PLASMINOGEN-ACTIVATOR INHIBITOR-1 REGULATION IN CULTURED RAT PERITUBULAR CELLS BY BASIC FIBROBLAST GROWTH-FACTOR AND TRANSFORMING GROWTH-FACTOR-ALPHA

45In the present study we examined the in vitro regulation of plasmino gen activator inhibitor I (PAI-1) expression in peritubular cells reco vered from 20-day-old rat testes. We tested two growth factors, basic fibroblast growth factor (bFGF) and transforming growth factor-alpha ( TGF alpha). They are synthesized by Sertoli cells, and peritubular cel ls exhibit the corresponding high affinity receptors. After exposure t o bFGF or TGF alpha (0.1-30 ng/ml), PAI-1 messenger RNA levels, as det ermined by Northern hybridization analysis, increased in a dose-depend ent manner. The first significant effects were noted after 2-h exposur e to bFGF or TGF alpha (10 ng/ml), and PAI-1 messenger RNA levels were maximally stimulated approximately 12-fold (bFGF) and 8-fold (TGF alp ha) after 4 h. The two growth factors increased the amount of immunore active (Western blots) and biologically active (Stachrom) PAI-1 measur ed in the culture medium. Actinomycin D inhibited the effects of these factors, whereas cycloheximide augmented them. Phorbol myristate acet ate, an activator of protein kinase C, mimicked the effects of bFGF an d TGF alpha. Interestingly, long term (24-h) pretreatment with phorbol myristate acetate resulted in a severe loss of responsiveness to bFGF or TGF alpha. Staurosporine, an inhibitor of protein kinase C, also s ignificantly reduced the effects of bFGF and TGF alpha. Given that PAI -1 inhibits Sertoli cell plasminogen activator activity and that bFGF and TGF alpha are synthesized by Sertoli cells, these factors are like ly to interact to regulate protease activity in localized regions of t he seminiferous tubule.