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Transforming growth factor β induction of insulin gene expression is mediated by pancreatic and duodenal homeobox gene‐1 in rat insulinoma cells

Sayo, Yoshitaka, Hosokawa, Hitoshi, Imachi, Hitomi, Murao, Koji, Sato, Makoto, Wong, Norman C. W., Ishida, Toshihiko, Takahara, Jiro
European journal of biochemistry 2000 v.267 no.4 pp. 971-978
Western blotting, binding sites, gel electrophoresis, gene expression, genes, insulin, islets of Langerhans, messenger RNA, mutants, rats, transcription factors, transforming growth factor beta
Although transforming growth factor‐beta (TGF‐β) stimulates pancreatic islet cells to synthesize and secret insulin, the mechanism underlying this effect is not known. To investigate this question, we examined the insulin promoter activity focusing on a transcription factor, pancreatic and duodenal homeobox gene‐1 (PDX‐1) that binds to the A3 element of the rat insulin promoter. Studies performed using the rat insulinoma cell line, INS‐1 showed that TGF‐β stimulation of endogenous insulin mRNA expression correlated with increased activity of a reporter construct containing the insulin promoter. A potential mechanism for this increase arose from, electrophoretic mobility shift assay showing that the nuclear extract from TGF‐β treated cells contained higher levels of A3 binding activity. Western blot analysis confirmed that PDX‐1 was increased in the nuclear extract from INS‐1 cells treated with TGF‐β. As expected, a mutant insulin promoter that lacked the PDX‐1 binding site was not stimulated by TGF‐β. In summary, the results of these studies show that TGF‐β stimulates the transcription of insulin gene and this action is mediated by the transcription factor, PDX‐1.