Mitogen-Activated Protein Kinase Kinase Activity Is Required for the G2/M Transition of the Cell Cycle in Mammalian Fibroblasts

The mitogen-activated protein kinase (MAPK) cascade is required for mitogensis in somatic mammalian cells and is activated by a wide variety of oncogenic stimuli. Specific roles for this signaling module in growth were dissected by inhibiting MAPK kinase 1 (MAPKK1) activity in highly synchronized NIH 3T3 cells. In addition to the known role of this kinase in cell-cycle entry from G0, the level of MAPKK activity was observed to affect the kinetics of progression through both the G1and G2phases of the cell cycle in NIH 3T3 cells. Ectopic expression of dominant-negative forms of MAPKK1, which was previously shown to inhibit G0/G1progression, was found to also delay progression of cells through G2. In addition, treatment of cells with the specific MAPKK inhibitor PD 98059 during a synchronous S phase arrested the cells in the following G2phase. These data demonstrate a novel role for the MAPK cascade in progression from G2into mitosis in NIH 3T3 cells.