ASSOCIATION OF PROLIFERATING CELL NUCLEAR ANTIGEN WITH CYCLIN-DEPENDENT KINASES AND CYCLINS IN NORMAL AND TRANSFORMED HUMAN T-LYMPHOCYTES

The proliferating cell nuclear antigen (PCNA) is an auxiliary protein of DNA polymerase delta and appears to be needed for both DNA synthesi s and DNA repair. It is present in low amount in resting normal human T lymphocytes and, upon mitogenic stimulation with phorbol dibutyrate and ionomycin, begins to increase in mid-G1 phase, approximately 12 to 15 hours before entry into S phase. PCNA continues to increase in amo unt throughout the cell cycle and remains high in proliferating cultur es. PCNA was extracted from activated normal T cells and from the tran sformed T-lymphoblastoid cell line Jurkat by a method that recovered a pproximately 98% of total cellular PCNA but yet retained its associati ons with other proteins. PCNA immunoprecipitates possessed H1 histone kinase activity, which increased in parallel with increasing cellular content of PCNA. Both the cdc2 and cdk2 kinases were found associated with PCNA in normal T cells, in amounts consistent with detected kinas e activity. The results indicate that PCNA is not an inhibitory molecu le of cdk/cyclin activity. Both normal and transformed T cells contain ed PCNA in association with cdk2, cdk4, cdk5, and cdk6, with the amoun t of PCNA associated with these molecules increasing in the order list ed. Relatively high amounts of PCNA were also found associated with cy clins D2 and D3, the major cyclin partners of cdk6 in T cells. Though detected in normal cells, PCNA/cdc2 complexes were present in exceedin gly low amount, if at all, in Jurkat cells. This cell line appeared to contain more of nearly all of the cdk and cyclin molecules analyzed, but there seemed to be little difference in the patterns of associatio n of these molecules with PCNA in the cell line as compared with norma l human T cells. (C) 1994 by The American Society of Hematology.