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Citterio CE, Kim K, Rajesh B, Pena K, Clarke OB, Arvan P. Structural features of thyroglobulin linked to protein trafficking. Protein Sci 2023; 32:e4784. [PMID: 37717261 PMCID: PMC10578121 DOI: 10.1002/pro.4784] [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: 06/18/2023] [Revised: 09/06/2023] [Accepted: 09/14/2023] [Indexed: 09/19/2023]
Abstract
Thyroglobulin must pass endoplasmic reticulum (ER) quality control to become secreted for thyroid hormone synthesis. Defective thyroglobulin, blocked in trafficking, can cause hypothyroidism. Thyroglobulin is a large protein (~2750 residues) spanning regions I-II-III plus a C-terminal cholinesterase-like domain. The cholinesterase-like domain functions as an intramolecular chaperone for regions I-II-III, but the folding pathway leading to successful thyroglobulin trafficking remains largely unknown. Here, informed by the recent three-dimensional structure of thyroglobulin as determined by cryo-electron microscopy, we have bioengineered three novel classes of mutants yielding three entirely distinct quality control phenotypes. Specifically, upon expressing recombinant thyroglobulin, we find that first, mutations eliminating a disulfide bond enclosing a 200-amino acid loop in region I have surprisingly little impact on the ability of thyroglobulin to fold to a secretion-competent state. Next, we have identified a mutation on the surface of the cholinesterase-like domain that has no discernible effect on regional folding yet affects contact between distinct regions and thereby triggers impairment in the trafficking of full-length thyroglobulin. Finally, we have probed a conserved disulfide in the cholinesterase-like domain that interferes dramatically with local folding, and this defect then impacts on global folding, blocking the entire thyroglobulin in the ER. These data highlight variants with distinct effects on ER quality control, inhibiting domain-specific folding; folding via regional contact; neither; or both.
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Affiliation(s)
- Cintia E. Citterio
- Division of Metabolism, Endocrinology & Diabetes, Department of Internal MedicineUniversity of MichiganAnn ArborMichiganUSA
- Department of Biomedical and Pharmaceutical SciencesChapman UniversityIrvineCaliforniaUSA
| | - Kookjoo Kim
- Departments of Anesthesiology, and Physiology and Cellular BiophysicsIrving Institute for Clinical and Translational Research, Columbia University Irving Medical CenterNew YorkNew YorkUSA
| | - Bhavana Rajesh
- Division of Metabolism, Endocrinology & Diabetes, Department of Internal MedicineUniversity of MichiganAnn ArborMichiganUSA
| | - Kevin Pena
- Division of Metabolism, Endocrinology & Diabetes, Department of Internal MedicineUniversity of MichiganAnn ArborMichiganUSA
| | - Oliver Biggs Clarke
- Departments of Anesthesiology, and Physiology and Cellular BiophysicsIrving Institute for Clinical and Translational Research, Columbia University Irving Medical CenterNew YorkNew YorkUSA
| | - Peter Arvan
- Division of Metabolism, Endocrinology & Diabetes, Department of Internal MedicineUniversity of MichiganAnn ArborMichiganUSA
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Rao A, McBride EL, Zhang G, Xu H, Cai T, Notkins AL, Aronova MA, Leapman RD. Determination of secretory granule maturation times in pancreatic islet β-cells by serial block-face electron microscopy. J Struct Biol 2020; 212:107584. [PMID: 32736074 DOI: 10.1016/j.jsb.2020.107584] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2019] [Revised: 07/19/2020] [Accepted: 07/21/2020] [Indexed: 01/19/2023]
Abstract
It is shown how serial block-face electron microscopy (SBEM) of insulin-secreting β-cells in wild-type mouse pancreatic islets of Langerhans can be used to determine maturation times of secretory granules. Although SBEM captures the β-cell structure at a snapshot in time, the observed ultrastructure can be considered representative of a dynamic equilibrium state of the cells since the pancreatic islets are maintained in culture in approximate homeostasis. It was found that 7.2 ± 1.2% (±st. dev.) of the β-cell volume is composed of secretory granule dense-cores exhibiting angular shapes surrounded by wide (typically ≳100 nm) electron-lucent halos. These organelles are identified as mature granules that store insulin for regulated release through the plasma membrane, with a release time of 96 ± 12 h, as previously obtained from pulsed 35S-radiolabeling of cysteine and methionine. Analysis of β-cell 3D volumes reveals a subpopulation of secretory organelles without electron-lucent halos, identified as immature secretory granules. Another subpopulation of secretory granules is found with thin (typically ≲30 nm) electron-lucent halos, which are attributed to immature granules that are transforming from proinsulin to insulin by action of prohormone convertases. From the volume ratio of proinsulin in the immature granules to insulin in the mature granules, we estimate that the newly formed immature granules remain in morphologically-defined immature states for an average time of 135 ± 14 min, and the immature transforming granules for an average time of 130 ± 17 min.
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Affiliation(s)
- A Rao
- Laboratory of Cellular Imaging and Macromolecular Biophysics, National Institute of Biomedical Imaging and Bioengineering, National Institutes of Health, Bethesda, MD 20892, USA
| | - E L McBride
- Laboratory of Cellular Imaging and Macromolecular Biophysics, National Institute of Biomedical Imaging and Bioengineering, National Institutes of Health, Bethesda, MD 20892, USA
| | - G Zhang
- Laboratory of Cellular Imaging and Macromolecular Biophysics, National Institute of Biomedical Imaging and Bioengineering, National Institutes of Health, Bethesda, MD 20892, USA
| | - H Xu
- Experimental Medicine Section, National Institute of Dental and Craniofacial Research, National Institutes of Health, Bethesda, MD 20892, USA
| | - T Cai
- Experimental Medicine Section, National Institute of Dental and Craniofacial Research, National Institutes of Health, Bethesda, MD 20892, USA
| | - A L Notkins
- Experimental Medicine Section, National Institute of Dental and Craniofacial Research, National Institutes of Health, Bethesda, MD 20892, USA
| | - M A Aronova
- Laboratory of Cellular Imaging and Macromolecular Biophysics, National Institute of Biomedical Imaging and Bioengineering, National Institutes of Health, Bethesda, MD 20892, USA
| | - R D Leapman
- Laboratory of Cellular Imaging and Macromolecular Biophysics, National Institute of Biomedical Imaging and Bioengineering, National Institutes of Health, Bethesda, MD 20892, USA.
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3
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Ohshima H. Oral biosciences: The annual review 2017. J Oral Biosci 2018. [DOI: 10.1016/j.job.2017.12.001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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4
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Determinants for selective transport of exogenously expressed cargo proteins into regulated and constitutive secretory pathways. J Oral Biosci 2017. [DOI: 10.1016/j.job.2017.01.001] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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Blank B, von Blume J. Cab45-Unraveling key features of a novel secretory cargo sorter at the trans-Golgi network. Eur J Cell Biol 2017; 96:383-390. [PMID: 28372832 DOI: 10.1016/j.ejcb.2017.03.001] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2016] [Revised: 02/27/2017] [Accepted: 03/02/2017] [Indexed: 12/15/2022] Open
Abstract
The accurate and efficient delivery of proteins to specific domains of the plasma membrane or to the extracellular space is critical for the ordered function of surface receptors and proteins such as insulin, collagens, antibodies, extracellular proteases. The trans-Golgi network is responsible for sorting proteins onto specific carriers for transport to their final destination. The role of the mannose-6-phosphate receptor in the sorting of hydrolases destined for lysosomes has been studied extensively, but the sorting mechanisms for secreted proteins remains poorly understood. We recently described a novel process that links the cytoplasmic actin cytoskeleton to the membrane-anchored Ca2+ ATPase SPCA1 and the lumenal Ca2+-binding protein Cab45, which mediates sorting of a subset of secretory proteins at the TGN. In response to Ca2+ influx, Cab45 forms oligomers, enabling it to bind a variety of specific cargo molecules. Thus, we suggest that this represents a novel way to export cargo molecules without the need for a bona fide transmembrane cargo receptor. This review focuses on Cab45's molecular function and highlights its possible role in disease.
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Affiliation(s)
- Birgit Blank
- Max Planck Institute of Biochemistry, Am Klopferspitz 18, 82152 Martinsried, Germany
| | - Julia von Blume
- Max Planck Institute of Biochemistry, Am Klopferspitz 18, 82152 Martinsried, Germany.
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Luo J, Li Z, Zhu H, Wang C, Zheng W, He Y, Song J, Wang W, Zhou X, Lu X, Zhang S, Chen J. A Novel Role of Cab45-G in Mediating Cell Migration in Cancer Cells. Int J Biol Sci 2016; 12:677-87. [PMID: 27194945 PMCID: PMC4870711 DOI: 10.7150/ijbs.11037] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2014] [Accepted: 03/19/2016] [Indexed: 12/16/2022] Open
Abstract
Ca2+-binding protein of 45 kDa (Cab45), a CREC family member, is reported to be associated with Ca2+-dependent secretory pathways and involved in multiple diseases including cancers. Cab45-G, a Cab45 isoform protein, plays an important role in protein sorting and secretion at Golgi complex. However, its role in cancer cell migration remains elusive. In this study, we demonstrate that Cab45-G exhibited an increased expression in cell lines with higher metastatic potential and promoted cell migration in multiple types of cancer cells. Overexpression of Cab45-G resulted in an altered expression of the molecular mediators of epithelial-mesenchymal transition (EMT), which is a critical step in the tumor metastasis. Quantitative real-time PCR showed that overexpression of Cab45-G increased the expression of matrix metalloproteinase-2 and -7 (MMP-2 and MMP-7). Conversely, knock-down of Cab45-G reduced the expression of the above MMPs. Moreover, forced expression of Cab45-G upregulated the level of phosphorylated ERK and modulated the secretion of extracellular proteins fibronectin and fibulin. Furthermore, in human cervical and esophageal cancer tissues, the expression of Cab45-G was found to be significantly correlated with that of MMP-2, further supporting the importance of Cab45-G on regulating cancer metastasis. Taken together, these results suggest that Cab45-G could regulate cancer cell migration through various molecular mechanisms, which may serve as a therapeutic target for the treatment of cancers.
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Affiliation(s)
- Judong Luo
- 1. Department of Radiotherapy, Changzhou Tumor Hospital, Soochow University, Changzhou, 213001, China;; 2. Department of Radiation Oncology, Shandong Cancer Hospital affiliated to Shandong University, Shandong Academy of Medical Sciences, Jinan , 250117, China
| | - Zengpeng Li
- 3. Key Laboratory Breeding Base of Marine Genetic Resources, Third Institute of Oceanography, State Oceanic Administration, Xiamen 361005, China
| | - Hong Zhu
- 4. Department of Radiation Oncology, Minhang Branch of Cancer Hospital of Fudan University, Shanghai 200240, China
| | - Chenying Wang
- 3. Key Laboratory Breeding Base of Marine Genetic Resources, Third Institute of Oceanography, State Oceanic Administration, Xiamen 361005, China
| | - Weibin Zheng
- 3. Key Laboratory Breeding Base of Marine Genetic Resources, Third Institute of Oceanography, State Oceanic Administration, Xiamen 361005, China
| | - Yan He
- 5. School of Radiation Medicine and Protection and Jiangsu Provincial Key Laboratory of Radiation Medicine and Protection, Medical College of Soochow University, Suzhou 215123, China
| | - Jianyuan Song
- 5. School of Radiation Medicine and Protection and Jiangsu Provincial Key Laboratory of Radiation Medicine and Protection, Medical College of Soochow University, Suzhou 215123, China
| | - Wenjie Wang
- 6. Collaborative Innovation Center of Radiation Medicine of Jiangsu Higher Education Institutions and School for Radiological and Interdisciplinary Sciences (RAD-X), Soochow University, Suzhou 215123, China
| | - Xifa Zhou
- 1. Department of Radiotherapy, Changzhou Tumor Hospital, Soochow University, Changzhou, 213001, China
| | - Xujing Lu
- 1. Department of Radiotherapy, Changzhou Tumor Hospital, Soochow University, Changzhou, 213001, China
| | - Shuyu Zhang
- 5. School of Radiation Medicine and Protection and Jiangsu Provincial Key Laboratory of Radiation Medicine and Protection, Medical College of Soochow University, Suzhou 215123, China;; 6. Collaborative Innovation Center of Radiation Medicine of Jiangsu Higher Education Institutions and School for Radiological and Interdisciplinary Sciences (RAD-X), Soochow University, Suzhou 215123, China
| | - Jianming Chen
- 3. Key Laboratory Breeding Base of Marine Genetic Resources, Third Institute of Oceanography, State Oceanic Administration, Xiamen 361005, China
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Serine/threonine kinase 16 and MAL2 regulate constitutive secretion of soluble cargo in hepatic cells. Biochem J 2014; 463:201-13. [PMID: 25084525 DOI: 10.1042/bj20140468] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
MAL2 (myelin and lymphocyte protein 2) is thought to regulate at least two steps in the hepatic apical transcytotic pathway. As vesicle budding and delivery at each step are driven by complex machineries, we predicted that MAL2 participates in several large protein complexes with multiple binding partners. To identify novel MAL2 interactors, we performed split-ubiquitin yeast two-hybrid assays and identified STK16 (serine/threonine kinase 16) as a putative interactor which we verified morphologically and biochemically. As STK16 is a Golgi-associated constitutively active kinase implicated in regulating secretion and because of the massive constitutive secretory capacity of hepatic cells, we tested whether MAL2 and STK16 function in secretion. Expression of a dominant-negative kinase-dead STK16 mutant (E202A) or knockdown of MAL2 impaired secretion that correlated with decreased expression of albumin and haptoglobin. By using 19°C temperature blocks and lysosome deacidification, we determined that E202A expression or MAL2 knockdown did not interfere with albumin synthesis or processing, but led to albumin lysosomal degradation. We conclude that MAL2 and the constitutively active STK16 function to sort secretory soluble cargo into the constitutive secretory pathway at the TGN (trans-Golgi network) in polarized hepatocytes.
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Carson BP, Del Bas JM, Moreno-Navarrete JM, Fernandez-Real JM, Mora S. The rab11 effector protein FIP1 regulates adiponectin trafficking and secretion. PLoS One 2013; 8:e74687. [PMID: 24040321 PMCID: PMC3770573 DOI: 10.1371/journal.pone.0074687] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2013] [Accepted: 08/07/2013] [Indexed: 12/28/2022] Open
Abstract
Adiponectin is an adipokine secreted by white adipocytes involved in regulating insulin sensitivity in peripheral tissues. Secretion of adiponectin in adipocytes relies on the endosomal system, however, the intracellular machinery involved in mediating adiponectin release is unknown. We have previously reported that intracellular adiponectin partially compartmentalizes with rab 5 and rab11, markers for the early/sorting and recycling compartments respectively. Here we have examined the role of several rab11 downstream effector proteins (rab11 FIPs) in regulating adiponectin trafficking and secretion. Overexpression of wild type rab11 FIP1, FIP3 and FIP5 decreased the amount of secreted adiponectin expressed in HEK293 cells, whereas overexpression of rab11 FIP2 or FIP4 had no effect. Furthermore shRNA-mediated depletion of FIP1 enhanced adiponectin release whereas knock down of FIP5 decreased adiponectin secretion. Knock down of FIP3 had no effect. In 3T3L1 adipocytes, endogenous FIP1 co-distributed intracellularly with endogenous adiponectin and FIP1 depletion enhanced adiponectin release without altering insulin-mediated trafficking of the glucose transporter Glut4. While adiponectin receptors internalized with transferrin receptors, there were no differences in transferrin receptor recycling between wild type and FIP1 depleted adipocytes. Consistent with its inhibitory role, FIP1 expression was decreased during adipocyte differentiation, by treatment with thiazolidinediones, and with increased BMI in humans. In contrast, FIP1 expression increased upon exposure of adipocytes to TNFα. In all, our findings identify FIP1 as a novel protein involved in the regulation of adiponectin trafficking and release.
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Affiliation(s)
- Brian P. Carson
- Department of Cellular and Molecular Physiology, Institute of Translational Medicine, the University of Liverpool, Liverpool, United Kingdom
| | - Josep Maria Del Bas
- Department of Cellular and Molecular Physiology, Institute of Translational Medicine, the University of Liverpool, Liverpool, United Kingdom
| | | | | | - Silvia Mora
- Department of Cellular and Molecular Physiology, Institute of Translational Medicine, the University of Liverpool, Liverpool, United Kingdom
- * E-mail:
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9
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Haataja L, Snapp E, Wright J, Liu M, Hardy AB, Wheeler MB, Markwardt ML, Rizzo M, Arvan P. Proinsulin intermolecular interactions during secretory trafficking in pancreatic β cells. J Biol Chem 2012; 288:1896-906. [PMID: 23223446 DOI: 10.1074/jbc.m112.420018] [Citation(s) in RCA: 66] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Classically, exit from the endoplasmic reticulum (ER) is rate-limiting for secretory protein trafficking because protein folding/assembly occurs there. In this study, we have exploited "hPro-CpepSfGFP," a human proinsulin bearing "superfolder" green fluorescent C-peptide expressed in pancreatic β cells where it is processed to human insulin and CpepSfGFP. Remarkably, steady-state accumulation of hPro-CpepSfGFP and endogenous proinsulin is in the Golgi region, as if final stages of protein folding/assembly were occurring there. The Golgi regional distribution of proinsulin is dynamic, influenced by fasting/refeeding, and increased with β cell zinc deficiency. However, coexpression of ER-entrapped mutant proinsulin-C(A7)Y shifts the steady-state distribution of wild-type proinsulin to the ER. Endogenous proinsulin coprecipitates with hPro-CpepSfGFP and even more so with hProC(A7)Y-CpepSfGFP. Using Cerulean and Venus-tagged proinsulins, we find that both WT-WT and WT-mutant proinsulin pairs exhibit FRET. The data demonstrate that wild-type proinsulin dimerizes within the ER but accumulates at a poorly recognized slow step within the Golgi region, reflecting either slow kinetics of proinsulin hexamerization, steps in formation of nascent secretory granules, or other unknown molecular events. However, in the presence of ongoing misfolding of a subpopulation of proinsulin in β cells, the rate-limiting step in transport of the remaining proinsulin shifts to the ER.
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Affiliation(s)
- Leena Haataja
- Division of Metabolism, Endocrinology, and Diabetes, University of Michigan Medical School, Ann Arbor, Michigan 48105, USA
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Abstract
Endothelial cells are reported to contain several distinct populations of regulated secretory organelles, including Weibel-Palade bodies (WPBs), the tissue plasminogen activator (tPA) organelle, and the type-2 chemokine-containing organelle. We show that the tPA and type-2 organelles in human endothelial cells represent a single compartment primarily responsible for unstimulated secretion of tPA or, in cells exposed to interleukin-1β (IL-1β), the cytokines IL-8, IL-6, monocyte chemoattractant protein-1 (MCP-1), and growth-regulated oncogene-α (GRO-α). This compartment was distinct from WPBs in that it lacked detectable von Willebrand factor, P-selectin, Rab27a, or CD63 immunoreactivity, displayed no time-dependent decrease in intragranule pH, underwent detectable unstimulated exocytosis, and was very poorly responsive to Ca(2+)-elevating secretagogues. WPBs could also contain tPA, and in IL-1β-treated cells, IL-8, IL-6, MCP-1, and GRO-α, and were the primary source for histamine or ionomycin-stimulated secretion of these molecules. However, analysis of the storage efficiency of cytokines and tPA revealed that all were very poorly stored compared with von Willebrand factor. The nonmammalian, nonsecretory protein EGFP, when expressed in the secretory pathway, also entered WPBs and had a storage efficiency similar to tPA and the cytokines tested. Based on these data, we proposed a revised model for storage and secretion of cytokines and tPA.
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11
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Honoré B. The rapidly expanding CREC protein family: members, localization, function, and role in disease. Bioessays 2009; 31:262-77. [PMID: 19260022 DOI: 10.1002/bies.200800186] [Citation(s) in RCA: 108] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Although many aspects of the physiological and pathophysiological mechanisms remain unknown, recent advances in our knowledge suggest that the CREC proteins are promising disease biomarkers or targets for therapeutic intervention in a variety of diseases. The CREC family of low affinity, Ca2+-binding, multiple EF-hand proteins are encoded by five genes, RCN1, RCN2, RCN3, SDF4, and CALU, resulting in reticulocalbin, ER Ca2+-binding protein of 55 kDa (ERC-55), reticulocalbin-3, Ca2+-binding protein of 45 kDa (Cab45), and calumenin. Alternative splicing increases the number of gene products. The proteins are localized in the cytosol, in various parts of the secretory pathway, secreted to the extracellular space or localized on the cell surface. The emerging functions appear to be highly diverse. The proteins interact with several different ligands. Rather well-described functions are attached to calumenin with the inhibition of several proteins in the endoplasmic or sarcoplasmic reticulum membrane, the vitamin K(1) 2,3-epoxide reductase, the gamma-carboxylase, the ryanodine receptor, and the Ca2+-transporting ATPase. Other functions concern participation in the secretory process, chaperone activity, signal transduction as well as participation in a large variety of disease processes.
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Affiliation(s)
- Bent Honoré
- Department of Medical Biochemistry, Aarhus University, Aarhus C, Denmark.
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12
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Hill EJ, Vernallis AB. Polarized secretion of leukemia inhibitory factor. BMC Cell Biol 2008; 9:53. [PMID: 18801170 PMCID: PMC2556326 DOI: 10.1186/1471-2121-9-53] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2008] [Accepted: 09/18/2008] [Indexed: 11/16/2022] Open
Abstract
Background The direction of cytokine secretion from polarized cells determines the cytokine's cellular targets. Leukemia inhibitory factor (LIF) belongs to the interleukin-6 (IL-6) family of cytokines and signals through LIFR/gp130. Three factors which may regulate the direction of LIF secretion were studied: the site of stimulation, signal peptides, and expression levels. Stimulation with IL-1β is known to promote IL-6 secretion from the stimulated membrane (apical or basolateral) in the human intestinal epithelial cell line Caco-2. Since LIF is related to IL-6, LIF secretion was also tested in Caco-2 following IL-1β stimulation. Signal peptides may influence the trafficking of LIF. Two isoforms of murine LIF, LIF-M and LIF-D, encode different signal peptides which have been associated with different locations of the mature protein in fibroblasts. To determine the effect of the signal peptides on LIF secretion, secretion levels were compared in Madin-Darby canine kidney (MDCK) clones which expressed murine LIF-M or LIF-D or human LIF under the control of an inducible promoter. Low and high levels of LIF expression were also compared since saturation of the apical or basolateral route would reveal specific transporters for LIF. Results When Caco-2 was grown on permeable supports, LIF was secreted constitutively with around 40% secreted into the apical chamber. Stimulation with IL-1β increased LIF production. After treating the apical surface with IL-1β, the percentage secreted apically remained similar to the untreated, whereas, when the cells were stimulated at the basolateral surface only 20% was secreted apically. In MDCK cells, an endogenous LIF-like protein was detected entirely in the apical compartment. The two mLIF isoforms showed no difference in their secretion patterns in MDCK. Interestingly, about 70% of murine and human LIF was secreted apically from MDCK over a 400-fold range of expression levels within clones and a 200,000-fold range across clones. Conclusion The site of stimulation affected the polarity of LIF secretion, while, signal peptides and expression levels did not. Exogenous LIF is transported in MDCK without readily saturated steps.
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Affiliation(s)
- Eric J Hill
- School of Life and Health Sciences, Aston University, Birmingham, UK.
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Sharma R, Tsuchiya M, Bartlett JD. Fluoride induces endoplasmic reticulum stress and inhibits protein synthesis and secretion. ENVIRONMENTAL HEALTH PERSPECTIVES 2008; 116:1142-1146. [PMID: 18795154 PMCID: PMC2535613 DOI: 10.1289/ehp.11375] [Citation(s) in RCA: 70] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 02/15/2008] [Accepted: 05/15/2008] [Indexed: 05/26/2023]
Abstract
BACKGROUND Exposure to excessive amounts of fluoride (F(-)) causes dental fluorosis in susceptible individuals; however, the mechanism of F(-)-induced toxicity is unclear. Previously, we have shown that high-dose F(-) activates the unfolded protein response (UPR) in ameloblasts that are responsible for dental enamel formation. The UPR is a signaling pathway responsible for either alleviating endoplasmic reticulum (ER) stress or for inducing apoptosis of the stressed cells. OBJECTIVES In this study we determined if low-dose F(-) causes ER stress and activates the UPR, and we also determined whether F(-) interferes with the secretion of proteins from the ER. METHODS We stably transfected the ameloblast-derived LS8 cell line with secreted alkaline phosphatase (SEAP) and determined activity and localization of SEAP and F(-)-mediated induction of UPR proteins. Also, incisors from mice given drinking water containing various concentrations of F(-) were examined for eucaryotic initiation factor-2, subunit alpha (eIF2alpha) phosphorylation. RESULTS We found that F(-) decreases the extracellular secretion of SEAP in a linear, dose-dependent manner. We also found a corresponding increase in the intracellular accumulation of SEAP after exposure to F(-). These changes are associated with the induction of UPR proteins such as the molecular chaperone BiP and phosphorylation of the UPR sensor PKR-like ER kinase, and its substrate, eIF2alpha. Importantly, F(-)-induced phosphorylation of eIF2alphawas confirmed in vivo. CONCLUSIONS These data suggest that F(-) initiates an ER stress response in ameloblasts that interferes with protein synthesis and secretion. Consequently, ameloblast function during enamel development may be impaired, and this may culminate in dental fluorosis.
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Affiliation(s)
- Ramaswamy Sharma
- Department of Cytokine Biology, Forsyth Institute, Boston, Massachusetts, USA
- Department of Developmental Biology, Harvard School of Dental Medicine, Boston, Massachusetts, USA
| | - Masahiro Tsuchiya
- Division of Aging and Geriatric Dentistry, Graduate School of Dentistry, Tohoku University, Sendai, Japan
| | - John D. Bartlett
- Department of Cytokine Biology, Forsyth Institute, Boston, Massachusetts, USA
- Department of Developmental Biology, Harvard School of Dental Medicine, Boston, Massachusetts, USA
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Samuni Y, Cawley NX, Zheng C, Cotrim AP, Loh YP, Baum BJ. Sorting behavior of a transgenic erythropoietin-growth hormone fusion protein in murine salivary glands. Hum Gene Ther 2008; 19:279-86. [PMID: 18303958 DOI: 10.1089/hum.2007.0136] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Salivary glands are useful gene transfer target sites for the production of therapeutic proteins, and can secrete proteins into both saliva and the bloodstream. The mechanisms involved in this differential protein sorting are not well understood, although it is believed, at least in part, to be based on the amino acid sequence of the encoded protein. We hypothesized that a transgenic protein, human erythropoietin (hEpo), normally sorted from murine salivary glands into the bloodstream, could be redirected into saliva by fusing it with human growth hormone (hGH). After transfection, the hEpo-hGH fusion protein was expressed and glycosylated in both HEK 293 and A5 cells. When packaged in an adenovirus serotype 5 vector and delivered to murine submandibular cells in vivo via retroductal cannulation, the hEpo-hGH fusion protein was also expressed, albeit at approximately 26% of the levels of hEpo expression. Importantly, in multiple experiments with different cohorts of mice, the hEpo-hGH fusion protein was sorted more frequently into saliva, versus the bloodstream, than was the hEpo protein (p < 0.001). These studies show it is possible to redirect the secretion of a transgenic constitutive pathway protein from salivary gland cells after gene transfer in vivo, a finding that may facilitate developing novel treatments for certain upper gastrointestinal tract disorders.
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Affiliation(s)
- Yuval Samuni
- Gene Therapy and Therapeutics Branch, National Institute of Dental and Craniofacial Research, National Institutes of Health, Department of Health and Human Services, Bethesda, MD 20892, USA
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15
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Origins of the regulated secretory pathway. THE GOLGI APPARATUS 2008. [PMCID: PMC7121582 DOI: 10.1007/978-3-211-76310-0_30] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Modes of transport of soluble (or luminal) secretory proteins synthesized in the endoplasmic reticulum (ER) could be divided into two groups. The socalled constitutive secretory pathway (CSP) is common to all eukaryotic cells, constantly delivering constitutive soluble secretory proteins (CSSPs) linked to the rate of protein synthesis but largely independent of external stimuli. In regulated secretion, protein is sorted from the Golgi into storage/secretory granules (SGs) whose contents are released when stimuli trigger their final fusion with the plasma membrane (Hannah et al. 1999).
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