1
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Junjappa RP, Kim HK, Park SY, Bhattarai KR, Kim KW, Soh JW, Kim HR, Chae HJ. Expression of TMBIM6 in Cancers: The Involvement of Sp1 and PKC. Cancers (Basel) 2019; 11:cancers11070974. [PMID: 31336725 PMCID: PMC6678130 DOI: 10.3390/cancers11070974] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2019] [Revised: 06/28/2019] [Accepted: 07/08/2019] [Indexed: 12/29/2022] Open
Abstract
Transmembrane Bax Inhibitor Motif-containing 6 (TMBIM6) is upregulated in several cancer types and involved in the metastasis. Specific downregulation of TMBIM6 results in cancer cell death. However, the TMBIM6 gene transcriptional regulation in normal and cancer cells is least studied. Here, we identified the core promoter region (−133/+30 bp) sufficient for promoter activity of TMBIM6 gene. Reporter gene expression with mutations at transcription factor binding sites, EMSA, supershift, and ChIP assays demonstrated that Sp1 is an essential transcription factor for basal promoter activity of TMBIM6. The TMBIM6 mRNA expression was increased with Sp1 levels in a concentration dependent manner. Ablation of Sp1 through siRNA or inhibition with mithramycin-A reduced the TMBIM6 mRNA expression. We also found that the protein kinase-C activation stimulates promoter activity and endogenous TMBIM6 mRNA by 2- to 2.5-fold. Additionally, overexpression of active mutants of PKCι, PKCε, and PKCδ increased TMBIM6 expression by enhancing nuclear translocation of Sp1. Immunohistochemistry analyses confirmed that the expression levels of PKCι, Sp1, and TMBIM6 were correlated with one another in samples from human breast, prostate, and liver cancer patients. Altogether, this study suggests the involvement of Sp1 in basal transcription and PKC in the enhanced expression of TMBIM6 in cancer.
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Affiliation(s)
- Raghu Patil Junjappa
- Department of Pharmacology and New Drug Development Research Institute, Chonbuk National University Medical School, Jeonju 54896, Korea
| | - Hyun-Kyoung Kim
- Department of Pharmacology and New Drug Development Research Institute, Chonbuk National University Medical School, Jeonju 54896, Korea
| | - Seong Yeol Park
- Department of Pharmacology and New Drug Development Research Institute, Chonbuk National University Medical School, Jeonju 54896, Korea
| | - Kashi Raj Bhattarai
- Department of Pharmacology and New Drug Development Research Institute, Chonbuk National University Medical School, Jeonju 54896, Korea
| | - Kyung-Woon Kim
- Animal Biotechnology Division, National Institute of Animal Science, Rural Development Administration (RDA), Wanju-gun, Chonbuk 54875, Korea
| | - Jae-Won Soh
- Department of Chemistry, Inha University, Incheon 402-751, Korea
| | - Hyung-Ryong Kim
- College of Dentistry, Institute of Tissue Regeneration Engineering (ITREN), Dankook University, Cheonan 31116, Korea.
| | - Han-Jung Chae
- Department of Pharmacology and New Drug Development Research Institute, Chonbuk National University Medical School, Jeonju 54896, Korea.
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2
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Cai J, Wei S, Lu Y, Wu Z, Qin Q, Jian J. Bax inhibitor-1 from orange spotted grouper, Epinephelus coioides involved in viral infection. FISH & SHELLFISH IMMUNOLOGY 2018; 78:91-99. [PMID: 29679759 DOI: 10.1016/j.fsi.2018.04.020] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/13/2018] [Revised: 04/05/2018] [Accepted: 04/07/2018] [Indexed: 06/08/2023]
Abstract
Bax inhibitor-1 (BI-1) is a conserved anti-apoptotic protein that suppresses endoplasmic reticulum (ER) stress-induced cell death. However, the function of fish BI-1 is not quite clear. In the present study, a bi-1 homolog (Ecbi-1) from orange spotted grouper, Epinephelus coioides was identified and its roles in viral infection were investigated. EcBI-1 encoded 237 amino acids protein, contained six transmembrane regions and a conservative C-terminus motif. Ecbi-1 predominantly expressed in kidney and spleen of healthy grouper. After SGIV stimulation, Ecbi-1 transcript was significantly increased in vitro. Subcellular localization analysis revealed that EcBI-1 was localized throughout the cytoplasm and co-localized with ER. Furthermore, overexpression of EcBI-1 suppressed SGIV infection induced cell death, caspase-3 activity and viral genes transcription. And C-terminus motif was critical for regulation roles of EcBI-1 during SGIV infection. In addition, EcBI-1 could interact with EcBNIP3 in vitro. Together, our data firstly demonstrated that fish BI-1 play important roles in response to viral infection.
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Affiliation(s)
- Jia Cai
- College of Fishery, Guangdong Ocean University, Zhanjiang 524088, PR China; Guangdong Provincial Key Laboratory of Pathogenic Biology and Epidemiology for Aquatic Economic Animals, Zhanjiang 524088, PR China; Guangdong Key Laboratory of Control for Diseases of Aquatic Economic Animals, Zhanjiang 524088, PR China
| | - Shina Wei
- College of Marine Sciences, South China Agricultural University, Guangzhou 510642, PR China
| | - Yishan Lu
- College of Fishery, Guangdong Ocean University, Zhanjiang 524088, PR China; Guangdong Provincial Key Laboratory of Pathogenic Biology and Epidemiology for Aquatic Economic Animals, Zhanjiang 524088, PR China; Guangdong Key Laboratory of Control for Diseases of Aquatic Economic Animals, Zhanjiang 524088, PR China
| | - Zaohe Wu
- Guangdong Provincial Key Laboratory of Pathogenic Biology and Epidemiology for Aquatic Economic Animals, Zhanjiang 524088, PR China; Guangdong Key Laboratory of Control for Diseases of Aquatic Economic Animals, Zhanjiang 524088, PR China
| | - Qiwei Qin
- College of Marine Sciences, South China Agricultural University, Guangzhou 510642, PR China.
| | - Jichang Jian
- College of Fishery, Guangdong Ocean University, Zhanjiang 524088, PR China; Guangdong Provincial Key Laboratory of Pathogenic Biology and Epidemiology for Aquatic Economic Animals, Zhanjiang 524088, PR China; Guangdong Key Laboratory of Control for Diseases of Aquatic Economic Animals, Zhanjiang 524088, PR China.
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3
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Carrara G, Parsons M, Saraiva N, Smith GL. Golgi anti-apoptotic protein: a tale of camels, calcium, channels and cancer. Open Biol 2018; 7:rsob.170045. [PMID: 28469007 PMCID: PMC5451544 DOI: 10.1098/rsob.170045] [Citation(s) in RCA: 27] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2017] [Accepted: 04/10/2017] [Indexed: 12/11/2022] Open
Abstract
Golgi anti-apoptotic protein (GAAP), also known as transmembrane Bax inhibitor-1 motif-containing 4 (TMBIM4) or Lifeguard 4 (Lfg4), shares remarkable amino acid conservation with orthologues throughout eukaryotes, prokaryotes and some orthopoxviruses, suggesting a highly conserved function. GAAPs regulate Ca2+ levels and fluxes from the Golgi and endoplasmic reticulum, confer resistance to a broad range of apoptotic stimuli, promote cell adhesion and migration via the activation of store-operated Ca2+ entry, are essential for the viability of human cells, and affect orthopoxvirus virulence. GAAPs are oligomeric, multi-transmembrane proteins that are resident in Golgi membranes and form cation-selective ion channels that may explain the multiple functions of these proteins. Residues contributing to the ion-conducting pore have been defined and provide the first clues about the mechanistic link between these very different functions of GAAP. Although GAAPs are naturally oligomeric, they can also function as monomers, a feature that distinguishes them from other virus-encoded ion channels that must oligomerize for function. This review summarizes the known functions of GAAPs and discusses their potential importance in disease.
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Affiliation(s)
- Guia Carrara
- Department of Pathology, University of Cambridge, Cambridge, CB2 1QP, UK
| | - Maddy Parsons
- Randall Division of Cell and Molecular Biophysics, King's College London, London SE1 1UL, UK
| | - Nuno Saraiva
- Department of Pathology, University of Cambridge, Cambridge, CB2 1QP, UK .,CBIOS, Universidade Lusófona Research Centre for Biosciences and Health Technologies, Campo Grande 376, Lisbon 1749-024, Portugal
| | - Geoffrey L Smith
- Department of Pathology, University of Cambridge, Cambridge, CB2 1QP, UK
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4
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Cheng CH, Luo SW, Wang AL, Guo ZX. Molecular and immune response characterizations of a novel Bax inhibitor-1 gene in pufferfish, Takifugu obscurus. FISH PHYSIOLOGY AND BIOCHEMISTRY 2017; 43:965-975. [PMID: 28553691 DOI: 10.1007/s10695-016-0337-9] [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: 10/11/2016] [Accepted: 12/21/2016] [Indexed: 06/07/2023]
Abstract
Apoptosis plays a crucial role in many biological processes, including development, cellular homeostasis, and immune responses. Bax inhibitor-1 (BI-1) is an anti-apoptotic protein that protects cells from endoplasmic reticulum stress-induced apoptosis. In this study, a BI-1 gene from the pufferfish Takifugu obscurus (Pf-BI-1) was identified and characterized. The full length of Pf-BI-1 cDNA was 1387 bp, including a 5'-UTR of 82 bp, a 3'-UTR of 591 bp containing a poly-(A) tail, and an open reading frame (ORF) of 714 bp that encodes a polypeptide of 237 amino acids. Pf-BI-1 was ubiquitously expressed in various tissues, with the highest expression levels in the blood, brain, and gill. The expression of Pf-BI-1 was up-regulated in a time-dependent manner after heat shock stress, ammonia stress, and bacterial challenge. Intracellular localization revealed that Pf-BI-1 was primarily localized in the cell cytoplasm. Furthermore, over-expression of Pf-BI-1 could active NF-кB reporter genes in HeLa cells. These results indicated that Pf-BI-1 may be involved in the apoptosis and immunity process against ambient stressors in pufferfish.
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Affiliation(s)
- Chang-Hong Cheng
- Key Laboratory of South China Sea Fishery Resources Exploitation & Utilization, Ministry of Agriculture, South China Sea Fisheries Research Institute, Chinese Academy of Fishery Sciences, Guangzhou, Guangdong, 510300, China
| | - Sheng-Wei Luo
- Key Laboratory of Ecology and Environmental Science of Guangdong, Higher Education Institutes, Guangdong Provincial Key Laboratory for Healthy and Safe Aquaculture, School of Life Science, South China Normal University, Guangzhou, 510631, People's Republic of China
| | - An-Li Wang
- Key Laboratory of Ecology and Environmental Science of Guangdong, Higher Education Institutes, Guangdong Provincial Key Laboratory for Healthy and Safe Aquaculture, School of Life Science, South China Normal University, Guangzhou, 510631, People's Republic of China.
| | - Zhi-Xun Guo
- Key Laboratory of South China Sea Fishery Resources Exploitation & Utilization, Ministry of Agriculture, South China Sea Fisheries Research Institute, Chinese Academy of Fishery Sciences, Guangzhou, Guangdong, 510300, China.
- South China Sea Bio-Resource Exploitation and Utilization Collaborative Innovation Center (SCS-REPIC), Guangzhou, People's Republic of China.
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5
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Lee GH, Kim HR, Chae HJ. BI-1 enhances Fas-induced cell death through a Na+/H+-associated mechanism. BMB Rep 2015; 47:393-8. [PMID: 24314142 PMCID: PMC4163852 DOI: 10.5483/bmbrep.2014.47.7.194] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2013] [Indexed: 11/20/2022] Open
Abstract
The role of Bax inhibitor-1 (BI-1) in the protective mechanism against apoptotic stimuli has been studied; however, as little is known about its role in death receptor-mediated cell death, this study was designed to investigate the effect of BI-1 on Fas-induced cell death, and the underlying mechanisms. HT1080 adenocarcinoma cells were cultured in high concentration of glucose media and transfected with vector alone (Neo cells) or BI-1-vector (BI-1 cells), and treated with Fas. In cell viability, apoptosis, and caspase-3 analyses, the BI-1 cells showed enhanced sensitivity to Fas. Fas significantly decreased cytosolic pH in BI-1 cells, compared with Neo cells, and this decrease correlated with BI-1 oligomerization, mitochondrial Ca2+ accumulation, and significant inhibition of sodium-hydrogen exchanger (NHE) activity. Compared with Neo cells, a single treatment of BI-1 cells with the NHE inhibitor EIPA or siRNA against NHE significantly increased cell death, which suggests that the viability of BI-1 cells is affected by the maintenance of intracellular pH homeostasis through NHE.
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Affiliation(s)
- Geum-Hwa Lee
- Department of Pharmacology, School of Medicine, Chonbuk National University, Jeonju 560-182, Korea
| | - Hyung-Ryong Kim
- Department of Dental Pharmacology, Wonkwang Dental Research Institute, School of Dentistry, Wonkwang University, Iksan 570-749, Korea
| | - Han-Jung Chae
- Department of Pharmacology, School of Medicine, Chonbuk National University, Jeonju 560-182, Korea
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6
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Carrara G, Saraiva N, Parsons M, Byrne B, Prole DL, Taylor CW, Smith GL. Golgi anti-apoptotic proteins are highly conserved ion channels that affect apoptosis and cell migration. J Biol Chem 2015; 290:11785-801. [PMID: 25713081 PMCID: PMC4416878 DOI: 10.1074/jbc.m115.637306] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/08/2015] [Indexed: 12/03/2022] Open
Abstract
Golgi anti-apoptotic proteins (GAAPs) are multitransmembrane proteins that are expressed in the Golgi apparatus and are able to homo-oligomerize. They are highly conserved throughout eukaryotes and are present in some prokaryotes and orthopoxviruses. Within eukaryotes, GAAPs regulate the Ca2+ content of intracellular stores, inhibit apoptosis, and promote cell adhesion and migration. Data presented here demonstrate that purified viral GAAPs (vGAAPs) and human Bax inhibitor 1 form ion channels and that vGAAP from camelpox virus is selective for cations. Mutagenesis of vGAAP, including some residues conserved in the recently solved structure of a related bacterial protein, BsYetJ, altered the conductance (E207Q and D219N) and ion selectivity (E207Q) of the channel. Mutation of residue Glu-207 or -178 reduced the effects of GAAP on cell migration and adhesion without affecting protection from apoptosis. In contrast, mutation of Asp-219 abrogated the anti-apoptotic activity of GAAP but not its effects on cell migration and adhesion. These results demonstrate that GAAPs are ion channels and define residues that contribute to the ion-conducting pore and affect apoptosis, cell adhesion, and migration independently.
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Affiliation(s)
- Guia Carrara
- From the Department of Pathology, University of Cambridge, Cambridge CB2 1QP, United Kingdom
| | - Nuno Saraiva
- From the Department of Pathology, University of Cambridge, Cambridge CB2 1QP, United Kingdom
| | - Maddy Parsons
- the Randall Division of Cell and Molecular Biophysics, King's College London, London SE1 1UL, United Kingdom
| | - Bernadette Byrne
- the Division of Molecular Biosciences, Imperial College London, London SW7 2AZ, United Kingdom, and
| | - David L Prole
- the Department of Pharmacology, University of Cambridge, Cambridge CB2 1PD, United Kingdom,
| | - Colin W Taylor
- the Department of Pharmacology, University of Cambridge, Cambridge CB2 1PD, United Kingdom,
| | - Geoffrey L Smith
- From the Department of Pathology, University of Cambridge, Cambridge CB2 1QP, United Kingdom,
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7
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TMBIM protein family: ancestral regulators of cell death. Oncogene 2014; 34:269-80. [DOI: 10.1038/onc.2014.6] [Citation(s) in RCA: 75] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2013] [Revised: 12/27/2013] [Accepted: 01/02/2014] [Indexed: 12/13/2022]
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8
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B L, R.K Y, G.S J, H.-R K, H.-J C. The characteristics of Bax inhibitor-1 and its related diseases. Curr Mol Med 2014; 14:603-15. [PMID: 24894176 PMCID: PMC4083451 DOI: 10.2174/1566524014666140603101113] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2013] [Revised: 10/01/2013] [Accepted: 11/24/2013] [Indexed: 11/28/2022]
Abstract
Bax inhibitor-1 (BI-1) is an evolutionarily-conserved endoplasmic reticulum protein. The expression of BI-1 in mammalian cells suppresses apoptosis induced by Bax, a pro-apoptotic member of the Bcl-2 family. BI-1 has been shown to be associated with calcium (Ca(2+)) levels, reactive oxygen species (ROS) production, cytosolic acidification, and autophagy as well as endoplasmic reticulum stress signaling pathways. According to both in vitro and clinical studies, BI-1 promotes the characteristics of cancers. In other diseases, BI-1 has also been shown to regulate insulin resistance, adipocyte differentiation, hepatic dysfunction and depression. However, the roles of BI-1 in these disease conditions are not fully consistent among studies. Until now, the molecular mechanisms of BI-1 have not directly explained with regard to how these conditions can be regulated. Therefore, this review investigates the physiological role of BI-1 through molecular mechanism studies and its application in various diseases.
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Affiliation(s)
- Li B
- Department of Pharmacology, Medical School, Chonbuk National University, Jeonju, 561-181, Republic of Korea
| | - Yadav R.K
- Department of Pharmacology, Medical School, Chonbuk National University, Jeonju, 561-181, Republic of Korea
| | - Jeong G.S
- Department of Pharmacology, Medical School, Chonbuk National University, Jeonju, 561-181, Republic of Korea
| | - Kim H.-R
- Department of Dental Pharmacology and Wonkwang Dental Research Institute, School of Dentistry, Wonkwang University, Iksan, 570-749, Republic of Korea
| | - Chae H.-J
- Department of Pharmacology, Medical School, Chonbuk National University, Jeonju, 561-181, Republic of Korea
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9
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Liang Y, Li X, Lin R, Zhang X, Wang H, Tan N, Li K, Tang X, Zhou K, Li T. Combinatorial gene targeting hTERT and BI-1 in CNE-2 nasopharyngeal carcinoma cell line. Biomed Rep 2012; 1:285-293. [PMID: 24648937 DOI: 10.3892/br.2012.39] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2012] [Accepted: 10/16/2012] [Indexed: 01/22/2023] Open
Abstract
Nasopharyngeal carcinoma (NPC) is a common malignant tumor. In recent studies, we demonstrated that overexpression of the Bax inhibitor-1 (BI-1) induces cell transformation in NIH3T3 cells and that knockdown of BI-1 and human telomerase reverse transcriptase (hTERT) gene expression suppresses NPC cell proliferation and induces apoptosis. To evaluate the combination anti-tumor effects of siRNAs against hTERT and BI-1 in the CNE-2 NPC cell line, combined and separate short-hairpin (sh)RNA plasmids targeting hTERT and BI-1, respectively, were constructed. hTERT and BI-1 mRNA and protein levels were examined by real-time polymerase chain reaction (PCR) and western blot analysis. Cell proliferation, colony formation and migration ability were measured by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT), soft agar and wound healing assay. Cell apoptosis was observed by flow cytometry, Hoechst 33258 staining and caspase-3 activity. hTERT, BI-1 and combined shRNA plasmids were injected into xenograft NPC tumor tissues, and expression of hTERT and BI-1 was detected by real-time PCR and immunohistochemistry. Tumor growth was measured by tumor volume and apoptosis in vivo was confirmed by TdT-mediated dUTP nick end-labeling (TUNEL). Our results showed that combined shRNA specific for hTERT and BI-1 markedly suppressed hTERT and BI-1 gene expression in vitro and in vivo. In addition, CNE-2 cell proliferation was inhibited in vitro as well as in vivo. Following the knockdown of the two gene expressions, CNE-2 exhibited a decrease in colony formation and migration ability and an increase in the apoptotic rate compared to the control groups. Our in vitro and in vivo study showed that the combinative silencing of the two genes enhanced the therapeutic effect compared to the silencing of each individual shRNA. These data suggested that combinatorial gene therapy targeting hTERT and BI-1 may be beneficial as a tumor therapy strategy against human NPCs.
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Affiliation(s)
- Yan Liang
- Key Laboratory for Medical Molecular Diagnostics of Guangdong Province, Guangdong Medical College, Dongguan, Guangdong 523808, P.R. China
| | - Xiangyong Li
- Key Laboratory for Medical Molecular Diagnostics of Guangdong Province, Guangdong Medical College, Dongguan, Guangdong 523808, P.R. China
| | - Rongwen Lin
- Key Laboratory for Medical Molecular Diagnostics of Guangdong Province, Guangdong Medical College, Dongguan, Guangdong 523808, P.R. China
| | - Xin Zhang
- Key Laboratory for Medical Molecular Diagnostics of Guangdong Province, Guangdong Medical College, Dongguan, Guangdong 523808, P.R. China
| | - Huimin Wang
- Key Laboratory for Medical Molecular Diagnostics of Guangdong Province, Guangdong Medical College, Dongguan, Guangdong 523808, P.R. China
| | - Ning Tan
- Key Laboratory for Medical Molecular Diagnostics of Guangdong Province, Guangdong Medical College, Dongguan, Guangdong 523808, P.R. China
| | - Keshen Li
- Key Laboratory for Medical Molecular Diagnostics of Guangdong Province, Guangdong Medical College, Dongguan, Guangdong 523808, P.R. China
| | - Xudong Tang
- Key Laboratory for Medical Molecular Diagnostics of Guangdong Province, Guangdong Medical College, Dongguan, Guangdong 523808, P.R. China
| | - Keyuan Zhou
- Key Laboratory for Medical Molecular Diagnostics of Guangdong Province, Guangdong Medical College, Dongguan, Guangdong 523808, P.R. China
| | - Tao Li
- Key Laboratory for Medical Molecular Diagnostics of Guangdong Province, Guangdong Medical College, Dongguan, Guangdong 523808, P.R. China
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11
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Bultynck G, Kiviluoto S, Henke N, Ivanova H, Schneider L, Rybalchenko V, Luyten T, Nuyts K, De Borggraeve W, Bezprozvanny I, Parys JB, De Smedt H, Missiaen L, Methner A. The C terminus of Bax inhibitor-1 forms a Ca2+-permeable channel pore. J Biol Chem 2011; 287:2544-57. [PMID: 22128171 DOI: 10.1074/jbc.m111.275354] [Citation(s) in RCA: 73] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
Bax inhibitor-1 (BI-1) is a multitransmembrane domain-spanning endoplasmic reticulum (ER)-located protein that is evolutionarily conserved and protects against apoptosis and ER stress. Furthermore, BI-1 is proposed to modulate ER Ca(2+) homeostasis by acting as a Ca(2+)-leak channel. Based on experimental determination of the BI-1 topology, we propose that its C terminus forms a Ca(2+) pore responsible for its Ca(2+)-leak properties. We utilized a set of C-terminal peptides to screen for Ca(2+) leak activity in unidirectional (45)Ca(2+)-flux experiments and identified an α-helical 20-amino acid peptide causing Ca(2+) leak from the ER. The Ca(2+) leak was independent of endogenous ER Ca(2+)-release channels or other Ca(2+)-leak mechanisms, namely translocons and presenilins. The Ca(2+)-permeating property of the peptide was confirmed in lipid-bilayer experiments. Using mutant peptides, we identified critical residues responsible for the Ca(2+)-leak properties of this BI-1 peptide, including a series of critical negatively charged aspartate residues. Using peptides corresponding to the equivalent BI-1 domain from various organisms, we found that the Ca(2+)-leak properties were conserved among animal, but not plant and yeast orthologs. By mutating one of the critical aspartate residues in the proposed Ca(2+)-channel pore in full-length BI-1, we found that Asp-213 was essential for BI-1-dependent ER Ca(2+) leak. Thus, we elucidated residues critically important for BI-1-mediated Ca(2+) leak and its potential channel pore. Remarkably, one of these residues was not conserved among plant and yeast BI-1 orthologs, indicating that the ER Ca(2+)-leak properties of BI-1 are an added function during evolution.
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Affiliation(s)
- Geert Bultynck
- Department of Molecular Cell Biology, Laboratory of Molecular and Cellular Signaling, K.U. Leuven, B-3000 Leuven, Belgium.
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12
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Cebulski J, Malouin J, Pinches N, Cascio V, Austriaco N. Yeast Bax inhibitor, Bxi1p, is an ER-localized protein that links the unfolded protein response and programmed cell death in Saccharomyces cerevisiae. PLoS One 2011; 6:e20882. [PMID: 21673967 PMCID: PMC3108976 DOI: 10.1371/journal.pone.0020882] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2011] [Accepted: 05/11/2011] [Indexed: 12/27/2022] Open
Abstract
Bax inhibitor-1 (BI-1) is an anti-apoptotic gene whose expression is upregulated in a wide range of human cancers. Studies in both mammalian and plant cells suggest that the BI-1 protein resides in the endoplasmic reticulum and is involved in the unfolded protein response (UPR) that is triggered by ER stress. It is thought to act via a mechanism involving altered calcium dynamics. In this paper, we provide evidence that the Saccharomyces cerevisiae protein encoded by the open reading frame, YNL305C, is a bona fide homolog for BI-1. First, we confirm that yeast cells from two different strain backgrounds lacking YNL305C, which we have renamed BXI1, are more sensitive to heat-shock induced cell death than wildtype controls even though they have indistinguishable growth rates at 30°C. They are also more susceptible both to ethanol-induced and to glucose-induced programmed cell death. Significantly, we show that Bxi1p-GFP colocalizes with the ER localized protein Sec63p-RFP. We have also discovered that Δbxi1 cells are not only more sensitive to drugs that induce ER stress, but also have a decreased unfolded protein response as measured with a UPRE-lacZ reporter. Finally, we have discovered that deleting BXI1 diminishes the calcium signaling response in response to the accumulation of unfolded proteins in the ER as measured by a calcineurin-dependent CDRE-lacZ reporter. In toto, our data suggests that the Bxi1p, like its metazoan homologs, is an ER-localized protein that links the unfolded protein response and programmed cell death.
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Affiliation(s)
- James Cebulski
- Department of Biology, Providence College, Providence, Rhode Island, United States of America
| | - Joshua Malouin
- Department of Biology, Providence College, Providence, Rhode Island, United States of America
| | - Nathan Pinches
- Department of Biology, Providence College, Providence, Rhode Island, United States of America
| | - Vincent Cascio
- Department of Biology, Providence College, Providence, Rhode Island, United States of America
| | - Nicanor Austriaco
- Department of Biology, Providence College, Providence, Rhode Island, United States of America
- * E-mail:
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