Human Phosphatidylethanolamine-binding Protein Facilitates Heterotrimeric G Protein-dependent Signaling

Abstract

In this study we report that human phosphatidylethanolamine-binding protein (hPBP) facilitates heterotrimeric G protein-coupled signaling. In Xenopus laevis oocytes, coexpression of hPBP with human μ opioid receptor, human δ opioid receptor, or human somatostatin receptor 2 evoked an agonist-induced increase in potassium conductance of G protein-activated inwardly rectifying potassium channels. This activation of heterotrimeric G protein signaling in oocytes could also be elicited by injection of bacterially overexpressed and purified hPBP. Stimulatory effect was pertussis toxin-sensitive and present even in the absence of coexpressed receptors. Additionally, an increase in G protein-mediated inhibition of adenylate cyclase activity, measured by the inhibition of forskolin-mediated cAMP accumulation, could be detected in HEK293 and NIH3T3 cells after expression of hPBP and in Xenopus oocytes after injection of hPBP. As [35S]guanosine 5′-3-O-(thio) triphosphate (GTPγS) binding to membranes prepared from hPBP-expressing cells was significantly elevated and recombinant hPBP dose-dependently stimulated [35S]GTPγS binding to native membranes, the results presented provide strong evidence that hPBP-induced effects are G protein-dependent. These data suggest a novel function of hPBP in regulating G protein and G protein-coupled receptor signaling in vivo.