ACTIVATION OF T-CELL RAF-1 AT MITOSIS REQUIRES THE PROTEIN-TYROSINE KINASE LCK

The serine/threonine protein kinase Raf-1 is activated in response to a variety of growth factors in fibroblasts and hematopoietic cells. In T cells, Raf-1 is activated in response to stimulation through the T cell antigen receptor, the interleukin-2 receptor, and by stimulation of protein kinase C. We demonstrate here that in T cells, Raf-1 is als o activated during mitosis. The mitotic activation of Raf-1 was not ob served in the Lck-deficient cell line, J.CaM.1. During mitosis, Raf-1 was found to interact selectively with a mitotic form of Lck that migr ated with a reduced electrophoretic mobility on SDS-polyacrylamide gel s. We conclude that Raf-1 is activated during mitosis in T cells and t hat this mitotic activation of Raf-1 is dependent on the presence of L ck.