1
|
Nebbioso G, Yosief R, Koshkin V, Qiu Y, Peng C, Elisseev V, Krylov SN. Automated identification and tracking of cells in Cytometry of Reaction Rate Constant (CRRC). PLoS One 2023; 18:e0282990. [PMID: 37399195 DOI: 10.1371/journal.pone.0282990] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2022] [Accepted: 02/28/2023] [Indexed: 07/05/2023] Open
Abstract
Cytometry of Reaction Rate Constant (CRRC) is a method for studying cell-population heterogeneity using time-lapse fluorescence microscopy, which allows one to follow reaction kinetics in individual cells. The current and only CRRC workflow utilizes a single fluorescence image to manually identify cell contours which are then used to determine fluorescence intensity of individual cells in the entire time-stack of images. This workflow is only reliable if cells maintain their positions during the time-lapse measurements. If the cells move, the original cell contours become unsuitable for evaluating intracellular fluorescence and the CRRC experiment will be inaccurate. The requirement of invariant cell positions during a prolonged imaging is impossible to satisfy for motile cells. Here we report a CRRC workflow developed to be applicable to motile cells. The new workflow combines fluorescence microscopy with transmitted-light microscopy and utilizes a new automated tool for cell identification and tracking. A transmitted-light image is taken right before every fluorescence image to determine cell contours, and cell contours are tracked through the time-stack of transmitted-light images to account for cell movement. Each unique contour is used to determine fluorescence intensity of cells in the associated fluorescence image. Next, time dependencies of the intracellular fluorescence intensities are used to determine each cell's rate constant and construct a kinetic histogram "number of cells vs rate constant." The new workflow's robustness to cell movement was confirmed experimentally by conducting a CRRC study of cross-membrane transport in motile cells. The new workflow makes CRRC applicable to a wide range of cell types and eliminates the influence of cell motility on the accuracy of results. Additionally, the workflow could potentially monitor kinetics of varying biological processes at the single-cell level for sizable cell populations. Although our workflow was designed ad hoc for CRRC, this cell-segmentation/cell-tracking strategy also represents an entry-level, user-friendly option for a variety of biological assays (i.e., migration, proliferation assays, etc.). Importantly, no prior knowledge of informatics (i.e., training a model for deep learning) is required.
Collapse
Affiliation(s)
- Giammarco Nebbioso
- Department of Chemistry, York University, Toronto, Ontario, Canada
- Centre for Research on Biomolecular Interactions, York University, Toronto, Ontario, Canada
| | - Robel Yosief
- Department of Chemistry, York University, Toronto, Ontario, Canada
- Centre for Research on Biomolecular Interactions, York University, Toronto, Ontario, Canada
| | - Vasilij Koshkin
- Department of Chemistry, York University, Toronto, Ontario, Canada
- Centre for Research on Biomolecular Interactions, York University, Toronto, Ontario, Canada
| | - Yumin Qiu
- Centre for Research on Biomolecular Interactions, York University, Toronto, Ontario, Canada
- Department of Biology, York University, Toronto, Ontario, Canada
| | - Chun Peng
- Centre for Research on Biomolecular Interactions, York University, Toronto, Ontario, Canada
- Department of Biology, York University, Toronto, Ontario, Canada
| | - Vadim Elisseev
- IBM Research Europe, The Hartree Centre, Daresbury Laboratory, Warrington, United Kingdom
- Wrexham Glyndwr University, Wrexham, United Kingdom
| | - Sergey N Krylov
- Department of Chemistry, York University, Toronto, Ontario, Canada
- Centre for Research on Biomolecular Interactions, York University, Toronto, Ontario, Canada
| |
Collapse
|
2
|
Koshkin V, De Oliveira MB, Peng C, Ailles LE, Liu G, Covens A, Krylov SN. Multi-drug-resistance efflux in cisplatin-naive and cisplatin-exposed A2780 ovarian cancer cells responds differently to cell culture dimensionality. Mol Clin Oncol 2021; 15:161. [PMID: 34295468 PMCID: PMC8273925 DOI: 10.3892/mco.2021.2323] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2021] [Accepted: 06/02/2021] [Indexed: 01/20/2023] Open
Abstract
A primary reason for chemotherapy failure is chemoresistance, which is driven by various mechanisms. Multi-drug resistance (MDR) is one such mechanism that is responsible for drug extrusion from the intracellular space. MDR can be intrinsic and thus, may pre-exist the first application of chemotherapy. However, MDR may also be acquired during tumor exposure to chemotherapeutic agents. To understand whether cell clustering can influence intrinsic and acquired MDR, the present study assessed cultured monolayers (representing individual cells) and spheroids (representing clusters) formed by cisplatin-naïve (intrinsic MDR) and cisplatin-exposed (acquired MDR) lines of ovarian cancer A2780 cells by determining the cytometry of reaction rate constant (CRRC). MDR efflux was characterized using accurate and robust cell number vs. MDR efflux rate constant (kMDR) histograms. Both cisplatin-naïve and cisplatin-exposed monolayer cells presented unimodal histograms; the histogram of cisplatin-exposed cells was shifted towards a higher kMDR value suggesting greater MDR activity. Spheroids of cisplatin-naïve cells presented a bimodal histogram indicating the presence of two subpopulations with different MDR activity. In contrast, spheroids of cisplatin-exposed cells presented a unimodal histogram qualitatively similar to that of the monolayers of cisplatin-exposed cells but with a moderate shift towards greater MDR activity. A flow-cytometry assessment of multidrug resistance-associated protein 1 transporter levels in monolayers and dissociated spheroids revealed distributions similar to those of kMDR, thus, suggesting a plausible molecular mechanism for the observed differences in MDR activity. The observed greater effect of cell clustering on intrinsic rather than in acquired MDR can help guide the development of new therapeutic strategies targeting clusters of circulating tumor cells.
Collapse
Affiliation(s)
- Vasilij Koshkin
- Centre for Research on Biomolecular Interactions, York University, Toronto, Ontario M3J 1P3, Canada
| | | | - Chun Peng
- Centre for Research on Biomolecular Interactions, York University, Toronto, Ontario M3J 1P3, Canada
| | - Laurie E Ailles
- Department of Medical Biophysics, University of Toronto, Toronto, Ontario M5G 1L7, Canada
| | - Geoffrey Liu
- Department of Medicine, Medical Oncology, Princess Margaret Cancer Centre, Toronto, Ontario M5G 2M9, Canada
| | - Allan Covens
- Sunnybrook Odette Cancer Centre, Toronto, Ontario M4N 3M5, Canada
| | - Sergey N Krylov
- Centre for Research on Biomolecular Interactions, York University, Toronto, Ontario M3J 1P3, Canada
| |
Collapse
|
3
|
Bleker de Oliveira M, Koshkin V, Liu G, Krylov SN. Analytical Challenges in Development of Chemoresistance Predictors for Precision Oncology. Anal Chem 2020; 92:12101-12110. [PMID: 32790291 DOI: 10.1021/acs.analchem.0c02644] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Chemoresistance, i.e., tumor insensitivity to chemotherapy, shortens life expectancy of cancer patients. Despite the availability of new treatment options, initial systemic regimens for solid tumors are dominated by a set of standard chemotherapy drugs, and alternative therapies are used only when a patient has demonstrated chemoresistance clinically. Chemoresistance predictors use laboratory parameters measured on tissue samples to predict the patient's response to chemotherapy and help to avoid application of chemotherapy to chemoresistant patients. Despite thousands of publications on putative chemoresistance predictors, there are only about a dozen predictors that are sufficiently accurate for precision oncology. One of the major reasons for inaccuracy of predictors is inaccuracy of analytical methods utilized to measure their laboratory parameters: an inaccurate method leads to an inaccurate predictor. The goal of this study was to identify analytical challenges in chemoresistance-predictor development and suggest ways to overcome them. Here we describe principles of chemoresistance predictor development via correlating a clinical parameter, which manifests disease state, with a laboratory parameter. We further classify predictors based on the nature of laboratory parameters and analyze advantages and limitations of different predictors using the reliability of analytical methods utilized for measuring laboratory parameters as a criterion. Our eventual focus is on predictors with known mechanisms of reactions involved in drug resistance (drug extrusion, drug degradation, and DNA damage repair) and using rate constants of these reactions to establish accurate and robust laboratory parameters. Many aspects and conclusions of our analysis are applicable to all types of disease biomarkers built upon the correlation of clinical and laboratory parameters.
Collapse
Affiliation(s)
- Mariana Bleker de Oliveira
- Department of Chemistry and Centre for Research on Biomolecular Interactions, York University, Toronto M3J 1P3, Canada
| | - Vasilij Koshkin
- Department of Chemistry and Centre for Research on Biomolecular Interactions, York University, Toronto M3J 1P3, Canada
| | - Geoffrey Liu
- Department of Medicine, Medical Oncology, Princess Margaret Cancer Centre, Toronto M5G 2M9, Canada
| | - Sergey N Krylov
- Department of Chemistry and Centre for Research on Biomolecular Interactions, York University, Toronto M3J 1P3, Canada
| |
Collapse
|
4
|
Koshkin V, Bleker de Oliveira M, Peng C, Ailles LE, Liu G, Covens A, Krylov SN. Spheroid-Based Approach to Assess the Tissue Relevance of Analysis of Dispersed-Settled Tissue Cells by Cytometry of the Reaction Rate Constant. Anal Chem 2020; 92:9348-9355. [PMID: 32522000 DOI: 10.1021/acs.analchem.0c01667] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Cytometry of Reaction Rate Constant (CRRC) uses time-lapse fluorescence microscopy to measure a rate constant of a catalytic reaction in individual cells and, thus, facilitate accurate size determination for cell subpopulations with distinct efficiencies of this reaction. Reliable CRRC requires uniform exposure of cells to the reaction substrate followed by their uniform imaging, which in turn, requires that a tissue sample be disintegrated into a suspension of dispersed cells, and these cells settle on the support surface before being analyzed by CRRC. We call such cells "dispersed-settled" to distinguish them from cells cultured as a monolayer. Studies of the dispersed-settled cells can be tissue-relevant only if the cells maintain their 3D tissue state during the multi-hour CRRC procedure. Here, we propose an approach for assessing tissue relevance of the CRRC-based analysis of the dispersed-settled cells. Our approach utilizes cultured multicellular spheroids as a 3D cell model and cultured cell monolayers as a 2D cell model. The CRRC results of the dispersed-settled cells derived from spheroids are compared to those of spheroids and monolayers in order to find if the dispersed-settled cells are representative of the spheroids. To demonstrate its practical use, we applied this approach to a cellular reaction of multidrug resistance (MDR) transport, which was followed by extrusion of a fluorescent substrate from the cells. The approach proved to be reliable and revealed long-term maintenance of MDR transport in the dispersed-settled cells obtained from cultured ovarian cancer spheroids. Accordingly, CRRC can be used to determine accurately the size of a cell subpopulation with an elevated level of MDR transport in tumor samples, which makes CRRC a suitable method for the development of MDR-based predictors of chemoresistance. The proposed spheroid-based approach for validation of CRRC is applicable to other types of cellular reactions and, thus, will be an indispensable tool for transforming CRRC from an experimental technique into a practical analytical tool.
Collapse
Affiliation(s)
- Vasilij Koshkin
- Centre for Research on Biomolecular Interactions, York University, Toronto, Ontario M3J 1P3, Canada
| | | | - Chun Peng
- Centre for Research on Biomolecular Interactions, York University, Toronto, Ontario M3J 1P3, Canada
| | - Laurie E Ailles
- Princess Margaret Cancer Centre and Department of Medical Biophysics, University of Toronto, Toronto, Ontario M5G 1L7, Canada.,Department of Medical Biophysics, University of Toronto, Toronto, Ontario N5G 1L7, Canada
| | - Geoffrey Liu
- Department of Medicine, Medical Oncology, Princess Margaret Cancer Centre, Toronto, Ontario M5G 2M9, Canada
| | - Allan Covens
- Sunnybrook Odette Cancer Centre, Toronto, Ontario M4N 3M5, Canada
| | - Sergey N Krylov
- Centre for Research on Biomolecular Interactions, York University, Toronto, Ontario M3J 1P3, Canada
| |
Collapse
|
5
|
Koshkin V, Kochmann S, Sorupanathan A, Peng C, Ailles LE, Liu G, Krylov SN. Cytometry of Reaction Rate Constant: Measuring Reaction Rate Constant in Individual Cells To Facilitate Robust and Accurate Analysis of Cell-Population Heterogeneity. Anal Chem 2019; 91:4186-4194. [PMID: 30829484 DOI: 10.1021/acs.analchem.9b00388] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Robust and accurate analysis of cell-population heterogeneity is challenging but required in many areas of biology and medicine. In particular, it is pivotal to the development of reliable cancer biomarkers. Here, we prove that cytometry of reaction rate constant (CRRC) can facilitate such analysis when the kinetic mechanism of a reaction associated with the heterogeneity is known. In CRRC, the cells are loaded with a reaction substrate, and its conversion into a product is followed by time-lapse fluorescence microscopy at the single-cell level. A reaction rate constant is determined for every cell, and a kinetic histogram "number of cells versus the rate constant" is used to determine quantitative parameters of reaction-based cell-population heterogeneity. Such parameters include, for example, the number and sizes of subpopulations. In this work, we applied CRRC to a reaction of substrate extrusion from cells by ATP-binding cassette (ABC) transporters. This reaction is viewed as a potential basis for predictive biomarkers of chemoresistance in cancer. CRRC proved to be robust (insensitive to variations in experimental settings) and accurate for finding quantitative parameters of cell-population heterogeneity. In contrast, a typical nonkinetic analysis, performed on the same data sets, proved to be both nonrobust and inaccurate. Our results suggest that CRRC can potentially facilitate the development of reliable cancer biomarkers on the basis of quantitative parameters of cell-population heterogeneity. A plausible implementation scenario of CRRC-based development, validation, and clinical use of a predictor of ovarian cancer chemoresistance to its frontline therapy is presented.
Collapse
Affiliation(s)
| | | | | | | | - Laurie E Ailles
- Department of Medical Biophysics , University of Toronto , Toronto , Ontario N5G 1L7 , Canada
| | - Geoffrey Liu
- Department of Medicine, Medical Oncology , Princess Margaret Cancer Centre , Toronto , Ontario M5G 2M9 , Canada
| | | |
Collapse
|
6
|
Koshkin V, Ailles LE, Liu G, Krylov SN. Metabolic Suppression of a Drug-Resistant Subpopulation in Cancer Spheroid Cells. J Cell Biochem 2016; 117:59-65. [PMID: 26054050 DOI: 10.1002/jcb.25247] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2015] [Accepted: 05/29/2015] [Indexed: 12/15/2022]
Abstract
Inhibition of metabolic features which distinguish cancer cells from their non-malignant counterparts is a promising approach to cancer treatment. Energy support for drug extrusion in multidrug resistance (MDR) is a potential target for metabolic inhibition. Two major sources of ATP-based metabolic energy are partial (glycolysis) and complete (mitochondrial oxidative phosphorylation) oxidation of metabolic fuels. In cancer cells, the balance between them tends to be shifted toward glycolysis; this shift is considered to be characteristic of the cancer metabolic phenotype. Numerous earlier studies, conducted with cells cultured in a monolayer (2-D model), suggested inhibition of glycolytic ATP production as an efficient tool to suppress MDR in cancer cells. Yet, more recent work challenged the appropriateness of the 2-D model for such studies and suggested that a more clinically relevant approach would utilize a more advanced cellular model such as a 3-D model. Here, we show that the transition from the 2-D model (cultured monolayer) to a 3-D model (cultured spheroids) introduces essential changes into the concept of energetic suppression of MDR. The 3-D cell organization leads to the formation of a discrete cell subpopulation (not formed in the 2-D model) with elevated MDR transport capacity. This subpopulation has a specific metabolic phenotype (mixed glycolytic/oxidative MDR support) different from that of cells cultured in the 2-D model. Finally, the shift to the oxidative phenotype becomes greater when the spheroids are grown under conditions of lactic acidosis that are typical for solid tumors. The potential clinical significance of these findings is discussed.
Collapse
Affiliation(s)
- Vasilij Koshkin
- Department of Chemistry and Centre for Research on Biomolecular Interactions, York University, Toronto, Ontario, Canada, M3J 1P3
| | - Laurie E Ailles
- Department of Medical Biophysics, University of Toronto, Toronto, Ontario, Canada, N5G 1L7
| | - Geoffrey Liu
- Division of Medical Oncology and Hematology, Department of Medicine, Princess Margaret Hospital, Toronto, Ontario, Canada, M5G 2C4
| | - Sergey N Krylov
- Department of Chemistry and Centre for Research on Biomolecular Interactions, York University, Toronto, Ontario, Canada, M3J 1P3
| |
Collapse
|
7
|
Koshkin V, Ailles LE, Liu G, Krylov SN. Preservation of the 3D Phenotype Upon Dispersal of Cultured Cell Spheroids Into Monolayer Cultures. J Cell Biochem 2016; 118:154-162. [DOI: 10.1002/jcb.25621] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2016] [Accepted: 06/08/2016] [Indexed: 12/21/2022]
Affiliation(s)
- Vasilij Koshkin
- Department of Chemistry and Centre for Research on Biomolecular Interactions; York University; Toronto Ontario Canada M3J 1P3
| | - Laurie E. Ailles
- Department of Medical Biophysics; University of Toronto; Toronto Ontario Canada N5G 1L7
| | - Geoffrey Liu
- Department of Medicine, Medical Oncology and Haematology; Princess Margaret Hospital; Toronto Ontario Canada M5G 2C4
| | - Sergey N. Krylov
- Department of Chemistry and Centre for Research on Biomolecular Interactions; York University; Toronto Ontario Canada M3J 1P3
| |
Collapse
|
8
|
Abstract
Multidrug resistance (MDR) driven by ABC (ATP binding cassette) membrane transporters is one of the major causes of treatment failure in human malignancy. MDR capacity is thought to be unevenly distributed among tumor cells, with higher capacity residing in tumor-initiating cells (TIC) (though opposite finding are occasionally reported). Functional evidence for enhanced MDR of TICs was previously provided using a "side population" assay. This assay estimates MDR capacity by a single parameter - cell's ability to retain fluorescent MDR substrate, so that cells with high MDR capacity ("side population") demonstrate low substrate retention. In the present work MDR in TICs was investigated in greater detail using a kinetic approach, which monitors MDR efflux from single cells. Analysis of kinetic traces obtained allowed for the estimation of both the velocity (V max) and affinity (K M) of MDR transport in single cells. In this way it was shown that activation of MDR in TICs occurs in two ways: through the increase of V max in one fraction of cells, and through decrease of K M in another fraction. In addition, kinetic data showed that heterogeneity of MDR parameters in TICs significantly exceeds that of bulk cells. Potential consequences of these findings for chemotherapy are discussed.
Collapse
Affiliation(s)
- Vasilij Koshkin
- Department of Chemistry and Centre for Research on Biomolecular Interactions, York University, Toronto, Ontario, Canada
| | - Burton B. Yang
- Sunnybrook Research Institute, Sunnybrook Health Sciences Centre, Toronto, Ontario, Canada
| | - Sergey N. Krylov
- Department of Chemistry and Centre for Research on Biomolecular Interactions, York University, Toronto, Ontario, Canada
| |
Collapse
|
9
|
Koshkin V, Krylov SN. Single-Cell-Kinetics Approach to Discover Functionally Distinct Subpopulations within Phenotypically Uniform Populations of Cells. Anal Chem 2013; 85:2578-81. [DOI: 10.1021/ac400151v] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Affiliation(s)
- Vasilij Koshkin
- Department of Chemistry and Centre
for Research on Biomolecular Interactions, York University, Toronto, Ontario M3J 1P3, Canada
| | - Sergey N. Krylov
- Department of Chemistry and Centre
for Research on Biomolecular Interactions, York University, Toronto, Ontario M3J 1P3, Canada
| |
Collapse
|
10
|
Koshkin V, Krylov SN. Correlation between multi-drug resistance-associated membrane transport in clonal cancer cells and the cell cycle phase. PLoS One 2012; 7:e41368. [PMID: 22848474 PMCID: PMC3405118 DOI: 10.1371/journal.pone.0041368] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2012] [Accepted: 06/20/2012] [Indexed: 02/07/2023] Open
Abstract
Multidrug resistance driven by ABC membrane transporters is one of the major reasons for treatment failure in human malignancy. Some limited evidence has previously been reported on the cell cycle dependence of ABC transporter expression. However, it has never been demonstrated that the functional activity of these transporters correlates with the cell cycle position. Here, we studied the rate of intrinsic ABC transport in different phases of the cell cycle in cultured MCF-7 breast cancer cells. The rate was characterized in terms of the efflux kinetics from cells loaded with an ABC transporter substrate. As averaging the kinetics over a cell population could lead to errors, we studied kinetics of ABC transport at the single-cell level. We found that the rate of ABC transport in MCF-7 cells could be described by Michaelis-Menten kinetics with two classical parameters, V(max) and K(M). Each of these parameters showed similar unimodal distributions with different positions of maxima for cell subpopulations in the 2c and 4c states. Compared to the 2c cells, the 4c cells exhibited greater V(max) values, indicating a higher activity of transport. They also exhibited a greater V(max)/K(M) ratio, indicating a higher efficiency of transport. Our findings suggest that cell cycle-related modulation of MDR may need to be taken into account when designing chemotherapy regimens which include cytostatic agents.
Collapse
Affiliation(s)
- Vasilij Koshkin
- Centre for Research on Biomolecular Interactions, York University, Toronto, Ontario, Canada
| | - Sergey N. Krylov
- Centre for Research on Biomolecular Interactions, York University, Toronto, Ontario, Canada
- * E-mail:
| |
Collapse
|
11
|
Ahlstrand R, Margolin B, Akbashev I, Chyrko L, Kostylev V, Yurchenko E, Piminov V, Nikolaev Y, Koshkin V, Kharshenko V, Bukhanov V. TAREG 2.01/00 project, “Validation of neutron embrittlement for VVER 1000 and 440/213 RPVs, with emphasis on integrity assessment”. Progress in Nuclear Energy 2012. [DOI: 10.1016/j.pnucene.2012.02.007] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/28/2022]
|
12
|
Krylova SM, Koshkin V, Bagg E, Schofield CJ, Krylov SN. Mechanistic studies on the application of DNA aptamers as inhibitors of 2-oxoglutarate-dependent oxygenases. J Med Chem 2012; 55:3546-52. [PMID: 22471443 PMCID: PMC4681096 DOI: 10.1021/jm300243h] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The Escherichia coli (E. coli) AlkB protein and its functional human homologues belong to a subfamily of 2-oxoglutarate (2OG) dependent oxygenases (2OG oxygenases for simplicity) that enable the repair of cytotoxic methylation damage in nucleic acids and that catalyze t-RNA oxidations. DNA alkylation is a major mechanism of action for cytotoxic anticancer drugs. Thus, the inhibition of oxidative demethylation, catalyzed by these enzymes, has the potential to improve the efficacy of chemotherapies. Here we report that oligonucleotide aptamers constitute a new class of potent inhibitors of 2OG oxygenases. DNA aptamers can selectively bind to AlkB, with nanomolar affinity, and efficiently inhibit catalysis. The mechanism of inhibition was studied by capillary electrophoresis (CE) with laser-induced fluorescence (LIF) detection. Inhibition constants of the aptamers were determined and shown to correlate well with K(d) values. The results of kinetic analyses imply that the aptamers bind AlkB away from the active site. Our findings should stimulate the development of oligonucleotide aptamers for human homologues of AlkB and further their study as potential enhancers of chemotherapy efficiency.
Collapse
Affiliation(s)
- Svetlana M. Krylova
- Department of Chemistry and Centre for Research on Biomolecular Interactions, York University, Toronto, Ontario, M3J 1P3, Canada
| | - Vasilij Koshkin
- Department of Chemistry and Centre for Research on Biomolecular Interactions, York University, Toronto, Ontario, M3J 1P3, Canada
| | - Eleanor Bagg
- Department of Chemistry and the Oxford Centre for Integrative Systems Biology, University of Oxford, Oxford, OX1 3TA, United Kingdom
| | - Christopher J. Schofield
- Department of Chemistry and the Oxford Centre for Integrative Systems Biology, University of Oxford, Oxford, OX1 3TA, United Kingdom
| | - Sergey N. Krylov
- Department of Chemistry and Centre for Research on Biomolecular Interactions, York University, Toronto, Ontario, M3J 1P3, Canada
| |
Collapse
|
13
|
Robson-Doucette CA, Sultan S, Allister EM, Wikstrom JD, Koshkin V, Bhatacharjee A, Prentice KJ, Sereda SB, Shirihai OS, Wheeler MB. Beta-cell uncoupling protein 2 regulates reactive oxygen species production, which influences both insulin and glucagon secretion. Diabetes 2011; 60:2710-9. [PMID: 21984579 PMCID: PMC3198081 DOI: 10.2337/db11-0132] [Citation(s) in RCA: 109] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Abstract
OBJECTIVE The role of uncoupling protein 2 (UCP2) in pancreatic β-cells is highly debated, partly because of the broad tissue distribution of UCP2 and thus limitations of whole-body UCP2 knockout mouse models. To investigate the function of UCP2 in the β-cell, β-cell-specific UCP2 knockout mice (UCP2BKO) were generated and characterized. RESEARCH DESIGN AND METHODS UCP2BKO mice were generated by crossing loxUCP2 mice with mice expressing rat insulin promoter-driven Cre recombinase. Several in vitro and in vivo parameters were measured, including respiration rate, mitochondrial membrane potential, islet ATP content, reactive oxygen species (ROS) levels, glucose-stimulated insulin secretion (GSIS), glucagon secretion, glucose and insulin tolerance, and plasma hormone levels. RESULTS UCP2BKO β-cells displayed mildly increased glucose-induced mitochondrial membrane hyperpolarization but unchanged rates of uncoupled respiration and islet ATP content. UCP2BKO islets had elevated intracellular ROS levels that associated with enhanced GSIS. Surprisingly, UCP2BKO mice were glucose-intolerant, showing greater α-cell area, higher islet glucagon content, and aberrant ROS-dependent glucagon secretion under high glucose conditions. CONCLUSIONS Using a novel β-cell-specific UCP2KO mouse model, we have shed light on UCP2 function in primary β-cells. UCP2 does not behave as a classical metabolic uncoupler in the β-cell, but has a more prominent role in the regulation of intracellular ROS levels that contribute to GSIS amplification. In addition, β-cell UCP2 contributes to the regulation of intraislet ROS signals that mediate changes in α-cell morphology and glucagon secretion.
Collapse
Affiliation(s)
| | - Sobia Sultan
- Department of Physiology, University of Toronto, Toronto, Ontario, Canada
| | - Emma M. Allister
- Department of Physiology, University of Toronto, Toronto, Ontario, Canada
| | - Jakob D. Wikstrom
- Department of Medicine, Boston University School of Medicine, Boston, Massachusetts
- The Wenner-Gren Institute, Stockholm University, Stockholm, Sweden
| | - Vasilij Koshkin
- Department of Physiology, University of Toronto, Toronto, Ontario, Canada
| | | | - Kacey J. Prentice
- Department of Physiology, University of Toronto, Toronto, Ontario, Canada
| | - Samuel B. Sereda
- Department of Medicine, Boston University School of Medicine, Boston, Massachusetts
| | - Orian S. Shirihai
- Department of Medicine, Boston University School of Medicine, Boston, Massachusetts
| | - Michael B. Wheeler
- Department of Physiology, University of Toronto, Toronto, Ontario, Canada
- Corresponding author: Michael B. Wheeler,
| |
Collapse
|
14
|
Koshkin V, Krylov SN. Single-Cell-Kinetics Approach to Compare Multidrug Resistance-Associated Membrane Transport in Subpopulations of Cells. Anal Chem 2011; 83:6132-4. [DOI: 10.1021/ac201690t] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Affiliation(s)
- Vasilij Koshkin
- Department of Chemistry and Centre for Research on Biomolecular Interactions, York University, Toronto, Ontario M3J 1P3, Canada
| | - Sergey N. Krylov
- Department of Chemistry and Centre for Research on Biomolecular Interactions, York University, Toronto, Ontario M3J 1P3, Canada
| |
Collapse
|
15
|
Wijesekara N, Dai FF, Hardy AB, Giglou PR, Bhattacharjee A, Koshkin V, Chimienti F, Gaisano HY, Rutter GA, Wheeler MB. Beta cell-specific Znt8 deletion in mice causes marked defects in insulin processing, crystallisation and secretion. Diabetologia 2010; 53:1656-68. [PMID: 20424817 PMCID: PMC6101216 DOI: 10.1007/s00125-010-1733-9] [Citation(s) in RCA: 219] [Impact Index Per Article: 15.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/18/2009] [Accepted: 02/05/2010] [Indexed: 02/01/2023]
Abstract
AIMS/HYPOTHESIS Zinc is highly concentrated in pancreatic beta cells, is critical for normal insulin storage and may regulate glucagon secretion from alpha cells. Zinc transport family member 8 (ZnT8) is a zinc efflux transporter that is highly abundant in beta cells. Polymorphisms of ZnT8 (also known as SLC30A8) gene in man are associated with increased risk of type 2 diabetes. While global Znt8 knockout (Znt8KO) mice have been characterised, ZnT8 is also present in other islet cell types and extra-pancreatic tissues. Therefore, it is important to find ways of understanding the role of ZnT8 in beta and alpha cells without the difficulties caused by the confounding effects of ZnT8 in these other tissues. METHODS We generated mice with beta cell-specific (Znt8BKO) and alpha cell-specific (Znt8AKO) knockout of Znt8, and performed in vivo and in vitro characterisation of the phenotypes to determine the functional and anatomical impact of ZnT8 in these cells. Thus we assessed zinc accumulation, insulin granule morphology, insulin biosynthesis and secretion, and glucose homeostasis. RESULTS Znt8BKO mice are glucose-intolerant, have reduced beta cell zinc accumulation and atypical insulin granules. They also display reduced first-phase glucose-stimulated insulin secretion, reduced insulin processing enzyme transcripts and increased proinsulin levels. In contrast, Znt8AKO mice show no evident abnormalities in plasma glucagon and glucose homeostasis. CONCLUSIONS/INTERPRETATION This is the first report of specific beta and alpha cell deletion of Znt8. Our data indicate that while, under the conditions studied, ZnT8 is absolutely essential for proper beta cell function, it is largely dispensable for alpha cell function.
Collapse
Affiliation(s)
- N Wijesekara
- Department of Physiology, University of Toronto, 1 King's College Circle Room 3352, Toronto, ON, Canada M5S 1A8
| | | | | | | | | | | | | | | | | | | |
Collapse
|
16
|
Lu H, Koshkin V, Allister EM, Gyulkhandanyan AV, Wheeler MB. Molecular and metabolic evidence for mitochondrial defects associated with beta-cell dysfunction in a mouse model of type 2 diabetes. Diabetes 2010; 59:448-59. [PMID: 19903739 PMCID: PMC2809957 DOI: 10.2337/db09-0129] [Citation(s) in RCA: 147] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
OBJECTIVE The inability of pancreatic beta-cells to appropriately respond to glucose and secrete insulin are primary defects associated with beta-cell failure in type 2 diabetes. Mitochondrial dysfunction has been implicated as a key factor in the development of type 2 diabetes; however, a link between mitochondrial dysfunction and defective insulin secretion is unclear. RESEARCH DESIGN AND METHODS We investigated the changes in islet mitochondrial function and morphology during progression from insulin resistance (3 weeks old), immediately before hyperglycemia (5 weeks old), and after diabetes onset (10 weeks old) in transgenic MKR mice compared with controls. The molecular and protein changes at 10 weeks were determined using microarray and iTRAQ proteomic screens. RESULTS At 3 weeks, MKR mice were hyperinsulinemic but normoglycemic and beta-cells showed negligible mitochondrial or morphological changes. At 5 weeks, MKR islets displayed abrogated hyperpolarization of mitochondrial membrane potential (DeltaPsi(m)), reduced mitochondrial Ca(2+) uptake, slightly enlarged mitochondria, and reduced glucose-stimulated insulin secretion. By 10 weeks, MKR mice were hyperglycemic and hyperinsulinemic and beta-cells contained swollen mitochondria with disordered cristae. beta-Cells displayed impaired stimulus-secretion coupling including reduced hyperpolarization of DeltaPsi(m), impaired Ca(2+)-signaling, and reduced glucose-stimulated ATP/ADP and insulin release. Furthermore, decreased cytochrome c oxidase-dependent oxygen consumption and signs of oxidative stress were observed in diabetic islets. Protein profiling of diabetic islets revealed that 36 mitochondrial proteins were differentially expressed, including inner membrane proteins of the electron transport chain. CONCLUSIONS We provide novel evidence for a critical role of defective mitochondrial oxidative phosphorylation and morphology in the pathology of insulin resistance-induced beta-cell failure.
Collapse
Affiliation(s)
- Hongfang Lu
- From the Departments of Physiology and Medicine, Faculty of Medicine, University of Toronto, Toronto, Canada
| | - Vasilij Koshkin
- From the Departments of Physiology and Medicine, Faculty of Medicine, University of Toronto, Toronto, Canada
| | - Emma M. Allister
- From the Departments of Physiology and Medicine, Faculty of Medicine, University of Toronto, Toronto, Canada
| | - Armen V. Gyulkhandanyan
- From the Departments of Physiology and Medicine, Faculty of Medicine, University of Toronto, Toronto, Canada
| | - Michael B. Wheeler
- From the Departments of Physiology and Medicine, Faculty of Medicine, University of Toronto, Toronto, Canada
- Corresponding author: Michael B. Wheeler,
| |
Collapse
|
17
|
Nicolson TJ, Bellomo EA, Wijesekara N, Loder MK, Baldwin JM, Gyulkhandanyan AV, Koshkin V, Tarasov AI, Carzaniga R, Kronenberger K, Taneja TK, da Silva Xavier G, Libert S, Froguel P, Scharfmann R, Stetsyuk V, Ravassard P, Parker H, Gribble FM, Reimann F, Sladek R, Hughes SJ, Johnson PR, Masseboeuf M, Burcelin R, Baldwin SA, Liu M, Lara-Lemus R, Arvan P, Schuit FC, Wheeler MB, Chimienti F, Rutter GA. Insulin storage and glucose homeostasis in mice null for the granule zinc transporter ZnT8 and studies of the type 2 diabetes-associated variants. Diabetes 2009; 58:2070-83. [PMID: 19542200 PMCID: PMC2731533 DOI: 10.2337/db09-0551] [Citation(s) in RCA: 284] [Impact Index Per Article: 18.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/15/2009] [Accepted: 06/02/2009] [Indexed: 12/03/2022]
Abstract
OBJECTIVE Zinc ions are essential for the formation of hexameric insulin and hormone crystallization. A nonsynonymous single nucleotide polymorphism rs13266634 in the SLC30A8 gene, encoding the secretory granule zinc transporter ZnT8, is associated with type 2 diabetes. We describe the effects of deleting the ZnT8 gene in mice and explore the action of the at-risk allele. RESEARCH DESIGN AND METHODS Slc30a8 null mice were generated and backcrossed at least twice onto a C57BL/6J background. Glucose and insulin tolerance were measured by intraperitoneal injection or euglycemic clamp, respectively. Insulin secretion, electrophysiology, imaging, and the generation of adenoviruses encoding the low- (W325) or elevated- (R325) risk ZnT8 alleles were undertaken using standard protocols. RESULTS ZnT8(-/-) mice displayed age-, sex-, and diet-dependent abnormalities in glucose tolerance, insulin secretion, and body weight. Islets isolated from null mice had reduced granule zinc content and showed age-dependent changes in granule morphology, with markedly fewer dense cores but more rod-like crystals. Glucose-stimulated insulin secretion, granule fusion, and insulin crystal dissolution, assessed by total internal reflection fluorescence microscopy, were unchanged or enhanced in ZnT8(-/-) islets. Insulin processing was normal. Molecular modeling revealed that residue-325 was located at the interface between ZnT8 monomers. Correspondingly, the R325 variant displayed lower apparent Zn(2+) transport activity than W325 ZnT8 by fluorescence-based assay. CONCLUSIONS ZnT8 is required for normal insulin crystallization and insulin release in vivo but not, remarkably, in vitro. Defects in the former processes in carriers of the R allele may increase type 2 diabetes risks.
Collapse
Affiliation(s)
- Tamara J. Nicolson
- Section of Cell Biology, Division of Medicine, Imperial College London, London, U.K
| | - Elisa A. Bellomo
- Section of Cell Biology, Division of Medicine, Imperial College London, London, U.K
| | | | - Merewyn K. Loder
- Section of Cell Biology, Division of Medicine, Imperial College London, London, U.K
| | - Jocelyn M. Baldwin
- Institute of Membrane and Systems Biology, University of Leeds, Leeds, U.K
| | | | - Vasilij Koshkin
- Department of Physiology, University of Toronto, Toronto, Canada
| | - Andrei I. Tarasov
- Section of Cell Biology, Division of Medicine, Imperial College London, London, U.K
| | | | | | - Tarvinder K. Taneja
- Section of Cell Biology, Division of Medicine, Imperial College London, London, U.K
| | | | | | - Philippe Froguel
- Section of Genomic Medicine, Division of Medicine, Imperial College London, London, U.K
- Centre National de la Recherche Scientifique Unite Mixte de Recherche 8090, Institute of Biology, Lille, France
| | | | | | - Philippe Ravassard
- Centre National de la Recherche Scientifique and Université Pierre et Marie Curie, Paris, France
| | - Helen Parker
- Cambridge Institute for Medical Research, University of Cambridge, Cambridge, U.K
| | - Fiona M. Gribble
- Cambridge Institute for Medical Research, University of Cambridge, Cambridge, U.K
| | - Frank Reimann
- Cambridge Institute for Medical Research, University of Cambridge, Cambridge, U.K
| | - Robert Sladek
- Department of Human Genetics, McGill University, Montreal, Canada
| | - Stephen J. Hughes
- Nuffield Department of Surgery, University of Oxford, Oxfordshire, U.K
| | - Paul R.V. Johnson
- Nuffield Department of Surgery, University of Oxford, Oxfordshire, U.K
| | - Myriam Masseboeuf
- Institut de Medecine Moleculaire de Rangueil, INSERM U858, IFR31, Toulouse III University, CHU Rangueil, Toulouse Cedex, Toulouse, France
| | - Remy Burcelin
- Institut de Medecine Moleculaire de Rangueil, INSERM U858, IFR31, Toulouse III University, CHU Rangueil, Toulouse Cedex, Toulouse, France
| | - Stephen A. Baldwin
- Institute of Membrane and Systems Biology, University of Leeds, Leeds, U.K
| | - Ming Liu
- Division of Metabolism, Endocrinology & Diabetes, University of Michigan Medical School, Ann Arbor, Michigan
| | - Roberto Lara-Lemus
- Division of Metabolism, Endocrinology & Diabetes, University of Michigan Medical School, Ann Arbor, Michigan
| | - Peter Arvan
- Division of Metabolism, Endocrinology & Diabetes, University of Michigan Medical School, Ann Arbor, Michigan
| | - Frans C. Schuit
- Gene Expression Unit, Department of Molecular Cell Biology, Katholieke Universiteit Leuven, Leuven, Belgium
| | - Michael B. Wheeler
- Institute of Membrane and Systems Biology, University of Leeds, Leeds, U.K
| | - Fabrice Chimienti
- Section of Genomic Medicine, Division of Medicine, Imperial College London, London, U.K
| | - Guy A. Rutter
- Section of Cell Biology, Division of Medicine, Imperial College London, London, U.K
| |
Collapse
|
18
|
Koshkin V, Dai FF, Robson-Doucette CA, Chan CB, Wheeler MB. Limited Mitochondrial Permeabilization Is an Early Manifestation of Palmitate-induced Lipotoxicity in Pancreatic β-Cells. J Biol Chem 2008; 283:7936-48. [DOI: 10.1074/jbc.m705652200] [Citation(s) in RCA: 56] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
|
19
|
Targonsky ED, Dai F, Koshkin V, Karaman GT, Gyulkhandanyan AV, Zhang Y, Chan CB, Wheeler MB. alpha-lipoic acid regulates AMP-activated protein kinase and inhibits insulin secretion from beta cells. Diabetologia 2006; 49:1587-98. [PMID: 16752177 DOI: 10.1007/s00125-006-0265-9] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/15/2005] [Accepted: 02/27/2006] [Indexed: 01/08/2023]
Abstract
AIMS/HYPOTHESIS The antioxidant compound alpha-lipoic acid (alpha-LA) possesses antidiabetic and anti-obesity properties. In the hypothalamus, alpha-LA suppresses appetite and prevents obesity by inhibiting AMP-activated protein kinase (AMPK). Given the therapeutic potential of alpha-LA for the treatment of type 2 diabetes and obesity, and the importance of AMPK in beta cells, we examined the effect of alpha-LA on pancreatic beta cell function. MATERIALS AND METHODS Isolated rat islets and MIN6 beta cells were treated acutely (15-90 min) or chronically (18-24 h) with alpha-LA or the known AMPK-activating compounds 5'-amino-imidazole-4-carboxamide ribonucleoside (AICAR) and metformin. Insulin secretion, the AMPK-signalling pathway, mitochondrial function and cell growth were assessed. RESULTS Acute or chronic treatment of islets and MIN6 cells with alpha-LA led to dose-dependent rises in phosphorylation of the AMPK alpha-subunit and acetyl CoA carboxylase. Chronic exposure to alpha-LA, AICAR or metformin caused a reduction in insulin secretion. alpha-LA inhibited the p70 s6 kinase translational control pathway, and inhibited MIN6 growth in a manner similar to rapamycin. Unlike AICAR and metformin, alpha-LA also acutely inhibited insulin secretion. Examination of the effect of alpha-LA on mitochondrial function showed that acute treatment with this compound elevated reactive oxygen species (ROS) production and enhanced mitochondrial depolarisation induced by Ca(2+). CONCLUSIONS/INTERPRETATION This study is the first to demonstrate that alpha-LA directly affects beta cell function. The chronic effects of alpha-LA include AMPK activation and reductions in insulin secretion and content, and cell growth. Acutely, alpha-LA also inhibits insulin secretion, an effect probably involving the ROS-induced impairment of mitochondrial function.
Collapse
Affiliation(s)
- E D Targonsky
- Department of Physiology, University of Toronto, 1 King's College Circle, Toronto, ON, Canada, M5S 1A8
| | | | | | | | | | | | | | | |
Collapse
|
20
|
Joseph JW, Koshkin V, Saleh MC, Sivitz WI, Zhang CY, Lowell BB, Chan CB, Wheeler MB. Free fatty acid-induced beta-cell defects are dependent on uncoupling protein 2 expression. J Biol Chem 2004; 279:51049-56. [PMID: 15448158 DOI: 10.1074/jbc.m409189200] [Citation(s) in RCA: 142] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023] Open
Abstract
Chronic exposure to elevated free fatty acids (lipotoxicity) induces uncoupling protein (UCP2) in the pancreatic beta-cell, and therefore a causal link between UCP2 and beta-cell defects associated with obesity may exist. Recently, we showed that lipid treatment in vivo and in vitro in UCP2(-/-) mice/islets does not result in any loss in beta-cell glucose sensitivity. We have now assessed the mechanism of maintained beta-cell function in UCP2(-/-) mice by exposing islets to 0.4 mM palmitate for 48 h. Palmitate treatment increased triglyceride concentrations in wild type (WT) but not UCP2(-/-) islets because of higher palmitate oxidation rates in the UCP2(-/-) islets. Dispersed beta-cells from the palmitate-exposed WT islets had reduced glucose-stimulated hyperpolarization of the mitochondrial membrane potential compared with both control WT and palmitate-exposed UCP2(-/-) beta-cells. The glucose-stimulated increases in the ATP/ADP ratio and cytosolic Ca2+ are attenuated in palmitate-treated WT but not UCP2(-/-) beta-cells. Exposure to palmitate reduced glucose-stimulated insulin secretion (GSIS) in WT islets, whereas UCP2(-/-) islets had enhanced GSIS. Overexpression of recombinant UCP2 but not enhanced green fluorescent protein in beta-cells resulted in a loss of glucose-stimulated hyperpolarization of the mitochondrial membrane potential and GSIS similar to that seen in WT islets exposed to palmitate. Reactive oxygen species (ROS) are known to increase the activity of UCP2. We showed that ROS levels were elevated in control UCP2(-/-) islets as compared with WT and UCP2(-/-) islets overexpressing UCP2 and that palmitate increased ROS in WT and UCP2(-/-) islets overexpressing UCP2 but not in UCP2(-/-) islets. Thus, UCP2(-/-) islets resisted the toxic effects of palmitate by maintaining glucose-dependent metabolism-secretion coupling. We propose that higher free fatty acid oxidation rates prevent accumulation of triglyceride in UCP2(-/-) islets, such accumulation being a phenomenon associated with lipotoxicity.
Collapse
Affiliation(s)
- Jamie W Joseph
- Departments of Medicine and Physiology, University of Toronto, Ontario M5S 1A8, Canada
| | | | | | | | | | | | | | | |
Collapse
|
21
|
Koshkin V, Bikopoulos G, Chan CB, Wheeler MB. The characterization of mitochondrial permeability transition in clonal pancreatic beta-cells. Multiple modes and regulation. J Biol Chem 2004; 279:41368-76. [PMID: 15231823 DOI: 10.1074/jbc.m406914200] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Mitochondrial permeability transition (MPT), which contributes substantially to the regulation of normal mitochondrial metabolism, also plays a crucial role in the initiation of cell death. It is known that MPT is regulated in a tissue-specific manner. The importance of MPT in the pancreatic beta-cell is heightened by the fact that mitochondrial bioenergetics serve as the main glucose-sensing regulator and energy source for insulin secretion. In the present study, using MIN6 and INS-1 beta-cells, we revealed that both Ca(2+)-phosphate- and oxidant-induced MPT is remarkably different from other tissues. Ca(2+)-phosphate-induced transition is accompanied by a decline in mitochondrial reactive oxygen species production related to a significant potential dependence of reactive oxygen species formation in beta-cell mitochondria. Hydroperoxides, which are indirect MPT co-inducers active in liver and heart mitochondria, are inefficient in beta-cell mitochondria, due to the low mitochondrial ability to metabolize them. Direct cross-linking of mitochondrial thiols in pancreatic beta-cells induces the opening of a low conductance ion permeability of the mitochondrial membrane instead of the full scale MPT opening typical for liver mitochondria. Low conductance MPT is independent of both endogenous and exogenous Ca(2+), suggesting a novel type of nonclassical MPT in beta-cells. It results in the conversion of electrical transmembrane potential into DeltapH instead of a decrease in total protonmotive force, thus mitochondrial respiration remains in a controlled state. Both Ca(2+)- and oxidant-induced MPTs are phosphate-dependent and, through the "phosphate flush" (associated with stimulation of insulin secretion), are expected to participate in the regulation in beta-cell glucose-sensing and secretory activity.
Collapse
Affiliation(s)
- Vasilij Koshkin
- Departments of Physiology and Medicine, University of Toronto, Toronto M5S 1A8, Canada
| | | | | | | |
Collapse
|
22
|
Abstract
Stressors such as chronic hyperglycemia or hyperlipidemia may lead to insufficient insulin secretion in susceptible individuals, contributing to type 2 diabetes. The molecules mediating this effect are just beginning to be identified. Uncoupling protein (UCP)-2 may be one such negative modulator of insulin secretion. Accumulating evidence shows that beta-cell UCP2 expression is upregulated by glucolipotoxic conditions and that increased activity of UCP2 decreases insulin secretion. Mitochondrial superoxide has been identified as a posttranslational regulator of UCP2 activity in islets; thus, UCP2 may provide protection to beta-cells at one level while simultaneously having detrimental effects on insulin secretion. Interestingly, the latter appears to be the dominant outcome, because UCP2 knockout mice display an increased beta-cell mass and retained insulin secretion capacity in the face of glucolipotoxicity.
Collapse
Affiliation(s)
- Catherine B Chan
- Department of Biomedical Sciences, University of Prince Edward Island, Charlottetown, Prince Edward, Canada.
| | | | | | | |
Collapse
|
23
|
Wang X, Li H, De Leo D, Guo W, Koshkin V, Fantus IG, Giacca A, Chan CB, Der S, Wheeler MB. Gene and protein kinase expression profiling of reactive oxygen species-associated lipotoxicity in the pancreatic beta-cell line MIN6. Diabetes 2004; 53:129-40. [PMID: 14693707 DOI: 10.2337/diabetes.53.1.129] [Citation(s) in RCA: 73] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
Oligonucleotide microarrays were used to define oleic acid (OA)-regulated gene expression and proteomic technology to screen protein kinases in MIN6 insulinoma cells. The effects of oxidative stress caused by OA and potential protective effects of N-acetyl-L-cysteine (NAC), a scavenger of reactive oxygen species (ROS), on global gene expression and beta-cell function were investigated. Long-term exposure of MIN6 cells to OA led to a threefold increase in basal insulin secretion, a 50% decrease in insulin content, an inhibition of glucose-stimulated insulin secretion (GSIS), and a twofold increase in the level of ROS. The addition of NAC normalized both the OA-induced insulin content and ROS elevation, but it failed to restore GSIS. Microarray studies and subsequent quantitative PCR analysis showed that OA consistently regulated the expression of 45 genes involved in metabolism, cell growth, signal transduction, transcription, and protein processing. The addition of NAC largely normalized the expression of the OA-regulated genes involved in cell growth and differentiation but not other functions. A protein kinase screen showed that OA regulated the expression and/or phosphorylation levels of kinases involved in stress-response mitogen-activated protein kinase, phosphatidylinositol 3-kinase, and cell cycle control pathways. Importantly, these findings indicate that chronic OA exposure can impair beta-cell function through ROS-dependent and -independent mechanisms.
Collapse
Affiliation(s)
- Xiaolin Wang
- Department of Physiology, University of Toronto, Toronto, Ontario, Canada
| | | | | | | | | | | | | | | | | | | |
Collapse
|
24
|
Koshkin V, Wang X, Scherer PE, Chan CB, Wheeler MB. Mitochondrial functional state in clonal pancreatic beta-cells exposed to free fatty acids. J Biol Chem 2003; 278:19709-15. [PMID: 12642585 DOI: 10.1074/jbc.m209709200] [Citation(s) in RCA: 97] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
Excessive free fatty acid (FFA) exposure represents a potentially important diabetogenic condition that can impair insulin secretion from pancreatic beta-cells. Because mitochondrial oxidative phosphorylation is a main link between glucose metabolism and insulin secretion, in the present work we investigated the effects of the FFA oleate (OE) on mitochondrial function in the clonal pancreatic beta-cell line, MIN6. Both the long term (72 h) and short term (immediately after application) impact of OE exposure on beta-cells was investigated. After 72 h of exposure to OE (0.4 mm, 0.5% bovine serum albumin) cells were washed and permeabilized, and mitochondrial function (respiration, phosphorylation, membrane potential formation, production of reactive oxygen species) was measured in the absence or presence of OE. MIN6 cells exposed to OE for 72 h showed impaired glucose-stimulated insulin secretion and decreased cellular ATP. Mitochondria in OE-exposed cells retained normal functional characteristics in FFA-free medium; however, they were significantly more sensitive to the acute uncoupling effect of OE treatment. The mitochondria of OE-exposed cells displayed increased depolarization caused by acute OE treatment, which is attributable to the elevation in the FFA-transporting function of uncoupling protein 2 and the dicarboxylate carrier. These cells also had an increased production of reactive oxygen species in complex I of the mitochondrial respiratory chain that could be activated by FFA. A high level of reduction of respiratory complex I augmented acute FFA-induced uncoupling in a way compatible with activation of mitochondrial uncoupling protein by intramitochondrial superoxide. A stronger augmentation was observed in OE-exposed cells. Together, these events may underlie FFA-induced depression of the ATP/ADP ratio in beta-cells, which accounts for the defective glucose-stimulated insulin secretion associated with lipotoxicity.
Collapse
Affiliation(s)
- Vasilij Koshkin
- Departments of Physiology and Medicine, University of Toronto, Ontario M5S 1A8, Canada
| | | | | | | | | |
Collapse
|
25
|
Abstract
Uncoupling protein 2 (UCP2) may act as an important regulator of insulin secretion. In this study, beta-cell function in UCP2-deficient mice was examined after a 45% high-fat diet (HFD) to assess its role during the development of diet-induced type 2 diabetes. HFD-fed UCP2 (-/-) mice have lower fasting blood glucose and elevated insulin levels when compared with wild-type (WT) mice. UCP2 (-/-) mice also have enhanced beta-cell glucose sensitivity compared with WT mice after HFD, a result that is due in part to the deterioration of glucose responsiveness in WT mice. HFD-fed UCP2 (-/-) mice have increased insulin secretory capacity as a result of increased pancreatic beta-cell mass and insulin content per islet. Islets from WT mice exposed to 0.5 mmol/l palmitate for 48 h have significantly reduced mitochondrial membrane potential, ATP concentrations, and glucose responsiveness compared with UCP2 (-/-) islets, suggesting that elevated UCP2 in WT mice increases proton leak and decreases mitochondrial ATP production. Highly increased carnitine palmitoyl transferase-1 gene expression in UCP2 (-/-) mice is suggestive of enhanced fatty acid oxidizing capacity, particularly after HFD stress. These results further establish UCP2 as a component in glucose sensing and suggest a possible new aspect of UCP2 function during the progression of type 2 diabetes.
Collapse
Affiliation(s)
- Jamie W Joseph
- Department of Medicine, University of Toronto, Ontario, Canada
| | | | | | | | | | | | | |
Collapse
|
26
|
Abstract
The role of cardiolipin in mitochondrial function was studied by comparing the energy-transforming and osmotic properties of mitochondria isolated from the Saccharomyces cerevisiae cardiolipin synthase-null mutant crd1Delta, which has no cardiolipin, and the isogenic wild type. The results indicated that the importance of cardiolipin for energetic coupling strongly depends on the rate of oxidative phosphorylation, which was set by using NADH (maximal rate limited by coupling mechanism) or ethanol (moderate rate limited by electron supply) as a respiratory substrate, or by modulating the steady-state rate of NADH supply. The absence of cardiolipin resulted in only a small effect on oxidative phosphorylation proceeding at a moderate rate, but led to significant uncoupling (decreased ADP/O and increased state 4 respiration) at the maximal rate of respiration. This indicates that cardiolipin prevents rate-dependent uncoupling in the energy-transforming apparatus. This role of cardiolipin may derive from its strong interaction with, and modulation of the function of, respiratory complexes, and from its effects on the physical properties of the membrane. The importance of cardiolipin for mitochondrial osmotic properties was determined by comparing oxidative phosphorylation, release of matrix enzyme, shrinking ability and volume dynamics upon hypotonically induced swelling in crd1Delta and wild-type mitochondria. Opening of the yeast mitochondrial unspecific channel (YMUC) in the wild-type and mutant mitochondria was also tested. It was found that the lack of cardiolipin strongly undermines the osmotic stability of the mitochondrial membrane.
Collapse
Affiliation(s)
- Vasilij Koshkin
- Department of Biological Sciences, Wayne State University, Detroit, MI 48202, U.S.A
| | | |
Collapse
|
27
|
Koshkin V, Greenberg ML. Oxidative phosphorylation in cardiolipin-lacking yeast mitochondria. Biochem J 2000; 347 Pt 3:687-91. [PMID: 10769171 PMCID: PMC1221004] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/16/2023]
Abstract
The role of cardiolipin in mitochondrial energy transformation was studied by comparing oxidative phosphorylation in the Saccharomyces cerevisiae cardiolipin synthase null mutant crd1Delta, and in isogenic wild type. Oxygen consumption experiments and membrane potential kinetics during the phosphorylation cycle in isolated mitochondria indicated that the absence of cardiolipin causes only a moderate deficiency of mitochondrial energy-transforming machinery at 25 degrees C. However, at 40 degrees C, respiration was completely uncoupled from phosphorylation for the mutant mitochondria, in contrast with that for the wild-type. Membranepotential kinetics demonstrated an increased susceptibility of the mutant mitochondria to gradual deterioration during in vitro incubation. These results suggest that cardiolipin, although normally associated with several of the major enzymes of oxidative phosphorylation and required in vitro for their maximal activity, is not absolutely necessary for mitochondrial energy transformation under optimal conditions. The role of cardiolipin is, rather, to improve efficiency of oxidative phosphorylation and its resistance to unfavourable conditions, such as increased temperature.
Collapse
Affiliation(s)
- V Koshkin
- Department of Biological Sciences, Wayne State University, Detroit, MI 48202, USA
| | | |
Collapse
|
28
|
Abstract
In this study the reactions between nitric oxide (NO) and horseradish peroxidase (HRP) compounds I and II were investigated. The reaction between compound I and NO has biphasic kinetics with a clearly dominant initial fast phase and an apparent second-order rate constant of (7.0 +/- 0.3) x 10(5) M(-1) s(-1) for the fast phase. The reaction of compound II and NO was found to have an apparent second-order rate constant of k(app) = (1.3 +/- 0.1) x 10(6) M(-1) s(-1) or (7.4 +/- 0.7) x 10(5) M(-1) s(-1) when measured at 409 nm (the isosbestic point between HRP and HRP-NO) and 419 nm (lambda(max) of compound II and HRP-NO), respectively. Interestingly, the reaction of compound II with NO is unusually high relative to that of compound I, which is usually the much faster reaction. Since horseradish peroxidase is prototypical of mammalian peroxidases with respect to the oxidation of small substrates, these results may have important implications regarding the lifetime and biochemistry of NO in vivo after inflammation where both NO and H(2)O(2) generation are increased several fold.
Collapse
Affiliation(s)
- R E Glover
- Laboratory of Pharmacology and Chemistry, National Institute of Environmental Health Science, National Institutes of Health, Research Triangle Park, North Carolina 27709, USA
| | | | | | | |
Collapse
|
29
|
Koshkin V, Dunford HB. Reactions of prostaglandin endoperoxide synthase with hydroperoxide and reducing substrates under single turnover conditions. Biochim Biophys Acta 1999; 1431:47-52. [PMID: 10209278 DOI: 10.1016/s0167-4838(99)00041-2] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
The peroxidase reaction of prostaglandin endoperoxide synthase was investigated by transient state kinetics using stoichiometric amounts of substrates. The rate constants for the conversion of compound I to intermediate II determined with a stoichiometric amount of hydroperoxide were found to be lower by an order of magnitude than when an excess of hydroperoxide was used. The difference was attributed to ability of the compound I of prostaglandin endoperoxide synthase to be reduced by the excess of hydroperoxide. This suggests that the true rate constant of unimolecular conversion compound I to intermediate II at 3 degrees C is 5-10 s-1 instead of 50-200 s-1 as reported before. The latter value rather characterizes the combined process of spontaneous and hydroperoxide-dependent transformation of compound I. Stoichiometric amounts of reducing substrates significantly stimulated transformation of compound I. This effect could not be entirely explained by their reducing action, which was measured by following the oxidation kinetics. The results of the global fit of the experimental data suggest that reducing substrates, in addition to their direct action in reducing compound I to compound II, indirectly stimulate transformation of compound I to the tyrosyl radical form of intermediate II, thereby stimulating the cyclooxygenase reaction.
Collapse
Affiliation(s)
- V Koshkin
- Department of Chemistry, University of Alberta, Edmonton, Alta. T6G 2G2, Canada
| | | |
Collapse
|
30
|
Abstract
Interrelations between peroxidase and cyclooxygenase reactions catalyzed by prostaglandin endoperoxide synthase (prostaglandin H synthase) were analyzed in terms of the mutual influence of these reactions. The original branched-chain mechanism predicts competition between these two reactions for enzyme, so that peroxidase cosubstrate should inhibit the cyclooxygenase reaction and the cyclooxygenase substrate is expected to inhibit the peroxidase reaction. In stark contrast, the peroxidase reducing substrate is well known to strongly stimulate the cyclooxygenase reaction. In the present work the opposite effect, the influence of the cyclooxygenase substrate on the peroxidase reaction was studied. Experiments were conducted on the effect of arachidonic acid on the consumption of p-coumaric acid by prostaglandin H synthase and 5-phenyl-4-pentenyl-1-hydroperoxide. Neither the steady-state rates nor the total extent of p-coumaric acid consumption was affected by the addition of arachidonic acid. This suggests that the cyclooxygenase substrate does not influence observable velocities of the peroxidase reaction, namely oxidation and regeneration of the resting enzyme. The data support coupling of the cyclooxygenase and peroxidase reactions. A combination of the branched-chain and tightly coupled mechanisms is proposed, which includes a tyrosyl radical active enzyme intermediate regenerated through the peroxidase cycle. Numerical integration of the proposed reaction scheme agrees with the observed relations between peroxidase and cyclooxygenase reactions in the steady state.
Collapse
Affiliation(s)
- V Koshkin
- Department of Chemistry, University of Alberta, Edmonton, Alta. T6G 2G2, Canada
| | | |
Collapse
|
31
|
Abstract
The pre-steady-state phase of the oxygenase reaction of prostaglandin endoperoxide synthase with cis,cis-eicosa-11, 14-dienoic acid has been studied using stopped flow techniques. Because some intermediate forms of prostaglandin endoperoxide synthase are spectrally indistinguishable, the enzyme and substrate transformations were monitored in parallel to simplify the interpretation of the kinetics. Over a wide range of conditions, the formation of the enzyme intermediate II, the form of compound I containing the tyrosyl radical, precedes substrate oxidation. This result supports the occurrence of a unimolecular conversion of compound I into intermediate II. Furthermore, the rate of intermediate II formation was stimulated by increased concentration of dienoic acid, perhaps because of increased occupation of the fatty acid binding site. The importance of the unimolecular formation of intermediate II was confirmed by simulated kinetics of the oxygenase reaction. These results provide evidence that intermediate II is the primary oxidant in the reaction of prostaglandin synthase with the dienoic acid, as it is with arachidonic acid.
Collapse
Affiliation(s)
- V Koshkin
- Department of Chemistry, University of Alberta, Edmonton, Alberta T6G 2G2, Canada
| | | |
Collapse
|
32
|
Diatchuk V, Lotan O, Koshkin V, Wikstroem P, Pick E. Inhibition of NADPH oxidase activation by 4-(2-aminoethyl)-benzenesulfonyl fluoride and related compounds. J Biol Chem 1997; 272:13292-301. [PMID: 9148950 DOI: 10.1074/jbc.272.20.13292] [Citation(s) in RCA: 161] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
The elicitation of an oxidative burst in phagocytes rests on the assembly of a multicomponental complex (NADPH oxidase) consisting of a membrane-associated flavocytochrome (cytochrome b559), representing the redox element responsible for the NADPH-dependent reduction of oxygen to superoxide (O-2), two cytosolic components (p47(phox), p67(phox)), and the small GTPase Rac (1 or 2). We found that 4-(2-aminoethyl)-benzenesulfonyl fluoride (AEBSF), an irreversible serine protease inhibitor, prevented the elicitation of O-2 production in intact macrophages and the amphiphile-dependent activation of NADPH oxidase in a cell-free system, consisting of solubilized membrane or purified cytochrome b559 combined with total cytosol or a mixture of recombinant p47(phox), p67(phox), and Rac1. AEBSF acted at the activation step and did not interfere with the ensuing electron flow. It did not scavenge oxygen radicals and did not affect assay reagents. Five other serine protease inhibitors (three irreversible and two reversible) were found to lack an inhibitory effect on cell-free activation of NADPH oxidase. A structure-function study of AEBSF analogues demonstrated that the presence of a sulfonyl fluoride group was essential for inhibitory activity and that compounds containing an aminoalkylbenzene moiety were more active than amidinobenzene derivatives. Exposure of the membrane fraction or of purified cytochrome b559, but not of cytosol or recombinant cytosolic components, to AEBSF, in the presence of a critical concentration of the activating amphiphile lithium dodecyl sulfate, resulted in a marked impairment of their ability to support cell-free NADPH oxidase activation upon complementation with untreated cytosol or cytosolic components. Kinetic analysis of the effect of varying the concentration of each of the three cytosolic components on the inhibitory potency of AEBSF indicated that this was inversely related to the concentrations of p47(phox) and, to a lesser degree, p67(phox). AEBSF also prevented the amphiphile-elicited translocation of p47(phox) and p67(phox) to the membrane. These results are interpreted as indicating that AEBSF interferes with the binding of p47(phox) and/or p67(phox) to cytochrome b559, probably by a direct effect on cytochrome b559.
Collapse
Affiliation(s)
- V Diatchuk
- Julius Friedrich Cohnheim-Minerva Center for Phagocyte Research, Department of Human Microbiology, Sackler School of Medicine, Tel Aviv University, Tel Aviv 69978, Israel
| | | | | | | | | |
Collapse
|
33
|
Abstract
The superoxide (O2-)-generating NADPH oxidase of phagocytic cells is composed of a membrane-bound flavocytochrome (cytochrome b-559) and three cytosolic components, p47-phox, p67-phox, and the small GTPase rac-1 (or 2). Cytochrome b-559 bears the NADPH binding site and the redox centers (FAD and heme). Electron flow through the redox centers, from NADPH to oxygen, is activated consequent to the assembly of the three cytosolic components with cytochrome b-559. We studied the kinetics of electron flow through the redox centers of NADPH oxidase in a cell-free system, consisting of purified relipidated and reflavinated cytochrome b-559 and recombinant cytosolic components, activated by the anionic amphiphile, lithium dodecyl sulphate. The NADPH oxidase complex assembled in vitro exhibited: (a) a high steady-state electron flow (165 electrons/heme/s); (b) low stationary levels of FAD and heme reduction (about 10%), and (c) a high rate constant of heme oxidation by oxygen (1720 s-1). Surprisingly, the kinetic properties of NADPH oxidase assembled in a semi-recombinant cell-free system, lacking p47-phox (found to generate significant amounts of O2-), were similar to those of the complete system, as shown by a steady-state electron flow of 83 electrons/heme/s, low stationary levels of FAD and heme reduction (10%), and a rate constant of heme oxidation by oxygen of 1455 s-1. The kinetic features of NADPH oxidase assembled in vitro from purified and recombinant components differ considerably from those of solubilized enzyme preparations derived from intact stimulated phagocytes. The fast operation of the cell-free system is best explained by the activation-related facilitation of electron flow at both the FAD-->heme and the heme-->oxygen steps.
Collapse
Affiliation(s)
- V Koshkin
- Julius Friedrich Cohnheim-Minerva Center for Phagocyte Research, Department of Human Microbiology, Sackler School of Medicine, Tel Aviv University, Israel
| | | | | |
Collapse
|
34
|
Koshkin V, Lotan O, Pick E. The cytosolic component p47(phox) is not a sine qua non participant in the activation of NADPH oxidase but is required for optimal superoxide production. J Biol Chem 1996; 271:30326-9. [PMID: 8939991 DOI: 10.1074/jbc.271.48.30326] [Citation(s) in RCA: 125] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
The superoxide (O-2)-generating NADPH oxidase of phagocytes is a multicomponent complex consisting of a membrane-associated flavocytochrome (cytochrome b559), bearing the NADPH binding site and two redox centers (FAD and heme) and three cytosolic activating components: p47(phox), p67(phox), and the small GTPase Rac (1 or 2). The canonical view is that the induction of O-2 generation involves the stimulus-dependent assembly of all three cytosolic components with cytochrome b559, a process mimicked in vitro by a cell-free system activated by anionic amphiphiles. We studied the requirement for individual cytosolic components in the activation of NADPH oxidase in a cell-free system consisting of purified and relipidated cytochrome b559, recombinant p47(phox), p67(phox), and Rac1, and the amphiphile, lithium dodecyl sulfate. We found that pronounced activation of NADPH oxidase can be achieved by exposing cytochrome b559 to p67(phox) and Rac1, in the total absence of p47(phox) (turnover = 60 mol O-2/s/mol cytochrome b559). However, maximal activation (turnover = 153 mol O-2/s/mol cytochrome b559) could only be obtained in the presence of p47(phox). O-2 production, in the absence of p47(phox), was dependent on: high molar ratios of p67(phox) and Rac1 to cytochrome b559, Rac1 being in the GTP-bound form, cytochrome b559 being saturated with FAD, and an optimal concentration of amphiphile. Single cytosolic components or combinations of two cytosolic components, other than p67(phox) and Rac1, were incapable of activation. We conclude that p67(phox) and Rac1 are the only cytosolic components directly involved in the induction of electron transport in cytochrome b559. p47(phox) appears to facilitate or stabilize the interaction of p67(phox) and, possibly, Rac1 with cytochrome b559, and is required for optimal generation of O-2 under physiological conditions.
Collapse
Affiliation(s)
- V Koshkin
- Julius Friedrich Cohnheim-Minerva Center for Phagocyte Research, Department of Human Microbiology, Sackler School of Medicine, Tel Aviv University, Tel Aviv 69978, Israel
| | | | | |
Collapse
|
35
|
Abstract
Cytochrome b-559 reconstituted with phospholipids and FAD represents the simplest model of the respiratory burst NADPH oxidase and reproduces the main catalytic features of this system (Koshkin, V. and Pick, E. (1993) FEBS Lett. 327, 57-62; (1994) FEBS Lett. 338, 285-289). In the present report it is shown that activation by oxygen, characteristic of the NADPH oxidase complex, is an intrinsic property of flavocytochrome b-559, in principle independent of its complexation with the other components of NADPH oxidase. Facilitation of electron transfer from NADPH to FAD is found to be the reason for this phenomenon. Kinetic studies of anaerobic operation of flavocytochrome b-559 revealed the functional heterogeneity of two hemes, manifested as a dramatic difference in their reducibility under these conditions.
Collapse
Affiliation(s)
- V Koshkin
- Julius Friedrich Cohnheim Center for Phagocyte Research, Tel-Aviv University, Israel
| |
Collapse
|
36
|
Abstract
Purified cytochrome b-559 reconstituted into liposomes, consisting of certain azolectin-based phospholipid mixtures, is capable of NADPH-supported FAD-dependent superoxide (O2-) production in the absence of cytosolic activators. This system, representing the simplest model of the respiratory burst NADPH oxidase, was used to study cytochrome b-559 enzymology and distinguish putative mechanisms of NADPH oxidase activation (Koshkin, V. and Pick, E. (1993) FEBS Lett. 327, 57-62; (1994) FEBS Lett. 338, 285-289). In the present report, representing an extension of our earlier investigations, two types of vesicle-incorporated and reflavinated cytochrome b-559 preparation were distinguished by their ability to catalyze vectorial electrogenic or scalar electron transport from NADPH to oxygen. This can be explained by the existence of two distinct membranal locations of cytochrome b-559, with NADPH-binding and O2-reducing sites exposed on different or on the same side of the membrane. The mode of cytochrome b-559 insertion into the membrane depended on the reconstitution method employed. Both states of the reconstituted cytochrome b-559 were functionally competent judging by their susceptibility to additional activation by cytosolic NADPH oxidase components. The capability of flavocytochrome b-559 to function as a transmembrane electrogenic electron carrier points to its crucial role in the respiratory burst not only in its catalytical but also in its vectorial aspect. The scalar mode of its action may be related to respiratory burst pathology.
Collapse
Affiliation(s)
- V Koshkin
- Department of Human Microbiology, Sackler School of Medicine, Tel-Aviv University, Israel
| |
Collapse
|
37
|
Joseph G, Gorzalczany Y, Koshkin V, Pick E. Inhibition of NADPH oxidase activation by synthetic peptides mapping within the carboxyl-terminal domain of small GTP-binding proteins. Lack of amino acid sequence specificity and importance of polybasic motif. J Biol Chem 1994; 269:29024-31. [PMID: 7961867] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023] Open
Abstract
The small GTP-binding protein (G protein) Rac1 is an obligatory participant in the assembly of the superoxide (O2-.)-generating NADPH oxidase complex of macrophages. We investigated the effect of synthetic peptides, mapping within the near carboxyl-terminal domains of Rac1 and of related G proteins, on the activity of NADPH oxidase in a cell-free system consisting of solubilized guinea pig macrophage membrane, a cytosolic fraction enriched in p47phox and p67phox (or total cytosol), highly purified Rac1-GDP dissociation inhibitor for Rho (Rho GDI) complex, and the activating amphiphile, lithium dodecyl sulfate. Peptides Rac1-(178-188) and Rac1-(178-191), but not Rac2-(178-188), inhibited NADPH oxidase activity in a Rac1-dependent system when added prior to or simultaneously with the initiation of activation. However, undecapeptides corresponding to the near carboxyl-terminal domains of RhoA and RhoC and, most notably, a peptide containing the same amino acids as Rac1-(178-188), but in reversed orientation, were also inhibitory. Surprisingly, O2-. production in a Rac2-dependent cell-free system was inhibited by Rac1-(178-188) but not by Rac2-(178-188). Finally, basic polyamino acids containing lysine, histidine, or arginine, also inhibited NADPH oxidase activation. We conclude that inhibition of NADPH oxidase activation by synthetic peptides mapping within the carboxyl-terminal domain of certain small G proteins is not amino acid sequence-specific but related to the presence of a polybasic motif. It has been proposed that such a motif serves as a plasma membrane targeting signal for a number of small G proteins (Hancock, J.F., Paterson, H., and Marshall, C.J. (1990) Cell 63, 133-139).
Collapse
Affiliation(s)
- G Joseph
- Department of Human Microbiology, Sackler School of Medicine, Tel Aviv University, Israel
| | | | | | | |
Collapse
|
38
|
Abstract
Purified cytochrome b559 relipidated with either a mixture of phosphatidylcholine and phosphatidic acid or with phosphatidylcholine only exhibits high and low superoxide (O2-) producing ability, respectively, in the absence of cytosolic activators [Koshkin, V. and Pick, E. (1993) FEBS Lett. 327, 57-62]. This system was used as a model for the study of the mechanism of NADPH oxidase activation. It is shown that, depending on the composition of the phospholipid environment, cytochrome b599 binds FAD with high or low affinity, this being accompanied by changes in flavin absorbance and fluorescence. High affinity binding of FAD to cytochrome b559 relipidated with phosphatidylcholine combined with phosphatidic acid is associated with an enhanced NADPH-driven O2- producing capacity. A kinetic study of O2- production by cytochrome b559 reflavinated under stoichiometric FAD binding conditions revealed an FAD/heme ratio of 1:2. A further kinetic study of O2- production by high- and low-activity relipidated and reflavinated cytochrome b559, at varying substrate concentrations, and the determination of steady-state difference spectra of such preparations, reduced by NADPH, indicated that O2- production is activated by facilitation of electron transfer from NADPH to FAD rather than by an enhancement of NADPH binding.
Collapse
Affiliation(s)
- V Koshkin
- Department of Human Microbiology, Sackler School of Medicine, Tel-Aviv University, Israel
| | | |
Collapse
|
39
|
Abstract
Purified cytochrome b559 from guinea pig macrophages was relipidated with several phospholipid mixtures. Relipidated cytochrome b559 was found capable of NADPH-dependent superoxide (O2-) production in the absence of the cytosolic components of the NADPH oxidase complex. The rate of O2- generation by cytochrome b559 varied with the type of phospholipid utilized for relipidation, was absolutely dependent on exogenous FAD, and was enhanced by a critical concentration of anionic amphiphile. It is demonstrated that exogenous FAD acts by binding to cytochrome b559. These results provide firm experimental evidence for the proposal that cytochrome b559 comprises the complete electron transporting apparatus of the O2- forming NADPH oxidase and that the cytosolic components function merely as activators.
Collapse
Affiliation(s)
- V Koshkin
- Department of Human Microbiology, Sackler School of Medicine, Tel-Aviv University, Israel
| | | |
Collapse
|