EFFECT OF INTERLEUKIN-1β ON GROWTH HORMONE GENE EXPRESSION AND ITS POSSIBLE MOLECULAR MECHANISM IN RAT MtT/S SOMATOTROPH CELLS

Objective To elucidate the effect ofinterleukin-1β (IL-1β) on human growth hormone (hGH) gene expression in a rat somatotropic pituitary cell line MtT/S.Methods Stably transfected MtT/S ceils 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-1β 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 103 U/mL IL-1β stimulated secretion and synthesis of GH,and promoted the 5'-promoter activity of GH gane in stably transfected MtT/SGL cells with the action of 1.38 times above the control.Among inhibitors of signaling transduetinn pathways,mitogen-aetivated 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-1β,and phosphatidylinositol-3-kinase (PI3-K) inhibitor LY294002 partly abolished the effect of IL,-1β.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-1β.A series of deletion constructs of hGH promoter were created to identify the DNA sequence that mediated the effect of IL- 1β,and results showed that the stimulatory effect of IL-1β was abolished following deletion of the-196 to-132 bp fragment.Conclusions IL-1β promotes GH secretion and synthesis in rat MtT/S somatotroph cells.The stimulatory effect of IL-1β 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.