Studies on negative regulation of insulin gene expression in non-pancreatic cells

胰岛素基因仅在胰腺B细胞中表达。因此，我们研究了人胰岛素基因5‘-分支区对其在非胰腺细胞中表达的影响。含有胰岛素基因增强子的区域(-339~-169bp)的存在显著抑制了胰岛素基因的启动子活性。这种抑制现象可以通过加入Forshlin或二丁酰cAMP来恢复，这表明在细胞外刺激增加细胞内cAMP水平的情况下，单靠这个区域不足以完全抑制胰岛素基因的表达。为了阐明葡萄糖转运蛋白(GLUT)是否是胰腺B细胞的葡萄糖感受器，我们还对GLUT进行了研究。我们从大鼠胰岛中提取了RNA，证实存在GLUT2和GLUT1的mRNA。我们还证实了葡萄糖对GLUT2基因表达的调节作用。通过以Zucker肥胖大鼠和Wistar肥胖大鼠为肥胖和糖尿病模型，我们发现GLUT2在两种模型大鼠中的表达均升高，提示GLUT2的表达升高可能与肥胖的发生有关

Insulin gene is expressed only in pancreatic B cells. So we have examined the effect of the 5'-branking region of the human insulin gene on its expression in non-pancreatic cells. The presence of the region containing the insulin gene enhancer (-339 to -169 bp) markedly repressed the promoter activity of the insulin gene. This suppressive phenomenon was restored by the addition of forsholin or dibutyryl cAMP suggesting that this region alone is not sufficient to repress completely insulin gene expression in the presence of extracellular stimuli which increase the intracellular cAMP level. These results show negative regulation of human insulin gene expression in non-pancreatu cells by these regions.In order to clarify whether glucose transporter (GLUT) is glucosensor of pancreatic B cells, we have also studied GLUT. We isolated RNA from rat islets of Langerhans and confirmed the presence of GLUT2 mRNA and GLUT1 mRNA. And we also demonstrated glucose regulates GLUT2 mRNA expression. These results suggest GLUT2 may be glucosensor of pancreatic B cells.By using Zucker fatty and Wistar fatty rats as models of obesity and diabetes, we showed that GLUT2 mRNA levels increase in both model rats and suggest that increassed GLUT2 mRNA levels may be associated with the development of obesity