Abstract

An imbalance between proliferation and apoptosis is an important causal factor for disorders involving abnormal cell accumulation. The role and mechanism of how G protein-coupled receptors are linked to apoptosis are poorly understood. Endothelin-1 (ET-1), a 21-amino acid peptide that binds to G protein-coupled receptors with mitogenic and vasoconstricting activities, suppressed apoptosis of human prostatic smooth muscle cells induced by paclitaxel treatment or serum withdrawal. Serum withdrawal or paclitaxel (1–10 μM) treatment for 48 h resulted in DNA fragmentation, a characteristic of apoptosis. The addition of ET-1 attenuated DNA fragmentation. The attenuating effect of ET-1 on DNA fragmentation was not affected by wortmannin, bisindolylmaleimide I, tyrphostin AG490, or AG1478. However, PD98059, an inhibitor for the extracellular signal-regulated kinase (ERK) kinase, induced apoptosis, potentiated the effect of serum withdrawal on inducing apoptosis, and blocked the antiapoptotic effect of ET-1. The ERK1/2 activity in these cells decreased rapidly after paclitaxel treatment or serum withdrawal, but was maintained at a 2-fold higher level in the presence of ET-1 for at least 4 h. These results suggest that the ERK1/2 pathway is activated by ET-1, and blocking this pathway abolishes the antiapoptotic effect of ET-1.