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Yang L, Zhang S, Zheng L, Kong F, Pu P, Li X, Jia L. Association of ADP‑ribosylation factor family genes with prognosis and immune infiltration of breast cancer. Oncol Lett 2024; 27:280. [PMID: 38699662 PMCID: PMC11063756 DOI: 10.3892/ol.2024.14413] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2024] [Accepted: 03/19/2024] [Indexed: 05/05/2024] Open
Abstract
Breast cancer (BC) is the most common type of cancer found in women. ADP-ribosylation factors (ARFs) are a group of small proteins that bind to GTP and are involved in controlling different cellular functions. The function and evolution of multiple ARFs in BC have remained to be fully elucidated, despite existing studies on this protein family in Homo sapiens and other species. In the present study, a systematic analysis of ARF expression levels in BC tissues compared to normal breast tissues was performed using data from The Cancer Genome Atlas database. The analysis revealed significantly higher expression of ARFs in BC tissues. In addition, the prognostic significance of ARF1 and ARF3-6 expression levels was assessed in patients with BC. Of note, elevated ARF1 expression was associated with reduced rates of distant metastasis-free survival (DMFS), overall survival (OS) and recurrence-free survival (RFS) in affected individuals. Similarly, patients with high expression levels of ARF3 had lower post-progression survival (PPS) rates. In addition, patients with higher ARF4 expression had worse PPS and patients with high ARF5 expression exhibited lower DMFS. Patients with high ARF6 expression had worse DMFS, OS, RFS and predictive power score values. Furthermore, the expression of ARF was found to be strongly linked to the infiltration of various immune cell types, namely dendritic cells, macrophages, neutrophils, CD8+ T cells and B cells. These significant associations offer a solid foundation for the potential utilization of new therapeutic targets and predictive markers for the treatment of BC.
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Affiliation(s)
- Lixian Yang
- Department of Breast Surgery, Xingtai People's Hospital, Xingtai, Hebei 054000, P.R. China
| | - Shiyu Zhang
- Department of Breast Surgery, Xingtai People's Hospital, Xingtai, Hebei 054000, P.R. China
| | - Lei Zheng
- Department of Breast Surgery, Xingtai People's Hospital, Xingtai, Hebei 054000, P.R. China
| | - Fanting Kong
- Department of Breast Surgery, Xingtai People's Hospital, Xingtai, Hebei 054000, P.R. China
| | - Pengpeng Pu
- Department of Breast Surgery, Xingtai People's Hospital, Xingtai, Hebei 054000, P.R. China
| | - Xiaowei Li
- Department of Breast Surgery, Xingtai People's Hospital, Xingtai, Hebei 054000, P.R. China
| | - Lining Jia
- Department of Breast Surgery, Xingtai People's Hospital, Xingtai, Hebei 054000, P.R. China
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2
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Chau DDL, Li W, Chan WWR, Sun JKL, Zhai Y, Chow HM, Lau KF. Insulin stimulates atypical protein kinase C-mediated phosphorylation of the neuronal adaptor FE65 to potentiate neurite outgrowth by activating ARF6-Rac1 signaling. FASEB J 2022; 36:e22594. [PMID: 36250347 DOI: 10.1096/fj.202200757r] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2022] [Revised: 08/21/2022] [Accepted: 09/26/2022] [Indexed: 11/11/2022]
Abstract
Neurite outgrowth is a fundamental process in neurons that produces extensions and, consequently, neural connectivity. Neurite damage and atrophy are observed in various brain injuries and disorders. Understanding the intrinsic pathways of neurite outgrowth is essential for developing strategies to stimulate neurite regeneration. Insulin is a pivotal hormone in the regulation of glucose homeostasis. There is increasing evidence for the neurotrophic functions of insulin, including the induction of neurite outgrowth. However, the associated mechanism remains elusive. Here, we demonstrate that insulin potentiates neurite outgrowth mediated by the small GTPases ADP-ribosylation factor 6 (ARF6) and Ras-related C3 botulinum toxin substrate 1 (Rac1) through the neuronal adaptor FE65. Moreover, insulin enhances atypical protein kinase Cι/λ (PKCι/λ) activation and FE65 phosphorylation at serine 459 (S459) in neurons and mouse brains. In vitro and cellular assays show that PKCι/λ phosphorylated FE65 at S459. Consistently, insulin potentiates FE65 S459 phosphorylation only in the presence of PKCι/λ. Phosphomimetic studies show that an FE65 S459E mutant potently activates ARF6, Rac1, and neurite outgrowth. Notably, this phosphomimetic mutation enhances the FE65-ARF6 interaction, a process that promotes ARF6-Rac1-mediated neurite outgrowth. Likewise, insulin treatment and PKCι/λ overexpression potentiate the FE65-ARF6 interaction. Conversely, PKCι/λ knockdown suppresses the stimulatory effect of FE65 on ARF6-Rac1-mediated neurite outgrowth. The effect of insulin on neurite outgrowth is also markedly attenuated in PKCι/λ knockdown neurons, in the presence and absence of FE65. Our findings reveal a novel mechanism linking insulin with ARF6-Rac1-dependent neurite extension through the PKCι/λ-mediated phosphorylation of FE65.
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Affiliation(s)
- Dennis Dik-Long Chau
- School of Life Sciences, Faculty of Science, The Chinese University of Hong Kong, Hong Kong, China
| | - Wen Li
- School of Life Sciences, Faculty of Science, The Chinese University of Hong Kong, Hong Kong, China.,Research Laboratory for Biomedical Optics and Molecular Imaging, Shenzhen Institutes of Advanced Technology, Chinese Academy of Sciences, Shenzhen, China
| | - Wai Wa Ray Chan
- School of Life Sciences, Faculty of Science, The Chinese University of Hong Kong, Hong Kong, China
| | - Jacquelyne Ka-Li Sun
- School of Life Sciences, Faculty of Science, The Chinese University of Hong Kong, Hong Kong, China
| | - Yuqi Zhai
- School of Life Sciences, Faculty of Science, The Chinese University of Hong Kong, Hong Kong, China
| | - Hei-Man Chow
- School of Life Sciences, Faculty of Science, The Chinese University of Hong Kong, Hong Kong, China
| | - Kwok-Fai Lau
- School of Life Sciences, Faculty of Science, The Chinese University of Hong Kong, Hong Kong, China
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3
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Luciano AK, Korobkina E, Lyons SP, Haley JA, Fluharty S, Jung SM, Kettenbach AN, Guertin DA. Proximity labeling of endogenous RICTOR identifies mTOR Complex 2 regulation by ADP ribosylation factor ARF1. J Biol Chem 2022; 298:102379. [PMID: 35973513 PMCID: PMC9513271 DOI: 10.1016/j.jbc.2022.102379] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2021] [Revised: 07/22/2022] [Accepted: 08/09/2022] [Indexed: 01/08/2023] Open
Abstract
Mechanistic target of rapamycin (mTOR) complex 2 (mTORC2) regulates metabolism, cell proliferation, and cell survival. mTORC2 activity is stimulated by growth factors, and it phosphorylates the hydrophobic motif site of the AGC kinases AKT, SGK, and PKC. However, the proteins that interact with mTORC2 to control its activity and localization remain poorly defined. To identify mTORC2-interacting proteins in living cells, we tagged endogenous RICTOR, an essential mTORC2 subunit, with the modified BirA biotin ligase BioID2 and performed live-cell proximity labeling. We identified 215 RICTOR-proximal proteins, including proteins with known mTORC2 pathway interactions, and 135 proteins (63%) not previously linked to mTORC2 signaling, including nuclear and cytoplasmic proteins. Our imaging and cell fractionation experiments suggest nearly 30% of RICTOR is in the nucleus, hinting at potential nuclear functions. We also identified 29 interactors containing RICTOR-dependent, insulin-stimulated phosphorylation sites, thus providing insight into mTORC2-dependent insulin signaling dynamics. Finally, we identify the endogenous ADP ribosylation factor 1 (ARF1) GTPase as an mTORC2-interacting protein. Through gain-of-function and loss-of-function studies, we provide functional evidence that ARF1 may negatively regulate mTORC2. In summary, we present a new method of studying endogenous mTORC2, a resource of RICTOR/mTORC2 protein interactions in living cells, and a potential mechanism of mTORC2 regulation by the ARF1 GTPase.
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Affiliation(s)
- Amelia K Luciano
- Program in Molecular Medicine, University of Massachusetts Chan Medical School, Worcester, MA 01605
| | - Ekaterina Korobkina
- Program in Molecular Medicine, University of Massachusetts Chan Medical School, Worcester, MA 01605
| | - Scott P Lyons
- Department of Biochemistry and Cell Biology, Geisel School of Medicine at Dartmouth, Hanover, NH 03755
| | - John A Haley
- Program in Molecular Medicine, University of Massachusetts Chan Medical School, Worcester, MA 01605
| | - Shelagh Fluharty
- Program in Molecular Medicine, University of Massachusetts Chan Medical School, Worcester, MA 01605
| | - Su Myung Jung
- Program in Molecular Medicine, University of Massachusetts Chan Medical School, Worcester, MA 01605
| | - Arminja N Kettenbach
- Department of Biochemistry and Cell Biology, Geisel School of Medicine at Dartmouth, Hanover, NH 03755; Norris Cotton Cancer Center, Geisel School of Medicine at Dartmouth, Hanover, NH 03755
| | - David A Guertin
- Program in Molecular Medicine, University of Massachusetts Chan Medical School, Worcester, MA 01605; Department of Molecular, Cell and Cancer Biology, University of Massachusetts Chan Medical School, Worcester, MA 01605.
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4
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Roberts BS, Yang CQ, Neher SB. Characterization of lipoprotein lipase storage vesicles in 3T3-L1 adipocytes. J Cell Sci 2022; 135:jcs258734. [PMID: 34382637 PMCID: PMC8403984 DOI: 10.1242/jcs.258734] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2021] [Accepted: 07/10/2021] [Indexed: 12/12/2022] Open
Abstract
Lipoprotein lipase (LPL) is a secreted triglyceride lipase involved in the clearance of very-low-density lipoproteins and chylomicrons from circulation. LPL is expressed primarily in adipose and muscle tissues and transported to the capillary lumen. LPL secretion is regulated by insulin in adipose tissue; however, few studies have examined the regulatory and trafficking steps involved in secretion. Here, we describe the intracellular localization and insulin-dependent trafficking of LPL in 3T3-L1 adipocytes. We compared LPL trafficking to the better characterized trafficking pathways taken by leptin and GLUT4 (also known as SLC2A4). We show that the LPL trafficking pathway shares some characteristics of these other pathways, but that LPL subcellular localization and trafficking are distinct from those of GLUT4 and leptin. LPL secretion occurs slowly in response to insulin and rapidly in response to the Ca2+ ionophore ionomycin. This regulated trafficking is dependent on Golgi protein kinase D and the ADP-ribosylation factor GTPase ARF1. Together, these data give support to a new trafficking pathway for soluble cargo that is active in adipocytes.
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Affiliation(s)
| | | | - Saskia B. Neher
- Department of Biochemistry and Biophysics, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA
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5
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Pan T, Li X, Li Y, Tao Z, Yao H, Wu Y, Chen G, Zhang K, Zhou Y, Huang Y. USP7 inhibition induces apoptosis in glioblastoma by enhancing ubiquitination of ARF4. Cancer Cell Int 2021; 21:508. [PMID: 34556124 PMCID: PMC8461901 DOI: 10.1186/s12935-021-02208-z] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2021] [Accepted: 09/11/2021] [Indexed: 12/21/2022] Open
Abstract
Background Glioblastomas (GBMs) are grade IV central nervous system tumors characterized by a poor prognosis and a short median overall survival. Effective induction of GBM cell death is difficult because the GBM cell population is genetically unstable, resistant to chemotherapy and highly angiogenic. In recent studies, ubiquitin-specific protease 7 (USP7) is shown to scavenge ubiquitin from oncogenic protein substrates, so effective inhibition of USP7 may be a potential key treatment for GBM. Methods Immunohistochemistry and western blotting were used to detect the expression of USP7 in GBM tissues. In vitro apoptosis assay of USP7 inhibition was performed by western blotting, immunofluorescence, and flow cytometry. Anti-apoptotic substrates of USP7 were defined by Co-IP and TMT proteomics. Western blotting and IP were used to verify the relationship between USP7 and its substrate. In an in vivo experiment using an intracranial xenograft model in nude mice was constructed to assess the therapeutic effect of target USP7. Results Immunohistochemistry and western blotting confirmed that USP7 was significantly upregulated in glioblastoma samples. In in vitro experiments, inhibition of USP7 in GBM induced significant apoptosis. Co-IP and TMT proteomics identified a key anti-apoptotic substrate of USP7, ADP-ribosylation factor 4 (ARF4). Western blotting and IP confirmed that USP7 interacted directly with ARF4 and catalyzed the removal of the K48-linked polyubiquitinated chain that binded to ARF4. In addition, in vivo experiments revealed that USP7 inhibition significantly suppressed tumor growth and promoted the expression of apoptotic genes. Conclusions Targeted inhibition of USP7 enhances the ubiquitination of ARF4 and ultimately mediates the apoptosis of GBM cells. In a clinical sense, P5091 as a novel specific inhibitor of USP7 may be an effective approach for the treatment of GBM. Supplementary Information The online version contains supplementary material available at 10.1186/s12935-021-02208-z.
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Affiliation(s)
- Tingzheng Pan
- Neurosurgery & Brain and Nerve Research Laboratory, The First Affiliated Hospital of Soochow University, Jiangsu, Suzhou, People's Republic of China
| | - Xuetao Li
- Department of Neurosurgery, Dushu Lake Hospital Affiliated of Soochow University, Jiangsu, Suzhou, People's Republic of China
| | - Yanyan Li
- Neurosurgery & Brain and Nerve Research Laboratory, The First Affiliated Hospital of Soochow University, Jiangsu, Suzhou, People's Republic of China
| | - Zhennan Tao
- Neurosurgery & Brain and Nerve Research Laboratory, The First Affiliated Hospital of Soochow University, Jiangsu, Suzhou, People's Republic of China
| | - Hui Yao
- Neurosurgery & Brain and Nerve Research Laboratory, The First Affiliated Hospital of Soochow University, Jiangsu, Suzhou, People's Republic of China
| | - Yue Wu
- Neurosurgery & Brain and Nerve Research Laboratory, The First Affiliated Hospital of Soochow University, Jiangsu, Suzhou, People's Republic of China
| | - Guangliang Chen
- Neurosurgery & Brain and Nerve Research Laboratory, The First Affiliated Hospital of Soochow University, Jiangsu, Suzhou, People's Republic of China
| | - Kai Zhang
- Neurosurgery & Brain and Nerve Research Laboratory, The First Affiliated Hospital of Soochow University, Jiangsu, Suzhou, People's Republic of China
| | - Youxin Zhou
- Neurosurgery & Brain and Nerve Research Laboratory, The First Affiliated Hospital of Soochow University, Jiangsu, Suzhou, People's Republic of China.
| | - Yulun Huang
- Neurosurgery & Brain and Nerve Research Laboratory, The First Affiliated Hospital of Soochow University, Jiangsu, Suzhou, People's Republic of China. .,Department of Neurosurgery, Dushu Lake Hospital Affiliated of Soochow University, Jiangsu, Suzhou, People's Republic of China.
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6
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Zangerolamo L, Soares GM, Vettorazzi JF, do Amaral ME, Carneiro EM, Olalla-Saad ST, Boschero AC, Barbosa-Sampaio HC. ARHGAP21 deficiency impairs hepatic lipid metabolism and improves insulin signaling in lean and obese mice. Can J Physiol Pharmacol 2019; 97:1018-1027. [PMID: 31247150 DOI: 10.1139/cjpp-2018-0691] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2023]
Abstract
ARHGAP21 is a Rho-GAP that controls GTPases activity in several tissues, but its role on liver lipid metabolism is unknown. Thus, to achieve the Rho-GAP role in the liver, control and ARHGAP21-haplodeficient mice were fed chow (Ctl and Het) or high-fat diet (Ctl-HFD and Het-HFD) for 12 weeks, and pyruvate and insulin tolerance tests, insulin signaling, liver glycogen and triglycerides content, gene and protein expression, and very-low-density lipoprotein secretion were measured. Het mice displayed reduced body weight and plasma triglycerides levels, and increased liver insulin signaling. Reduced gluconeogenesis and increased glycogen content were observed in Het-HFD mice. Gene and protein expression of microsomal triglyceride transfer protein were reduced in both Het mice, while the lipogenic genes SREBP-1c and ACC were increased. ARHGAP21 knockdown resulted in hepatic steatosis through increased hepatic lipogenesis activity coupled with decreases in CPT1a expression and very-low-density lipoprotein export. In conclusion, liver of ARHGAP21-haplodeficient mice are more insulin sensitive, associated with higher lipid synthesis and lower lipid export.
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Affiliation(s)
- Lucas Zangerolamo
- Department of Structural and Functional Biology, Institute of Biology, University of Campinas, UNICAMP, Campinas, SP, Brazil
| | - Gabriela Moreira Soares
- Department of Structural and Functional Biology, Institute of Biology, University of Campinas, UNICAMP, Campinas, SP, Brazil
| | - Jean Franciesco Vettorazzi
- Department of Structural and Functional Biology, Institute of Biology, University of Campinas, UNICAMP, Campinas, SP, Brazil
| | - Maria Esméria do Amaral
- Graduate Program in Biomedical Sciences, FHO-Herminio Ometto University Center, UNIARARAS, Araras, SP, Brazil
| | - Everardo Magalhães Carneiro
- Department of Structural and Functional Biology, Institute of Biology, University of Campinas, UNICAMP, Campinas, SP, Brazil
| | | | - Antonio Carlos Boschero
- Department of Structural and Functional Biology, Institute of Biology, University of Campinas, UNICAMP, Campinas, SP, Brazil
| | - Helena Cristina Barbosa-Sampaio
- Department of Structural and Functional Biology, Institute of Biology, University of Campinas, UNICAMP, Campinas, SP, Brazil
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7
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Kumar M, Ojha S, Rai P, Joshi A, Kamat SS, Mallik R. Insulin activates intracellular transport of lipid droplets to release triglycerides from the liver. J Cell Biol 2019; 218:3697-3713. [PMID: 31604801 PMCID: PMC6829650 DOI: 10.1083/jcb.201903102] [Citation(s) in RCA: 20] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2019] [Revised: 06/18/2019] [Accepted: 07/26/2019] [Indexed: 01/13/2023] Open
Abstract
Kumar et al. describe a detailed pathway for channeling fat from the liver into blood across fed/fasted cycles. Insulin, phosphatidic acid, and kinesin collaborate in hepatocytes to deliver lipid droplets to the smooth ER, where they are catabolized to supply fat for lipoprotein production and secretion. Triglyceride-rich lipid droplets (LDs) are catabolized with high efficiency in hepatocytes to supply fatty acids for producing lipoprotein particles. Fasting causes a massive influx of adipose-derived fatty acids into the liver. The liver in the fasted state is therefore bloated with LDs but, remarkably, still continues to secrete triglycerides at a constant rate. Here we show that insulin signaling elevates phosphatidic acid (PA) dramatically on LDs in the fed state. PA then signals to recruit kinesin-1 motors, which transport LDs to the peripherally located smooth ER inside hepatocytes, where LDs are catabolized to produce lipoproteins. This pathway is down-regulated homeostatically when fasting causes insulin levels to drop, thus preventing dangerous elevation of triglycerides in the blood. Further, we show that a specific peptide against kinesin-1 blocks triglyceride secretion without any apparent deleterious effects on cells. Our work therefore reveals fundamental mechanisms that maintain lipid homeostasis across metabolic states and leverages this knowledge to propose a molecular target against hyperlipidemia.
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Affiliation(s)
- Mukesh Kumar
- Department of Biological Sciences, Tata Institute of Fundamental Research, Mumbai, India
| | - Srikant Ojha
- Department of Biological Sciences, Tata Institute of Fundamental Research, Mumbai, India
| | - Priyanka Rai
- Department of Biological Sciences, Tata Institute of Fundamental Research, Mumbai, India
| | - Alaumy Joshi
- Department of Biology, Indian Institute of Science Education and Research, Pune, India
| | - Siddhesh S Kamat
- Department of Biology, Indian Institute of Science Education and Research, Pune, India
| | - Roop Mallik
- Department of Biological Sciences, Tata Institute of Fundamental Research, Mumbai, India
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8
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Chakraborti S, Sarkar J, Bhuyan R, Chakraborti T. Role of catechins on ET-1-induced stimulation of PLD and NADPH oxidase activities in pulmonary smooth muscle cells: determination of the probable mechanism by molecular docking studies. Biochem Cell Biol 2018; 96:417-432. [PMID: 29206487 DOI: 10.1139/bcb-2017-0179] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The treatment of human pulmonary artery smooth muscle cells with ET-1 stimulates the activity of PLD and NADPH oxidase, but this stimulation is inhibited by pretreatment with bosentan (ET-1 receptor antagonist), FIPI (PLD inhibitor), apocynin (NADPH oxidase inhibitor), and EGCG and ECG (catechins having a galloyl group), but not EGC and EC (catechins devoid of a galloyl group). Herein, using molecular docking analyses based on our biochemical studies, we determined the probable mechanism by which the catechins containing a galloyl group inhibit the stimulation of PLD activity induced by ET-1. The ET-1-induced stimulation of PLD activity was inhibited by SecinH3 (inhibitor of cytohesin). Arf6 and cytohesin-1 are associated in the cell membrane, which is not inhibited by the catechins during ET-1 treatment of the cells. However, EGCG and ECG inhibited the binding of GTPγS with Arf6, even in the presence of cytohesin-1. The molecular docking analyses revealed that the catechins containing a galloyl group (EGCG and ECG) with cytohesin-1–Arf6GDP, but not the catechins without a galloyl group (EGC and EC), prevent GDP–GTP exchange in Arf6, which seems to be an important mechanism for inhibiting the activation of PLD induced by ET-1, and subsequently increases the activity of NADPH oxidase.
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Affiliation(s)
- Sajal Chakraborti
- Department of Biochemistry and Biophysics, University of Kalyani, Kalyani 741235, West Bengal, India
- Department of Biochemistry and Biophysics, University of Kalyani, Kalyani 741235, West Bengal, India
| | - Jaganmay Sarkar
- Department of Biochemistry and Biophysics, University of Kalyani, Kalyani 741235, West Bengal, India
- Department of Biochemistry and Biophysics, University of Kalyani, Kalyani 741235, West Bengal, India
| | - Rajabrata Bhuyan
- Department of Biochemistry and Biophysics, University of Kalyani, Kalyani 741235, West Bengal, India
- Department of Biochemistry and Biophysics, University of Kalyani, Kalyani 741235, West Bengal, India
| | - Tapati Chakraborti
- Department of Biochemistry and Biophysics, University of Kalyani, Kalyani 741235, West Bengal, India
- Department of Biochemistry and Biophysics, University of Kalyani, Kalyani 741235, West Bengal, India
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9
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Abstract
The liver secretes lipids in a controlled manner despite vast changes in its internal lipid content. This buffering function of the liver is essential for lipid/energy homeostasis, but its molecular and cellular mechanism is unknown. We show that motor protein kinesin transports lipid droplets (LDs) to the endoplasmic reticulum (ER) in liver cells, engineering ER−droplet contacts and supplying lipids to the ER for secretion as lipoprotein. However, when fasting induces massive lipid accumulation in liver, kinesin is removed from LDs, inhibiting lipid supply to the ER and homeostatically tempering lipid secretion from liver in a fasted state. Interestingly, reducing kinesin also blocks propagation of hepatitis-C virus inside liver cells, possibly because viral proteins cannot transfer from the ER to LDs. Despite massive fluctuations in its internal triglyceride content, the liver secretes triglyceride under tight homeostatic control. This buffering function is most visible after fasting, when liver triglyceride increases manyfold but circulating serum triglyceride barely fluctuates. How the liver controls triglyceride secretion is unknown, but is fundamentally important for lipid and energy homeostasis in animals. Here we find an unexpected cellular and molecular mechanism behind such control. We show that kinesin motors are recruited to triglyceride-rich lipid droplets (LDs) in the liver by the GTPase ARF1, which is a key activator of lipolysis. This recruitment is activated by an insulin-dependent pathway and therefore responds to fed/fasted states of the animal. In fed state, ARF1 and kinesin appear on LDs, consequently transporting LDs to the periphery of hepatocytes where the smooth endoplasmic reticulum (sER) is present. Because the lipases that catabolize LDs in hepatocytes reside on the sER, LDs can now be catabolized efficiently to provide triglyceride for lipoprotein assembly and secretion from the sER. Upon fasting, insulin is lowered to remove ARF1 and kinesin from LDs, thus down-regulating LD transport and sER–LD contacts. This tempers triglyceride availabiity for very low density lipoprotein assembly and allows homeostatic control of serum triglyceride in a fasted state. We further show that kinesin knockdown inhibits hepatitis-C virus replication in hepatocytes, likely because translated viral proteins are unable to transfer from the ER to LDs.
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10
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Chakraborti S, Sarkar J, Chowdhury A, Chakraborti T. Role of ADP ribosylation factor6- Cytohesin1-PhospholipaseD signaling axis in U46619 induced activation of NADPH oxidase in pulmonary artery smooth muscle cell membrane. Arch Biochem Biophys 2017; 633:1-14. [PMID: 28822840 DOI: 10.1016/j.abb.2017.08.012] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2017] [Revised: 08/12/2017] [Accepted: 08/15/2017] [Indexed: 01/07/2023]
Abstract
Treatment of human pulmonary artery smooth muscle cells (HPASMCs) with the thromboxane A2 receptor antagonist, SQ29548 inhibited U46619 stimulation of phospholipase D (PLD) and NADPH oxidase activities in the cell membrane. Pretreatment with apocynin inhibited U46619 induced increase in NADPH oxidase activity. The cell membrane contains predominantly PLD2 along with PLD1 isoforms of PLD. Pretreatment with pharmacological and genetic inhibitors of PLD2, but not PLD1, attenuated U46619 stimulation of NADPH oxidase activity. U46619 stimulation of PLD and NADPH oxidase activities were insensitive to BFA and Clostridium botulinum C3 toxin; however, pretreatment with secinH3 inhibited U46619 induced increase in PLD and NADPH oxidase activities suggesting a major role of cytohesin in U46619-induced increase in PLD and NADPH oxidase activities. Arf-1, Arf-6, cytohesin-1 and cytohesin-2 were observed in the cytosolic fraction, but only Arf-6 and cytohesin-1 were translocated to the cell membrane upon treatment with U46619. Coimmunoprecipitation study showed association of Arf-6 with cytohesin-1 in the cell membrane fraction. In vitro binding of GTPγS with Arf-6 required the presence of cytohesin-1 and that occurs in BFA insensitive manner. Overall, BFA insensitive Arf6-cytohesin1 signaling axis plays a pivotal role in U46619-mediated activation of PLD leading to stimulation of NADPH oxidase activity in HPASMCs.
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Affiliation(s)
- Sajal Chakraborti
- Department of Biochemistry and Biophysics, University of Kalyani, Kalyani 741235, West Bengal, India.
| | - Jaganmay Sarkar
- Department of Biochemistry and Biophysics, University of Kalyani, Kalyani 741235, West Bengal, India.
| | - Animesh Chowdhury
- Department of Biochemistry and Biophysics, University of Kalyani, Kalyani 741235, West Bengal, India.
| | - Tapati Chakraborti
- Department of Biochemistry and Biophysics, University of Kalyani, Kalyani 741235, West Bengal, India.
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11
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Chakraborti S, Sarkar J, Bhuyan R, Chakraborti T. Role of curcumin in PLD activation by Arf6-cytohesin1 signaling axis in U46619-stimulated pulmonary artery smooth muscle cells. Mol Cell Biochem 2017; 438:97-109. [PMID: 28780751 DOI: 10.1007/s11010-017-3117-7] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/24/2017] [Accepted: 07/15/2017] [Indexed: 01/01/2023]
Abstract
Phospholipase D (PLD) catalyzes the hydrolysis of phosphatidylcholine to produce phosphatidic acid (PA) which in some cell types play a pivotal role in agonist-induced increase in NADPH oxidase-derived [Formula: see text]production. Involvement of ADP ribosylation factor (Arf) in agonist-induced activation of PLD is known for smooth muscle cells of systemic arteries, but not in pulmonary artery smooth muscle cells (PASMCs). Additionally, role of cytohesin in this scenario is unknown in PASMCs. We, therefore, determined the involvement of Arf and cytohesin in U46619-induced stimulation of PLD in PASMCs, and the probable mechanism by which curcumin, a natural phenolic compound, inhibits the U46619 response. Treatment of PASMCs with U46619 stimulated PLD activity in the cell membrane, which was inhibited upon pretreatment with SQ29548 (Tp receptor antagonist), FIPI (PLD inhibitor), SecinH3 (inhibitor of cytohesins), and curcumin. Transfection of the cells with Tp, Arf-6, and cytohesin-1 siRNA inhibited U46619-induced activation of PLD. Upon treatment of the cells with U46619, Arf-6 and cytohesin-1 were translocated and associated in the cell membrane, which were not inhibited upon pretreatment of the cells with curcumin. Cytohesin-1 appeared to be necessary for in vitro binding of GTPγS with Arf-6; however, addition of curcumin inhibited binding of GTPγS with Arf-6 even in the presence of cytohesin-1. Our computational study suggests that although curcumin to some extent binds with Tp receptor, yet the inhibition of Arf6GDP to Arf6GTP conversion appeared to be an important mechanism by which curcumin inhibits U46619-induced increase in PLD activity in PASMCs.
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Affiliation(s)
- Sajal Chakraborti
- Department of Biochemistry and Biophysics, University of Kalyani, Kalyani, West Bengal, 741235, India.
| | - Jaganmay Sarkar
- Department of Biochemistry and Biophysics, University of Kalyani, Kalyani, West Bengal, 741235, India
| | - Rajabrata Bhuyan
- Department of Biochemistry and Biophysics, University of Kalyani, Kalyani, West Bengal, 741235, India
| | - Tapati Chakraborti
- Department of Biochemistry and Biophysics, University of Kalyani, Kalyani, West Bengal, 741235, India
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MiR-221-3p targets ARF4 and inhibits the proliferation and migration of epithelial ovarian cancer cells. Biochem Biophys Res Commun 2017; 497:1162-1170. [PMID: 28057486 DOI: 10.1016/j.bbrc.2017.01.002] [Citation(s) in RCA: 45] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2016] [Accepted: 01/01/2017] [Indexed: 01/03/2023]
Abstract
Epithelial ovarian cancer (EOC) is the most lethal gynecologic cancer. Although molecular diagnostic tools and targeted therapies have been developed over the past few decades, the survival rate is still rather low. Numerous researches suggest that some microRNAs (miRNAs) are key regulators of tumor progression. Among those miRNAs that has attracted much attention for their multiple roles in human cancers, the function of miR-221-3p in EOC has not been elucidated. Herein, we examined the expression of miR-221-3p in EOC patients and cell lines. Our data revealed that higher expression of miR-221-3p was linked to better overall survival in EOC patients. In-vitro experiments indicated that miR-221-3p inhibited EOC cell proliferation and migration. By performing subsequent systematic molecular biological and bioinformatic analyses, we found ADP-ribosylation factor (ARF) 4 is one of the putative target genes, the direct binding relationship was further confirmed by dual-luciferase reporter assay. Finally, a distinct gene expression between miR-221-3p and ARF4 in EOC group and normal group was identified, and the negative correlation between their expression levels in EOC specimens was further confirmed. Taken together, our research uncovered the tumor suppressive role of miR-221-3p in EOC and directly targeted ARF4, suggesting that miR-221-3p might be a novel potential candidate for clinical prognosis and therapeutics of EOC.
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13
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Chen SS, Hu Z, Zhong XP. Diacylglycerol Kinases in T Cell Tolerance and Effector Function. Front Cell Dev Biol 2016; 4:130. [PMID: 27891502 PMCID: PMC5103287 DOI: 10.3389/fcell.2016.00130] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2016] [Accepted: 10/27/2016] [Indexed: 12/21/2022] Open
Abstract
Diacylglycerol kinases (DGKs) are a family of enzymes that regulate the relative levels of diacylglycerol (DAG) and phosphatidic acid (PA) in cells by phosphorylating DAG to produce PA. Both DAG and PA are important second messengers cascading T cell receptor (TCR) signal by recruiting multiple effector molecules, such as RasGRP1, PKCθ, and mTOR. Studies have revealed important physiological functions of DGKs in the regulation of receptor signaling and the development and activation of immune cells. In this review, we will focus on recent progresses in our understanding of two DGK isoforms, α and ζ, in CD8 T effector and memory cell differentiation, regulatory T cell development and function, and invariant NKT cell development and effector lineage differentiation.
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Affiliation(s)
- Shelley S Chen
- Division of Allergy and Immunology, Department of Pediatrics, Duke University Medical Center Durham, NC, USA
| | - Zhiming Hu
- Division of Allergy and Immunology, Department of Pediatrics, Duke University Medical CenterDurham, NC, USA; Institute of Biotherapy, School of Biotechnology, Southern Medical UniversityGuangzhou, China
| | - Xiao-Ping Zhong
- Division of Allergy and Immunology, Department of Pediatrics, Duke University Medical CenterDurham, NC, USA; Department of Immunology, Duke University Medical CenterDurham, NC, USA; Hematologic Malignancies and Cellular Therapies Program, Duke Cancer Institute, Duke University Medical CenterDurham, NC, USA
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14
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Bruntz RC, Lindsley CW, Brown HA. Phospholipase D signaling pathways and phosphatidic acid as therapeutic targets in cancer. Pharmacol Rev 2015; 66:1033-79. [PMID: 25244928 DOI: 10.1124/pr.114.009217] [Citation(s) in RCA: 165] [Impact Index Per Article: 18.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Phospholipase D is a ubiquitous class of enzymes that generates phosphatidic acid as an intracellular signaling species. The phospholipase D superfamily plays a central role in a variety of functions in prokaryotes, viruses, yeast, fungi, plants, and eukaryotic species. In mammalian cells, the pathways modulating catalytic activity involve a variety of cellular signaling components, including G protein-coupled receptors, receptor tyrosine kinases, polyphosphatidylinositol lipids, Ras/Rho/ADP-ribosylation factor GTPases, and conventional isoforms of protein kinase C, among others. Recent findings have shown that phosphatidic acid generated by phospholipase D plays roles in numerous essential cellular functions, such as vesicular trafficking, exocytosis, autophagy, regulation of cellular metabolism, and tumorigenesis. Many of these cellular events are modulated by the actions of phosphatidic acid, and identification of two targets (mammalian target of rapamycin and Akt kinase) has especially highlighted a role for phospholipase D in the regulation of cellular metabolism. Phospholipase D is a regulator of intercellular signaling and metabolic pathways, particularly in cells that are under stress conditions. This review provides a comprehensive overview of the regulation of phospholipase D activity and its modulation of cellular signaling pathways and functions.
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Affiliation(s)
- Ronald C Bruntz
- Department of Pharmacology (R.C.B., C.W.L., H.A.B.) and Vanderbilt Center for Neuroscience Drug Discovery (C.W.L.), Vanderbilt University Medical Center; Department of Chemistry, Vanderbilt Institute of Chemical Biology (C.W.L., H.A.B.); Vanderbilt Specialized Chemistry for Accelerated Probe Development (C.W.L.); and Department of Biochemistry, Vanderbilt-Ingram Cancer Center (H.A.B.), Vanderbilt University, Nashville, Tennessee
| | - Craig W Lindsley
- Department of Pharmacology (R.C.B., C.W.L., H.A.B.) and Vanderbilt Center for Neuroscience Drug Discovery (C.W.L.), Vanderbilt University Medical Center; Department of Chemistry, Vanderbilt Institute of Chemical Biology (C.W.L., H.A.B.); Vanderbilt Specialized Chemistry for Accelerated Probe Development (C.W.L.); and Department of Biochemistry, Vanderbilt-Ingram Cancer Center (H.A.B.), Vanderbilt University, Nashville, Tennessee
| | - H Alex Brown
- Department of Pharmacology (R.C.B., C.W.L., H.A.B.) and Vanderbilt Center for Neuroscience Drug Discovery (C.W.L.), Vanderbilt University Medical Center; Department of Chemistry, Vanderbilt Institute of Chemical Biology (C.W.L., H.A.B.); Vanderbilt Specialized Chemistry for Accelerated Probe Development (C.W.L.); and Department of Biochemistry, Vanderbilt-Ingram Cancer Center (H.A.B.), Vanderbilt University, Nashville, Tennessee
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15
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Babenko NA, Kharchenko VS. Modulation of Insulin Sensitivity of Hepatocytes by the Pharmacological Downregulation of Phospholipase D. Int J Endocrinol 2015; 2015:794838. [PMID: 26089893 PMCID: PMC4458285 DOI: 10.1155/2015/794838] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/05/2015] [Revised: 04/30/2015] [Accepted: 05/11/2015] [Indexed: 12/13/2022] Open
Abstract
Background. The role of phospholipase D (PLD) as a positive modulator of glucose uptake activation by insulin in muscle and adipose cells has been demonstrated. The role of PLD in the regulation of glucose metabolism by insulin in the primary hepatocytes has been determined in this study. Methods. For this purpose, we studied effects of inhibitors of PLD on glucose uptake and glycogen synthesis stimulation by insulin. To determine the PLD activity, the method based on determination of products of transphosphatidylation reaction, phosphatidylethanol or phosphatidylbutanol, was used. Results. Inhibition of PLD by a general antagonist (1-butanol) or specific inhibitor, halopemide, or N-hexanoylsphingosine, or by cellular ceramides accumulated in doxorubicin-treated hepatocytes decreased insulin-stimulated glucose metabolism. Doxorubicin-induced hepatocytes resistance to insulin action could be abolished by inhibition of ceramide production. Halopemide could nullify this effect. Addition of propranolol, as well as inhibitors of phosphatidylinositol 3-kinase (PI3-kinase) (wortmannin, LY294002) or suppressors of Akt phosphorylation/activity, luteolin-7-O-glucoside or apigenin-7-O-glucoside, to the culture media could block cell response to insulin action. Conclusion. PLD plays an important role in the insulin signaling in the hepatocytes. PLD is activated downstream of PI3-kinase and Akt and is highly sensitive to ceramide content in the liver cells.
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Affiliation(s)
- Nataliya A. Babenko
- Department of Physiology of Ontogenesis, Biology Research Institute, Karazin Kharkov National University, Svobody Square 4, Kharkov 61022, Ukraine
- *Nataliya A. Babenko:
| | - Vitalina S. Kharchenko
- Department of Physiology of Ontogenesis, Biology Research Institute, Karazin Kharkov National University, Svobody Square 4, Kharkov 61022, Ukraine
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16
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Abstract
The insulin receptor (IR) is an important hub in insulin signaling and its activation is tightly regulated. Upon insulin stimulation, IR is activated through autophosphorylation, and consequently phosphorylates several insulin receptor substrate (IRS) proteins, including IRS1-6, Shc and Gab1. Certain adipokines have also been found to activate IR. On the contrary, PTP, Grb and SOCS proteins, which are responsible for the negative regulation of IR, are characterized as IR inhibitors. Additionally, many other proteins have been identified as IR substrates and participate in the insulin signaling pathway. To provide a more comprehensive understanding of the signals mediated through IR, we reviewed the upstream and downstream signal molecules of IR, summarized the positive and negative modulators of IR, and discussed the IR substrates and interacting adaptor proteins. We propose that the molecular events associated with IR should be integrated to obtain a better understanding of the insulin signaling pathway and diabetes.
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Affiliation(s)
- Yipeng Du
- National Laboratory of Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing, 100101, China
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17
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Krishna S, Zhong XP. Regulation of Lipid Signaling by Diacylglycerol Kinases during T Cell Development and Function. Front Immunol 2013; 4:178. [PMID: 23847619 PMCID: PMC3701226 DOI: 10.3389/fimmu.2013.00178] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/02/2013] [Accepted: 06/19/2013] [Indexed: 01/14/2023] Open
Abstract
Diacylglycerol (DAG) and phosphatidic acid (PA) are bioactive lipids synthesized when the T cell receptor binds to a cognate peptide-MHC complex. DAG triggers signaling by recruiting Ras guanyl-releasing protein 1, PKCθ, and other effectors, whereas PA binds to effector molecules that include mechanistic target of rapamycin, Src homology region 2 domain-containing phosphatase 1, and Raf1. While DAG-mediated pathways have been shown to play vital roles in T cell development and function, the importance of PA-mediated signals remains less clear. The diacylglycerol kinase (DGK) family of enzymes phosphorylates DAG to produce PA, serving as a molecular switch that regulates the relative levels of these critical second messengers. Two DGK isoforms, α and ζ, are predominantly expressed in T lineage cells and play an important role in conventional αβ T cell development. In mature T cells, the activity of these DGK isoforms aids in the maintenance of self-tolerance by preventing T cell hyper-activation and promoting T cell anergy. In this review, we discuss the roles of DAG-mediated pathways, PA-effectors, and DGKs in T cell development and function. We also highlight recent work that has uncovered previously unappreciated roles for DGK activity, for instance in invariant NKT cell development, anti-tumor and anti-viral CD8 responses, and the directional secretion of soluble effectors.
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Affiliation(s)
- Sruti Krishna
- Department of Pediatrics, Division of Allergy and Immunology, Duke University Medical Center , Durham, NC , USA ; Department of Immunology, Duke University Medical Center , Durham, NC , USA
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18
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Jang SY, Jang SW, Ko J. Regulation of ADP-ribosylation factor 4 expression by small leucine zipper protein and involvement in breast cancer cell migration. Cancer Lett 2011; 314:185-97. [PMID: 22004728 DOI: 10.1016/j.canlet.2011.09.028] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2011] [Revised: 09/19/2011] [Accepted: 09/22/2011] [Indexed: 12/21/2022]
Abstract
ADP-ribosylation factor 4 (ARF4) is a member of the Ras superfamily of small guanine nucleotide-binding proteins. ARF4 is known to interact with the epidermal growth factor receptor (EGFR) and mediates the EGF-dependent signal pathway, and has an anti-apoptotic function in human glioblastoma-derived U373MG cells. Although ARF4 plays a role in cancer cells, the molecular mechanism underlying regulation of its expression and its exact functions in breast cancer are unknown. In this study, we investigated the regulatory mechanism of ARF4 expression and its involvement in breast cancer cell migration. Our results show that phorbol 12-myristate 13-acetate (PMA) treatment increases ARF4 expression at both the transcriptional and translational levels. We found that the novel transcription factor small leucine zipper protein (sLZIP) binds directly to the CRE motif of the -43 to -35 region in the ARF4 promoter and regulates PMA-induced ARF4 expression. We also found that PMA-stimulated ARF4 expression increases AP-1 promoter activity, leading to induction of breast cancer cell migration. These results indicate that sLZIP-regulated ARF4 expression in response to PMA is involved in breast cancer cell migration, and sLZIP and ARF4 are potential therapeutic target molecules for treating breast cancer invasion and metastasis.
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Affiliation(s)
- Soon Young Jang
- School of Life Sciences and Biotechnology, Korea University, Seoul 136-701, South Korea
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19
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Ma WN, Park SY, Han JS. Role of phospholipase D1 in glucose-induced insulin secretion in pancreatic Beta cells. Exp Mol Med 2010; 42:456-64. [PMID: 20448441 DOI: 10.3858/emm.2010.42.6.047] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
As glucose is known to induce insulin secretion in pancreatic Beta cells, this study investigated the role of a phospholipase D (PLD)-related signaling pathway in insulin secretion caused by high glucose in the pancreatic Beta-cell line MIN6N8. It was found that the PLD activity and PLD1 expression were both increased by high glucose (33.3 mM) treatment. The dominant negative PLD1 inhibited glucose-induced Beta2 expression, and glucose-induced insulin secretion was blocked by treatment with 1-butanol or PLD1-siRNA. These results suggest that high glucose increased insulin secretion through a PLD1-related pathway. High glucose induced the binding of Arf6 to PLD1. Pretreatment with brefeldin A (BFA), an Arf inhibitor, decreased the PLD activity as well as the insulin secretion. Furthermore, BFA blocked the glucose-induced mTOR and p70S6K activation, while mTOR inhibition with rapamycin attenuated the glucose induced Beta2 expression and insulin secretion. Thus, when taken together, PLD1 would appear to be an important regulator of glucose-induced insulin secretion through an Arf6/PLD1/mTOR/p70S6K/ Beta2 pathway in MIN6N8 cells.
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Affiliation(s)
- Wei-na Ma
- Department of Biochemistry and Molecular Biology, College of Medicine, Hanyang University, Seoul 133-791, Korea
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20
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Sanda M, Kamata A, Katsumata O, Fukunaga K, Watanabe M, Kondo H, Sakagami H. The postsynaptic density protein, IQ-ArfGEF/BRAG1, can interact with IRSp53 through its proline-rich sequence. Brain Res 2008; 1251:7-15. [PMID: 19083995 DOI: 10.1016/j.brainres.2008.11.061] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2008] [Revised: 11/11/2008] [Accepted: 11/15/2008] [Indexed: 10/21/2022]
Abstract
IQ-ArfGEF/BRAG1, a guanine nucleotide exchange factor for Arf1 and Arf6, is localized at the postsynaptic density (PSD) and interacts with PSD-95. In this study, we identified a novel interaction of IQ-ArfGEF/BRAG1 with insulin receptor tyrosine kinase substrate of 53 kDa (IRSp53), also known as brain-specific angiogenesis inhibitor 1-associated protein 2. The interaction was mediated by the binding of the C-terminal proline-rich sequence of IQ-ArfGEF/BRAG1 to the SH3 domain of IRSp53. IQ-ArfGEF/BRAG1 and IRSp53 were colocalized at the PSD of excitatory synapses of certain neuronal populations. Our present findings suggest that IQ-ArfGEF/BRAG1 may play roles downstream of NMDA receptors through the interaction with multivalent PSD proteins such as IRSp53 and PSD-95.
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Affiliation(s)
- Masashi Sanda
- Department of Anatomy, Kitasato University School of Medicine, 1-15-1 Kitasato, Sagamihara, Kanagawa 228-8555, Japan
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21
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Heyward CA, Pettitt TR, Leney SE, Welsh GI, Tavaré JM, Wakelam MJO. An intracellular motif of GLUT4 regulates fusion of GLUT4-containing vesicles. BMC Cell Biol 2008; 9:25. [PMID: 18492238 PMCID: PMC2405794 DOI: 10.1186/1471-2121-9-25] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2007] [Accepted: 05/20/2008] [Indexed: 01/17/2023] Open
Abstract
Background Insulin stimulates glucose uptake by adipocytes through increasing translocation of the glucose transporter GLUT4 from an intracellular compartment to the plasma membrane. Fusion of GLUT4-containing vesicles at the cell surface is thought to involve phospholipase D activity, generating the signalling lipid phosphatidic acid, although the mechanism of action is not yet clear. Results Here we report the identification of a putative phosphatidic acid-binding motif in a GLUT4 intracellular loop. Mutation of this motif causes a decrease in the insulin-induced exposure of GLUT4 at the cell surface of 3T3-L1 adipocytes via an effect on vesicle fusion. Conclusion The potential phosphatidic acid-binding motif identified in this study is unique to GLUT4 among the sugar transporters, therefore this motif may provide a unique mechanism for regulating insulin-induced translocation by phospholipase D signalling.
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Affiliation(s)
- Catherine A Heyward
- CR-UK Institute for Cancer Studies, Birmingham University, Birmingham B15 2TT, UK.
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22
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Chen Y, Rodrik V, Foster DA. Alternative phospholipase D/mTOR survival signal in human breast cancer cells. Oncogene 2005; 24:672-9. [PMID: 15580312 DOI: 10.1038/sj.onc.1208099] [Citation(s) in RCA: 86] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Cancer cells generate survival signals to suppress default apoptotic programs that protect from cancer. Phosphatidylinositol-3-kinase (PI3K) generates a survival signal that is frequently dysregulated in human cancers. Phospholipase D (PLD) has also been implicated in signals that promote survival. One of the targets of PLD signaling is mTOR (mammalian target of rapamycin), a critical regulator of cell cycle progression and cell growth. We report here that elevated PLD activity in the MDA-MB-231 human breast cancer cell line generates an mTOR-dependent survival signal that is independent of PI3K. In contrast, MDA-MB-435S breast cancer cells, which have very low levels of PLD activity, are dependent on PI3K for survival signals. The data presented here identify an alternative survival signal that is dependent on PLD and mTOR and is active in a breast cancer cell line where the PI3K survival pathway is not active.
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Affiliation(s)
- Yuhong Chen
- Department of Biological Sciences, Hunter College of The City University of New York, New York, NY 10021, USA
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23
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Seidel RD, Amor JC, Kahn RA, Prestegard JH. Conformational changes in human Arf1 on nucleotide exchange and deletion of membrane-binding elements. J Biol Chem 2004; 279:48307-18. [PMID: 15308674 DOI: 10.1074/jbc.m402109200] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Conformational changes associated with nucleotide exchange or truncation of the N-terminal alpha-helix of human Arf1 have been investigated by using forms of easily acquired NMR data, including residual dipolar couplings and amide proton exchange rates. ADP-ribosylation factors (Arfs) are 21-kDa GTPases that regulate aspects of membrane traffic in all eukaryotic cells. An essential component of the biological actions of Arfs is their ability to reversibly bind to membranes, a process that involves exposure of the myristoylated N-terminal amphipathic alpha-helix upon activation and GTP binding. Deletion of this helix results in a protein, termed Delta17Arf1, that has a reduced affinity for GDP and the ability to bind GTP in the absence of lipids or detergents. Previous studies, comparing crystal structures for Arf1.GDP and Delta17Arf1.GTP, identified several regions of structural variation and suggested that these be associated with nucleotide exchange rather than removal of the N-terminal helix. However, separation of conformational changes because of nucleotide binding and N-terminal truncation cannot be addressed in comparing these structures, because both the bound nucleotide and the N terminus differ. Resolving the two effects is important as any structural changes involving the N terminus may represent membrane-mediated conformational adjustments that precede GTP binding. Results from NMR experiments presented here on Arf1.GDP and Delta17Arf1.GDP in solution reveal substantial structural differences that can only be associated with N-terminal truncation.
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Affiliation(s)
- Ronald D Seidel
- Complex Carbohydrate Research Center, University of Georgia, Athens, Georgia 30602-4712, USA
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24
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Abstract
Insulin-stimulated Glut-4 translocation is regulated through a complex pathway. Increasing attention is being paid to the role undertaken in this process by Phospholipase D, a signal transduction-activated enzyme that generates the lipid second-messenger phosphatidic acid. Phospholipase D facilitates Glut-4 translocation at potentially multiple steps in its outward movement. Current investigation is centered on Phospholipase D promotion of Glut-4-containing membrane vesicle trafficking and vesicle fusion into the plasma membrane, in part through activation of atypical protein kinase C isoforms.
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Affiliation(s)
- Ping Huang
- Department of Pharmacology and the Center for Developmental Genetics, University Medical Center at Stony Brook, Stony Brook, NY 11794-5140, USA
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25
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Li HS, Shome K, Rojas R, Rizzo MA, Vasudevan C, Fluharty E, Santy LC, Casanova JE, Romero G. The guanine nucleotide exchange factor ARNO mediates the activation of ARF and phospholipase D by insulin. BMC Cell Biol 2003; 4:13. [PMID: 12969509 PMCID: PMC212319 DOI: 10.1186/1471-2121-4-13] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2003] [Accepted: 09/11/2003] [Indexed: 11/30/2022] Open
Abstract
BACKGROUND Phospholipase D (PLD) is involved in many signaling pathways. In most systems, the activity of PLD is primarily regulated by the members of the ADP-Ribosylation Factor (ARF) family of GTPases, but the mechanism of activation of PLD and ARF by extracellular signals has not been fully established. Here we tested the hypothesis that ARF-guanine nucleotide exchange factors (ARF-GEFs) of the cytohesin/ARNO family mediate the activation of ARF and PLD by insulin. RESULTS Wild type ARNO transiently transfected in HIRcB cells was translocated to the plasma membrane in an insulin-dependent manner and promoted the translocation of ARF to the membranes. ARNO mutants: DeltaCC-ARNO and CC-ARNO were partially translocated to the membranes while DeltaPH-ARNO and PH-ARNO could not be translocated to the membranes. Sec7 domain mutants of ARNO did not facilitate the ARF translocation. Overexpression of wild type ARNO significantly increased insulin-stimulated PLD activity, and mutations in the Sec7 and PH domains, or deletion of the PH or CC domains inhibited the effects of insulin. CONCLUSIONS Small ARF-GEFs of the cytohesin/ARNO family mediate the activation of ARF and PLD by the insulin receptor.
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Affiliation(s)
- Hai-Sheng Li
- Departments of Pharmacology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15261 USA
| | - Kuntala Shome
- Departments of Pharmacology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15261 USA
| | - Raúl Rojas
- Departments of Pharmacology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15261 USA
- Cell Biology and Physiology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15261 USA
| | - Megan A Rizzo
- Departments of Pharmacology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15261 USA
| | - Chandrasekaran Vasudevan
- Departments of Pharmacology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15261 USA
| | - Eric Fluharty
- Departments of Pharmacology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15261 USA
| | - Lorraine C Santy
- Department of Cell Biology, University of Virginia School of Medicine, Charlottesville, VA 22908 USA
| | - James E Casanova
- Department of Cell Biology, University of Virginia School of Medicine, Charlottesville, VA 22908 USA
| | - Guillermo Romero
- Departments of Pharmacology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15261 USA
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26
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Chen Y, Zheng Y, Foster DA. Phospholipase D confers rapamycin resistance in human breast cancer cells. Oncogene 2003; 22:3937-42. [PMID: 12813467 DOI: 10.1038/sj.onc.1206565] [Citation(s) in RCA: 154] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
mTOR (mammalian target of rapamycin) is a protein kinase that regulates cell cycle progression and cell growth. Rapamycin is a highly specific inhibitor of mTOR in clinical trials for the treatment of breast and other cancers. mTOR signaling was reported to require phosphatidic acid (PA), the metabolic product of phospholipase D (PLD). PLD, like mTOR, has been implicated in survival signaling and the regulation of cell cycle progression. PLD activity is frequently elevated in breast cancer. We have investigated the effect of rapamycin on breast cancer cell lines with different levels of PLD activity. MCF-7 cells, with relatively low levels of PLD activity, were highly sensitive to the growth-arresting effects of rapamycin, whereas MDA-MB-231 cells, with a 10-fold higher PLD activity than MCF-7 cells, were highly resistant to rapamycin. Elevating PLD activity in MCF-7 cells led to rapamycin resistance; and inhibition of PLD activity in MDA-MB-231 cells increased rapamycin sensitivity. Elevated PLD activity in MCF-7 cells also caused rapamycin resistance for S6 kinase phosphorylation and serum-induced Myc expression. These data implicate mTOR as a critical target for survival signals generated by PLD and suggest that PLD levels in breast cancer could be a valuable indicator of the likely efficacy of rapamycin treatment.
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Affiliation(s)
- Yuhong Chen
- Department of Biological Sciences, Hunter College of The City University of New York, 695 Park Avenue, New York, NY 10021, USA
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Kim SW, Hayashi M, Lo JF, Yang Y, Yoo JS, Lee JD. ADP-ribosylation factor 4 small GTPase mediates epidermal growth factor receptor-dependent phospholipase D2 activation. J Biol Chem 2003; 278:2661-8. [PMID: 12446727 DOI: 10.1074/jbc.m205819200] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The epidermal growth factor receptor (EGFR) plays a critical role in the development, proliferation, and differentiation of cells of epithelial and mesenchymal origin. These EGFR-dependent cellular processes are mediated by a repertoire of intracellular signaling pathways triggered by the activation of the EGFR cytoplasmic domain, which originates from ligand binding of its extracellular domain. To understand the molecular mechanisms by which the intracellular domain of EGFR transmits mitogenic messages to the downstream signaling pathways, we used the cytoplasmic region of EGFR as bait in yeast two-hybrid screening. We found that ADP-ribosylation factor 4 (ARF4) interacts with the intracellular part of EGFR and mediates the EGF-dependent cellular activation of phospholipase D2 (PLD2) but does not mediate the activation of PLD1. In addition, ARF4-mediated PLD2 activation leads to dramatic activation of the transcription factor activator protein 1 (AP-1), and, importantly, ARF4 activity is required for EGF-induced activation of cellular AP-1. Our findings indicate that ARF4 is a critical molecule that directly regulates cellular PLD2 activity and that this ARF4-mediated PLD2 activation stimulates AP-1-dependent transcription in the EGF-induced cellular response.
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Affiliation(s)
- Sung-Woo Kim
- Department of Immunology, The Scripps Research Institute, La Jolla, California 92037, USA
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28
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Xu L, Frankel P, Jackson D, Rotunda T, Boshans RL, D'Souza-Schorey C, Foster DA. Elevated phospholipase D activity in H-Ras- but not K-Ras-transformed cells by the synergistic action of RalA and ARF6. Mol Cell Biol 2003; 23:645-54. [PMID: 12509462 PMCID: PMC151535 DOI: 10.1128/mcb.23.2.645-654.2003] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
Phospholipase D (PLD) activity is elevated in response to the oncogenic stimulus of H-Ras but not K-Ras. H-Ras and K-Ras have been reported to localize to different membrane microdomains, with H-Ras localizing to caveolin-enriched light membrane fractions. We reported previously that PLD activity elevated in response to mitogenic stimulation is restricted to the caveolin-enriched light membrane fractions. PLD activity in H-Ras-transformed cells is dependent upon RalA, and consistent with a lack of elevated PLD activity in K-Ras-transformed cells, RalA was not activated in K-Ras-transformed cells. Although H-Ras-induced PLD activity is dependent upon RalA, an activated mutant of RalA is not sufficient to elevate PLD activity. We reported previously that RalA interacts with PLD activating ADP ribosylation factor (ARF) proteins. In cells transformed by H-Ras, we found increased coprecipitation of ARF6 with RalA. Moreover, ARF6 colocalized with RalA in light membrane fractions. Interestingly, ARF6 protein levels were elevated in H-Ras- but not K-Ras-transformed cells. A dominant-negative mutant of ARF6 inhibited PLD activity in H-Ras-transformed NIH 3T3 cells. Activated mutants of either ARF6 or RalA were not sufficient to elevate PLD activity in NIH 3T3 cells; however, expression of both activated RalA and activated ARF6 in NIH 3T3 cells led to increased PLD activity. These data suggest a model whereby H-Ras stimulates the activation of both RalA and ARF6, which together lead to the elevation of PLD activity.
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Affiliation(s)
- Lizhong Xu
- Department of Biological Sciences, Hunter College of The City University of New York, New York, New York 10021, USA
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29
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Andresen BT, Rizzo MA, Shome K, Romero G. The role of phosphatidic acid in the regulation of the Ras/MEK/Erk signaling cascade. FEBS Lett 2002; 531:65-8. [PMID: 12401205 DOI: 10.1016/s0014-5793(02)03483-x] [Citation(s) in RCA: 141] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Phosphatidic acid (PA) is an important second messenger produced by the activation of numerous cell surface receptors. Recent data have suggested that PA regulates multiple cellular processes. This review addresses primarily the role of PA in the regulation of the Erk1/2 cascade pathway. A model for the regulation of Erk1/2 phosphorylation by cell surface receptors is presented. According to this model, agonists stimulate the binding of GTP to Ras and the activation of phospholipase D to generate phosphatidic acid. PA promotes the binding of cRaf-1 kinase to the membrane, where it interacts with Ras.GTP and other regulatory components of the pathway. Ras-Raf complexes remain bound to the surface of endosomes, where scaffolding complexes involving Ras, cRaf-1, MEK and Erk are formed. Complete activation and coupling of the cascade requires endocytosis, a process that is also modulated by PA.
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Affiliation(s)
- Bradley T Andresen
- Department of Pharmacology, University of Pittsburgh, Pittsburgh, PA 15261, USA
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30
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Affiliation(s)
- J H Exton
- Howard Hughes Medical Institute, Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, TN, USA
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Rizzo M, Romero G. Pharmacological importance of phospholipase D and phosphatidic acid in the regulation of the mitogen-activated protein kinase cascade. Pharmacol Ther 2002; 94:35-50. [PMID: 12191592 DOI: 10.1016/s0163-7258(02)00170-5] [Citation(s) in RCA: 54] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
The stimulation of cells with many extracellular agonists leads to the activation of phospholipase (PL)D. PLD metabolizes phosphatidylcholine to generate phosphatidic acid (PA). Neither the mechanism through which cell surface receptors regulate PLD activation nor the functional consequences of PLD activity in mitogenic signaling are completely understood. PLD is activated by protein kinase C, phospholipids, and small GTPases of the ADP-ribosylation factor and Rho families, but the mechanisms linking cell surface receptors to the activation of PLD still require detailed analysis. Furthermore, the latest data on the functional consequences of the generation of cellular PA suggest an important role for this lipid in the regulation of membrane traffic and on the activation of the mitogen-activated protein kinase cascade. This review addresses these issues, examining some novel models for the physiological role of PLD and PA and discussing their potential usefulness as specific targets for the development of new therapies.
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Affiliation(s)
- Mark Rizzo
- Department of Pharmacology, W 1345 BSTWR, University of Pittsburgh School of Medicine, Pittsburgh, PA 15261, USA
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32
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Salvador LM, Mukherjee S, Kahn RA, Lamm ML, Fazleabas AT, Maizels ET, Bader MF, Hamm H, Rasenick MM, Casanova JE, Hunzicker-Dunn M. Activation of the luteinizing hormone/choriogonadotropin hormone receptor promotes ADP ribosylation factor 6 activation in porcine ovarian follicular membranes. J Biol Chem 2001; 276:33773-81. [PMID: 11448949 DOI: 10.1074/jbc.m101498200] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Previously we demonstrated in a cell-free ovarian follicular plasma membrane model that agonist-dependent desensitization of the luteinizing hormone/choriogonadotropin receptor (LH/CG R) is GTP-dependent, mimicked by the addition of ADP-ribosylation factor (ARF) nucleotide binding site opener, which acts as a guanine nucleotide exchange factor for ARFs 1 and 6, and selectively inhibited by synthetic N-terminal ARF6 peptides. We therefore sought direct evidence that activation of the LH/CG R promotes activation of ARF1 and/or ARF6. Using a classic ARF activation assay, the cholera toxin-catalyzed ADP-ribosylation of G alpha(s), results show that LH/CG R activation stimulates an ARF protein by a brefeldin A-independent mechanism. Synthetic N-terminal inhibitory ARF6 but not ARF1 peptide blocks LH/CG R-stimulated ARF activity. LH/CG R activation also promotes the binding of a photoaffinity GTP analog to a protein that migrates on one- and two-dimensional polyacrylamide gel electrophoresis with ARF6. These results suggest that ARF6 is the predominant ARF activated by the LH/CG R. To activate ARF6, the LH/CG R does not appear to signal through the C-terminal regions of G alpha(i) or G alpha(q) or through the second or third intracellular loops or the N terminus of the cytoplasmic tail of the LH/CG R. Although exogenous recombinant ARNO promotes only a small increase in ARF6 activation in the presence of activated LH/CG R, hCG-stimulated ARF6 activation is reduced to basal levels by catalytically inactive ARF nucleotide binding-site opener. These results provide direct evidence that LH/CG R activation leads to the activation of membrane-delimited ARF6.
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Affiliation(s)
- L M Salvador
- Department of Cell and Molecular Biology, Northwestern University Medical School, Chicago, Illinois 60611, USA
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33
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Kristiansen S, Nielsen JN, Bourgoin S, Klip A, Franco M, Richter EA. GLUT-4 translocation in skeletal muscle studied with a cell-free assay: involvement of phospholipase D. Am J Physiol Endocrinol Metab 2001; 281:E608-18. [PMID: 11500317 DOI: 10.1152/ajpendo.2001.281.3.e608] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
GLUT-4-containing membranes immunoprecipitated from insulin-stimulated rat skeletal muscle produce the phospholipase D (PLD) product phosphatidic acid. In vitro stimulation of PLD in crude membrane with ammonium sulfate (5 mM) resulted in transfer of GLUT-4 (3.0-fold vs. control) as well as transferrin receptor proteins from large to small membrane structures. The in vitro GLUT-4 transfer could be blocked by neomycin (a PLD inhibitor), and neomycin also reduced insulin-stimulated glucose transport in intact incubated soleus muscles. Furthermore, protein kinase B(beta) (PKB(beta)) was found to associate with the GLUT-4 protein and was transferred to small vesicles in response to ammonium sulfate in vitro. Finally, addition of cytosolic proteins, prepared from basal skeletal muscle, and GTP nucleotides to an enriched GLUT-4 membrane fraction resulted in in vitro transfer of GLUT-4 to small membranes (6.8-fold vs. unstimulated control). The cytosol and nucleotide-induced GLUT-4 transfer could be blocked by neomycin and N-ethylmaleimide. In conclusion, we have developed a cell-free assay that demonstrates in vitro GLUT-4 transfer. This transfer may suggest release of GLUT-4-containing vesicles from donor GLUT-4 membranes involving PLD activity and binding of PKB(beta) to GLUT-4.
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Affiliation(s)
- S Kristiansen
- Copenhagen Muscle Research Center, Department of Human Physiology, University of Copenhagen, 13 Universitetsparken, DK-2100 Copenhagen, Denmark
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34
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Lee S, Park JB, Kim JH, Kim Y, Kim JH, Shin KJ, Lee JS, Ha SH, Suh PG, Ryu SH. Actin Directly Interacts with Phospholipase D, Inhibiting Its Activity. J Biol Chem 2001; 276:28252-60. [PMID: 11373276 DOI: 10.1074/jbc.m008521200] [Citation(s) in RCA: 90] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Mammalian phospholipase D (PLD) plays a key role in several signal transduction pathways and is involved in many diverse functions. To elucidate the complex molecular regulation of PLD, we investigated PLD-binding proteins obtained from rat brain extract. Here we report that a 43-kDa protein in the rat brain, beta-actin, acts as a major PLD2 direct-binding protein as revealed by peptide mass fingerprinting in combination with matrix-assisted laser desorption ionization/time-of-flight mass spectrometry. We also determined that the region between amino acids 613 and 723 of PLD2 is required for the direct binding of beta-actin, using bacterially expressed glutathione S-transferase fusion proteins of PLD2 fragments. Intriguingly, purified beta-actin potently inhibited both phosphatidylinositol-4,5-bisphosphate- and oleate-dependent PLD2 activities in a concentration-dependent manner (IC50 = 5 nm). In a previous paper, we reported that alpha-actinin inhibited PLD2 activity in an interaction-dependent and an ADP-ribosylation factor 1 (ARF1)-reversible manner (Park, J. B., Kim, J. H., Kim, Y., Ha, S. H., Kim, J. H., Yoo, J.-S., Du, G., Frohman, M. A., Suh, P.-G., and Ryu, S. H. (2000) J. Biol. Chem. 275, 21295-21301). In vitro binding analyses showed that beta-actin could displace alpha-actinin binding to PLD2, demonstrating independent interaction between cytoskeletal proteins and PLD2. Furthermore, ARF1 could steer the PLD2 activity in a positive direction regardless of the inhibitory effect of beta-actin on PLD2. We also observed that beta-actin regulates PLD1 and PLD2 with similar binding and inhibitory potencies. Immunocytochemical and co-immunoprecipitation studies demonstrated the in vivo interaction between the two PLD isozymes and actin in cells. Taken together, these results suggest that the regulation of PLD by cytoskeletal proteins, beta-actin and alpha-actinin, and ARF1 may play an important role in cytoskeleton-related PLD functions.
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Affiliation(s)
- S Lee
- Division of Molecular and Life Sciences, Pohang University of Science and Technology, Pohang 790-784, Republic of Korea
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35
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Farese RV. Insulin-sensitive phospholipid signaling systems and glucose transport. Update II. Exp Biol Med (Maywood) 2001; 226:283-95. [PMID: 11368419 DOI: 10.1177/153537020122600404] [Citation(s) in RCA: 65] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
Abstract
Insulin provokes rapid changes in phospholipid metabolism and thereby generates biologically active lipids that serve as intracellular signaling factors that regulate glucose transport and glycogen synthesis. These changes include: (i) activation of phosphatidylinositol 3-kinase (PI3K) and production of PIP3; (ii) PIP3-dependent activation of atypical protein kinase Cs (PKCs); (iii) PIP3-dependent activation of PKB; (iv) PI3K-dependent activation of phospholipase D and hydrolysis of phosphatidylcholine with subsequent increases in phosphatidic acid (PA) and diacylglycerol (DAG); (v) PI3K-independent activation of glycerol-3-phosphate acylytansferase and increases in de novo synthesis of PA and DAG; and (vi) activation of DAG-sensitive PKCs. Recent findings suggest that atypical PKCs and PKB serve as important positive regulators of insulin-stimulated glucose metabolism, whereas mechanisms that result in the activation of DAG-sensitive PKCs serve mainly as negative regulators of insulin signaling through PI3K. Atypical PKCs and PKB are rapidly activated by insulin in adipocytes, liver, skeletal muscles, and other cell types by a mechanism requiring PI3K and its downstream effector, 3-phosphoinositide-dependent protein kinase-1 (PDK-1), which, in conjunction with PIP3, phosphorylates critical threonine residues in the activation loops of atypical PKCs and PKB. PIP3 also promotes increases in autophosphorylation and allosteric activation of atypical PKCs. Atypical PKCs and perhaps PKB appear to be required for insulin-induced translocation of the GLUT 4 glucose transporter to the plasma membrane and subsequent glucose transport. PKB also appears to be the major regulator of glycogen synthase. Together, atypical PKCs and PKB serve as a potent, integrated PI3K/PDK-1-directed signaling system that is used by insulin to regulate glucose metabolism.
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Affiliation(s)
- R V Farese
- JA Haley Veterans' Hospital Research Service and Department of Internal Medicine, University of South Florida College of Medicine, Tampa 33612, USA.
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36
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Maranda B, Brown D, Bourgoin S, Casanova JE, Vinay P, Ausiello DA, Marshansky V. Intra-endosomal pH-sensitive recruitment of the Arf-nucleotide exchange factor ARNO and Arf6 from cytoplasm to proximal tubule endosomes. J Biol Chem 2001; 276:18540-50. [PMID: 11278939 DOI: 10.1074/jbc.m011577200] [Citation(s) in RCA: 116] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Kidney proximal tubule epithelial cells have an extensive apical endocytotic apparatus that is critical for the reabsorption and degradation of proteins that traverse the glomerular filtration barrier and that is also involved in the extensive recycling of functionally important apical plasma membrane transporters. We show here that an Arf-nucleotide exchange factor, ARNO (ADP-ribosylation factor nucleotide site opener) as well as Arf6 and Arf1 small GTPases are located in the kidney proximal tubule receptor-mediated endocytosis pathway, and that ARNO and Arf6 recruitment from cytosol to endosomes is pH-dependent. In proximal tubules in situ, ARNO and Arf6 partially co-localized with the V-ATPase in apical endosomes in proximal tubules. Arf1 was localized both at the apical pole of proximal tubule epithelial cells, but also in the Golgi. By Western blot analysis ARNO, Arf6, and Arf1 were detected both in purified endosomes and in proximal tubule cytosol. A translocation assay showed that ATP-driven endosomal acidification triggered the recruitment of ARNO and Arf6 from proximal tubule cytosol to endosomal membranes. The translocation of both ARNO and Arf6 was reversed by V-type ATPase inhibitors and by uncouplers of endosomal intralumenal pH, and was correlated with the magnitude of intra-endosomal acidification. Our data suggest that V-type ATPase-dependent acidification stimulates the selective recruitment of ARNO and Arf6 to proximal tubule early endosomes. This mechanism may play an important role in the pH-dependent regulation of receptor-mediated endocytosis in proximal tubules in situ.
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Affiliation(s)
- B Maranda
- Program in Membrane Biology & Renal Unit, Massachusetts General Hospital, and Department of Medicine, Harvard Medical School, Boston, Massachusetts, 02129-2020, USA
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37
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Asp L, Claesson C, Boren J, Olofsson SO. ADP-ribosylation factor 1 and its activation of phospholipase D are important for the assembly of very low density lipoproteins. J Biol Chem 2000; 275:26285-92. [PMID: 10843997 DOI: 10.1074/jbc.m003520200] [Citation(s) in RCA: 54] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The role of ADP-ribosylation factor 1 (ARF-1) in the assembly of very low density lipoproteins (VLDL) was investigated by expressing dominant-negative mutants in McA-RH7777 cells. Transient expression of ARF-1(T31N), a GDP-restrictive mutant, significantly inhibited apolipoprotein B-100 (apoB-100) VLDL production without influencing the biosynthesis of apoB-100 low density lipoproteins or total apoB production (indicating that it inhibited the second step of VLDL assembly) and without altering total protein production or biosynthesis of transferrin, phosphatidylcholine, or triglycerides. These effects were confirmed in stable inducible transfectants. In contrast, expression of an ARF-1 mutant lacking the N-terminal 17 amino acids, which has no myristoylation site and cannot interact with the microsomal membrane, did not affect VLDL assembly. Thus, active ARF-1 is needed for the second step of the process. To further explore these observations, we developed a cell-free system based on the postnuclear supernatant isolated from McA-RH7777 cells. In this system, 10-15% of the apoB-100 pool was converted to VLDL in a time- and temperature-dependent way. The assembly process was highly dependent on a heat-stable factor in the d > 1.21 g/ml infranatant of fetal calf serum; this factor was not present in low density lipoproteins or VLDL. Brefeldin A inhibited VLDL assembly in this system, as did a synthetic peptide (corresponding to N-terminal amino acids 2-17 of ARF-1) that displaces ARF-1 from the membrane. Thus, active ARF-1 is also needed for cell-free assembly of VLDL. Guanosine 5'-3-O-(thio)triphosphate also inhibited VLDL assembly in this system, indicating that the process requires ongoing hydrolysis of GTP. 1-Butanol, which inhibits the formation of phosphatidic acid (PA) and instead gives rise to phosphatidylbutanol, inhibited VLDL assembly, whereas 2-butanol, which does not inhibit PA formation, failed to do so. Thus, phospholipase D (PLD)-catalyzed formation of PA from phosphatidylcholine is essential for VLDL assembly. In support of this conclusion, exogenous PLD prevented brefeldin A from inhibiting the assembly process. Our results indicate that ARF-1 participates in the second step of VLDL assembly through a process that involves activation of PLD and production of PA.
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Affiliation(s)
- L Asp
- Department of Medical Biochemistry and the Wallenberg Laboratory for Cardiovascular Research, University of Göteborg, SE 405 30 Göteborg, Sweden
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38
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Rizzo MA, Shome K, Watkins SC, Romero G. The recruitment of Raf-1 to membranes is mediated by direct interaction with phosphatidic acid and is independent of association with Ras. J Biol Chem 2000; 275:23911-8. [PMID: 10801816 DOI: 10.1074/jbc.m001553200] [Citation(s) in RCA: 252] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
The serine/threonine kinase Raf-1 is an essential component of the MAPK cascade. Activation of Raf-1 by extracellular signals is initiated by association with intracellular membranes. Recruitment of Raf-1 to membranes has been reported to be mediated by direct association with Ras and by the phospholipase D product phosphatidic acid (PA). Here we report that insulin stimulation of HIRcB fibroblasts leads to accumulation of Ras, Raf-1, phosphorylated MEK, phosphorylated MAPK, and PA on endosomal membranes. Mutations that disrupt Raf-PA interactions prevented recruitment of Raf-1 to membranes, whereas disruption of Ras-Raf interactions did not affect agonist-dependent translocation. Expression of a dominant-negative Ras mutant did not prevent insulin-dependent Raf-1 translocation, but inhibited phosphorylation of MAPK. Finally, the PA-binding region of Raf-1 was sufficient to target green fluorescent protein to membranes, and its overexpression blocked recruitment of Raf-1 to membranes and disrupted insulin-dependent MAPK phosphorylation. These results indicate that agonist-dependent Raf-1 translocation is primarily mediated by a direct interaction with PA and is independent of association with Ras.
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Affiliation(s)
- Megan A Rizzo
- Departments of Pharmacology and Cell Biology and Physiology, University of Pittsburgh, Pittsburgh, Pennsylvania 15261, USA
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39
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Martin ME, Hidalgo J, Rosa JL, Crottet P, Velasco A. Effect of protein kinase A activity on the association of ADP-ribosylation factor 1 to golgi membranes. J Biol Chem 2000; 275:19050-9. [PMID: 10858454 DOI: 10.1074/jbc.275.25.19050] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The small GTP-binding protein ADP-ribosylation factor 1 (ARF1) is an essential component of the molecular machinery that catalyzes the formation of membrane-bound transport intermediates. By using an in vitro assay that reproduces recruitment of cytosolic proteins onto purified, high salt-washed Golgi membranes, we have analyzed the role of cAMP-dependent protein kinase A (PKA) on ARF1 incorporation. Addition to this assay of either pure catalytic subunits of PKA (C-PKA) or cAMP increased ARF1 binding. By contrast, ARF1 association was inhibited following C-PKA inactivation with either PKA inhibitory peptide or RIIalpha as well as after cytosol depletion of C-PKA. C-PKA also stimulated recruitment and activation of a recombinant form of human ARF1 in the absence of additional cytosolic components. The binding step could be dissociated from the activation reaction and found to be independent of guanine nucleotides and saturable. This step was stimulated by C-PKA in an ATP-dependent manner. Dephosphorylated Golgi membranes exhibited a decreased ability to recruit ARF1, and this effect was reverted by addition of C-PKA. Following an increase in the intracellular level of cAMP, ARF proteins redistributed from cytosol to the perinuclear Golgi region of intact cells. Collectively, the results show that PKA exerts a key regulatory role in the recruitment of ARF1 onto Golgi membranes. In contrast, PKA modulators did not affect recruitment of beta-COP onto Golgi membranes containing prebound ARF1.
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Affiliation(s)
- M E Martin
- Department of Cell Biology, University of Seville, 41012 Seville, Spain
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Shome K, Rizzo MA, Vasudevan C, Andresen B, Romero G. The activation of phospholipase D by endothelin-1, angiotensin II, and platelet-derived growth factor in vascular smooth muscle A10 cells is mediated by small G proteins of the ADP-ribosylation factor family. Endocrinology 2000; 141:2200-8. [PMID: 10830309 DOI: 10.1210/endo.141.6.7517] [Citation(s) in RCA: 43] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
We show here that A10 cells express the phospholipase D (PLD) isoforms PLD1b and PLD2. The activation of PLD in these cells by angiotensin II (AngII), endothelin-1 (ET-1), and platelet-derived growth factor (PDGF) was found to be sensitive to inhibitors of the activation of ADP-ribosylation factor (ARF) but not to blockers of Rho protein function. PDGF, AngII, and ET-1 induced the binding of ARF proteins to cell membranes in a permeabilized cell assay. Cells permeabilized and depleted of ARF were no longer sensitive to stimulation with AngII, ET-1, or PDGF, but the addition of recombinant myristoylated human ARF1 restored agonist-dependent PLD activity. Expression of dominant negative ARF mutants blocked receptor-dependent activation of PLD. PLD activity was also potently stimulated by treatment with phorbol esters, but this activity was only partially inhibited by brefeldin A or by the overexpression of ARF dominant negative mutants. Transient expression of catalytically inactive mutants of PLD2, but not PLD1, inhibited significantly PDGF- and AngII-dependent PLD activity. We conclude: 1) the activation of PLD by cell surface receptors occurs primarily by an ARF-dependent mechanism in A10 cells, whereas the activation of PLD by protein kinase C-dependent pathways is only partially dependent on the regulation of ARF proteins; and 2) cell surface receptors, such as AngII and PDGF, signal primarily via PLD2 in A10 cells.
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Affiliation(s)
- K Shome
- Department of Pharmacology of the University of Pittsburgh School of Medicine, Pennsylvania 15261, USA
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41
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Bychenok S, Foster DA. A low molecular weight factor from dividing cells activates phospholipase D in caveolin-enriched membrane microdomains. Arch Biochem Biophys 2000; 377:139-45. [PMID: 10775453 DOI: 10.1006/abbi.2000.1766] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Phospholipase D (PLD) activity is elevated in Ras-transformed NIH 3T3 cells. This difference in PLD activity between Ras-transformed and nontransformed parental cells disappeared in isolated membranes from these cells. In reconstitution experiments, heat-denatured cytosolic fractions from Ras-transformed, but not parental, NIH 3T3 cells elevated PLD activity in isolated membranes. This heat-resistant PLD-stimulating activity from the Ras-transformed cells was sensitive to proteases and passed through a 1-kDa MW cutoff membrane, suggesting that the factor is a peptide of less than 10 amino acids. The ability of this PLD-stimulating factor, designated PLD-SF, to elevate PLD activity in isolated membranes was restricted to the caveolin-enriched light membranes, where many signaling molecules are localized. PLD-SF was also elevated in v-Src- and v-Raf-transformed cells and in serum-stimulated NIH 3T3 cells. PLD-SF was detected in a variety of rat tissues but was highest in testes, where a large percentage of cells are dividing. A similar low molecular weight PLD-stimulating activity was found in actively dividing, but not stationary yeast, cells. The data here provide evidence for a highly conserved PLD-stimulating peptide that is elevated in response to mitogenic stimuli.
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Affiliation(s)
- S Bychenok
- Department of Biological Sciences, Hunter College of The City University of New York, New York, NY 10021, USA
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42
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Emoto M, Klarlund JK, Waters SB, Hu V, Buxton JM, Chawla A, Czech MP. A role for phospholipase D in GLUT4 glucose transporter translocation. J Biol Chem 2000; 275:7144-51. [PMID: 10702282 DOI: 10.1074/jbc.275.10.7144] [Citation(s) in RCA: 57] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Based on recent studies showing that phospholipase D (PLD)1 is associated with intracellular membranes and promotes membrane budding from the trans-Golgi, we tested its possible role in the membrane trafficking of GLUT4 glucose transporters. Using immunofluorescence confocal microscopy, expressed Myc epitope-tagged PLD1 was found to associate with intracellular vesicular structures by a mechanism that requires its N-terminal pleckstrin homology domain. Partial co-localization with expressed GLUT4 fused to green fluorescent protein in both 3T3-L1 adipocytes and Chinese hamster ovary cells was evident. Furthermore, microinjection of purified PLD into cultured adipocytes markedly potentiated the effect of a submaximal concentration of insulin to stimulate GLUT4 translocation to cell surface membranes. Insulin stimulated PLD activity in cells expressing high levels of insulin receptors but no such insulin effect was detected in 3T3-L1 adipocytes. Taken together, these results are consistent with the hypothesis that PLD1 associated with GLUT4-containing membranes acts in a constitutive manner to promote the mechanism of GLUT4 translocation by insulin.
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Affiliation(s)
- M Emoto
- Program in Molecular Medicine and Department of Biochemistry and Molecular Biology, University of Massachusetts Medical School, Worcester, Massachusetts 01655, USA
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43
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Sauvage M, Mazière P, Fathallah H, Giraud F. Insulin stimulates NHE1 activity by sequential activation of phosphatidylinositol 3-kinase and protein kinase C zeta in human erythrocytes. EUROPEAN JOURNAL OF BIOCHEMISTRY 2000; 267:955-62. [PMID: 10672002 DOI: 10.1046/j.1432-1327.2000.01084.x] [Citation(s) in RCA: 60] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
The signaling cascade linking insulin receptor stimulation to the activation of Na/H exchanger (NHE) was investigated in human erythrocytes, a simple cell model expressing the NHE1 isoform and protein kinase C (PKC) alpha and zeta isoforms only. Our results demonstrate the presence of phosphatidylinositol (PtdIns) 3-kinase in these cells and its activation by insulin. With a similar time-course, insulin also promoted both the translocation and activation of PKC zeta, but had no effect on PKC alpha. Inhibition of PtdIns 3-kinase with wortmannin prevented the activation of PKC zeta by insulin. Stimulation of NHE1 was observed after 10 min of insulin treatment and persisted for at least 60 min. This effect was totally abolished by wortmannin or GF 109203X, an inhibitor of all PKC isoforms, but not by Gö 6976, a specific inhibitor of conventional and novel PKCs (e.g. PKC alpha). These data indicate that PKC zeta activation is mediated by a PtdIns 3-kinase-dependent mechanism and that NHE1 stimulation involves the sequential activation of PtdIns 3-kinase and PKC zeta. In addition, insulin stimulation of NHE1 occurred without altering the phosphorylation state of the exchanger, suggesting that the phosphorylation of an ancillary protein by PKC zeta would be responsible for activation of the transporter.
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Affiliation(s)
- M Sauvage
- Laboratoire des Biomembranes et Messagers Cellulaires, Université Paris XI, Orsay, France
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Abstract
ARF proteins are important regulators of membrane dynamics and protein transport within the eukaryotic cell. The Sec7 domain is approximately 200 amino acids in size and stimulates guanine-nucleotide exchange on members of the ARF class of small GTPases. The members of one subclass of Sec7-domain proteins are direct targets of the secretion-inhibiting drug brefeldin A, which blocks the exchange reaction by trapping a reaction intermediate in an inactive, abortive complex. A separate subclass of Sec7-domain proteins is involved in signal transduction and possess a domain that mediates membrane binding in response to extracellular signals.
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Affiliation(s)
- C L Jackson
- Service de Biochimie et Génétique Moléculaire, CEA/Saclay, Gif-sur-Yvette, France.
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45
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Voss M, Weernink PA, Haupenthal S, Möller U, Cool RH, Bauer B, Camonis JH, Jakobs KH, Schmidt M. Phospholipase D stimulation by receptor tyrosine kinases mediated by protein kinase C and a Ras/Ral signaling cascade. J Biol Chem 1999; 274:34691-8. [PMID: 10574935 DOI: 10.1074/jbc.274.49.34691] [Citation(s) in RCA: 59] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Stimulation of phospholipase D (PLD) in HEK-293 cells expressing the M(3) muscarinic receptor by phorbol ester-activated protein kinase C (PKC) apparently involves Ral GTPases. We report here that PKC, but not muscarinic receptor-induced PLD stimulation in these cells, is strongly and specifically reduced by expression of dominant-negative RalA, G26A RalA, as well as dominant-negative Ras, S17N Ras. In contrast, overexpression of the Ras-activated Ral-specific guanine nucleotide exchange factor, Ral-GDS, specifically enhanced PKC-induced PLD stimulation. Moreover, recombinant Ral-GDS potentiated Ral-dependent PKC-induced PLD stimulation in membranes. Epidermal growth factor, platelet-derived growth factor, and insulin, ligands for receptor tyrosine kinases (RTKs) endogenously expressed in HEK-293 cells, apparently use the PKC- and Ras/Ral-dependent pathway for PLD stimulation. First, PLD stimulation by the RTK agonists was prevented by PKC inhibition and PKC down-regulation. Second, expression of dominant-negative RalA and Ras mutants strongly reduced RTK-induced PLD stimulation. Third, overexpression of Ral-GDS largely potentiated PLD stimulation by the RTK agonists. Finally, using the Ral binding domain of the Ral effector RLIP as an activation-specific probe for Ral proteins, it is demonstrated that endogenous RalA is activated by phorbol ester and RTK agonists. Taken together, strong evidence is provided that RTK-induced PLD stimulation in HEK-293 cells is mediated by PKC and a Ras/Ral signaling cascade.
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Affiliation(s)
- M Voss
- Institut für Pharmakologie, Universitätsklinikum Essen, D-45122 Essen, Germany
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46
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Yang CZ, Mueckler M. ADP-ribosylation factor 6 (ARF6) defines two insulin-regulated secretory pathways in adipocytes. J Biol Chem 1999; 274:25297-300. [PMID: 10464254 DOI: 10.1074/jbc.274.36.25297] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
ADP-ribosylation factor 6 (ARF6) appears to play an essential role in the endocytic/recycling pathway in several cell types. To determine whether ARF6 is involved in insulin-regulated exocytosis, 3T3-L1 adipocytes were infected with recombinant adenovirus expressing wild-type ARF6 or an ARF6 dominant negative mutant (D125N) that encodes a protein with nucleotide specificity modified from guanine to xanthine. Overexpression of these ARF6 proteins affected neither basal nor insulin-regulated glucose uptake in 3T3-L1 adipocytes, nor did it affect the subcellular distribution of Glut1 or Glut4. In contrast, the secretion of adipsin, a serine protease specifically expressed in adipocytes, was increased by the expression of wild-type ARF6 and was inhibited by the expression of D125N. These results indicate a requirement for ARF6 in basal and insulin-regulated adipsin secretion but not in glucose transport. Our results suggest the existence of at least two distinct pathways that undergo insulin-stimulated exocytosis in 3T3-L1 adipocytes, one for adipsin release and one for glucose transporter translocation.
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Affiliation(s)
- C Z Yang
- Department of Cell Biology and Physiology, Washington University School of Medicine, St. Louis, Missouri 63110, USA
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Frohman MA, Sung TC, Morris AJ. Mammalian phospholipase D structure and regulation. BIOCHIMICA ET BIOPHYSICA ACTA 1999; 1439:175-86. [PMID: 10425394 DOI: 10.1016/s1388-1981(99)00093-1] [Citation(s) in RCA: 234] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The recent identification of cDNA clones for phospholipase D1 and 2 has opened the door to new studies on its structure and regulation. PLD activity is encoded by at least two different genes that contain catalytic domains that relate their mechanism of action to phosphodiesterases. In vivo roles for PLD suggest that it may be important for multiple specialized steps in receptor dependent and constitutive processes of secretion, endocytosis, and membrane biogenesis.
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Affiliation(s)
- M A Frohman
- Department of Pharmacological Sciences, Institute for Cell and Developmental Biology, SUNY at Stony Brook, Stony Brook, NY 1794-8651, USA.
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48
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Liscovitch M, Czarny M, Fiucci G, Lavie Y, Tang X. Localization and possible functions of phospholipase D isozymes. BIOCHIMICA ET BIOPHYSICA ACTA 1999; 1439:245-63. [PMID: 10425399 DOI: 10.1016/s1388-1981(99)00098-0] [Citation(s) in RCA: 117] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
The activation of PLD is believed to play an important role in the regulation of cell function and cell fate by extracellular signal molecules. Multiple PLD activities have been characterized in mammalian cells and, more recently, several PLD genes have been cloned. Current evidence indicates that diverse PLD activities are localized in most, if not all, cellular organelles, where they are likely to subserve different functions in signal transduction, membrane vesicle trafficking and cytoskeletal dynamics.
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Affiliation(s)
- M Liscovitch
- Department of Biological Regulation, Weizmann Institute of Science, Rehovot 76100, Israel
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49
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Larner J, Allan G, Kessler C, Reamer P, Gunn R, Huang LC. Phosphoinositol glycan derived mediators and insulin resistance. Prospects for diagnosis and therapy. J Basic Clin Physiol Pharmacol 1999; 9:127-37. [PMID: 10212830 DOI: 10.1515/jbcpp.1998.9.2-4.127] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
While much work remains, the evidence has become strong that IPG generation following insulin action is a significant signaling mechanism. A considerable body of data has established IPG release by insulin and other growth factors from cell membranes, cells and in human blood and muscle biopsies in vivo. Two separate IPG species containing D-chiro-inositol and myo-inositol have been separated by ion exchange. These IPGs have separate actions in vitro and are both active as insulin surrogates in vivo. A deficiency of the chiro-inositol system has been demonstrated in urine and tissues in humans and directly related to insulin resistance. Accordingly, D-chiro-inositol was administered to STZ diabetic rats and rhesus monkeys and shown to decrease hyperglycemia and enhance glucose disposal. Two trials in humans with impaired glucose tolerance and women with PCOS have now also proven successful. Thus, the pathophysiology in the chiro-inositol system related to insulin resistance and its reversal by chiro-inositol administration, in addition to the basic work, argues strongly for the physiological significance of this novel signaling system in the control of glucose metabolism.
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Affiliation(s)
- J Larner
- Department of Pharmacology, University of Virginia School of Medicine, Charlottesville 22908, USA
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50
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Abstract
Insulin modulates many intracellular processes including cellular metabolism, cell proliferation and cell differentiation. Some of these processes involve significant changes in the traffic of intracellular vesicles or in the structural organization of the cell. These phenomena have been linked to the activity of regulatory GTP-binding proteins. Most, if not all functions, of the insulin receptor are associated with its tyrosine kinase activity. Thus, over the past few years, a significant effort has been dedicated to elucidate the cross-talk between the tyrosine kinase activity of the receptor and the regulation of G protein-mediated pathways. Recent progress indicates that G proteins may mediate the control of several of insulin's intracellular functions. These include the regulation of the MAP kinase pathway, the activation of phospholipase D and the regulation of glucose uptake. This article discusses some recent advances in this area.
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Affiliation(s)
- M A Rizzo
- Department of Pharmacology, University of Pittsburgh School of Medicine, PA 15261, USA
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