Degradation of Cdc25A by β-TrCP during S phase and in response to DNA damage

Abstract

The Cdc25A phosphatase is essential for cell-cycle progression because of its function in dephosphorylating cyclin-dependent kinases. In response to DNA damage or stalled replication, the ATM and ATR protein kinases activate the checkpoint kinases Chk1 and Chk2, which leads to hyperphosphorylation of Cdc25A. These events stimulate the ubiquitin-mediated proteolysis of Cdc25A and contribute to delaying cell-cycle progression, thereby preventing genomic instability. Here we report that beta-TrCP is the F-box protein that targets phosphorylated Cdc25A for degradation by the Skp1/Cul1/F-box protein complex. Downregulation of beta-TrCP1 and beta-TrCP2 expression by short interfering RNAs causes an accumulation of Cdc25A in cells progressing through S phase and prevents the degradation of Cdc25A induced by ionizing radiation, indicating that beta-TrCP may function in the intra-S-phase checkpoint. Consistent with this hypothesis, suppression of beta-TrCP expression results in radioresistant DNA synthesis in response to DNA damage--a phenotype indicative of a defect in the intra-S-phase checkpoint that is associated with an inability to regulate Cdc25A properly. Our results show that beta-TrCP has a crucial role in mediating the response to DNA damage through Cdc25A degradation.

Cyclin F suppresses B-Myb activity to promote cell cycle checkpoint control

“…2c), resulting in downregulation of CDC25A protein levels (Fig. 2d), which is essential for G2 checkpoint activation 21 . Since checkpoint activation occurred independently of cyclin F, we reasoned that adding continuous DNA damage or a second delayed dose of IR would lead to prolonged checkpoint control.…”

Human Cdc14A Reverses CDK1 Phosphorylation of Cdc25A on Serines 115 and 320

“…Counterbalancing the de novo synthesis, the ubiquitin ligase complexes APC/C Cdh1 , upon exit from mitosis, and SCF bTrCP , during interphase and upon DNA damage, mediate its ubiquitin-proteasome degradation. 30,31 Moreover, multiple phosphorylation sites of Cdc25A by several kinases seem to tightly regulate its degradation mechanisms and the final protein levels, which could afford the cell different thresholds of activity, depending on the cell cycle phase or stress-induced situations (reviewed in ref. 32).…”

Differential mitotic degradation of the CDC25B phosphatase variants

“…Thus, CDC25A degradation was proposed to be under the control of a dual regulatory mechanism (Donzelli et al, 2002). The F-box protein that targets phosphorylated CDC25A for degradation by the SCF protein complex on DNA damage and during interphase was subsequently reported to be the b-TrCP protein (Busino et al, 2003;Jin et al, 2003). A DSG binding motif within a (DSG(X) 4 S) consensus sequence present in a number of SCF substrates was identified on CDC25A, but recognition of CDC25A by b-TrCP was found to occur via a sequential phosphorylation of S76 by the CHK1 kinase and S82 by an unknown kinase (Jin et al, 2003;Donzelli et al, 2004).…”