REVERSION OF RAS-HYDROLYZING AND PHOSPHATIDYLCHOLINE-HYDROLYZING PHOSPHOLIPASE C-MEDIATED TRANSFORMATION OF NIH 3T3 CELLS BY A DOMINANT INTERFERING MUTANT OF PROTEIN-KINASE-C-LAMBDA IS ACCOMPANIED BY THE LOSS OF CONSTITUTIVE NUCLEAR MITOGEN-ACTIVATED PROTEIN KINASE EXTRACELLULARSIGNAL-REGULATED KINASE-ACTIVITY/

The transformed phenotype of v-Ras- or Bacillus cereus phosphatidylcho line-hydrolyzing phospholipase C (PC-PLC)-expressing NIH 3T3 cells is reverted by expressing a kinase defective mutant of protein kinase C l ambda (lambda PKC). We report here that extracellular signal-regulated kinase (ERK)-1 and -2 are constitutively activated in v-Ras- and PC-P LC-transformed cells in the absence of added growth factors, Interesti ngly, the activated ERKs were exclusively localized to the cell nucleu s, Consistently, the transactivating potential of the C-terminal domai n of Elk-1, which is activated upon ERK-mediated phosphorylation, was strongly induced in serum-starved cells expressing v-Ras or PC-PLC, Re version of v-Ras- or PC-PLC-induced transformation by expression of do minant negative lambda PKC abolished the nuclear ERK activation sugges ting lambda PKC as a novel, direct or indirect, activator of mitogen-a ctivated protein kinase/ERK kinase in response to activated Pas or ele vated levels of phosphatidylcholine derived diacylglycerol, Transient transfection experiments confirmed that lambda PKC acts downstream of Pas but upstream of mitogen-activated protein kinase/ERK kinase. We fo und both the v-Rasand PC-PLC-transformed cells to be insensitive to st imulation with platelet-derived growth factor (PDGF), No detectable re ceptor level, autophosphorylation, or superinduction of DNA synthesis could be observed in response to treatment with PDGF, Reversion of the transformed cell lines by expression of dominant negative lambda PKC restored the receptor level and the ability to respond to PDGF in term s of receptor autophosphorylation, ERK activation, and induction of DN A synthesis.