Objective To investigate the effect of interleukin-6（IL-6）on the human growth hormone（hGH）gene expression in a rat somatotropic pituitary cell line MtT/S.Methods The plasmids containing various lengths of hGH gene 5’-promoter fragments were constructed.Stably transfected MtT/S cells were created by cotransfecting the above plasmids and pcDNA3.1（+）with DMRIE-C transfection reagent.After the administration of these cells with IL-6 and/or various inhibitors of signaling transduction pathways

the luciferase activities in MtT/S cells lysis were assayed to demonstrate the effects of IL-6 on hGH gene promoter activity and possibly involved mechanism.Results The 103 U/mL IL-6 stimulated GH secretion and synthesis

and promoted the 5’-promoter activity of GH gene in stably transfected MtT/SGL cells with the action of 1.69 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-6.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 IL-6 induction of hGH promoter activity.A series of deletion constructs of hGH promoter were created to identify the DNA sequence that mediated the effect of IL-6.The results showed that the stimulatory effect of IL-6 was abolished following deletion of the-196 to-132 bp fragment.Conclusions IL-6 promotes GH secretion and synthesis by rat MtT/S somatotroph cells.The stimulatory effect of IL-6 on hGH gene promoter appears to require the activation of MEK and p38 MAPK

and a fragment of promoter sequence that spans the-196 to-132 bp of the gene

but may be unlinked with Pit-1 protein.