Platelet-derived endothelial cell growth factor inhibits DNA synthesis in vascular smooth muscle cells

Platelet-derived endothelial cell growth factor (PD-ECGF) is linked to angiogenesis in human cancer. Direct studies have demonstrated that PD-ECGF is a potent mitogen for endothelial cells in vivo. Because endothelial repair and smooth muscle cell proliferation are two processes that affect arterial wall structure and tone, we analyzed the effects of PD-ECGF on DNA synthesis and creatine kinase BB-specific activity (CK) in human umbilical artery smooth muscle cells (SMC) and in a human umbilical endothelial cell line (E304). In SMC, PD-ECGF (0.001 to 10 U/mL) inhibited DNA synthesis dose dependently (−24% + 6% to −63% + 15%) assessed by ³[H]thymidine incorporation into DNA, whereas in E304 it stimulated DNA synthesis dose dependently (30% + 4% to 100% + 4%). In both SMC and E304, however, PD-ECGF elicited an increase in CK-specific activity by 54% to 130% and 79% to 163%, respectively. These effects were reversed by a specific anti-PD-ECGF antibody. In E304 cells PD-ECGF enhanced 17β-estradiol (E₂) or dihydrotestosterone (DHT)-induced DNA synthesis from 56% to 122% and from 127% to 359%, and CK activity from 70% to 180% and from 90% to 190%, respectively. In SMC PD-ECGF, an inhibitor of ³[H]thymidine incorporation by itself, markedly enhanced the stimulatory effect of low concentrations of E₂ and DHT on ³[H]thymidine incorporation. It also increased E₂ and DHT CK induction from 40% to 140% and from 52% to 120%, respectively. In both E304 and SMC, PD-ECGF inhibited the proliferative and the CK-inducing effects of platelet-derived growth factor (PDGF) and immunoglobulin F₁ (IGF₁). Thus, PD-ECGF, an established growth promoter for endothelial cells, is a potent inhibitor of DNA synthesis in human arterial SMC. However, in both E304 endothelial cells and SMC, PD-ECGF enhances the stimulatory effect of low concentrations of gonadal steroids on ³[H]thymidine incorporation. PD-ECGF antagonizes PDGF- and IGF₁-induced DNA synthesis in both E304 and SMC cells. By inhibiting arterial SMC proliferation and accelerating endothelial cell replication, PD-ECGF may buffer the effect of PDGF and favorably modulate arterial wall response to injury.