MULTIPLE PATHWAYS FOR ACTIVATION OF MAP KINASES

p42/Mitogen activated protein kinase (MAPK) and MAP Kinase Kinase (MAP KK) activities are constitutively elevated in v-raf transformed NIH3T3 cells, which correlates with increased tyrosine phosphorylation of p4 2mapk protein. These activities can be further enhanced to a moderate extent by treatment of raf-transformed cells with either serum, tetrad ecanoyl phorbol acetate (TPA), or aluminium fluoride. A similar activa tion of MAPK is observed in a cell line (M17raf) coexpressing a domina nt inhibitory ras mutant (N-17 ras) along with v-raf. However, in this cell line, both the serum and TPA stimulated response of MAPK activit y is reduced compared to similarly treated raf-transformed cells, whil e aluminium fluoride is equally potent in all the cell lines tested. T hese studies indicate that in addition to c-Raf-1, serine/threonine ki nase, which is an upstream activator of MAPK, other c-ras dependent as well as c-ras independent pathways also can contribute to MAPK activa tion.