An Investigation of Melanin-concentrating Hormone Receptor Internalization – Or Lack Thereof

Abstract

Melanin-concentrating hormone (MCH), a cyclic peptide hormone involved in energy homeostasis, is known to bind to two G protein-coupled receptors (GPCRs) in mammals. These receptors, melanin-concentrating hormone receptor 1 (MCHR1) and melanin-concentrating hormone receptor 2 (MCHR2), have been a popular target for MCH antagonists in an effort to fight the ongoing epidemic of obesity. In the presence of prolonged stimulus it is common for GPCRs to undergo rapid desensitization. However, the desensitization mechanisms of MCHR1 and MCHR2 are as yet poorly understood. This study aims to create epitope-tagged expression vectors to allow for the expression of MCHR1 and MCHR2 in a tissue model. Utilizing a modified cell-based ELISA and fluorescence microscopy, the sequestration of MCHR1 and MCHR2 would be measured after agonist stimulus. Receptor interactions with GRK2 and ?-arrestins would also be measured. The over expression of both MCHR1 and MCHR2 proved to be cytotoxic to BHK570 cells. The overexpression of GRK2, ?-arrestin 1, and ?-arrestin 2 showed a relatively small but statistically significant increase in receptor internalization. Fluorescence microscopy suggests that the interaction between MCHR1 and ?-arrestins were transient in nature. These finding suggest that MCHR1 can be internalized via the clathrin-mediated pathway. It is likely MCH signaling is mediated a cell specific manner based on the cellular expression levels of GRKs and ?-arrestins.