Journal of Biological Chemistry  
CHK1 and CHK2 are key mediators that link the machineries that monitor DNA integrity to components of the cell cycle engine. Despite the similarity and potential redundancy in their functions, CHK1 and CHK2 are unrelated protein kinases, each having a distinctive regulatory domain. Here we compare how the regulatory domains of human CHK1 and CHK2 modulate the respective kinase activities. Recombinant CHK1 has only low basal activity when expressed in cultured cells. Surprisingly, disruption of
more » ... gly, disruption of the C-terminal regulatory domain activates CHK1 even in the absence of stress. Unlike the full-length protein, C-terminally truncated CHK1 displays autophosphorylation, phosphorylates CDC25C on Ser 216 , and delays cell cycle progression. Intriguingly, enzymatic activity decreases when the entire regulatory domain is removed, suggesting that the regulatory domain contains both inhibitory and stimulatory elements. Conversely, the kinase domain suppresses Ser 345 phosphorylation, a major ATM/ATR phosphorylation site in the regulatory domain. In marked contrast, CHK2 expressed in either mammalian cells or in bacteria is already active as a kinase against itself and CDC25C and can delay cell cycle progression. Unlike CHK1, disruption of the regulatory domain of CHK2 abolishes its kinase activity. Moreover, the regulatory domain of CHK2, but not that of CHK1, can oligomerize. Finally, CHK1 but not CHK2 is phosphorylated during the spindle assembly checkpoint, which correlates with the inhibition of the kinase. The mitotic phosphorylation of CHK1 requires the regulatory domain, does not involve Ser 345 , and is independent on ATM. Collectively, these data reveal the very different mode of regulation between CHK1 and CHK2.
doi:10.1074/jbc.m312215200 pmid:14681223 fatcat:urops5jwdnfs7ojntdboi7yqcu