Department of Endocrinology and Metabolism, Faculty of Medicine, Kagawa University, Kita-gun, Kagawa, Japan.
Life Science Research Center, Kagawa University, Kita-gun, Kagawa, Japan.
J Mol Endocrinol. 2018 Oct 15;61(4):185-193. doi: 10.1530/JME-18-0167.
ATP-binding cassette transporter A1 (ABCA1), a 254-kD membrane protein, is a key regulator of lipid efflux from cells to apolipoproteins. ABCA1 in pancreatic β-cells influences insulin secretion and cholesterol homeostasis. Tumor necrosis factor (TNF)-α is a pleiotropic cytokine that elicits a wide spectrum of physiological events, including cell proliferation, differentiation, and apoptosis, and is also known to decrease glucose-dependent insulin secretion in pancreatic islets. In the present study, we examined the role of TNF-α on ABCA1 expression in rat pancreatic islets and INS-1 cells. ABCA1 protein levels decreased in response to rising concentrations of TNF-α in pancreatic islets. Real-time polymerase chain reaction analysis showed a significant decrease in ABCA1 mRNA expression. In parallel with its effect on endogenous ABCA1 mRNA levels, TNF-α suppressed the activity of a reporter construct containing the ABCA1 promoter. This effect was abrogated by BIRB796, but not by SB203580 or PD98095. The constitutively active form of p38 mitogen-activated protein kinase (MAPK) γ suppressed ABCA1 promoter activity but not p38-MAPK (α, β), while a dominant-negative mutant of p38-MAPK γ blocked the effect of TNF-α on ABCA1 promoter activity. BIRB796 inhibited the increased cholesterol ester content induced by TNF-α. However, BIRB796 had no effect on the decreased insulin content nor ABCA1 suppression caused by TNF-α in INS-1 cells. In summary, TNF-α suppressed the expression of endogenous ABCA1 in pancreatic islets and INS-1 cells. These findings raise the possibility that TNF-α may affect insulin secretion by controlling ABCA1 expression.
三磷酸腺苷结合盒转运子 A1（ABCA1），一种 254kD 的膜蛋白，是细胞内脂质向载脂蛋白转运的关键调节蛋白。胰腺β细胞中的 ABCA1 影响胰岛素分泌和胆固醇稳态。肿瘤坏死因子（TNF）-α 是一种多效细胞因子，可引发广泛的生理事件，包括细胞增殖、分化和凋亡，也已知会降低胰岛中的葡萄糖依赖性胰岛素分泌。在本研究中，我们研究了 TNF-α 在大鼠胰岛和 INS-1 细胞中对 ABCA1 表达的作用。胰腺胰岛中 TNF-α 浓度升高时，ABCA1 蛋白水平下降。实时聚合酶链反应分析显示 ABCA1 mRNA 表达显著下降。与对内源性 ABCA1 mRNA 水平的作用平行，TNF-α 抑制含有 ABCA1 启动子的报告构建体的活性。这种作用被 BIRB796 消除，但 SB203580 或 PD98095 没有。组成型激活的 p38 丝裂原激活蛋白激酶（MAPK）γ抑制 ABCA1 启动子活性，但不抑制 p38-MAPK（α、β），而 p38-MAPK γ的显性失活突变阻止了 TNF-α 对 ABCA1 启动子活性的影响。BIRB796 抑制了 TNF-α 诱导的胆固醇酯含量增加。然而，BIRB796 对 TNF-α引起的 INS-1 细胞中胰岛素含量减少或 ABCA1 抑制没有影响。总之，TNF-α 抑制了胰腺胰岛和 INS-1 细胞中内源性 ABCA1 的表达。这些发现提示 TNF-α 可能通过控制 ABCA1 表达来影响胰岛素分泌。
