Using a small interfering RNA that enables the specific elimination of Chk1 expression, we show that the observed proteolysis of Cdc25A is mediated through Chk1. Moreover, Cdc25A overexpression abrogates the Chk1-mediated degradation and overcomes the doxorubicin-induced G2 arrest through dephosphorylation and activation of Cdc2/Cdk1 in a dose-dependent manner ... from full text, H1299 cells and tyrosine 15 phosphorylation of CDC2
beta-TrCP2 siRNA also inhibits Smad3-induced Cdc25A degradation.
The consequential loss of CDC25A results in G1/S arrest, due to the inefficient loading of CDC45 at the origin of replication. In addition, activated ATM, ATR, DNA–PK, Chk2, and Chk1 all aid in the phosphorylation and activation of p53, a key player in DNA-damage checkpoints. Activated p53 transactivates p21, which inhibits two G1/S-promoting cyclin-dependent kinases (CDKs), CDK2 and CDK4.
Transfection with dominant-negative Cdk mutants demonstrated that only a Cdk2 mutant increased Cdc25A protein levels; Cdk1 and Cdk3 mutants had no effect. The increased Cdc25A protein levels were the result of an increase in the half-life of the protein
beta-TRCP is a versatile F-box protein that recognizes several cell-cycle regulators EMI1-2, WEE1A and CDC25A-B in addition to its classical substrates, beta-catenin and IkappaB. In some cancers, beta-TRCP mutation or overexpression is found.
phosphorylation of Cdc25A on Ser-75 by Chk1 and its subsequent degradation is required to delay cell cycle progression in response to UV-induced DNA lesions.
Mitotic stabilization of Cdc25A reflects its phosphorylation on Ser17 and Ser115 by cyclin B-Cdk1, modifications required to uncouple Cdc25A from its ubiquitin-proteasome-mediated turnover
Depletion of beta-TRCP stabilizes Cdc25A, leading to hyperactive Cdk2 activity. SCFbeta-TRCP promotes Chk1-dependent Cdc25A ubiquitination in vitro, and this involves serine 76, a known Chk1 phosphorylation site.
The basal turnover of Cdc25A operating in unperturbed S phase required Chk1-dependent phosphorylation of serines 123, 178, 278, and 292. IR-induced acceleration of Cdc25A proteolysis correlated with increased phosphate incorporation into these residues generated by a combined action of Chk1 and Chk2 kinases. Finally, phosphorylation of Chk1 by ATM was required to fully accelerate the IR-induced degradation of Cdc25A ... from full text, U2OS cells and ATM-dependent CHEK1 phosphorylation at S317 and S345
BEL Commons is developed and maintained in an academic capacity by Charles Tapley Hoyt and Daniel Domingo-Fernández at the Fraunhofer SCAI Department of Bioinformatics with support from the IMI project, AETIONOMY. It is built on top of the open source project, PyBEL. Please feel free to contact us here to give us feedback or report any issues.