QUANTITATION OF PLATELET-DERIVED GROWTH-FACTOR RECEPTORS IN HUMAN ARTERIAL SMOOTH-MUSCLE CELLS IN-VITRO

Platelet-derived growth factor (PDGF) is suggested to play an importan t role in the development of atherosclerosis as a migratory and mitoge nic stimulus to arterial smooth muscle cells (ASMCs). Stimulated and u nstimulated ASMCs were studied with respect to PDGF receptor (PDGF-R) mRNA and protein expression. Quantitative RT-PCR was developed for sim ultaneous evaluation of both PDGF-R alpha and -R beta mRNA expression and a quantitative ELISA for estimation of corresponding PDGF-R subuni ts. On the mRNA level, the overall PDGF-R beta expression was approxim ately 100 times lower than that of PDGF-R alpha. Furthermore, although PDGF-R alpha mRNA levels were high irrespective of hASMC phenotype, P DGF-R beta mRNA was influenced by serum stimulation with lower copy nu mbers in proliferating and confluent cells compared with quiescent cel ls. On the protein level, quiescent hASMCs expressed 10 times more PDG F-R beta than PDGF-R alpha. Serum stimulation decreased cell surface P DGF-Rs, with most prominent loss of PDGF-R alpha (ELISA and immunohist ochemistry). Our results suggest a differential regulatory pattern for PDGF-R alpha and -R beta and are compatible with the usage of alterna tive promoters for regulation of -R alpha expression. Further, it seem s that the number of available receptor subunits is not the only deter minant of variations in cell stimulation with different PDGF isoforms.