THE BRADYKININ B-2 RECEPTOR IS A DELAYED EARLY RESPONSE GENE FOR PLATELET-DERIVED GROWTH-FACTOR IN ARTERIAL SMOOTH-MUSCLE CELLS

Bradykinin and platelet-derived growth factor (PDGF) are inflammatory mediators important in the response to vascular injury. Based upon the known effect of oncogenic Ras to increase bradykinin receptor express ion and the ability of PDGF to stimulate Ras, we examined whether PDGF regulates bradykinin B-2 receptor expression in cultured arterial smo oth muscle cells. Treatment with PDGF (AB and BB, but not AA) produced a dose-and time-dependent increase in both mRNA (6-7-fold increase at 2-4 h) and cell surface receptors (2-4-fold at 6-12 h) for the B-2 re ceptor. There was a 60-min delay between exposure to PDGF and the init ial increase in B-2 receptor mRNA. Transcriptional inhibitors, actinom ycin D or 5,6-dichloro-1-beta-D-ribofuranosylbenzimidazole, completely blocked the increase in B-2 receptor mRNA when added up to 60 min aft er stimulation with PDGF. However, protein synthesis was not required, as treatment with cycloheximide did not block but rather superinduced the PDGF-induced increase in B-2 receptor mRNA. Comparison wit the im mediate early response gene c-fos demonstrated that the increase in B- 2 receptor mRNA was similarly inhibited by the tyrosine kinase inhibit or, tyrphostin, as well as staurosporine. However, stimulation of c-fo s was slightly more sensitive to genistein, while the B-2 receptor mRN A was more sensitive to inhibition by the protein kinase C inhibitor, calphostin C. the increase in cell surface B-2 receptors were function ally coupled to an increase in phosphoinositide-specific phospholipase C, and the effects of PDGF were selective as there was no increase in either angiotensin II- or arginine vasopressin-induced inositol phosp hate formation of intracellular calcium release. Taken together, these results demonstrate that the B-2 receptor is a delayed early response gene for PDGF in vascular smooth muscle cells.