Tomas Alejandra, Yermen Barbara, Min Le, Pessin Jeffrey E, Halban Philippe A
Department of Genetic Medicine and Development, University of Geneva Medical School, Switzerland.
J Cell Sci. 2006 May 15;119(Pt 10):2156-67. doi: 10.1242/jcs.02942. Epub 2006 Apr 25.
We have previously isolated two MIN6 beta-cell sublines, B1, highly responsive to glucose-stimulated insulin secretion, and C3, markedly refractory (Lilla, V., Webb, G., Rickenbach, K., Maturana, A., Steiner, D. F., Halban, P. A. and Irminger, J. C. (2003) Endocrinology 144, 1368-1379). We now demonstrate that C3 cells have substantially increased amounts of F-actin stress fibres whereas B1 cells have shorter cortical F-actin. Consistent with these data, B1 cells display glucose-dependent actin remodelling whereas, in C3 cells, F-actin is refractory to this secretagogue. Furthermore, F-actin depolymerisation with latrunculin B restores glucose-stimulated insulin secretion in C3 cells. In parallel, glucose-stimulated ERK1/2 activation is greater in B1 than in C3 cells, and is potentiated in both sublines following F-actin depolymerisation. Glucose-activated phosphoERK1/2 accumulates at actin filament tips adjacent to the plasma membrane, indicating that these are the main sites of action for this kinase during insulin secretion. In addition, B1 cell expression of the calcium-dependent F-actin severing protein gelsolin is >100-fold higher than that of C3 cells. Knock-down of gelsolin reduced glucose-stimulated insulin secretion, whereas gelsolin over-expression potentiated secretion from B1 cells. Gelsolin localised along depolymerised actin fibres after glucose stimulation. Taken together, these data demonstrate that F-actin reorganization prior to insulin secretion requires gelsolin and plays a role in the glucose-dependent MAPK signal transduction that regulates beta-cell insulin secretion.
我们之前分离出了两个MIN6β细胞亚系，即对葡萄糖刺激的胰岛素分泌高度敏感的B1细胞系和明显难治的C3细胞系（Lilla, V., Webb, G., Rickenbach, K., Maturana, A., Steiner, D. F., Halban, P. A.和Irminger, J. C. (2003) Endocrinology 144, 1368 - 1379）。我们现在证明，C3细胞中F - 肌动蛋白应力纤维的数量大幅增加，而B1细胞中的皮质F - 肌动蛋白较短。与这些数据一致的是，B1细胞表现出葡萄糖依赖性肌动蛋白重塑，而在C3细胞中，F - 肌动蛋白对这种促分泌剂不敏感。此外，用拉特罗霉素B使F - 肌动蛋白解聚可恢复C3细胞中葡萄糖刺激的胰岛素分泌。同时，葡萄糖刺激的ERK1/2激活在B1细胞中比在C3细胞中更强，并且在两个亚系中F - 肌动蛋白解聚后均增强。葡萄糖激活的磷酸化ERK1/2在质膜附近的肌动蛋白丝末端积累，表明这些是该激酶在胰岛素分泌过程中的主要作用位点。此外，钙依赖性F - 肌动蛋白切断蛋白凝溶胶蛋白在B1细胞中的表达比在C3细胞中高100倍以上。敲低凝溶胶蛋白可降低葡萄糖刺激的胰岛素分泌，而凝溶胶蛋白的过表达则增强B1细胞的分泌。葡萄糖刺激后，凝溶胶蛋白定位于解聚的肌动蛋白纤维上。综上所述，这些数据表明胰岛素分泌之前的F - 肌动蛋白重组需要凝溶胶蛋白，并在调节β细胞胰岛素分泌的葡萄糖依赖性MAPK信号转导中发挥作用。
