Genistein inhibits pressure-induced expression of c-fos in isolated mesenteric arteries

We have previously demonstrated that elevating intraluminal pressure from 9 0 to 140 mm Hg in isolated mesenteric arteries increases the expression of proto-oncogenes. These proto-oncogenes encode nuclear transcription factors that regulate the expression of target genes during various: stages of the cell cycle. Thus, pressure-induced proto-oncogene expression may represent a mechanism by which pressure can induce growth and/or proliferation of va scular smooth muscle. The purpose of this study was to determine the intrac ellular signals that contribute to the pressure-induced increase in c-fos e xpression. Small mesenteric arteries were isolated from male Wistar rats an d transferred to a dual-vessel chamber. The arteries were cannulated and sl owly equilibrated to initial-conditions (90 mm Hg, 37 degrees C) while bein g continuously superfused with a HEPES-bicarbonate-buffered Krebs' solution . After the equilibration period, the intraruminal pressure in 1 artery was increased to 140 mm Hg for 1 hour. In experiments designed to determine th e intracellular signals involved in the pressure-induced increase in c-fos expression, specific inhibitors were introduced to the superfusate reservoi r of both arteries before the pressure increase. The arteries were then fix ed in phosphate-buffered formalin and embedded in paraffin blocks. Sections of paraffin-embedded arteries were I fixed on slides, and the expression o f c-fos was determined by in situ hybridization with the use of S-35-labele d riboprobes. The pressure-induced expression of c-fos was not inhibited by nitrendipine (10 mu moL/L), a calcium-free Krebs' solution containing EGTA (1 to 2 mmol/L), calphostin C (0.1 mu mol/L), or cytochalasin D (0.4 mu mo l/L) but was inhibited by genistein (30 mu mol/L). The results suggest that activation of a tyrosine kinase is required for pressure-induced c-fos exp ression, but the signaling pathway:does not require extracellular calcium e ntry, intact actin filaments, or protein kinase C. As we have shown previou sly,the expression of c-fos correlated, with wall stress.