COMPARTMENTALIZATION OF AUTOCRINE SIGNAL-TRANSDUCTION PATHWAYS IN SIS-TRANSFORMED NIH 3T3 CELLS

The transforming protein of simian sarcoma virus is homologous to the platelet-derived growth factor (PDGF) B-chain. Fibroblasts transformed with simian sarcoma virus constitutively produce a growth factor that stimulates the endogenous tyrosine kinase of PDGF receptors in an aut ocrine manner, Autophosphorylation of PDGF receptors upon ligand stimu lation provides binding sites for Src homology 2 domains of intracellu lar signaling molecules, which thereby become activated, We have chara cterized the PDGF receptor-mediated signal transduction in NIH 3T3 cel ls transformed with a PDGF B-chain cDNA (Sis 3T3 cells) in the absence and presence of suramin, a polyanionic compound that quenches PDGF-in duced mitogenicity and reverts the transformed phenotype of the Sis 3T 3 cells, Our data show that in the presence of suramin the general lev el of tyrosine phosphorylation was decreased, Nevertheless, autophosph orylated receptors complexed with substrates persisted in the cells, S uramin had no effect on activation of phosphatidylinositol 3'-kinase o r an tyrosine phosphorylation of phospholipase C-gamma and GTPase-acti vating protein of Ras. On the other hand, kinase activation of Src and Raf-1, phosphorylation of protein-tyrosine phosphatase 1D/Syp and Shc , and complex formation with Grb2 were greatly diminished by suramin. A possible explanation for our findings is that different PDGF recepto r-coupled signaling pathways are active in different structural or fun ctional compartments in the cell, Those pathways that are not affected by suramin might elicit distinct cellular responses, which are not su fficient for growth and transformation.