npg Axin/TNKS/KIF3A complex regulates GLUT4 translocation 1246 ORIGINAL ARTICLE Cell Research (2012) 22:1246-1257. © 2012 IBCB, SIBS, CAS All rights reserved 1001-0602/12 www.nature.com/cr npg The Axin/TNKS complex interacts with KIF3A and is required for insulin-stimulated GLUT4 translocation Hui-Ling Guo1, *, Cixiong Zhang1, *, Qi Liu1, *, Qinxi Li1, Guili Lian1, Di Wu1, Xuebin Li1, Wei Zhang1, Yuemao Shen1, 2, Zhiyun Ye1, Shu-Yong Lin1, Sheng-Cai Lin1 1State Key Laboratory of Stress Cell Biology, School of Life Sciences, Xiamen University, Xiamen, Fujian 361005, China; 2State Key Laboratory of Microbial Technology, School of Life Sciences, Shandong University, Jinan, Shandong 250100, China Insulin-stimulated glucose uptake by the glucose transporter GLUT4 plays a central role in whole-body glucose homeostasis, dysregulation of which leads to type 2 diabetes. However, the molecular components and mechanisms regulating insulin-stimulated glucose uptake remain largely unclear. Here, we demonstrate that Axin interacts with the ADP-ribosylase tankyrase 2 (TNKS2) and the kinesin motor protein KIF3A, forming a ternary complex crucial for GLUT4 translocation in response to insulin. Specific knockdown of the individual components of the complex attenuated insulin-stimulated GLUT4 translocation to the plasma membrane. Importantly, TNKS2−/− mice exhibit reduced insulin sensitivity and higher blood glucose levels when re-fed after fasting. Mechanistically, we demonstrate that in the absence of insulin, Axin, TNKS and KIF3A are co-localized with GLUT4 on the trans-Golgi network. Insulin treatment suppresses the ADP-ribosylase activity of TNKS, leading to a reduction in ADP ribosylation and ubiquitination of both Axin and TNKS, and a concurrent stabilization of the complex. Inhibition of Akt, the major effector kinase of insulin signaling, abrogates the insulin-mediated complex stabilization. We have thus elucidated a new protein complex that is directly associated with the motor protein kinesin in insulin-stimulated GLUT4 translo- cation. Keywords: Axin; TNKS; KIF3A; GLUT4 translocation Cell Research (2012) 22:1246-1257. doi:10.1038/cr.2012.52; published online 3 April 2012 Introduction Glucose homeostasis is tightly governed by multiple levels of regulation, involving many different mol- ecules, cell types and hormones. GLUT4, one type of glucose transporter, is predominantly expressed in skel- etal muscles and adipose tissues, and serves as a major mediator of insulin-stimulated glucose uptake in these tissues [1-4]. In the basal state, GLUT4 is sequestered in intracellular membrane compartments known as GLUT4 storage vesicles (GSVs) formed from either endosomes or the trans-Golgi network (TGN). When blood glu- cose levels are elevated, insulin secretion is heightened, *These three authors contributed equally to this work. Correspondence: Sheng-Cai Lin Tel: +86-592-2182993; Fax: +86-592-2184687 E-mail: linsc@xmu.edu.cn Received 5 September 2011; revised 21 December 2011; accepted 22 Feb- ruary 2012; published online 3 April 2012 stimulating glucose uptake into adipocytes and muscle cells by inducing rapid translocation of GLUT4 vesicles to the cell membrane. The main established pathway for insulin-stimulated GLUT4 translocation involves the ac- tivation of the insulin receptor and the two downstream kinases PI3K [5, 6] and Akt [7]. Combined depletion of Akt1 and Akt2 markedly attenuates the effect of insulin on GLUT4 movement, in which Akt2 plays a prominent role [8] as mice lacking Akt2 exhibit insulin resistance and a diabetes mellitus-like syndrome [9]. Insulin-medi- ated GLUT4 translocation is also dependent on the mi- crotubule network [10, 11], which motor proteins such as kinesins can use as a track [12] for GSV trafficking. However, the role of microtubule-based cytoskeleton in GLUT4 trafficking remains controversial [13-16]. The kinesin proteins known to participate in anterograde GSV transport include KIF5B [17] and KIF3 [18]. KIF3 consists of KIF3A and KIF3B, forming the kinesin-2 subfamily of the kinesin superfamily, which is linked to cargo vesicles by the kinesin-associated protein [18]. Cell Research | Vol 22 No 8 | August 2012