NUCLEAR SIGNALING BY ENDOTHELIN-1 - A RAS PATHWAY FOR ACTIVATION OF THE C-FOS SERUM RESPONSE ELEMENT

Endothelin-1 (ET-1) regulates gene expression and growth of vascular c ells by triggering signals that link its cognate, G protein-coupled re ceptor in the plasma membrane to transcriptional activation of immedia te early genes in the nucleus, To define the nature of these signals, we asked whether Ras proteins contribute to activation of the c-fos se rum response element (SRE) by ET-1 in mesangial cells, a microvascular cell from the renal glomerulus, ET-1 stimulated Ras by increasing Ras GTP loading, Addition of ET-1 or transfection with a plasmid expressi ng v-Ha-Ras stimulated SRE dependent transcription, Activation of the c-fos SRE by ET-1 was blocked by a dominant negative Asn-17 c-Ha-Ras m utant, Expression of v-Ha-Ras reversed inhibition of ET-1-stimulated S RE transcriptional activity by Asn-17 c-Ha-Ras, ET-1 also stimulated k inase activity of c-Raf-1, a downstream effector in Ras signaling casc ades, Activation of the c-fos SRE by transfection with a plasmid expre ssing constitutively activated Delta Raf-1 was consistent with a role for Ras-Raf-1 in ET-1 signaling, Interestingly, Ras dependent SRE acti vation in cells treated with ET-1 was blocked by point mutations in th e SRE CArG DNA sequence, which binds the serum response factor, but no t by mutations that inhibit binding of ternary complex factors (p62(TC F)) to the Ets DNA sequence of the SRE, Thus, Ras contributes to a nuc lear signaling cascade linking ET-1 receptors to transcriptional activ ation through the CArG cis-element of the c-fos SRE.