Human growth hormone receptor (GHR) expression in obesity: II. Regulation of the human GHR gene by obesity-related factors

• Published in: International Journal of Obesity Vol. 35; no. 12; pp. 1520 - 1529
• Main Authors: Erman, A, Wabitsch, M, Goodyer, C.G
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group 01.12.2011; Nature Publishing Group UK
• Subjects: 631/208/200; 692/699/2743/393; Activities; Adipocytes; Adipocytes - metabolism; Adipose tissue; Adipose Tissue - metabolism; Analysis; Arrhythmias, Cardiac - metabolism; Arrhythmias, Cardiac - pathology; Biological and medical sciences; Biomarkers - metabolism; Body fat; chromatin; Chromatin Immunoprecipitation; Development and progression; dexamethasone; Down-Regulation; Drug dosages; Epidemiology; gene expression regulation; gene overexpression; genes; Genetic aspects; Genetic Diseases, X-Linked; Gigantism - metabolism; Gigantism - pathology; glucocorticoids; Glucocorticoids - genetics; Glucocorticoids - metabolism; Growth hormones; Health Promotion and Disease Prevention; Heart Defects, Congenital - metabolism; Heart Defects, Congenital - pathology; HEK293 Cells; Hormone receptors; human growth; Humans; Hypoxia; Hypoxia-Inducible Factor 1, alpha Subunit - genetics; Hypoxia-Inducible Factor 1, alpha Subunit - metabolism; Intellectual Disability - metabolism; Intellectual Disability - pathology; Internal Medicine; Medical sciences; Medicine; Medicine & Public Health; Membrane Proteins - genetics; Membrane Proteins - metabolism; messenger RNA; Metabolic Diseases; Mutagenesis; Mutagenesis, Site-Directed; Obesity; Obesity - metabolism; original-article; Pediatrics; Physiological aspects; precipitin tests; Public Health; response elements; Reverse Transcriptase Polymerase Chain Reaction; RNA, Messenger - metabolism; site-directed mutagenesis; Somatotropin; somatotropin receptors; transcription (genetics); transcription factor NF-kappa B; Transcription, Genetic; tumor necrosis factor-alpha; Tumor Necrosis Factor-alpha - genetics; Tumor Necrosis Factor-alpha - metabolism; Tumor necrosis factor-TNF; Tumors; Canada; Montreal Quebec Canada; hypoxia; TNFα; GH resistance; growth hormone receptor; adipocyte; HIF-1α; glucocorticoids; Adipocyte; Glucocorticoid; Regulation(control); Gene; Genetics; Nutritional status; Tumor necrosis factor α; Human; Obesity; Oxygen; Nutrition; Cytokine; Nutrition disorder; Metabolic diseases; Gene expression; Resistance; Somatotropin; Adenohypophyseal hormone; Hypoxia; Transcription factor HIF1
• ISSN: 0307-0565; 1476-5497
• DOI: 10.1038/ijo.2011.10

Background and methods: In our previous analyses, we found significantly lower levels of growth hormone receptor (GHR) mRNA in adipose tissues of obese than in those of lean individuals, suggesting that idiopathic obesity involves GH resistance due to decreased GHR availability. To understand the mechanism(s) behind this downregulation, we performed an in silico analysis of the three most relevant GHR gene promoters, which revealed putative response elements (REs) for a number of obesity adipose-associated factors, including tumor necrosis factor-alpha (TNFα), hypoxia-inducible factor-1-alpha (HIF-1α) and glucocorticoids. We then characterized the dose-dependent effects of these factors on GHR expression in HEK293 cells and in mature human SGBS (Simpson–Golabi–Behmel syndrome) adipocytes using quantitative reverse transcriptase-PCR and assessed the function of their putative REs by luciferase-reporter assays, site-directed mutagenesis and chromatin immunoprecipitation (ChIP) assays. Results: TNFα treatments significantly reduced GHR mRNA levels and GHR promoter activities at doses 10 ng ml−1 in both cell lines. Transient overexpression of HIF-1α or exposure to the hypoxia mimetic CoCl2 significantly increased GHR mRNA levels and promoter activities. Dexamethasone had biphasic effects: there was a significant increase in GHR mRNA levels at 10−10 M and in promoter activities at 10−10 and 10−8 M, whereas a significant decrease in both mRNA levels and promoter activities occurred at 10−6 M. Site-directed mutagenesis of the putative nuclear factor-κB, HIF-1α and glucocorticoid REs resulted in the loss of these effects, whereas ChIP analysis confirmed specific transcription factor–promoter interactions. Conclusions: Our results suggest that the increased activity of TNFα, HIF-1α and glucocorticoids in obese adipose tissues could alter GHR gene transcription through specific REs and that TNFα may be involved in the development of GH resistance.