Phosphorylation of RIalpha by cyclin-dependent kinase CDK 2/cyclin E modulates the dissociation of the RIalpha-RFC40 complex.

We have previously demonstrated that the nuclear transport of the second subunit of the Replication Factor C complex, RFC40, by the regulatory subunit, RIalpha, of PKA is cell cycle specific and impairment in this transport results in G(1) arrest. In this study, we have investigated whether the cyclin-dependent kinases play ...
a role in regulating the RIalpha-RFC40 complex formation. In this context, we have identified RIalpha as a novel substrate for the G(1)/S-Cyclin-dependent kinase, CDK2/Cyclin E, and found that RIalpha is specifically phosphorylated at the serine residue. Treatment of MCF7 cells with a CDK inhibitor, olomoucine, resulted in a significant accumulation in the RIalpha-RFC40 complex by 3.10 +/- 0.08 fold and a parallel decrease in the RFC40-37 complex formation by 73.73 +/- 11.81%. Furthermore, in vitro phosphorylation experiments suggest that, phosphorylation of RIalpha by CDK2/CyclinE kinase promotes the dissociation of the RIalpha-RFC40 complex and that once RIalpha is phosphorylated it cannot complex with RFC40. Inhibition of the serine-threonine phosphatase, PP1, by Calyculin A, significantly reduced the RIalpha-RFC40 complex formation, substantiating the in vitro phosphorylation data. Taken together, these findings suggest that CDK2/Cyclin E may function as downstream modulator that regulates the dissociation of the RIalpha-RFC40 complex and subsequently the association of the RFC40-RFC37 complex.
Mesh Terms:
Active Transport, Cell Nucleus, Cell Line, Tumor, Cyclic AMP-Dependent Protein Kinase RIalpha Subunit, Cyclic AMP-Dependent Protein Kinases, Cyclin E, Cyclin-Dependent Kinase 2, Down-Regulation, Enzyme Inhibitors, Humans, Phosphorylation, Replication Protein C
Cell Cycle
Date: Mar. 01, 2006
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