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Sekine Y, Kikkawa K, Honda S, Sasaki Y, Kawahara S, Mizushima A, Togi S, Fujimuro M, Oritani K, Matsuda T. STAP-2 facilitates insulin signaling through binding to CAP/c-Cbl and regulates adipocyte differentiation. Sci Rep 2024; 14:5799. [PMID: 38461189 PMCID: PMC10925025 DOI: 10.1038/s41598-024-56533-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2023] [Accepted: 03/07/2024] [Indexed: 03/11/2024] Open
Abstract
Signal-transducing adaptor protein-2 (STAP-2) is an adaptor molecule involved in several cellular signaling cascades. Here, we attempted to identify novel STAP-2 interacting molecules, and identified c-Cbl associated protein (CAP) as a binding protein through the C-terminal proline-rich region of STAP-2. Expression of STAP-2 increased the interaction between CAP and c-Cbl, suggesting that STAP-2 bridges these proteins and enhances complex formation. CAP/c-Cbl complex is known to regulate GLUT4 translocation in insulin signaling. STAP-2 overexpressed human hepatocyte Hep3B cells showed enhanced GLUT4 translocation after insulin treatment. Elevated levels of Stap2 mRNA have been observed in 3T3-L1 cells and mouse embryonic fibroblasts (MEFs) during adipocyte differentiation. The differentiation of 3T3-L1 cells into adipocytes was highly promoted by retroviral overexpression of STAP-2. In contrast, STAP-2 knockout (KO) MEFs exhibited suppressed adipogenesis. The increase in body weight with high-fat diet feeding was significantly decreased in STAP-2 KO mice compared to WT animals. These data suggest that the expression of STAP-2 correlates with adipogenesis. Thus, STAP-2 is a novel regulatory molecule that controls insulin signal transduction by forming a c-Cbl/STAP-2/CAP ternary complex.
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Affiliation(s)
- Yuichi Sekine
- Department of Cell Biology, Kyoto Pharmaceutical University, Kyoto, 607-8412, Japan.
| | - Kazuna Kikkawa
- Department of Cell Biology, Kyoto Pharmaceutical University, Kyoto, 607-8412, Japan
| | - Sachie Honda
- Department of Cell Biology, Kyoto Pharmaceutical University, Kyoto, 607-8412, Japan
| | - Yuto Sasaki
- Department of Immunology, Graduate School of Pharmaceutical Sciences, Hokkaido University, Sapporo, 060-0812, Japan
| | - Shoya Kawahara
- Department of Immunology, Graduate School of Pharmaceutical Sciences, Hokkaido University, Sapporo, 060-0812, Japan
| | - Akihiro Mizushima
- Department of Immunology, Graduate School of Pharmaceutical Sciences, Hokkaido University, Sapporo, 060-0812, Japan
| | - Sumihito Togi
- Division of Genomic Medicine, Department of Advanced Medicine, Medical Research Institute, Kanazawa Medical University, Kahoku, Ishikawa, 920-0293, Japan
| | - Masahiro Fujimuro
- Department of Cell Biology, Kyoto Pharmaceutical University, Kyoto, 607-8412, Japan
| | - Kenji Oritani
- Department of Hematology, International University of Health and Welfare, Narita, Chiba, 286-8686, Japan
| | - Tadashi Matsuda
- Department of Immunology, Graduate School of Pharmaceutical Sciences, Hokkaido University, Sapporo, 060-0812, Japan.
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Li R, Tian JZ, Wang MR, Zhu LN, Sun JS. EsGLUT4 and CHHBP are involved in the regulation of glucose homeostasis in the crustacean Eriocheir sinensis. Biol Open 2017; 6:1279-1289. [PMID: 28751307 PMCID: PMC5612244 DOI: 10.1242/bio.027532] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Glucose is an essential energy source for both vertebrates and invertebrates. In mammals, glucose uptake is mediated primarily by glucose transporters (GLUTs), members of the major facilitator superfamily (MFS) of passive transporters. Among the GLUTs, GLUT4 is the main glucose transporter in muscles and adipocytes. In skeletal muscle cells, GLUT4 interacts with the lipid raft protein flotillin to transport glucose upon stimulation by insulin. Although several studies have examined GLUT4 function in mammals, few have been performed in crustaceans, which also use glucose as their main energy source. Crustacean hyperglycemic hormone (CHH) is a multifunctional neurohormone found only in arthropods, and one of its roles is to regulate glucose homeostasis. However, the molecular mechanism that underlies CHH regulation and whether GLUT4 is involved in its regulation in crustaceans remain unclear. In the present study, we identified a full-length GLUT4 cDNA sequence (defined herein as EsGLUT4) from the Chinese mitten crab Eriocheir sinensis and analyzed its tissue distribution and cellular localization. By the ForteBio Octet system, two large hydrophilic regions within EsGLUT4 were found to interact with the CHH binding protein (CHHBP), an E. sinensis flotillin-like protein. Interestingly, live-cell imaging indicated that EsGLUT4 and CHHBP responded simultaneously upon stimulation by CHH, resulting in glucose release. In contrast to insulin-dependent GLUT4, however, EsGLUT4 and CHHBP were present within cytoplasmic vesicles, both translocating to the plasma membrane upon CHH stimulation. In conclusion, our results provide new evidence for the involvement of EsGLUT4 and CHHBP in the regulation of glucose homeostasis in crustacean carbohydrate metabolism. Summary: Here we identified that Glucose transporter 4 (GLUT4) could interact with CHH binding protein (CHHBP) to regulate CHH-stimulated glucose release in Eriocheir sinensis.
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Affiliation(s)
- Ran Li
- Tianjin Key Laboratory of Animal and Plant Resistance, College of Life Science, Tianjin Normal University, Tianjin 300387, People's Republic of China
| | - Jin-Ze Tian
- Tianjin Key Laboratory of Animal and Plant Resistance, College of Life Science, Tianjin Normal University, Tianjin 300387, People's Republic of China
| | - Mo-Ran Wang
- Tianjin Key Laboratory of Aqua-ecology and Aquaculture, Department of Fisheries Science, Tianjin Agricultural University, Tianjin 300384, People's Republic of China
| | - Li-Na Zhu
- Tianjin Key Laboratory of Animal and Plant Resistance, College of Life Science, Tianjin Normal University, Tianjin 300387, People's Republic of China
| | - Jin-Sheng Sun
- Tianjin Key Laboratory of Animal and Plant Resistance, College of Life Science, Tianjin Normal University, Tianjin 300387, People's Republic of China .,Tianjin Center for Control and Prevention of Aquatic Animal Infectious Disease, Tianjin 300221, People's Republic of China
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3
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Flotillins in receptor tyrosine kinase signaling and cancer. Cells 2014; 3:129-49. [PMID: 24709906 PMCID: PMC3980747 DOI: 10.3390/cells3010129] [Citation(s) in RCA: 51] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2013] [Revised: 02/11/2014] [Accepted: 02/12/2014] [Indexed: 01/23/2023] Open
Abstract
Flotillins are highly conserved proteins that localize into specific cholesterol rich microdomains in cellular membranes. They have been shown to be associated with, for example, various signaling pathways, cell adhesion, membrane trafficking and axonal growth. Recent findings have revealed that flotillins are frequently overexpressed in various types of human cancers. We here review the suggested functions of flotillins during receptor tyrosine kinase signaling and in cancer. Although flotillins have been implicated as putative cancer therapy targets, we here show that great caution is required since flotillin ablation may result in effects that increase instead of decrease the activity of specific signaling pathways. On the other hand, as flotillin overexpression appears to be related with metastasis formation in certain cancers, we also discuss the implications of these findings for future therapy aspects.
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YAMAMOTO N, ASHIDA H. Evaluation Methods for Facilitative Glucose Transport in Cells and Their Applications. FOOD SCIENCE AND TECHNOLOGY RESEARCH 2012. [DOI: 10.3136/fstr.18.493] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Affiliation(s)
- Norio YAMAMOTO
- Food Science Research Center, House Wellness Foods Corporation
| | - Hitoshi ASHIDA
- Department of Agrobioscience, Graduate School of Agricultural Science, Kobe University
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5
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Lee HY, Lee JJ, Park J, Park SB. Development of fluorescent glucose bioprobes and their application on real-time and quantitative monitoring of glucose uptake in living cells. Chemistry 2011; 17:143-50. [PMID: 21207611 DOI: 10.1002/chem.201002560] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
We developed a novel fluorescent glucose bioprobe, GB2-Cy3, for the real-time and quantitative monitoring of glucose uptake in living cells. We synthesized a series of fluorescent glucose analogues by adding Cy3 fluorophores to the α-anomeric position of D-glucose through various linkers. Systematic and quantitative analysis of these Cy3-labeled glucose analogues revealed that GB2-Cy3 was the ideal fluorescent glucose bioprobe. The cellular uptake of this probe competed with the cellular uptake of D-glucose in the media and was mediated by a glucose-specific transport system, and not by passive diffusion. Flow cytometry and fluorescence microscopy analyses revealed that GB2-Cy3 is ten times more sensitive than 2-NBDG, a leading fluorescent glucose bioprobe. GB2-Cy3 can also be utilized for the quantitative flow cytometry monitoring of glucose uptake in metabolically active C2C12 myocytes under various treatment conditions. As opposed to a glucose uptake assay performed by using radioisotope-labeled deoxy-D-glucose and a scintillation counter, GB2-Cy3 allows the real-time monitoring of glucose uptake in living cells under various experimental conditions by using fluorescence microscopy or confocal laser scanning microscopy (CLSM). Therefore, we believe that GB2-Cy3 can be utilized in high-content screening (HCS) for the discovery of novel therapeutic agents and for making significant advances in biomedical studies and diagnosis of various diseases, especially metabolic diseases.
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Affiliation(s)
- Hyang Yeon Lee
- Department of Chemistry, Seoul National University, Seoul 151-747, Korea
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6
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Abstract
Recent studies have demonstrated that a number of E3 ubiquitin ligases, including Cbl, Smurf1, Smurf2, HDM2, BCA2, SCF(beta-TRCP) and XRNF185, play important roles in cell adhesion and migration. Cbl negatively regulates cell adhesion via alpha integrin and Rap1 and inhibits actin polymerization by ubiquitinating mDab1 and WAVE2. Smurf1 regulates cell migration through ubiquitination of RhoA, talin head domain and hPEM2, while Smurf2 ubiquitinates Smurf1, TGFbeta type I receptor and RaplB to modulate cell migration and adhesion. HDM2 negatively regulates cell migration by targeting NFAT (a transcription factor) for ubiquitination and degradation, while SCF(beta-TRCP) ubiquitinates Snail (a transcriptional repressor of E-cadherin) to inhibit cell migration. TRIM32 promotes cell migration through ubiquitination of Abl interactor 2 (Abi2), a tumor suppressor. RNF5 and XRNF185 modulate cell migration by ubiquitinating paxillin. Thus, these E3 ubiquitin ligases regulate cell adhesion and (or) migration through ubiquitination of their specific substrates.
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Affiliation(s)
- Cai Huang
- Department of Cell and Developmental Biology, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA.
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Hong KW, Jin HS, Lim JE, Go MJ, Lee JY, Hwang SY, Park HK, Oh BS. Identification of Genetic Variations in CBL, SORBS1, CRK, and RHOQ, Key Modulators in the CAP/TC10 Pathway of Insulin Signal Transduction, and Their Association with Type 2 Diabetes Mellitus in the Korean Population. Genomics Inform 2009. [DOI: 10.5808/gi.2009.7.2.053] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
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8
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Sun XJ, Liu F. Phosphorylation of IRS proteins Yin-Yang regulation of insulin signaling. VITAMINS AND HORMONES 2009; 80:351-87. [PMID: 19251044 DOI: 10.1016/s0083-6729(08)00613-4] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Growing evidence reveals that insulin signal pathway is not static, but is rather a dynamic, flexible, and fed in by negative (Yin) and positive (Yang) regulation in response to environmental changes. Normal insulin response reflects the balance between Yin and Yang regulation acting upon insulin signaling pathway. Conceivably, imbalance between the Yin and Yang results in abnormal insulin sensitivity such as insulin resistance. IRS-proteins are insulin receptor substrates that mediate insulin signaling via multiple tyrosyl phosphorylations. However, they are also substrates for many serine/threonine kinases downstream of other signaling network and become serine phosphorylated in response to various conditions such as inflammation, stress and over nutrients. The serine phosphorylation of IRS-proteins alters the capacities of IRS-proteins to be phosphorylated on tyrosyl, therefore, able to mediate insulin signaling. The unique structure of IRS-proteins render them idea molecules to fulfill the task to sense the environmental cues and integrate them into insulin sensitivity through serine/threonine phosphorylation. This review intends to summarize the role of IRS-proteins in insulin signaling with focuses on the role of Yin and Yang regulation of insulin signaling pathway. Understanding the dynamic of these complicated regulation net work not only provide us a complete picture of what happens in the normal conditions, but also pathaphysiological conditions such as obesity and insulin resistance.
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Affiliation(s)
- Xiao Jian Sun
- Department of Medicine, The University of Chicago, Chicago, Illinois 60637, USA
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Boura-Halfon S, Zick Y. Serine kinases of insulin receptor substrate proteins. VITAMINS AND HORMONES 2009; 80:313-49. [PMID: 19251043 DOI: 10.1016/s0083-6729(08)00612-2] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Signaling of insulin and insulin-like growth factor-I (IGF-1) at target tissues is essential for growth, development and for normal homeostasis of glucose, fat, and protein metabolism. Control over this process is therefore tightly regulated. It can be achieved by a negative-feedback control mechanism, whereby downstream components inhibit upstream elements along the insulin and IGF-1 signaling pathway or by signals from other pathways that inhibit insulin/IGF-1 signaling thus leading to insulin/IGF-1 resistance. Phosphorylation of insulin receptor substrates (IRS) proteins on serine residues has emerged as a key step in these control processes both under physiological and pathological conditions. The list of IRS kinases is growing rapidly, concomitant with the list of potential Ser/Thr phosphorylation sites in IRS proteins. Here we review a range of conditions that activate IRS kinases to phosphorylate IRS proteins on selected domains. The specificity of this reaction is discussed and its characteristic as an "array" phosphorylation is suggested. Finally, its implications on insulin/IGF-1 signaling, insulin/IGF-1 resistance and diabetes, an emerging epidemic of the twenty-first century are outlined.
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Affiliation(s)
- Sigalit Boura-Halfon
- Department of Molecular Cell Biology, Weizmann Institute of Science, Rehovot 76100, Israel
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10
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Vegiopoulos A, Herzig S. Glucocorticoids, metabolism and metabolic diseases. Mol Cell Endocrinol 2007; 275:43-61. [PMID: 17624658 DOI: 10.1016/j.mce.2007.05.015] [Citation(s) in RCA: 325] [Impact Index Per Article: 19.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/22/2007] [Revised: 05/14/2007] [Accepted: 05/17/2007] [Indexed: 12/14/2022]
Abstract
Since the discovery of the beneficial effects of adrenocortical extracts for treating adrenal insufficiency more than 80 years ago, glucocorticoids (GC) and their cognate, intracellular receptor, the glucocorticoid receptor (GR) have been characterized as critical components of the delicate hormonal control system that determines energy homeostasis in mammals. Whereas physiological levels of GCs are required for proper metabolic control, excessive GC action has been tied to a variety of pandemic metabolic diseases, such as type II diabetes and obesity. Highlighted by its importance for human health, the investigation of molecular mechanisms of GC/GR action has become a major focus in biomedical research. In particular, the understanding of tissue-specific functions of the GC-GR pathway has been proven to be of substantial value for the identification of novel therapeutic options in the treatment of severe metabolic disorders. Therefore, this review focuses on the role of the GC-GR axis for metabolic homeostasis and dysregulation, emphasizing tissue-specific functions of GCs in the control of energy metabolism.
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11
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Hou JC, Pessin JE. Ins (endocytosis) and outs (exocytosis) of GLUT4 trafficking. Curr Opin Cell Biol 2007; 19:466-73. [PMID: 17644329 PMCID: PMC2041936 DOI: 10.1016/j.ceb.2007.04.018] [Citation(s) in RCA: 112] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2007] [Accepted: 04/17/2007] [Indexed: 12/21/2022]
Abstract
Glucose transporter 4 (GLUT4) is the major insulin-regulated glucose transporter expressed mainly in muscle and adipose tissue. GLUT4 is stored in a poorly characterized intracellular vesicular compartment and translocates to the cell surface in response to insulin stimulation resulting in an increased glucose uptake. This process is essential for the maintenance of normal glucose homeostasis and involves a complex interplay of trafficking events and intracellular signaling cascades. Recent studies have identified sortilin as an essential element for the formation of GLUT4 storage vesicles during adipogenesis and Golgi-localized gamma-ear-containing Arf-binding protein (GGA) as a key coat adaptor for the entry of newly synthesized GLUT4 into the specialized compartment. Insulin-stimulated GLUT4 translocation from this compartment to the plasma membrane appears to require the Akt/protein kinase B substrate termed AS160 (Akt substrate of 160kDa). In addition, the VPS9 domain-containing protein Gapex-5 in complex with CIP4 appears to function as a Rab31 guanylnucleotide exchange factor that is necessary for insulin-stimulated GLUT4 translocation. Here, we attempt to summarize recent advances in GLUT4 vesicle biogenesis, intracellular trafficking and membrane fusion.
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Affiliation(s)
- June Chunqiu Hou
- Department of Pharmacological Sciences, Stony Brook University, Stony Brook, NY 11794, USA.
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12
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Abstract
The dissection of mechanisms that regulate glucose transport by insulin has revealed an intricate network of signaling molecules scattered from the insulin receptor to the intracellular glucose transporter GLUT4. It is also appreciated that some insulin receptor signals jaunt in different directions to regulate events essential for the efficient redistribution of GLUT4 to the plasma membrane. Moreover key assists in the process appear to be arranged by membrane lipids and cytoskeletal proteins. Following current considerations of insulin signals regulating GLUT4, this review will focus on in vitro and in vivo evidence that supports an essential role for phosphoinositides and actin filaments in the control of glucose transport. The discussion will visit recent cell culture, whole animal, and human data highlighting membrane and cytoskeletal aspects of insulin resistance.
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Affiliation(s)
- Joseph T Brozinick
- Eli Lilly and Company, Lilly Corporate Center, Indianapolis, IN 46285, USA.
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13
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Abstract
Previous studies have suggested that activation of the Rho family member GTPase TC10 is necessary but not sufficient for the stimulation of glucose transport by insulin. We show here that endogenous TC10alpha is rapidly activated in response to insulin in 3T3L1 adipocytes in a phosphatidylinositol 3-kinase-independent manner, whereas platelet-derived growth factor was without effect. Knockdown of TC10alpha but not TC10beta by RNA interference inhibited insulin-stimulated glucose uptake as well as the translocation of the insulin-sensitive glucose transporter GLUT4 from intracellular sites to the plasma membrane. In contrast, loss of TC10alpha had no effect on the stimulation of Akt by insulin. Additionally, knockdown of TC10alpha inhibited insulin-stimulated translocation of its effector CIP4. These data indicate that TC10alpha is specifically required for insulin-stimulated glucose uptake in adipocytes.
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Affiliation(s)
- Louise Chang
- Life Sciences Institute, University of Michigan Medical Center, Ann Arbor, Michigan 48109-2216, USA
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14
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Liu XJ, He AB, Chang YS, Fang FD. Atypical protein kinase C in glucose metabolism. Cell Signal 2006; 18:2071-6. [PMID: 16787739 DOI: 10.1016/j.cellsig.2006.04.007] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2006] [Accepted: 04/28/2006] [Indexed: 01/17/2023]
Abstract
Type 2 diabetes mellitus is a multigenic disease with evident genetic predisposition, and complex pathogenesis in which environmental and genetic factors interact. The disorder of body utilization glucose is a crucial reason for causing diabetes. Atypical PKCs, belonging to Ser/Thr protein kinase, have many important biological functions in vivo, and may be involved in the pathogenesis of diabetes mellitus. APKCs participate in glucose metabolism by regulating glucose transport and absorption, glycogen synthesis, and insulin secretion. The exact mechanism by which aPKCs participate in glucose metabolism remains unclear. So far, the clarification of which will be helpful for the prevention and cure of type 2 diabetes.
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Affiliation(s)
- Xiao-Jun Liu
- National Laboratory of Medical Molecular Biology, Institute of Basic Medical Sciences Chinese Academy of Medical Sciences and School of Basic Medicine Peking Union Medical College, Beijing 100005, China
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15
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Liu LZ, He AB, Liu XJ, Li Y, Chang YS, Fang FD. Protein kinase Czeta and glucose uptake. BIOCHEMISTRY (MOSCOW) 2006; 71:701-6. [PMID: 16903823 DOI: 10.1134/s0006297906070017] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
Protein kinase Czeta (PKCzeta) is a member of the PKC family, serving downstream of insulin receptor and phosphatidylinositol (PI) 3-kinase. Many evidences suggest that PKCzeta plays a very important role in activating glucose transport response. Not only insulin but also glucose and exercise can activate PKCzeta through diverse pathways. PKCzeta activation and activity are impaired with insulin resistance in muscle and adipose tissues of type II diabetes individuals, but heightened in liver tissue, wherein it also increases lipid synthesis mediated by SREBP-1c (sterol-regulatory element-binding protein). Many studies have focused on linkage between PKCzeta and GLUT4 translocation and activation. Exploring the molecular mechanisms and pathways by which PKCzeta mediates glucose transport will highlight the insulin-signaling pathway.
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Affiliation(s)
- Li-Zhong Liu
- National Laboratory of Medical Molecular Biology, Institute of Basic Medical Sciences, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, 100005, China
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16
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Prada PO, Pauli JR, Ropelle ER, Zecchin HG, Carvalheira JBC, Velloso LA, Saad MJA. Selective modulation of the CAP/Cbl pathway in the adipose tissue of high fat diet treated rats. FEBS Lett 2006; 580:4889-94. [PMID: 16919274 DOI: 10.1016/j.febslet.2006.08.004] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2006] [Revised: 07/28/2006] [Accepted: 08/01/2006] [Indexed: 02/07/2023]
Abstract
A high-fat diet (HFD) is associated with reduced glucose uptake in muscle, but not in adipose tissue. In the present study, we investigated whether a HFD can modulate glucose uptake in adipose tissue by increasing signal transduction through the CAP/Cbl pathway, independently of the PI3-K/Akt pathway. Our results suggest that, in HFD, the differential regulation of insulin-induced glucose uptake between skeletal muscle and adipose tissue may, in part, be a consequence of the CAP/Cbl/C3G pathway, since the expression of CAP and Cbl, and also the activation of this pathway were increased in adipose tissue but not in muscle.
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Affiliation(s)
- Patrícia Oliveira Prada
- Departamento de Clínica Médica da Universidade Estadual de Campinas, FCM-UNICAMP, Campinas, São Paulo 13083-970, Brazil
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17
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Abstract
In skeletal muscle and adipose tissue, insulin-stimulated glucose uptake is dependent upon translocation of the insulin-responsive glucose transporter GLUT4 from intracellular storage compartments to the plasma membrane. This insulin-induced redistribution of GLUT4 protein is achieved through a series of highly organized membrane trafficking events, orchestrated by insulin receptor signals. Recently, several key molecules linking insulin receptor signals and membrane trafficking have been identified, and emerging evidence supports the importance of subcellular compartmentalization of signaling components at the right time and in the right place. In addition, the translocation of GLUT4 in adipocytes requires insulin stimulation of dynamic actin remodeling at the inner surface of the plasma membrane (cortical actin) and in the perinuclear region. This results from at least two independent insulin receptor signals, one leading to the activation of phosphatidylinositol (PI) 3-kinase and the other to the activation of the Rho family small GTP-binding protein TC10. Thus, both spatial and temporal regulations of actin dynamics, both beneath the plasma membrane and around endomembranes, by insulin receptor signals are also involved in the process of GLUT4 translocation.
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Affiliation(s)
- Makoto Kanzaki
- TUBERO/Tohoku University Biomedical Engineering Research Organization, Tohoku University, Sendai, Japan
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18
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Wang Y, Li R, Du D, Zhang C, Yuan H, Zeng R, Chen Z. Proteomic analysis reveals novel molecules involved in insulin signaling pathway. J Proteome Res 2006; 5:846-55. [PMID: 16602692 DOI: 10.1021/pr050391m] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The binding of insulin to its receptor triggers a signaling cascade regulated by protein complexes via tyrosine phosphorylation events on a multitude of associated proteins. To search novel phosphotyrosine proteins or associated proteins involved in insulin signaling pathway, we employed a method in which Rat1 cells stably expressing the human insulin receptor were stimulated with or without insulin and sub-fractionated prior to enrichment of phosphotyrosine proteins by immunoprecipitation and analysis by LC-MS/MS. Bioinformatic analysis and manual confirmation of peptide phosphorylation site assignments led to identification of 35 phosphotyrosine sites derived from 31 protein groups. Over 50% of these proteins were reported for the first time as tyrosine phosphorylated, including gigaxonin, XIAP and CDK10. In addition, we also found that calcium/calmodulin-dependent protein serine kinase (CASK), a key protein in protein-targeting and vesicle transport in neurons, forms a complex with two unidentified phosphotyrosine proteins pp100 and pp95 in response to insulin-stimulation, though CASK is not itself tyrosine phosphorylated. Furthermore, insulin was able to decrease CASK nuclear location, as well as down-regulate the expression of CASK targeted genes. Our results imply CASK as a novel joint knot connecting CASK-mediated pathways with the insulin signaling. Our data provide a wealth of information potentially paving the way to identify new components in the insulin signaling network.
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Affiliation(s)
- Yiguo Wang
- Key Laboratory of Proteomics, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, 320 Yue Yang Road, Shanghai 200031, China
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19
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Lazar DF, Saltiel AR. Lipid phosphatases as drug discovery targets for type 2 diabetes. Nat Rev Drug Discov 2006; 5:333-42. [PMID: 16582877 DOI: 10.1038/nrd2007] [Citation(s) in RCA: 85] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
The soaring incidence of type 2 diabetes has created pressure for new pharmaceutical strategies to treat this devastating disease. With much of the focus on overcoming insulin resistance, investigation has focused on finding ways to restore activation of the phosphatidylinositol 3'-kinase pathway, which is diminished in many patients with type 2 diabetes. Here we review the evidence that lipid phosphatases, specifically PTEN and SHIP2, attenuate this important insulin signalling pathway. Both in vivo and in vitro studies indicate their role in regulating whole-body energy metabolism, and possibly weight gain as well. The promise and challenges presented by this new class of drug discovery targets will also be discussed.
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Affiliation(s)
- Dan F Lazar
- Eli Lilly and Co., Endocrine Division, Lilly Research Laboratories, Indianapolis, Indianapolis 46285, USA.
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20
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Inoue M, Chiang SH, Chang L, Chen XW, Saltiel AR. Compartmentalization of the exocyst complex in lipid rafts controls Glut4 vesicle tethering. Mol Biol Cell 2006; 17:2303-11. [PMID: 16525015 PMCID: PMC1446102 DOI: 10.1091/mbc.e06-01-0030] [Citation(s) in RCA: 97] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
Lipid raft microdomains act as organizing centers for signal transduction. We report here that the exocyst complex, consisting of Exo70, Sec6, and Sec8, regulates the compartmentalization of Glut4-containing vesicles at lipid raft domains in adipocytes. Exo70 is recruited by the G protein TC10 after activation by insulin and brings with it Sec6 and Sec8. Knockdowns of these proteins block insulin-stimulated glucose uptake. Moreover, their targeting to lipid rafts is required for glucose uptake and Glut4 docking at the plasma membrane. The assembly of this complex also requires the PDZ domain protein SAP97, a member of the MAGUKs family, which binds to Sec8 upon its translocation to the lipid raft. Exocyst assembly at lipid rafts sets up targeting sites for Glut4 vesicles, which transiently associate with these microdomains upon stimulation of cells with insulin. These results suggest that the TC10/exocyst complex/SAP97 axis plays an important role in the tethering of Glut4 vesicles to the plasma membrane in adipocytes.
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Affiliation(s)
- Mayumi Inoue
- Life Sciences Institute, Department of Internal Medicine, University of Michigan, Ann Arbor, MI 48109, USA
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Sun Y, Ma YC, Huang J, Chen KY, McGarrigle DK, Huang XY. Requirement of SRC-family tyrosine kinases in fat accumulation. Biochemistry 2006; 44:14455-62. [PMID: 16262245 DOI: 10.1021/bi0509090] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Src-family tyrosine kinases mediate many receptor signals to various biological responses. Here we investigate the requirement of Src-family tyrosine kinases in adipogenesis. The biochemical mechanism by which insulin induces adipogenesis, converting fibroblast cells to adipocytes, is not clear. We show that fibroblast cells deficient of three ubiquitously expressed Src-family members (Src, Yes, and Fyn), SYF cells, are refractory to hormonally induced fat accumulation. The defect is rescued by reintroduction of c-Src into SYF cells. Furthermore, Src-family tyrosine kinases are required in the early steps of insulin signaling; it is responsible for the tyrosine phosphorylation of adaptor protein c-Cbl. Deficiency of c-Cbl blocked adipogenesis. These genetic and biochemical data clearly demonstrate that Src-family tyrosine kinases serve as a critical signal relay, via phosphorylation of c-Cbl, for fat accumulation, and provide potential new strategies for treating obesity.
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Affiliation(s)
- Yutong Sun
- Department of Physiology, Weill Medical College, Cornell University, New York, New York 10021, USA
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22
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Fecchi K, Volonte D, Hezel MP, Schmeck K, Galbiati F. Spatial and temporal regulation of GLUT4 translocation by flotillin-1 and caveolin-3 in skeletal muscle cells. FASEB J 2006; 20:705-7. [PMID: 16455755 PMCID: PMC4288748 DOI: 10.1096/fj.05-4661fje] [Citation(s) in RCA: 89] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Skeletal muscle tissue is one of the main sites where glucose uptake occurs in response to insulin. The glucose transporter type-4 (GLUT4) is primarily responsible for the insulin-stimulated increase in glucose uptake. Upon insulin stimulation, GLUT4 is recruited from intracellular reserves to the plasma membrane. The molecular mechanisms that regulate the translocation of GLUT4 to the sarcolemma remain to be fully identified. Here, we demonstrate that GLUT4 is localized to perinuclear stores that contain flotillin-1, a marker of lipid rafts, in skeletal muscle cells. Stimulation with insulin for 10 min results in the translocation of flotillin-1/GLUT4-containing domains to the plasma membrane in a PI3K- and PKCzeta-dependent manner. We also demonstrate that caveolin-3, a marker of caveolae, is required for the insulin receptor-mediated activation of the PI3K-dependent pathway, which occurs 2 min after insulin stimulation. In fact, we demonstrate that lack of caveolin-3 significantly reduces insulin-stimulated glucose uptake in caveolin-3 null myotubes by inhibiting both PI3K and Akt, as well as the movement of GLUT4 to the plasma membrane. Interestingly, caveolin-3 moves away from the plasma membrane toward the cytoplasm 5 min after insulin stimulation and temporarily interacts with flotillin-1/GLUT4-containing domains before they reach the sarcolemma, with the consequent movement of the insulin receptor from caveolin-3-containing domains to flotillin-1-containing domains. Such translocation temporally matches the insulin-stimulated movement of Cbl and CrkII in flotillin-1/GLUT4-containing domains, as well as the activation of the GDP-GTP exchange factor C3G. Disruption of flotillin-1-based domains prevents the activation of C3G, movement of GLUT4 to the sarcolemma, and glucose uptake in response to insulin. Thus, the activation of the Cbl/C3G/TC10-dependent pathway, which occurs before flotillin-1/GLUT4-containing domains reach the plasma membrane, is flotillin-1 mediated and follows the activation of the PI3K-mediated signaling. Taken together, these results indicate that flotillin-1 and caveolin-3 may regulate muscle energy metabolism through the spatial and temporal segregation of key components of the insulin signaling.
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Affiliation(s)
- Katia Fecchi
- Department of Pharmacology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, USA
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23
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Sebastian BM, Nagy LE. Decreased insulin-dependent glucose transport by chronic ethanol feeding is associated with dysregulation of the Cbl/TC10 pathway in rat adipocytes. Am J Physiol Endocrinol Metab 2005; 289:E1077-84. [PMID: 16105861 PMCID: PMC1283127 DOI: 10.1152/ajpendo.00296.2005] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
Heavy alcohol consumption is an independent risk factor for type 2 diabetes. Although the exact mechanism by which alcohol contributes to the increased risk is unknown, impaired glucose disposal is a likely target. Insulin-stimulated glucose disposal in adipocytes is regulated by two separate and independent pathways, the PI3K pathway and the Cbl/TC10 pathway. Previous studies suggest that chronic ethanol feeding impairs insulin-stimulated glucose transport in adipocytes in a PI3K-independent manner. In search of potential targets of ethanol that would affect insulin-stimulated glucose transport, we investigated the effects of 4-wk ethanol feeding to male Wistar rats on the Cbl/TC10 pathway in isolated adipocytes. Chronic ethanol feeding inhibited insulin-stimulated cCbl phosphorylation compared with pair feeding. Insulin receptor and Akt/PKB phosphorylation were not affected by ethanol feeding. Chronic ethanol exposure also impaired cCbl and TC10 recruitment to a lipid raft fraction isolated from adipocytes by detergent extraction. Furthermore, chronic ethanol feeding increased the amount of activated TC10 and filamentous actin in adipocytes at baseline and abrogated the ability of insulin to further activate TC10 or polymerize actin. These results demonstrate that the impairment in insulin-stimulated glucose transport observed in adipocytes after chronic ethanol feeding to rats is associated with a disruption of insulin-mediated Cbl/TC10 signaling and actin polymerization.
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Affiliation(s)
- Becky M Sebastian
- Dept. of Nutrition, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, OH 44106-4906, USA
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24
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Guo L, Tabrizchi R. Peroxisome proliferator-activated receptor gamma as a drug target in the pathogenesis of insulin resistance. Pharmacol Ther 2005; 111:145-73. [PMID: 16305809 DOI: 10.1016/j.pharmthera.2005.10.009] [Citation(s) in RCA: 78] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2005] [Accepted: 10/03/2005] [Indexed: 01/08/2023]
Abstract
Peroxisome proliferator-activated receptors (PPARs) are ligand-activated transcription factors that belong to the nuclear hormone receptor superfamily. The activation of PPAR-gamma, an isotype of PPARs, can either increase or decrease the transcription of target genes. The genes controlled by this form of PPAR have been shown to encode proteins or peptides that participate in the pathogenesis of insulin resistance. Insulin resistance is defined as a state of reduced responsiveness to normal circulating concentrations of insulin and it often co-exists with central obesity, hypertension, dyslipidemia, and atherosclerosis. There is substantial evidence that links obesity with insulin resistance and type-2 diabetes. The early phase of obesity-related insulin resistance has 2 components: (a) interruption of lipid homeostasis leading to the increased plasma concentration of fatty acids that is normally suppressed by the activation of PPAR-gamma, and (b) activation of factors such as cytokines depressed by PPAR-gamma that cause insulin resistance. Therefore, it is logical to suggest that activation of PPAR-gamma may partially reverse the state of insulin resistance. Evidently, activation of the nuclear receptor, PPAR-gamma, by thiazolidinediones has been reported to ameliorate insulin resistance. Although hepatotoxity and possibility to induce congestive heart failure (CHF) limit the widely use of thiazolodinediones, they are still powerful weapon to fight against insulin resistance and type-2 diabetes if use properly. This article reviews the physiology of PPAR-gamma and insulin-signaling transduction, the pathogenesis of insulin resistance in obesity-related type-2 diabetes, the pharmacological role of PPAR-gamma in insulin resistance, and additional effects of thiazolidinediones.
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Affiliation(s)
- Liang Guo
- Division of Basic Medical Sciences, Faculty of Medicine, Memorial University of Newfoundland, St. John's, NL, Canada A1B 3V6
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25
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Pike LJ. Growth factor receptors, lipid rafts and caveolae: an evolving story. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2005; 1746:260-73. [PMID: 15951036 DOI: 10.1016/j.bbamcr.2005.05.005] [Citation(s) in RCA: 210] [Impact Index Per Article: 11.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/23/2005] [Revised: 04/25/2005] [Accepted: 05/13/2005] [Indexed: 11/16/2022]
Abstract
Growth factor receptors have been shown to be localized to lipid rafts and caveolae. Consistent with a role for these cholesterol-enriched membrane domains in growth factor receptor function, the binding and kinase activities of growth factor receptors are susceptible to regulation by changes in cholesterol content. Furthermore, knockouts of caveolin-1, the structural protein of caveolae, have confirmed that this protein, and by implication caveolae, modulate the ability of growth factor receptors to signal. This article reviews the findings pertinent to the relationship between growth factor receptors, lipid rafts and caveolae and presents a model for understanding the disparate observations regarding the role of membrane microdomains in the regulation of growth factor receptor function.
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Affiliation(s)
- Linda J Pike
- Washington University School of Medicine, Department of Biochemistry and Molecular Biophysics, 660 So. Euclid, Box 8231, St. Louis, MO 63110, USA.
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26
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Bernard JR, Crain AM, Rivas DA, Herr HJ, Reeder DW, Yaspelkis BB. Chronic aerobic exercise enhances components of the classical and novel insulin signalling cascades in Sprague-Dawley rat skeletal muscle. ACTA ACUST UNITED AC 2005; 183:357-66. [PMID: 15799772 DOI: 10.1111/j.1365-201x.2005.01408.x] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
Abstract
AIM The aim of this study was to provide a more extensive evaluation of the effects of chronic aerobic exercise on various components of the insulin signalling cascade in normal rodent skeletal muscle because of the limited body of literature that exists in this area of investigation. METHODS Male Sprague-Dawley rats were assigned to either control (n = 7) or chronic aerobic exercise (n = 7) groups. Aerobic exercise animals were run 3 day week(1) for 45 min on a motor-driven treadmill (32 m min(1), 15% grade) for a 12 week period. Following the training period, all animals were subjected to hind limb perfusion in the presence of 500 microU mL(1) insulin to determine what effect chronic aerobic training had on various components of the insulin signalling cascade, c-Cbl protein concentration and c-Cbl phosphorylation. RESULTS Twelve weeks of aerobic training did not alter skeletal muscle Akt 1/2 protein concentration, Akt Ser 473 phosphorylation, Akt Thr 308 phosphorylation, Akt 1 activity, aPKC-zeta protein concentration, aPKC-lambda protein concentration or c-Cbl protein concentration. In contrast, chronic aerobic exercise increased insulin-stimulated phosphatidylinositol 3-kinase, Akt 2 kinase and aPKC-zeta/lambda kinase activities, as well as c-Cbl tyrosine phosphorylation, in a fibre type specific response to aerobic training. In addition, chronic aerobic exercise enhanced insulin-stimulated plasma membrane glucose transporter 4 (GLUT4) protein concentration. CONCLUSION Collectively, these findings suggest that chronic aerobic exercise enhances components of both the classical and novel insulin signalling cascades in normal rodent skeletal muscle, which may contribute to an increased insulin-stimulated plasma membrane GLUT4 protein concentration.
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Affiliation(s)
- J R Bernard
- Exercise Biochemistry Laboratory, Department of Kinesiology, College of Health and Human Development, California State University Northridge, 91330-8287, USA
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27
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Harmon AW, Paul DS, Patel YM. MEK inhibitors impair insulin-stimulated glucose uptake in 3T3-L1 adipocytes. Am J Physiol Endocrinol Metab 2004; 287:E758-66. [PMID: 15172888 DOI: 10.1152/ajpendo.00581.2003] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Abstract
In 3T3-L1 adipocytes, insulin activates three major signaling cascades, the phosphoinositide 3-kinase (PI3K) pathway, the Cbl pathway, and the mitogen-activated protein kinase (MAPK) pathway. Although PI3K and Cbl mediate insulin-stimulated glucose uptake by promoting the translocation of the insulin-responsive glucose transporter (GLUT4) to the plasma membrane, the MAPK pathway does not have an established role in insulin-stimulated glucose uptake. We demonstrate in this report that PI3K inhibitors also inhibit the MAPK pathway. To investigate the role of the MAPK pathway separately from that of the PI3K pathway in insulin-stimulated glucose uptake, we used two specific inhibitors of MAPK kinase (MEK) activity, PD-98059 and U-0126, which reduced insulin-stimulated glucose uptake by approximately 33 and 50%, respectively. Neither MEK inhibitor affected the activation of Akt or PKCzeta/lambda, downstream signaling molecules in the PI3K pathway. Inhibition of MEK with U-0126 did not prevent GLUT4 from translocating to the plasma membrane, nor did it inhibit the subsequent docking and fusion of GLUT4-myc with the plasma membrane. MEK inhibitors affected glucose transport mediated by GLUT4 but not GLUT1. Importantly, the presence of MEK inhibitors only at the time of the transport assay markedly impaired both insulin-stimulated glucose uptake and MAPK signaling. Conversely, removal of MEK inhibitors before the transport assay restored glucose uptake and MAPK signaling. Collectively, our studies suggest a possible role for MEK in the activation of GLUT4.
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Affiliation(s)
- Anne W Harmon
- Department of Nutrition, University of North Carolina School of Public Health, Chapel Hill 27599, USA
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28
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Funaki M, Randhawa P, Janmey PA. Separation of insulin signaling into distinct GLUT4 translocation and activation steps. Mol Cell Biol 2004; 24:7567-77. [PMID: 15314166 PMCID: PMC507006 DOI: 10.1128/mcb.24.17.7567-7577.2004] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
GLUT4 (glucose transporter 4) plays a pivotal role in insulin-induced glucose uptake to maintain normal blood glucose levels. Here, we report that a cell-permeable phosphoinositide-binding peptide induced GLUT4 translocation to the plasma membrane without inhibiting IRAP (insulin-responsive aminopeptidase) endocytosis. However, unlike insulin treatment, the peptide treatment did not increase glucose uptake in 3T3-L1 adipocytes, indicating that GLUT4 translocation and activation are separate events. GLUT4 activation can occur at the plasma membrane, since insulin was able to increase glucose uptake with a shorter time lag when inactive GLUT4 was first translocated to the plasma membrane by pretreating the cells with this peptide. Inhibition of phosphatidylinositol (PI) 3-kinase activity failed to inhibit GLUT4 translocation by the peptide but did inhibit glucose uptake when insulin was added following peptide treatment. Insulin, but not the peptide, stimulated GLUT1 translocation. Surprisingly, the peptide pretreatment inhibited insulin-induced GLUT1 translocation, suggesting that the peptide treatment has both a stimulatory effect on GLUT4 translocation and an inhibitory effect on insulin-induced GLUT1 translocation. These results suggest that GLUT4 requires translocation to the plasma membrane, as well as activation at the plasma membrane, to initiate glucose uptake, and both of these steps normally require PI 3-kinase activation.
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Affiliation(s)
- Makoto Funaki
- Department of Physiology, Institute for Medicine and Engineering, University of Pennsylvania, 1080 Vagelos Research Laboratories, 3340 Smith Walk, Philadelphia, PA 19104, USA.
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29
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Kanzaki M, Mora S, Hwang JB, Saltiel AR, Pessin JE. Atypical protein kinase C (PKCzeta/lambda) is a convergent downstream target of the insulin-stimulated phosphatidylinositol 3-kinase and TC10 signaling pathways. ACTA ACUST UNITED AC 2004; 164:279-90. [PMID: 14734537 PMCID: PMC2172328 DOI: 10.1083/jcb.200306152] [Citation(s) in RCA: 76] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
Insulin stimulation of adipocytes resulted in the recruitment of atypical PKC (PKCzeta/lambda) to plasma membrane lipid raft microdomains. This redistribution of PKCzeta/lambda was prevented by Clostridium difficile toxin B and by cholesterol depletion, but was unaffected by inhibition of phosphatidylinositol (PI) 3-kinase activity. Expression of the constitutively active GTP-bound form of TC10 (TC10Q/75L), but not the inactive GDP-bound mutant (TC10/T31N), targeted PKCzeta/lambda to the plasma membrane through an indirect association with the Par6-Par3 protein complex. In parallel, insulin stimulation as well as TC10/Q75L resulted in the activation loop phosphorylation of PKCzeta. Although PI 3-kinase activation also resulted in PKCzeta/lambda phosphorylation, it was not recruited to the plasma membrane. Furthermore, insulin-induced GSK-3beta phosphorylation was mediated by both PI 3-kinase-PKB and the TC10-Par6-atypical PKC signaling pathways. Together, these data demonstrate that PKCzeta/lambda can serve as a convergent downstream target for both the PI 3-kinase and TC10 signaling pathways, but only the TC10 pathway induces a spatially restricted targeting to the plasma membrane.
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Affiliation(s)
- Makoto Kanzaki
- Dept. of Pharmacological Sciences, State University of New York at Stony Brook, Stony Brook, NY 11794-8651, USA
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30
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Mitra P, Zheng X, Czech MP. RNAi-based Analysis of CAP, Cbl, and CrkII Function in the Regulation of GLUT4 by Insulin. J Biol Chem 2004; 279:37431-5. [PMID: 15258163 DOI: 10.1074/jbc.c400180200] [Citation(s) in RCA: 82] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Stimulation of glucose transport by insulin in cultured adipocytes through translocation of intracellular GLUT4 glucose transporters to the plasma membrane has been suggested to require phosphatidylinositol (PI) 3-kinase-dependent and independent mechanisms. To test the involvement of a PI 3-kinase-independent pathway leading to activation of the TC10 GTPase, the putative intermediates CAP, c-Cbl, Cbl-b, and CrkII were selectively depleted in 3T3-L1 adipocytes using highly efficient small interfering (si) RNAs. Simultaneous depletion of the ubiquitination factors c-Cbl plus Cbl-b in cultured adipocytes had the expected effect of delaying dephosphorylation of EGF receptors upon removal of EGF. However, siRNA-mediated gene silencing of both Cbl isoforms or CAP or CrkII in these cells failed to attenuate insulin-stimulated deoxyglucose transport or Myc-tagged GLUT4-GFP translocation at either sub-maximal or maximal concentrations of insulin. The dose-response relationship for insulin stimulation of deoxyglucose transport in primary adipocytes derived from c-Cbl knock-out mice was also identical to insulin action on adipocytes from wild type mice. These data are consistent with the hypothesis that CAP, Cbl iso-forms, and CrkII are not required components of insulin signaling to GLUT4 transporters.
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Affiliation(s)
- Prasenjit Mitra
- Program in Molecular Medicine, University of Massachusetts Medical School, Worcester, Massachusetts 01605, USA
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31
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Brozinick JT, Hawkins ED, Strawbridge AB, Elmendorf JS. Disruption of cortical actin in skeletal muscle demonstrates an essential role of the cytoskeleton in glucose transporter 4 translocation in insulin-sensitive tissues. J Biol Chem 2004; 279:40699-706. [PMID: 15247264 PMCID: PMC2409066 DOI: 10.1074/jbc.m402697200] [Citation(s) in RCA: 91] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023] Open
Abstract
Cell culture work suggests that signaling to polymerize cortical filamentous actin (F-actin) represents a required pathway for the optimal redistribution of the insulin-responsive glucose transporter, GLUT4, to the plasma membrane. Recent in vitro study further suggests that the actin-regulatory neural Wiskott-Aldrich syndrome protein (N-WASP) mediates the effect of insulin on the actin filament network. Here we tested whether similar cytoskeletal mechanics are essential for insulin-regulated glucose transport in isolated rat epitrochlearis skeletal muscle. Microscopic analysis revealed that cortical F-actin is markedly diminished in muscle exposed to latrunculin B. Depolymerization of cortical F-actin with latrunculin B caused a time- and concentration-dependent decline in 2-deoxyglucose transport. The loss of cortical F-actin and glucose transport was paralleled by a decline in insulin-stimulated GLUT4 translocation, as assessed by photolabeling of cell surface GLUT4 with Bio-LC-ATB-BMPA. Although latrunculin B impaired insulin-stimulated GLUT4 translocation and glucose transport, activation of phosphatidylinositol 3-kinase and Akt by insulin was not rendered ineffective. In contrast, the ability of insulin to elicit the cortical F-actin localization of N-WASP was abrogated. These data provide the first evidence that actin cytoskeletal mechanics are an essential feature of the glucose transport process in intact skeletal muscle. Furthermore, these findings support a distal actin-based role for N-WASP in insulin action in vivo.
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32
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Bazuine M, Carlotti F, Tafrechi RSJ, Hoeben RC, Maassen JA. Mitogen-Activated Protein Kinase (MAPK) Phosphatase-1 and -4 Attenuate p38 MAPK during Dexamethasone-Induced Insulin Resistance in 3T3-L1 Adipocytes. Mol Endocrinol 2004; 18:1697-707. [PMID: 15184525 DOI: 10.1210/me.2003-0213] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
Prolonged use of glucocorticoids induces pronounced insulin resistance in vivo. In vitro, treatment of 3T3-L1 adipocytes with dexamethasone for 48 h reduces the maximal level of insulin- and stress (arsenite)-induced glucose uptake by approximately 50%. Although phosphatidylinositol 3-kinase signaling was slightly attenuated, phosphorylation of its downstream effectors such as protein kinase B and protein kinase C-lambda remained intact. Nor was any effect of dexamethasone treatment observed on insulin- or arsenite-induced translocation of glucose transporter 4 (GLUT4) toward the plasma membrane. However, for a maximal response to either arsenite- or insulin-induced glucose uptake in these cells, functional p38 MAPK signaling is required. Dexamethasone treatment markedly attenuated p38 MAPK phosphorylation coincident with an up-regulation of the MAPK phosphatases MKP-1 and MKP-4. Employing lentivirus-mediated ectopic expression in fully differentiated 3T3-L1 adipocytes demonstrated a differential effect of these phosphatases: whereas MKP-1 was a more potent inhibitor of insulin-induced glucose uptake, MKP-4 more efficiently inhibited arsenite-induced glucose uptake. This coincided with the effects of these phosphatases on p38 MAPK phosphorylation, i.e. MKP-1 and MKP-4 attenuated p38 MAPK phosphorylation by insulin and arsenite, respectively. Taken together, these data provide evidence that in 3T3-L1 adipocytes dexamethasone inhibits the activation of the GLUT4 in the plasma membrane by a p38 MAPK-dependent process, rather than in a defect in GLUT4 translocation per se.
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Affiliation(s)
- Merlijn Bazuine
- Department of Molecular Cell Biology, Leiden University Medical Center, 2333 AL Leiden, The Netherlands
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33
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Abstract
Although the effects of insulin on glucose and lipid metabolism are well documented, gaps remain in our understanding of the precise molecular mechanisms of signal transduction. Recent evidence suggests that compartmentalization of signaling molecules and metabolic enzymes may explain the unique cellular effects of the hormone. Signal initiation from the insulin receptor is restricted in part to caveolae microdomains of the plasma membrane. A fraction of the insulin receptor directly interacts with caveolin, thus directing the protein to caveolae. Following its activation by insulin, the receptor recruits a series of adapter proteins, resulting in the activation of the G protein TC10, which also resides in caveolae. TC10 can influence a number of cellular processes, including changes in the actin cytoskeleton, recruitment of effector including the adapter protein CIP4, and assembly of the exocyst complex. These events play crucial roles in the trafficking, docking and fusion of vesicles containing the insulin-responsive glucose transporter Glut4 at the plasma membrane.
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Affiliation(s)
- Alan R Saltiel
- Life Sciences Institute, University of Michigan, Ann Arbor, MI 48109-0650, USA.
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Ahn MY, Katsanakis KD, Bheda F, Pillay TS. Primary and Essential Role of the Adaptor Protein APS for Recruitment of Both c-Cbl and Its Associated Protein CAP in Insulin Signaling. J Biol Chem 2004; 279:21526-32. [PMID: 15031295 DOI: 10.1074/jbc.m307740200] [Citation(s) in RCA: 54] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
APS (adapter protein with Pleckstrin homology and Src homology 2 domains) is recruited by the autophosphorylated insulin receptor and is essential for Glut4 translocation. Although both APS and CAP (c-Cbl-associated protein) interact with c-Cbl during insulin signaling, the relative importance of each protein in recruiting c-Cbl has not been clear. We performed a side-by-side comparison by ectopic expression of APS or Src homology 2-Balpha (SH2-Balpha) and CAP in Chinese hamster ovary (CHO) cells. In cells co-expressing insulin receptor and CAP, without APS, no association of the insulin receptor and CAP could be detected and no insulin-stimulated phosphorylation of Cbl was observed. Insulin-stimulated Cbl phosphorylation was reconstituted when APS was co-expressed with insulin receptor, with or without CAP. APS or SH2-Balpha and CAP interacted in the basal state, and in the case of APS this interaction was mediated by the C terminus of APS. Insulin stimulation resulted in the dissociation of APS and CAP. Similarly, insulin stimulation also resulted in the dissociation of SH2-Balpha and CAP in CHO cells. CAP was localized to the membrane in the presence of APS. Insulin stimulation resulted in the re-localization of CAP to the cytosol only when APS was co-expressed. In 3T3-L1 adipocytes, small interfering RNA-mediated knockdown of the mouse APS gene abolished the insulin-stimulated phosphorylation of c-Cbl. Taken together, these results indicate that APS plays a central role in recruiting both CAP and c-Cbl to the insulin receptor after insulin stimulation and is necessary and sufficient for the insulin-stimulated phosphorylation of c-Cbl, whereas SH2-Balpha may provide an alternative pathway for the recruitment of CAP.
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Affiliation(s)
- Mee-Young Ahn
- Institute of Cell Signaling and School of Biomedical Sciences, University of Nottingham Medical School, Queen's Medical Centre, Nottingham NG7 2UH, United Kingdom
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35
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Cariou B, Postic C, Boudou P, Burcelin R, Kahn CR, Girard J, Burnol AF, Mauvais-Jarvis F. Cellular and molecular mechanisms of adipose tissue plasticity in muscle insulin receptor knockout mice. Endocrinology 2004; 145:1926-32. [PMID: 14684612 DOI: 10.1210/en.2003-0882] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
White adipose tissue (WAT) plays a critical role in the development of insulin resistance via secretion of free fatty acids (FFA) and adipocytokines. Muscle-specific insulin receptor knockout (MIRKO) mice do not develop insulin resistance or diabetes under physiological conditions despite a marked increase in adiposity and plasma FFA. On the contrary, WAT of MIRKO is sensitized to insulin action during a euglycemic clamp, and WAT glucose utilization is dramatically increased. To get insight into the potential antidiabetic role of MIRKO adiposity, we have studied insulin action in WAT during a euglycemic, hyperinsulinemic clamp, and we have characterized the morphology and biology of WAT. During the clamp, there is no alteration in the expression or activation in the insulin signaling molecules involved in glucose transport through the phosphoinositide 3-kinase/Akt and CAP/Cbl pathways in WAT from MIRKO. The 53% increase in WAT mass results from a 48% increase in adipocyte number (P < 0.05) without alteration in cell size and contemporary to a 300% increase in mRNA levels of the adipogenic transcription factor CCAAT enhancer binding protein-alpha (C/EBP-alpha) (P < 0.05). There is a 39.5% increase in serum adiponectin (P < 0.01) without modification in serum leptin, resistin, and TNF-alpha. In conclusion, the MIRKO mouse displays muscle insulin resistance, visceral obesity, and dyslipidemia but does not develop hyperinsulinemia or diabetes. There is an accelerated differentiation of small insulin sensitive adipocytes, an increased secretion of the insulin sensitizer adiponectin, and maintenance of leptin sensitivity. The MIRKO mouse confirms the importance of WAT plasticity in the maintenance of whole body insulin sensitivity and represents an interesting model to search for new secreted molecules that positively alter adipose tissue biology.
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Affiliation(s)
- Bertrand Cariou
- Department of Endocrinology, Institut National de la Santé et de la Recherche Médicale, Unité 567-Centre National de la Recherche Scientifique, Paris, France
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36
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Shen Q, Cline GW, Shulman GI, Leibowitz MD, Davies PJA. Effects of rexinoids on glucose transport and insulin-mediated signaling in skeletal muscles of diabetic (db/db) mice. J Biol Chem 2004; 279:19721-31. [PMID: 14998989 DOI: 10.1074/jbc.m311729200] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Rexinoids and thiazolidinediones (TZDs) are two classes of nuclear receptor ligands that induce insulin sensitization in diabetic rodents. TZDs are peroxisome proliferator-activated receptor gamma (PPARgamma) activators, whereas rexinoids are selective ligands for the retinoid X receptors (RXRs). Activation of both the insulin receptor substrates (IRSs)/Akt and the c-Cbl-associated protein (CAP)/c-Cbl pathways are important in regulating insulin-stimulated glucose transport. We have compared the effects of a rexinoid (LG268) and a TZD (rosiglitazone) on these two signal pathways in skeletal muscle of diabetic (db/db) mice. The results we have obtained show that treatment of db/db mice with either LG268 or rosiglitazone for 2 weeks results in a significant increase in insulin-stimulated glucose transport activity in skeletal muscle. Treatment with LG268 increases insulin-stimulated IRS-1 tyrosine phosphorylation and Akt phosphorylation in skeletal muscle without affecting the activity of the CAP/c-Cbl pathway. In contrast, rosiglitazone increases the levels of CAP expression and insulin-stimulated c-Cbl phosphorylation without affecting the IRS-1/Akt pathway. The effects of LG268 on the IRS-1/Akt pathway were associated with a decrease in the level of IRS-1 Ser(307) phosphorylation. Taken together, these data suggest that rexinoids improve insulin sensitivity via changes in skeletal muscle metabolism that are distinct from those induced by TZDs. Rexinoids represent a novel class of insulin sensitizers with potential applications in the treatment of insulin resistance.
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Affiliation(s)
- Qi Shen
- Department of Integrative Biology and Pharmacology, University of Texas Medical School, 6431 Fannin Street, Houston, TX 77225, USA
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37
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Wadley GD, Bruce CR, Konstantopoulos N, Macaulay SL, Howlett KF, Hawley JA, Cameron-Smith D. The effect of insulin and exercise on c-Cbl protein abundance and phosphorylation in insulin-resistant skeletal muscle in lean and obese Zucker rats. Diabetologia 2004; 47:412-419. [PMID: 14730380 DOI: 10.1007/s00125-003-1322-2] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/13/2003] [Revised: 10/31/2003] [Indexed: 10/26/2022]
Abstract
AIMS/HYPOTHESIS Recruitment of the protein c-Cbl to the insulin receptor (IR) and its tyrosine phosphorylation via a pathway that is independent from phosphatidylinositol 3'-kinase is necessary for insulin-stimulated GLUT4 translocation in 3T3-L1 adipocytes. The activation of this pathway by insulin or exercise has yet to be reported in skeletal muscle. METHODS Lean and obese Zucker rats were randomly assigned to one of three treatment groups: (i). control, (ii). insulin-stimulated or (iii). acute, exhaustive exercise. Hind limb skeletal muscle was removed and the phosphorylation state of IR, Akt and c-Cbl measured. RESULTS Insulin receptor phosphorylation was increased 12-fold after insulin stimulation ( p<0.0001) in lean rats and threefold in obese rats. Acute exercise had no effect on IR tyrosine phosphorylation. Similar results were found for serine phosphorylation of Akt. Exercise did not alter c-Cbl tyrosine phosphorylation in skeletal muscle of lean or obese rats. However, in contrast to previous studies in adipocytes, c-Cbl tyrosine phosphorylation was reduced after insulin treatment ( p<0.001). CONCLUSIONS/INTERPRETATION We also found that c-Cbl associating protein expression is relatively low in skeletal muscle of Zucker rats compared to 3T3-L1 adipocytes and this could account for the reduced c-Cbl tyrosine phosphorylation after insulin treatment. Interestingly, basal levels of c-Cbl tyrosine phosphorylation were higher in skeletal muscle from insulin-resistant Zucker rats ( p<0.05), but the physiological relevance is not clear. We conclude that the regulation of c-Cbl phosphorylation in skeletal muscle differs from that previously reported in adipocytes.
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Affiliation(s)
- G D Wadley
- School of Health Sciences, Deakin University, Burwood, Victoria, 3125, Australia
| | - C R Bruce
- School of Medical Sciences, RMIT University, Bundoora, Victoria, Australia
| | - N Konstantopoulos
- Health Sciences and Nutrition, Commonwealth Scientific and Industrial Research Organisation, Parkville, Victoria, Australia
| | - S L Macaulay
- Health Sciences and Nutrition, Commonwealth Scientific and Industrial Research Organisation, Parkville, Victoria, Australia
| | - K F Howlett
- School of Health Sciences, Deakin University, Burwood, Victoria, 3125, Australia
| | - J A Hawley
- School of Medical Sciences, RMIT University, Bundoora, Victoria, Australia
| | - D Cameron-Smith
- School of Health Sciences, Deakin University, Burwood, Victoria, 3125, Australia.
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38
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Affiliation(s)
- Stuart A Ross
- Department of Cardiovascular and Metabolic Diseases, Mail Zone T2E, Pharmacia Corporation, 800 North Lindbergh Boulevard, St Louis, Missouri 63167, USA
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39
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Thirone ACP, Carvalheira JBC, Hirata AE, Velloso LA, Saad MJA. Regulation of Cbl-associated protein/Cbl pathway in muscle and adipose tissues of two animal models of insulin resistance. Endocrinology 2004; 145:281-93. [PMID: 14525909 DOI: 10.1210/en.2003-0575] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
The phosphatidylinositol 3-kinase-independent pathway to induce glucose transport may involve the tyrosine phosphorylation of the protooncogene c-Cbl. In the present study, we examined whether acute exposure to insulin stimulates the tyrosine phosphorylation of Cbl and its association with Cbl-associated protein (CAP) in muscle and adipose tissue of rats in vivo. We report herein that insulin induces Cbl tyrosine phosphorylation and association with CAP in adipose tissue but not in muscle. We also examined the expression and tyrosyl-phosphorylation state of Cbl and CAP/Cbl association in adipose tissue of rats submitted to prolonged fasting and in monosodium glutamate (MSG)-insulin-resistant rats. An increase in Cbl phosphorylation is observed in the fat of MSG rats, parallel with an increase in association of CAP-Cbl as well as an augment in CAP and Cbl protein expression in the adipose tissue of these animals. These events are accompanied by a decrease in insulin-stimulated insulin receptor/ insulin receptor substrate (IRS)-1 tyrosine phosphorylation and an increase in the IRS-2/phosphatidylinositol 3-kinase/Akt/Foxo1 pathway. In adipocytes of fasted rats, there is a decrease in CAP and Cbl protein expression, insulin-induced Cbl phosphorylation, and the association with CAP. In parallel, there is also a decrease in the insulin receptor/IRSs/Akt/Foxo1 pathway. Thus, insulin is able to induce Cbl tyrosine phosphorylation and its association with CAP in the adipose tissue of normal rats. In addition, our data provide evidence that the CAP-Cbl pathway may have a role in the modulation of adiposity in fasting and in MSG-treated rats.
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Affiliation(s)
- Ana C P Thirone
- Departamento de Clínica Médica, Faculdade de Ciências Médicas, Universidade Estadual de Campinas, 13081-970 Campinas, São Paulo, Brazil
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40
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41
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Cohen AW, Combs TP, Scherer PE, Lisanti MP. Role of caveolin and caveolae in insulin signaling and diabetes. Am J Physiol Endocrinol Metab 2003; 285:E1151-60. [PMID: 14607781 DOI: 10.1152/ajpendo.00324.2003] [Citation(s) in RCA: 153] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
Abstract
Caveolae are specialized membrane microdomains present within the plasma membrane of the vast majority of cell types. They have a unique composition in that they are highly enriched in cholesterol, sphingolipids, and their coat proteins the caveolins (-1, -2, and -3). In recent years it has been recognized that caveolae act as signaling platforms, serving as a concentrating point for numerous signaling molecules, as well as regulating flux through many distinct signaling cascades. Although caveolae are found in a variety of cell types, they are most abundant in adipose tissue. This fact has led to the intense study of the function of these organelles in adipocytes. It has now become apparent that effective insulin signaling in the adipocyte may be strictly dependent on localization of at least two insulin-responsive elements to caveolae (insulin receptor and GLUT4), as well as on a direct functional interaction between caveolin-1 and the insulin receptor. We present a critical discussion of these recent findings.
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Affiliation(s)
- Alex W Cohen
- Department of Molecular Pharmacology, Albert Einstein Diabetes Research and Training Center, Albert Einstein College of Medicine, 1300 Morris Park Ave., Bronx, NY 10461, USA
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42
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Liu P, Leffler BJ, Weeks LK, Chen G, Bouchard CM, Strawbridge AB, Elmendorf JS. Sphingomyelinase activates GLUT4 translocation via a cholesterol-dependent mechanism. Am J Physiol Cell Physiol 2003; 286:C317-29. [PMID: 14522816 DOI: 10.1152/ajpcell.00073.2003] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
A basis for the insulin mimetic effect of sphingomyelinase on glucose transporter isoform GLUT4 translocation remains unclear. Because sphingomyelin serves as a major determinant of plasma membrane cholesterol and a relationship between plasma membrane cholesterol and GLUT4 levels has recently become apparent, we assessed whether GLUT4 translocation induced by sphingomyelinase resulted from changes in membrane cholesterol content. Exposure of 3T3-L1 adipocytes to sphingomyelinase resulted in a time-dependent loss of sphingomyelin from the plasma membrane and a concomitant time-dependent accumulation of plasma membrane GLUT4. Degradation products of sphingomyelin did not mimic this stimulatory action. Plasma membrane cholesterol amount was diminished in cells exposed to sphingomyelinase. Restoration of membrane cholesterol blocked the stimulatory effect of sphingomyelinase. Increasing concentrations of methyl-beta-cyclodextrin, which resulted in a dose-dependent reversible decrease in membrane cholesterol, led to a dose-dependent reversible increase in GLUT4 incorporation into the plasma membrane. Although increased plasma membrane GLUT4 content by cholesterol extraction with concentrations of methyl-beta-cyclodextrin above 5 mM most likely reflected decreased GLUT4 endocytosis, translocation stimulated by sphingomyelinase or concentrations of methyl-beta-cyclodextrin below 2.5 mM occurred without any visible changes in the endocytic retrieval of GLUT4. Furthermore, moderate loss of cholesterol induced by sphingomyelinase or low concentrations of methyl-beta-cyclodextrin did not alter membrane integrity or increase the abundance of other plasma membrane proteins such as the GLUT1 glucose transporter or the transferrin receptor. Regulation of GLUT4 translocation by moderate cholesterol loss did not involve known insulin-signaling proteins. These data reveal that sphingomyelinase enhances GLUT4 exocytosis via a novel cholesterol-dependent mechanism.
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Affiliation(s)
- Ping Liu
- Department of Cellular and Integrative Physiology, Indiana University School of Medicine, Center for Diabetes Research, Indianapolis, IN 46202, USA
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43
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Liu J, DeYoung SM, Hwang JB, O'Leary EE, Saltiel AR. The roles of Cbl-b and c-Cbl in insulin-stimulated glucose transport. J Biol Chem 2003; 278:36754-62. [PMID: 12842890 DOI: 10.1074/jbc.m300664200] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Previous studies suggest that the stimulation of glucose transport by insulin involves the tyrosine phosphorylation of c-Cbl and the translocation of the c-Cbl/CAP complex to lipid raft subdomains of the plasma membrane. We now demonstrate that Cbl-b also undergoes tyrosine phosphorylation and membrane translocation in response to insulin in 3T3-L1 adipocytes. Ectopic expression of APS facilitated insulin-stimulated phosphorylation of tyrosines 665 and 709 in Cbl-b. The phosphorylation of APS produced by insulin drove the translocation of both c-Cbl and Cbl-b to the plasma membrane. Like c-Cbl, Cbl-b associates constitutively with CAP and interacts with Crk upon insulin stimulation. Cbl proteins formed homo- and heterodimers in vivo, which required the participation of a conserved leucine zipper domain. A Cbl mutant incapable of dimerization failed to interact with APS and to undergo tyrosine phosphorylation in response to insulin, indicating an essential role of Cbl dimerization in these processes. Thus, both c-Cbl and Cbl-b can initiate a phosphatidylinositol 3-kinase/protein kinase B-independent signaling pathway critical to insulin-stimulated GLUT4 translocation.
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Affiliation(s)
- Jun Liu
- Departments of Internal Medicine and Physiology, Life Sciences Institute, University of Michigan Medical Center, Ann Arbor, Michigan 48109, USA
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44
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Whiteman EL, Chen JJ, Birnbaum MJ. Platelet-derived growth factor (PDGF) stimulates glucose transport in 3T3-L1 adipocytes overexpressing PDGF receptor by a pathway independent of insulin receptor substrates. Endocrinology 2003; 144:3811-20. [PMID: 12933652 DOI: 10.1210/en.2003-0480] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
Insulin is unique among growth factors and hormones in its ability to control metabolic functions such as the stimulation of glucose uptake and glucose transporter (GLUT4) translocation in physiological target tissues, such as muscle and adipose cells. Nonetheless, the mechanisms underlying this specificity have remained incompletely understood, particularly in view of the ability of some growth factors to mimic insulin-dependent early signaling events. In this study, we have probed the basis of insulin specificity by overexpressing in hormone-responsive 3T3-L1 adipocytes wild-type platelet-derived growth factor (PDGF) receptor (PDGFR)-beta and selected, informative mutant receptor proteins. We show that such adipocytes overexpressing wild-type PDGFR on exposure to cognate growth factor activate glucose transport, GLUT4 translocation, and the serine-threonine protein kinase Akt/protein kinase B to a degree comparable with that produced in response to insulin. In addition, PDGF elicits the robust generation of phosphatidylinositol-3,4,5-trisphosphate in vivo in PDGFR-overexpressing 3T3-L1 adipocytes. Expression of PDGFR-beta mutant proteins demonstrates that these responses require the presence of an intact phosphatidylinositol 3-kinase (PI3K)-binding site on the overexpressed PDGF receptor. Furthermore, PDGF stimulates these effects independent of insulin receptor substrate(IRS)-1 or IRS-2 tyrosine phosphorylation or docking to activated PI3K. These data demonstrate that 1) the basis of insulin-specific glucose transport in cultured adipocytes is the low level of receptors for other growth factors and 2) in the presence of adequate receptors, PDGF is fully capable of activating glucose transport in a manner requiring PI3K and subsequent phosphatidylinositol-3,4,5-trisphosphate accumulation but independent of insulin, insulin receptor, and IRS proteins.
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Affiliation(s)
- Eileen L Whiteman
- Howard Hughes Medical Institute, Cox Institute, Cell and Molecular Biology Graduate Group, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104, USA
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45
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Chunqiu Hou J, Pessin JE. Lipid Raft targeting of the TC10 amino terminal domain is responsible for disruption of adipocyte cortical actin. Mol Biol Cell 2003; 14:3578-91. [PMID: 12972548 PMCID: PMC196551 DOI: 10.1091/mbc.e03-01-0012] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
Overexpression of the Rho family member TC10alpha, disrupts adipocyte cortical actin structure and inhibits insulin-stimulated GLUT4 translocation when targeted to lipid raft microdomains. This appears to be independent of effecter domain function because overexpression of the wild-type (TC10/WT), constitutively GTP-bound (TC10/Q75L), and constitutively GDP bound (TC10/T31N) all inhibit adipocyte cortical actin structure and GLUT4 translocation. To examine the structural determinants responsible for these effects, we generated a series of chimera proteins between TC10 with that of H-Ras and K-Ras. Chimera containing the 79 (TC10-79/H-Ras), 41 (TC10-41/H-Ras), or 16 (TC10-16/H-Ras) amino acids of the TC10 amino terminal extension fused to H-Ras disrupted cortical actin and inhibited insulin-stimulated GLUT4 translocation. In contrast, the same amino terminal TC10 extensions fused to K-Ras had no significant effect on either GLUT4 translocation or cortical actin structure. Similarly, expression of TC10beta was without effect, whereas fusion of the amino terminal 8 amino acid of TC10alpha onto TC10beta resulted in an inhibition of insulin-stimulated GLUT4 translocation. Within the amino terminal extension point mutation analysis demonstrated that both a GAG and GPG sequences when lipid raft targeted was essential for these effects. Furthermore, expression of the amino terminal TC10 deletions DeltaNT-TC10/WT or DeltaNT-TC10/T31N had no detectable effect on cortical actin organization and did not perturb insulin-stimulated GLUT4 translocation. Surprisingly, however, expression of DeltaNT-TC10/Q75L remained fully capable of inhibiting insulin-stimulated GLUT4 translocation without affecting cortical actin. These data demonstrate that inhibitory effect of TC10 overexpression on adipocyte cortical actin organization is due to the specific lipid raft targeting of the unusual TC10 amino terminal extension.
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Affiliation(s)
- June Chunqiu Hou
- The Department of Pharmacological Sciences, State University of New York at Stony Brook, Stony Brook, New York 11794-8651, USA
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46
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Moon B, Kwan JJM, Duddy N, Sweeney G, Begum N. Resistin inhibits glucose uptake in L6 cells independently of changes in insulin signaling and GLUT4 translocation. Am J Physiol Endocrinol Metab 2003; 285:E106-15. [PMID: 12618360 DOI: 10.1152/ajpendo.00457.2002] [Citation(s) in RCA: 101] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Elevated levels of resistin have been proposed to cause insulin resistance and therefore may serve as a link between obesity and type 2 diabetes. However, its role in skeletal muscle metabolism is unknown. In this study, we examined the effect of resistin on insulin-stimulated glucose uptake and the upstream insulin-signaling components in L6 rat skeletal muscle cells that were either incubated with recombinant resistin or stably transfected with a vector containing the myc-tagged mouse resistin gene. Transfected clones expressed intracellular resistin, which was released in the medium. Incubation with recombinant resistin resulted in a dose-dependent inhibition of insulin-stimulated 2-deoxyglucose (2-DG) uptake. The inhibitory effect of resistin on insulin-stimulated 2-DG uptake was not the result of impaired GLUT4 translocation to the plasma membrane. Furthermore, resistin did not alter the insulin receptor (IR) content and its phosphorylation, nor did it affect insulin-stimulated insulin receptor substrate (IRS)-1 tyrosine phosphorylation, its association with the p85 subunit of phosphatidylinositol (PI) 3-kinase, or IRS-1-associated PI 3-kinase enzymatic activity. Insulin-stimulated phosphorylation of Akt/protein kinase B-alpha, one of the downstream targets of PI 3-kinase and p38 MAPK phosphorylation, was also not affected by resistin. Expression of resistin also inhibited insulin-stimulated 2-DG uptake when compared with cells expressing the empty vector (L6Neo) without affecting GLUT4 translocation, GLUT1 content, and IRS-1/PI 3-kinase signaling. We conclude that resistin does not alter IR signaling but does affect insulin-stimulated glucose uptake, presumably by decreasing the intrinsic activity of cell surface glucose transporters.
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MESH Headings
- Animals
- Antimetabolites/pharmacology
- Blotting, Northern
- Blotting, Western
- Cell Line
- DNA, Complementary/biosynthesis
- DNA, Complementary/genetics
- Deoxyglucose/pharmacology
- Escherichia coli/metabolism
- Genes, myc/genetics
- Glucose/metabolism
- Glucose Transporter Type 4
- Hormones, Ectopic/biosynthesis
- Hormones, Ectopic/genetics
- Hormones, Ectopic/pharmacology
- Hypoglycemic Agents/pharmacology
- Insulin/pharmacology
- Insulin/physiology
- Intercellular Signaling Peptides and Proteins
- Mice
- Microscopy, Confocal
- Monosaccharide Transport Proteins/metabolism
- Muscle Fibers, Skeletal/metabolism
- Muscle Proteins
- Muscle, Skeletal/cytology
- Muscle, Skeletal/drug effects
- Muscle, Skeletal/metabolism
- Nerve Growth Factor
- Phosphorylation
- Proteins
- RNA, Messenger/biosynthesis
- Rats
- Receptor, Insulin/drug effects
- Receptor, Insulin/physiology
- Recombinant Proteins/biosynthesis
- Recombinant Proteins/pharmacology
- Resistin
- Signal Transduction/drug effects
- Subcellular Fractions/drug effects
- Subcellular Fractions/metabolism
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Affiliation(s)
- Byoung Moon
- Diabetes Research Laboratory, Winthrop University Hospital, Mineola, New York 11501, USA
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47
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Harmon AW, Patel YM. Naringenin inhibits phosphoinositide 3-kinase activity and glucose uptake in 3T3-L1 adipocytes. Biochem Biophys Res Commun 2003; 305:229-34. [PMID: 12745063 DOI: 10.1016/s0006-291x(03)00720-4] [Citation(s) in RCA: 64] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Previous studies have shown that flavonoids inhibit glucose uptake in cultured cells. In this report, we show that the grapefruit flavanone naringenin inhibited insulin-stimulated glucose uptake in 3T3-L1 adipocytes in a dose-dependent manner. Naringenin acts by inhibiting the activity of phosphoinositide 3-kinase (PI3K), a key regulator of insulin-induced GLUT4 translocation. Although naringenin did not alter the phosphotyrosine status of the insulin receptor, insulin receptor substrate proteins, or PI3K, it did inhibit the phosphorylation of the downstream signaling molecule Akt. In an in vitro kinase assay, naringenin inhibited PI3K activity. A physiologically attainable dose of 6 microM naringenin reduced insulin-stimulated glucose uptake by approximately 20%. This inhibitory effect remained 24h after the removal of naringenin from the culture medium. Collectively, our findings suggest that the regular consumption of naringenin in grapefruit may exacerbate insulin resistance in susceptible individuals via impaired glucose uptake in adipose tissue.
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Affiliation(s)
- Anne W Harmon
- Department of Nutrition, University of North Carolina School of Public Health, Chapel Hill, NC 27599, USA
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48
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Kawashima J, Tsuruzoe K, Motoshima H, Shirakami A, Sakai K, Hirashima Y, Toyonaga T, Araki E. Insulin down-regulates resistin mRNA through the synthesis of protein(s) that could accelerate the degradation of resistin mRNA in 3T3-L1 adipocytes. Diabetologia 2003; 46:231-40. [PMID: 12627322 DOI: 10.1007/s00125-002-1022-3] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/22/2002] [Revised: 10/14/2002] [Indexed: 01/23/2023]
Abstract
AIMS/HYPOTHESIS Resistin is a peptide secreted by adipocytes and recognized as a hormone that could link obesity to insulin resistance. This study was designed to examine the effect and mechanism(s) of insulin on resistin expression in 3T3-L1 adipocytes. METHODS Differentiated 3T3-L1 adipocytes were stimulated with insulin and resistin mRNA expression was examined by Northern blot analysis. In some experiments, the insulin signal was blocked by several chemical inhibitors or overexpression of a dominant negative form (Deltap85) of the p85 subunit of phosphatidylinositol 3-kinase (PI 3-kinase). RESULTS Insulin treatment caused a reduction of resistin mRNA in time-dependent and dose-dependent manners in 3T3-L1 adipocytes. Pre-treatment with PD98059, an inhibitor of extracellular signal-regulated kinase 1/2 (ERK1/2) pathway, or SB203580, an inhibitor of p38 mitogen-activated protein-kinase (p38 MAP-kinase) pathway, did not influence insulin-induced reduction of resistin mRNA. Inhibition of PI 3-kinase by LY294002 or Deltap85 also failed to block insulin-induced reduction of resistin mRNA. Cycloheximide, a protein synthesis inhibitor, completely blocked insulin-induced reduction of resistin mRNA. Actinomycin D, a RNA synthesis inhibitor, also blocked insulin-induced reduction of resistin mRNA, and the decreasing rate of resistin mRNA in cells treated with insulin alone was faster than that with actinomycin D. CONCLUSION/INTERPRETATION Insulin downregulates resistin mRNA via PI 3-kinase, ERK or p38 MAP-kinase independent pathways in 3T3-L1 adipocytes. The downregulation mechanism of resistin mRNA by insulin would be an indirect event through the synthesis of novel protein(s) that could accelerate the degradation of resistin mRNA.
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Affiliation(s)
- J Kawashima
- Department of Metabolic Medicine, Kumamoto University School of Medicine, 1-1-1 Honjo, 860-8556 Kumamoto, Japan
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49
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Abstract
The incidence of type 2 diabetes mellitus (T2D) and obesity is increasing rapidly worldwide, reaching epidemic proportions. Insulin resistance is a key feature in both conditions and plays an important pathophysiological role. Over the last two decades a central role in the origin of insulin resistance has emerged for defects in the intracellular insulin signaling cascade leading to glucose uptake. Herein, we will 1) review insulin signaling pathways leading to glucose uptake, 2) review mouse models of insulin resistance that demonstrate the pathophysiologic importance of specific defects of these pathways and 3) discuss the molecular basis for insulin resistance in some human disease states known to be associated with insulin resistance. Finally, we will briefly mention some novel treatment targets for T2D stemming from this knowledge.
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Affiliation(s)
- Peter Vollenweider
- Department of Internal Medicine, Centre Hospitalier Universitaire Vaudois, Lausanne, Switzerland.
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50
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Tobe K, Asai S, Matuoka K, Yamamoto T, Chida K, Kaburagi Y, Akanuma Y, Kuroki T, Takenawa T, Kimura S, Nagai R, Kadowaki T. Cytoskeletal reorganization induced by insulin: involvement of Grb2/Ash, Ras and phosphatidylinositol 3-kinase signalling. Genes Cells 2003; 8:29-40. [PMID: 12558797 DOI: 10.1046/j.1365-2443.2003.00611.x] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
BACKGROUND Cytoskeletal reorganization is important for a wide variety of insulin-mediated biological actions, including cell growth, migration and metabolism, but the intracellular signalling pathways leading to insulin-induced cytoskeletal reorganization have largely been unknown. We therefore investigated the involvement of Grb2/Ash-Ras and phosphatidylinositol (PI) 3-kinase in the insulin-induced morphological changes in fibroblasts over-expressing human insulin receptors (HIRcB cells). RESULTS Insulin, as well as 12-O-tetradecanoylphorbol-13-acetate (TPA) and 8-bromo-cAMP, induced a unique morphological change associated with actin cytoskeletal reorganization characterized by the disruption of actin stress fibres and thicker actin bundle formation. Microinjection of an anti-Grb2/Ash antibody, but not control IgG, inhibited the insulin-induced actin reorganization, whereas the TPA- and 8-bromo-cAMP-induced morphological changes were not inhibited by microinjection of the anti-Grb2/Ash antibody. In addition, microinjection of dominant negative ras p21 protein, but not the heat-treated protein, inhibited insulin-induced cytoskeletal reorganization. Microinjection of activated p21ras protein resulted in very similar cytoskeletal reorganization with actin bundle formation in the cytoplasm. The PI3-kinase inhibitor wortmannin inhibited insulin-induced cytoskeletal reorganization, but not the TPA- nor 8-bromo-cAMP-induced reorganization. Interestingly, wortmannin also inhibited the activated p21ras-induced morphological change. CONCLUSIONS We concluded that Grb2/Ash-Ras activation and probably Ras-associated PI3-kinase activation are involved in the insulin-induced morphological change.
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Affiliation(s)
- Kazuyuki Tobe
- Department of Internal Medicine, Graduate School of Medicine, University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-8655, Japan
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