Hettiarachchi K D, Zimmet P Z, Myers M A
Department of Biochemistry and Molecular Biology, Monash University, Clayton, Victoria, Australia.
Cell Biol Toxicol. 2006 May;22(3):169-81. doi: 10.1007/s10565-006-0054-8.
Inhibition of endosomal acidification disturbs insulin signaling in both liver and adipose cells. In this study we used MIN6 beta cells to determine whether bafilomycin, a potent inhibitor of the proton-translocating vacuolar ATPase, disrupts insulin signaling in islet beta cells. Pretreatment of MIN6 cells with varying concentrations of bafilomycin according to a time course revealed concentration and time-dependent changes in phosphorylation of insulin receptor signaling components. Increased phosphorylation of insulin receptor (IR), IRS2 and Akt was prolonged at low bafilomycin concentrations (10 and 50 nmol/L), whereas at high concentrations (100 and 200 nmol/L) phosphorylation rapidly returned to basal levels or below. Akt activation was demonstrated by transient increases in phosphorylation of BAD, cytoplasmic retention of FoxO1 and increased preproinsulin mRNA. Bcl2 expression was also transiently increased but reduced after 30 min exposure to bafilomycin, and this coincided with reduced cell viability. Thus, in beta cells inhibition of endosomal acidification by low concentrations of bafilomycin transiently increases insulin signaling, whereas high concentrations promote cell death. Bafilomycin and other agents that interfere with insulin signaling may contribute to diabetes development through disturbing homeostatic control of beta cell growth.
内体酸化的抑制会扰乱肝脏和脂肪细胞中的胰岛素信号传导。在本研究中，我们使用MIN6β细胞来确定质子转运液泡ATP酶的强效抑制剂巴弗洛霉素是否会破坏胰岛β细胞中的胰岛素信号传导。根据时间进程用不同浓度的巴弗洛霉素预处理MIN6细胞，结果显示胰岛素受体信号传导成分的磷酸化存在浓度和时间依赖性变化。在低浓度巴弗洛霉素（10和50 nmol/L）下，胰岛素受体（IR）、IRS2和Akt的磷酸化增加持续时间延长，而在高浓度（100和200 nmol/L）下，磷酸化迅速恢复到基础水平或更低。BAD磷酸化的短暂增加、FoxO1的细胞质滞留以及前胰岛素原mRNA的增加证明了Akt的激活。Bcl2表达也短暂增加，但在暴露于巴弗洛霉素30分钟后降低，这与细胞活力降低相吻合。因此，在β细胞中，低浓度巴弗洛霉素对内体酸化的抑制会短暂增加胰岛素信号传导，而高浓度则会促进细胞死亡。巴弗洛霉素和其他干扰胰岛素信号传导的药物可能通过扰乱β细胞生长的稳态控制而导致糖尿病的发展。
