The Human Liver Growth Hormone Receptor*

Abstract

Human livers, obtained from donors at the time of transplant, were homogenized in 0.25 M sucrose and fractionated by differential centrifugation. The specific binding of [125I] human (h) GH to total particulate fractions from 18 livers varied from 0.4-5.1% of the total radioactivity/100 micrograms protein. Binding affinity was 2.0 +/- 0.3 X 10(9) M-1, and binding capacity ranged from 14-53 fmol/mg protein. A different proportion of receptors occupied by endogenous hGH did not explain the large variation in binding. Binding sites were specific for hGH. Dissociation of the hormone-receptor complex was extremely slow. No specific binding of [125I]hPRL was observed. Specific binding of insulin was found in fractions from all livers and varied less than hGH binding. Cross-linking of [125I]hGH to plasma membrane and microsome receptors yielded two major autoradiographic bands corresponding to an estimated mol wt of 103,000 for the receptor, with a possible subunit of 54,000. Human liver primary fractions were characterized. The binding of hGH and insulin displayed a nucleo-microsomal distribution pattern in the primary fractions; 54.2% and 27.9% of the hGH-binding activity were found in the microsomes and the nuclear fraction, respectively, whereas insulin binds equally to nuclear and microsomal elements. Our findings suggest that hGH-binding sites are present in the plasma membrane and also in one or more intracellular compartments, whereas a high proportion of insulin receptors is associated with the plasma membrane.

The D152H mutation found in growth hormone insensitivity syndrome impairs expression and function of human growth hormone receptor but is silent in rat receptor

“…Specificity and affinity of the human wild-type GHR expressed in 293 cells were those expected for a human receptor (Hocquette et al 1989). The binding affinity of the D152H receptor was similar to the wild-type GHR, whereas the number of receptors expressed in 293 cells, whatever the amount of cDNA transfected, was lower for the mutant than for the wild-type GHR.…”

Lack of hormone binding in COS-7 cells expressing a mutated growth hormone receptor found in Laron dwarfism.

“…The molecular masses of the full-length receptor and of the BP, 88,000 and 38,000, respectively, are those expected for the two forms (23 (7), who found GH binding activity in a lysosomal fraction prepared from COS-7 cells expressing the mutant hGH receptor. The distribution of the hGH receptor that was presented by these authors and that lead them to conclude that there was an abnormal processing of the mutant receptor is difficult to reconcile with respect to previous studies (24,25). Their results showing the complete absence of wild type hGH receptors in a microsomal fraction make the interpretation of their binding studies difficult.…”

Developmental changes in the human GH receptor and its signal transduction pathways

“…In the present study, we asked whether there are factors other than the levels of hGHR, which may be responsible for the decreased responsiveness to hGH in fetal tissues. We focused on Based on its amino acid sequence, the nascent hGHR is predicted to be w70 kDa in size while, when resolved on SDS-PAGE gels under reducing conditions, the mature hGHR migrates at 100-140 kDa (Hocquette et al 1989, Alele et al 1998, Zhang et al 2001, Cowan et al 2005. These differences are due primarily to the presence of five asparagine-linked glycosylation sites within the extracellular domain, a variable number of which are glycosylated in the mature hGHR (Harding et al 1994).…”