ORNITHINE DECARBOXYLASE-INDUCED AND RAS-INDUCED CELL TRANSFORMATIONS - REVERSAL BY PROTEIN-TYROSINE KINASE INHIBITORS AND ROLE OF PP130(CAS)

We have found that overexpression of human ornithine decarboxylase (OD C) induces cell transformation in NIH 3T3 and Rat-1 cells (M. Auvinen, A. Paasinen, L, C, Andersson, and E, Holtta, Nature (London) 360:355- 358, 1992), The ODC-transformed cells display increased levels of tyro sine phosphorylation, in particular of a cluster of 130-kDa proteins, Here we show that one of the proteins with enhanced levels of tyrosine phosphorylation in ODC-overexpressing cells is the previously describ ed p130 substrate of pp60(v-src), known to associate also with v-Crk a nd designated p130(CAS). We also studied the role of protein tyrosine phosphorylation in the ODC-induced cell transformation by exposing the cells to herbimycin A, a potent inhibitor of Src-family kinases, and to other inhibitors of protein tyrosine kinases, Treatment with the in hibitors reversed the phenotype of ODC-transformed cells to normal, wi th an organized, filamentous actin cytoskeleton. Coincidentally, the t yrosine hyperphosphorylation of p130 was markedly reduced, while the l evel of activity of ODC remained highly elevated, A similar reduction in pp130 phosphorylation and reversion of morphology by herbimycin A w ere observed in v-src- and c-Ha-vas-transformed cells. In addition, we show that expression of antisense mRNA for p130(CAS) resulted in reve rsion of the transformed phenotype of all these cell lines, An increas ed level of tyrosine kinase activity, not caused by c-Src or c-Abl, wa s further detected in the cytoplasmic fraction of ODC-transformed cell s. Preliminary characteristics of this kinase are shown. These data in dicate that p130(CAS) is involved in cell transformation by ODC, c-rns , and v-ire oncogenes, raise the intriguing possibility that p130(CAS) may be generally required for transformation, and imply that there is at least one protein tyrosine kinase downstream of ODC that is instru mental for cell transformation.