beta-arrestin-dependent desensitization of luteinizing hormone choriogonadotropin receptor is prevented by a synthetic peptide corresponding to the third intracellular loop of the receptor

Desensitization is a ubiquitous response of guanine nucleotide-binding prot ein-coupled receptors (GPCRs) characterized by the waning of effector activ ity despite continued presence of agonist, Binding of an arrestin to the ac tivated, often phosphorylated GPCR triggers desensitization. We reported fo r the luteinizing hormone/choriogonadotropin receptor (LH/CG R) that beta-a rrestin tightly bound to porcine ovarian follicular membranes mediates agon ist-dependent desensitization of LH/CG R-stimulated adenylyl cyclase (AC) a ctivity (Mukherjee, S,, Palczewski, K,, Gurevich, V, V., Benovic, J, L,, Ba nga, J, P., and Hunzicker-Dunn, M. (1999) Proc. Natl, Acad, Sci. U, S, A. 9 6, 493-498). We now show that addition of a synthetic peptide corresponding to the entire third intracellular loop (3i) of the LH/CG R completely and specifically reverses desensitization of AC activity, with an ED50 of 10 mu M but does not modulate basal, hCG-stimulated, or forskolin-stimulated AC activities. beta-Arrestin binds selectively to the 3i peptide coupled to ac tivated Sepharose, Desensitization of LH/CG R-stimulated AC activity is res cued when the 3i peptide is preincubated with exogenous beta-arrestin, Thes e results show that endogenous beta-arrestin participates in cell-free dese nsitization of agonist-dependent LH/CG R-stimulated AC activity in follicul ar membranes by interacting directly with the 3i loop of the receptor, ther eby preventing G(s) activation.