The Significance of the Short Form of the Growth Hormone Receptor in Rat Adipocytes

Abstract

Abstract

An isoform of the growth hormone (GH) receptor that lacks the transmembrane and intracellular domains is formed in adipocytes by alternate splicing of mRNA. This isoform is identical to the circulating GH-binding protein. The short isoform is about six times as abundant as the long isoform in rat adipocytes. It is located largely in the cytosolic compartment in association with intracellular membranes, but about 20% is present on the adipocyte surface as judged by the susceptibility to digestion by trypsin. In contrast, about 80% of the long isoform of the receptor is present on the cell surface. The two isoforms turn over at different rates and appear to be independently regulated. Both appear to contribute equally to GH binding. In preliminary studies, immunoneutralization of the short isoform decreased the magnitude of the effect of GH on glucose metabolism, suggesting that the short isoform may mediate some of the responses to GH.