Enhancing and Limiting Endothelin‐1 Signaling with a Cell‐penetrating Peptide Mimicking the Third Intracellular Loop of the ETB Receptor

TAT (a 13‐mer derived from the HIV‐1 Tat protein)‐linked cell‐permeable peptides deliver plasma membrane impermeable cargos into the cell. We investigated the effect of a TAT‐linked intracellular third loop of the endothelin‐1 type B receptor on endothelin‐1 activation of ERK. The effect of this peptide on ERK activation was determined in ETB receptor cDNA‐transfected Chinese hamster ovary cells and in ETA‐ and ETB‐expressing human pulmonary artery smooth muscle cells obtained from a normal and a bone morphogenetic protein‐2 receptor, exon 1–8 deletion subject, with pulmonary hypertension. In the Chinese hamster ovary cells the peptide, at optimum 10 μ m concentration, suppressed endothelin‐1 activation. In the normal human pulmonary artery smooth muscle cells, the peptide marginally enhanced endothelin‐1 activation of ERK. However, it markedly enhanced the endothelin‐1 activation of ERK in the bone morphogenetic protein‐2 receptor human pulmonary artery smooth muscle cells. While the effective concentration for endothelin‐1 activation of ERK remained unchanged in the bone morphogenetic protein‐2 receptor human pulmonary artery smooth muscle cells, the number of ETB receptors declined by 2/3. These data point to the intracellular third loop peptide as having variable receptor interactive effects with both signal repressive and enhancing capabilities. Peptides that can alter endothelin‐1 signal capabilities are potentially important in the study and treatment of pulmonary hypertension.