The GH Receptor and Signal Transduction

Abstract

The primary structure of the growth hormone (GH) receptor in rabbits and humans determined by complementary DNA cloning revealed a single membrane-spanning protein of ∼ 620 amino acids. A binding protein (bp) specific for GH has been identified in the serum of a number of species. In rabbits and man, a single 4.5-kb transcript has been identified that encodes the full-length receptor. In rats and mice, however, a smaller transcript produced by alternative splicing has been reported which is specific for the GHbp. Recently, the X-ray crystallographic structure of GH and its receptor have clearly shown the formation of an unusual homodimer, consisting of one molecule of GH and two molecules of hGHbp. Formation of the GH dimer is a necessary prerequisite for biological activity. The transcriptional activity of wild-type and mutant forms of GH receptor has been determined by co-transfecting the promoter of a GH-responsive gene, coupled to CAT along with the receptor cDNA. A 25-amino acid region near the transmembrane domain has been shown to be important for functional activity, although 8 amino acids (known as Box 1), rich in prolines, is essential. Alanine scanning mutagenesis has revealed that individual substitution of each residue is without effect, while the replacement of the last 2 or all 4 of the prolines abolishes activity. Finally, GH has been shown to induce rapid tyrosine phosphorylation of several proteins in cells expressing the receptor, one of which has recently been identified as the kinase JAK2 and another as MAP kinase. Future studies will investigate the role of these and other kinases in the mechanism of GH action.

Comprehensive Alanine-scanning Mutagenesis ofEscherichia coliCsrA Defines Two Subdomains of Critical Functional Importance

“…Alanine replacement has an extensive history in structure-function studies (25)(26)(27)(28)(29)(30)(31) and is well suited for use in site-directed mutagenesis because it is abundant in many types of secondary structures and displays an uncharged and nonintrusive side chain that typically is compatible with native protein folding (32). In vivo examination of CsrA-repressed (glgCAP, pgaABCD) and activated (flhDC) operons in the presence of this series of mutants uncovered two regions within the primary structure of CsrA that are essential for its roles in repression and activation of gene expression.…”

Molecular and cellular actions of a structural domain of human growth hormone (AOD9401) on lipid metabolism in Zucker fatty rats

“…The lipolytic and antilipogenic actions of hGH have been well documented (Goodman & Grichting 1983, Davidson 1987, Brummer & Bengtsson 1995) although the precise molecular events involved in eliciting the metabolic changes remain largely unknown. Previous work from our laboratory has demonstrated that G proteins play a role in the longer-term effects of growth hormone, and protein kinase C is involved in the acute effects of the hormone (Roupas et al 1991, Kelly et al 1994, Roupas & Herington 1994. Treatment of rat adipocytes with hGH resulted in a transient and biphasic production of DAG which is present in signalling pathways involving both G proteins and protein kinase C. Protein kinase C is involved in mediating the lipolytic action of hGH (Gorin et al 1990).…”

Solubilization of Hydrophobic Peptides by Reversible Cysteine PEGylation

“…The TM sepents of single-spanning membrane proteins can serve merely to localize and anchor the protein in the membrane, as in the case of some ce11 adhesion molecules (Jones, 1996). A single-spanning TM segment can however be directly involved in function, as in the TM dimerization of certain proteins involved in signal transduction (Kelly et al, 1994).…”