GLUT4在胰岛素调控葡萄糖转运中作用

机体的血糖平衡调节主要依赖于胰岛素,其中一个重要的机制是胰岛素通过调控GLUT4的囊泡运转来调节脂肪细胞和肌细胞对葡萄糖的摄取。由胰岛素受体介导的一系列磷酸化过程能调节一些关键的GLUT4转运相关蛋白质的活性,这些蛋白质包括小GTP酶、拴系复合体和囊泡融合体。而这些蛋白质又反过来通过内膜系统调节GLUT4储存囊泡的生成、滞留,并调控这些囊泡的靶向出胞方式。了解这些过程有助于解释2型糖尿病中胰岛素耐受的机制,并可能为糖尿病提供新的靶向治疗方法。     

地塞米松和胰岛素调节猪脂肪细胞SOCS-3、OB、 GLUT4和PPARg 基因的表达

猪是研究糖尿病最理想的模型动物, 研究胰岛素和胰岛素抵抗是研究糖尿病的重要环节。为明确SOCS-3在胰岛素抵抗中的作用, 分别用100 nmol/L的胰岛素, 300 nmol/L的地塞米松处理原代培养的猪脂肪细胞诱导胰岛素抵抗; 利用半定量RT-PCR技术分别检测SOCS-3、OB、GLUT4和PPARg 基因表达变化。结果发现, 胰岛素增加了GLUT4、SOCS-3和PPARg 基因的表达, 对OB基因表达变化没有显著性影响; 地塞米松诱导的胰岛素抵抗状态下OB和SOCS-3基因表达水平升高, 而GLUT4和PPARγ基因表达水平显著下调。研究结果表明, GLUT4基因表达量水平的升高可能是由于PPARg的高表达引起, SOCS-3基因的不同表达水平对胰岛素信号的抑制效果不同。地塞米松诱导的胰岛素抵抗不仅表现在对葡萄糖转运的抑制, 也反映在抑制了胰岛素信号; 而SOCS-3基因可能是消除胰岛素抵抗的一个有效靶基因。     

地塞米松和胰岛素调节猪脂肪细胞SOCS-3、OB、GLUT4和PPARγ基因的表达

猪是研究糖尿病最理想的模型动物,研究胰岛素和胰岛素抵抗是研究糖尿病的重要环节。为明确SOCS-3在胰岛素抵抗中的作用,分别用100nmol／L的胰岛素,300nmol／L的地基米松处理原代培养的猪脂肪细胞诱导胰岛素抵抗;利用半定量RT-PCR技术分别检测SOCS-3、OB、GLUT4和PPARγ基因表达变化。结果发现,胰岛素增加了GLUT4、SOCS-3和PPARγ基因的表达,对OB基因表达变化没有显著性影响;地塞米松诱导的胰岛素抵抗状态下OB和SOCS-3基因表达水平升高,而GLUT4和PPARγ基因表达水平显著下调。研究结果表明,GLUT4基因表达量水平的升高可能是由于PPARγ的高表达引起,SOCS-3基因的不同表达水平对胰岛素信号的抑制效果不同。地塞米松诱导的胰岛素抵抗不仅表现在对葡萄糖转运的抑制,也反映在抑制了胰岛素信号;而SOCS-3基因可能是消除胰岛素抵抗的一个有效靶基因。     

灵芝多糖对3T3-L1胰岛素抵抗细胞模型PI-3K p85和GLUT4蛋白表达的影响

目的 研究灵芝多糖对3T3-L1胰岛素抵抗细胞模型PI-3K p85和GLUT4蛋白表达的影响,探讨灵芝多糖改善胰岛素抵抗的分子机制.方法 3T3-L1前脂肪细胞经1-甲基-3-异丁基-黄嘌呤、地塞米松、胰岛素诱导分化成3T3-L1脂肪细胞,以葡萄糖氧化酶法测定培养液中残余的葡萄糖含量.比较二甲双胍组,检测培养液中葡萄糖含量及PI-3K p85和GLUT4蛋白表达变化.结果 地塞米松联合胰岛素诱导3T3-L1脂肪细胞产生胰岛素抵抗,细胞对葡萄糖的摄取量减少.灵芝多糖可改善3T3-L1脂肪细胞胰岛素抵抗.胰岛素抵抗细胞的PI-3K p85和GLUT4蛋白表达明显减少;应用灵芝多糖后,相关蛋白表达增加.结论 灵芝多糖通过提高PI-3K p85和GLUT4蛋白的表达,参与胰岛素抵抗状态下3T3-L1细胞的葡萄糖代谢.     

脂肪细胞中Munc18c的缺失不影响胰岛素诱导的GLUT4转运(已撤稿2016-01-13)

动物脂肪和肌肉组织中葡萄糖的摄取是通过受胰岛素调控的GLUT4储存囊泡的运输实现的.Sec1p的同源物Munc18c被认为是通过控制SNARE复合物的装配来使GLUT4囊泡锚定到质膜上的重要物质.我们发现Munc18c的缺失没有影响GLUT4的转运上膜,也没有影响Syntaxin4在细胞膜上的定位.在缺少Munc18c和功能性Syntaxin2的时候,GLUT4的转运可能和Munc18b有关.在3T3-L1脂肪细胞中与Syntaxin4具有强烈相互作用的是Munc18c而不是Munc18a和Munc18b.然而,当缺少Munc18c时,Munc18a和Munc18b与Syntaxin4体现出较弱的相互作用.因此,Syntaxin4可能在胰岛素刺激GLUT4转运过程中起到重要的作用,且与SM蛋白的相互作用是有代偿性的.     

磷脂酰肌醇信号在GLUT4囊泡转运中的调控作用

葡萄糖转运蛋白4(glucose transporter 4,GLUT4)参与胰岛素敏感的脂肪细胞和肌肉细胞中的葡萄糖转运,对机体葡萄糖代谢至关重要。磷脂酰肌醇作为各种蛋白质的定位信号,参与调控细胞生长和新陈代谢,在胰岛素信号转导过程中起着关键作用。在过去的几十年里,关于磷脂酰肌醇信号调控GLUT4囊泡转运方面已有了很大的进展。该文总结了磷脂酰肌醇在GLUT4囊泡转运中的调控作用。     

脂肪细胞中Munc18c的缺失不影响胰岛素诱导的GLUT4转运

动物脂肪和肌肉组织中葡萄糖的摄取是通过受胰岛素调控的GLUT4储存囊泡的运输实现的.Sec1p的同源物Munc18c被认为是通过控制SNARE复合物的装配来使GLUT4囊泡锚定到质膜上的重要物质.我们发现Munc18c的缺失没有影响GLUT4的转运上膜,也没有影响Syntaxin4在细胞膜上的定位.在缺少Munc18c和功能性Syntaxin2的时候,GLUT4的转运可能和Munc18b有关.在3T3-L1脂肪细胞中与Syntaxin4具有强烈相互作用的是Munc18c而不是Munc18a和Munc18b.然而,当缺少Munc18c时,Munc18a和Munc18b与Syntaxin4体现出较弱的相互作用.因此,Syntaxin4可能在胰岛素刺激GLUT4转运过程中起到重要的作用,且与SM蛋白的相互作用是有代偿性的.     

以消散场成像和单微粒跟踪技术揭示GLUT4囊泡和分泌囊泡的不同动态过程

葡萄糖转运子蛋白4(glucose transporter 4,GLUT4)在维持体内葡萄糖动态平衡的过程中起着至关重要的作用。GLUT4贮存囊泡(GLUT4 storage vesicle,GSV)和神经内分泌细胞中的分泌囊泡含有许多相同的蛋白。研究证明这些蛋白调节了分泌囊泡的胞内转运过程,但是GLUT4囊泡和分泌囊泡是否具有相同的胞内动态过程还未阐明。文章以3T3-L1纤维原细胞中的GSV和神经内分泌细胞PC12细胞中的分泌囊泡:致密核心大囊泡(large dense core vesicle,LDCV)为研究对象,使用消散场显微成像技术和单微粒跟踪技术直观观察了活体细胞内单个GSV和LDCV的三维运动轨迹。通过以适当方程拟合单个囊泡的均方位移曲线,发现两种囊泡都具有三种运动模式。定量分析显示作自由扩散运动和方向性扩散运动的GSV数量明显多于LDCV。对比GSV和LDCV的三维扩散系数,发现GSV的扩散系数中值为7.2×10-4μm2/s,而LDCV的扩散系数中值仅为1.94×10-4μm2/s。这一结果说明GSV的活动性远大于LDCV,提示GSV的胞内转运过程涉及不同的分子机制。     

Rab蛋白在葡萄糖转运中的作用

在脂肪和骨骼肌细胞中,胰岛素可迅速刺激葡萄糖转运,即通常所说的GLUT4转运。 GLUT4转运是指Rabs与GTP结合时,促进囊泡与微管和微丝蛋白结合,并通过锚定和融合作用使GLUT4囊泡与目标膜结构融合。多数 Rab 家族成员广泛表达于各种组织细胞中,且在细胞内定位十分广泛,几乎存在于真核细胞所有的膜相关的细胞器的胞浆侧。 Rab 蛋白作为囊泡运输的分子开关,通过调节运输小泡的停泊和融合,在囊泡的形成、转运、粘附、锚定、融合等过程中起着重要的作用。 Rab蛋白受到多种上游调节蛋白的调节,同时调控着下游的多种效应蛋白,构成了复杂的调控网络：任何一个环节改变都可能会导致蛋白质转运的异常,进而引发疾病。本文系统阐述了Rab蛋白在葡萄糖转运过程中的作用及该领域的最新进展。     

葡萄糖转运的胰岛素敏感性以及forskolin, dipyridamole和pentobarbital对三种L6 骨骼肌细胞葡萄糖转运的抑制作用

用稳定过表达并带有myc表位的葡萄糖转运子1(glucose transporter 1, GLUT1)或葡萄糖转运子4(glucose transporter 4, GLUT4)的L6骨骼肌细胞株定征GLUT1和GLUT4对胰岛素的响应. 所筛选的L6-GLUT1myc细胞克隆分化前后的葡萄糖摄取量均在线性范围. 100 nmol/L胰岛素使L6-GLUT1myc和L6-GLUT4myc肌原细胞膜上GLUT1或GLUT4的量分别达到基础组的(1.58±0.01)倍和(1.96±0.11)倍, 2-脱氧葡萄糖摄取量分别达到了(1.53±0.09)倍和(1.86±0.17)倍, 此作用可被渥曼青霉素(wortmannin)抑制. 胰岛素刺激了此2种细胞中的Akt磷酸化. L6-GLUT1myc肌原细胞的葡萄糖摄取量对胰岛素浓度呈剂量依赖性, 但与野生型细胞相比, 其对胰岛素的敏感性和最大响应没有改变. 但L6-GLUT4myc肌原细胞的葡萄糖摄取量对胰岛素的敏感性和最大响应均增加. 以前的研究提示毛喉素(forskolin)可能影响胰岛素刺激的GLUT4转位. 本研究表明, 在L6-GLUT4myc细胞中, 毛喉素使胰岛素刺激的葡萄糖摄取减少了65%, 此作用是由它对GLUT4的直接抑制而不是由其对GLUT4转位的影响造成的. 毛喉素和dipyridamole对GLUT4比对GLUT1有更强的抑制作用, 而戊巴比妥(pentobarbital)对GLUT1的抑制作用强于GLUT4. 应用这些抑制剂的结果表明、L6肌原细胞中基础状态下和胰岛素刺激状态下的葡萄糖主要由过表达的GLUT1或GLUT4转运. 因此, L6-GLUT1myc和L6-GLUT4myc细胞株为筛查对肌肉细胞GLUT1或GLUT4的活性或转位有不同作用的化合物提供了一个平台.     

Dimethyl sulfoxide enhances GLUT4 translocation through a reduction in GLUT4 endocytosis in insulin-stimulated 3T3-L1 adipocytes

Insulin increases muscle and fat cell glucose uptake by inducing the translocation of glucose transporter GLUT4 from intracellular compartments to the plasma membrane. Here, we have demonstrated that in 3T3-L1 adipocytes, DMSO at concentrations higher than 7.5% augmented cell surface GLUT4 levels in the absence and presence of insulin, but that at lower concentrations, DMSO only enhanced GLUT4 levels in insulin-stimulated cells. At a 5% concentration, DMSO also increased cell surface levels of the transferrin receptor and GLUT1. Glucose uptake experiments indicated that while DMSO enhanced cell surface glucose transporter levels, it also inhibited glucose transporter activity. Our studies further demonstrated that DMSO did not sensitize the adipocytes for insulin and that its effect on GLUT4 was readily reversible (t1/2∼12 min) and maintained in insulin-resistant adipocytes. An enhancement of insulin-induced GLUT4 translocation was not observed in 3T3-L1 preadipocytes and L6 myotubes, indicating cell specificity. DMSO did not enhance insulin signaling nor exocytosis of GLUT4 vesicles, but inhibited GLUT4 internalization. While other chemical chaperones (glycerol and 4-phenyl butyric acid) also acutely enhanced insulin-induced GLUT4 translocation, these effects were not mediated via changes in GLUT4 endocytosis. We conclude that DMSO is the first molecule to be described that instantaneously enhances insulin-induced increases in cell surface GLUT4 levels in adipocytes, at least in part through a reduction in GLUT4 endocytosis.     

HIV protease inhibitors act as competitive inhibitors of the cytoplasmic glucose binding site of GLUTs with differing affinities for GLUT1 and GLUT4

The clinical use of several first generation HIV protease inhibitors (PIs) is associated with the development of insulin resistance. Indinavir has been shown to act as a potent reversible noncompetitive inhibitor of zero-trans glucose influx via direct interaction with the insulin responsive facilitative glucose transporter GLUT4. Newer drugs within this class have differing effects on insulin sensitivity in treated patients. GLUTs are known to contain two distinct glucose-binding sites that are located on opposite sides of the lipid bilayer. To determine whether interference with the cytoplasmic glucose binding site is responsible for differential effects of PIs on glucose transport, intact intracellular membrane vesicles containing GLUT1 and GLUT4, which have an inverted transporter orientation relative to the plasma membrane, were isolated from 3T3-L1 adipocytes. The binding of biotinylated ATB-BMPA, a membrane impermeable bis-mannose containing photolabel, was determined in the presence of indinavir, ritonavir, atazanavir, tipranavir, and cytochalasin b. Zero-trans 2-deoxyglucose transport was measured in both 3T3-L1 fibroblasts and primary rat adipocytes acutely exposed to these compounds. PI inhibition of glucose transport correlated strongly with the PI inhibition of ATB-BMPA/transporter binding. At therapeutically relevant concentrations, ritonavir was not selective for GLUT4 over GLUT1. Indinavir was found to act as a competitive inhibitor of the cytoplasmic glucose binding site of GLUT4 with a K(I) of 8.2 μM. These data establish biotinylated ATB-BMPA as an effective probe to quantify accessibility of the endofacial glucose-binding site in GLUTs and reveal that the ability of PIs to block this site differs among drugs within this class. This provides mechanistic insight into the basis for the clinical variation in drug-related metabolic toxicity.     

A pre-docking role for microtubules in insulin-stimulated glucose transporter 4 translocation

Insulin stimulates glucose uptake by inducing translocation of glucose transporter 4 (GLUT4) from intracellular resides to the plasma membrane. How GLUT4 storage vesicles are translocated from the cellular interior to the plasma membrane remains to be elucidated. In the present study, intracellular transport of GLUT4 storage vesicles and the kinetics of their docking at the plasma membrane were comprehensively investigated at single vesicle level in control and microtubule-disrupted 3T3-L1 adipocytes by time-lapse total internal reflection fluorescence microscopy. It is demonstrated that microtubule disruption substantially inhibited insulin-stimulated GLUT4 translocation. Detailed analysis reveals that microtubule disruption blocked the recruitment of GLUT4 storage vesicles to underneath the plasma membrane and abolished the docking of them at the plasma membrane. These data suggest that transport of GLUT4 storage vesicles to the plasma membrane takes place along microtubules and that this transport is obligatory for insulin-stimulated GLUT4 translocation.     

Conventional kinesin KIF5B mediates insulin-stimulated GLUT4 movements on microtubules

Insulin stimulates glucose uptake in muscle and adipose cells by mobilizing intracellular membrane vesicles containing GLUT4 glucose transporter proteins to the plasma membrane. Here we show in live cultured adipocytes that intracellular membranes containing GLUT4-yellow fluorescent protein (YFP) move along tubulin-cyan fluorescent protein-labeled microtubules in response to insulin by a mechanism that is insensitive to the phosphatidylinositol 3 (PI3)-kinase inhibitor wortmannin. Insulin increased by several fold the observed frequencies, but not velocities, of long-range movements of GLUT4-YFP on microtubules, both away from and towards the perinuclear region. Genomics screens show conventional kinesin KIF5B is highly expressed in adipocytes and this kinesin is partially co-localized with perinuclear GLUT4. Dominant-negative mutants of conventional kinesin light chain blocked outward GLUT4 vesicle movements and translocation of exofacial Myc-tagged GLUT4-green fluorescent protein to the plasma membrane in response to insulin. These data reveal that insulin signaling targets the engagement or initiates the movement of GLUT4-containing membranes on microtubules via conventional kinesin through a PI3-kinase-independent mechanism. This insulin signaling pathway regulating KIF5B function appears to be required for GLUT4 translocation to the plasma membrane.     

Effects of chromium picolinate on glucose uptake in insulin-resistant 3T3-L1 adipocytes involve activation of p38 MAPK

Chromium picolinate (CrPic) has been discovered as a supplemental or alternative medication for type 2 diabetes, but its mechanism of action is not well understood. The purpose of this study was to explore the possible anti-diabetic mechanisms of CrPic in insulin-resistant 3T3-L1 adipocytes; the insulin resistance was induced by treatment with high glucose and insulin for 24 h. The effects of CrPic on glucose metabolism and the glucose uptake-inducing activity of CrPic were investigated. Meanwhile, the effects of CrPic on glucose transporter 4 (GLUT4) translocation were visualized by immonofluorescence microscopy. In addition, its effects on insulin signaling pathways and mitogen-activated protein kinase (MAPK) signaling cascades were assessed by immunoblotting analysis and real-time PCR. The results showed that CrPic induced glucose metabolism and uptake, as well as GLUT4 translocation to plasma membrane (PM) in both control and insulin-resistant 3T3-L1 adipocytes without any changes in insulin receptor β (IR-β), protein kinase B (AKt), c-Cbl, extracellular signal-regulated kinase (ERK), c-Jun phosphorylation and c-Cbl-associated protein (CAP) mRNA levels. Interestingly, CrPic was able to increase the basal and insulin-stimulated levels of p38 MAPK activation in the control and insulin-resistant cells. Pretreatment with the specific p38 MAPK inhibitor SB203580 partially inhibited the CrPic-induced glucose transport, but CrPic-activated translocation of GLUT4 was not inhibited by SB203580. This study provides an experimental evidence of the effects of CrPic on glucose uptake through the activation of p38 MAPK and it is independent of the effect on GLUT4 translocation. The findings also suggest exciting new insights into the role of p38 MAPK in glucose uptake and GLUT4 translocation.     

Insulin-mediated GLUT4 translocation is dependent on the microtubule network

The GLUT4 facilitative glucose transporter is recruited to the plasma membrane by insulin. This process depends primarily on the exocytosis of a specialized pool of vesicles containing GLUT4 in their membranes. The mechanism of GLUT4 vesicle exocytosis in response to insulin is not understood. To determine whether GLUT4 exocytosis is dependent on intact microtubule network, we measured insulin-mediated GLUT4 exocytosis in 3T3-L1 adipocytes in which the microtubule network was depolymerized by pretreatment with nocodazole. Insulin-mediated GLUT4 translocation was inhibited by more than 80% in nocodazole-treated cells. Phosphorylation of insulin receptor substrate 1 (IRS-1), activation of IRS-1 associated phosphatidylinositide 3-kinase, and phosphorylation of protein kinase B/Akt-1 were not inhibited by nocodazole treatment indicating that the microtubule network was not required for proximal insulin signaling. An intact microtubule network is specifically required for insulin-mediated GLUT4 translocation since nocodazole treatment did not affect insulin-mediated GLUT1 translocation or adipsin secretion. By using in vitro microtubule binding, we demonstrated that both GLUT4 vesicles and IRS-1 bind specifically to microtubules, implicating microtubules in both insulin signaling and GLUT4 translocation. Vesicle binding to microtubules was not mediated through direct binding of GLUT4 or insulin-responsive aminopeptidase to microtubules. A model microtubule-dependent translocation of GLUT4 is proposed.     

Exosomal Mst1 transfer from cardiac microvascular endothelial cells to cardiomyocytes deteriorates diabetic cardiomyopathy

Diabetic cardiomyopathy (DCM) is characterized by cardiac microvascular endothelial cells (CMECs) injury and cardiomyocyte (CM) dysfunction. Exosomes mediated cellular communication between CMECs and CM has emerging roles in the pathogenesis of DCM, but the underlining mechanisms are unclear. Mammalian sterile 20-like kinase 1 (Mst1), a key component in Hippo pathway which participates in regulating organ size, apoptosis and autophagy, is involved in the development of DCM. We generated the endothelial-specific Mst1 transgenic mice (Tg-Mst1^EC) and constructed diabetic model with streptozotocin (STZ). Interestingly, Tg-Mst1^EC mice suffered from worse cardiac function and aggravated insulin resistance compared with non-transgenic (NTg) diabetic mice. The content of Mst1 protein was increased, while Mst1 mRNA had no significant change in CM isolated from diabetic Tg-Mst1^EC mice. In vitro, CMECs-derived exosomes were taken up by CM and increased Mst1 protein content which inhibited autophagy, as well as enhanced apoptosis in high glucose (HG) cultured CM as evidenced by immunofluorescence and western blot analysis. In addition, Mst1 inhibited glucose uptake under diabetic condition by disrupting the glucose transporter type 4 (GLUT4) membrane translocation through decreasing the interaction between Daxx and GLUT4, as well as enhancing the association of Mst1 and Daxx. Our study exemplifies pleiotropic effects of Mst1-enriched exosomes released from CMECs on inhibiting autophagy, promoting apoptosis and suppressing the glucose metabolism in CM.     

Epigallocatechin-3-O-gallate (EGCG) protects the insulin sensitivity in rat L6 muscle cells exposed to dexamethasone condition

The tea polyphenol epigallocatechin-3-O-gallate (EGCG) displays some antidiabetic effects; however the mechanisms are incompletely understood. In the present study, the investigation of the effects of EGCG on insulin resistance was performed in rat L6 cells treated with dexamethasone. We found that dexamethasone increased Ser307 phosphorylation of insulin receptor substrate-1 (IRS-1) and reduced phosphorylation of AMPK and Akt. Furthermore, glucose uptake and glucose transporter (GLUT4) translocation were inhibited by dexamethasone. However, the treatment of EGCG improved insulin-stimulated glucose uptake by increasing GLUT4 translocation to plasma membrane. Furthermore, we also demonstrated these EGCG effects essentially depended on the AMPK and Akt activation. Together, our data suggested that EGCG inhibited dexamethasone-induced insulin resistance through AMPK and PI3K/Akt pathway.     

Role of EHD1 and EHBP1 in perinuclear sorting and insulin-regulated GLUT4 recycling in 3T3-L1 adipocytes

Insulin stimulates glucose transport in muscle and adipose tissues by recruiting intracellular membrane vesicles containing the glucose transporter GLUT4 to the plasma membrane. The mechanisms involved in the biogenesis of these vesicles and their translocation to the cell surface are poorly understood. Here, we report that an Eps15 homology (EH) domain-containing protein, EHD1, controls the normal perinuclear localization of GLUT4-containing membranes and is required for insulin-stimulated recycling of these membranes in cultured adipocytes. EHD1 is a member of a family of four closely related proteins (EHD1, EHD2, EHD3, and EHD4), which also contain a P-loop near the N terminus and a central coiled-coil domain. Analysis of cultured adipocytes stained with anti-GLUT4, anti-EHD1, and anti-EHD2 antibodies revealed that EHD1, but not EHD2, partially co-localizes with perinuclear GLUT4. Expression of a dominant-negative construct of EHD1 missing the EH domain (DeltaEH-EHD1) markedly enlarged endosomes, dispersed perinuclear GLUT4-containing membranes throughout the cytoplasm, and inhibited GLUT4 translocation to the plasma membranes of 3T3-L1 adipocytes stimulated with insulin. Similarly, small interfering RNA-mediated depletion of endogenous EHD1 protein also markedly dispersed perinuclear GLUT4 in cultured adipocytes. Moreover, EHD1 is shown to interact through its EH domain with the protein EHBP1, which is also required for insulin-stimulated GLUT4 movements and hexose transport. In contrast, disruption of EHD2 function was without effect on GLUT4 localization or translocation to the plasma membrane. Taken together, these results show that EHD1 and EHBP1, but not EHD2, are required for perinuclear localization of GLUT4 and reveal that loss of EHBP1 disrupts insulin-regulated GLUT4 recycling in cultured adipocytes.