The Chk1 Protein Kinase and the Cdc25C Regulatory Pathways Are Targets of the Anticancer Agent UCN-01*

By Paul Graves, Lijia Yu, J. Schwarz, Janis Gales, E. Sausville, P. O'Connor, H. Piwnica-Worms. Journal of Biological Chemistry, 2000

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A checkpoint operating in the G2 phase of the cell cycle prevents entry into mitosis in the presence of DNA damage. UCN-01, a protein kinase inhibitor currently undergoing clinical trials for cancer treatment, abrogates G2 checkpoint function and sensitizes p53-defective cancer cells to DNA-damaging agents. In most species, the G2 checkpoint prevents the Cdc25 phosphatase from removing inhibitory phosphate groups from the mitosis-promoting kinase Cdc2. This is accomplished by maintaining Cdc25 in a phosphorylated form that binds 14-3-3 proteins. The checkpoint kinases, Chk1 and Cds1, are proposed to regulate the interactions between human Cdc25C and 14-3-3 proteins by phosphorylating Cdc25C on serine 216. 14-3-3 proteins, in turn, function to keep Cdc25C out of the nucleus. Here we report that UCN-01 caused loss of both serine 216 phosphorylation and 14-3-3 binding to Cdc25C in DNA-damaged cells. In addition, UCN-01 potently inhibited the ability of Chk1 to phosphorylate Cdc25C in vitro. In contrast, Cds1 was refractory to inhibition by UCN-01in vitro, and Cds1 was still phosphorylated in irradiated cells treated with UCN-01. Thus, neither Cds1 nor kinases upstream of Cds1, such as ataxia telangiectasia-mutated, are targets of UCN-01 action in vivo. Taken together our results identify the Chk1 kinase and the Cdc25C pathway as potential targets of G2 checkpoint abrogation by UCN-01.

Subfields: Cell Biology, Molecular Biology

View Paper: https://www.semanticscholar.org/paper/777923d72e93ee47da09240b8b098763f301f3bc

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Citations in the corpus

PDK1, the master regulator of AGC kinase signal transduction. (2004, background): “[72] Graves PR, Yu L, Schwarz JK, Gales J, Sausville EA, O’Connor”
p53-deficient cells rely on ATM- and ATR-mediated checkpoint signaling through the p38MAPK/MK2 pathway for survival after DNA damage. (2007, methodology): “UCN-01 inhibits Chk1 with an IC 50 that is $1000 fold lower than that for Chk2, and hence has been used experimentally as a Chk1-specific inhibitor (Graves et al., 2000; Syljuasen et al., 2005).”
ATR-Mediated Checkpoint Pathways Regulate Phosphorylation and Activation of Human Chk1 (2001, methodology): “This substrate has previously been used to monitor the activity of Chk1 (25, 56).”
Regulation of the G2/M transition by p53 (2001, background): “For example, DNA damage stimulates the kinases Atm and Atr, which activate the Chk1 and Chk2 kinases, which then phosphorylate Cdc25, causing it to bind to 14-3-3 proteins, which anchor Cdc25 in the cytoplasm where it cannot activate Cdc2.”
Topoisomerase I inhibitors: camptothecins and beyond (2006, neutral): “UCN-01 is a relatively broad serine-threonine protein kinase inhibitor that inhibits CHK1 (Ref”
Specificity and mechanism of action of some commonly used protein kinase inhibitors (2000, background): “Subsequently it was reported to inhibit CHK1, one of the protein kinases that inactivates cdc25 to arrest the cell cycle when DNA is damaged [ 39 ].”