Differential effects of endomorphin-1, endomorphin-2, and Tyr-W-MIF-1 on activation of G-proteins in SH-SYS5Y human neuroblastoma membranes

Endomorphin-1 (Tyr-Pro-Trp-Phe-NH2) and encomorphin-2 (Tyr-Pro-Phe-Phe-NH2), peptides recently isolated from bovine and human brain, have high affinity and selectivity for CL opiate receptors. They share sequence similarity with the endogenous opiate-modulating peptide Tyr-W-MIF-1 (Tyr-Pro-Trp-Gly-NH2). The efficacies of these endogenous peptides and of the enkephalin analog DAMGO were compared by measuring their effects on the binding of guanosine-5'-O-(gamma-[S-35]thio)triphosphate ([S-35]GTP gamma S) to G-proteins in membranes from SH-SY5Y human neuroblastoma cells. DAMGO, endomorphin-1, and endomorphin-1 stimulated [S-35]GTP gamma S binding dose dependently, with maximal effects of 60 +/- 9%, 47 +/- 9%, and 43 +/- 6% stimulation above basal and ED50 of 49 +/- 8 nM, 38 +/- 8 nM, and 64 +/- 13 nM, respectively. Tyr-W-MIF-1 showed only a small stimulation of binding (5% stimulation above basal, ED50 = 2 mu M). When given in combination with the other opioids, however, Tyr-W-MIF-1 attenuated their ability to activate G-proteins. Thus, the endogenous opioids endomorphin-1 and endomorphin-2 activate G-proteins similarly to the synthetic agonist DAMGO, but the structurally similar peptide Tyr-W-MIF-1 produces only minimal stimulation of G-proteins. (C) 1998 Elsevier Science Inc.