Differential regulation of fos and jun gene expression and AP-1 cis-element activity by endothelin isopeptides. Possible implications for mitogenic signaling by endothelin.

Endothelins (ET) are potent vasoconstrictor peptides that also function as mitogens for numerous cell types. Although regulation of second messenger pathways by ET peptides has been extensively investigated, little is known about the pathways of nuclear signaling by which ET controls gene expression. The present experiments investigated whether fos and jun contribute to nuclear signaling and gene regulation by ET isopeptides. ET isopeptides induced a subset of fos and jun mRNAs in mesangial cells, including c-fos, fra-1, c-jun, and JunB. fos and jun mRNAs were induced as members of the immediate-early gene response. Activation of the high affinity ET receptor moderately increased c-fos and fra-1 mRNA, whereas activation of the low affinity receptor markedly induced both fos and jun mRNAs. Thus, different ET receptor subtypes evoke distinct patterns of fos and jun induction. Prominent isopeptide- and cell-specific differences in the magnitude and kinetics of fos and jun expression were observed. Most striking was the marked elevation of c-fos steady-state mRNA and protein by ET-1, as compared with ET-3. In addition, ET-1, but not ET-3, increased transcriptional activity conferred by an AP-1 cis-element and directed collagenase gene expression. These results suggest that differential regulation of fos and jun expression and of AP-1 cis-element activity by ET isopeptides contributes to regulation of gene expression by ET. Furthermore, a role for AP-1 in mitogenic signaling by ET is suggested by the close correlation between AP-1 cis-element activity and cell growth.