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The Rat Gonadotropin-Releasing Hormone Receptor Internalizes via a β-Arrestin-Independent, but Dynamin-Dependent, Pathway: Addition of a Carboxyl-Terminal Tail Confers β-Arrestin Dependency.

This study examined the mechanism underlying the rat GnRH receptor (GnRH-R) internalization pathway by investigating the role of added/extended C-terminal tails and the effect of β-arrestins and dynamin. The internalization of the wild-type (WT) rat GnRH-R, stop codon mutants, GnRH-R/TRH receptor (TRH-R) chimera, rat TRH-R, and catfish GnRH-R was examined using radioligand binding assay. Overexpression of β-arrestin in COS-7 cells expressing each of the receptor constructs substantially increased endocytosis rate constants (ke) of the TRH-R, catfish GnRH-R, and GnRH-R/TRH-R chimera, but not of the WT rat GnRH-R and stop codon mutants. Theβ -arrestin-promoted increase in the ke value was diminished by cotransfecting cells with the dominant negativeβ -arrestin-(319–418) mutant, whereas WT GnRH-R and stop codon mutant internalization were unaffected. Additionally, confocal microscopy showed that activated GnRH-Rs failed to induce time-dependent redistribution of either β-arrestin-1- or β-arrestin-2-green flu...