Growth hormone regulates growth hormone receptor gene transcription in primary human thyroid cells

Isolated GHD: investigation and implication of JAK/STAT related genes before and after rhGH treatment

Isolated GH deficiency (IGHD) is a rare disorder that occurs as an idiopathic form in most cases. The pathway JAK/STAT promotes cellular growth and it could be implicated in this condition. In order to characterize IGHD in the pediatric population and identify genes differently expressed before and after GH therapy, we performed a quantitative evaluation of 84 genes related to the JAK/STAT pathway which, by promoting cellular growth. RT(2) Profiler PCR Array and the other/subsequent evaluations were performed in three children with severe IGHD before and after 6 months of GH therapy and in three matched normal children. Gene profiling was modified by the IGHD status and the GH therapy, with a modulation of GHR and some inflammatory genes such as CRP. We found a heterozygous nonsense mutation R43X in the GHR gene in two out of three IGHD subjects, despite a good response to therapy. After therapy cardiovascular markers linked to genes as IL6, IL8 and TNF-α displayed a trend toward reduction. Pre- and post therapy status differently affects gene expression. Mutational screening of GHR may be useful in investigating IGHD's etiology. Genes linked to inflammation suggest to evaluate cardiovascular risks also in pediatric IGHD subjects.

Insulin regulation of growth hormone receptor gene expression. Evidence for a transcriptional mechanism of down-regulation in rat hepatoma cells

The role of insulin in regulating responsiveness to growth hormone (GH) remains unclear. Continuous insulin treatment reduces GH binding, which suggests that insulin may effect growth hormone receptor (GHR) levels. The present study used rat hepatoma cells to examine the effects of insulin and GH on GHR gene expression. Prolonged insulin treatment (greater than 3h) significantly reduced GHR mRNA, and removal of insulin led to a gradual recovery. This effect of insulin occurred at physiologic concentrations, occurred many hours before the insulin-regulated decrease in GHR protein, and was mediated by reduction of GHR transcription. GH treatment dramatically reduced GHR protein, but caused only a modest reduction in GHR mRNA. These findings indicate that the heterologous reduction of GHR by insulin occurs via transcriptional downregulation, and the homologous reduction of GHR by GH occurs via a different mechanism. Furthermore, with insulin, extended time of exposure may be necessary for appreciable reduction of GHR.

IL-6-overexpression brings about growth impairment potentially through a GH receptor defect

This paper is concerned with growth retardation associated with overproduction of interleukin-6 (IL-6). As a model, we used MUP/hIL-6 transgenic mice in which human IL-6 cDNA is overexpressed under the control of a MUP gene enhancer/promoter. The growth-retardation of MUP/hIL-6 transgenic mice was paralleled by reduced serum levels of IGF-I. As shown, hepatic IGF-I mRNA levels were reduced in the transgenic mice. MUP/hIL-6 transgenic mice are in a state of growth hormone (GH)-resistance, since their serum GH levels are either normal or elevated. To identify possible steps in GH signaling which might be perturbed in the transgenic mice, we examined the synthesis of GH receptor (GHR) mRNA. We noted a twofold reduction of hepatic GHR mRNA in the transgenic mice. We therefore conclude that overexpression of IL-6 brings about growth impairment in part through a GH receptor defect.