SPHINGOSINE 1-PHOSPHATE STIMULATES TYROSINE PHOSPHORYLATION OF CRK

The proto-oncogene molecule c-Crk plays a role in growth factor-induce d activation of Pas. Sphingosine 1-phosphate (SPP), a metabolite of ce llular sphingolipids, has previously been shown to play a role in grow th factor receptor signaling (Olivera, A., and Spiegel, S. (1993) Natu re 365, 557-560), SPP was found to strongly induce tyrosine phosphoryl ation of Crk, but not She, in NIH-3T3 parental, insulin-like growth fa ctor-I receptor-overexpressing and Crk-overexpressing (3T3-Crk) fibrob lasts. Sphingosine, a metabolic precursor of SPP, also produced a slig ht increase in tyrosine phosphorylation of Crk. In contrast, other sph ingolipid metabolites including ceramide did not alter Crk tyrosine ph osphorylation. Furthermore, Crk enhanced SPP-induced mitogenesis, as m easured by SPP-stimulated [H-3]thymidine incorporation in a manner pro portional to the level of Crk expression in 3T3-Crk cells. This stimul ation appears to be Ras dependent, whereas SPP stimulation of MAP kina se activity is Ras independent. These data indicate that SPP activates a tyrosine kinase that phosphorylates Crk and that Crk is a positive effector of SPP-induced mitogenesis.