Overexpression of platelet-derived growth factor B and downregulation of PDGF-receptor alpha in human immortalized fibroblasts.

Since immortalization of cells is critical in multistep carcinogenesis, efforts should be made to elucidate the mechanisms of the immortalization. To determine whether platelet-derived growth factor (PDGF) signal pathways play a role in immortalization of cells, we compared mRNA expressions of PDGFs and their receptors in three immortalized human fibroblast cell lines (SUSM-1, OUMS-24F, and KMST-6) with their normal parent cells. As a result, mRNA expression of PDGF-B (oncogene: c-sis) was upregulated in these immortalized cells. Unexpectedly, the expression of alpha- and beta-PDGF receptor genes was downregulated. PDGFR-alpha mRNA was remarkably decreased. When exogenous PDGFR-alpha was expressed transiently in the KMST-6 cells, the morphology of the cells resembled that of normal cells. These results suggest that the overexpression of PDGF-B (c-sis) and downregulation of PDGFR-alpha are related to the phenotypic characteristics of immortalized human cells.