The growth hormone-binding protein in rat serum is an alternatively spliced form of the rat growth hormone receptor.

Abstract

A cDNA clone isolated from rat liver was demonstrated to encode a soluble, secreted growth hormone (GH)-binding protein consistent with the properties of the newly discovered serum GH-binding protein. The protein coding region of this cDNA was identical in sequence to the extracellular domain of the rat liver GH receptor up to three amino acids before the putative transmembrane domain. At this point, an additional 17 amino acids were encoded in the GH-binding protein before a stop codon was encountered. This cDNA clone was shown to be representative of the structure of the mRNA present in rat liver. These results suggest that the mechanism for production of the rat serum GH-binding protein is by alternative splicing of the gene for the rat GH receptor.[Key Words: Growth hormone; receptor; binding protein]Received April 27, 1989; revised version accepted June 7, 1989. Growth hormone (GH) is a polypeptide secreted by the anterior pituitary that acts through specific high-affinity cell-surface receptors located primarily in the liver (Hughes and Frieson 1985). Recently a specific high-af finity protein that binds GH has been identified in serum (Ymer and Herington 1985;Baumann et al. 1986;Herington et al. 1986). This serum GH-binding protein has a close structural relationship to the GH receptor present on the surface of cells. Genetic, immimological, and biochemical data suggest colinearity and identity between the extracellular domain of the GH receptor and the GH-binding protein (Eshet et al. 1985;Barnard and Waters 1986; Baumaim et al. 1987;Daughaday and Trivedi 1987;Leung et al. 1987; Baumann and Shaw 1988;Spencer et al. 1988). It has been proposed that the GH-binding protein is produced by proteolytic cleavage of the GH receptor (Leung et al. 1987;Spencer et al. 1988;Trivedi and Daughaday 1988).We now report the isolation and characterization of two classes of cDNA clones, both of which encode pro teins that bind GH in vitro. One class encodes a mem brane-bound protein, which is the GH receptor. The other class of cDNA clones encodes a soluble secreted protein that contains the same putative GH-binding re gion but lacks the transmembrane and intracellular do mains. These regions are replaced with a 17-amino-acid hydrophilic segment that is followed by a unique 3'-un translated region. The data suggest that the serum GHbinding protein in rats is likely to be an alternatively spliced form of the GH receptor. 'Corresponding author. ^Present address: Embryogen, Princeton Forrestal Center, Princeton, New Jersey 08540 USA. Results Isolation and characterization of GH receptor and GHbinding protein cDNAsTo isolate clones that encode the rat GH receptor, a rat liver cDNA library was screened with two oligonucleo tide probes and a fragment of a rabbit GH receptor cDNA. On the basis of restriction mapping and prelimi nary DNA sequence analysis, the clones could be sepa rated into two classes. Two clones, RatRl and RatBPl, as representatives of each class, were sequenced com pletely. Figure 1 shows the nucleotide se...

Identification and Modulation of a Growth Hormone-Binding Protein in Rainbow Trout (Oncorhynchus mykiss) Plasma during Seawater Adaptation

“…GH-BP may arise from proteolytic cleavage of the membrane receptor (Baumann, 1991;Sotiropoulos et al, 1993) encoded by a single transcript of 4.5 kb (Leung et al, 1987) or by alternative splicing of a primary transcript which gives rise to two different mRNAs (Baumbach et al, 1989). One mRNA of 4.5 kb encodes the membrane receptor and another of 1.2 kb encodes the GH-BP, i.e., the extracellular domain of the GH receptor lacking the transmembrane and cytoplasmic domains.…”

Inactivation of Kupffer cells by gadolinium administration prevents lipopolysaccharide-induced decrease in liver insulin-like growth factor-I and IGF-binding protein-3 gene expression

“…IGF-I and growth hormone receptor (GHR) mRNA hepatic levels were measured by Northern blot hybridization using riboprobes (Roberts et al 1987, Baumbach et al 1989. The rat IGF-I and GHR probes were derived from a HindIII fragment of the pGEM-3 plasmid vector (Promega).…”

Identification of Sp1 as the transcription factor for the alternative promoter P2 of the bovine growth hormone receptor gene

“…In liver, where the highest levels of GHR mRNA are usually detected (Baumbach et al 1989, Mathews et al 1989, Hauser et al 1990, Martini et al 1997, GH-induced IGF-I enters the blood and accounts for the majority of the circulating IGF-I (Schwander et al 1983, Yakar et al 1999. In non-hepatic tissues, GH acts on GHR and may stimulate the local production of IGF-I.…”