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Ugrankar-Banerjee R, Tran S, Bowerman J, Kovalenko A, Paul B, Henne WM. The fat body cortical actin network regulates Drosophila inter-organ nutrient trafficking, signaling, and adipose cell size. eLife 2023; 12:e81170. [PMID: 37144872 PMCID: PMC10202455 DOI: 10.7554/elife.81170] [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: 06/17/2022] [Accepted: 04/25/2023] [Indexed: 05/06/2023] Open
Abstract
Defective nutrient storage and adipocyte enlargement (hypertrophy) are emerging features of metabolic syndrome and type 2 diabetes. Within adipose tissues, how the cytoskeletal network contributes to adipose cell size, nutrient uptake, fat storage, and signaling remain poorly understood. Utilizing the Drosophila larval fat body (FB) as a model adipose tissue, we show that a specific actin isoform-Act5C-forms the cortical actin network necessary to expand adipocyte cell size for biomass storage in development. Additionally, we uncover a non-canonical role for the cortical actin cytoskeleton in inter-organ lipid trafficking. We find Act5C localizes to the FB cell surface and cell-cell boundaries, where it intimately contacts peripheral LDs (pLDs), forming a cortical actin network for cell architectural support. FB-specific loss of Act5C perturbs FB triglyceride (TG) storage and LD morphology, resulting in developmentally delayed larvae that fail to develop into flies. Utilizing temporal RNAi-depletion approaches, we reveal that Act5C is indispensable post-embryogenesis during larval feeding as FB cells expand and store fat. Act5C-deficient FBs fail to grow, leading to lipodystrophic larvae unable to accrue sufficient biomass for complete metamorphosis. In line with this, Act5C-deficient larvae display blunted insulin signaling and reduced feeding. Mechanistically, we also show this diminished signaling correlates with decreased lipophorin (Lpp) lipoprotein-mediated lipid trafficking, and find Act5C is required for Lpp secretion from the FB for lipid transport. Collectively, we propose that the Act5C-dependent cortical actin network of Drosophila adipose tissue is required for adipose tissue size-expansion and organismal energy homeostasis in development, and plays an essential role in inter-organ nutrient transport and signaling.
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Affiliation(s)
| | - Son Tran
- Department of Cell Biology, UT Southwestern Medical CenterDallasUnited States
| | - Jade Bowerman
- Department of Cell Biology, UT Southwestern Medical CenterDallasUnited States
| | | | - Blessy Paul
- Department of Cell Biology, UT Southwestern Medical CenterDallasUnited States
| | - W Mike Henne
- Department of Cell Biology, UT Southwestern Medical CenterDallasUnited States
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2
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Wang H, Wan X, Pilch PF, Ellisen LW, Fried SK, Liu L. An AMPK-dependent, non-canonical p53 pathway plays a key role in adipocyte metabolic reprogramming. eLife 2020; 9:63665. [PMID: 33320092 PMCID: PMC7758072 DOI: 10.7554/elife.63665] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2020] [Accepted: 12/14/2020] [Indexed: 12/27/2022] Open
Abstract
It has been known adipocytes increase p53 expression and activity in obesity, however, only canonical p53 functions (i.e. senescence and apoptosis) are attributed to inflammation-associated metabolic phenotypes. Whether or not p53 is directly involved in mature adipocyte metabolic regulation remains unclear. Here we show p53 protein expression can be up-regulated in adipocytes by nutrient starvation without activating cell senescence, apoptosis, or a death-related p53 canonical pathway. Inducing the loss of p53 in mature adipocytes significantly reprograms energy metabolism and this effect is primarily mediated through a AMP-activated protein kinase (AMPK) pathway and a novel downstream transcriptional target, lysosomal acid lipase (LAL). The pathophysiological relevance is further demonstrated in a conditional and adipocyte-specific p53 knockout mouse model. Overall, these data support a non-canonical p53 function in the regulation of adipocyte energy homeostasis and indicate that the dysregulation of this pathway may be involved in developing metabolic dysfunction in obesity.
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Affiliation(s)
- Hong Wang
- Departments of Pharmacology & Experimental Therapeutics, Boston University, School of Medicine, Boston, United States
| | - Xueping Wan
- Departments of Pharmacology & Experimental Therapeutics, Boston University, School of Medicine, Boston, United States
| | - Paul F Pilch
- Biochemistry, Boston University, School of Medicine, Boston, United States
| | - Leif W Ellisen
- Massachusetts General Hospital Cancer Center, Boston, United States.,Harvard Medical School, Boston, United States
| | - Susan K Fried
- Diabetes Obesity and Metabolism Institute, Icahn School of Medicine at Mount Sinai, New York, United States
| | - Libin Liu
- Departments of Pharmacology & Experimental Therapeutics, Boston University, School of Medicine, Boston, United States
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3
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Wang H, Pilch PF, Liu L. Cavin-1/PTRF mediates insulin-dependent focal adhesion remodeling and ameliorates high-fat diet-induced inflammatory responses in mice. J Biol Chem 2019; 294:10544-10552. [PMID: 31126986 DOI: 10.1074/jbc.ra119.008824] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2019] [Revised: 05/20/2019] [Indexed: 11/06/2022] Open
Abstract
Cavin-1/polymerase I and transcript release factor (PTRF) is a requisite component of caveolae, small plasma membrane invaginations that are highly abundant in adipocytes. Cavin-1 is a dynamic molecule whose dissociation from caveolae plays an important role in mechanoprotection and rRNA synthesis. In the former situation, the acute dissociation of cavin-1 from caveolae allows cell membrane expansion that occurs upon insulin-aided lipid uptake into the fat cells. Cavin-1 dissociation from caveolae and membrane flattening alters the cytoskeleton and the interaction of plasma membrane proteins with the extracellular matrix through interactions with focal adhesion structures. Here, using cavin-1 knockout mice, subcellular fractionation, and immunoblotting methods, we addressed the relationship of cavin-1 with focal adhesion complexes following nutritional stimulation. We found that cavin-1 is acutely translocated to focal complex compartments upon insulin stimulation, where it regulates focal complex formation through an interaction with paxillin. We found that loss of cavin-1 impairs focal complex remodeling and focal adhesion formation and causes a mechanical stress response, concomitant with activation of proinflammatory and senescence/apoptosis pathways. We conclude that cavin-1 plays key roles in dynamic remodeling of focal complexes upon metabolic stimulation. This mechanism also underlies the crucial role of caveolae in the long-term healthy expansion of the adipocyte.
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Affiliation(s)
- Hong Wang
- From the Departments of Biochemistry
| | - Paul F Pilch
- From the Departments of Biochemistry.,Medicine, and
| | - Libin Liu
- From the Departments of Biochemistry, .,Pharmacology and Experimental Therapeutics, Boston University School of Medicine, Boston, Massachusetts 02118
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4
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Aslamy A, Thurmond DC. Exocytosis proteins as novel targets for diabetes prevention and/or remediation? Am J Physiol Regul Integr Comp Physiol 2017; 312:R739-R752. [PMID: 28356294 DOI: 10.1152/ajpregu.00002.2017] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/03/2017] [Revised: 03/24/2017] [Accepted: 03/24/2017] [Indexed: 12/17/2022]
Abstract
Diabetes remains one of the leading causes of morbidity and mortality worldwide, affecting an estimated 422 million adults. In the US, it is predicted that one in every three children born as of 2000 will suffer from diabetes in their lifetime. Type 2 diabetes results from combinatorial defects in pancreatic β-cell glucose-stimulated insulin secretion and in peripheral glucose uptake. Both processes, insulin secretion and glucose uptake, are mediated by exocytosis proteins, SNARE (soluble N-ethylmaleimide-sensitive factor attachment protein receptor) complexes, Sec1/Munc18 (SM), and double C2-domain protein B (DOC2B). Increasing evidence links deficiencies in these exocytosis proteins to diabetes in rodents and humans. Given this, emerging studies aimed at restoring and/or enhancing cellular levels of certain exocytosis proteins point to promising outcomes in maintaining functional β-cell mass and enhancing insulin sensitivity. In doing so, new evidence also shows that enhancing exocytosis protein levels may promote health span and longevity and may also harbor anti-cancer and anti-Alzheimer's disease capabilities. Herein, we present a comprehensive review of the described capabilities of certain exocytosis proteins and how these might be targeted for improving metabolic dysregulation.
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Affiliation(s)
- Arianne Aslamy
- Department of Cellular and Integrative Physiology, Indiana University School of Medicine, Indianapolis, Indiana; and
| | - Debbie C Thurmond
- Department of Cellular and Integrative Physiology, Indiana University School of Medicine, Indianapolis, Indiana; and .,Department of Molecular and Cellular Endocrinology, Beckman Research Institute of City of Hope, Duarte, California
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5
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Chang YC, Chi LH, Chang WM, Su CY, Lin YF, Chen CL, Chen MH, Chang PMH, Wu ATH, Hsiao M. Glucose transporter 4 promotes head and neck squamous cell carcinoma metastasis through the TRIM24-DDX58 axis. J Hematol Oncol 2017; 10:11. [PMID: 28061796 PMCID: PMC5219690 DOI: 10.1186/s13045-016-0372-0] [Citation(s) in RCA: 31] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2016] [Accepted: 12/08/2016] [Indexed: 02/25/2023] Open
Abstract
BACKGROUND Head and neck squamous cell carcinoma (HNSCC) represents a unique and major health concern worldwide. Significant increases in glucose uptake and aerobic glycolysis have been observed in HNSCC cells. Glucose transporters (GLUTs) represent a major hub in the glycolysis pathway, with GLUT4 having the highest glucose affinity. However, GLUT4's role in HNSCC has not been fully appreciated. METHODS An in silico analysis was performed in HNSCC cohorts to identify the most significant glucose transporter associated with HNSCC patient prognosis. An immunohistochemical analysis of a tissue microarray with samples from 90 HNSCC patients was used to determine the association of GLUT4 with prognosis. Complementary functional expression and knockdown studies of GLUT4 were performed to investigate whether GLUT4 plays a role in HNSCC cell migration and invasion in vitro and in vivo. The detailed molecular mechanism of the function of GLUT4 in inducing HNSCC cell metastasis was determined. RESULTS Our clinicopathologic analysis showed that increased GLUT4 expression in oral squamous cell carcinoma patients was significantly associated with a poor overall survival (OS, P = 0.035) and recurrence-free survival (RFS, P = 0.001). Furthermore, the ectopic overexpression of GLUT4 in cell lines with low endogenous GLUT4 expression resulted in a significant increase in migratory ability both in vitro and in vivo, whereas the reverse phenotype was observed in GLUT4-silenced cells. Utilizing a GLUT4 overexpression model, we performed gene expression microarray and Ingenuity Pathway Analysis (IPA) to determine that the transcription factor tripartite motif-containing 24 (TRIM24) was the main downstream regulator of GLUT4. In addition, DDX58 was confirmed to be the downstream target of TRIM24, whose downregulation is essential for the migratory phenotype induced by GLUT4-TRIM24 activation in HNSCC cells. CONCLUSIONS Here, we identified altered glucose metabolism in the progression of HNSCC and showed that it could be partially attributed to the novel link between GLUT4 and TRIM24. This novel signaling axis may be used for the prognosis and therapeutic treatment of HNSCC in the future.
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Affiliation(s)
- Yu-Chan Chang
- Graduate Institute of Life Sciences, National Defense Medical Center, Taipei, Taiwan
- Genomics Research Center, Academia Sinica, Taipei, Taiwan
| | - Li-Hsing Chi
- Genomics Research Center, Academia Sinica, Taipei, Taiwan
- The Ph.D. Program for Translational Medicine, Taipei Medical University, Taipei, Taiwan
| | - Wei-Ming Chang
- Genomics Research Center, Academia Sinica, Taipei, Taiwan
- Graduate Institute of Medical Sciences, National Defense Medical Center, Taipei, Taiwan
| | - Chia-Yi Su
- Genomics Research Center, Academia Sinica, Taipei, Taiwan
| | - Yuang-Feng Lin
- Graduate Institute of Clinical Medicine, College of Medicine, Taipei Medical University, Taipei, Taiwan
| | - Chi-Long Chen
- Department of Pathology, Taipei Medical University Hospital, Taipei Medical University, Taipei, Taiwan
- Department of Pathology, College of Medicine, Taipei Medical University, Taipei, Taiwan
| | - Ming-Huang Chen
- Department of Oncology, Taipei Veterans General Hospital, Taipei, Taiwan
- Faculty of Medicine, National Yang Ming University, Taipei, Taiwan
| | - Peter Mu-Hsin Chang
- Department of Oncology, Taipei Veterans General Hospital, Taipei, Taiwan
- Faculty of Medicine, National Yang Ming University, Taipei, Taiwan
| | - Alex T H Wu
- The Ph.D. Program for Translational Medicine, Taipei Medical University, Taipei, Taiwan
| | - Michael Hsiao
- Graduate Institute of Life Sciences, National Defense Medical Center, Taipei, Taiwan.
- Genomics Research Center, Academia Sinica, Taipei, Taiwan.
- Department of Biochemistry, College of Medicine, Kaohsiung Medical University, Kaohsiung, Taiwan.
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Tunduguru R, Thurmond DC. Promoting Glucose Transporter-4 Vesicle Trafficking along Cytoskeletal Tracks: PAK-Ing Them Out. Front Endocrinol (Lausanne) 2017; 8:329. [PMID: 29209279 PMCID: PMC5701999 DOI: 10.3389/fendo.2017.00329] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/05/2017] [Accepted: 11/06/2017] [Indexed: 12/27/2022] Open
Abstract
Glucose is the principal cellular energy source in humans and maintenance of glucose homeostasis is critical for survival. Glucose uptake into peripheral skeletal muscle and adipose tissues requires the trafficking of vesicles containing glucose transporter-4 (GLUT4) from the intracellular storage compartments to the cell surface. Trafficking of GLUT4 storage vesicles is initiated via the canonical insulin signaling cascade in skeletal muscle and fat cells, as well as via exercise-induced contraction in muscle cells. Recent studies have elucidated steps in the signaling cascades that involve remodeling of the cytoskeleton, a process that underpins the mechanical movement of GLUT4 vesicles. This review is focused upon an alternate phosphoinositide-3 kinase-dependent pathway involving Ras-related C3 botulinum toxin substrate 1 signaling through the p21-activated kinase p21-activated kinase 1 and showcases related signaling events that co-regulate both the depolymerization and re-polymerization of filamentous actin. These new insights provide an enriched understanding into the process of glucose transport and yield potential new targets for interventions aimed to improve insulin sensitivity and remediate insulin resistance, pre-diabetes, and the progression to type 2 diabetes.
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Affiliation(s)
- Ragadeepthi Tunduguru
- Department of Molecular and Cellular Endocrinology, Diabetes and Metabolism Research Institute of City of Hope, Duarte, CA, United States
| | - Debbie C. Thurmond
- Department of Molecular and Cellular Endocrinology, Diabetes and Metabolism Research Institute of City of Hope, Duarte, CA, United States
- *Correspondence: Debbie C. Thurmond,
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7
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Liu L, Pilch PF. PTRF/Cavin-1 promotes efficient ribosomal RNA transcription in response to metabolic challenges. eLife 2016; 5. [PMID: 27528195 PMCID: PMC4987143 DOI: 10.7554/elife.17508] [Citation(s) in RCA: 35] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2016] [Accepted: 07/18/2016] [Indexed: 01/25/2023] Open
Abstract
Ribosomal RNA transcription mediated by RNA polymerase I represents the rate-limiting step in ribosome biogenesis. In eukaryotic cells, nutrients and growth factors regulate ribosomal RNA transcription through various key factors coupled to cell growth. We show here in mature adipocytes, ribosomal transcription can be acutely regulated in response to metabolic challenges. This acute response is mediated by PTRF (polymerase I transcription and release factor, also known as cavin-1), which has previously been shown to play a critical role in caveolae formation. The caveolae–independent rDNA transcriptional role of PTRF not only explains the lipodystrophy phenotype observed in PTRF deficient mice and humans, but also highlights its crucial physiological role in maintaining adipocyte allostasis. Multiple post-translational modifications of PTRF provide mechanistic bases for its regulation. The role of PTRF in ribosomal transcriptional efficiency is likely relevant to many additional physiological situations of cell growth and organismal metabolism. DOI:http://dx.doi.org/10.7554/eLife.17508.001 Obesity can cause several other health conditions to develop. Type 2 diabetes is one such condition, which arises in part because fat cells become unable to store excess fats. This makes certain tissues in the body less sensitive to the hormone insulin, and so the individual is less able to adapt to changing nutrient levels. Without treatment or a change in lifestyle, this insulin resistance may develop into diabetes. However, “healthy obese” individuals also exist, who can accommodate an overabundance of fat without developing insulin resistance and diabetes. Some forms of rare genetic disorders called lipodystrophies, which result in an almost complete lack of body fat, can also lead to type 2 diabetes. This raises the question of whether lipodystrophy and obesity share some common mechanisms that cause fat cells to trigger insulin resistance. One possible player in such mechanisms is a protein called PTRF. In rare cases, individuals with lipodystrophy lack this protein, and mice that have been engineered to lack PTRF also largely lack body fat and develop insulin resistance. Fat cells can respond rapidly to changes in nutrients during feeding or fasting, and to do so, they must produce new proteins. Structures called ribosomes, which are made up of proteins and ribosomal RNA, build proteins; thus when the cell needs to make new proteins, it also has to produce more ribosomes. PTRF is thought to play a role in ribosome production, but it is not clear how it does so. Liu and Pilch analyzed normal mice as well as those that lacked the PTRF protein. This revealed that in response to cycles of fasting and feeding, PTRF increases the production of ribosomal RNA in fat cells, enabling the cells to produce more proteins. By contrast, the fat cells of mice that lack PTRF have much lower levels of ribosomal RNA and proteins. Liu and Pilch then examined mouse fat cells that were grown in the laboratory. Exposing these cells to insulin caused phosphate groups to be attached to the PTRF proteins inside the cells. This modification caused PTRF to move into the cell’s nucleus, where it increased the production of ribosomal RNA. Overall, the results show that fat cells that lack PTRF are unable to produce the proteins that they need to deal with changing nutrient levels, leading to an increased likelihood of diabetes. The next steps are to investigate the mechanism by which PTRF is modified, and to see whether the mechanisms uncovered in this study also apply to humans. DOI:http://dx.doi.org/10.7554/eLife.17508.002
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Affiliation(s)
- Libin Liu
- Department of Biochemistry, Boston University School of Medicine, Boston, United States
| | - Paul F Pilch
- Department of Biochemistry, Boston University School of Medicine, Boston, United States.,Department of Medicine, Boston University School of Medicine, Boston, United States
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8
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System model network for adipose tissue signatures related to weight changes in response to calorie restriction and subsequent weight maintenance. PLoS Comput Biol 2015; 11:e1004047. [PMID: 25590576 PMCID: PMC4295881 DOI: 10.1371/journal.pcbi.1004047] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2014] [Accepted: 11/19/2014] [Indexed: 01/22/2023] Open
Abstract
Nutrigenomics investigates relationships between nutrients and all genome-encoded molecular entities. This holistic approach requires systems biology to scrutinize the effects of diet on tissue biology. To decipher the adipose tissue (AT) response to diet induced weight changes we focused on key molecular (lipids and transcripts) AT species during a longitudinal dietary intervention. To obtain a systems model, a network approach was used to combine all sets of variables (bio-clinical, fatty acids and mRNA levels) and get an overview of their interactions. AT fatty acids and mRNA levels were quantified in 135 obese women at baseline, after an 8-week low calorie diet (LCD) and after 6 months of ad libitum weight maintenance diet (WMD). After LCD, individuals were stratified a posteriori according to weight change during WMD. A 3 steps approach was used to infer a global model involving the 3 sets of variables. It consisted in inferring intra-omic networks with sparse partial correlations and inter-omic networks with regularized canonical correlation analysis and finally combining the obtained omic-specific network in a single global model. The resulting networks were analyzed using node clustering, systematic important node extraction and cluster comparisons. Overall, AT showed both constant and phase-specific biological signatures in response to dietary intervention. AT from women regaining weight displayed growth factors, angiogenesis and proliferation signaling signatures, suggesting unfavorable tissue hyperplasia. By contrast, after LCD a strong positive relationship between AT myristoleic acid (a fatty acid with low AT level) content and de novo lipogenesis mRNAs was found. This relationship was also observed, after WMD, in the group of women that continued to lose weight. This original system biology approach provides novel insight in the AT response to weight control by highlighting the central role of myristoleic acid that may account for the beneficial effects of weight loss. Obesity is an excess fat mass leading to metabolic diseases. Dietary management is a conventional strategy to promote weight loss. As energy buffering, in the form of esterified fatty acids, and secretory organ, the adipose tissue has a pivotal role in obesity and its related complications. A comprehensive insight of adipose tissue response during and after calorie restriction might improve obesity management. Modern nutrition research study the impact of diet on health by combining multiple datasets to provide an holistic view of tissue physiopathology. To identify significant clusters of fatty acids, transcripts or bio-clinical parameters related to weight change along calorie restriction and subsequent weight follow-up in obese individuals, the issue of different datasets integration must be resolved. Here, we implemented an innovative multistep approach to infer multi-data networks and compare clusters of network components. This original strategy highlighted an unexpected central role of a minor adipose tissue fatty acid, myristoleic acid, which is not provided by food. Its link to transcripts encoding enzymes from a pathway converting glucose into fat that mediates favorable metabolic effects makes myristoleic acid a key factor of the positive impact of fat mass reduction.
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Liu L, Hansen CG, Honeyman BJ, Nichols BJ, Pilch PF. Cavin-3 knockout mice show that cavin-3 is not essential for caveolae formation, for maintenance of body composition, or for glucose tolerance. PLoS One 2014; 9:e102935. [PMID: 25036884 PMCID: PMC4103889 DOI: 10.1371/journal.pone.0102935] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2014] [Accepted: 06/23/2014] [Indexed: 11/19/2022] Open
Abstract
The cavins are a family of proteins associated with caveolae, cavin-1, -2 and -3 being widely expressed while cavin-4 is restricted to striated muscle. Deletion of cavin-1 results in phenotypes including metabolic changes consistent with adipocyte dysfunction, and caveolae are completely absent. Deletion of cavin-2 causes tissue-specific loss of caveolae. The consequences of cavin-3 deletion are less clear, as there are divergent data on the abundance of caveolae in cavin-3 null mice. Here we examine the consequences of cavin-3 deficiency in vivo by making cavin-3 knockout mice. We find that loss of cavin-3 has minimal or no effects on the levels of other caveolar proteins, does not appear to play a major role in formation of protein complexes important for caveolar morphogenesis, and has no significant effect on caveolae abundance. Cavin-3 null mice have the same body weight and fat mass as wild type animals at ages 8 through 30 weeks on both normal chow and high fat diets. Likewise, the two mouse strains exhibit identical glucose tolerance tests on both diets. Microarray analysis from adipose tissue shows that the changes in mRNA expression between cavin-3 null and wild type mouse are minimal. We conclude that cavin-3 is not absolutely required for making caveolae, and suggest that the mechanistic link between cavin-3 and metabolic regulation remains uncertain.
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Affiliation(s)
- Libin Liu
- Department of Biochemistry, Boston University School of Medicine, Boston, Massachusetts, United States of America
| | - Carsten G. Hansen
- Laboratory of Molecular Biology, Medical Research Council, Cambridge, Cambridgeshire, United Kingdom
| | - Brian J. Honeyman
- Department of Biochemistry, Boston University School of Medicine, Boston, Massachusetts, United States of America
| | - Benjamin J. Nichols
- Laboratory of Molecular Biology, Medical Research Council, Cambridge, Cambridgeshire, United Kingdom
| | - Paul F. Pilch
- Department of Biochemistry, Boston University School of Medicine, Boston, Massachusetts, United States of America
- Department of Medicine, Boston University School of Medicine, Boston, Massachusetts, United States of America
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Beh JE, Khoo LT, Latip J, Abdullah MP, Alitheen NBM, Adam Z, Ismail A, Hamid M. SDF7, a group of Scoparia dulcis Linn. derived flavonoid compounds, stimulates glucose uptake and regulates adipocytokines in 3T3-F442a adipocytes. JOURNAL OF ETHNOPHARMACOLOGY 2013; 150:339-352. [PMID: 24029250 DOI: 10.1016/j.jep.2013.09.001] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/19/2013] [Revised: 08/07/2013] [Accepted: 09/03/2013] [Indexed: 06/02/2023]
Abstract
ETHNOPHARMACOLOGY RELEVANCE Adipocytes are major tissues involved in glucose uptake second to skeletal muscle and act as the main adipocytokines mediator that regulates glucose uptake mechanism and cellular differentiation. The objective of this study were to examine the effect of the SDF7, which is a fraction consists of four flavonoid compounds (quercetin: p-coumaric acid: luteolin: apigenin=8: 26: 1: 3) from Scoparia dulcis Linn., on stimulating the downstream components of insulin signalling and the adipocytokines expression on different cellular fractions of 3T3-F442a adipocytes. MATERIAL AND METHODS Morphology and lipid accumulation of differentiated 3T3-F442a adipocytes by 100 nM insulin treated with different concentrations of SDF7 and rosiglitazone were examined followed by the evaluation of glucose uptake activity expressions of insulin signalling downstream components (IRS-1, PI3-kinase, PKB, PKC, TC10 and GLUT4) from four cellular fractions (plasma membrane, cytosol, high density microsome and low density microsome). Next, the expression level of adipocytokines (TNF-α, adiponectin and leptin) and immunoblotting of treated 3T3-F442 adipocytes was determined at 30 min and 480 min. Glucose transporter 4 (GLUT4) translocation of 3T3-F442a adipocytes membrane was also determined. Lastly, mRNA expression of adiponectin and PPAR-γ of 3T3-F442a adipocytes were induced and compared with basal concentration. RESULTS It was found that SDF7 was able to induce adipocytes differentiation with great extends of morphological changes, lipid synthesis and lipid stimulation in vitro. SDF7 stimulation of glucose transport on 3T3-F442a adipocytes are found to be dose independent, time-dependent and plasma membrane GLUT4 expression-dependent. Moreover, SDF7 are observed to be able to suppress TNF-α and leptin expressions that were mediated by 3T3-F442a adipocytes, while stimulated adiponectin secretion on the cells. There was a significant expression (p<0.01) of protein kinase C and small G protein TC10 on 3T3-F442a adipocytes upon treatment with SDF7 as compared to the control. SDF7 was also found to be effective in stimulating adiponectin and PPAR-γ mRNA upregulation at 50 µg/ml. CONCLUSION SDF7 exhibited good lipogenesis, adiponectinesis and glucose uptake stimulatory properties on 3T3-F442a adipocytes.
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Affiliation(s)
- Joo Ee Beh
- Department of Microbiology, Faculty of Biotechnology and Biomolecular Sciences, Universiti Putra Malaysia, 43400 Serdang, Selangor, Malaysia
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11
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Signaling mechanisms of glucose-induced F-actin remodeling in pancreatic islet β cells. Exp Mol Med 2013; 45:e37. [PMID: 23969997 PMCID: PMC3789261 DOI: 10.1038/emm.2013.73] [Citation(s) in RCA: 105] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2013] [Accepted: 06/24/2013] [Indexed: 12/12/2022] Open
Abstract
The maintenance of whole-body glucose homeostasis is critical for survival, and is controlled by the coordination of multiple organs and endocrine systems. Pancreatic islet β cells secrete insulin in response to nutrient stimuli, and insulin then travels through the circulation promoting glucose uptake into insulin-responsive tissues such as liver, skeletal muscle and adipose. Many of the genes identified in human genome-wide association studies of diabetic individuals are directly associated with β cell survival and function, giving credence to the idea that β-cell dysfunction is central to the development of type 2 diabetes. As such, investigations into the mechanisms by which β cells sense glucose and secrete insulin in a regulated manner are a major focus of current diabetes research. In particular, recent discoveries of the detailed role and requirements for reorganization/remodeling of filamentous actin (F-actin) in the regulation of insulin release from the β cell have appeared at the forefront of islet function research, having lapsed in prior years due to technical limitations. Recent advances in live-cell imaging and specialized reagents have revealed localized F-actin remodeling to be a requisite for the normal biphasic pattern of nutrient-stimulated insulin secretion. This review will provide an historical look at the emergent focus on the role of the actin cytoskeleton and its regulation of insulin secretion, leading up to the cutting-edge research in progress in the field today.
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12
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Feussner KD, Ragini K, Kumar R, Soapi KM, Aalbersberg WG, Harper MK, Carte B, Ireland CM. Investigations of the marine flora and fauna of the Fiji Islands. Nat Prod Rep 2012; 29:1424-62. [DOI: 10.1039/c2np20055d] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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13
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Balamatsias D, Kong AM, Waters JE, Sriratana A, Gurung R, Bailey CG, Rasko JEJ, Tiganis T, Macaulay SL, Mitchell CA. Identification of P-Rex1 as a novel Rac1-guanine nucleotide exchange factor (GEF) that promotes actin remodeling and GLUT4 protein trafficking in adipocytes. J Biol Chem 2011; 286:43229-40. [PMID: 22002247 DOI: 10.1074/jbc.m111.306621] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023] Open
Abstract
Phosphoinositide 3-kinase (PI3K) signaling promotes the translocation of the glucose transporter, GLUT4, to the plasma membrane in insulin-sensitive tissues to facilitate glucose uptake. In adipocytes, insulin-stimulated reorganization of the actin cytoskeleton has been proposed to play a role in promoting GLUT4 translocation and glucose uptake, in a PI3K-dependent manner. However, the PI3K effectors that promote GLUT4 translocation via regulation of the actin cytoskeleton in adipocytes remain to be fully elucidated. Here we demonstrate that the PI3K-dependent Rac exchange factor, P-Rex1, enhances membrane ruffling in 3T3-L1 adipocytes and promotes GLUT4 trafficking to the plasma membrane at submaximal insulin concentrations. P-Rex1-facilitated GLUT4 trafficking requires a functional actin network and membrane ruffle formation and occurs in a PI3K- and Rac1-dependent manner. In contrast, expression of other Rho GTPases, such as Cdc42 or Rho, did not affect insulin-stimulated P-Rex1-mediated GLUT4 trafficking. P-Rex1 siRNA knockdown or expression of a P-Rex1 dominant negative mutant reduced but did not completely inhibit glucose uptake in response to insulin. Collectively, these studies identify a novel RacGEF in adipocytes as P-Rex1 that, at physiological insulin concentrations, functions as an insulin-dependent regulator of the actin cytoskeleton that contributes to GLUT4 trafficking to the plasma membrane.
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Affiliation(s)
- Demis Balamatsias
- Department of Biochemistry and Molecular Biology, Monash University, Clayton, Victoria 3800, Australia
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Meng F, Suchyna TM, Lazakovitch E, Gronostajski RM, Sachs F. Real Time FRET Based Detection of Mechanical Stress in Cytoskeletal and Extracellular Matrix Proteins. Cell Mol Bioeng 2011; 4:148-159. [PMID: 21625401 PMCID: PMC3101475 DOI: 10.1007/s12195-010-0140-0] [Citation(s) in RCA: 52] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
A molecular force sensing cassette (stFRET) was incorporated into actinin, filamin, and spectrin in vascular endothelial cells (BAECs) and into collagen-19 in Caenorhabditis elegans. To estimate the stress sensitivity of stFRET in solution, we used DNA springs. A 60-mer loop of single stranded DNA was covalently linked to the external cysteines of the donor and acceptor. When the complementary DNA was added it formed double stranded DNA with higher persistence length, stretching the linker and substantially reducing FRET efficiency. The probe stFRET detected constitutive stress in all cytoskeletal proteins tested, and in migrating cells the stress was greater at the leading edge than the trailing edge. The stress in actinin, filamin and spectrin could be reduced by releasing focal attachments from the substrate with trypsin. Inhibitors of actin polymerization produced a modest increase in stress on the three proteins suggesting they are mechanically in parallel. Local shear stress applied to the cell with a perfusion pipette showed gradients of stress leading from the site of perfusion. Transgenic C. elegans labeled in collagen-19 produced a behaviorally and anatomically normal animal with constitutive stress in the cuticle. Stretching the worm visibly stretched the probe in collagen showing that we can trace the distribution of mean tissue stress in specific molecules. stFRET is a general purpose dynamic sensor of mechanical stress that can be expressed intracellularly and extracellularly in isolated proteins, cells, tissues, organs and animals.
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Affiliation(s)
- Fanjie Meng
- Department of Physiology and Biophysics, Center for Single Molecule Biophysics, State University of New York at Buffalo, 301 Cary Hall, Buffalo, NY 14214, USA
| | - Thomas M. Suchyna
- Department of Physiology and Biophysics, Center for Single Molecule Biophysics, State University of New York at Buffalo, 301 Cary Hall, Buffalo, NY 14214, USA
| | - Elena Lazakovitch
- Department of Biochemistry, Developmental Genomics Group, New York State Center of Excellence in Bioinformatics and Life Sciences, State University of New York at Buffalo, 119 Farber Hall, Buffalo, NY 14214, USA
| | - Richard M. Gronostajski
- Department of Biochemistry, Developmental Genomics Group, New York State Center of Excellence in Bioinformatics and Life Sciences, State University of New York at Buffalo, 119 Farber Hall, Buffalo, NY 14214, USA
| | - Frederick Sachs
- Department of Physiology and Biophysics, Center for Single Molecule Biophysics, State University of New York at Buffalo, 301 Cary Hall, Buffalo, NY 14214, USA
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Hoffman NJ, Elmendorf JS. Signaling, cytoskeletal and membrane mechanisms regulating GLUT4 exocytosis. Trends Endocrinol Metab 2011; 22:110-6. [PMID: 21216617 PMCID: PMC3049829 DOI: 10.1016/j.tem.2010.12.001] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/09/2010] [Revised: 12/03/2010] [Accepted: 12/06/2010] [Indexed: 10/25/2022]
Abstract
Solving how insulin regulates glucose transport into skeletal muscle and adipose tissue remains a fundamental challenge in biology and a significant issue in medicine. A central feature of this process is the coordinated accumulation of the glucose transporter GLUT4 into the plasma membrane. New signaling and cytoskeletal mechanisms of insulin-stimulated GLUT4 exocytosis are of emerging interest, particularly those at or just beneath the plasma membrane. This review examines signals that functionally engage GLUT4 exocytosis, considers cytoskeletal regulation of the stimulated GLUT4 itinerary, and appraises the involvement of plasma membrane parameters in GLUT4 control. We also explore how these newly-defined signaling, cytoskeletal and membrane mechanisms could be of therapeutic interest in the treatment and/or prevention of GLUT4 dysregulation in disease.
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Affiliation(s)
- Nolan J Hoffman
- Department of Cellular and Integrative Physiology, Indiana University School of Medicine, Centers for Diabetes Research, Membrane Biosciences, and Vascular Biology and Medicine, VanNuys Medical Science Building Room 308A, Indianapolis, IN 46202, USA
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16
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Woronowicz K, Dilks JR, Rozenvayn N, Dowal L, Blair PS, Peters CG, Woronowicz L, Flaumenhaft R. The platelet actin cytoskeleton associates with SNAREs and participates in alpha-granule secretion. Biochemistry 2010; 49:4533-42. [PMID: 20429610 DOI: 10.1021/bi100541t] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
Abstract
Following platelet activation, platelets undergo a dramatic shape change mediated by the actin cytoskeleton and accompanied by secretion of granule contents. While the actin cytoskeleton is thought to influence platelet granule secretion, the mechanism for this putative regulation is not known. We found that disruption of the actin cytoskeleton by latrunculin A inhibited alpha-granule secretion induced by several different platelet agonists without significantly affecting activation-induced platelet aggregation. In a cell-free secretory system, platelet cytosol was required for alpha-granule secretion. Inhibition of actin polymerization prevented alpha-granule secretion in this system, and purified platelet actin could substitute for platelet cytosol to support alpha-granule secretion. To determine whether SNAREs physically associate with the actin cytoskeleton, we isolated the Triton X-100 insoluble actin cytoskeleton from platelets. VAMP-8 and syntaxin-2 associated only with actin cytoskeletons of activated platelets. Syntaxin-4 and SNAP-23 associated with cytoskeletons isolated from either resting or activated platelets. When syntaxin-4 and SNAP-23 were tested for actin binding in a purified protein system, only syntaxin-4 associated directly with polymerized platelet actin. These data show that the platelet cytoskeleton interacts with select SNAREs and that actin polymerization facilitates alpha-granule release.
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Affiliation(s)
- Kamil Woronowicz
- Division of Hemostasis and Thrombosis, Department of Medicine, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, Massachusetts 02215, USA
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Jewell JL, Oh E, Thurmond DC. Exocytosis mechanisms underlying insulin release and glucose uptake: conserved roles for Munc18c and syntaxin 4. Am J Physiol Regul Integr Comp Physiol 2010; 298:R517-31. [PMID: 20053958 DOI: 10.1152/ajpregu.00597.2009] [Citation(s) in RCA: 92] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
Type 2 diabetes has been coined "a two-hit disease," as it involves specific defects of glucose-stimulated insulin secretion from the pancreatic beta cells in addition to defects in peripheral tissue insulin action required for glucose uptake. Both of these processes, insulin secretion and glucose uptake, are mediated by SNARE (soluble N-ethylmaleimide-sensitive factor attachment protein receptor) protein core complexes composed of syntaxin, SNAP-23/25, and VAMP proteins. The SNARE core complex is regulated by the Sec1/Munc18 (SM) family of proteins, which selectively bind to their cognate syntaxin isoforms with high affinity. The process of insulin secretion uses multiple Munc18-syntaxin isoform pairs, whereas insulin action in the peripheral tissues appears to use only the Munc18c-syntaxin 4 pair. Importantly, recent reports have linked obesity and Type 2 diabetes in humans with changes in protein levels and single nucleotide polymorphisms (SNPs) of Munc18 and syntaxin isoforms relevant to these exocytotic processes, although the molecular mechanisms underlying the observed phenotypes remain incomplete (5, 104, 144). Given the conservation of these proteins in two seemingly disparate processes and the need to design and implement novel and more effective clinical interventions, it will be vitally important to delineate the mechanisms governing these conserved SNARE-mediated exocytosis events. Thus, we provide here an up-to-date historical review of advancements in defining the roles and molecular mechanisms of Munc18-syntaxin complexes in the pathophysiology of Type 2 diabetes.
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Affiliation(s)
- Jenna L Jewell
- Department of Pediatrics, Indiana University School of Medicine, Indianapolis, IN, USA
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18
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Affiliation(s)
- Debbie C Thurmond
- Departments of Pediatrics,Basic Diabetes Group of the Herman B Wells Center for Pediatric Research, Indiana University School of Medicine, Indianapolis, Indiana 46202, USA.
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Kanshin E, Wang S, Ashmarina L, Fedjaev M, Nifant'ev I, Mitchell GA, Pshezhetsky AV. The stoichiometry of protein phosphorylation in adipocyte lipid droplets: Analysis by N-terminal isotope tagging and enzymatic dephosphorylation. Proteomics 2009; 9:5067-77. [DOI: 10.1002/pmic.200800861] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
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20
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Lopez JA, Burchfield JG, Blair DH, Mele K, Ng Y, Vallotton P, James DE, Hughes WE. Identification of a distal GLUT4 trafficking event controlled by actin polymerization. Mol Biol Cell 2009; 20:3918-29. [PMID: 19605560 DOI: 10.1091/mbc.e09-03-0187] [Citation(s) in RCA: 65] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
The insulin-stimulated trafficking of GLUT4 to the plasma membrane in muscle and fat tissue constitutes a central process in blood glucose homeostasis. The tethering, docking, and fusion of GLUT4 vesicles with the plasma membrane (PM) represent the most distal steps in this pathway and have been recently shown to be key targets of insulin action. However, it remains unclear how insulin influences these processes to promote the insertion of the glucose transporter into the PM. In this study we have identified a previously uncharacterized role for cortical actin in the distal trafficking of GLUT4. Using high-frequency total internal reflection fluorescence microscopy (TIRFM) imaging, we show that insulin increases actin polymerization near the PM and that disruption of this process inhibited GLUT4 exocytosis. Using TIRFM in combination with probes that could distinguish between vesicle transport and fusion, we found that defective actin remodeling was accompanied by normal insulin-regulated accumulation of GLUT4 vesicles close to the PM, but the final exocytotic fusion step was impaired. These data clearly resolve multiple steps of the final stages of GLUT4 trafficking, demonstrating a crucial role for actin in the final stage of this process.
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Affiliation(s)
- Jamie A Lopez
- Diabetes and Obesity Research Program, The Garvan Institute of Medical Research, Sydney, NSW 2010, Australia
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21
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Compartmentalization and regulation of insulin signaling to GLUT4 by the cytoskeleton. VITAMINS AND HORMONES 2009; 80:193-215. [PMID: 19251039 DOI: 10.1016/s0083-6729(08)00608-0] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/21/2023]
Abstract
One of the early events in the development of Type 2 diabetes appears to be an inhibition of insulin-mediated GLUT4 redistribution to the cell surface in tissues that express GLUT4. Understanding this process, and how it begins to breakdown in the development of insulin resistance is quite important as we face treatment and prevention of metabolic diseases. Over the past few years, and increasing number of laboratories have produced compelling data to demonstrate a role for both the actin and microtubule networks in the regulation of insulin-mediated GLUT4 redistribution to the cell surface. In this review, we explore this process from insulin-signal transduction to fusion of GLUT4 membrane vesicles, focusing on studies that have implicated a role for the cytoskeleton. We see from this body of work that both the actin network and the microtubule cytoskeleton play roles as targets of insulin action and effectors of insulin signaling leading to changes in GLUT4 redistribution to the cell surface and insulin-mediated glucose uptake.
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22
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Jewell JL, Luo W, Oh E, Wang Z, Thurmond DC. Filamentous actin regulates insulin exocytosis through direct interaction with Syntaxin 4. J Biol Chem 2008; 283:10716-26. [PMID: 18285343 DOI: 10.1074/jbc.m709876200] [Citation(s) in RCA: 89] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Glucose-induced insulin exocytosis is coupled to associations between F-actin and SNARE proteins, although the nature and function of these interactions remains unknown. Toward this end we show here that both Syntaxin 1A and Syntaxin 4 associated with F-actin in MIN6 cells and that each interaction was rapidly and transiently diminished by stimulation of cells with d-glucose. Of the two isoforms, only Syntaxin 4 was capable of interacting directly with F-actin in an in vitro sedimentation assay, conferred by the N-terminal 39-112 residues of Syntaxin 4. The 39-112 fragment was capable of selective competitive inhibitory action, disrupting endogenous F-actin-Syntaxin 4 binding in MIN6 cells. Disruption of F-actin-Syntaxin 4 binding correlated with enhanced glucose-stimulated insulin secretion, mediated by increased granule accumulation at the plasma membrane and increased Syntaxin 4 accessibility under basal conditions. However, no increase in basal level Syntaxin 4-VAMP2 association occurred with either latrunculin treatment or expression of the 39-112 fragment. Taken together, these data disclose a new underlying mechanism by which F-actin negatively regulates exocytosis via binding and blocking Syntaxin 4 accessibility, but they also reveal the existence of additional signals and/or steps required to trigger the subsequent docking and fusion steps of exocytosis.
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Affiliation(s)
- Jenna L Jewell
- Department of Biochemistry and Molecular Biology, Center for Diabetes Research, Indiana University School of Medicine, Indianapolis, Indiana 46202, USA
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23
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Pilch PF. The mass action hypothesis: formation of Glut4 storage vesicles, a tissue-specific, regulated exocytic compartment. Acta Physiol (Oxf) 2008; 192:89-101. [PMID: 18171432 DOI: 10.1111/j.1748-1716.2007.01788.x] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
Insulin stimulates glucose uptake into the target tissues of fat and muscle by recruiting or translocating Glut4 glucose transport proteins to their functional location at the cell surface. In the basal state, Glut4 is sequestered intracellularly in several vesicular compartments, one of which has come to be known as Glut4 storage vesicles (GSVs). The GSVs represent a tissue-specific compartment that is an ultimate target of the insulin signalling cascade. Glut4 translocation has been extensively studied because of its intrinsic scientific importance to cell biology as well as its relevance to the pathology of type 2 diabetes mellitus. I review herein the ontogeny of GSVs and their composition as it relates to a tissue-specific, hormone-sensitive exocytic compartment and propose a mechanism for their formation.
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Affiliation(s)
- P F Pilch
- Department of Biochemistry, Boston University School of Medicine, Boston, MA 02118, USA.
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Chen CD, Podvin S, Gillespie E, Leeman SE, Abraham CR. Insulin stimulates the cleavage and release of the extracellular domain of Klotho by ADAM10 and ADAM17. Proc Natl Acad Sci U S A 2007; 104:19796-801. [PMID: 18056631 PMCID: PMC2148378 DOI: 10.1073/pnas.0709805104] [Citation(s) in RCA: 428] [Impact Index Per Article: 25.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Cleavage and release (shedding) of membrane proteins is a critical regulatory step in many normal and pathological processes. Evidence suggests that the antiaging transmembrane protein Klotho (KL) is shed from the cell surface by proteolytic cleavage. In this study, we attempted to identify the enzymes responsible for the shedding of KL by treating KL-transfected COS-7 cells with a panel of proteinase inhibitors and measuring cleavage products by Western blot. We report that metalloproteinase inhibitors, including EDTA, EGTA, and TAPI-1, inhibit the shedding of KL, whereas insulin increases shedding. The effects of the inhibitors in KL-transfected COS-7 cells were repeated in studies on rat kidney slices ex vivo, which validates the use of COS-7 cells as our model system. Tissue inhibitor of metalloproteinase (Timp)-3 effectively inhibits KL cleavage, whereas Timp-1 and Timp-2 do not, a profile that indicates the involvement of members of the A Desintegrin and Metalloproteinase (ADAM) family. Cotransfection of KL with either ADAM10 or ADAM17 enhances KL cleavage, whereas cotransfection of KL with small interference RNAs specific to ADAM10 and ADAM17 inhibits KL secretion. These results indicate that KL shedding is mediated mainly by ADAM10 and ADAM17 in KL-transfected COS-7 cells. The effect of insulin is abolished when ADAM10 or ADAM17 are silenced. Furthermore, we demonstrate that the effect of insulin on KL shedding is inhibited by wortmannin, showing that insulin acts through a PI3K-dependent pathway. Insulin enhances KL shedding without increasing ADAM10 and ADAM17 mRNA and protein levels, suggesting that it acts by stimulating their proteolytic activities.
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Affiliation(s)
| | | | | | - Susan E. Leeman
- †Pharmacology, and
- ‡To whom correspondence may be addressed. E-mail: or
| | - Carmela R. Abraham
- Departments of *Biochemistry,
- §Medicine, Boston University School of Medicine, Boston, MA 02118
- ‡To whom correspondence may be addressed. E-mail: or
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25
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Liu L, Pilch PF. A critical role of cavin (polymerase I and transcript release factor) in caveolae formation and organization. J Biol Chem 2007; 283:4314-22. [PMID: 18056712 DOI: 10.1074/jbc.m707890200] [Citation(s) in RCA: 216] [Impact Index Per Article: 12.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
Cavin (PTRF) has been shown to be a highly abundant protein component of caveolae, but its functional role there is unknown. Here, we confirm that cavin co-localizes with caveolin-1 in adipocytes by confocal microscopy and co-distributes with caveolin-1 in lipid raft fractions by sucrose gradient flotation. However, cavin does not directly associate with caveolin-1 as solubilization of caveolae disrupts their interaction. Cholesterol depletion with beta-cyclodextrin causes a significant down-regulation of cavin from plasma membrane lipid raft fractions. Overexpression of cavin in HEK293-Cav-1 cells and knockdown of cavin in 3T3-L1 adipocytes enhances and diminishes caveolin-1 levels, respectively, indicating an important role for cavin in maintaining the level of caveolin-1. A truncated form of cavin, eGFP-cavin-1-322, which lacks 74 amino acids from the C-terminal, reveals a microtubular network localization by confocal microscopy. Disruption of cytoskeletal elements with latrunculin B or nocodazole diminishes cavin expression without affecting the caveolin-1 amount. We propose that the presence of cavin on the inside surface of caveolae stabilizes these structures, probably through interaction with the cytoskeleton, and cavin therefore plays an important role in caveolae formation and organization.
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Affiliation(s)
- Libin Liu
- Department of Biochemistry, Boston University Medical School, Boston, Massachusetts 02118, USA
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26
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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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27
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Liu XJ, Yang C, Gupta N, Zuo J, Chang YS, Fang FD. Protein kinase C-zeta regulation of GLUT4 translocation through actin remodeling in CHO cells. J Mol Med (Berl) 2007; 85:851-61. [PMID: 17619838 DOI: 10.1007/s00109-007-0232-z] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2007] [Revised: 04/25/2007] [Accepted: 05/31/2007] [Indexed: 01/08/2023]
Abstract
Actin remodeling plays a crucial role in insulin-induced translocation of glucose transporter 4 (GLUT4) from the cytoplasm to the plasma membrane and subsequent glucose transport. Protein kinase C (PKC) zeta has been implicated in this translocation process, although the exact mechanism remains unknown. In this study, we investigated the effect of PKCzeta on actin cytoskeleton and translocation of GLUT4 in CHO-K1 cells expressing myc-tagged GLUT4. Insulin stimulated the phosphorylation of PKCzeta at Thr410 with no apparent effect on its protein expression. Moreover, insulin promoted colocalization of PKCzeta and actin that could be abolished by Latrunculin B. The overexpression of PKCzeta mimicked the insulin-induced change in actin cytoskeleton and translocation of GLUT4. These effects were also completely abrogated by Latrunculin B treatment. Using cell-permeable pseudosubstrate (PS) inhibitor of PKCzeta, the response to insulin could be alleviated. Our results strongly suggest that PKCzeta mediates the stimulatory effect of insulin on GLUT4 translocation through its interaction with actin cytoskeleton.
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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 & School of Basic Medicine Peking Union Medical College, Beijing, China
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