TGF-β1 selectively suppresses PDGF receptor signaling pathways in MG-63 human osteosarcoma cell

We previously found that TGF-β 1 inhibits PDGF mitogenicity in MG-63 cells and the inhibition is correlated with a suppression of the PDGF-induced receptor autophosphorylation. In this study, we analyze if all the PDGF receptor signaling pathways are similarly affected by the TGF-β1 pretreatment. We show that TGF-β1 suppresses PDGF-stimulated tyrosine phosphorylation of PLC-γ1, and the phosphorylation of Erk. In contrast, the tyrosine phosphorylation of P13-kinase is not affected. Thus, TGF-β1 selectively suppresses two out of three PDGF receptor signaling pathways despit of its prominent inhibition of the PDGF-induced receptor autophosphorylation. The results also indicate that activation of the P13-kinase pathway alone by PDGF is not sufficient in supporting the optimum growth of MG-63 cells under the culture conditions employed.