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Kan YY, Chang YS, Liao WC, Chao TN, Hsieh YL. Roles of Neuronal Protein Kinase Cε on Endoplasmic Reticulum Stress and Autophagic Formation in Diabetic Neuropathy. Mol Neurobiol 2024; 61:2481-2495. [PMID: 37906389 PMCID: PMC11043183 DOI: 10.1007/s12035-023-03716-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2023] [Accepted: 10/14/2023] [Indexed: 11/02/2023]
Abstract
In chronic diabetic neuropathy (DN), the cellular mechanisms of neuropathic pain remain unclear. Protein kinase C epsilon (PKCε) is an intracellular signaling molecule that mediates chronic pain. This paper addresses the long-term upregulated PKCε in DN associated with endoplasmic reticulum (ER) stress and autophagic formation and correlates to chronic neuropathic pain. We found that thermal hyperalgesia and mechanical allodynia course development were associated with PKCε upregulation after DN but not skin denervation. Pathologically, PKCε upregulation was associated with the expression of inositol-requiring enzyme 1α (IRE1α; ER stress-related molecule) and ubiquitin D (UBD), which are involved in the ubiquitin-proteasome system (UPS)-mediated degradation of misfolded proteins under ER stress. Manders coefficient analyses revealed an approximately 50% colocalized ratio for IRE1α(+):PKCε(+) neurons (0.34-0.48 for M1 and 0.40-0.58 for M2 Manders coefficients). The colocalized coefficients of UBD/PKCε increased (M1: 0.33 ± 0.03 vs. 0.77 ± 0.04, p < 0.001; M2: 0.29 ± 0.05 vs. 0.78 ± 0.04; p < 0.001) in the acute DN stage. In addition, the regulatory subunit p85 of phosphoinositide 3-kinase, which is involved in regulating insulin signaling, exhibited similar expression patterns to those of IRE1α and UBD; for example, it had highly colocalized ratios to PKCε. The ultrastructural examination further confirmed that autophagic formation was associated with PKCε upregulation. Furthermore, PKCεv1-2, a PKCε specific inhibitor, reverses neuropathic pain, ER stress, and autophagic formation in DN. This finding suggests PKCε plays an upstream molecule in DN-associated neuropathic pain and neuropathology and could provide a potential therapeutic target.
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Affiliation(s)
- Yu-Yu Kan
- School of Medicine, College of Medicine, National Sun Yat-sen University, Kaohsiung, 80424, Taiwan
| | - Ying-Shuang Chang
- Department of Anatomy, School of Medicine, College of Medicine, Kaohsiung Medical University, Kaohsiung, 80708, Taiwan
| | - Wen-Chieh Liao
- Doctoral Program in Tissue Engineering and Regenerative Medicine, College of Medicine, National Chung Hsing University, Taichung, 40227, Taiwan
- Department of Post-Baccalaureate Medicine, College of Medicine, National Chung Hsing University, Taichung, 40227, Taiwan
| | - Tzu-Ning Chao
- Department of Anatomy, School of Medicine, College of Medicine, Kaohsiung Medical University, Kaohsiung, 80708, Taiwan
| | - Yu-Lin Hsieh
- Department of Anatomy, School of Medicine, College of Medicine, Kaohsiung Medical University, Kaohsiung, 80708, Taiwan.
- School of Post-Baccalaureate Medicine, College of Medicine, Kaohsiung Medical University, Kaohsiung, 80708, Taiwan.
- Department of Medical Research, Kaohsiung Medical University Hospital, Kaohsiung, 80708, Taiwan.
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Totland MZ, Knudsen LM, Rasmussen NL, Omori Y, Sørensen V, Elster VCW, Stenersen JM, Larsen M, Jensen CL, Zickfeldt Lade AA, Bruusgaard E, Basing S, Kryeziu K, Brech A, Aasen T, Lothe RA, Leithe E. The E3 ubiquitin ligase ITCH negatively regulates intercellular communication via gap junctions by targeting connexin43 for lysosomal degradation. Cell Mol Life Sci 2024; 81:171. [PMID: 38597989 PMCID: PMC11006747 DOI: 10.1007/s00018-024-05165-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2023] [Revised: 01/27/2024] [Accepted: 02/05/2024] [Indexed: 04/11/2024]
Abstract
Intercellular communication via gap junctions has a fundamental role in regulating cell growth and tissue homeostasis, and its dysregulation may be involved in cancer development and radio- and chemotherapy resistance. Connexin43 (Cx43) is the most ubiquitously expressed gap junction channel protein in human tissues. Emerging evidence indicates that dysregulation of the sorting of Cx43 to lysosomes is important in mediating the loss of Cx43-based gap junctions in cancer cells. However, the molecular basis underlying this process is currently poorly understood. Here, we identified the E3 ubiquitin ligase ITCH as a novel regulator of intercellular communication via gap junctions. We demonstrate that ITCH promotes loss of gap junctions in cervical cancer cells, which is associated with increased degradation of Cx43 in lysosomes. The data further indicate that ITCH interacts with and regulates Cx43 ubiquitination and that the ITCH-induced loss of Cx43-based gap junctions requires its catalytic HECT (homologous to E6-AP C-terminus) domain. The data also suggest that the ability of ITCH to efficiently promote loss of Cx43-based gap junctions and degradation of Cx43 depends on a functional PY (PPXY) motif in the C-terminal tail of Cx43. Together, these data provide new insights into the molecular basis underlying the degradation of Cx43 and have implications for the understanding of how intercellular communication via gap junctions is lost during cancer development.
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Affiliation(s)
- Max Zachrisson Totland
- Department of Molecular Oncology, Institute for Cancer Research, Oslo University Hospital, Oslo, NO-0424, Norway
| | - Lars Mørland Knudsen
- Department of Molecular Oncology, Institute for Cancer Research, Oslo University Hospital, Oslo, NO-0424, Norway
| | - Nikoline Lander Rasmussen
- Department of Molecular Oncology, Institute for Cancer Research, Oslo University Hospital, Oslo, NO-0424, Norway
- Centre for Molecular Medicine Norway, Faculty of Medicine, Oslo, Norway
| | - Yasufumi Omori
- Department of Molecular and Tumour Pathology, Akita University Graduate School of Medicine, Akita, 010-8543, Japan
| | - Vigdis Sørensen
- Department of Core Facilities, Institute for Cancer Research, Oslo University Hospital, Oslo, NO-0424, Norway
- Centre for Cancer Cell Reprogramming, Faculty of Medicine, University of Oslo, Oslo, 0379, Norway
| | - Vilde C Wivestad Elster
- Department of Molecular Oncology, Institute for Cancer Research, Oslo University Hospital, Oslo, NO-0424, Norway
| | - Jakob Mørkved Stenersen
- Department of Molecular Oncology, Institute for Cancer Research, Oslo University Hospital, Oslo, NO-0424, Norway
| | - Mathias Larsen
- Department of Molecular Oncology, Institute for Cancer Research, Oslo University Hospital, Oslo, NO-0424, Norway
| | - Caroline Lunder Jensen
- Department of Molecular Oncology, Institute for Cancer Research, Oslo University Hospital, Oslo, NO-0424, Norway
| | - Anna A Zickfeldt Lade
- Department of Molecular Oncology, Institute for Cancer Research, Oslo University Hospital, Oslo, NO-0424, Norway
| | - Emilie Bruusgaard
- Department of Molecular Oncology, Institute for Cancer Research, Oslo University Hospital, Oslo, NO-0424, Norway
| | - Sebastian Basing
- Department of Molecular Oncology, Institute for Cancer Research, Oslo University Hospital, Oslo, NO-0424, Norway
| | - Kushtrim Kryeziu
- Department of Molecular Oncology, Institute for Cancer Research, Oslo University Hospital, Oslo, NO-0424, Norway
| | - Andreas Brech
- Department of Core Facilities, Institute for Cancer Research, Oslo University Hospital, Oslo, NO-0424, Norway
- Department of Molecular Cell Biology, Institute for Cancer Research, Oslo University Hospital, Oslo, 0379, Norway
- Department of Biosciences, Faculty of Mathematics and Natural Sciences, Oslo, 0316, Norway
| | - Trond Aasen
- Patologia Molecular Translacional, Vall d'Hebron Institut de Recerca (VHIR), Vall d'Hebron Hospital Universitari, Vall d'Hebron Barcelona Hospital Campus, Passeig Vall d'Hebron 119-129, Barcelona, 08035, Spain
| | - Ragnhild A Lothe
- Department of Molecular Oncology, Institute for Cancer Research, Oslo University Hospital, Oslo, NO-0424, Norway
- Department of Biosciences, Faculty of Mathematics and Natural Sciences, Oslo, 0316, Norway
- Institute of Clinical Medicine, Faculty of Medicine, University of Oslo, Oslo, 0317, Norway
| | - Edward Leithe
- Department of Molecular Oncology, Institute for Cancer Research, Oslo University Hospital, Oslo, NO-0424, Norway
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3
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Pun R, Kim MH, North BJ. Role of Connexin 43 phosphorylation on Serine-368 by PKC in cardiac function and disease. Front Cardiovasc Med 2023; 9:1080131. [PMID: 36712244 PMCID: PMC9877470 DOI: 10.3389/fcvm.2022.1080131] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2022] [Accepted: 12/19/2022] [Indexed: 01/13/2023] Open
Abstract
Intercellular communication mediated by gap junction channels and hemichannels composed of Connexin 43 (Cx43) is vital for the propagation of electrical impulses through cardiomyocytes. The carboxyl terminal tail of Cx43 undergoes various post-translational modifications including phosphorylation of its Serine-368 (S368) residue. Protein Kinase C isozymes directly phosphorylate S368 to alter Cx43 function and stability through inducing conformational changes affecting channel permeability or promoting internalization and degradation to reduce intercellular communication between cardiomyocytes. Recent studies have implicated this PKC/Cx43-pS368 circuit in several cardiac-associated diseases. In this review, we describe the molecular and cellular basis of PKC-mediated Cx43 phosphorylation and discuss the implications of Cx43 S368 phosphorylation in the context of various cardiac diseases, such as cardiomyopathy, as well as the therapeutic potential of targeting this pathway.
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Affiliation(s)
- Renju Pun
- Department of Biomedical Sciences, School of Medicine, Creighton University, Omaha, NE, United States
| | - Michael H. Kim
- CHI Health Heart Institute, School of Medicine, Creighton University, Omaha, NE, United States
| | - Brian J. North
- Department of Biomedical Sciences, School of Medicine, Creighton University, Omaha, NE, United States,*Correspondence: Brian J. North,
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Sychrová E, Yawer A, Labohá P, Basu A, Dydowiczová A, Virmani I, Babica P, Sovadinová I. In vitro testicular toxicity of environmentally relevant endocrine-disrupting chemicals: 2D vs. 3D models of prepubertal Leydig TM3 cells. ENVIRONMENTAL TOXICOLOGY AND PHARMACOLOGY 2022; 93:103869. [PMID: 35550872 DOI: 10.1016/j.etap.2022.103869] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/29/2021] [Revised: 03/22/2022] [Accepted: 04/26/2022] [Indexed: 06/15/2023]
Abstract
The testis is a priority organ for developing alternative models to assess male reproductive health hazards of chemicals. This study characterized a 3D in vitro model of murine prepubertal Leydig TM3 cells with improved expression of steroidogenesis markers suitable for image-based screening of testicular toxicity. This 3D scaffold-free spheroid model was applied to explore the impact of prototypical endocrine-disrupting chemicals (EDCs) and environmental reprotoxicants (benzo[a]pyrene, 2- and 9-methylanthracenes, fluoranthene, triclosan, triclocarban, methoxychlor) on male reproductive health. The results were compared to the male reprotoxicity potential of EDCs assessed in a traditional monolayer (2D) culture. The testicular toxicity was dependent not only on the type of culture (2D vs. 3D models) but also on the duration of exposure. Benzo[a]pyrene and triclocarban were the most active compounds, eliciting cytotoxic effects in prepubertal Leydig cells at low micromolar concentrations, which might be a mechanism contributing to their male reprotoxicity.
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Affiliation(s)
- Eliška Sychrová
- RECETOX, Faculty of Science, Masaryk University, Kotlarska 2, Brno, Czech Republic.
| | - Affiefa Yawer
- RECETOX, Faculty of Science, Masaryk University, Kotlarska 2, Brno, Czech Republic.
| | - Petra Labohá
- RECETOX, Faculty of Science, Masaryk University, Kotlarska 2, Brno, Czech Republic.
| | - Amrita Basu
- RECETOX, Faculty of Science, Masaryk University, Kotlarska 2, Brno, Czech Republic.
| | - Aneta Dydowiczová
- RECETOX, Faculty of Science, Masaryk University, Kotlarska 2, Brno, Czech Republic.
| | - Ishita Virmani
- RECETOX, Faculty of Science, Masaryk University, Kotlarska 2, Brno, Czech Republic.
| | - Pavel Babica
- RECETOX, Faculty of Science, Masaryk University, Kotlarska 2, Brno, Czech Republic.
| | - Iva Sovadinová
- RECETOX, Faculty of Science, Masaryk University, Kotlarska 2, Brno, Czech Republic.
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Applicability of Scrape Loading-Dye Transfer Assay for Non-Genotoxic Carcinogen Testing. Int J Mol Sci 2021; 22:ijms22168977. [PMID: 34445682 PMCID: PMC8396440 DOI: 10.3390/ijms22168977] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2021] [Revised: 07/30/2021] [Accepted: 07/31/2021] [Indexed: 12/27/2022] Open
Abstract
Dysregulation of gap junction intercellular communication (GJIC) is recognized as one of the key hallmarks for identifying non-genotoxic carcinogens (NGTxC). Currently, there is a demand for in vitro assays addressing the gap junction hallmark, which would have the potential to eventually become an integral part of an integrated approach to the testing and assessment (IATA) of NGTxC. The scrape loading-dye transfer (SL-DT) technique is a simple assay for the functional evaluation of GJIC in various in vitro cultured mammalian cells and represents an interesting candidate assay. Out of the various techniques for evaluating GJIC, the SL-DT assay has been used frequently to assess the effects of various chemicals on GJIC in toxicological and tumor promotion research. In this review, we systematically searched the existing literature to gather papers assessing GJIC using the SL-DT assay in a rat liver epithelial cell line, WB-F344, after treating with chemicals, especially environmental and food toxicants, drugs, reproductive-, cardio- and neuro-toxicants and chemical tumor promoters. We discuss findings derived from the SL-DT assay with the known knowledge about the tumor-promoting activity and carcinogenicity of the assessed chemicals to evaluate the predictive capacity of the SL-DT assay in terms of its sensitivity, specificity and accuracy for identifying carcinogens. These data represent important information with respect to the applicability of the SL-DT assay for the testing of NGTxC within the IATA framework.
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Protein Kinase C Regulates ASIC1a Protein Expression and Channel Function via NF-kB Signaling Pathway. Mol Neurobiol 2020; 57:4754-4766. [PMID: 32783140 DOI: 10.1007/s12035-020-02056-4] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2020] [Accepted: 08/03/2020] [Indexed: 10/23/2022]
Abstract
Tissue acidosis is a common feature in many pathological conditions. Activation of acid-sensing ion channel 1a (ASIC1a) plays a key role in acidosis-mediated neurotoxicity. Protein kinase C (PKC) activity has been proved to be associated with many physiological processes and pathological conditions; however, whether PKC activation regulates ASIC1a protein expression and channel function remains ill defined. In this study, we demonstrated that treatment with phorbol 12-myristate 13-acetate (PMA, a PKC activator) for 6 h significantly increased ASIC1a protein expression and ASIC currents in NS20Y cells, a neuronal cell line, and in primary cultured mouse cortical neurons. In contrast, treatment with Calphostin C (a nonselective PKC inhibitor) for 6 h or longer decreased ASIC1a protein expression and ASIC currents. Similar to Calphostin C, PKC α and βI inhibitor Go6976 exposure also reduced ASIC1a protein expression. The reduction in ASIC1a protein expression by PKC inhibition involves a change in ASIC1a protein degradation, which is mediated by ubiquitin-proteasome system (UPS)-dependent degradation pathway. In addition, we showed that PKC regulation of ASIC1a protein expression involves NF-κB signaling pathway. Consistent with their effects on ASIC1a protein expression and channel function, PKC inhibition protected NS20Y cells against acidosis-induced cytotoxicity, while PKC activation potentiated acidosis-induced cells injury. Together, these results indicate that ASIC1a protein expression and channel function are closely regulated by the activity of protein kinase C and its downstream signaling pathway(s).
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7
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Totland MZ, Bergsland CH, Fykerud TA, Knudsen LM, Rasmussen NL, Eide PW, Yohannes Z, Sørensen V, Brech A, Lothe RA, Leithe E. E3 ubiquitin ligase NEDD4 induces endocytosis and lysosomal sorting of connexin43 to promote loss of gap junctions. J Cell Sci 2017; 130:2867-2882. [DOI: 10.1242/jcs.202408] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2017] [Accepted: 07/12/2017] [Indexed: 01/07/2023] Open
Abstract
Intercellular communication via gap junctions has an important role in controlling cell growth and in maintaining tissue homeostasis. Connexin43 is the most abundantly expressed gap junction channel protein in humans and acts as a tumor suppressor in multiple tissue types. Connexin43 is often dysregulated at the post-translational level during cancer development, resulting in loss of gap junctions. However, the molecular basis underlying the aberrant regulation of connexin43 in cancer cells has remained elusive. Here, we demonstrate that the oncogenic E3 ubiquitin ligase NEDD4 regulates the connexin43 protein level in HeLa cells, both under basal conditions and in response to protein kinase C activation. Furthermore, overexpression of NEDD4, but not a catalytically inactive form of NEDD4, was found to result in nearly complete loss of gap junctions and increased lysosomal degradation of connexin43 in both HeLa and C33A cervical carcinoma cells. Collectively, the data provide new insights into the molecular basis underlying the regulation of gap junction size and represent the first evidence that an oncogenic E3 ubiquitin ligase promotes loss of gap junctions and connexin43 degradation in human carcinoma cells.
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Affiliation(s)
- Max Z. Totland
- Department of Molecular Oncology, Institute for Cancer Research, Oslo University Hospital, Oslo, Norway
- Centre for Cancer Biomedicine, Faculty of Medicine, University of Oslo, Oslo, Norway
- Institute for Biosciences, University of Oslo, Oslo, Norway
- K.G. Jebsen Colorectal Cancer Research Centre, Oslo University Hospital, Oslo, Norway
| | - Christian H. Bergsland
- Department of Molecular Oncology, Institute for Cancer Research, Oslo University Hospital, Oslo, Norway
- Centre for Cancer Biomedicine, Faculty of Medicine, University of Oslo, Oslo, Norway
- Institute for Biosciences, University of Oslo, Oslo, Norway
- K.G. Jebsen Colorectal Cancer Research Centre, Oslo University Hospital, Oslo, Norway
| | - Tone A. Fykerud
- Department of Molecular Oncology, Institute for Cancer Research, Oslo University Hospital, Oslo, Norway
- Centre for Cancer Biomedicine, Faculty of Medicine, University of Oslo, Oslo, Norway
- K.G. Jebsen Colorectal Cancer Research Centre, Oslo University Hospital, Oslo, Norway
| | - Lars M. Knudsen
- Department of Molecular Oncology, Institute for Cancer Research, Oslo University Hospital, Oslo, Norway
- Centre for Cancer Biomedicine, Faculty of Medicine, University of Oslo, Oslo, Norway
- Institute for Biosciences, University of Oslo, Oslo, Norway
- K.G. Jebsen Colorectal Cancer Research Centre, Oslo University Hospital, Oslo, Norway
| | - Nikoline L. Rasmussen
- Department of Molecular Oncology, Institute for Cancer Research, Oslo University Hospital, Oslo, Norway
- Centre for Cancer Biomedicine, Faculty of Medicine, University of Oslo, Oslo, Norway
- Institute for Biosciences, University of Oslo, Oslo, Norway
- K.G. Jebsen Colorectal Cancer Research Centre, Oslo University Hospital, Oslo, Norway
| | - Peter W. Eide
- Department of Molecular Oncology, Institute for Cancer Research, Oslo University Hospital, Oslo, Norway
- Centre for Cancer Biomedicine, Faculty of Medicine, University of Oslo, Oslo, Norway
- K.G. Jebsen Colorectal Cancer Research Centre, Oslo University Hospital, Oslo, Norway
| | - Zeremariam Yohannes
- Department of Molecular Oncology, Institute for Cancer Research, Oslo University Hospital, Oslo, Norway
- Centre for Cancer Biomedicine, Faculty of Medicine, University of Oslo, Oslo, Norway
- K.G. Jebsen Colorectal Cancer Research Centre, Oslo University Hospital, Oslo, Norway
| | - Vigdis Sørensen
- Centre for Cancer Biomedicine, Faculty of Medicine, University of Oslo, Oslo, Norway
- Department of Molecular Cell Biology, Institute for Cancer Research, Oslo University Hospital, Oslo, Norway
- Department of Core Facilities, Institute for Cancer Research, Oslo University Hospital, Oslo, Norway
| | - Andreas Brech
- Centre for Cancer Biomedicine, Faculty of Medicine, University of Oslo, Oslo, Norway
- Institute for Biosciences, University of Oslo, Oslo, Norway
- Department of Molecular Cell Biology, Institute for Cancer Research, Oslo University Hospital, Oslo, Norway
- Department of Core Facilities, Institute for Cancer Research, Oslo University Hospital, Oslo, Norway
| | - Ragnhild A. Lothe
- Department of Molecular Oncology, Institute for Cancer Research, Oslo University Hospital, Oslo, Norway
- Centre for Cancer Biomedicine, Faculty of Medicine, University of Oslo, Oslo, Norway
- Institute for Biosciences, University of Oslo, Oslo, Norway
- K.G. Jebsen Colorectal Cancer Research Centre, Oslo University Hospital, Oslo, Norway
| | - Edward Leithe
- Department of Molecular Oncology, Institute for Cancer Research, Oslo University Hospital, Oslo, Norway
- Centre for Cancer Biomedicine, Faculty of Medicine, University of Oslo, Oslo, Norway
- K.G. Jebsen Colorectal Cancer Research Centre, Oslo University Hospital, Oslo, Norway
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Leithe E. Regulation of connexins by the ubiquitin system: Implications for intercellular communication and cancer. Biochim Biophys Acta Rev Cancer 2016; 1865:133-46. [DOI: 10.1016/j.bbcan.2016.02.001] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2015] [Revised: 01/15/2016] [Accepted: 02/04/2016] [Indexed: 12/31/2022]
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Ni M, Ruan L, Zhang C. Antiarrhythmic Peptide AAP10 Prevents Arrhythmias Induced by Protein Kinase C Activation in Rabbit Left Ventricular Wedges. Int Heart J 2015; 56:234-8. [DOI: 10.1536/ihj.14-234] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Affiliation(s)
- Mingke Ni
- Department of Cardiology, Zhongshan Hospital
| | - Lei Ruan
- Department of Gerontology, Tongji Hospital, Tongji Medical College, Huazhong University of Science and Technology
| | - Cuntai Zhang
- Department of Gerontology, Tongji Hospital, Tongji Medical College, Huazhong University of Science and Technology
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Kabátková M, Svobodová J, Pěnčíková K, Mohatad DS, Šmerdová L, Kozubík A, Machala M, Vondráček J. Interactive effects of inflammatory cytokine and abundant low-molecular-weight PAHs on inhibition of gap junctional intercellular communication, disruption of cell proliferation control, and the AhR-dependent transcription. Toxicol Lett 2015; 232:113-21. [DOI: 10.1016/j.toxlet.2014.09.023] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2014] [Revised: 09/23/2014] [Accepted: 09/26/2014] [Indexed: 12/11/2022]
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Cone AC, Cavin G, Ambrosi C, Hakozaki H, Wu-Zhang AX, Kunkel MT, Newton AC, Sosinsky GE. Protein kinase Cδ-mediated phosphorylation of Connexin43 gap junction channels causes movement within gap junctions followed by vesicle internalization and protein degradation. J Biol Chem 2014; 289:8781-98. [PMID: 24500718 PMCID: PMC3979370 DOI: 10.1074/jbc.m113.533265] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2013] [Revised: 01/29/2014] [Indexed: 01/14/2023] Open
Abstract
Phosphorylation of gap junction proteins, connexins, plays a role in global signaling events involving kinases. Connexin43 (Cx43), a ubiquitous and important connexin, has several phosphorylation sites for specific kinases. We appended an imaging reporter tag for the activity of the δ isoform of protein kinase C (PKCδ) to the carboxyl terminus of Cx43. The FRET signal of this reporter is inversely related to the phosphorylation of serine 368 of Cx43. By activating PKC with the phorbol ester phorbol 12,13-dibutyrate (PDBu) or a natural stimulant, UTP, time lapse live cell imaging movies indicated phosphorylated Ser-368 Cx43 separated into discrete domains within gap junctions and was internalized in small vesicles, after which it was degraded by lysosomes and proteasomes. Mutation of Ser-368 to an Ala eliminated the response to PDBu and changes in phosphorylation of the reporter. A phosphatase inhibitor, calyculin A, does not change this pattern, indicating PKC phosphorylation causes degradation of Cx43 without dephosphorylation, which is in accordance with current hypotheses that cells control their intercellular communication by a fast and constant turnover of connexins, using phosphorylation as part of this mechanism.
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Affiliation(s)
- Angela C. Cone
- From the National Center for Microscopy and Imaging Research
| | - Gabriel Cavin
- From the National Center for Microscopy and Imaging Research
| | - Cinzia Ambrosi
- From the National Center for Microscopy and Imaging Research
| | | | | | | | | | - Gina E. Sosinsky
- From the National Center for Microscopy and Imaging Research
- the Department of Neurosciences, University of California, San Diego, California 92093
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NEDD4 is overexpressed in colorectal cancer and promotes colonic cell growth independently of the PI3K/PTEN/AKT pathway. Cell Signal 2012; 25:12-8. [PMID: 22974840 DOI: 10.1016/j.cellsig.2012.08.012] [Citation(s) in RCA: 58] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2012] [Revised: 08/28/2012] [Accepted: 08/30/2012] [Indexed: 11/23/2022]
Abstract
Ubiquitination controls multiple cellular processes relevant to cancer pathogenesis. Using Gene Set Enrichment Analysis of an mRNA transcriptome dataset, we have identified genes encoding components of the ubiquitin system that are differentially expressed in colorectal cancers as compared to normal colonic mucosa. Among the significantly overexpressed genes was NEDD4 (neural precursor cell-expressed developmentally down-regulated 4), the prototype member of the HECT (homologous to E6AP C-terminus) E3 ubiquitin ligase family. Previous studies have shown that NEDD4 may act as an oncoprotein by inducing ubiquitination and degradation of the tumor suppressor protein PTEN (phosphatase and tensin homolog). To investigate its functional importance in colorectal cancer, HCT-15 and LoVo colon cancer cells were depleted of NEDD4 by small interfering RNA. The depletion resulted in reduced growth and altered cell morphology in both cell lines. However, NEDD4 depletion did not affect the PTEN protein level or PI3K/AKT signaling pathway activation. Moreover, ectopic expression of NEDD4 did not influence the PTEN subcellular localization or protein level. Collectively, these data demonstrate that NEDD4 is overexpressed in colorectal cancers, and suggest that NEDD4 promotes growth of colon cancer cells independently of PTEN and PI3K/AKT signaling.
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13
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Kjenseth A, Fykerud TA, Sirnes S, Bruun J, Yohannes Z, Kolberg M, Omori Y, Rivedal E, Leithe E. The gap junction channel protein connexin 43 is covalently modified and regulated by SUMOylation. J Biol Chem 2012; 287:15851-61. [PMID: 22411987 PMCID: PMC3346107 DOI: 10.1074/jbc.m111.281832] [Citation(s) in RCA: 52] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2011] [Revised: 03/02/2012] [Indexed: 11/06/2022] Open
Abstract
SUMOylation is a posttranslational modification in which a member of the small ubiquitin-like modifier (SUMO) family of proteins is conjugated to lysine residues in specific target proteins. Most known SUMOylation target proteins are located in the nucleus, but there is increasing evidence that SUMO may also be a key determinant of many extranuclear processes. Gap junctions consist of arrays of intercellular channels that provide direct transfer of ions and small molecules between adjacent cells. Gap junction channels are formed by integral membrane proteins called connexins, of which the best-studied isoform is connexin 43 (Cx43). Here we show that Cx43 is posttranslationally modified by SUMOylation. The data suggest that the SUMO system regulates the Cx43 protein level and the level of functional Cx43 gap junctions at the plasma membrane. Cx43 was found to be modified by SUMO-1, -2, and -3. Evidence is provided that the membrane-proximal lysines at positions 144 and 237, located in the Cx43 intracellular loop and C-terminal tail, respectively, act as SUMO conjugation sites. Mutations of lysine 144 or lysine 237 resulted in reduced Cx43 SUMOylation and reduced Cx43 protein and gap junction levels. Altogether, these data identify Cx43 as a SUMOylation target protein and represent the first evidence that gap junctions are regulated by the SUMO system.
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Affiliation(s)
- Ane Kjenseth
- From the Department of Cancer Prevention, Institute for Cancer Research, Oslo University Hospital and
- Centre for Cancer Biomedicine, Faculty of Medicine, University of Oslo, 0310 Oslo, Norway and
| | - Tone A. Fykerud
- From the Department of Cancer Prevention, Institute for Cancer Research, Oslo University Hospital and
- Centre for Cancer Biomedicine, Faculty of Medicine, University of Oslo, 0310 Oslo, Norway and
| | - Solveig Sirnes
- From the Department of Cancer Prevention, Institute for Cancer Research, Oslo University Hospital and
- Centre for Cancer Biomedicine, Faculty of Medicine, University of Oslo, 0310 Oslo, Norway and
| | - Jarle Bruun
- From the Department of Cancer Prevention, Institute for Cancer Research, Oslo University Hospital and
- Centre for Cancer Biomedicine, Faculty of Medicine, University of Oslo, 0310 Oslo, Norway and
| | - Zeremariam Yohannes
- From the Department of Cancer Prevention, Institute for Cancer Research, Oslo University Hospital and
- Centre for Cancer Biomedicine, Faculty of Medicine, University of Oslo, 0310 Oslo, Norway and
| | - Matthias Kolberg
- From the Department of Cancer Prevention, Institute for Cancer Research, Oslo University Hospital and
- Centre for Cancer Biomedicine, Faculty of Medicine, University of Oslo, 0310 Oslo, Norway and
| | - Yasufumi Omori
- the Department of Molecular and Tumour Pathology, Akita University School of Medicine, Hondo 010-8543, Akita, Japan
| | - Edgar Rivedal
- From the Department of Cancer Prevention, Institute for Cancer Research, Oslo University Hospital and
- Centre for Cancer Biomedicine, Faculty of Medicine, University of Oslo, 0310 Oslo, Norway and
| | - Edward Leithe
- From the Department of Cancer Prevention, Institute for Cancer Research, Oslo University Hospital and
- Centre for Cancer Biomedicine, Faculty of Medicine, University of Oslo, 0310 Oslo, Norway and
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14
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Fykerud TA, Kjenseth A, Schink KO, Sirnes S, Bruun J, Omori Y, Brech A, Rivedal E, Leithe E. Smad ubiquitination regulatory factor-2 controls gap junction intercellular communication by modulating endocytosis and degradation of connexin43. J Cell Sci 2012; 125:3966-76. [DOI: 10.1242/jcs.093500] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023] Open
Abstract
Gap junctions consist of arrays of intercellular channels that enable adjacent cells to communicate both electrically and metabolically. Gap junction channels are made of a family of integral membrane proteins called connexins, of which the best-studied member is connexin43. Gap junctions are dynamic plasma membrane domains, and connexin43 has a high turnover rate in most tissue types. However, the mechanisms involved in the regulation of connexin43 endocytosis and transport to lysosomes are still poorly understood. Here, we demonstrate by live-cell imaging analysis that treatment of cells with 12-O-tetradecanoylphorbol 13-acetate (TPA) induces endocytosis of subdomains of connexin43 gap junctions. The internalized, connexin43-enriched vesicles were found to fuse with early endosomes, which was followed by transport of connexin43 to the lumen of early endosomes. The HECT E3 ubiquitin ligase smad ubiquitination regulatory factor-2 (Smurf2) was found to be recruited to connexin43 gap junctions in response to TPA treatment. Depletion of Smurf2 by small interfering RNA (siRNA) resulted in enhanced levels of connexin43 gap junctions between adjacent cells and increased gap junction intercellular communication. Smurf2 depletion also counteracted the TPA-induced endocytosis and degradation of connexin43. Collectively, these data identify Smurf2 as a novel regulator of connexin43 gap junctions.
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15
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Yang Y, Cao MH, Wang Q, Yuan DD, Li L, Tao L. The effects of 2-aminoethoxydiphenyl borate and diphenylboronic anhydride on gap junctions composed of Connexin43 in TM₄ sertoli cells. Biol Pharm Bull 2011; 34:1390-7. [PMID: 21881223 DOI: 10.1248/bpb.34.1390] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
2-Aminoethoxydiphenyl borate (2-APB) has recently been demonstrated to inhibit gap junction (GJ) channels, whereas the underlying mechanisms are still unknown. Using mouse TM₄ Sertoli cell which expresses connexin43 (Cx43), we explored the effects of 2-APB and its analogues on dye-coupling through junctional channels formed by Cx43 and on expression of Cx43. Exposure of the cells to 2-APB (1-50 µM) and one of its analogues diphenylboronic anhydride (DPBA) (1-30 µM) for 4 h leads to a significant decrease in dye coupling of GJ in a concentration-dependent manner. The inhibitory effects of 2-APB and DPBA are reversible since decreased GJ coupling resumes after the two compounds are washed out. The disfunction of GJ induced by 2-APB and DPBA is associated with a decrease in total amount of Cx43 protein and number of GJs on the cell membrane. 2-APB and DPBA do not alter Cx43 phosphorylation state and the level of Cx43 mRNA expression. The loss of Cx43 protein is prevented by either lysosomal or proteasomal inhibitor, suggesting that the decrease in Cx43 results from a 2-APB or DPBA-enhanced degradation of Cx43. The present results indicate that 2-APB and DPBA inhibit GJ communication through decreasing Cx43 expression in TM₄ cells.
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Affiliation(s)
- Yan Yang
- Department of Pharmacology, Zhongshan School of Medicine, Sun Yat-Sen University, China
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16
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Ping X, Ma Y, Li Y, Qi C, Sun X, Lv X, Cui C. Essential role of protein kinase C in morphine-induced rewarding memory. Neuropharmacology 2011; 62:959-66. [PMID: 22023848 DOI: 10.1016/j.neuropharm.2011.10.001] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2010] [Revised: 09/30/2011] [Accepted: 10/03/2011] [Indexed: 11/25/2022]
Abstract
Protein kinase C (PKC) is involved in intra-cellular signal transduction in various physiological and pathological processes including substance abuse. In the present study, the role of PKC in morphine-induced rewarding memory was investigated using the conditioned place preference (CPP) model. We found a significant translocation of PKCs from cytosol to membrane component in nucleus accumbens (NAc) of morphine-conditioned rats in a dose-dependent manner. The translocation was reduced gradually with the maintenance of morphine-induced CPP. Specifically, the protein level of PKCγ in membrane of the NAc was increased in morphine CPP rats, and decreased during the attenuation of morphine-induced CPP, while the protein level of PKCγ in cytosol of the NAc showed an opposite change. Furthermore, the PKC translocation inhibitor γV5-3 impaired the morphine-induced CPP when microinjected into the NAc. These findings indicated that PKC, especially the γ isoform, is essential for the acquisition and maintenance of morphine-associated reward memory. This article is part of a Special Issue entitled 'Post-Traumatic Stress Disorder'.
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Affiliation(s)
- Xingjie Ping
- Neuroscience Research Institute, Peking University, 38 Xueyuan Road, Beijing 100191, PR China
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17
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Li S, Lin W, Tchantchou F, Lai R, Wen J, Zhang Y. Protein kinase C mediates peroxynitrite toxicity to oligodendrocytes. Mol Cell Neurosci 2011; 48:62-71. [PMID: 21708260 DOI: 10.1016/j.mcn.2011.06.006] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2011] [Revised: 05/16/2011] [Accepted: 06/08/2011] [Indexed: 12/12/2022] Open
Abstract
Peroxynitrite has been suggested to be the potent oxidant causing toxicity to neurons and oligodendrocytes (OLs). Our previous studies have illustrated that intracellular zinc liberation contributes to peroxynitrite toxicity to mature OLs. In this study, we further investigated the signaling pathways involved in this event and identified protein kinase C (PKC) as an important early signaling molecule. We found that a non-selective PKC inhibitor bisindolylmaleimide-1 blocked OL toxicity induced by a peroxynitrite generator SIN-1 and exogenous zinc. The protective effects were due to its inhibition on ERK1/2 phosphorylation and ROS generation. The same phenomenon was also observed in OLs following prolonged treatment with phorbol 12 myristate 13 acetate (PMA), which downregulates the conventional and the novel PKC isoforms (cPKCs and nPKCs). To determine the role of specific PKC isoforms, we found that a specific nPKC inhibitor rottlerin significantly reduced SIN-1- or zinc-induced toxicity, whereas Go6976, a cPKC inhibitor, reduced OL toxicity triggered by zinc, but not by SIN-1 at high concentrations. Rottlerin was more potent than Go6976 to attenuate ERK1/2 phosphorylation and ROS generation induced by SIN-1 or zinc. Surprisingly, zinc only induced phosphorylation of PKCθ, but not PKCδ. Knockdown of PKCθ using lentiviral shRNA attenuated SIN-1- or zinc-induced toxicity. These results suggest that PKCθ might be the major PKC isoform involved in peroxynitrite and zinc toxicity to mature OLs, and provide a rationale for development of specific inhibitors of PKCθ in the treatment of multiple sclerosis and other neurodegenerative diseases, in which peroxynitrite formation plays a pathogenic role.
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Affiliation(s)
- Shihe Li
- Department of Anatomy, Physiology and Genetics, Uniformed Services University of the Health Sciences, Bethesda, MD 20814, USA
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18
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Remo BF, Qu J, Volpicelli FM, Giovannone S, Shin D, Lader J, Liu FY, Zhang J, Lent DS, Morley GE, Fishman GI. Phosphatase-resistant gap junctions inhibit pathological remodeling and prevent arrhythmias. Circ Res 2011; 108:1459-66. [PMID: 21527737 DOI: 10.1161/circresaha.111.244046] [Citation(s) in RCA: 96] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
RATIONALE Posttranslational phosphorylation of connexin43 (Cx43) has been proposed as a key regulatory event in normal cardiac gap junction expression and pathological gap junction remodeling. Nonetheless, the role of Cx43 phosphorylation in the context of the intact organism is poorly understood. OBJECTIVE To establish whether specific Cx43 phosphorylation events influence gap junction expression and pathological remodeling. METHODS AND RESULTS We generated Cx43 germline knock-in mice in which serines 325/328/330 were replaced with phosphomimetic glutamic acids (S3E) or nonphosphorylatable alanines (S3A). The S3E mice were resistant to acute and chronic pathological gap junction remodeling and displayed diminished susceptibility to the induction of ventricular arrhythmias. Conversely, the S3A mice showed deleterious effects on cardiac gap junction formation and function, developed electric remodeling, and were highly susceptible to inducible arrhythmias. CONCLUSIONS These data demonstrate a mechanistic link between posttranslational phosphorylation of Cx43 and gap junction formation, remodeling, and arrhythmic susceptibility.
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Affiliation(s)
- Benjamin F Remo
- Leon H. Charney Division of Cardiology, New York University School of Medicine, 522 First Ave, Smilow 801, New York, NY 10016, USA
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19
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Protein kinase C: an attractive target for cancer therapy. Cancers (Basel) 2011; 3:531-67. [PMID: 24212628 PMCID: PMC3756376 DOI: 10.3390/cancers3010531] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2010] [Revised: 01/19/2011] [Accepted: 01/26/2011] [Indexed: 12/21/2022] Open
Abstract
Apoptosis plays an important role during all stages of carcinogenesis and the development of chemoresistance in tumor cells may be due to their selective defects in the intracellular signaling proteins, central to apoptotic pathways. Consequently, many studies have focused on rendering the chemotherapy more effective in order to prevent chemoresistance and pre-clinical and clinical data has suggested that protein kinase C (PKC) may represent an attractive target for cancer therapy. Therefore, a complete understanding of how PKC regulates apoptosis and chemoresistance may lead to obtaining a PKC-based therapy that is able to reduce drug dosages and to prevent the development of chemoresistance.
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20
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Leithe E, Kjenseth A, Bruun J, Sirnes S, Rivedal E. Inhibition of connexin 43 gap junction channels by the endocrine disruptor ioxynil. Toxicol Appl Pharmacol 2010; 247:10-7. [PMID: 20510257 DOI: 10.1016/j.taap.2010.05.006] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2010] [Revised: 05/04/2010] [Accepted: 05/11/2010] [Indexed: 10/19/2022]
Abstract
Gap junctions are intercellular plasma membrane domains containing channels that mediate transport of ions, metabolites and small signaling molecules between adjacent cells. Gap junctions play important roles in a variety of cellular processes, including regulation of cell growth and differentiation, maintenance of tissue homeostasis and embryogenesis. The constituents of gap junction channels are a family of trans-membrane proteins called connexins, of which the best-studied is connexin 43. Connexin 43 functions as a tumor suppressor protein in various tissue types and is frequently dysregulated in human cancers. The pesticide ioxynil has previously been shown to act as an endocrine disrupting chemical and has multiple effects on the thyroid axis. Furthermore, both ioxynil and its derivative ioxynil octanoate have been reported to induce tumors in animal bioassays. However, the molecular mechanisms underlying the possible tumorigenic effects of these compounds are unknown. In the present study we show that ioxynil and ioxynil octanoate are strong inhibitors of connexin 43 gap junction channels. Both compounds induced rapid loss of connexin 43 gap junctions at the plasma membrane and increased connexin 43 degradation. Ioxynil octanoate, but not ioxynil, was found to be a strong activator of ERK1/2. The compounds also had different effects on the phosphorylation status of connexin 43. Taken together, the data show that ioxynil and ioxynil octanoate are potent inhibitors of intercellular communication via gap junctions.
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Affiliation(s)
- Edward Leithe
- Department of Cancer Prevention, Institute for Cancer Research, Norwegian Radium Hospital, Oslo University Hospital and Centre for Cancer Biomedicine, University of Oslo, Oslo, Norway
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21
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Deng F, Olesen P, Foldbjerg R, Dang DA, Guo X, Autrup H. Silver nanoparticles up-regulate Connexin43 expression and increase gap junctional intercellular communication in human lung adenocarcinoma cell line A549. Nanotoxicology 2010; 4:186-95. [DOI: 10.3109/17435390903576451] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
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22
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Leithe E, Kjenseth A, Sirnes S, Stenmark H, Brech A, Rivedal E. Ubiquitylation of the gap junction protein connexin-43 signals its trafficking from early endosomes to lysosomes in a process mediated by Hrs and Tsg101. J Cell Sci 2009; 122:3883-93. [PMID: 19808888 DOI: 10.1242/jcs.053801] [Citation(s) in RCA: 76] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
Gap junctions are dynamic plasma membrane domains, and their protein constituents, the connexins, have a high turnover rate in most tissue types. However, the molecular mechanisms involved in degradation of gap junctions have remained largely unknown. Here, we show that ubiquitin is strongly relocalized to connexin-43 (Cx43; also known as Gja1) gap junction plaques in response to activation of protein kinase C. Cx43 remained ubiquitylated during its transition to a Triton X-100-soluble state and along its trafficking to early endosomes. Following internalization, Cx43 partly colocalized with the ubiquitin-binding proteins Hrs (hepatocyte growth factor-regulated tyrosine kinase substrate; also known as Hgs) and Tsg101 (tumor susceptibility gene 101). Depletion of Hrs or Tsg101 by small interfering RNA abrogated trafficking of Cx43 from early endosomes to lysosomes. Under these conditions, Cx43 was able to undergo dephosphorylation and deubiquitylation, locate to the plasma membrane and form functional gap junctions. Simultaneous depletion of Hrs and Tsg101 caused accumulation of a phosphorylated and ubiquitylated subpopulation of Cx43 in early endosomes and in hybrid organelles between partly degraded annular gap junctions and endosomes. Collectively, these data reveal a central role of early endosomes in sorting of ubiquitylated Cx43, and identify Hrs and Tsg101 as crucial regulators of trafficking of Cx43 to lysosomes.
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Affiliation(s)
- Edward Leithe
- Centre for Cancer Biomedicine, Faculty of Medicine, University of Oslo and Institute for Cancer Research, Norwegian Radium Hospital, Oslo University Hospital, Montebello, Oslo, Norway.
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23
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Vinken M, Doktorova T, Decrock E, Leybaert L, Vanhaecke T, Rogiers V. Gap junctional intercellular communication as a target for liver toxicity and carcinogenicity. Crit Rev Biochem Mol Biol 2009; 44:201-22. [PMID: 19635038 DOI: 10.1080/10409230903061215] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Direct communication between hepatocytes, mediated by gap junctions, constitutes a major regulatory platform in the control of liver homeostasis, ranging from hepatocellular proliferation to hepatocyte cell death. Inherent to this pivotal task, gap junction functionality is frequently disrupted upon impairment of the homeostatic balance, as occurs during liver toxicity and carcinogenicity. In the present paper, the deleterious effects of a number of chemical and biological toxic compounds on hepatic gap junctions are discussed, including environmental pollutants, biological toxins, organic solvents, pesticides, pharmaceuticals, peroxides, metals and phthalates. Particular attention is paid to the molecular mechanisms that underlie the abrogation of gap junction functionality. Since hepatic gap junctions are specifically targeted by tumor promoters and epigenetic carcinogens, both in vivo and in vitro, inhibition of gap junction functionality is considered as a suitable indicator for the detection of nongenotoxic hepatocarcinogenicity.
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Affiliation(s)
- Mathieu Vinken
- Department of Toxicology, Faculty of Medicine and Pharmacy, Vrije Universiteit Brussel, Brussels, Belgium.
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24
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Interplay between PKC and the MAP kinase pathway in Connexin43 phosphorylation and inhibition of gap junction intercellular communication. Biochem Biophys Res Commun 2009; 382:41-5. [PMID: 19258009 DOI: 10.1016/j.bbrc.2009.02.141] [Citation(s) in RCA: 72] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2009] [Accepted: 02/21/2009] [Indexed: 11/22/2022]
Abstract
Gap junction channels are made of a family proteins called connexins. The best-studied type of connexin, Connexin43 (Cx43), is phosphorylated at several sites in its C-terminus. The tumor-promoting phorbol ester TPA strongly inhibits Cx43 gap junction channels. In this study we have investigated mechanisms involved in TPA-induced phosphorylation of Cx43 and inhibition of gap junction channels. The data show that TPA-induced inhibition of gap junction intercellular communication (GJIC) is dependent on both PKC and the MAP kinase pathway. The data suggest that PKC-induced activation of MAP kinase partly involves Src-independent trans-activation of the EGF receptor, and that TPA-induced shift in SDS-PAGE gel mobility of Cx43 is caused by MAP kinase phosphorylation, whereas phosphorylation of S368 by PKC does not alter gel migration of Cx43. We also show that TPA, in addition to phosphorylation of S368, also induces phosphorylation of S255 and S262, in a MAP kinase-dependent manner. The data add to our understanding of the molecular mechanisms involved in the interplay between signaling pathways in regulation of GJIC.
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25
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Sirnes S, Leithe E, Rivedal E. The detergent resistance of Connexin43 is lost upon TPA or EGF treatment and is an early step in gap junction endocytosis. Biochem Biophys Res Commun 2008; 373:597-601. [PMID: 18601906 DOI: 10.1016/j.bbrc.2008.06.095] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2008] [Accepted: 06/19/2008] [Indexed: 10/21/2022]
Abstract
Gap junctions are plasma membrane domains containing channels that directly connect the cytosols of neighbouring cells. Gap junction channels are made of a family of transmembrane proteins called connexins, of which the best studied is Connexin43 (Cx43). MAP kinase-induced phosphorylation of Cx43 has previously been shown to cause inhibition of gap junction channel permeability and increased Cx43 endocytosis. As Cx43 assembles into gap junction plaques, Cx43 acquires detergent resistance. Here we report that the detergent resistance is lost after activation of MAP kinase. Treatment of IAR20 rat liver epithelial cells with 12-O-tetradecanoylphorbol 13-acetate (TPA) or epidermal growth factor (EGF) caused a rapid increase in the solubility of Cx43 in Triton X-100. This process was mediated by MAP kinase and was initiated at the plasma membrane. The data suggest that loss of the detergent resistance of Cx43 is an early step in TPA- and EGF-induced endocytosis of gap junctions.
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Affiliation(s)
- Solveig Sirnes
- Department of Cancer Prevention, The Norwegian Radium Hospital, Rikshospitalet, Montebello, Oslo, Norway
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26
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Bellei B, Mastrofrancesco A, Briganti S, Aspite N, Ale-Agha N, Sies H, Picardo M. Ultraviolet A induced modulation of gap junctional intercellular communication by P38 MAPK activation in human keratinocytes. Exp Dermatol 2008; 17:115-24. [DOI: 10.1111/j.1600-0625.2007.00662.x] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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27
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PKC signaling in oxidative hepatic damage. Mol Aspects Med 2007; 29:36-42. [PMID: 18035409 DOI: 10.1016/j.mam.2007.09.001] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2007] [Accepted: 09/28/2007] [Indexed: 12/16/2022]
Abstract
Protein kinase C (PKC) is a family of isoenzymes differently involved in cell response to injury and many studies describe their role as "stress sensors". Oxidative stress is strictly involved in the pathogenesis of chronic liver diseases including alcohol- or drug-induced hepatotoxicity, iron overload, hepatitis and hepatocarcinoma development, but molecular mechanisms are not really defined. A crucial role of PKC as a redox sensitive signaling molecule has been widely accepted.
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28
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Wu J, Lin L, Luan T, Chan Gilbert YS, Lan C. Effects of organophosphorus pesticides and their ozonation byproducts on gap junctional intercellular communication in rat liver cell line. Food Chem Toxicol 2007; 45:2057-63. [PMID: 17601646 DOI: 10.1016/j.fct.2007.05.006] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2006] [Revised: 12/13/2006] [Accepted: 05/10/2007] [Indexed: 11/22/2022]
Abstract
The effects of organophosphorus pesticides (OPs), oxons and their ozonation byproducts on gap junctional intercellular communication (GJIC) on cultured BRL cell line were investigated using scrape loading and dye transfer (SL/DT) technique. The neutral red uptake assay was used to identify the non-cytotoxic levels of diazinon, parathion and methyl-parathion applied to GJIC assay. The concentration-dependent inhibition of GJIC was observed over a range of 50-350 mg/l diazinon, parathion and methyl-parathion after 90 min incubation compared with the vehicle control. However, oxons and ozonation byproducts of OPs had no inhibition effect on GJIC at any of the concentrations tested. The inhibition of GJIC by OPs was reversible after removal of the tested pesticides followed by incubation with fresh medium. The present study suggested that the ozonation treatment could be used for the detoxification of drinking water and food crops contaminated with diazinon, parathion and methyl-parathion without formation of GJIC toxicity.
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Affiliation(s)
- Jiguo Wu
- State Key Laboratory of Biocontrol, School of Life Sciences, Zhongshan (Sun Yat-sen) University, Guangzhou 510275, PR China
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29
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Leithe E, Rivedal E. Ubiquitination of gap junction proteins. J Membr Biol 2007; 217:43-51. [PMID: 17657522 DOI: 10.1007/s00232-007-9050-z] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2007] [Accepted: 05/14/2007] [Indexed: 12/01/2022]
Abstract
Gap junctions are plasma membrane domains containing arrays of channels that exchange ions and small molecules between neighboring cells. Gap junctional intercellular communication enables cells to directly cooperate both electrically and metabolically. Several lines of evidence indicate that gap junctions are important in regulating cell growth and differentiation and for maintaining tissue homeostasis. Gap junction channels consist of a family of transmembrane proteins called connexins. Gap junctions are dynamic structures, and connexins have a high turnover rate in most tissues. Connexin43 (Cx43), the best-studied connexin isoform, has a half-life of 1.5-5 h; and its degradation involves both the lysosomal and proteasomal systems. Increasing evidence suggests that ubiquitin is important in the regulation of Cx43 endocytosis. Ubiquitination of Cx43 is thought to occur at the plasma membrane and has been shown to be regulated by protein kinase C and the mitogen-activated protein kinase pathway. Cx43 binds to the E3 ubiquitin ligase Nedd4, in a process modulated by Cx43 phosphorylation. The interaction between Nedd4 and Cx43 is mediated by the WW domains of Nedd4 and involves a proline-rich sequence conforming to a PY (XPPXY) consensus motif in the C terminus of Cx43. In addition to the PY motif, an overlapping tyrosine-based sorting signal conforming to the consensus of an YXXphi motif is involved in Cx43 endocytosis, indicating that endocytosis of gap junctions involves both ubiquitin-dependent and -independent pathways. Here, we discuss current knowledge on the ubiquitination of connexins.
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Affiliation(s)
- Edward Leithe
- Department of Cancer Prevention, Institute for Cancer Research, Rikshospitalet-Radiumhospitalet Medical Center, 0310, Oslo, Norway.
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30
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Barnett ME, Madgwick DK, Takemoto DJ. Protein kinase C as a stress sensor. Cell Signal 2007; 19:1820-9. [PMID: 17629453 PMCID: PMC1986756 DOI: 10.1016/j.cellsig.2007.05.014] [Citation(s) in RCA: 75] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2007] [Revised: 05/24/2007] [Accepted: 05/25/2007] [Indexed: 11/22/2022]
Abstract
While there are many reviews which examine the group of proteins known as protein kinase C (PKC), the focus of this article is to examine the cellular roles of two PKCs that are important for stress responses in neurological tissues (PKC gamma and epsilon) and in cardiac tissues (PKC epsilon). These two kinases, in particular, seem to have overlapping functions and interact with an identical target, connexin 43 (Cx43), a gap junction protein which is central to proper control of signals in both tissues. While PKC gamma and PKC epsilon both help protect neural tissue from ischemia, PKC epsilon is the primary PKC isoform responsible for responding to decreased oxygen, or ischemia, in the heart. Both do this through Cx43. It is clear that both PKC gamma and PKC epsilon are necessary for protection from ischemia. However, the importance of these kinases has been inferred from preconditioning experiments which demonstrate that brief periods of hypoxia protect neurological and cardiac tissues from future insults, and that this depends on the activation, translocation, or ability for PKC gamma and/or PKC epsilon to interact with distinct cellular targets, especially Cx43. This review summarizes the recent findings which define the roles of PKC gamma and PKC epsilon in cardiac and neurological functions and their relationships to ischemia/reperfusion injury. In addition, a biochemical comparison of PKC gamma and PKC epsilon and a proposed argument for why both forms are present in neurological tissue while only PKC epsilon is present in heart, are discussed. Finally, the biochemistry of PKCs and future directions for the field are discussed, in light of this new information.
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Affiliation(s)
- Micheal E Barnett
- Department of Biochemistry, Kansas State University, Manhattan, Kansas 66506-3902, USA.
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31
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Procházka L, Turánek J, Tesarík R, Knotigová P, Polásková P, Andrysík Z, Kozubík A, Zák F, Sova P, Neuzil J, Machala M. Apoptosis and inhibition of gap-junctional intercellular communication induced by LA-12, a novel hydrophobic platinum(IV) complex. Arch Biochem Biophys 2007; 462:54-61. [PMID: 17466256 DOI: 10.1016/j.abb.2007.03.021] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2007] [Revised: 03/20/2007] [Accepted: 03/20/2007] [Indexed: 01/05/2023]
Abstract
A new hydrophobic platinum(IV) complex, LA-12, a very efficient anticancer drug lacking cross-resistance with cisplatin (CDDP), is now being tested in clinical trials. Here we investigated the apoptogenic activity of LA-12 and its effect on gap-junctional intercellular communication (GJIC) in the rat liver epithelial cell line WB-F344. LA-12 induced apoptosis much more efficiently than did CDDP due to a combination of rapid penetration into the cell and attack on DNA, leading to fast activation of p53 and caspase-3. Exposure of WB-F344 cells to LA-12 led to rapid induction of the time- and dose-dependent decrease in GJIC. On the molecular level, loss of GJIC induced by LA-12 was mediated by activation of extracellular signal-regulated kinase (ERK)-1 and ERK-2, as demonstrated by the use of inhibitors of ERK activation. Inhibition of GJIC was linked to rapid hyperphosphorylation of connexin-43 and disappearance of connexon clusters from membranes, which was not observed in the case of CDDP.
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Affiliation(s)
- Lubomír Procházka
- Veterinary Research Institute, Department of Immunology, Brno, Czech Republic
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Long AC, Colitz CMH, Bomser JA. Regulation of gap junction intercellular communication in primary canine lens epithelial cells: role of protein kinase C. Curr Eye Res 2007; 32:223-31. [PMID: 17453942 DOI: 10.1080/02713680601186714] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
Abstract
PURPOSE Gap junction intercellular communication (GJIC) is important in maintaining lens epithelial cell homeostasis and reductions in GJIC may be associated with the development of cataract. Protein kinase C (PKC) activation can disrupt gap junction communication via phosphorylation of connexin 43 (C x 43) proteins that compose gap junction channels. This study examined the role of PKC activation in modulating GJIC in a primary canine lens epithelial cell (LEC) line. METHODS TPA (12-O-tetradecanoyl-phorbol-acetate), a potent PKC activator and inhibitor of GJIC, was utilized in the present study. Primary cultures of canine LEC were treated with TPA (0-1000 ng/ml) for 0.5 hr and GJIC was assessed by scrape loading/dye transfer (SL/DT), and immunoblotting to detect phosphorylation of C x 43 protein. Inhibition of general and calcium-dependent PKC activity was achieved by pretreatment of cells with GF109203X and Gö6976, respectively. RESULTS Treatment with TPA (1-1000 ng/ml) significantly decreased GJIC in canine LEC as assessed by SL/DT. Pretreatment with 10 and 100 ng/ml TPA decreased GJIC by 80% as compared to controls and increased Cx43 phosphorylation as assessed by immunoblotting. Pretreatment of cells with GF109203X and Gö6976, partially restored TPA-inhibited GJIC by 40% and 60%, respectively, and reduced C x 43 phosphorylation. Expression of calcium dependent PKC isoforms was detected in canine whole lens and LEC. CONCLUSIONS Treatment with TPA significantly reduces GJIC in canine LEC. These effects are mediated, in part, by activation of calcium-dependent PKC isoforms. Primary canine LEC are a useful model in the study of the molecular mechanisms involved in GJIC and cataractogenesis.
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Affiliation(s)
- Amy C Long
- Ohio State University, Interdisciplinary Nutrition Program, The Ohio State University, Columbus, Ohio, USA
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Hakulinen P, Rintala E, Mäki-Paakkanen J, Komulainen H. Altered expression of connexin43 in the inhibition of gap junctional intercellular communication by chlorohydroxyfuranones in WB-F344 rat liver epithelial cells. Toxicol Appl Pharmacol 2006; 212:146-55. [PMID: 16122772 DOI: 10.1016/j.taap.2005.07.013] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2005] [Revised: 07/04/2005] [Accepted: 07/19/2005] [Indexed: 11/17/2022]
Abstract
3-Chloro-4-(dichloromethyl)-5-hydroxy-2(5H)-furanone (MX), 3,4-dichloro-5-hydroxy-2(5H)-furanone (MCA), and 3-chloro-4-methyl-5-hydroxy-2(5H)-furanone (MCF) promote foci formation in the two-stage cell transformation assay in vitro. These chlorohydroxyfuranones (CHFs) and their structural congener 3-chloro-4-(chloromethyl)-5-hydroxy-2(5H)-furanone (CMCF) inhibit gap junctional intercellular communication (GJIC) in Balb/c 3T3 mouse fibroblast cells. In the present study, the effects of MX, MCA, CMCF, and MCF on GJIC were evaluated in liver cells (WB-F344 rat liver epithelial cells), the target cells of MX-induced carcinogenicity, using the scrape-loading dye transfer technique. The CHFs inhibited GJIC after 1 h exposure in a concentration-dependent fashion. The order of potency was MX>CMCF approximately MCA>MCF. In terms of the lowest observed effective concentrations, the difference in the potency was about 27-fold (MX 1.875 microM, MCF 50 microM). After a prolonged exposure period (12 h), the inhibition of GJIC by MX and CMCF remained stable, but MCA and MCF exhibited increasing inhibitory effects. After removal of the CHFs, the GJIC slowly recovered. At the transcriptional level, CHFs caused essentially no change in the level of connexin43 (Cx43) mRNA. Preincubation of cells with the protein kinase C (PKC) inhibitor did not modify the response, but the specific MEK 1 inhibitor PD98059 decreased substantially the inhibition of GJIC by all four CHFs. Activation of the mitogen-activated protein kinases (MAPKs) signaling pathway was necessary for inhibition of GJIC. CHFs did not increase the basal phosphorylation state of the Cx43 protein, but all CHFs caused a concentration-dependent degradation of the Cx43 protein. The results indicate that all the studied CHFs inhibit GJIC in WB-F344 cells by altering Cx43 expression.
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Affiliation(s)
- Pasi Hakulinen
- National Public Health Institute, Laboratory of Toxicology, P.O.B. 95, FI-70701 Kuopio, Finland.
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Leithe E, Brech A, Rivedal E. Endocytic processing of connexin43 gap junctions: a morphological study. Biochem J 2006; 393:59-67. [PMID: 16162097 PMCID: PMC1383664 DOI: 10.1042/bj20050674] [Citation(s) in RCA: 62] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
Gap junctions are plasma membrane areas enriched in channels that provide direct intercellular communication. Gap junctions have a high turnover rate; however, the mechanisms by which gap junctions are degraded are incompletely understood. In the present study, we show that in response to phorbol ester treatment, the gap junction channel protein Cx43 (connexin43) is redistributed from the plasma membrane to intracellular vesicles positive for markers for early and late endosomes and for the endolysosomal protease cathepsin D. Immunoelectron microscopy studies indicate that the double membranes of internalized gap junctions undergo separation and cutting, resulting in multivesicular endosomes enriched in Cx43 protein. Using preloading of BSA-gold conjugates to mark lysosomes, we provide evidence suggesting that the degradation process of the double-membrane structure of annular gap junctions occurs prior to transport of Cx43 to the lysosome. The results further suggest that bafilomycin A1, an inhibitor of vacuolar H+-ATPases, causes accumulation of Cx43 in early endosomes. Taken together, these findings indicate that internalized gap junctions undergo a maturation process from tightly sealed double-membrane vacuoles to connexin-enriched multivesicular endosomes with a single limiting membrane. The results further suggest that along with the processing of the double-membrane structure of annular gap junctions, connexins are trafficked via early and late endosomes, finally resulting in their endolysosomal degradation.
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Affiliation(s)
- Edward Leithe
- Institute for Cancer Research, The Norwegian Radium Hospital, Montebello, N-0310 Oslo, Norway.
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Matsushita S, Kurihara H, Watanabe M, Okada T, Sakai T, Amano A. Alterations of phosphorylation state of connexin 43 during hypoxia and reoxygenation are associated with cardiac function. J Histochem Cytochem 2005; 54:343-53. [PMID: 16314445 DOI: 10.1369/jhc.4a6611.2005] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Gap junctions formed by connexins mediate cell-cell communication by electrical and chemical coupling. Recently, it has been shown that alterations in the phosphorylation state of the connexins result in functional alteration of cell-cell communication through gap junctions. Therefore, we focused on the association of alterations of phosphorylation state of connexin 43 (Cx43) with cardiac function in vivo. Rat hearts were transferred to Langendorff apparatus and submitted to hypoxia and then reoxygenated. In the control heart, Cx43 was phosphorylated and located at the intercalated disk. When the hearts were subjected to hypoxia, Cx43 at gap junctions was dephosphorylated and changed its localization to the entire plasma membrane. The area of cardiomyocytes stained with anti-phosphorylated Cx43 antibody was decreased in a time-dependent manner. Immunoblot data supported the decrease of phosphorylated Cx43 during hypoxia. ZO-1 did not change its localization at the intercalated disk during the hypoxic period. We also found that the area occupied by dephosphorylated Cx43 was correlated with the decrease of percent of rate-pressure product. These data indicate that dephosphorylation and redistribution of Cx43 is an early sign of cardiac injury after hypoxia. Detection of dephosphorylated Cx43 may serve as a diagnostic tool for examining ischemic heart disease.
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Affiliation(s)
- Satoshi Matsushita
- Department of Cardiovascular Surgery, Juntendo University School of Medicine, Tokyo, Japan
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Lan Z, Kurata WE, Martyn KD, Jin C, Lau AF. Novel rab GAP-like protein, CIP85, interacts with connexin43 and induces its degradation. Biochemistry 2005; 44:2385-96. [PMID: 15709751 PMCID: PMC2670246 DOI: 10.1021/bi048306w] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Gap junctions play critical roles in tissue function and homeostasis. Connexin43 (Cx43) is a major gap junction protein expressed in the mammalian heart and other tissues and may be regulated by its interaction with other cellular proteins. Using the yeast two-hybrid screen, we identified a novel Cx43-interacting protein of 85-kDa, CIP85, which contains a single TBC, SH3, and RUN domain, in addition to a short coiled coil region. Homologues containing this unique combination of domains were found in human, D. melanogaster, and C. elegans. CIP85 mRNA is expressed ubiquitously in mouse and human tissues. In vitro interaction assays and in vivo co-immunoprecipitation experiments confirmed the interaction of endogenous CIP85 with Cx43. In vitro interaction experiments using CIP85 mutants with in-frame deletions of the TBC, SH3, and RUN domains indicated that the SH3 domain of CIP85 is involved in its interaction with Cx43. Conversely, analysis of Cx43 mutants with proline to alanine substitutions in the two proline-rich regions of Cx43 revealed that the P(253)LSP(256) motif is an important determinant of the ability of Cx43 to interact with CIP85. Laser-scanning confocal microscopy showed that CIP85 colocalized with Cx43 at the cell periphery, particularly in areas reminiscent of gap junction plaques. The functional importance of the interaction between CIP85 and Cx43 was suggested by the observation that CIP85 appears to induce the turnover of Cx43 through the lysosomal pathway.
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Affiliation(s)
| | | | | | | | - Alan F. Lau
- To whom correspondence should be addressed: Natural Products and Cancer Biology Program, Cancer Research Center of Hawaii, 1236 Lauhala Street, Honolulu, HI 96813. Telephone: (808) 586−2959. Fax: (808) 586−2970. E-mail:
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Rivedal E, Leithe E. Connexin43 synthesis, phosphorylation, and degradation in regulation of transient inhibition of gap junction intercellular communication by the phorbol ester TPA in rat liver epithelial cells. Exp Cell Res 2005; 302:143-52. [PMID: 15561096 DOI: 10.1016/j.yexcr.2004.09.004] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2004] [Revised: 09/09/2004] [Indexed: 11/27/2022]
Abstract
The tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA) induces transient inhibition of gap junction intercellular communication (GJIC) in several cell types. The initial block in GJIC has been attributed to protein kinase C (PKC) mediated phosphorylation of connexin gap junction proteins, including connexin43 (Cx43). Restoration of GJIC, associated with normalization of the Cx43 phosphorylation status, has been ascribed to different events, including dephosphorylation of Cx43 and de novo synthesis of Cx43 or other, non-gap junctional, proteins. The data presented suggest that restoration of GJIC during continuous TPA exposure in normal and transformed rat liver epithelial cells is dependent on synthesis of Cx43 protein, as well as the transport of already synthesized Cx43 from intracellular pools to the plasma membrane. Reactivation of inactivated Cx43 by dephosphorylation does not appear to be involved in the recovery of GJIC. Both PKC and MAP kinase is involved in TPA-induced degradation of Cx43 and inhibition of GJIC. We show that coincubation of TPA with the protein synthesis inhibitor cycloheximide or the transcription inhibitor actinomycin D results in synergistic enhancement of the level of activated ERK1/2. Together, the present data highlight Cx43 degradation and synthesis as critical determinants in TPA-induced modifications of cell-cell communication via gap junctions.
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Affiliation(s)
- Edgar Rivedal
- Institute for Cancer Research, The Norwegian Radium Hospital, Montebello, N-0310 Oslo, Norway
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Leithe E, Rivedal E. Ubiquitination and down-regulation of gap junction protein connexin-43 in response to 12-O-tetradecanoylphorbol 13-acetate treatment. J Biol Chem 2004; 279:50089-96. [PMID: 15371442 DOI: 10.1074/jbc.m402006200] [Citation(s) in RCA: 135] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023] Open
Abstract
Gap junctions are specialized plasma membrane domains enriched in connexin proteins that form channels between adjacent cells. Gap junctions are highly dynamic, and modulation of the connexin turnover rate is considered to play an important role in the regulation of gap junctional intercellular communication. In the present study, we show that the tumor-promoting phorbol ester 12-O-tetradecanoylphorbol 13-acetate (TPA) induces ubiquitination of connexin-43 (Cx43) in IAR20 rat liver epithelial cells. The accelerated ubiquitination of Cx43 in response to TPA occurred concomitantly with Cx43 hyperphosphorylation and inhibition of cell-cell communication via gap junctions. The TPA-induced ubiquitination of Cx43 was mediated via protein kinase C and partly involved the mitogen-activated protein kinase pathway. Following ubiquitination, Cx43 was internalized and degraded. The loss of Cx43 protein was counteracted by ammonium chloride, indicating that acidification of internalized Cx43 gap junctions is a prerequisite for its degradation. Furthermore, the Cx43 degradation was partly counteracted by leupeptin, an inhibitor of cathepsin B, H, and L. Cx43 internalization and subsequent degradation were blocked by inhibitors of the proteasome. Evidence is provided that Cx43 is modified by multiple monoubiquitins rather than a polyubiquitin chain in response to TPA. Moreover, the TPA-induced ubiquitination of Cx43 was blocked by proteasomal inhibitors. Taken together, the data indicate that Cx43 ubiquitination is a highly regulated process. Moreover, the results suggest that the proteasome might play an indirect role in Cx43 degradation by affecting the level of monoubiquitin conjugation and trafficking of Cx43 to endosomal compartments.
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Affiliation(s)
- Edward Leithe
- Institute for Cancer Research at The Norwegian Radium Hospital, N-0310 Oslo, Norway.
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Hakulinen P, Mäki-Paakkanen J, Naarala J, Kronberg L, Komulainen H. Potent inhibition of gap junctional intercellular communication by 3-chloro-4-(dichloromethyl)-5-hydroxy-2(5H)-furanone (MX) in BALB/c 3T3 cells. Toxicol Lett 2004; 151:439-49. [PMID: 15261988 DOI: 10.1016/j.toxlet.2004.03.012] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2003] [Revised: 02/26/2004] [Accepted: 03/04/2004] [Indexed: 11/18/2022]
Abstract
The chlorohydroxyfuranones (CHFs) MX [3-chloro-4-(dichloromethyl)-5-hydroxy-2(5H)-furanone], MCA [3,4-dichloro-5-hydroxy-2(5H)-furanone], CMCF [3-chloro-4-(chloromethyl)-5-hydroxy-2(5H)-furanone], and MCF [3-chloro-4-methyl-5-hydroxy-2(5H)-furanone] are genotoxic disinfection by-products of drinking water chlorination. MX, MCA, and MCF also promote foci formation in the two-stage cell transformation assay. The cellular mechanisms underlying this apparent promotional effect are not known. In the present study, the effects of MX, MCA, CMCF, and MCF on gap junctional intercellular communication (GJIC) were measured in BALB/c 3T3 cells using the scrape loading dye technique. The effect of MX on apoptosis in the same cell line was explored by assaying caspase-3-like protease activity. All the four CHFs inhibited GJIC after 30 min exposure in a dose-dependent fashion but there was a marked difference in the ranges of their active concentrations. MX was almost as potent an inhibitor of GJIC (inhibition at nanomolar concentrations) as 12-O-tetradecanoylphorbol-13-acetate (TPA) (positive control), while MCA was 10 times weaker, CMCF 10,000 times weaker, and MCF 20,000 times weaker than MX. After prolonged exposure periods (up to 6 h), GJIC recovered somewhat upon MX and MCA exposures, the inhibition of GJIC by MCF remained constant but CMCF showed an irreversible increasing inhibitory effect. MX caused apoptosis as a "window" effect at concentrations 2000-4000-fold higher than those needed to inhibit GJIC. The results indicate that MX is a potent inhibitor of GJIC in BALB/c 3T3 cells and this inhibition might be one mechanism by which MX can promote malignant foci formation. MCA also has a specific potential to inhibit GJIC whereas MCF and CMCF affected GJIC at concentrations, similar to those evoking genotoxicity in vitro.
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Affiliation(s)
- Pasi Hakulinen
- National Public Health Institute, Laboratory of Toxicology, P.O. Box 95, Kuopio FIN-70701, Finland.
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Leithe E, Rivedal E. Epidermal growth factor regulates ubiquitination, internalization and proteasome-dependent degradation of connexin43. J Cell Sci 2004; 117:1211-20. [PMID: 14970263 DOI: 10.1242/jcs.00951] [Citation(s) in RCA: 134] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023] Open
Abstract
Connexins are membrane-spanning proteins that form gap junction channels between adjacent cells. Connexin43 (Cx43), the most widely expressed member of the connexin family in tissues and cell lines, has a rapid turnover rate and its degradation involves both the lysosomal and ubiquitin-proteasome pathway. It was previously shown that the proteasome is involved in regulating the number of functional gap junctions at the plasma membrane. However, little is known about how proteasome-dependent turnover of Cx43 is controlled. Epidermal growth factor (EGF) induces hyperphosphorylation of Cx43 and a rapid, transient decrease in gap junctional intercellular communication. In this study, we show that, along with inhibition of gap junctional intercellular communication, EGF induces disorganization, internalization and degradation of Cx43 gap junction plaques in IAR20 rat liver epithelial cells. These EGF-induced modifications of Cx43 were counteracted by the MEK1 inhibitor PD98059, indicating that the effects were mediated by the mitogen-activated protein kinase pathway. The EGF-induced destruction of Cx43 was proteasome-dependent, because the loss of Cx43 protein was counteracted by the proteasome inhibitor MG132 but not the lysosomal inhibitor leupeptin. Furthermore, EGF induced ubiquitination of Cx43, which was associated with the Cx43 hyperphosphorylation. The EGF-induced Cx43 ubiquitination was counteracted by PD98059. The EGF-induced internalization of Cx43 was blocked by hypertonic sucrose treatment, indicating that EGF mediates internalization of Cx43 via a clathrin-dependent mechanism. Our results indicate that ubiquitination of Cx43 occurs at the plasma membrane before Cx43 internalization. Taken together, these data provide the first evidence that EGF-induced phosphorylation of Cx43 induces binding of ubiquitin and targets Cx43 for internalization and degradation in a proteasome-dependent manner.
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Affiliation(s)
- Edward Leithe
- Institute for Cancer Research at The Norwegian Radium Hospital, N-0310 Oslo, Norway.
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