Epiregulin is a potent vascular smooth muscle cell-derived mitogen inducedby angiotensin II, endothelin-1, and thrombin

Vasoactive GTP-binding protein-coupled receptor agonists such as angiotensi n II (AII), endothelin-1 (ET-1), and alpha-thrombin (alpha-Thr) have been r eported to indirectly stimulate vascular smooth muscle cell (VSMC) prolifer ation by regulating the expression of one or more autocrine growth factors. Using ion-exchange, gel-filtration, and reverse-phase chromatographic puri fication methods, we isolated a major mitogenic protein present in AII-stim ulated rat aortic smooth muscle (RASM) cell conditioned medium. Twenty N-te rminal amino acids of the purified peptide were identified, and they had 75 % amino acid sequence identity with mouse epiregulin, an epidermal growth f actor (EGF)related growth factor. We cloned the cDNA for rat epiregulin to determine its pattern of expression in G-protein-coupled receptor agonist-s timulated cells and confirm its activity as a mitogen, After treatment of R ASM cells with AII, ET-1, or alpha-Thr for 1 h, induction of two epiregulin transcripts was observed, including a 4.8-kb transcript and a novel transc ript of approximately 1.2 kb. Recombinant rat epiregulin arts strongly mito genic for RASM cells, stimulating DNA synthesis to levels similar to those induced by serum or platelet-derived growth factor and approximately 3-fold above that observed with saturating concentrations of EGF. In addition, ep iregulin caused rapid EGF receptor activation in RASM cells, However, relat ive levels of EGF receptor tyrosine phosphorylation stimulated by epireguli n were less than those induced by EGF or betacellulin. Taken together, thes e results indicate that epiregulin is a potent VSMC-secreted mitogen, induc ed in common by AII, ET-1, and alpha-Thr, that may contribute to VSMC proli feration and vascular remodeling stimulated by vasoactive agonists.