RELEASE FROM G(0) G(1) ARREST INDUCED BY DIMETHYL-SULFOXIDE IN HUMAN LYMPHOID-CELLS - REGULATION OF SYNTHESIS AND ACTIVATION OF THE P33(CDK2) AND P34(CDC2) KINASES/

Raji cells, a human Burkitt's lymphoma-derived cell line, will accumul ate in a C-0-like state upon prolonged (5-6 days) incubation in medium containing 1.5% 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 21-2 4 h after release, which is about the length of the first C-1 phase of normal human lymphocytes which are stimulated in vitro to enter the c ell cycle. The G(0)-like state of arrested cells and the sequence of e vents occurring after release from DMSO mimic, in most ways studied, t hose of normal lymphocytes. Arrested Rail cells lack many cell cycle-r egulated molecules, including cyclin A, proliferating cell nuclear ant igen, and the p34(cdc2) kinase. They contain only hypophosphorylated p 110(Rb) and a low level of enzymatically inactive p33(cdk2) kinase. Af ter reentering the cell cycle, a series of events occurred, including phosphorylation of p110(Rb) and accumulation of the cyclin A and proli ferating cell nuclear antigen proteins in mid-G(1) and the accumulatio n of the p33(cdk2) and p34(cdc2) proteins beginning in late G(1), 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. T he time courses of activation of the p34(cdc2) and p33(cdk2) kinases w ere similar; both became detectable at about 21 h after release and in creased greatly in early S. This differs markedly from normal lymphocy tes in which activation of p33(cdk2) occurs in mid-G(1), many h before activation of p34(cdc2) which is an event characteristic of the G(2)/ M phase transition. The relative activities of the two cyclin-dependen t kinases seem not to be as closely regulated in the cell line. The po ssibility emerges that aberrations in the regulation of these key cell cycle regulatory kinases could be involved in or even responsible for the transformed phenotype of such cells.