The chicken gonadotropin-releasing hormone receptor (cGnRH-R) is notable for having a cytoplasmic carboxyl-terminal tail, which is not present in the mammalian GnRH-Rs. We have previously shown that the cGnRH-R undergoes rapid agonist-induced internalization, and requires the carboxyl-terminal tail for this process. To investigate the role of the carboxyl-terminal tail of the cGnRH-R in relation to its rapid internalization, and to identify the key residues involved, a series of mutant constructs were generated, whereby either the tail was progressively truncated, or serine and threonine residues located in the tail substituted with alanine. Truncations of the carboxyl-terminal tail resulted in receptors that internalized GnRH agonist at a slower rate, and to a lower extent than the wild type receptor. Our data demonstrate the presence of signals for agonist-induced internalization in two regions, from Ser337 to Ser346, and Asp356 to the carboxyl-terminus. We show that a threonine-doublet located near the carboxyl-terminus plays a critical role in mediating rapid internalization. Furthermore, we provide evidence to suggest that the cGnRH-R expressed in COS-7 cells preferentially undergoes rapid agonist-induced internalization in caveolae, in a dynamin-dependent manner. Additionally, cGnRH-Rs are mobilized to the beta-arrestin- and clathrin-coated vesicle-mediated endocytic pathway upon beta-arrestin overexpression.
03 - 04 Dec 2001
Society for Endocrinology