Rat skeletal myoblasts and arterial smooth muscle cells express the gene for the A chain but not the gene for the B chain (c-sis) of platelet-derived growth factor (PDGF) and produce a PDGF-like protein.

It is shown here that the myogenic cell line L6J1, primary skeletal myoblasts, and primary adult arterial smooth muscle cells express the gene for the A chain but not the gene for the B chain (c-sis) of platelet-derived growth factor (PDGF). It is further demonstrated that conditioned media from L6J1 cultures contain material that (i) competes with 125I-labeled PDGF for binding to human fibroblasts, (ii) is specifically precipitated by antibodies against PDGF, and (iii) has a relative molecular mass comparable to that of PDGF and, after reduction, its constituent subunit chains. The secretion of PDGF-receptor-competing activity was at a maximum in exponentially growing cultures but remained at a high level also after the cells had become confluent, stopped dividing, and fused to form multinucleate myotubes. Similarly, it was previously demonstrated that adult rat arterial smooth muscle cells in primary culture produce a mitogenic protein with immunological and structural properties similar to PDGF. In accordance with these findings, it was recently shown that secretion of PDGF-like mitogens by a number of human tumor cell lines correlates with expression of the gene for the A chain rather than the B chain of PDGF. The results suggest that production of homodimers of PDGF A chains may stimulate proliferation of skeletal myoblasts and arterial smooth muscle cells in an autocrine or paracrine manner. This could fulfill important functions during myogenesis in the embryo as well as in tissue repair and atherogenesis in the adult.