Growth hormone induces detergent insolubility of GH receptors in IM-9 cells

Abstract

In this study, we examined human growth hormone (hGH)-induced changes in nonionic detergent solubility characteristics of its receptor (hGHR). Exposure of IM-9 cells to hGH caused a time- and concentration-dependent loss of immunoblottable detergent-extractable hGHRs and a corresponding accumulation of receptors in a detergent-insoluble pool. At 37°C, the loss of detergent-soluble and the accumulation of detergent-insoluble hGHRs both preceded hGH-induced loss of total cell hGHRs. The detergent-insoluble receptor pool was progressively enriched in an apparent disulfide-linked form of the hGHR. Exposure to hGH at 4°C allowed hGH-induced hGHR disulfide linkage but did not promote changes in receptor detergent solubility, indicating that hGHR detergent insolubility cannot be explained solely by the formation of that linkage. Experiments carried out with hGH at 20°C and with the phorbol ester, phorbol-12,13-myristate acetate, at 37°C indicated that loss of detergent-soluble hGHRs can be uncoupled from accumulation of detergent-insoluble receptors. From these data, we envision at least two related, but separable, trafficking pathways taken by hGHRs after their surface interaction with hGH: 1) ligand-mediated endocytosis and degradation (accounting for only some of the receptors lost from the detergent-soluble fraction) and 2) ligand-mediated accumulation in a detergent-insoluble subcellular fraction (arising largely from receptors redistributed from the detergent-soluble fraction).