Mziaut Hassan, Mulligan Bernard, Hoboth Peter, Otto Oliver, Ivanova Anna, Herbig Maik, Schumann Desiree, Hildebrandt Tobias, Dehghany Jaber, Sönmez Anke, Münster Carla, Meyer-Hermann Michael, Guck Jochen, Kalaidzidis Yannis, Solimena Michele
Paul Langerhans Institute Dresden of the Helmholtz Center Munich at the Univ. Hospital, Faculty of Medicine Carl Gustav Carus, Technische Univ. Dresden, 01307 Dresden, Germany; German Center for Diabetes Research (DZD e.V.), 85674 Neuherberg, Germany.
Biotechnology Center Dresden, 01307 Dresden, Germany.
Mol Metab. 2016 Jun 10;5(8):656-668. doi: 10.1016/j.molmet.2016.05.015. eCollection 2016 Aug.
Insulin release from pancreatic islet β cells should be tightly controlled to avoid hypoglycemia and insulin resistance. The cortical actin cytoskeleton is a gate for regulated exocytosis of insulin secretory granules (SGs) by restricting their mobility and access to the plasma membrane. Prior studies suggest that SGs interact with F-actin through their transmembrane cargo islet cell autoantigen 512 (Ica512) (also known as islet antigen 2/Ptprn). Here we investigated how Ica512 modulates SG trafficking and exocytosis.
Transcriptomic changes in Ica512 (-/-) mouse islets were analyzed. Imaging as well as biophysical and biochemical methods were used to validate if and how the Ica512-regulated gene villin modulates insulin secretion in mouse islets and insulinoma cells.
The F-actin modifier villin was consistently downregulated in Ica512 (-/-) mouse islets and in Ica512-depleted insulinoma cells. Villin was enriched at the cell cortex of β cells and dispersed villin (-/-) islet cells were less round and less deformable. Basal mobility of SGs in villin-depleted cells was enhanced. Moreover, in cells depleted either of villin or Ica512 F-actin cages restraining cortical SGs were enlarged, basal secretion was increased while glucose-stimulated insulin release was blunted. The latter changes were reverted by overexpressing villin in Ica512-depleted cells, but not vice versa.
Our findings show that villin controls the size of the F-actin cages restricting SGs and, thus, regulates their dynamics and availability for exocytosis. Evidence that villin acts downstream of Ica512 also indicates that SGs directly influence the remodeling properties of the cortical actin cytoskeleton for tight control of insulin secretion.
胰腺胰岛β细胞的胰岛素释放应受到严格控制，以避免低血糖和胰岛素抵抗。皮质肌动蛋白细胞骨架通过限制胰岛素分泌颗粒（SGs）的移动性及其与质膜的接触，成为调节其胞吐作用的一道关卡。先前的研究表明，SGs通过其跨膜货物胰岛细胞自身抗原512（Ica512）（也称为胰岛抗原2/Ptprn）与F-肌动蛋白相互作用。在此，我们研究了Ica512如何调节SGs的运输和胞吐作用。
分析Ica512基因敲除（-/-）小鼠胰岛的转录组变化。采用成像以及生物物理和生化方法来验证Ica512调控的基因绒毛蛋白是否以及如何调节小鼠胰岛和胰岛素瘤细胞中的胰岛素分泌。
F-肌动蛋白修饰因子绒毛蛋白在Ica512基因敲除（-/-）小鼠胰岛和Ica512缺失的胰岛素瘤细胞中持续下调。绒毛蛋白在β细胞的细胞皮质富集，绒毛蛋白缺失（-/-）的胰岛细胞圆形度降低且变形能力减弱。绒毛蛋白缺失细胞中SGs的基础移动性增强。此外，在绒毛蛋白或Ica512缺失的细胞中，限制皮质SGs的F-肌动蛋白笼扩大，基础分泌增加，而葡萄糖刺激的胰岛素释放减弱。在Ica512缺失的细胞中过表达绒毛蛋白可逆转后者的变化，但反之则不然。
我们的研究结果表明，绒毛蛋白控制限制SGs的F-肌动蛋白笼的大小，从而调节其动力学和胞吐作用的可用性。绒毛蛋白在Ica512下游起作用的证据还表明，SGs直接影响皮质肌动蛋白细胞骨架的重塑特性，以严格控制胰岛素分泌。
