THROMBOXANE A(2) PROSTAGLANDIN H-2-STIMULATED MITOGENESIS OF CORONARY-ARTERY SMOOTH-MUSCLE CELLS INVOLVES ACTIVATION OF MITOGEN-ACTIVATED PROTEIN-KINASE AND S6 KINASE

Prostaglandin H-2 (PGH(2)) and thromboxane A(2) (TXA(2)) are potent ac tivators of platelets and vascular smooth muscle whose responses are m ediated through a common G protein coupled receptor (TXA(2)/PGH(2) rec eptor). Despite the many studies describing their ability to aggregate platelets and contract vascular smooth muscle, little is known concer ning the potential mitogenic capabilities of these autocoids. Mitogen- activated protein kinases (MAP kinases) and ribosomal S6 kinases are w ell characterized intracelluIar mediators involved in proliferation of cells. The present study was designed to examine the activation of MA P kinase and S6 kinase in guinea pig coronary artery smooth muscle cel ls (CASMC) in response to stimulation by a TXA(2)/PGH(2) mimetic, I-BO P ([1S-(1 alpha,2 beta(5Z),3 alpha(1E,3R),4 alpha)]-7-[3-(3-hydroxy- tenyl)-7-oxabicyclo[2.2.1]heptan-2-yl]-5-heptenoic acid), Equilibrium radioligand binding assays using [I-125]BOP defined a single class of high affinity TXA(2)/PGH(2), receptors on monolayers of guinea pig CAS MC (K-d = 0.18 +/- 0.03 nM; 26,476 +/- 3,600 sites/cell; 0.08 +/- 0.01 pmol/mg of protein; n = 12). I-BOP produced a concentration-dependent increase in [H-3]thymidine incorporation in these cells (EC(50) = 0.3 nM) which was inhibited by a series of TXA(2)/PGH(2) recep tor antago nists as well as by verapamil and staurosporine. I-BOP also produced a time-dependent increase in the activation of kinases phosphorylating myelin basic protein (MBP; a substrate for MAP kinase) and RRLSSLRA (S 6 peptide; a substrate for pp85(rsk) kinase), reaching a peak activati on between 5 and 10 min. Stimulated MBP kinases were identified as ERK 1 and ERK2. The activation of these kinases by I-BOP was inhibited by the TXA(2)/PGH(2) receptor antagonist SQ29548 and also by staurosporin e. These results indicate that I-BOP, a TXA(2)/PGH(2) mimetic, produce s growth of coronary artery vascular smooth muscle cells, which is pre ceded by activation of MAP kinase and S6 kinase.