To delineate potential angiogenic roles of platelet-derived growth factor (PDGF), we have investigated PDGF and its receptors on bovine aortic endothelial cells that exhibit spontaneous angiogenesis in vitro (angiogenic endothelial cells). Initiation of cord/tube formation by angiogenic endothelial cells required bovine or human serum. Neutralization of PDGF-BB in human serum with a monoclonal anti-PDGF-BB antibody reduced cord/tube formation by 37 +/- 10%, whereas neutralizing anti-PDGF-AA and an IgG isotype-matched control antibody had no effect. DNA synthesis in response to PDGF-BB increased as the cords and tubes developed; furthermore, PDGF-BB induced the incorporation of BrdU in the nuclei of cells associated with these structures. PDGF beta-receptor (PDGF-beta) mRNA increased concomitantly with cord/tube formation, and PDGFR-beta were specifically localized by immunocytochemistry to developing and mature cords and tubes. However, PDGFR-beta transcripts and protein were undetectable in nonangiogenic endothelial cells, and PDGF alpha-receptor mRNA was not expressed in either endothelial cell strain. In contrast to nonangiogenic endothelial cells, angiogenic endothelial cells did not express the PDGF B-chain, the required ligand for the PDGFR-beta. We conclude that (a) PDGF-BB can contribute to angiogenesis in vitro, (b) PDGFR-beta are specific for cord/tube-forming endothelial cells and mediate endothelial proliferation and cord/tube formation, and (c) in angiogenic and nonangiogenic endothelial cells, the expression of PDGFR-beta and PDGF B-chain is inversely correlated. We therefore suggest that paracrine PDGF might amplify angiogenesis via direct action on endothelially expressed PDGFR-beta.

In the present study, we have shown for the first time that both hCTGF mRNA and protein are expressed in human arteries in vivo and that hCTGF may represent a novel factor expressed at high levels specifically in advanced lesions and may play a role in the development and progression of atherosclerosis.

c-sis/platelet-derived growth factor 2 (PDGF-2) is a prototype growth factor with transforming potential. The c-sis/PDGF-2 transcript contains a long 5' untranslated sequence (UTS) that is highly G.C rich. To examine the influence of this sequence on sis/PDGF-2 expression, we localized the c-sis/PDGF-2 promoter and used this promoter or the simian virus 40 early promoter to drive expression of the bacterial chloramphenicol acetyltransferase or sis/PDGF-2 gene. The 5' UTS of c-sis/PDGF-2 mRNA had no effect on RNA expression but was shown to exert a potent inhibitory effect on translation. By deletion analysis, we demonstrated that the 5' UTS inhibited protein expression by as much as 40-fold. The inhibitory effect was independent of reporter gene, cell type, or promoter used. A highly G.C-rich 140-base-pair sequence immediately preceding the c-sis/PDGF-2 initiation codon was shown to be nearly as effective as the entire 5' UTS in translational inhibition. Transfection analysis demonstrated that the 5' UTS significantly reduced the transforming efficiency of the sis/PDGF-2 gene as well. Thus, our findings raise the possibility that changes in regulation at the level of sis/PDGF-2 translation may play a role in development of the neoplastic phenotype.