Effect of interleukin-1 beta on growth hormone gene expression and its possible molecular mechanism in rat MtT/S somatotroph cells.

OBJECTIVE:To elucidate the effect of interleukin-1 beta (IL-1 beta) on human growth hormone (hGH) gene expression in a rat somatotropic pituitary cell line MtT/S. METHODS:Stably transfected MtT/S cells were firstly established by transfecting 484-Luc1 plasmid which contained hGH gene promoter -484 to +30 bp and luciferase reporter gene. The effect of IL-1 beta on hGH gene expression was determined by assaying the luciferase activities. RT-PCR method was also used to determine whether IL-1 recepor mRNA was expressed in MtT/S cells. RESULTS:The 10(3) U/mL IL-1 beta stimulated secretion and synthesis of GH, and promoted the 5'-promoter activity of GH gene in stably transfected MtT/SGL cells with the action of 1.38 times above the control. Among inhibitors of signaling transduction pathways, mitogen-activated protein kinase kinase (MAPKK/MEK) inhibitor PD98059 (40 micromol/L) and p38 mitogen-activated protein kinase (MAPK) inhibitor SB203580 (5 micromol/L) completely blocked the stimulatory effect of IL-1 beta, and phosphatidylinositol-3-kinase (PI3-K) inhibitor LY294002 partly abolished the effect of IL-1 beta. Western blot analysis further confirmed the activation of phosphorylated MEK and p38 MAPK in MtT/SGL cells. Neither over-expression of Pit-1 nor inhibition of Pit-1 expression affected induction of hGH promoter activity by IL-1 beta. A series of deletion constructs of hGH promoter were created to identify the DNA sequence that mediated the effect of IL-1 beta, and results showed that the stimulatory effect of IL-1 beta was abolished following deletion of the -196 to -132 bp fragment. CONCLUSIONS:IL-1 beta promotes GH secretion and synthesis in rat MtT/S somatotroph cells. The stimulatory effect of IL-1 beta on hGH gene promoter appears to require the activation of MEK, p38 MAPK, PI3-K, and a fragment of promoter sequence that spans the -196 to -132 bp of the gene, but it may be unlinked with Pit-1 protein.