The DNA-binding subunit p140 of replication factor C is upregulated in cycling cells and associates with G(1) phase cell cycle regulatory proteins

The DNA-binding subunit of replication factor C (RFCp140) plays an importan t role in both DNA replication and DNA repair. The mechanisms regulating ac tivation of RFCp140 thereby controlling replication and cellular proliferat ion are largely unknown. We analyzed protein expression of RFCp140 during c ell cycle progression and investigated the association of RFCp140 with cell cycle regulatory proteins in cell lines of various tissue origin and in pr imary hematopoietic cells, Western and Northern blot analyses of RFCp140 fr om synchronized cells showed downregulation of RFCp140 when cells enter a G (0)-like quiescent state and upregulation of RFCp140 in cycling cells. Tran slocation from the cytoplasmic compartment to the nucleus did not account f or the significant increase in RFCp140 protein levels observed in cycling c ells. To investigate a potential association of RFCp140 with cell cycle reg ulatory proteins coimmunoprecipitation assays were performed. These studies demonstrated specific binding of RFCp140 to cdk4-kinase in hematopoietic a nd fibroblast cell lines. Additional coimmunoprecipitation studies revealed specific association of RFCp140 with cyclin D1, p21, proliferating cell nu clear antigen, and retinoblastoma protein. These findings link DNA replicat ion and repair factor RFCp140 to G(1) phase cell cycle regulatory elements critically involved in cell cycle control.