PDGF-like growth factor from SV40-transformed smooth muscle cells promotes growth in an autocrine or paracrine manner

We investigated the growth characteristics of smooth muscle cells transformed by oridefective simian virus 40 plasmid DNA (TSMCs). TSMCs demonstrated a significantly higher proliferative activity when compared with nontransformed smooth muscle cells (SMCs). The SMCs were not able to proliferate in media with 5% plasma-derived serum (PDS) instead of fetal bovine serum, while TSMCs grew under this condition. When the DNA synthesis of quiescent SMCs was reinitiated by the addition of serum or platelet-derived growth factor (PDGF), the amount of [3H]thymidine incorporation into DNA varied with the concentrations of serum or PDGF and decreased on type V collagen compared with the other collagen substrates. In contrast, the TSMCs showed no differences in the amount of [3H]thymidine incorporation into DNA among the various concentrations of serum or PDGF and different types of collagen. When quiescent SMCs were cocultured with TSMCs, they showed a remarkable increase in the amount of [3H]thymidine incorporation into DNA, which was most intensively inhibited by type V collagen. These results suggest that TSMCs can promote the growth of TSMCs and SMCs in either an autocrine or paracrine manner and that they proliferate independently of the collagen matrices. Trapidil, a pyrimidine derivative that may inhibit the action of PDGF, decreased the number and cAMC levels of TSMCs in the media with 5% PDS in a concentration-dependent manner. The addition of polyclonal anti-PDGF-B antibody induced up to 59.5% inhibition of enhancement of DNA synthesis of SMCs cocultured with TSMCs. The level of cyclic adenosine monophosphate (cAMP) increased in the TSMCs compared with the SMCs. There was, however, no difference in the cAMP levels of either cells between the various types of collagen. Thus, the release of PDGF-like growth factor and an accumulation of cellular cAMP may be related to an increased DNA synthesis of TSMCs.