Domain-dependent modulation of PDGFRβ by ganglioside GM1

The regulation of receptor tyrosine kinases (RTKs) is important in several cellular events, including proliferation, differentiation, and apoptosis. Gangliosides are sialic acid-containing glycosphingolipids that can regulate RTK activity. The addition of ganglioside GM1 to the medium of Swiss 3T3 fibroblasts inhibits both platelet-derived growth factor (PDGF)-mediated tyrosine phosphorylation of PDGF receptor beta (PDGFRbeta) and receptor-mediated endocytosis. However, GM1 did not affect PDGF-mediated receptor phosphorylation, neuritogenesis, or endocytosis in PC12 cells stably transfected with the gene for PDGFRbeta. The ability of GM1 to modulate PDGFRbeta in 3T3 cells but not in transfected PC12 cells indicates a cell context-dependent response. We hypothesized that this inhibition of PDGFRbeta by GM1 must map to one or more domains of the receptor. Thus, a chimeric receptor was created that possessed the extracellular and transmembrane domains of the nerve growth factor (NGF) receptor TrkA and the cytoplasmic domain of PDGFRbeta (TTbeta). In 3T3 cells transfected with the TTbeta construct, GM1 did not inhibit NGF-induced tyrosine phosphorylation of the chimeric receptor or of Erk1/2 in this cell line. GM1 still inhibited PDGF-mediated tyrosine phosphorylation of endogenous PDGFRbeta and of Erk1/2 in Swiss TTbeta cells. Thus, the cytoplasmic domain of PDGFRbeta is not required for GM1-dependent inhibition of PDGFRbeta in 3T3 cells. This suggests that the inhibition of PDGFRbeta by GM1 in Swiss 3T3 fibroblasts maps to either the extracellular and/or transmembrane domain of PDGFRbeta.