Regulation of cyclin E and p27kip during mitosis in BALB/c 3T3 cells.

Abstrad We haveexamined the level of cyclin E, a Gi cyclin, and p27”, a cyclin-dependent kinase inhibitor, in BALB/c 3T3 cells. Cell populations stimulated to undergo cell cycle traverse displayed little change in the level of cyclin E, while p27 was found to be reduced 50_80% in proliferating cells. Analysis of mitotic cells, however, revealed that cyclin E is virtually absent and begins to reaccumulate soon after mitosis is complete, as does p27 . Immunoprecipitation experiments revealed that p27 is associated with cyclin E in quiescent but not proliferating cells, indicating that it may fundion to prevent development of cyclin E adivity in the absence of growth fadors. Based on our charaderization of cyclin E and p27kIP in BALB/c 3T3 cells during progression of the cell cycle, we propose a model of growth regulation controlling the G1 phase of growing and quiescent cells involving mitotic degradation of cyclin E and recovery of p27’” inhibitory adivity in a late or postmitotic interval.