Effect of endothelin‐1 (1‐31) on extracellular signal‐regulated kinase and proliferation of human coronary artery smooth muscle cells

1 We have previously found that human chymase cleaves big endothelins (ETs) at the Tyr 31 ‐Gly 32 bond and produces 31‐amino acid ETs (1‐31), without any further degradation products. In this study, we investigated the effect of synthetic ET‐1 (1‐31) on the proliferation of cultured human coronary artery smooth muscle cells (HCASMCs). 2 ET‐1 (1‐31) increased [ 3 H]‐thymidine incorporation and cell numbers to a similar extent as ET‐1 at 100 n M . This ET‐1 (1‐31)‐induced [ 3 H]‐thymidine uptake was not affected by phosphoramidon, an inhibitor of ET‐converting enzyme. It was, however, inhibited by BQ123, an endothelin ET A receptor antagonist, but not by BQ788, an endothelin ET B receptor antagonist. 3 By using an in‐gel kinase assay, we demonstrated that ET‐1 (1‐31) activated extracellular signal‐regulated kinase 1/2 (ERK1/2) in a concentration‐dependent manner (100 p M to 1 μ M ) in HCASMCs. ET‐1 (1‐31)‐induced ERK1/2 activation was inhibited by BQ123, but not by BQ788 and phosphoramidon. Inhibition of protein kinase C (PKC) and ERK kinase also caused a reduction of ET‐1 (1‐31)‐induced ERK1/2 activation, whereas tyrosine kinase inhibition had little effect. 4 Gel‐mobility shift analysis revealed that the ERK1/2 activation was followed by an increase in transcription factor activator protein‐1 DNA binding activity in HCASMCs. 5 Our results strongly suggest that ET‐1 (1‐31) itself stimulates HCASMC proliferation probably through endothelin ET A or ET A ‐like receptors. The underlining mechanism of cell growth by ET‐1 (1‐31) may be explained in part by PKC‐dependent ERK1/2 activation. Since human chymase has been proposed to play a role in atherosclerosis, ET‐1 (1‐31) may be one of the mediators.British Journal of Pharmacology (1998) 125 , 1019–1027; doi: 10.1038/sj.bjp.0702141