THROMBOXANE PROSTAGLANDIN ENDOPEROXIDE-INDUCED HYPERTROPHY OF RAT VASCULAR SMOOTH-MUSCLE CELLS IS SIGNALED BY PROTEIN-KINASE C-DEPENDENT INCREASES IN TRANSFORMING GROWTH-FACTOR-BETA/

In the present study, we examined the effect of the thromboxane/prosta glandin endoperoxide analogue U46619 on proliferation and hypertrophy in cultured rat vascular smooth muscle cells and the roles of protein kinase C and transforming growth factor-beta (TGF-beta) in the mediati on of the hypertrophic response to U46619. Since an increase in basic fibroblast growth factor (bFGF) was previously shown to mediate the hy pertrophic response to U46619, we also assessed the relationship betwe en bFGF and TGF-beta in the expression of U46619 actions. U46619 incre ased [S-35]methionine incorporation into protein and protein content o f vascular smooth muscle cells but had no effect on cell number. A rol e for TGF-beta was supported by the following observations: (1) exogen ous human TGF-beta 1 increased protein synthesis; (2) antibody to TGF- beta blocked both TGF-beta- and U46619-induced increases in protein co ntent; (3) U46619 increased active and total TGF-beta bioactivities; a nd (4) the actions of U46619 on protein content and TGF-beta bioactivi ty were blocked by the thromboxane/prostaglandin endoperoxide receptor antagonist SQ 29,548. Previous observations had demonstrated a role f or bFGF in the expression of U46619 actions on protein synthesis. Resu lts of the present study suggest that TGF-beta and bFGF interact in me diating the protein synthetic response to U46619, First, the concentra tion of exogenous TGF-beta (10 pmol/L) alone required to produce a pro tein synthetic response equivalent to that induced by U46619 was much higher than the concentration of endogenous active TGF-beta that accum ulated in the media in response to U46619 (0.7 pmol/L). Second, bFGF ( 20 ng/mL) increased total TGF-beta bioactivity and stimulated protein synthesis. The hypertrophic response to bFGF was blocked by anti-TGF-b eta. The ability of U46619 and bFGF to increase protein synthesis and protein content in vascular smooth muscle cells was associated with TG F-beta-induced suppression of proliferation, as evidenced by the abili ty of antibody to TGF-beta to enhance U46619- and bFGF-induced increas es in [H-3]thymidine incorporation into DNA. Results of the present st udy also supported a role for protein kinase C in the expression of U4 6619 and bFGF actions. U46619 increased protein kinase C activity in t he particulate fraction of vascular smooth muscle cells. Moreover, the protein kinase C inhibitors GF109203X and staurosporine blocked U4661 9- and bFGF-induced increases in protein synthesis as well as active a nd total TGF-beta bioactivities. By contrast, the protein kinase C inh ibitors did not prevent the increases in protein synthesis induced by exogenous TGF-beta. The results demonstrate that thromboxane/prostagla ndin endoperoxide signals increased TGF-beta bioactivity via protein k inase C. Increases in both bFGF and TGF-beta are required for an optim al hypertrophic response to U46619. The hypertrophic response to TGF-b eta occurs through a protein kinase C-independent pathway.