Lim Chun-Yan, Han Weiping
a Laboratory of Metabolic Medicine; Singapore Bioimaging Consortium ; Agency for Science; Technology and Research ; Singapore , Republic of Singapore.
Bioarchitecture. 2014;4(6):210-4. doi: 10.1080/19490992.2015.1031949. Epub 2015 Aug 17.
It is well established that insulin-induced remodeling of actin filaments into a cortical mesh is required for insulin-stimulated GLUT4 exocytosis. Akt2 and its downstream effectors play a pivotal role in mediating the translocation and membrane fusion of GLUT4-storage vesicle (GSV). However, the direct downstream effector underlying the event of cortical actin reorganization has not been elucidated. In a recent study in Nature Communications, (1) Lim et al identify Tropomodulin3 (Tmod3) as a downstream target of the Akt2 kinase and describe the role of this pointed-end actin-capping protein in regulating insulin-dependent exocytosis of GSVs in adipocytes through the remodeling of the cortical actin network. Phosphorylation of Tmod3 by Akt2 on Ser71 modulates insulin-induced actin remodeling, a key step for GSV fusion with the plasma membrane (PM). Furthermore, the authors establish Tm5NM1 (Tpm3.1 in new nomenclature) (2) as the cognate tropomyosin partner of Tmod3, and an essential role of Tmod3-Tm5NM1 interaction for GSV exocytosis and glucose uptake. This study elucidates a novel effector of Akt2 that provides a direct mechanistic link between Akt2 signaling and actin reorganization essential for vesicle fusion, and suggests that a subset of actin filaments with specific molecular compositions may be dedicated for the process of vesicle fusion.
胰岛素诱导肌动蛋白丝重塑为皮质网状结构是胰岛素刺激的GLUT4胞吐作用所必需的,这一点已得到充分证实。Akt2及其下游效应器在介导GLUT4储存囊泡(GSV)的转运和膜融合中起关键作用。然而,皮质肌动蛋白重组事件背后的直接下游效应器尚未阐明。在最近发表于《自然通讯》的一项研究中,(1)Lim等人确定原肌球蛋白调节蛋白3(Tmod3)为Akt2激酶的下游靶点,并描述了这种肌动蛋白尖端封端蛋白通过重塑皮质肌动蛋白网络在调节脂肪细胞中GSV的胰岛素依赖性胞吐作用中的作用。Akt2在Ser71位点对Tmod3的磷酸化调节胰岛素诱导的肌动蛋白重塑,这是GSV与质膜(PM)融合的关键步骤。此外,作者确定Tm5NM1(新命名法中的Tpm3.1)(2)为Tmod3的同源原肌球蛋白伴侣,以及Tmod3-Tm5NM1相互作用对GSV胞吐作用和葡萄糖摄取的重要作用。这项研究阐明了Akt2的一种新效应器,它在Akt2信号传导和囊泡融合所必需的肌动蛋白重组之间提供了直接的机制联系,并表明具有特定分子组成的一部分肌动蛋白丝可能专门用于囊泡融合过程。
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