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Kang H, Kang T, Jackson L, Murphy A, Nitta T. Evidence for Involvement of ADP-Ribosylation Factor 6 in Intracellular Trafficking and Release of Murine Leukemia Virus Gag. Cells 2024; 13:270. [PMID: 38334661 PMCID: PMC10854678 DOI: 10.3390/cells13030270] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2023] [Revised: 01/29/2024] [Accepted: 01/29/2024] [Indexed: 02/10/2024] Open
Abstract
Murine leukemia viruses (MuLVs) are simple retroviruses that cause several diseases in mice. Retroviruses encode three basic genes: gag, pol, and env. Gag is translated as a polyprotein and moves to assembly sites where viral particles are shaped by cleavage of poly-Gag. Viral release depends on the intracellular trafficking of viral proteins, which is determined by both viral and cellular factors. ADP-ribosylation factor 6 (Arf6) is a small GTPase that regulates vesicular trafficking and recycling of different types of cargo in cells. Arf6 also activates phospholipase D (PLD) and phosphatidylinositol-4-phosphate 5-kinase (PIP5K) and produces phosphatidylinositol-4,5-bisphosphate (PI(4,5)P2). We investigated how Arf6 affected MuLV release with a constitutively active form of Arf6, Arf6Q67L. Expression of Arf6Q67L impaired Gag release by accumulating Gag at PI(4,5)P2-enriched compartments in the cytoplasm. Treatment of the inhibitors for PLD and PIP5K impaired or recovered MuLV Gag release in the cells expressing GFP (control) and Arf6Q67L, implying that regulation of PI(4,5)P2 through PLD and PIP5K affected MuLV release. Interference with the phosphoinositide 3-kinases, mammalian target of rapamycin (mTOR) pathway, and vacuolar-type ATPase activities showed further impairment of Gag release from the cells expressing Arf6Q67L. In contrast, mTOR inhibition increased Gag release in the control cells. The proteasome inhibitors reduced viral release in the cells regardless of Arf6Q67L expression. These data outline the differences in MuLV release under the controlled and overactivated Arf6 conditions and provide new insight into pathways for MuLV release.
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Affiliation(s)
- Hyokyun Kang
- Department of Biology, Savannah State University, Savannah, GA 31404, USA; (H.K.); (T.K.); (L.J.); (A.M.)
| | - Taekwon Kang
- Department of Biology, Savannah State University, Savannah, GA 31404, USA; (H.K.); (T.K.); (L.J.); (A.M.)
| | - Lauryn Jackson
- Department of Biology, Savannah State University, Savannah, GA 31404, USA; (H.K.); (T.K.); (L.J.); (A.M.)
| | - Amaiya Murphy
- Department of Biology, Savannah State University, Savannah, GA 31404, USA; (H.K.); (T.K.); (L.J.); (A.M.)
| | - Takayuki Nitta
- Department of Biology, Savannah State University, Savannah, GA 31404, USA; (H.K.); (T.K.); (L.J.); (A.M.)
- Department of Molecular Biology and Biochemistry, Cancer Research Institute, University of California, Irvine, CA 92697, USA
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Li Y, Li X, Yang Y, Li F, Chen Q, Zhao Z, Zhang N, Li H. Hepatocyte growth factor attenuates high glucose-disturbed mitochondrial dynamics in podocytes by decreasing ARF6-dependent DRP1 translocation. Biochim Biophys Acta Mol Cell Res 2024; 1871:119623. [PMID: 37913847 DOI: 10.1016/j.bbamcr.2023.119623] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/11/2023] [Revised: 10/23/2023] [Accepted: 10/24/2023] [Indexed: 11/03/2023]
Abstract
Diabetic nephropathy (DN), one of the most common complications of Diabetes Mellitus, is the leading cause of end-stage renal diseases worldwide. Our previous study proved that hepatocyte growth factor (HGF) alleviated renal damages in mice with type 1 Diabetes Mellitus by suppressing overproduction of reactive oxygen species (ROS) in podocytes, while the further mechanism of how HGF lessens ROS production had not been clarified yet. ADP-ribosylation factor 6 (ARF6), the member of the small GTPases superfamilies, is widely spread among epithelial cells and can be activated by the HGF/c-Met signaling. Thus, this study was aimed to explore whether HGF could function on mitochondrial homeostasis, the main resource of ROS, in podocytes exposed to diabetic conditions via ARF6 activation. Our in vivo data showed that HGF markedly ameliorated the pathological damages in kidneys of db/db mice, especially the sharp decline of podocyte number, which was mostly blocked by the ARF6 inhibitor SecinH3. Correspondingly, our in vitro data revealed that HGF protected against high glucose-induced podocyte injuries by increasing ARF6 activity. Besides, this ARF6-dependent beneficial effect of HGF on podocytes was accompanied by improved mitochondrial dynamics and declined DRP1 translocation from cytosol to mitochondria. Collectively, our findings confirm the ability of HGF maintaining mitochondrial homeostasis in diabetic podocytes via decreasing ARF6-dependent DRP1 translocation and shed light on the novel mechanism of HGF treatment for DN.
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Affiliation(s)
- Yankun Li
- Department of Pathology, School of Basic Medical Sciences, Fudan University, Shanghai 200032, China
| | - Xue Li
- Department of Pathology, School of Basic Medical Sciences, Fudan University, Shanghai 200032, China
| | - Yuling Yang
- Department of Pathology, School of Basic Medical Sciences, Fudan University, Shanghai 200032, China
| | - Fengxia Li
- Department of Pathology, School of Basic Medical Sciences, Fudan University, Shanghai 200032, China
| | - Qi Chen
- Department of Pathology, School of Basic Medical Sciences, Fudan University, Shanghai 200032, China
| | - Zhonghua Zhao
- Department of Pathology, School of Basic Medical Sciences, Fudan University, Shanghai 200032, China
| | - Nong Zhang
- Department of Pathology, School of Basic Medical Sciences, Fudan University, Shanghai 200032, China
| | - Hui Li
- Department of Pathology, School of Basic Medical Sciences, Fudan University, Shanghai 200032, China.
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Zhu Y, Wang X, He Z, Zhao P, Ren H, Qi Z. Enterovirus 71 enters human brain microvascular endothelial cells through an ARF6-mediated endocytic pathway. J Med Virol 2023; 95:e28915. [PMID: 37417384 DOI: 10.1002/jmv.28915] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2023] [Revised: 05/08/2023] [Accepted: 06/02/2023] [Indexed: 07/08/2023]
Abstract
Infection of the central nervous system caused by enterovirus 71 (EV71) remains the main cause of death in hand-foot-and-mouth disease. However, the mechanism responsible for how EV71 breaks through the blood-brain barrier to infect brain cells has yet to be elucidated. By performing a high-throughput small interfering RNA (siRNA) screening and validation, we found that the infection of human brain microvascular endothelial cells (HBMECs) by EV71 was independent of the endocytosis pathways mediated by caveolin, clathrin, and macropinocytosis but dependent on ADP-ribosylation factor 6 (ARF6), a small guanosinetriphosphate (GTP)-binding protein of the Ras superfamily. The specific siRNA targeting ARF6 markedly inhibited HBMECs susceptibility to EV71. EV71 infectivity was inhibited by NAV-2729, a specific inhibitor of ARF6, in a dose-dependent manner. The subcellular analysis demonstrated the co-localization of the endocytosed EV71 and ARF6, while knockdown of ARF6 with siRNA remarkably influenced EV71 endocytosis. By immunoprecipitation assays, we found a direct interaction of ARF6 with EV71 viral protein. Furthermore, ARF1, another small GTP-binding protein, was also found to participate in ARF6-mediated EV71 endocytosis. Murine experiments demonstrated that NAV-2729 significantly alleviated mortality caused by EV71 infection. Our study revealed a new pathway by which EV71 enters the HBMECs and provides new targets for drug development.
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Affiliation(s)
- Yongzhe Zhu
- Department of Microbiology, Faculty of Naval Medicine, Naval Medical University, Shanghai, China
| | - Xiaohang Wang
- Department of Microbiology, Faculty of Naval Medicine, Naval Medical University, Shanghai, China
| | - Zhiwei He
- Department of Microbiology, Faculty of Naval Medicine, Naval Medical University, Shanghai, China
| | - Ping Zhao
- Department of Microbiology, Faculty of Naval Medicine, Naval Medical University, Shanghai, China
| | - Hao Ren
- Department of Microbiology, Faculty of Naval Medicine, Naval Medical University, Shanghai, China
| | - Zhongtian Qi
- Department of Microbiology, Faculty of Naval Medicine, Naval Medical University, Shanghai, China
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Zhang J, Yao Y, Li H, Ye S. miR-28-3p inhibits prostate cancer cell proliferation, migration and invasion, and promotes apoptosis by targeting ARF6. Exp Ther Med 2021; 22:1205. [PMID: 34584550 PMCID: PMC8422405 DOI: 10.3892/etm.2021.10639] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2019] [Accepted: 06/28/2021] [Indexed: 12/24/2022] Open
Abstract
Previous studies have reported that the expression levels of microRNA (miR)-28-3p are downregulated in prostate cancer (PCa) compared with those in adjacent normal tissues. However, to the best of our knowledge, the function and underlying mechanisms of miR-28-3p in PCa have not been reported. The present study aimed to explore the role of miR-28-3p and its mechanism in the development of PCa. In the present study, miR-28-3p and ADP-ribosylation factor 6 (ARF6) expression levels were analyzed using reverse transcription-quantitative PCR (RT-qPCR). Cell proliferation, colony formation, apoptosis, migration and invasion were determined using Cell Counting Kit-8, colony forming, flow cytometry and Transwell assays, respectively. The association between miR-28-3p and ARF6 was investigated using a dual luciferase reporter assay. ARF6, Rac1, Erk1/2 and phosphorylated (p)-Erk1/2 protein expression levels were analyzed using western blotting. The results of the present study revealed that miR-28-3p expression levels were downregulated, whereas ARF6 expression levels were upregulated in PCa cell lines (LNCaP, 22Rv-1, PC-3 and DU145) compared with those in the normal prostate line RWPE-1. The overexpression of miR-28-3p promoted cell apoptosis, and inhibited cell proliferation, colony formation, migration and invasion. However, the knockdown of miR-28-3p exerted the opposite results. The results of the dual luciferase reporter assays, RT-qPCR and western blotting indicated that ARF6 was a target gene of miR-28-3p. Finally, rescue experiments demonstrated that ARF6 overexpression attenuated the effects of the miR-28-3p mimic by upregulating Rac1 and p-Erk1/2 expression in PCa cells. In conclusion, these findings indicated that miR-28-3p may inhibit the biological behaviors of PCa cells by targeting ARF6, and therefore may represent a novel therapeutic candidate for PCa.
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Affiliation(s)
- Jiabin Zhang
- Department of Urology, Mindong Hospital Affiliated to Fujian Medical University, Ningde, Fujian 355000, P.R. China
| | - Yi Yao
- Department of Urology, Mindong Hospital Affiliated to Fujian Medical University, Ningde, Fujian 355000, P.R. China
| | - Huizhang Li
- Department of Urology, Mindong Hospital Affiliated to Fujian Medical University, Ningde, Fujian 355000, P.R. China
| | - Shihua Ye
- Department of Urology, Mindong Hospital Affiliated to Fujian Medical University, Ningde, Fujian 355000, P.R. China
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Wang S, Wang T, Gu P. microRNA-145-5p Inhibits Migration, Invasion, and Metastasis in Hepatocellular Carcinoma by Inhibiting ARF6. Cancer Manag Res 2021; 13:3473-3484. [PMID: 33907470 PMCID: PMC8071082 DOI: 10.2147/cmar.s300678] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2021] [Accepted: 04/02/2021] [Indexed: 12/17/2022] Open
Abstract
Purpose Hepatocellular carcinoma (HCC) has the fourth highest rate of mortality among the different types of cancer worldwide. This study aimed to investigate the functions of microRNA-145-5p and AFR6 on migration, invasion and metastasis in HCC. Methods A total of 150 pairs of tumor and their matched adjacent nontumor liver tissues were collected from HCC patients. Expressions of microRNA-145-5p and AFR6 were measured by real-time PCR in HCC tissues and in HCC cell lines. The correlations between microRNA-145-5p and HCC prognosis were investigated. The proliferation, migration, invasion, cell cycle progression, and apoptosis of HCCLM3 cells were evaluated with CCK8, wound healing, transwell, and flow cytometric experiments. Results The expression of miR-145-5p was confirmed to be downregulated not only in HCC tissues but also in several HCC cell lines compared with normal controls. A low expression level of miR-145-5p was notably associated with poor prognosis in patients with HCC and certain characteristics of metastatic tumors. In vitro, miR-145-5p negatively regulated cell proliferation, migration, and invasion and induced apoptosis in HCCLM3 cells. Subsequent experiments further verified that ARF6 is a novel target of miR-145-5p and is significantly overexpressed in HCC tissues. Overexpression of ARF6 circumvented the effects of miR-145-5p in HCCLM3 cells. Conclusion miR-145-5p may play a pivotal role in HCC metastasis via regulating ARF6, and these findings may both provide further insights into the key factors of HCC metastasis and prove to be useful in the development of novel treatment options for HCC.
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Affiliation(s)
- Shuo Wang
- Department of Orthopedics Surgery, The First Affiliated Hospital, Zhejiang University School of Medicine, Hangzhou, Zhejiang, 310006, People's Republic of China
| | - Tianjiao Wang
- Zhejiang Provincial Center for Disease Control and Prevention, Hangzhou, Zhejiang, 310051, People's Republic of China
| | - Pengcheng Gu
- Department of Orthopedics Surgery, The First Affiliated Hospital, Zhejiang University School of Medicine, Hangzhou, Zhejiang, 310006, People's Republic of China
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Nakamura Y, Dryanovski DI, Kimura Y, Jackson SN, Woods AS, Yasui Y, Tsai SY, Patel S, Covey DP, Su TP, Lupica CR. Cocaine-induced endocannabinoid signaling mediated by sigma-1 receptors and extracellular vesicle secretion. eLife 2019; 8:e47209. [PMID: 31596232 PMCID: PMC6850780 DOI: 10.7554/elife.47209] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2019] [Accepted: 10/03/2019] [Indexed: 12/24/2022] Open
Abstract
Cocaine is an addictive drug that acts in brain reward areas. Recent evidence suggests that cocaine stimulates synthesis of the endocannabinoid 2-arachidonoylglycerol (2-AG) in midbrain, increasing dopamine neuron activity via disinhibition. Although a mechanism for cocaine-stimulated 2-AG synthesis is known, our understanding of 2-AG release is limited. In NG108 cells and mouse midbrain tissue, we find that 2-AG is localized in non-synaptic extracellular vesicles (EVs) that are secreted in the presence of cocaine via interaction with the chaperone protein sigma-1 receptor (Sig-1R). The release of EVs occurs when cocaine causes dissociation of the Sig-1R from ADP-ribosylation factor (ARF6), a G-protein regulating EV trafficking, leading to activation of myosin light chain kinase (MLCK). Blockade of Sig-1R function, or inhibition of ARF6 or MLCK also prevented cocaine-induced EV release and cocaine-stimulated 2-AG-modulation of inhibitory synapses in DA neurons. Our results implicate the Sig-1R-ARF6 complex in control of EV release and demonstrate that cocaine-mediated 2-AG release can occur via EVs.
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Affiliation(s)
- Yoki Nakamura
- Cellular Pathobiology Section, Intramural Research ProgramNational Institute on Drug Abuse, National Institutes of HealthBaltimoreUnited States
| | - Dilyan I Dryanovski
- Electrophysiology Research Section, Intramural Research ProgramNational Institute on Drug Abuse, National Institutes of HealthBaltimoreUnited States
| | - Yuriko Kimura
- Cellular Pathobiology Section, Intramural Research ProgramNational Institute on Drug Abuse, National Institutes of HealthBaltimoreUnited States
| | - Shelley N Jackson
- Structural Biology Unit, Intramural Research ProgramNational Institute on Drug Abuse, National Institutes of HealthBaltimoreUnited States
| | - Amina S Woods
- Structural Biology Unit, Intramural Research ProgramNational Institute on Drug Abuse, National Institutes of HealthBaltimoreUnited States
| | - Yuko Yasui
- Cellular Pathobiology Section, Intramural Research ProgramNational Institute on Drug Abuse, National Institutes of HealthBaltimoreUnited States
| | - Shang-Yi Tsai
- Cellular Pathobiology Section, Intramural Research ProgramNational Institute on Drug Abuse, National Institutes of HealthBaltimoreUnited States
| | - Sachin Patel
- Cellular Pathobiology Section, Intramural Research ProgramNational Institute on Drug Abuse, National Institutes of HealthBaltimoreUnited States
- Department of Psychiatry and Behavioral Sciences, Vanderbilt Brain InstituteVanderbilt University Medical Center, Vanderbilt UniversityNashvilleUnited States
| | - Daniel P Covey
- Department of Anatomy and NeurobiologyUniversity of Maryland School of MedicineBaltimoreUnited States
| | - Tsung-Ping Su
- Cellular Pathobiology Section, Intramural Research ProgramNational Institute on Drug Abuse, National Institutes of HealthBaltimoreUnited States
| | - Carl R Lupica
- Electrophysiology Research Section, Intramural Research ProgramNational Institute on Drug Abuse, National Institutes of HealthBaltimoreUnited States
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Qiu J, Tao L, Wei Q, Zhang P. Knockdown of Arf6 increases drug sensitivity and inhibits proliferation, migration and invasion in gastric cancer SGC-7901 cells. Oncol Lett 2017; 15:2147-2152. [PMID: 29434918 PMCID: PMC5777091 DOI: 10.3892/ol.2017.7558] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2017] [Accepted: 11/02/2017] [Indexed: 12/13/2022] Open
Abstract
ADP-ribosylation factor 6 (Arf6), a member of the ADP-ribosylation factor family, is overexpressed in different types of cancer cell and promotes invasion, metastasis and drug resistance. However, the potential functions of Arf6 in gastric cancer (GC), and the molecular mechanism underlying these functions, remain to be fully elucidated. In the present study, the results demonstrated that in vitro knockdown of Arf6 decreased proliferation, colony formation, migration and invasion in SGC-7901 cells. Arf6 knockdown also markedly decreased the activity of the extracellular signal-regulated kinase 1/2 (ERK1/2) signaling pathway. Furthermore, knockdown of Arf6 was associated with elevated chemosensitivity of SGC-7901 cells to 5-fluorouracil through inactivation of the ERK1/2 signaling pathway. Taken together, these results suggest that Arf6 is involved in regulating proliferation, migration, invasion and drug resistance in GC, and may be a potential therapeutic target for the treatment of GC.
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Affiliation(s)
- Junlan Qiu
- Department of General Surgery, Nanjing Drum Tower Hospital Clinical College, Nanjing Medical University, Nanjing, Jiangsu 210008, P.R. China
| | - Liang Tao
- Department of General Surgery, Nanjing Drum Tower Hospital Clinical College, Nanjing Medical University, Nanjing, Jiangsu 210008, P.R. China
| | - Qiang Wei
- Nanjing Emergency Medical Center, Nanjing, Jiangsu 210003, P.R. China
| | - Pingyang Zhang
- Department of Cardiovascular Ultrasound, Nanjing First Hospital Affiliated to Nanjing Medical University, Nanjing, Jiangsu 210006, P.R. China
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Wang L, Li H, Zhou Y, Qin Y, Wang Y, Liu B, Qian H. Molecular cloning and characterization of an ADP-ribosylation factor 6 gene (ptARF6) from Pisolithus tinctorius. Can J Microbiol 2016; 62:383-93. [PMID: 26928195 DOI: 10.1139/cjm-2015-0550] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
ADP-ribosylation factor 6 (ARF6) is an evolutionarily conserved molecule that has an essential function in intracellular trafficking and organelle structure. To better understand its role during presymbiosis between plant roots and compatible filamentous fungi, the full-length cDNA sequence of ARF6 from Pisolithus tinctorius was cloned and a variety of bioinformatics analyses performed. The full-length sequence was 849 bp long and contained a 549 bp open reading frame encoding a protein of 182 amino acids. A phylogenetic analysis showed that ptARF6 was the ortholog of the ADP ribosylation factor 6/GTPase SAR1 gene from the white-rot basidiomycete Trametes versicolor. A domain architecture analysis of the ARF6 protein revealed a repeat region, which is a common feature of ARF6 in other species. Recombinant ARF6 protein was expressed with an N-terminal 6×His tag and purified using Ni(2+)-NTA affinity chromatography. The molecular mass of the recombinant protein was estimated by SDS-PAGE to be 25 kDa. The recombinant ARF6 protein bound strongly to 18:1 and 18:2 phosphatidic acids. Thus, ARF6 may participate in the signaling pathways involved in membrane phospholipid composition. The intracellular distribution of ptADP6 in HEK239T cells also indicates that ptADP6 may function not only in plasma membrane events but also in endosomal membranes events. Real-time quantitative PCR revealed that the differential expression of ptARF6 was associated with the presymbiotic stage. ptARF6 may be induced by presymbiosis during the regulation of mycorrhizal formation.
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Affiliation(s)
- Liling Wang
- a Zhejiang Forestry Academy, Zhejiang Provincial Key Laboratory of Forest Food, Hangzhou, 310023, People's Republic of China
| | - Haibo Li
- a Zhejiang Forestry Academy, Zhejiang Provincial Key Laboratory of Forest Food, Hangzhou, 310023, People's Republic of China
| | - Yifeng Zhou
- b Zhejiang University of Science and Technology, Hangzhou, 310023, People's Republic of China
| | - Yuchuan Qin
- a Zhejiang Forestry Academy, Zhejiang Provincial Key Laboratory of Forest Food, Hangzhou, 310023, People's Republic of China
| | - Yanbin Wang
- a Zhejiang Forestry Academy, Zhejiang Provincial Key Laboratory of Forest Food, Hangzhou, 310023, People's Republic of China
| | - Bentong Liu
- a Zhejiang Forestry Academy, Zhejiang Provincial Key Laboratory of Forest Food, Hangzhou, 310023, People's Republic of China
| | - Hua Qian
- a Zhejiang Forestry Academy, Zhejiang Provincial Key Laboratory of Forest Food, Hangzhou, 310023, People's Republic of China
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van den Bosch MTJ, Poole AW, Hers I. Cytohesin-2 phosphorylation by protein kinase C relieves the constitutive suppression of platelet dense granule secretion by ADP-ribosylation factor 6. J Thromb Haemost 2014; 12:726-35. [PMID: 24581425 PMCID: PMC4238808 DOI: 10.1111/jth.12542] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2013] [Accepted: 02/19/2014] [Indexed: 11/30/2022]
Abstract
BACKGROUND Protein kinase C (PKC) is a major regulator of platelet function and secretion. The underlying molecular pathway from PKC to secretion, however, is poorly understood. By a proteomics screen we identified the guanine nucleotide exchange factor cytohesin-2 as a candidate PKC substrate. OBJECTIVES We aimed to validate cytohesin-2 as a PKC substrate in platelets and to determine its role in granule secretion and other platelet responses. METHODS AND RESULTS Immunoprecipitation was performed with a phosphoserine PKC substrate antibody followed by mass spectrometry, leading to the identification of cytohesin-2. By western blotting we showed that different agonists induced cytohesin-2 phosphorylation by PKC. Protein function was investigated using a pharmacological approach. The cytohesin inhibitor SecinH3 significantly enhanced platelet dense granule secretion and aggregation, as measured by lumi-aggregometry. Flow cytometry data indicate that α-granule release and integrin αII b β3 activation were not affected by cytohesin-2 inhibition. Lysosome secretion was assessed by a colorimetric assay and was also unchanged. As shown by western blotting, ARF6 interacted with cytohesin-2 and was present in an active GTP-bound form under basal conditions. Upon platelet stimulation, this interaction was largely lost and ARF6 activation decreased, both of which could be rescued by PKC inhibition. CONCLUSIONS Cytohesin-2 constitutively suppresses platelet dense granule secretion and aggregation by keeping ARF6 in a GTP-bound state. PKC-mediated phosphorylation of cytohesin-2 relieves this inhibitory effect, thereby promoting platelet secretion and aggregation.
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Abstract
Nucleic acid cellular uptake into endosomes is critical in eliciting nucleotide-sensing toll-like receptors (TLRs) innate immune responses. ADP-ribosylation factor 6 (ARF6) is a member of the Ras superfamily, which is critical to a wide variety of cellular events including endocytosis. Our previous report indicated that ARF6 plays a critical role in CpG ODN/TLR9-mediated responses. Here, we further explored that the basal level of active ARF6 is nonspecifically responsible for initiation of ODNs uptake, which is relatively CpG motif independent. While the initiation of CpG ODN uptake but not GpC ODN uptake can promote TLR9 responses thereby enhancing ARF6 activation which may lead to further nonspecifically increase of cellular uptake of stimulatory CpG ODN as well as nonstimulatory GpC ODN. Because nucleotide-sensing TLR9 plays a role in contributing to immune diseases, selective activation or inhibition of ARF6 might be useful in certain immunological or therapeutic applications.
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Affiliation(s)
- Jing-Yiing Wu
- Institute of Cellular and System Medicine; National Health Research Institutes; Zhunan, Miaoli, Taiwan
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