Zhang S, Kim K H
Department of Biochemistry, Purdue University, West Lafayette, IN 47907, USA.
Cell Signal. 1998 Jan;10(1):35-42. doi: 10.1016/s0898-6568(97)00070-3.
The current model of the nutrient sensing mechanism in pancreatic beta-cells implies that malonyl-CoA plays a key role. According to this hypothesis, glucose activation of acetyl-CoA carboxylase triggers a rapid production of malonyl-CoA which inhibits carnitine palmitoyltransferase 1 and the importation of fatty acyl-CoA into the mitochondria for oxidation. The increase in cytosolic long chain fatty acyl-CoA leads to the exocytosis of insulin by a mechanism which has not yet been clearly defined. To obtain direct evidence that ACC plays a central role in this process, we generated stable transfectants of an insulin secreting cell line (INS-1) that express ACC specific antisense mRNA. The amounts of ACC mRNA and the protein level were specifically decreased in these stable clones compared to those of the control cells. The glucose activation of ACC in these cells was also significantly diminished. Both acute and long-term induction of insulin secretion by glucose were decreased. This decrease was inversely correlated to the levels of ACC activity in clones. In these clones, the insulin secretion induced by other nutrients, amino acids and ketocaproate, is also impaired, while the KCl-induced insulin secretion remains unchanged. Decreased ACC expression was accompanied by impaired malonyl-CoA production and elevated fatty acid oxidation. The expressions of the pancreatic specific glucokinase, glucose transporter 2 or beta-actin in these cells, as well as glucose utilisation were not affected, suggesting that the effect of the expression of the ACC mRNA specific gene on insulin secretion is specifically related to the decrease in the amount of ACC gene products. These results provide direct evidence of a causal relationship between ACC and insulin secretion.
目前胰腺β细胞中营养物质感应机制的模型表明，丙二酰辅酶A起着关键作用。根据这一假说，乙酰辅酶A羧化酶的葡萄糖激活引发丙二酰辅酶A的快速产生，丙二酰辅酶A抑制肉碱棕榈酰转移酶1以及脂肪酸辅酶A进入线粒体进行氧化。胞质长链脂肪酸辅酶A的增加通过一种尚未明确的机制导致胰岛素的胞吐作用。为了获得直接证据证明乙酰辅酶A羧化酶（ACC）在此过程中起核心作用，我们构建了表达ACC特异性反义mRNA的胰岛素分泌细胞系（INS-1）的稳定转染子。与对照细胞相比，这些稳定克隆中ACC mRNA的量和蛋白质水平均特异性降低。这些细胞中ACC的葡萄糖激活也显著减弱。葡萄糖对胰岛素分泌的急性和长期诱导均减少。这种减少与克隆中ACC活性水平呈负相关。在这些克隆中，由其他营养物质、氨基酸和酮己酸诱导的胰岛素分泌也受损，而氯化钾诱导的胰岛素分泌保持不变。ACC表达降低伴随着丙二酰辅酶A产生受损和脂肪酸氧化增加。这些细胞中胰腺特异性葡萄糖激酶、葡萄糖转运蛋白2或β-肌动蛋白的表达以及葡萄糖利用均未受影响，这表明ACC mRNA特异性基因表达对胰岛素分泌的影响与ACC基因产物量的减少特异性相关。这些结果提供了ACC与胰岛素分泌之间因果关系的直接证据。
