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


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 Cdc25A1,2,3. These events stimulate the ubiquitin-mediated proteolysis of Cdc25A1,4,5 and contribute to delaying cell-cycle progression, thereby preventing genomic instability1,2,3,4,5,6,7. Here we report that β-TrCP is the F-box protein that targets phosphorylated Cdc25A for degradation by the Skp1/Cul1/F-box protein complex. Downregulation of β-TrCP1 and β-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 β-TrCP may function in the intra-S-phase checkpoint. Consistent with this hypothesis, suppression of β-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 β-TrCP has a crucial role in mediating the response to DNA damage through Cdc25A degradation.

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Figure 1: Cdc25A interacts with β-TrCP1 and β-TrCP2 in vivo.
Figure 2: Interaction with β-TrCP protein through a phosphorylated DSG motif is required for Cdc25A degradation and polyubiquitination.
Figure 3: β-TrCP controls Cdc25A abundance during progression of S phase.
Figure 4: β-TrCP is required for degradation of Cdc25A induced by ionizing radiation in the intra-S-phase checkpoint.


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We thank T. K. Ko for his contribution; Z. G. Pan and S. Reed for reagents; G. Ossolengo for producing and purifying the anti-phosphoS82/S88 antibody; and M. Squatrito and E. De Billy for discussion. This work was supported by an Italian American Cancer Foundation fellowship and a Susan Komen Breast Cancer Foundation fellowship to D.G.; a Irma Hirschl Scholarship and grants from the NIH to M.P.; and grants from the Italian Association for Cancer Research (AIRC), the Italian Foundation for Cancer Research (FIRC) and Telethon to G.F.D.

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Correspondence to Maddalena Donzelli.

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Busino, L., Donzelli, M., Chiesa, M. et al. Degradation of Cdc25A by β-TrCP during S phase and in response to DNA damage. Nature 426, 87–91 (2003).

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