Release from G0/G1 arrest induced by dimethyl sulfoxide in human lymphoid cells: regulation of synthesis and activation of the p33cdk2 and p34cdc2 kinases

Raji cells, a human Burkitt’s lymphoma-derived cell line, will accumulate in a G0-like state upon prolonged (5-6 days) incubation in medium containing 1.5#{176}Io dimethyl sulfoxide (DMSO). After removal of DMSO, the cells reenter the cell cycle in a synchronous manner and proliferate. After 5.5 days incubation in DMSO, S phase entry occurs at about 21-24 h after release, which is about the length of the first G1 phase of normal human lymphocytes which are stimulated in vitro to enter the cell cycle. The G0-like state of arrested cells and the sequence of events occurring after release from DMSO mimic, in most ways studied, those of normal lymphocytes. Arrested Raji cells lack many cell cycleregulated molecules, including cyclin A, proliferating cell nuclear antigen, and the p34��C2 kinase. They contain only hypophosphorylated p1 10Rb and a low level of enzymatically inadive p33cdk2 kinase. After reentering the cell cycle, a series of events occurred, including phosphorylation of p1 10Rb and accumulation of the cyclin A and proliferating cell nuclear antigen proteins in mid-G1 and the accumulation of the p33cdk2 and p34(�2 proteins beginning in late G1, just prior to S-phase entry. Cyclin E levels in Raji cells appeared to be less regulated than in normal cells, with high levels of this protein being present in resting cells and throughout the entire cell cycle. The time courses of activation of