[Mechanism of interleukin-1beta increasing growth hormone expression in rat pituitary GH3 cells].

Objective: To investigate the effect(s) of interleukin-1beta (IL-1beta) on the activity of human growth hormone (hGH) gene promoter in rat pituitary GH3 cells and the molecular mechanism.

Methods: The method of luciferase reporter gene was used. We firstly established stable GH3 cell line which contains hGH gene promoter -484-30 bp and luciferase reporter gene. After treating these cells with IL-1beta or IL-1beta plus various signaling transduction inhibitors, the concentration of GH in the medium and lysate of GH3 cells and luciferase activities in GH3 cells were measured to reflect the effect of IL-1beta on secretion and synthesis of GH and the promoter activity of the hGH gene and the molecular mechanism. Results IL-1beta (10-10(4)U/ml) increased secretion and synthesis of GH. IL-1beta at levels of 10(2)-10(4) U/ml promoted the luciferase expression in stable GH3 cells, and the maximal action was 1.61 times of the control (P < 0.001). Among the inhibitors of intracellular signaling transduction pathways, mitogen-activated protein kinases (MAPK) inhibitor PD98059 (40 micromol/L) and p38 MAPK inhibitor SB203580 (5 micromol/L) completely blocked the stimulatory effect of IL-1beta, and phosphoinositide 3-kinase (PI3-K) inhibitor LY294002 (10 micromol/L) partly blocked the induction of IL-1beta. Neither overexpression of Pit-1 nor inhibiting Pit-1 expression affected IL-1beta induction of hGH promoter activity. The stimulatory effect of IL-1beta was abolished following deletion of the -196 to -132 bp fragment.

Conclusions: IL-1beta increases the activity of hGH gene promoter in rat pituitary GH3 cells. This stimulatory effect of IL-1beta appears to require the intracellular MAPK, p38 MAPK, and PI3-K dependent signaling pathways. The effect of IL-1beta requires the promoter sequence that spans the -196 to -132 bp fragment of the gene, but it is unrelated to Pit-1 protein.