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

ObjectiveTo elucidate the effect of interleukin-lβ (IL-Iβ) on human growth hormone (hGH) gene expression in a rat somatotropic pituitary cell line MtT/S.MethodsStably transfected MtT/S cells were firstly established by transfecting 484-Lucl plasmid which contained hGH gene promoter −484 to +30 bp and luciferase reporter gene. The effect of IL-Iβ 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.ResultsThe 103U/mL IL-lβ 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 μmol/L) and p38 mitogen-activated protein kinase (MAPK) inhibitor SB203580 (5 μmol/L) completely blocked the stimulatory effect of IL-lβ, and phosphatidylinositol-3-kinase (PI3-K) inhibitor LY294002 partly abolished the effect of IL-lβ. 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-lβ. A series of deletion constructs of hGH promoter were created to identify the DNA sequence that mediated the effect of IL-lβ, and results showed that the stimulatory effect of IL-lβ was abolished following deletion of the — 196 to −132 bp fragment.ConclusionsIL-lβ promotes GH secretion and synthesis in rat MtT/S somatotroph cells. The stimulatory effect of IL-lβ 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.