Role of PDGF-A expression in the control of vascular smooth muscle cell growth by transforming growth factor-beta.
Transforming growth factor-beta (TGF-beta) is a multifunctional regulatory peptide that can inhibit or promote the proliferation of cultured vascular smooth muscle cells (SMCs), depending on cell density (Majack, R. A. 1987. J. Cell Biol. 105:465-471). In this study, we have examined the mechanisms underlying the growth-promoting effects of TGF-beta in confluent SMC cultures. In mitogenesis assays using confluent cells, TGF-beta was found to potentiate the stimulatory effects of serum, PDGF, and basic fibroblast growth factor (bFGF), and was shown to act individually as a mitogen for SMC. In gene and protein expression experiments, TGF-beta was found to regulate the expression of PDGF-A and thrombospondin, two potential mediators of SMC proliferative events. The induction of thrombospondin protein and mRNA was density-dependent, delayed relative to its induction by PDGF and, based on cycloheximide experiments, appeared to depend on the de novo synthesis of an intermediary protein (probably PDGF-A). The relationship between PDGF-A expression and TGF-beta-mediated mitogenesis was investigated, and it was determined that a PDGF-like activity (probably PDGF-A) was the biological mediator of the growth-stimulatory effects of TGF-beta on confluent SMC. The effects of purified homodimers of PDGF-A on SMC replication were investigated, and it was determined that PDGF-AA was mitogenic for cultured SMC, particularly when used in combination with other growth factors such as bFGF and PDGF-BB. The data suggest several molecular mechanisms that may account for the ability of TGF-beta to promote the growth of confluent SMC in culture.
Majack
R A
RA
Upjohn Company, Kalamazoo, Michigan 49001.
Majesky
M W
MW
Goodman
L V
LV
D000818:Animals; D001011:Aorta / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D015152:Blotting, Northern; D002455:Cell Division / Q000187:drug effects; D002478:Cells, Cultured; D015342:DNA Probes; D008562:Membrane Glycoproteins / Q000235:genetics; D009131:Muscle, Smooth, Vascular / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism; D010982:Platelet-Derived Growth Factor / Q000235:genetics* / Q000494:pharmacology; D012313:RNA / Q000235:genetics / Q000302:isolation & purification; D012333:RNA, Messenger / Q000235:genetics; D051381:Rats; D011994:Recombinant Proteins / Q000494:pharmacology; D019699:Thrombospondins; D015291:Transforming Growth Factors / Q000494:pharmacology*
D015342:DNA Probes; D008562:Membrane Glycoproteins; D010982:Platelet-Derived Growth Factor; D012333:RNA, Messenger; D011994:Recombinant Proteins; D019699:Thrombospondins; D012313:RNA; D015291:Transforming Growth Factors