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Mitochondrial GTP Links Nutrient Sensing to β Cell Health, Mitochondrial Morphology, and Insulin Secretion Independent of OxPhos. Cell Rep 2020; 28:759-772.e10. [PMID: 31315053 DOI: 10.1016/j.celrep.2019.06.058] [Citation(s) in RCA: 40] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2017] [Revised: 02/15/2019] [Accepted: 06/14/2019] [Indexed: 12/18/2022] Open
Abstract
Mechanisms coordinating pancreatic β cell metabolism with insulin secretion are essential for glucose homeostasis. One key mechanism of β cell nutrient sensing uses the mitochondrial GTP (mtGTP) cycle. In this cycle, mtGTP synthesized by succinyl-CoA synthetase (SCS) is hydrolyzed via mitochondrial PEPCK (PEPCK-M) to make phosphoenolpyruvate, a high-energy metabolite that integrates TCA cycling and anaplerosis with glucose-stimulated insulin secretion (GSIS). Several strategies, including xenotopic overexpression of yeast mitochondrial GTP/GDP exchanger (GGC1) and human ATP and GTP-specific SCS isoforms, demonstrated the importance of the mtGTP cycle. These studies confirmed that mtGTP triggers and amplifies normal GSIS and rescues defects in GSIS both in vitro and in vivo. Increased mtGTP synthesis enhanced calcium oscillations during GSIS. mtGTP also augmented mitochondrial mass, increased insulin granule number, and membrane proximity without triggering de-differentiation or metabolic fragility. These data highlight the importance of the mtGTP signal in nutrient sensing, insulin secretion, mitochondrial maintenance, and β cell health.
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Abstract
Glucose-induced (physiological) insulin secretion from the islet β-cell involves interplay between cationic (i.e., changes in intracellular calcium) and metabolic (i.e., generation of hydrophobic and hydrophilic second messengers) events. A large body of evidence affirms support for novel regulation, by G proteins, of specific intracellular signaling events, including actin cytoskeletal remodeling, transport of insulin-containing granules to the plasma membrane for fusion, and secretion of insulin into the circulation. This article highlights the following aspects of GPCR-G protein biology of the islet. First, it overviews our current understanding of the identity of a wide variety of G protein regulators and their modulatory roles in GPCR-G protein-effector coupling, which is requisite for optimal β-cell function under physiological conditions. Second, it describes evidence in support of novel, noncanonical, GPCR-independent mechanisms of activation of G proteins in the islet. Third, it highlights the evidence indicating that abnormalities in G protein function lead to islet β-cell dysregulation and demise under the duress of metabolic stress and diabetes. Fourth, it summarizes observations of potential beneficial effects of GPCR agonists in preventing/halting metabolic defects in the islet β-cell under various pathological conditions (e.g., metabolic stress and inflammation). Lastly, it identifies knowledge gaps and potential avenues for future research in this evolving field of translational islet biology. Published 2020. Compr Physiol 10:453-490, 2020.
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Affiliation(s)
- Anjaneyulu Kowluru
- Department of Pharmaceutical Sciences, Eugene Applebaum College of Pharmacy and Health Sciences, Center for Translational Research in Diabetes, Biomedical Research Service, John D. Dingell VA Medical Center, Wayne State University, Detroit, Michigan, USA
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Chen L, Liu C, Gao J, Xie Z, Chan LWC, Keating DJ, Yang Y, Sun J, Zhou F, Wei Y, Men X, Yang S. Inhibition of Miro1 disturbs mitophagy and pancreatic β-cell function interfering insulin release via IRS-Akt-Foxo1 in diabetes. Oncotarget 2017; 8:90693-90705. [PMID: 29207597 PMCID: PMC5710878 DOI: 10.18632/oncotarget.20963] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2017] [Accepted: 08/29/2017] [Indexed: 11/25/2022] Open
Abstract
Mitochondrial function is essential to meet metabolic demand of pancreatic beta cells respond to high nutrient stress. Mitophagy is an essential component to normal pancreatic β-cell function and has been associated with β-cell failure in Type 2 diabetes (T2D). Our previous studies have indicated that mitochondrial Rho (Miro) GTPase-mediated mitochondrial dysfunction under high nutrient stress leads to NOD-like receptor 3 (NLRP3)-dependent proinflammatory responses and subsequent insulin resistance. However, the in vivo mechanism by which Miro1 underlies mitophagy has not been identified. Here we show firstly that the expression of Miro is reduced in human T2D and mouse db/db islets and in INS-1 cell line exposed to high glucose and palmitate. β-cell specific ablation of Miro1 (Miro1f/f: Rip-cre mice, or (IKO) under high nutrient stress promotes the development of hyperglycemia. β-cells from IKO mice display an inhibition of mitophagy under oxidative stress and induces mitochondrial dysfunction. Dysfunctional mitophagy in IKO mice is represented by damaged islet beta cell mitochondrial and secretory capacity, unbalanced downstream MKK-JNK signalling without affecting the levels of MEK, ERK or p38 activation and subsequently, impaired insulin secretion signaling via inhibition IRS-AKT-Foxo1 pathway, leading to worsening glucose tolerance in these mice. Thus, these data suggest that Miro1 may be responsible for mitophagy deficiency and β-cell dysfunction in T2D and that strategies target Miro1 in vivo may provide a therapeutic target to enhance β-cell mitochondrial quality and insulin secretion to ameliorate complications associated with T2D.
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Affiliation(s)
- Lingling Chen
- ABSL-3 Laboratory at the Center for Animal Experiment and Institute of Animal Model for Human Disease, Wuhan University School of Medicine, Wuhan, P. R. China.,Department of Cell Biology, College of Life Science, Nanjing Normal University, Nanjing, Jiangsu, P.R. China
| | - Chunyan Liu
- ABSL-3 Laboratory at the Center for Animal Experiment and Institute of Animal Model for Human Disease, Wuhan University School of Medicine, Wuhan, P. R. China
| | - Jianfeng Gao
- ABSL-3 Laboratory at the Center for Animal Experiment and Institute of Animal Model for Human Disease, Wuhan University School of Medicine, Wuhan, P. R. China
| | - Zhiwen Xie
- School of Bioscience and Technology , Weifang Medical University, Weifang Shandong, P.R. China
| | - Lawrence W C Chan
- Department of Health Technology and Informatics, Hong Kong Polytechnic University, Hong Kong, Hong Kong
| | - Damien J Keating
- Department of Human Physiology and Centre for Neuroscience, Flinders University, Adelaide, South Australia, Australia
| | - Yibin Yang
- Department of Endocrinology, Zhongnan Hospital of Wuhan University, Wuhan, Hubei, P.R. China
| | - Jiazhong Sun
- Department of Respiratory, Zhongnan Hospital of Wuhan University, Wuhan, Hubei, P.R. China
| | - Fuling Zhou
- Department of Hematology and Radiation, Zhongnan Hospital of Wuhan University, Wuhan, Hubei, P.R. China
| | - Yongchang Wei
- Department of Medical Oncology, Zhongnan Hospital of Wuhan University, Wuhan, Hubei, P.R. China
| | - Xiuli Men
- School of Basic Medical Sciences, North China University of Science and Technology, Tangshan, P.R. China
| | - Sijun Yang
- ABSL-3 Laboratory at the Center for Animal Experiment and Institute of Animal Model for Human Disease, Wuhan University School of Medicine, Wuhan, P. R. China
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Stark R, Kibbey RG. The mitochondrial isoform of phosphoenolpyruvate carboxykinase (PEPCK-M) and glucose homeostasis: has it been overlooked? BIOCHIMICA ET BIOPHYSICA ACTA 2014; 1840:1313-30. [PMID: 24177027 PMCID: PMC3943549 DOI: 10.1016/j.bbagen.2013.10.033] [Citation(s) in RCA: 64] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/09/2013] [Revised: 10/13/2013] [Accepted: 10/18/2013] [Indexed: 01/03/2023]
Abstract
BACKGROUND Plasma glucose levels are tightly regulated within a narrow physiologic range. Insulin-mediated glucose uptake by tissues must be balanced by the appearance of glucose from nutritional sources, glycogen stores, or gluconeogenesis. In this regard, a common pathway regulating both glucose clearance and appearance has not been described. The metabolism of glucose to produce ATP is generally considered to be the primary stimulus for insulin release from beta-cells. Similarly, gluconeogenesis from phosphoenolpyruvate (PEP) is believed to be the primarily pathway via the cytosolic isoform of phosphoenolpyruvate carboxykinase (PEPCK-C). These models cannot adequately explain the regulation of insulin secretion or gluconeogenesis. SCOPE OF REVIEW A metabolic sensing pathway involving mitochondrial GTP (mtGTP) and PEP synthesis by the mitochondrial isoform of PEPCK (PEPCK-M) is associated with glucose-stimulated insulin secretion from pancreatic beta-cells. Here we examine whether there is evidence for a similar mtGTP-dependent pathway involved in gluconeogenesis. In both islets and the liver, mtGTP is produced at the substrate level by the enzyme succinyl CoA synthetase (SCS-GTP) with a rate proportional to the TCA cycle. In the beta-cell PEPCK-M then hydrolyzes mtGTP in the production of PEP that, unlike mtGTP, can escape the mitochondria to generate a signal for insulin release. Similarly, PEPCK-M and mtGTP might also provide a significant source of PEP in gluconeogenic tissues for the production of glucose. This review will focus on the possibility that PEPCK-M, as a sensor for TCA cycle flux, is a key mechanism to regulate both insulin secretion and gluconeogenesis suggesting conservation of this biochemical mechanism in regulating multiple aspects of glucose homeostasis. Moreover, we propose that this mechanism may be important for regulating insulin secretion and gluconeogenesis compared to canonical nutrient sensing pathways. MAJOR CONCLUSIONS PEPCK-M, initially believed to be absent in islets, carries a substantial metabolic flux in beta-cells. This flux is intimately involved with the coupling of glucose-stimulated insulin secretion. PEPCK-M activity may have been similarly underestimated in glucose producing tissues and could potentially be an unappreciated but important source of gluconeogenesis. GENERAL SIGNIFICANCE The generation of PEP via PEPCK-M may occur via a metabolic sensing pathway important for regulating both insulin secretion and gluconeogenesis. This article is part of a Special Issue entitled Frontiers of Mitochondrial Research.
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Affiliation(s)
- Romana Stark
- Department of Physiology, Monash University, Clayton, Victoria 3800, Australia.
| | - Richard G Kibbey
- Department of Internal Medicine, Yale University School of Medicine, New Haven, Connecticut 06520-8020, USA.
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Kowluru A. Emerging roles for protein histidine phosphorylation in cellular signal transduction: lessons from the islet beta-cell. J Cell Mol Med 2008; 12:1885-908. [PMID: 18400053 PMCID: PMC4506158 DOI: 10.1111/j.1582-4934.2008.00330.x] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
Protein phosphorylation represents one of the key regulatory events in physiological insulin secretion from the islet β-cell. In this context, several classes of protein kinases (e.g. calcium-, cyclic nucleotide- and phospholipid-dependent protein kinases and tyrosine kinases) have been characterized in the β-cell. The majority of phosphorylated amino acids identified include phosphoserine, phosphothreonine and phosphotyrosine. Protein histidine phosphorylation has been implicated in the prokaryotic and eukaryotic cellular signal transduction. Most notably, phoshohistidine accounts for 6% of total protein phosphorylation in eukaryotes, which makes it nearly 100-fold more abundant than phosphotyrosine, but less abundant than phosphoserine and phosphothreonine. However, very little is known about the number of proteins with phosphohistidines, since they are highly labile and are rapidly lost during phosphoamino acid identification under standard experimental conditions. The overall objectives of this review are to: (i) summarize the existing evidence indicating the subcellular distribution and characterization of various histidine kinases in the islet β-cell, (ii) describe evidence for functional regulation of these kinases by agonists of insulin secretion, (iii) present a working model to implicate novel regulatory roles for histidine kinases in the receptor-independent activation, by glucose, of G-proteins endogenous to the β-cell, (iv) summarize evidence supporting the localization of protein histidine phosphatases in the islet β-cell and (v) highlight experimental evidence suggesting potential defects in the histidine kinase signalling cascade in islets derived from the Goto-Kakizaki (GK) rat, a model for type 2 diabetes. Potential avenues for future research to further decipher regulatory roles for protein histidine phosphorylation in physiological insulin secretion are also discussed.
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Affiliation(s)
- Anjaneyulu Kowluru
- Department of Pharmaceutical Sciences, Eugene Applebaum College of Pharmacy and Health Sciences, Wayne State University, Detroit, MI 48201, USA.
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MacDonald MJ, Smith AD, Hasan NM, Sabat G, Fahien LA. Feasibility of pathways for transfer of acyl groups from mitochondria to the cytosol to form short chain acyl-CoAs in the pancreatic beta cell. J Biol Chem 2007; 282:30596-606. [PMID: 17724028 DOI: 10.1074/jbc.m702732200] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The mitochondria of pancreatic beta cells are believed to convert insulin secretagogues into products that are translocated to the cytosol where they participate in insulin secretion. We studied the hypothesis that short chain acyl-CoA (SC-CoAs) might be some of these products by discerning the pathways of SC-CoA formation in beta cells. Insulin secretagogues acutely stimulated 1.5-5-fold increases in acetoacetyl-CoA, succinyl-CoA, malonyl-CoA, hydroxymethylglutaryl-CoA (HMG-CoA), and acetyl-CoA in INS-1 832/13 cells as judged from liquid chromatography-tandem mass spectrometry measurements. Studies of 12 relevant enzymes in rat and human pancreatic islets and INS-1 832/13 cells showed the feasibility of at least two redundant pathways, one involving acetoacetate and the other citrate, for the synthesis SC-CoAs from secretagogue carbon in mitochondria and the transfer of their acyl groups to the cytosol where the acyl groups are converted to SC-CoAs. Knockdown of two key cytosolic enzymes in INS-1 832/13 cells with short hairpin RNA supported the proposed scheme. Lowering ATP citrate lyase 88% did not inhibit glucose-induced insulin release indicating citrate is not the only carrier of acyl groups to the cytosol. However, lowering acetoacetyl-CoA synthetase 80% partially inhibited glucose-induced insulin release indicating formation of SC-CoAs from acetoacetate in the cytosol is important for insulin secretion. The results indicate beta cells possess enzyme pathways that can incorporate carbon from glucose into acetyl-CoA, acetoacetyl-CoA, and succinyl-CoA and carbon from leucine into these three SC-CoAs plus HMG-CoA in their mitochondria and enzymes that can form acetyl-CoA, acetoacetyl-CoA, malonyl-CoA, and HMG-CoA in their cytosol.
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Affiliation(s)
- Michael J MacDonald
- Childrens Diabetes Center, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin 53706, USA.
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Kibbey RG, Pongratz RL, Romanelli AJ, Wollheim CB, Cline GW, Shulman GI. Mitochondrial GTP regulates glucose-stimulated insulin secretion. Cell Metab 2007; 5:253-64. [PMID: 17403370 PMCID: PMC1876711 DOI: 10.1016/j.cmet.2007.02.008] [Citation(s) in RCA: 130] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/11/2006] [Revised: 12/01/2006] [Accepted: 02/15/2007] [Indexed: 11/15/2022]
Abstract
Nucleotide-specific isoforms of the tricarboxylic acid (TCA) cycle enzyme succinyl-CoA synthetase (SCS) catalyze substrate-level synthesis of mitochondrial GTP (mtGTP) and ATP (mtATP). While mtATP yield from glucose metabolism is coupled with oxidative phosphorylation and can vary, each molecule of glucose metabolized within pancreatic beta cells produces approximately one mtGTP, making mtGTP a potentially important fuel signal. In INS-1 832/13 cells and cultured rat islets, siRNA suppression of the GTP-producing pathway (DeltaSCS-GTP) reduced glucose-stimulated insulin secretion (GSIS) by 50%, while suppression of the ATP-producing isoform (DeltaSCS-ATP) increased GSIS 2-fold. Insulin secretion correlated with increases in cytosolic calcium, but not with changes in NAD(P)H or the ATP/ADP ratio. These data suggest a role for mtGTP in controlling pancreatic GSIS through modulation of mitochondrial metabolism, possibly involving mitochondrial calcium. Furthermore, in light of its tight coupling to TCA oxidation rates, mtGTP production may serve as an important molecular signal of TCA-cycle activity.
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Affiliation(s)
- Richard G. Kibbey
- Department of Internal Medicine, Howard Hughes Medical Institute Yale University School of Medicine New Haven, CT 06520, USA
| | - Rebecca L. Pongratz
- Department of Internal Medicine, Howard Hughes Medical Institute Yale University School of Medicine New Haven, CT 06520, USA
| | - Anthony J. Romanelli
- Department of Internal Medicine, Howard Hughes Medical Institute Yale University School of Medicine New Haven, CT 06520, USA
| | - Claes B. Wollheim
- Department of Cell Physiology and Metabolism University Medical Center CH-1211 Geneva 4, Switzerland
| | - Gary W. Cline
- Department of Internal Medicine, Howard Hughes Medical Institute Yale University School of Medicine New Haven, CT 06520, USA
| | - Gerald I. Shulman
- Department of Internal Medicine, Howard Hughes Medical Institute Yale University School of Medicine New Haven, CT 06520, USA
- Department of Cellular, Howard Hughes Medical Institute Yale University School of Medicine New Haven, CT 06520, USA
- Department of Molecular Physiology, Howard Hughes Medical Institute Yale University School of Medicine New Haven, CT 06520, USA
- *To whom correspondence should be addressed. E-mail:
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Kowluru A, Veluthakal R, Kaetzel DM. Regulatory roles for nm23/nucleoside diphosphate kinase-like enzymes in insulin secretion from the pancreatic islet beta cell. J Bioenerg Biomembr 2007; 38:227-32. [PMID: 16957985 DOI: 10.1007/s10863-006-9038-x] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Recent studies from multiple laboratories, including our own, provided fresh insights into the contributory roles for GTP-binding proteins (G-proteins) in glucose-stimulated insulin secretion (GSIS) from the islet beta cell. However, the precise mechanisms underlying the activation of this class of signaling proteins by insulin secretagogues remain only partially understood. We recently proposed that nm23/nucleoside diphosphate kinase (NDPK) catalyzes an alternate, non-receptor-dependent activation of islet endogenous G-proteins. In further support of this proposal, we report, herein, that overexpression of wild type (WT) nm23-H1 mutant in INS cells markedly potentiated GSIS. However, an inactive mutant of nm23-H1(H118F), which is deficient in histidine kinase and NDPK activities, was considerably less effective in potentiating GSIS from these cells, suggesting that both of these activities may be relevant for the potentiating effects of nm23-H1. Potential significance of these findings in relation to contributory roles for nm23/NDPK-like enzymes in the stimulus-secretion coupling of GSIS is discussed.
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Affiliation(s)
- Anjaneyulu Kowluru
- Department of Pharmaceutical Sciences, Wayne State University and beta Cell Biochemistry Laboratory, John D. Dingell VA Medical Center, Detroit, MI, 48201, USA.
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Pongratz RL, Kibbey RG, Shulman GI, Cline GW. Cytosolic and mitochondrial malic enzyme isoforms differentially control insulin secretion. J Biol Chem 2006; 282:200-7. [PMID: 17102138 DOI: 10.1074/jbc.m602954200] [Citation(s) in RCA: 107] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
In islet beta-cells and INS-1 cells both the high activity of malic enzyme and the correlation of insulin secretion rates with pyruvate carboxylase (PC) flux suggest that a pyruvate-malate cycle is functionally relevant to insulin secretion. Expression of the malic enzyme isoforms in INS-1 cells and rat islets was measured, and small interfering RNA was used to selectively reduce isoform mRNA expression in INS-1 cells to evaluate its impact on insulin secretion. The cytosolic NADP(+)-specific isoform (ME1) was the most abundant, with the mitochondrial isoforms NAD(+)-preferred (ME2) expressed at approximately 50%, and the NADP(+)-specific (ME3) at approximately 10% compared with ME1. Selective reduction (89 +/- 2%) of cytosolic ME1 mRNA expression and enzyme activity significantly reduced glucose (15 mM:41 +/- 6%, p < 0.01) and amino acid (4 mM glutamine +/- 10 mM leucine: 39 +/- 6%, p < 0.01)-stimulated insulin secretion. Selective small interfering RNA reduction (51 +/- 6%) of mitochondrial ME2 mRNA expression did not impact glucose-induced insulin secretion, but decreased amino acid-stimulated insulin secretion by 25 +/- 4% (p < 0.01). Modeling of the metabolism of [U-(13)C]glucose by its isotopic distribution in glutamate indicates a second pool of pyruvate distinct from glycolytically derived pyruvate in INS-1 cells. ME1 knockdown decreased flux of both pools of pyruvate through PC. In contrast, ME2 knockdown affected only PC flux of the pyruvate derived from glutamate metabolism. These results suggest a physiological basis for two metabolically and functionally distinct pyruvate cycles. The cycling of pyruvate by ME1 generates cytosolic NADPH, whereas mitochondrial ME2 responds to elevated amino acids and serves to supply sufficient pyruvate for increased Krebs cycle flux when glucose is limiting.
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Affiliation(s)
- Rebecca L Pongratz
- Department of Internal Medicine, Yale University School of Medicine, New Haven, CT 06520, USA
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Hunt KJ, Lehman DM, Arya R, Fowler S, Leach RJ, Göring HHH, Almasy L, Blangero J, Dyer TD, Duggirala R, Stern MP. Genome-wide linkage analyses of type 2 diabetes in Mexican Americans: the San Antonio Family Diabetes/Gallbladder Study. Diabetes 2005; 54:2655-62. [PMID: 16123354 DOI: 10.2337/diabetes.54.9.2655] [Citation(s) in RCA: 62] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
The San Antonio Family Diabetes/Gallbladder Study was initiated to identify susceptibility genes for type 2 diabetes. Evidence was previously reported of linkage to diabetes on 10q with suggestive evidence on 3p and 9p in a genome-wide scan of 440 individuals from 27 pedigrees ascertained through a single diabetic proband. Subsequently, the study was expanded to include 906 individuals from 39 extended Mexican-American pedigrees, two additional examination cycles approximately 5.3 and 7.6 years after baseline, and genotypes for a new set of genome-wide markers. Therefore, we completed a second genome-wide linkage scan. Using information from a participant's most recent exam, the prevalence of diabetes in nonprobands was 21.8%. We performed genome-wide variance components-based genetic analysis on the discrete trait diabetes using a liability model and on the quantitative Martingale residual obtained from modeling age of diabetes diagnosis using Cox proportional hazard models. Controlling for age and age(2), our strongest evidence for linkage to the trait diabetes and the quantitative Martingale residual was on chromosome 3p at marker D3S2406 with multipoint empirical logarithm of odds scores of 1.87 and 3.76, respectively. In summary, we report evidence for linkage to diabetes on chromosome 3p in a region previously identified in at least three independent populations.
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Affiliation(s)
- Kelly J Hunt
- Division of Clinical Epidemiology, Department of Medicine, University of Texas Health Science Center at San Antonio, 7703 Floyd Curl Dr., San Antonio, TX 78229-3900, USA.
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Seifert M, Welter C, Mehraein Y, Seitz G. Expression of the nm23 homologues nm23-H4, nm23-H6, and nm23-H7 in human gastric and colon cancer. J Pathol 2005; 205:623-32. [PMID: 15726650 DOI: 10.1002/path.1724] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
Eight members of the nm23-gene family have been described. The involvement of nm23-H1 and nm23-H2 in tumour progression and metastasis, as well as in gene regulation and apoptosis, has been shown in numerous studies. Whether nm23-H4, -H6, and -H7 play a role in tumours is, however, largely unknown. This study describes data on the expression of these three nm23 homologues in human colon and gastric cancer by real-time RT-PCR and immunohistochemistry. Increased expression of these genes, most strikingly nm23-H4 and -H7, was observed in the majority of tumours analysed. No correlation with tumour stage according to the TNM classification was found. In contrast, by immunohistochemical analysis, nm23-H4 and -H6 overexpression correlated with the intestinal tumour type in gastric cancer tissues, whereas no increased immunoreactivity for the three nm23 proteins was noted in the diffuse type tumour specimens. These findings indicate that nm23-H6, and particularly nm23-H4 and -H7, may be involved in the development of colon and gastric carcinoma, the latter possibly in a type-specific manner. A contribution to tumour progression or metastasis could not, however, be proven. Elucidation of the specific mechanisms by which the nm23 homologues nm23-H4, -H6, and -H7 are involved in tumour development requires further studies.
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Affiliation(s)
- M Seifert
- Department of Human Genetics, Saarland University, University Hospital, Homburg/Saar, Germany.
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12
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Kowluru A. Differential regulation by fatty acids of protein histidine phosphorylation in rat pancreatic islets. Mol Cell Biochem 2005; 266:175-82. [PMID: 15646040 DOI: 10.1023/b:mcbi.0000049157.03855.74] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Long-chain fatty acids (e.g. arachidonic acid) have been implicated in physiological control of insulin secretion. We previously reported histidine phosphorylation of at least two islet proteins (e.g., NDP kinase and the beta subunit of trimeric G-proteins), and suggested that such a signalling step may have regulatory roles in beta cell signal transduction, specifically at the level of G-protein activation. Since our earlier findings also indicated potential regulation by long-chain fatty acids of islet G-proteins, we undertook the current study to verify putative regulation, by fatty acids, of protein histidine phosphorylation of NDP kinase and Gbeta subunit in normal rat islets. The phosphoenzyme formation of NDP kinase was stimulated by various fatty acids in the following rank order: linoleic acid > arachidonic acid > oleic acid > palmitic acid = stearic acid = control. Furthermore, the catalytic activity of NDP kinase was stimulated by these fatty acids in the rank order of: oleic acid > arachidonic acid > linoleic acid > palmitic acid = stearic acid = control. Arachidonic acid methyl ester, an inactive analog of arachidonic acid, did not significantly affect either the phosphoenzyme formation or the catalytic activity of NDP kinase. Interestingly, arachidonic acid exerted dual effects on the histidine phosphorylation of beta subunit; it significantly stimulated the phosphorylation at 33 microM beyond which it was inhibitory. Together, these findings identify additional loci (e.g., NDP kinase and Gbeta subunit) at which unsaturated, but not saturated, fatty acids could exert their intracellular effects leading to exocytotic secretion of insulin.
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Affiliation(s)
- Anjaneyulu Kowluru
- Department of Pharmaceutical Sciences, Wayne State University and beta Cell Biochemistry Laboratory, John D Dingell VA Medical Center, Detroit, MI 48202, USA.
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13
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Kowluru A. Regulatory roles for small G proteins in the pancreatic beta-cell: lessons from models of impaired insulin secretion. Am J Physiol Endocrinol Metab 2003; 285:E669-84. [PMID: 12959934 DOI: 10.1152/ajpendo.00196.2003] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Emerging evidence suggests that GTP-binding proteins (G proteins) play important regulatory roles in physiological insulin secretion from the islet beta-cell. Such conclusions were drawn primarily from experimental data derived through the use of specific inhibitors of G protein function. Data from gene depletion experiments appear to further substantiate key roles for these signaling proteins in the islet metabolism. The first part of this review will focus on findings supporting the hypothesis that activation of specific G proteins is essential for insulin secretion, including regulation of their function by posttranslational modifications at their COOH-terminal cysteines (e.g., isoprenylation). The second part will overview novel, non-receptor-dependent mechanism(s) whereby glucose might activate specific G proteins via protein histidine phosphorylation. The third section will review findings that appear to link abnormalities in the expression and/or functional activation of these key signaling proteins to impaired insulin secretion. It is hoped that this review will establish a basis for future research in this area of islet signal transduction, which presents a significant potential, not only in identifying key signaling proteins that are involved in physiological insulin secretion, but also in examining potential abnormalities in this signaling cascade that lead to islet dysfunction and onset of diabetes.
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Affiliation(s)
- Anjaneyulu Kowluru
- Department of Pharmaceutical Sciences 3601, Applebaum College of Pharmacy and Health Sciences, Wayne State University, 259 Mack Avenue, Detroit, MI 48202.
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14
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Kowluru A. Defective protein histidine phosphorylation in islets from the Goto-Kakizaki diabetic rat. Am J Physiol Endocrinol Metab 2003; 285:E498-503. [PMID: 12799314 DOI: 10.1152/ajpendo.00121.2003] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
We recently described novel regulatory roles for protein histidine phosphorylation of key islet proteins (e.g., nucleoside diphosphate kinase and succinyl thiokinase) in insulin secretion from the islet beta-cell (Kowluru A. Diabetologia 44: 89-94, 2001; Kowluru A, Tannous M, and Chen HQ. Arch Biochem Biophys 398: 160-169, 2002). In this context, we also characterized a novel, ATP- and GTP-sensitive protein histidine kinase in isolated beta-cells that catalyzed the histidine phosphorylation of islet (endogenous) proteins as well as exogenously added histone 4, and we implicated this kinase in the activation of islet endogenous G proteins (Kowluru A. Biochem Pharmacol 63: 2091-2100, 2002). In the present study, we describe abnormalities in ATP- or GTP-mediated histidine phosphorylation of nucleoside diphosphate kinase in islets derived from the Goto-Kakizaki (GK) rat, a model for non-insulin-dependent diabetes. Furthermore, we provide evidence for a marked reduction in the activities of ATP- or GTP-sensitive histidine kinases in GK rat islets. On the basis of these observations, we propose that alterations in protein histidine phosphorylation could contribute toward insulin-secretory abnormalities demonstrable in the diabetic islet.
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Affiliation(s)
- Anjaneyulu Kowluru
- Department of Pharmaceutical Sciences, 3601 Applebaum Bldg., Wayne State University, 259 Mack Ave., Detroit, MI 48202, USA.
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Kowluru A, Chen HQ, Tannous M. Novel roles for the rho subfamily of GTP-binding proteins in succinate-induced insulin secretion from betaTC3 cells: further evidence in support of the succinate mechanism of insulin release. Endocr Res 2003; 29:363-76. [PMID: 14535637 DOI: 10.1081/erc-120025043] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Abstract
We have previously demonstrated regulatory roles for Rho subfamily of G-proteins in glucose- and calcium-induced insulin secretion. Herein, we examined regulation by these proteins of insulin secretion from betaTC3 cells elicited by mitochondrial fuels, such as the succinic acid methyl ester (SAME). Preincubation of these cells with Clostridium difficile toxin-B (200 ng/mL), which monoglucosylates and inactivates Cdc42 and Rac1, markedly decreased (> 70%) SAME-induced insulin secretion. Furthermore, exposure of betaTC3 cells to GGTI-2147 (20 microM), a selective inhibitor of the requisite prenylation of Rac1 and Cdc42, significantly reduced (> 80%) SAME-induced insulin release, suggesting that post-translational prenylation of these proteins is necessary for SAME-induced insulin release. Western blot analysis indicated localization of Cdc42, Rac1, and Ras in the beta cell mitochondrial fraction. Confocal microscopy revealed a modest, but inconsistent, increase in the association of either Rac1 or Cdc42 with Mitotracker, a mitochondrial marker, following exposure to SAME. These data suggest that activation of preexisting intramitochondrial Rac1 and Cdc42 may be sufficient to regulate SAME-induced insulin secretion. Together, our findings support a role for G-proteins in insulin secretion at a step dependent on mitochondrial metabolism. They also identify mevalonate-derived, isoprenoid modified Rho G-proteins as specific signaling molecules in recently proposed succinate mechanism of insulin release.
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Affiliation(s)
- Anjaneyulu Kowluru
- Department of Pharmaceutical Sciences, Eugene Applebaum College of Pharmacy and Health Sciences, Wayne State University, Detroit, Michigan 48201, USA.
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Steeg PS, Palmieri D, Ouatas T, Salerno M. Histidine kinases and histidine phosphorylated proteins in mammalian cell biology, signal transduction and cancer. Cancer Lett 2003; 190:1-12. [PMID: 12536071 DOI: 10.1016/s0304-3835(02)00499-8] [Citation(s) in RCA: 75] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Intensive investigation of protein tyrosine, serine and threonine phosphorylation has lead to advances in signal transduction research and cancer treatment. This feature summarizes research on mammalian proteins exhibiting histidine phosphorylation. Histidine kinases are well known in prokaryotic and lower eukaryotic systems where they form the 'two-component' signal transduction system. The relative invisibility of histidine phosphorylation in mammalian cells may result from technical obstacles such as its acid lability, which precludes detection in electrophoretic systems, amino acid sequencing, etc. Emerging data have identified mammalian histidine kinases for the kinase suppressor of ras, a scaffold molecule for the Map kinase pathway, as well as histone H4, aldolase C and the beta-subunit of heterotrimeric G proteins. Additional mammalian proteins of interest to signal transduction and cancer research exhibit histidine phosphorylation, including P-selectin, annexin I and the 20S proteasome. Other candidate histidine phosphorylated proteins are identified. These data suggest the existence of another series of phosphorylation patterns in signal transduction.
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Affiliation(s)
- Patricia S Steeg
- Women's Cancers Section, Laboratory of Pathology, Center for Cancer Research, National Cancer Institute, Building 10, Room 2A33, Bethesda, MD 20892, USA.
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Abstract
Nutrient secretagogues can increase the production of succinyl-CoA in rat pancreatic islets. When succinate esters are the secretagogue, succinyl-CoA can be generated via the succinate thiokinase reaction. Other secretagogues can increase production of succinyl-CoA secondary to increasing alpha-ketoglutarate production by glutamate dehydrogenase or mitochondrial aspartate aminotransferase followed by the alpha-ketoglutarate dehydrogenase reaction. Although secretagogues can increase the production of succinyl-CoA, they do not increase the level of this metabolite until after they decrease the level of 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA). This suggests that the generated succinyl-CoA initially reacts with acetoacetate to yield acetoacetyl-CoA plus succinate in the succinyl-CoA-acetoacetate transferase reaction. This would be followed by acetoacetyl-CoA reacting with acetyl-CoA to generate HMG-CoA in the HMG-CoA synthetase reaction. HMG-CoA will then be reduced by NADPH to mevalonate in the HMG-CoA reductase reaction and/or cleaved to acetoacetate plus acetyl-CoA by HMG cleavage enzyme. Succinate derived from either exogenous succinate esters or generated by succinyl-CoA-acetoacetate transferase is metabolized to malate followed by the malic enzyme reaction. Increased production of NADPH by the latter reaction then increases reduction of HMG-CoA and accounts for the decrease in the level of HMG-CoA produced by secretagogues. Pyruvate carboxylation catalyzed by pyruvate carboxylase will supply oxaloacetate to mitochondrial aspartate aminotransferase. This would enable this aminotransferase to supply alpha-ketoglutarate to the alpha-ketoglutarate dehydrogenase complex and would, in part, account for secretagogues increasing the islet level of succinyl-CoA after they decrease the level of HMG-CoA. Mevalonate could be a trigger of insulin release as a result of its ability to alter membrane proteins and/or cytosolic Ca(2+). This is consistent with the fact that insulin secretagogues decrease the level of the mevalonate precursor HMG-CoA. In addition, inhibitors of HMG-CoA reductase interfere with insulin release and this inhibition can be reversed by mevalonate.
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Affiliation(s)
- Leonard A Fahien
- Department of Pharmacology, University of Wisconsin Medical School, Madison, Wisconsin 53706, USA.
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Alarcon C, Wicksteed B, Prentki M, Corkey BE, Rhodes CJ. Succinate is a preferential metabolic stimulus-coupling signal for glucose-induced proinsulin biosynthesis translation. Diabetes 2002; 51:2496-504. [PMID: 12145163 DOI: 10.2337/diabetes.51.8.2496] [Citation(s) in RCA: 75] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
The secondary signals emanating from increased glucose metabolism, which lead to specific increases in proinsulin biosynthesis translation, remain elusive. It is known that signals for glucose-stimulated insulin secretion and proinsulin biosynthesis diverge downstream of glycolysis. Consequently, the mitochondrial products ATP, Krebs cycle intermediates, glutamate, and acetoacetate were investigated as candidate stimulus-coupling signals specific for glucose-induced proinsulin biosynthesis in rat islets. Decreasing ATP levels by oxidative phosphorylation inhibitors showed comparable effects on proinsulin biosynthesis and total protein synthesis. Although it is a cofactor, ATP is unlikely to be a metabolic stimulus-coupling signal specific for glucose-induced proinsulin biosynthesis. Neither glutamic acid methyl ester nor acetoacetic acid methyl ester showed a specific effect on glucose-stimulated proinsulin biosynthesis. Interestingly, among Krebs cycle intermediates, only succinic acid monomethyl ester specifically stimulated proinsulin biosynthesis. Malonic acid methyl ester, an inhibitor of succinate dehydrogenase, also specifically increased glucose-induced proinsulin biosynthesis without affecting islet ATP levels or insulin secretion. Glucose caused a 40% increase in islet intracellular succinate levels, but malonic acid methyl ester showed no further effect, probably due to efficient conversion of succinate to succinyl-CoA. In this regard, a GTP-dependent succinyl-CoA synthetase activity was found in cytosolic fractions of pancreatic islets. Thus, succinate and/or succinyl-CoA appear to be preferential metabolic stimulus-coupling factors for glucose-induced proinsulin biosynthesis translation.
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Affiliation(s)
- Cristina Alarcon
- Pacific Northwest Research Institute, Seattle, Washington 98122, USA
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Kowluru A. Identification and characterization of a novel protein histidine kinase in the islet beta cell: evidence for its regulation by mastoparan, an activator of G-proteins and insulin secretion. Biochem Pharmacol 2002; 63:2091-100. [PMID: 12110368 DOI: 10.1016/s0006-2952(02)01025-0] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
Using insulin-secreting cells, we previously demonstrated that specific proteins associated with the cytosolic, secretory granule, and mitochondrial fractions undergo a novel type of phosphorylation on their histidine residues. Subsequently, we identified these proteins as the nucleoside diphosphate kinase (NDPK) [Kowluru and Metz, Biochemistry 1994;33:12495-503], the beta subunit of trimeric GTP-binding proteins [Kowluru et al., Biochem J 1996;313:97-107], and the alpha subunit of succinyl-CoA synthetase [Kowluru, Diabetologia 2001;44:89-94], respectively. Since several other enzymes of intermediary metabolism (e.g. ATP-citrate lyase and glucose-6-phosphatase) also undergo histidine phosphorylation, these initial findings may have a more generalized significance to beta cells. Herein, we characterized a novel protein histidine kinase in pancreatic beta cells, and determined it to be acid- and heat-labile as well as alkali-resistant in its phosphorylation of histone 4. Such an activity was detected in normal rat islets, human islets, and clonal beta (HIT-T15 and INS-1) cells, and could utilize either ATP or GTP as a phosphoryl donor (with K(m) values in the range of 60-100 microM). On a size-exclusion column, its molecular mass was estimated to be in the range of 60-70 kDa. It was stimulated by divalent cations (Mg(2+)>Mn(2+)>control=Ca(2+)=Zn(2+)=Co(2+)), but was resistant to polyamines. It was inactivated by known in vitro inhibitors of protein histidine phosphorylation (e.g. UDP or cromoglycate). Mastoparan, a global activator of G-proteins and insulin secretion from isolated beta cells, but not mastoparan-17, its inactive analog, stimulated histidine kinase activity and histidine phosphorylation of G(beta) subunit and insulin secretion from isolated rat islets. These studies identify, for the first time, a protein kinase activity in the pancreatic beta cell that does not act on traditional -Ser, -Tyr, or -Thr residues. They also establish a possible link between histidine kinase activity and G(beta) phosphorylation in isolated beta cells.
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Affiliation(s)
- Anjaneyulu Kowluru
- Department of Pharmaceutical Sciences, College of Pharmacy and Allied Health Professions, Wayne State University, Detroit, MI 48201, USA.
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Kowluru A, Tannous M, Chen HQ. Localization and characterization of the mitochondrial isoform of the nucleoside diphosphate kinase in the pancreatic beta cell: evidence for its complexation with mitochondrial succinyl-CoA synthetase. Arch Biochem Biophys 2002; 398:160-9. [PMID: 11831846 DOI: 10.1006/abbi.2001.2710] [Citation(s) in RCA: 88] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Nucleoside diphosphate kinase (NDPK) catalyzes the transfer of terminal phosphates from nucleoside triphosphates to nucleoside diphosphates to yield nucleotide triphosphates. The present study was undertaken to localize and characterize the mitochondrial isoform of NDPK (mNDPK) in the pancreatic beta cell since it could contribute to the generation of mitochondrial nucleotide triphosphates and, thereby, to the mitochondrial high-energy phosphate metabolism of the pancreatic beta cell. Mitochondrial fractions from the insulin-secreting beta cells were isolated by differential centrifugation. mNDPK activity was assayed as the amount of [(3)H]GTPgammaS formed from ATPgammaS and [(3)H]GDP. Incubation of isolated mitochondrial extracts with either [gamma-(32)P]ATP or GTP resulted in the formation [(32)P]NDPK, which could be immunoprecipitated by an anti-NDPK serum. mNDPK exhibited saturation kinetics with respect to its nucleoside diphosphate acceptors and nucleoside triphosphate donors and sensitivity to known inhibitors of NDPK (e.g., uridine diphosphate and cromoglycate). By Western blot analyses, at least three isoforms of NDPK were identified in various subcellular fractions of the beta cell. The nm23-H1 (NDPK-A) was predominantly soluble whereas nm23-H2 (NDPK-B) was associated with the soluble as well as membranous fractions. The mitochondrial isoform of NDPK, nm23-H4, was uniformly distributed in the beta cell mitochondrial subfractions. A significant amount of NDPK (as determined by the catalytic activity and immunological methods) was recovered in the immunoprecipitates of mitochondrial fraction precipitated with an antiserum directed against succinyl-CoA synthetase (SCS), suggesting that NDPK might remain complexed with SCS. We provide the first evidence for the localization of a mitochondrial isoform of the NDPK in the islet beta cell and thus offer a potential mechanism for the generation of intramitochondrial GTP which, unlike ATP, is not transported into mitochondria via the classical nucleotide translocase. Further work will be required to determine the importance of the NDPK/SCS complex to normal beta cell function in the secretion of insulin.
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Affiliation(s)
- Anjaneyulu Kowluru
- Department of Pharmaceutical Sciences, Wayne State University, Detroit, Michigan 48202, USA.
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