THE HALF-LIVES OF PLATELET-DERIVED GROWTH-FACTOR A-CHAIN AND B-CHAIN MESSENGER-RNAS ARE SIMILAR IN ENDOTHELIAL-CELLS AND UNAFFECTED BY HEPARIN-BINDING GROWTH FACTOR-I OR CYCLOHEXIMIDE

Platelet-derived growth factor (PDGF) is mitogenic and chemotactic for vascular smooth muscle cells cultured in vitro, and, thus, may play a role in the smooth muscle cell proliferation and migration that occurs during atherosclerotic lesion development. Two related PDGF polypeptides, designated as the A and B chains, form functionally active PDGF-AA, AB, or BB dimers. The PDGF A- and B-chain genes are both transcribed in human umbilical vein endothelial (HUVE) cells and their expression is regulated by cytokines, growth factors, endotoxin, and phorbol ester. We reported previously that the angiogenic polypeptide heparin-binding growth factor (HBGF)-1 induces PDGF A-chain gene expression, but does not affect PDGF B-chain gene expression. In this study, we determined whether mRNA stabilization contributed to this induction by measuring the half-life of PDGF A-chain mRNA in quiescent, HBGF-1-stimulated, and proliferating HUVE cells. PDGF A-chain mRNA levels increase when quiescent HUVE cells are treated with the protein synthesis inhibitor cycloheximide; therefore, the effect of cycloheximide on PDGF A-chain mRNA decay was also investigated. The half-life of PDGF A-chain transcripts in quiescent cells was approximately 2.4 h and neither HBGF-1 nor cycloheximide significantly altered this decay rate. We also estimated the half-life of PDGF B-chain mRNA under the three different growth conditions and in the absence or presence of cycloheximide. The half-life in quiescent cells was approximately 1.8 h and was unaffected by HBGF-1 or protein synthesis inhibition. Therefore, the PDGF mRNAs have similar decay rates in HUVE cells, even though the 3' untranslated region of B-chain transcripts, but not A-chain transcripts, contains AU-rich sequence motifs postulated to confer rapid turnover in vivo.