Differential ligand binding and agonist-induced regulation characteristics of the two rainbow trout GH receptors, Ghr1 and Ghr2, in transfected cells

Abstract

Previously, we isolated and characterized two distinct GH receptor (GHR)-encoding mRNAs, ghr1 and ghr2, from rainbow trout. In this study, Chinese hamster ovary-K1 cells were individually transfected with plasmids that contained cDNAs encoding rainbow trout ghr1 or ghr2. High affinity binding of 125 I-salmonid GH (sGH) by the expressed receptors was saturable, displaceable, and ligand selective. Whole-cell binding analysis revealed a single class of binding site; for Ghr1While salmonid prolactin (sPrl) displaced 125 I-sGH from both Ghr1 and Ghr2, the affinity of either receptor subtype for sPrl was substantially less than for sGH; salmonid somatolactin, another member of the GH-PRL family, did not displace labeled sGH except at pharmacological concentrations.125 I-sGH was internalized by Ghr1-and Ghr2-expressing cells in a time-dependent manner; the maximum internalization reached was 71% for Ghr1 and 55% for Ghr2. Long-term exposure (24 h) of transfected cells to sGH up-regulated surface expression of both Ghr1 and Ghr2; however, sGH induced surface expression of Ghr1 to a greater extent than that of Ghr2. These results indicate that rainbow trout ghrs display both overlapping and distinct characteristics that may be important for ligand selection and differential action in target organs.

Lack of hormonal stimulation prevents the landlocked Biwa salmon (Oncorhynchus masousubspecies) from adapting to seawater

“…However, it depended on the strains, of which subtype showed a change; in masu salmon, ghr2 showed a peak in April, whereas ghr1 increased from November to December in amago salmon. Although differences in the ligand-binding characters and agonist-induced regulation features between trout Ghr1 and Ghr2 expressed in a mammalian cell line have been reported (41), their relative roles in smoltification are not known at present. Comparing these strains may be useful to further investigate the roles of two Ghrs.…”

Growth hormone-stimulated insulin-like growth factor-1 expression in rainbow trout (Oncorhynchus mykiss) hepatocytes is mediated by ERK, PI3K-AKT, and JAK-STAT

“…The ability of antibodies to human ERK, Akt, JAK2, and STAT5 to detect their counterparts in hepatocytes isolated from rainbow trout compared with Chinese hamster ovary-K1 cells (American Type Culture Collection, Rockville, MD), cultured as described previously (25), was assessed by Western blot analysis ( Fig. 1).…”

“…GHRs have been characterized from over 100 species, including some 25 species of fish. Fish possess multiple GHRs that appear to have derived from several genome duplication events over the course of their evolution (8,25).…”

Rapid evolution of osmoregulatory function by modification of gene transcription in steelhead trout

“…GHRII acts to modulate tissue-specific activity of GH (Norbeck et al 2007). The role of GHRII as the receptor of growth hormone has been verified by protein-protein interaction experiments (Reindl et al 2009). GHRII is upregulated during saltwater exposure (Poppinga et al 2007), differentially expressed among anadromous and landlocked strains of Atlantic salmon (S. salar), and exhibits seasonal elevations that are associated with smolting and growth in Atlantic salmon (Nilsen et al 2008).…”