Roche E, Assimacopoulos-Jeannet F, Witters L A, Perruchoud B, Yaney G, Corkey B, Asfari M, Prentki M
Molecular Nutrition Unit, Department of Nutrition, University of Montreal, H3C 3J7 Montréal, Québec, Canada.
J Biol Chem. 1997 Jan 31;272(5):3091-8. doi: 10.1074/jbc.272.5.3091.
Chronic elevation in glucose has pleiotropic effects on the pancreatic beta-cell including a high rate of insulin secretion at low glucose, beta-cell hypertrophy, and hyperplasia. These actions of glucose are expected to be associated with the modulation of the expression of a number of glucose-regulated genes that need to be identified. To further investigate the molecular mechanisms implicated in these adaptation processes to hyperglycemia, we have studied the regulation of genes encoding key glycolytic enzymes in the glucose-responsive beta-cell line INS-1. Glucose (from 5 to 25 mM) induced phosphofructokinase-1 (PFK-1) isoform C, glyceraldehyde-3-phosphate dehydrogenase (GAPDH) (4-fold), and L-pyruvate kinase (L-PK) (7-fold) mRNAs. In contrast the expression level of the glucokinase (Gk) and 6-phosphofructo-2-kinase transcripts remained unchanged. Following a 3-day exposure to elevated glucose, a similar induction was observed at the protein level for PFK-1 (isoforms C, M, and L), GAPDH, and L-PK, whereas M-PK expression only increased slightly. The study of the mechanism of GAPDH induction indicated that glucose increased the transcriptional rate of the GAPDH gene but that both transcriptional and post transcriptional effects contributed to GAPDH mRNA accumulation. 2-Deoxyglucose did not mimic the inductive effect of glucose, suggesting that increased glucose metabolism is involved in GAPDH gene induction. These changes in glycolytic enzyme expression were associated with a 2-3-fold increase in insulin secretion at low (2-5 mM) glucose. The metabolic activity of the cells was also elevated, as indicated by the reduction of the artificial electron acceptor 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium. A marked deposition of glycogen, which was readily mobilized upon lowering of the ambient glucose, and increased DNA replication were also observed in cells exposed to elevated glucose. The results suggest that a coordinated induction of key glycolytic enzymes as well as massive glycogen deposition are implicated in the adaptation process of the beta-cell to hyperglycemia to allow for chronically elevated glucose metabolism, which, in this particular fuel-sensitive cell, is linked to metabolic coupling factor production and cell activation.
长期血糖升高对胰腺β细胞具有多效性作用，包括在低糖水平下胰岛素分泌率高、β细胞肥大和增生。葡萄糖的这些作用预计与许多有待确定的葡萄糖调节基因的表达调控有关。为了进一步研究这些适应高血糖过程中涉及的分子机制，我们研究了葡萄糖反应性β细胞系INS-1中编码关键糖酵解酶的基因的调控。葡萄糖（从5到25 mM）诱导磷酸果糖激酶-1（PFK-1）同工型C、甘油醛-3-磷酸脱氢酶（GAPDH）（4倍）和L-丙酮酸激酶（L-PK）（7倍）的mRNA表达。相比之下，葡萄糖激酶（Gk）和6-磷酸果糖-2-激酶转录本的表达水平保持不变。在暴露于高糖3天后，在蛋白质水平上观察到PFK-1（同工型C、M和L）、GAPDH和L-PK有类似的诱导，而M-PK表达仅略有增加。对GAPDH诱导机制的研究表明，葡萄糖增加了GAPDH基因的转录速率，但转录和转录后效应都有助于GAPDH mRNA的积累。2-脱氧葡萄糖不能模拟葡萄糖的诱导作用，表明葡萄糖代谢增加参与了GAPDH基因的诱导。糖酵解酶表达的这些变化与低（2-5 mM）葡萄糖水平下胰岛素分泌增加2-3倍有关。细胞的代谢活性也升高了，这通过人工电子受体3-[4,5-二甲基噻唑-2-基]-2,5-二苯基四氮唑的减少来表明。在暴露于高糖的细胞中还观察到糖原的大量沉积，当环境葡萄糖降低时糖原很容易被动员，以及DNA复制增加。结果表明，关键糖酵解酶的协同诱导以及大量糖原沉积参与了β细胞对高血糖的适应过程，以允许长期升高的葡萄糖代谢，在这个对特定燃料敏感的细胞中，这与代谢偶联因子的产生和细胞激活有关。
