Mitogen-activated protein kinase kinase activity is required for the G(2)/M transition of the cell cycle in mammalian fibroblasts

The mitogen-activated protein kinase (MAPK) cascade is required for mitogen esis in somatic mammalian cells and is activated by a wide variety of oncog enic stimuli. Specific roles for this signaling module in growth were disse cted by inhibiting MAPK kinase 1 (MAPKK1) activity in highly synchronized N IH 3T3 cells, In addition to the known role of this kinase in cell-cycle en try from G(0), the level of MAPKK activity was observed to affect the kinet ics of progression through both the G(1) and G(2) phases of the cell cycle in NIH 3T3 cells. Ectopic expression of dominant-negative forms of MAPKK1, which was previously shown to inhibit G(0)/G(1) progression, was found to a lso delay progression of cells through G(2). In addition, treatment of cell s with the specific MAPIiK inhibitor PD 98059 during a synchronous S phase arrested the cells in the following G(2) phase. These data demonstrate a no vel role for the MAPK cascade in progression from G(2) into mitosis in NIH 3T3 cells.