Filamentous actin (F-actin) cytoskeletal remodeling is critical for glucose-stimulated insulin secretion (GSIS) in pancreatic β-cells, and its dysregulation causes type 2 diabetes. The adaptor protein APPL1 promotes first-phase GSIS by up-regulating soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) protein expression. However, whether APPL2 (a close homology of APPL1 with the same domain organization) plays a role in β-cell functions is unknown. Here, we show that APPL2 enhances GSIS by promoting F-actin remodeling via the small GTPase Rac1 in pancreatic β-cells. β-cell specific abrogation of APPL2 impaired GSIS, leading to glucose intolerance in mice. APPL2 deficiency largely abolished glucose-induced first- and second-phase insulin secretion in pancreatic islets. Real-time live-cell imaging and phalloidin staining revealed that APPL2 deficiency abolished glucose-induced F-actin depolymerization in pancreatic islets. Likewise, knockdown of APPL2 expression impaired glucose-stimulated F-actin depolymerization and subsequent insulin secretion in INS-1E cells, which were attributable to the impairment of Ras-related C3 botulinum toxin substrate 1 (Rac1) activation. Treatment with the F-actin depolymerization chemical compounds or overexpression of gelsolin (a F-actin remodeling protein) rescued APPL2 deficiency-induced defective GSIS. In addition, APPL2 interacted with Rac GTPase activating protein 1 (RacGAP1) in a glucose-dependent manner via the bin/amphiphysin/rvs-pleckstrin homology (BAR-PH) domain of APPL2 in INS-1E cells and HEK293 cells. Concomitant knockdown of RacGAP1 expression reverted APPL2 deficiency-induced defective GSIS, F-actin remodeling, and Rac1 activation in INS-1E cells. Our data indicate that APPL2 interacts with RacGAP1 and suppresses its negative action on Rac1 activity and F-actin depolymerization thereby enhancing GSIS in pancreatic β-cells.

丝状肌动蛋白（F-actin）的细胞骨架重塑对于胰腺β细胞中葡萄糖刺激的胰岛素分泌（GSIS）至关重要，其失调会导致2型糖尿病。衔接蛋白APPL1通过上调可溶性N促进第一阶段GSIS-乙基马来酰亚胺敏感因子附着蛋白受体（SNARE）的蛋白表达。然而，尚不清楚APPL2（具有相同域结构的APPL1的紧密同源性）是否在β细胞功能中起作用。在这里，我们显示APPL2通过促进胰腺β细胞中小的GTPase Rac1促进F-肌动蛋白重塑来增强GSIS。APPL2的β细胞特异性消除会破坏GSIS，导致小鼠体内葡萄糖不耐受。APPL2缺乏症在很大程度上消除了胰岛中葡萄糖诱导的第一阶段和第二阶段胰岛素分泌。实时活细胞成像和鬼笔环肽染色显示，APPL2缺乏症消除了胰岛中葡萄糖诱导的F-肌动蛋白解聚。同样地，APPL2表达的敲低会损害葡萄糖刺激的F-肌动蛋白的解聚作用，进而损害INS-1E细胞中的胰岛素分泌，这归因于与Ras相关的C3肉毒杆菌毒素底物1（Rac1）激活的损伤。用F-肌动蛋白解聚化合物或过表达凝溶胶蛋白（F-肌动蛋白重塑蛋白）的治疗可以挽救APPL2缺乏症引起的GSIS缺陷。此外，APPL2通过INS-1E细胞和HEK293细胞中APPL2的bin /两性/ rvs-pleckstrin同源性（BAR-PH）域以葡萄糖依赖的方式与Rac GTPase活化蛋白1（RacGAP1）相互作用。伴随敲低RacGAP1表达可恢复INS-1E细胞中APPL2缺陷诱导的缺陷GSIS，F-肌动蛋白重塑和Rac1激活。我们的数据表明APPL2与RacGAP1相互作用并抑制其对Rac1活性和F-肌动蛋白解聚的负面作用，从而增强了胰腺β细胞的GSIS。