LOCALIZATION OF PLATELET-DERIVED GROWTH FACTOR-STIMULATED PHOSPHORYLATION CASCADE TO CAVEOLAE

Previously we showed that interleukin 1 beta stimulates the conversion of sphingomyelin to ceramide in the caveolae fraction of normal human fibroblasts. The ceramide, in turn, blocked platelet-derived growth f actor (PDGF) stimulated DNA synthesis. We now present evidence that th e PDGF receptor initiates signal transduction from caveolae. Cell frac tionation and immunocytochemistry show caveolae to be the principal lo cation of PDGF receptors at the cell surface. Multiple caveolae protei ns acquire phosphotyrosine when PDGF binds to its receptor, but the ho rmone appears to have little effect on the tyrosine phosphorylation of non-caveolae membrane proteins. Five proteins known to interact with the phosphorylated receptor were found to be highly enriched in caveol ae membrane. PDGF caused the concentration of three of these proteins to significantly increase in the caveolae fraction. Finally, PDGF stim ulated the association of a 190-kDa phosphoprotein with the caveolae m arker protein, caveolin. Therefore, ceramide may modulate PDGF recepto r function directly in caveolae.