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Est CB, Murphy RM. An in vitro model for vitamin A transport across the human blood-brain barrier. eLife 2023; 12:RP87863. [PMID: 37934575 PMCID: PMC10629827 DOI: 10.7554/elife.87863] [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] [Indexed: 11/08/2023] Open
Abstract
Vitamin A, supplied by the diet, is critical for brain health, but little is known about its delivery across the blood-brain barrier (BBB). Brain microvascular endothelial-like cells (BMECs) differentiated from human-derived induced pluripotent stem cells (iPSCs) form a tight barrier that recapitulates many of the properties of the human BBB. We paired iPSC-derived BMECs with recombinant vitamin A serum transport proteins, retinol-binding protein (RBP), and transthyretin (TTR), to create an in vitro model for the study of vitamin A (retinol) delivery across the human BBB. iPSC-derived BMECs display a strong barrier phenotype, express key vitamin A metabolism markers, and can be used for quantitative modeling of retinol accumulation and permeation. Manipulation of retinol, RBP, and TTR concentrations, and the use of mutant RBP and TTR, yielded novel insights into the patterns of retinol accumulation in, and permeation across, the BBB. The results described herein provide a platform for deeper exploration of the regulatory mechanisms of retinol trafficking to the human brain.
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Affiliation(s)
- Chandler B Est
- Department of Chemical and Biological Engineering, University of WisconsinMadisonUnited States
| | - Regina M Murphy
- Department of Chemical and Biological Engineering, University of WisconsinMadisonUnited States
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2
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Est CB, Murphy RM. An in vitro model for vitamin A transport across the human blood-brain barrier. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.04.11.536348. [PMID: 37090623 PMCID: PMC10120720 DOI: 10.1101/2023.04.11.536348] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/25/2023]
Abstract
Vitamin A, supplied by the diet, is critical for brain health, but little is known about its delivery across the blood-brain barrier (BBB). Brain microvascular endothelial-like cells (BMECs) differentiated from human-derived induced pluripotent stem cells (iPSC) form a tight barrier that recapitulates many of the properties of the human BBB. We paired iPSC-derived BMECs with recombinant vitamin A serum transport proteins, retinol binding protein (RBP) and transthyretin (TTR), to create an in vitro model for the study of vitamin A (retinol) delivery across the human BBB. iPSC-derived BMECs display a strong barrier phenotype, express key vitamin A metabolism markers and can be used for quantitative modeling of retinol accumulation and permeation. Manipulation of retinol, RBP and TTR concentrations, and the use of mutant RBP and TTR, yielded novel insights into the patterns of retinol accumulation in, and permeation across, the BBB. The results described herein provide a platform for deeper exploration of the regulatory mechanisms of retinol trafficking to the human brain.
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Affiliation(s)
| | - Regina M. Murphy
- Department of Chemical and Biological Engineering, University of Wisconsin – Madison 1415 Engineering Dr., Madison, WI 53706
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3
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Kim N, Priefer R. Retinol binding protein 4 antagonists and protein synthesis inhibitors: Potential for therapeutic development. Eur J Med Chem 2021; 226:113856. [PMID: 34547506 DOI: 10.1016/j.ejmech.2021.113856] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2021] [Revised: 09/07/2021] [Accepted: 09/13/2021] [Indexed: 12/12/2022]
Abstract
Retinol-binding protein 4 (RBP4) is a serum protein that transports Vitamin A. RBP4 is correlated with numerous diseases and metabolic syndromes, including insulin resistance in type 2 diabetes, cardiovascular diseases, obesity, and macular degeneration. Recently, RBP4 antagonists and protein synthesis inhibitors are under development to regulate the effect of RBP4. Several RBP4 antagonists, especially BPN-14136, have demonstrated promising safety profiles and potential therapeutic benefits in animal studies. Two RBP4 antagonists, specifically tinlarebant (Belite Bio) and STG-001 (Stargazer) are currently undergoing clinical trials. Some antidiabetic drugs and nutraceuticals have been reported to reduce RBP4 expression, but more clinical data is needed to evaluate their therapeutical benefits. As regulating RBP4 levels or its activities would benefit a wide range of patients, further research is highly recommended to develop clinically useful RBP4 antagonists or protein synthesis inhibitors.
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Affiliation(s)
- Noheul Kim
- Massachusetts College of Pharmacy and Health Sciences University, Boston, MA, USA
| | - Ronny Priefer
- Massachusetts College of Pharmacy and Health Sciences University, Boston, MA, USA.
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Retinal toxicities of systemic anticancer drugs. Surv Ophthalmol 2021; 67:97-148. [PMID: 34048859 DOI: 10.1016/j.survophthal.2021.05.007] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2020] [Revised: 05/08/2021] [Accepted: 05/10/2021] [Indexed: 01/07/2023]
Abstract
Newer anticancer drugs have revolutionized cancer treatment in the last decade, but conventional chemotherapy still occupies a central position in many cancers, with combination therapy and newer methods of delivery increasing their efficacy while minimizing toxicities. We discuss the retinal toxicities of anticancer drugs with an emphasis on the mechanism of toxicity. Uveitis is seen with the use of v-raf murine sarcoma viral oncogene homolog B editing anticancer inhibitors as well as immunotherapy. Most of the cases are mild with only anterior uveitis, but severe cases of posterior uveitis, panuveitis, and Vogt-Koyanagi-Harada-like disease may also occur. In the retina, a transient neurosensory detachment is observed in almost all patients on mitogen-activated protein kinase kinase (MEK) inhibitors. Microvasculopathy is often seen with interferon α, but vascular occlusion is a more serious toxicity caused by interferon α and MEK inhibitors. Crystalline retinopathy with or without macular edema may occur with tamoxifen; however, even asymptomatic patients may develop cavitatory spaces seen on optical coherence tomography. A unique macular edema with angiographic silence is characteristic of taxanes. Delayed dark adaptation has been observed with fenretinide. Interestingly, this drug is finding potential application in Stargardt disease and age-related macular degeneration.
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Cioffi CL, Muthuraman P, Raja A, Varadi A, Racz B, Petrukhin K. Discovery of Bispecific Antagonists of Retinol Binding Protein 4 That Stabilize Transthyretin Tetramers: Scaffolding Hopping, Optimization, and Preclinical Pharmacological Evaluation as a Potential Therapy for Two Common Age-Related Comorbidities. J Med Chem 2020; 63:11054-11084. [DOI: 10.1021/acs.jmedchem.0c00996] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Affiliation(s)
- Christopher L. Cioffi
- Departments of Basic and Clinical Sciences and Pharmaceutical Sciences, Albany College of Pharmacy and Health Sciences, 106 New Scotland Avenue, Albany, New York 12208, United States
| | - Parthasarathy Muthuraman
- Departments of Basic and Clinical Sciences and Pharmaceutical Sciences, Albany College of Pharmacy and Health Sciences, 106 New Scotland Avenue, Albany, New York 12208, United States
| | - Arun Raja
- Departments of Basic and Clinical Sciences and Pharmaceutical Sciences, Albany College of Pharmacy and Health Sciences, 106 New Scotland Avenue, Albany, New York 12208, United States
| | - Andras Varadi
- Department of Ophthalmology, Columbia University Medical Center, New York, New York 10032, United States
| | - Boglarka Racz
- Department of Ophthalmology, Columbia University Medical Center, New York, New York 10032, United States
| | - Konstantin Petrukhin
- Department of Ophthalmology, Columbia University Medical Center, New York, New York 10032, United States
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Haaker MW, Vaandrager AB, Helms JB. Retinoids in health and disease: A role for hepatic stellate cells in affecting retinoid levels. Biochim Biophys Acta Mol Cell Biol Lipids 2020; 1865:158674. [PMID: 32105672 DOI: 10.1016/j.bbalip.2020.158674] [Citation(s) in RCA: 20] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2019] [Revised: 02/20/2020] [Accepted: 02/21/2020] [Indexed: 12/13/2022]
Abstract
Vitamin A (retinol) is important for normal growth, vision and reproduction. It has a role in the immune response and the development of metabolic syndrome. Most of the retinol present in the body is stored as retinyl esters within lipid droplets in hepatic stellate cells (HSCs). In case of liver damage, HSCs release large amounts of stored retinol, which is partially converted to retinoic acid (RA). This surge of RA can mediate the immune response and enhance the regeneration of the liver. If the damage persists activated HSCs change into myofibroblast-like cells producing extracellular matrix, which increases the chance of tumorigenesis to occur. RA has been shown to decrease proliferation and metastasis of hepatocellular carcinoma. The levels of RA and RA signaling are influenced by the possibility to esterify retinol towards retinyl esters. This suggests a complex regulation between different retinoids, with an important regulatory role for HSCs.
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Affiliation(s)
- Maya W Haaker
- Department of Biomolecular Health Sciences, Faculty of Veterinary Medicine, Utrecht University, Utrecht, the Netherlands
| | - Arie B Vaandrager
- Department of Biomolecular Health Sciences, Faculty of Veterinary Medicine, Utrecht University, Utrecht, the Netherlands
| | - J Bernd Helms
- Department of Biomolecular Health Sciences, Faculty of Veterinary Medicine, Utrecht University, Utrecht, the Netherlands.
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Est CB, Murphy RM. Retinol binding protein IV purified from Escherichia coli using intein-mediated cleavage as a suitable replacement for serum sources. Protein Expr Purif 2019; 167:105542. [PMID: 31756375 DOI: 10.1016/j.pep.2019.105542] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2019] [Revised: 10/22/2019] [Accepted: 11/18/2019] [Indexed: 12/27/2022]
Abstract
Retinol binding protein IV (RBP) functions as the principal carrier of retinol (Vitamin A) in the blood, where RBP circulates bound to another serum protein, transthyretin. Isolation of pure RBP from the transthyretin complex in human serum can be difficult, but expression of RBP in recombinant systems can circumvent these purification issues. Human recombinant RBP has previously been successfully expressed and purified from E. coli, but recovery of active protein typically requires extensive processing steps, such as denaturing and refolding, and complex purification steps, such as multi-modal chromatography. Furthermore, these methods produce recombinant proteins, often tagged, that display different functional and structural characteristics across systems. In this work, we optimized downstream processing by use of an intein-based expression system in E. coli to produce tag-free, human recombinant RBP (rRBP) with intact native amino termini at yields of up to ~15 mg/L off column. The novel method requires solubilization of inclusion bodies and subsequent oxidative refolding in the presence of retinol, but importantly allows for one-step chromatographic purification that yields high purity rRBP with no N-terminal Met or other tag. Previously reported purification methods typically require two or more chromatographic separation steps to recover tag-free rRBP. Given the interest in mechanistic understanding of RBP transport of retinol in health and disease, we characterized our purified product extensively to confirm rRBP is both structurally and functionally a suitable replacement for serum-derived RBP.
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Affiliation(s)
- Chandler B Est
- Department of Chemical and Biological Engineering, University of Wisconsin - Madison, 1415 Engineering Dr., Madison, WI, 53706, USA
| | - Regina M Murphy
- Department of Chemical and Biological Engineering, University of Wisconsin - Madison, 1415 Engineering Dr., Madison, WI, 53706, USA.
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Silvaroli JA, Widjaja-Adhi MAK, Trischman T, Chelstowska S, Horwitz S, Banerjee S, Kiser PD, Blaner WS, Golczak M. Abnormal Cannabidiol Modulates Vitamin A Metabolism by Acting as a Competitive Inhibitor of CRBP1. ACS Chem Biol 2019; 14:434-448. [PMID: 30721022 DOI: 10.1021/acschembio.8b01070] [Citation(s) in RCA: 17] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
Cellular retinol-binding proteins (CRBPs) facilitate the uptake and intracellular transport of vitamin A. They integrate retinoid metabolism, playing an important role in regulating the synthesis of bioactive vitamin A metabolites. Thus, CRBPs constitute potential pharmacological targets to modulate cellular retinoid status that in turn may have applications in the treatment of certain immunological, metabolic, and ocular disorders. Here we identify abnormal cannabidiol (abn-CBD) as a nonretinoid inhibitor of cellular retinol-binding protein 1 (CRBP1). X-ray crystal structures of CRBP1 in complex with abn-CBD and its derivatives revealed a distinctive mode of protein-ligand interaction and provided a molecular basis for the high affinity and selectivity of this compound. We demonstrated that abn-CBD modulates the flux of retinoids via the retinoid cycle in vivo. Furthermore, the biological activity of abn-CBD was evidenced by its ability to protect against light-induced retinal damage in Balb/cJ mice. Altogether, our findings indicate that targeting selected CRBPs with a small-molecule inhibitor can potentially lead to the development of new therapeutic agents to counteract diseases with etiologies involving imbalance in retinoid metabolism or signaling.
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Affiliation(s)
| | | | | | | | | | - Surajit Banerjee
- Department of Chemistry and Chemical Biology, Cornell University, Ithaca, NY, United States
- Northeastern Collaborative Access Team, Argonne National Laboratory, Argonne, IL, United States
| | - Philip D. Kiser
- Research Service, Louis Stokes Cleveland VA Medical Center, Cleveland, OH, United States
| | - William S. Blaner
- Department of Medicine, College of Physicians and Surgeons, Columbia University, New York, NY, United States
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Hajny S, Christoffersen C. A Novel Perspective on the ApoM-S1P Axis, Highlighting the Metabolism of ApoM and Its Role in Liver Fibrosis and Neuroinflammation. Int J Mol Sci 2017; 18:ijms18081636. [PMID: 28749426 PMCID: PMC5578026 DOI: 10.3390/ijms18081636] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2017] [Revised: 07/18/2017] [Accepted: 07/25/2017] [Indexed: 02/07/2023] Open
Abstract
Hepatocytes, renal proximal tubule cells as well as the highly specialized endothelium of the blood brain barrier (BBB) express and secrete apolipoprotein M (apoM). ApoM is a typical lipocalin containing a hydrophobic binding pocket predominantly carrying Sphingosine-1-Phosphate (S1P). The small signaling molecule S1P is associated with several physiological as well as pathological pathways whereas the role of apoM is less explored. Hepatic apoM acts as a chaperone to transport S1P through the circulation and kidney derived apoM seems to play a role in S1P recovery to prevent urinal loss. Finally, polarized endothelial cells constituting the lining of the BBB express apoM and secrete the protein to the brain as well as to the blood compartment. The review will provide novel insights on apoM and S1P, and its role in hepatic fibrosis, neuroinflammation and BBB integrity.
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Affiliation(s)
- Stefan Hajny
- Department of Clinical Biochemistry, University Hospital of Copenhagen, Rigshospitalet, Blegdamsvej 9, 2100 Copenhagen, Denmark.
- Department of Biomedical Sciences, Faculty of Health and Science, University of Copenhagen, Blegdamsvej 3, 2200 Copenhagen, Denmark.
| | - Christina Christoffersen
- Department of Clinical Biochemistry, University Hospital of Copenhagen, Rigshospitalet, Blegdamsvej 9, 2100 Copenhagen, Denmark.
- Department of Biomedical Sciences, Faculty of Health and Science, University of Copenhagen, Blegdamsvej 3, 2200 Copenhagen, Denmark.
- Department of Cardiology, University Hospital of Copenhagen, Rigshospitalet, Blegdamsvej 9, 2100 Copenhagen, Denmark.
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10
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Metzler MA, Sandell LL. Enzymatic Metabolism of Vitamin A in Developing Vertebrate Embryos. Nutrients 2016; 8:E812. [PMID: 27983671 PMCID: PMC5188467 DOI: 10.3390/nu8120812] [Citation(s) in RCA: 43] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2016] [Revised: 12/09/2016] [Accepted: 12/13/2016] [Indexed: 12/16/2022] Open
Abstract
Embryonic development is orchestrated by a small number of signaling pathways, one of which is the retinoic acid (RA) signaling pathway. Vitamin A is essential for vertebrate embryonic development because it is the molecular precursor of the essential signaling molecule RA. The level and distribution of RA signaling within a developing embryo must be tightly regulated; too much, or too little, or abnormal distribution, all disrupt embryonic development. Precise regulation of RA signaling during embryogenesis is achieved by proteins involved in vitamin A metabolism, retinoid transport, nuclear signaling, and RA catabolism. The reversible first step in conversion of the precursor vitamin A to the active retinoid RA is mediated by retinol dehydrogenase 10 (RDH10) and dehydrogenase/reductase (SDR family) member 3 (DHRS3), two related membrane-bound proteins that functionally activate each other to mediate the interconversion of retinol and retinal. Alcohol dehydrogenase (ADH) enzymes do not contribute to RA production under normal conditions during embryogenesis. Genes involved in vitamin A metabolism and RA catabolism are expressed in tissue-specific patterns and are subject to feedback regulation. Mutations in genes encoding these proteins disrupt morphogenesis of many systems in a developing embryo. Together these observations demonstrate the importance of vitamin A metabolism in regulating RA signaling during embryonic development in vertebrates.
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Affiliation(s)
- Melissa A Metzler
- Department of Molecular, Cellular and Craniofacial Biology, University of Louisville, Louisville, KY 40201, USA.
| | - Lisa L Sandell
- Department of Molecular, Cellular and Craniofacial Biology, University of Louisville, Louisville, KY 40201, USA.
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Libien J, Kupersmith MJ, Blaner W, McDermott MP, Gao S, Liu Y, Corbett J, Wall M. Role of vitamin A metabolism in IIH: Results from the idiopathic intracranial hypertension treatment trial. J Neurol Sci 2016; 372:78-84. [PMID: 28017254 DOI: 10.1016/j.jns.2016.11.014] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2016] [Revised: 11/05/2016] [Accepted: 11/08/2016] [Indexed: 10/20/2022]
Abstract
INTRODUCTION Vitamin A and its metabolites (called retinoids) have been thought to play a role in the development of idiopathic intracranial hypertension (IIH). The IIH Treatment Trial (IIHTT) showed the efficacy of acetazolamide (ACZ) in improving visual field function, papilledema grade, quality of life and cerebrospinal fluid (CSF) pressure. We postulated that IIH patients would demonstrate elevated measures of vitamin A metabolites in the serum and CSF. METHODS Comprehensive measures of serum vitamin A and its metabolites were obtained from 96 IIHTT subjects, randomly assigned to treatment with ACZ or placebo, and 25 controls with similar gender, age and body mass index (BMI). These included retinol, retinol binding protein, all-trans retinoic acid (ATRA), alpha- and beta-carotenes, and beta-cryptoxanthin. The IIHTT subjects also had CSF and serum vitamin A and metabolite measurements obtained at study entry and at six months. RESULTS At study entry, of the vitamin A metabolites only serum ATRA was significantly different in IIHTT subjects (median 4.33nM) and controls (median 5.04nM, p=0.02). The BMI of IIHTT subjects showed mild significant negative correlations with serum ATRA, alpha- and beta-carotene, and beta-cryptoxanthin. In contrast, the control subject BMI correlated only with serum ATRA. At six months, the serum retinol, alpha-carotene, beta-carotene, and CSF retinol were increased from baseline in the ACZ treated group, but only increases in alpha-carotene (p=0.02) and CSF ATRA (p=0.04) were significantly greater in the ACZ group compared with the placebo group. No other vitamin A measures were significantly altered over the six months in either treatment group. Weight loss correlated with only with the change in serum beta-carotene (r=-0.44, p=0.006) and the change in CSF retinol (r=-0.61, p=0.02). CONCLUSION Vitamin A toxicity is unlikely a contributory factor in the causation of IIH. Our findings differ from those of prior reports in part because of our use of more accurate quantitative methods and measuring vitamin A metabolites in both serum and CSF. ACZ may alter retinoid metabolism in IIH patients.
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Affiliation(s)
- J Libien
- Pathology, State University of New York, Downstate School of Medicine, Brooklyn, NY, United States
| | - M J Kupersmith
- Neurology and Ophthalmology, Mount Sinai West, Icahn School of Medicine at Mount Sinai, New York, NY, United States.
| | - W Blaner
- Medicine, College of Physicians and Surgeons, Columbia University School of Medicine, New York, NY, United States
| | - M P McDermott
- Biostatistics, University of Rochester, Rochester, NY, United States
| | - S Gao
- Biostatistics, University of Rochester, Rochester, NY, United States
| | - Y Liu
- Pathology, State University of New York, Downstate School of Medicine, Brooklyn, NY, United States
| | - J Corbett
- Neurology, University of Mississippi School of Medicine, Jackson, MS, United States
| | - M Wall
- Neurology, University of Iowa School of Medicine, Iowa City, IA, United States
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Noy N, Li L, Abola MV, Berger NA. Is retinol binding protein 4 a link between adiposity and cancer? Horm Mol Biol Clin Investig 2016; 23:39-46. [PMID: 26136304 DOI: 10.1515/hmbci-2015-0019] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2015] [Accepted: 05/23/2015] [Indexed: 01/30/2023]
Abstract
Retinol binding protein 4 (RBP4) is synthesized in the liver where it binds vitamin A, retinol, and transports it to tissues throughout the body. It has been shown in some studies that the level of circulating RBP4 increases with body mass, and the protein has been implicated as a mediator in the development of insulin resistance and the metabolic disease. Adipose tissue serves as another site of RBP4 synthesis, accounting for its designation as an adipokine. In addition to its function as a transport protein, RBP4 serves as a signaling molecule which, by binding to the membrane receptor STRA6, triggers downstream activation of pro-oncogenic pathways including JAK2/STAT3/5. Taken together, available information suggests the possibility that RBP4 may be a link between obesity and cancer.
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Abstract
Vitamin A, retinol, circulates in blood bound to retinol-binding protein (RBP4) which, in turn, associates with another serum protein, transthyretin (TTR), to form a ternary retinol-RBP4-TTR complex. At some tissues, retinol-bound (holo-) RBP4 is recognised by a receptor termed stimulated by retinoic acid 6 (STRA6) which transports retinol into cells. This mini-review summarises evidence demonstrating that, in addition to functioning as a retinol transporter, STRA6 is also a signalling receptor which is activated by holo-RBP4. The data show that STRA6-mediated retinol transport induces receptor phosphorylation, in turn activating a Janus kinases2/signal transducers and activators of transcription (STAT)3/5 cascade that culminates in induction of STAT target genes. STRA6-mediated retinol transport and cell signalling are inter-dependent, and both functions critically rely on intracellular retinol trafficking and metabolism. Hence, STRA6 couples 'sensing' of vitamin A homeostasis and metabolism to cell signalling, allowing it to control important biological functions. For example, by inducing the expression of the STAT target gene suppressor of cytokine signalling 3, STRA6 potently suppresses insulin responses. These observations provide a rationale for understanding the reports that elevation in serum levels of RBP4, often observed in obese mice and human subjects, causes insulin resistance. The observations indicate that the holo-RBP4 /STRA6 signalling cascade may comprise an important link through which obesity leads to insulin resistance and suggest that the pathway may be a novel target for treatment of metabolic diseases.
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Abstract
Vitamin A, retinol, circulates in blood bound to retinol binding protein (RBP). In some tissues, the retinol-RBP complex (holo-RBP) is recognized by a membrane receptor, termed STRA6, which mediates uptake of retinol into cells. Recent studies have revealed that, in addition to serving as a retinol transporter, STRA6 is a ligand-activated cell surface signaling receptor that, upon binding of holo-RBP activates JAK/STAT signaling, culminating in the induction of STAT target genes. It has further been shown that retinol transport and cell signaling by STRA6 are critically interdependent and that both are coupled to intracellular vitamin A metabolism. The molecular mechanism of action of STRA6 and its associated machinery is beginning to be revealed, but further work is needed to identify and characterize the complete range of genes and associated signaling cascades that are regulated by STRA6 in different tissues. An understanding of STRA6 is clinically relevant, as for example, it has been shown to be hyper- activated in obese animals, leading to insulin resistance. A potential role for STRA6 in other pathologies, including cancer, awaits further investigation.
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Affiliation(s)
- Noa Noy
- Department of Cellular and Molecular Medicine, Lerner Research Institute, Cleveland Clinic Foundation, Cleveland, OH, 44195, USA.
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15
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Cioffi CL, Racz B, Freeman EE, Conlon MP, Chen P, Stafford DG, Schwarz DMC, Zhu L, Kitchen DB, Barnes KD, Dobri N, Michelotti E, Cywin CL, Martin WH, Pearson PG, Johnson G, Petrukhin K. Bicyclic [3.3.0]-Octahydrocyclopenta[c]pyrrolo Antagonists of Retinol Binding Protein 4: Potential Treatment of Atrophic Age-Related Macular Degeneration and Stargardt Disease. J Med Chem 2015; 58:5863-88. [PMID: 26181715 DOI: 10.1021/acs.jmedchem.5b00423] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
Antagonists of retinol-binding protein 4 (RBP4) impede ocular uptake of serum all-trans retinol (1) and have been shown to reduce cytotoxic bisretinoid formation in the retinal pigment epithelium (RPE), which is associated with the pathogenesis of both dry age-related macular degeneration (AMD) and Stargardt disease. Thus, these agents show promise as a potential pharmacotherapy by which to stem further neurodegeneration and concomitant vision loss associated with geographic atrophy of the macula. We previously disclosed the discovery of a novel series of nonretinoid RBP4 antagonists, represented by bicyclic [3.3.0]-octahydrocyclopenta[c]pyrrolo analogue 4. We describe herein the utilization of a pyrimidine-4-carboxylic acid fragment as a suitable isostere for the anthranilic acid appendage of 4, which led to the discovery of standout antagonist 33. Analogue 33 possesses exquisite in vitro RBP4 binding affinity and favorable drug-like characteristics and was found to reduce circulating plasma RBP4 levels in vivo in a robust manner (>90%).
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Affiliation(s)
| | - Boglarka Racz
- §Department of Ophthalmology, Columbia University Medical Center, New York, New York 10032, United States
| | | | | | | | | | | | | | | | | | - Nicoleta Dobri
- §Department of Ophthalmology, Columbia University Medical Center, New York, New York 10032, United States
| | - Enrique Michelotti
- #National Institute of Mental Health, National Institutes of Health, Bethesda, Maryland 20892, United States
| | - Charles L Cywin
- ○National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland 20892, United States
| | - William H Martin
- ⊥WHM Consulting LLC, 111 Sterling City Road, Lyme, Connecticut 06371, United States
| | - Paul G Pearson
- ∥iCuraVision LLC, 31194 La Baya Drive, Suite 101, Westlake Village, California 91362, United States
| | - Graham Johnson
- ∥iCuraVision LLC, 31194 La Baya Drive, Suite 101, Westlake Village, California 91362, United States
| | - Konstantin Petrukhin
- §Department of Ophthalmology, Columbia University Medical Center, New York, New York 10032, United States
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Zhang Z, Wang C, Zha Y, Hu W, Gao Z, Zang Y, Chen J, Zhang J, Dong L. Corona-directed nucleic acid delivery into hepatic stellate cells for liver fibrosis therapy. ACS NANO 2015; 9:2405-19. [PMID: 25587629 DOI: 10.1021/nn505166x] [Citation(s) in RCA: 97] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/20/2023]
Abstract
Strategies to modify nanoparticles with biological ligands for targeted drug delivery in vivo have been widely studied but met with limited clinical success. A possible reason is that, in the blood circulation, serum proteins could rapidly form a layer of protein "corona" on the vehicle surface, which might block the modified ligands and hamper their targeting functions. We speculate that strategies for drug delivery can be designed based upon elegant control of the corona formation on the vehicle surfaces. In this study, we demonstrate a retinol-conjugated polyetherimine (RcP) nanoparticle system that selectively recruited the retinol binding protein 4 (RBP) in its corona components. RBP was found to bind retinol, and direct the antisense oligonucleotide (ASO)-laden RcP carrier to hepatic stellate cells (HSC), which play essential roles in the progression of hepatic fibrosis. In both mouse fibrosis models, induced by carbon tetrachloride (CCl4) and bile duct ligation (BDL), respectively, the ASO-laden RcP particles effectively suppressed the expression of type I collagen (collagen I), and consequently ameliorated hepatic fibrosis. Such findings suggest that this delivery system, designed to exploit the power of corona proteins, can serve as a promising tool for targeted delivery of therapeutic agents for the treatment of hepatic fibrosis.
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Affiliation(s)
- Zhengping Zhang
- †State Key Laboratory of Pharmaceutical Biotechnology, School of Life Sciences, Nanjing University, Nanjing 210093, China
| | - Chunming Wang
- ‡State Key Laboratory of Quality Research in Chinese Medicine, Institute of Chinese Medical Sciences, University of Macau, Taipa, Macau SAR, China
| | - Yinhe Zha
- †State Key Laboratory of Pharmaceutical Biotechnology, School of Life Sciences, Nanjing University, Nanjing 210093, China
| | - Wei Hu
- †State Key Laboratory of Pharmaceutical Biotechnology, School of Life Sciences, Nanjing University, Nanjing 210093, China
| | - Zhongfei Gao
- †State Key Laboratory of Pharmaceutical Biotechnology, School of Life Sciences, Nanjing University, Nanjing 210093, China
| | - Yuhui Zang
- †State Key Laboratory of Pharmaceutical Biotechnology, School of Life Sciences, Nanjing University, Nanjing 210093, China
| | - Jiangning Chen
- †State Key Laboratory of Pharmaceutical Biotechnology, School of Life Sciences, Nanjing University, Nanjing 210093, China
| | - Junfeng Zhang
- †State Key Laboratory of Pharmaceutical Biotechnology, School of Life Sciences, Nanjing University, Nanjing 210093, China
| | - Lei Dong
- †State Key Laboratory of Pharmaceutical Biotechnology, School of Life Sciences, Nanjing University, Nanjing 210093, China
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Noy N. Signaling by retinol and its serum binding protein. Prostaglandins Leukot Essent Fatty Acids 2015; 93:3-7. [PMID: 25481334 PMCID: PMC4323939 DOI: 10.1016/j.plefa.2014.10.004] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/15/2014] [Revised: 10/10/2014] [Accepted: 10/20/2014] [Indexed: 01/13/2023]
Abstract
Vitamin A, retinol, circulates in blood bound to retinol-binding protein (RBP) which, in turn, associates with transthyretin (TTR) to form a retinol-RBP-TTR ternary complex. At some tissues, retinol-bound (holo-) RBP is recognized by a membrane protein termed STRA6, which transports retinol from extracellular RBP into cells and, concomitantly, activates a JAK2/STAT3/5 signaling cascade that culminates in induction of STAT target genes. STRA6-mediated retinol transport and cell signaling are critically inter-dependent, and they both require the presence of cellular retinol-binding protein 1 (CRBP1), an intracellular retinol acceptor, as well as a retinol-metabolizing enzyme such as lecithin:retinol acyltransferase (LRAT). STRA6 thus functions as a "cytokine signaling transporter" which couples vitamin A homeostasis and metabolism to cell signaling, thereby regulating gene transcription. Recent studies provided molecular level insights into the mode of action of this unique protein.
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Affiliation(s)
- Noa Noy
- Department of Cellular and Molecular Medicine, Lerner Research Institute, Cleveland Clinic Foundation, and Department of Nutrition, Case Western Reserve University School of Medicine, 9500 Euclid Ave., Cleveland, OH 44195, USA.
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Cioffi CL, Dobri N, Freeman EE, Conlon MP, Chen P, Stafford DG, Schwarz DMC, Golden KC, Zhu L, Kitchen DB, Barnes KD, Racz B, Qin Q, Michelotti E, Cywin CL, Martin WH, Pearson PG, Johnson G, Petrukhin K. Design, synthesis, and evaluation of nonretinoid retinol binding protein 4 antagonists for the potential treatment of atrophic age-related macular degeneration and Stargardt disease. J Med Chem 2014; 57:7731-57. [PMID: 25210858 PMCID: PMC4174998 DOI: 10.1021/jm5010013] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
![]()
Accumulation of lipofuscin in the
retina is associated with pathogenesis
of atrophic age-related macular degeneration and Stargardt disease.
Lipofuscin bisretinoids (exemplified by N-retinylidene-N-retinylethanolamine) seem to mediate lipofuscin toxicity.
Synthesis of lipofuscin bisretinoids depends on the influx of retinol
from serum to the retina. Compounds antagonizing the retinol-dependent
interaction of retinol-binding protein 4 (RBP4) with transthyretin
in the serum would reduce serum RBP4 and retinol and inhibit bisretinoid
formation. We recently showed that A1120 (3), a potent
carboxylic acid based RBP4 antagonist, can significantly reduce lipofuscin
bisretinoid formation in the retinas of Abca4–/– mice. As part of the NIH
Blueprint Neurotherapeutics Network project we undertook the in vitro exploration to identify novel conformationally flexible and constrained
RBP4 antagonists with improved potency and metabolic stability. We
also demonstrate that upon acute and chronic dosing in rats, 43, a potent cyclopentyl fused pyrrolidine antagonist, reduced
circulating plasma RBP4 protein levels by approximately 60%.
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Affiliation(s)
- Christopher L Cioffi
- Department of Medicinal Chemistry, Albany Molecular Research, Inc. , East Campus, C-Wing, Rensselaer, New York 12144, United States
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Pan J, Guleria RS, Zhu S, Baker KM. Molecular Mechanisms of Retinoid Receptors in Diabetes-Induced Cardiac Remodeling. J Clin Med 2014; 3:566-94. [PMID: 26237391 PMCID: PMC4449696 DOI: 10.3390/jcm3020566] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2014] [Revised: 03/17/2014] [Accepted: 03/25/2014] [Indexed: 02/07/2023] Open
Abstract
Diabetic cardiomyopathy (DCM), a significant contributor to morbidity and mortality in diabetic patients, is characterized by ventricular dysfunction, in the absence of coronary atherosclerosis and hypertension. There is no specific therapeutic strategy to effectively treat patients with DCM, due to a lack of a mechanistic understanding of the disease process. Retinoic acid, the active metabolite of vitamin A, is involved in a wide range of biological processes, through binding and activation of nuclear receptors: retinoic acid receptors (RAR) and retinoid X receptors (RXR). RAR/RXR-mediated signaling has been implicated in the regulation of glucose and lipid metabolism. Recently, it has been reported that activation of RAR/RXR has an important role in preventing the development of diabetic cardiomyopathy, through improving cardiac insulin resistance, inhibition of intracellular oxidative stress, NF-κB-mediated inflammatory responses and the renin-angiotensin system. Moreover, downregulated RAR/RXR signaling has been demonstrated in diabetic myocardium, suggesting that impaired RAR/RXR signaling may be a trigger to accelerate diabetes-induced development of DCM. Understanding the molecular mechanisms of retinoid receptors in the regulation of cardiac metabolism and remodeling under diabetic conditions is important in providing the impetus for generating novel therapeutic approaches for the prevention and treatment of diabetes-induced cardiac complications and heart failure.
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Affiliation(s)
- Jing Pan
- Division of Molecular Cardiology, Department of Medicine, College of Medicine, Texas A & M Health Science Center, Baylor Scott & White Health, Central Texas Veterans Health Care System, Temple, TX, 76504, USA.
| | - Rakeshwar S Guleria
- Division of Molecular Cardiology, Department of Medicine, College of Medicine, Texas A & M Health Science Center, Baylor Scott & White Health, Central Texas Veterans Health Care System, Temple, TX, 76504, USA.
| | - Sen Zhu
- Division of Molecular Cardiology, Department of Medicine, College of Medicine, Texas A & M Health Science Center, Baylor Scott & White Health, Central Texas Veterans Health Care System, Temple, TX, 76504, USA.
| | - Kenneth M Baker
- Division of Molecular Cardiology, Department of Medicine, College of Medicine, Texas A & M Health Science Center, Baylor Scott & White Health, Central Texas Veterans Health Care System, Temple, TX, 76504, USA.
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20
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Reply to "How free retinol behaves differently from RBP-bound retinol in RBP receptor-mediated vitamin A uptake". Mol Cell Biol 2014; 34:2111-2. [PMID: 24803603 DOI: 10.1128/mcb.01700-12] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
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21
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Dobri N, Qin Q, Kong J, Yamamoto K, Liu Z, Moiseyev G, Ma JX, Allikmets R, Sparrow JR, Petrukhin K. A1120, a nonretinoid RBP4 antagonist, inhibits formation of cytotoxic bisretinoids in the animal model of enhanced retinal lipofuscinogenesis. Invest Ophthalmol Vis Sci 2013; 54:85-95. [PMID: 23211825 DOI: 10.1167/iovs.12-10050] [Citation(s) in RCA: 65] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023] Open
Abstract
PURPOSE Excessive accumulation of lipofuscin is associated with pathogenesis of atrophic age-related macular degeneration (AMD) and Stargardt disease. Pharmacologic inhibition of the retinol-induced interaction of retinol-binding protein 4 (RBP4) with transthyretin (TTR) in the serum may decrease the uptake of serum retinol to the retina and reduce formation of lipofuscin bisretinoids. We evaluated in vitro and in vivo properties of the new nonretinoid RBP4 antagonist, A1120. METHODS RBP4 binding potency, ability to antagonize RBP4-TTR interaction, and compound specificity were analyzed for A1120 and for the prototypic RBP4 antagonist fenretinide. A1120 ability to inhibit RPE65-mediated isomerohydrolase activity was assessed in the RPE microsomes. The in vivo effect of A1120 administration on serum RBP4, visual cycle retinoids, lipofuscin bisretinoids, and retinal visual function was evaluated using a combination of biochemical and electrophysiologic techniques. RESULTS In comparison to fenretinide, A1120 did not act as a RARα agonist, while exhibiting superior in vitro potency in RBP4 binding and RBP4-TTR interaction assays. A1120 did not inhibit isomerohydrolase activity in the RPE microsomes. A1120 dosing in mice induced 75% reduction in serum RBP4, which correlated with reduction in visual cycle retinoids and ocular levels of lipofuscin fluorophores. A1120 dosing did not induce changes in kinetics of dark adaptation. CONCLUSIONS A1120 significantly reduces accumulation of lipofuscin bisretinoids in the Abca4(-/-) animal model. This activity correlates with reduction in serum RBP4 and visual cycle retinoids confirming the mechanism of action for A1120. In contrast to fenretinide, A1120 does not act as a RARα agonist indicating a more favorable safety profile for this nonretinoid compound.
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Affiliation(s)
- Nicoleta Dobri
- Department of Ophthalmology, Columbia University, New York, New York 10032, USA
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22
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Transthyretin blocks retinol uptake and cell signaling by the holo-retinol-binding protein receptor STRA6. Mol Cell Biol 2012; 32:3851-9. [PMID: 22826435 DOI: 10.1128/mcb.00775-12] [Citation(s) in RCA: 51] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
Vitamin A is secreted from cellular stores and circulates in blood bound to retinol-binding protein (RBP). In turn, holo-RBP associates in plasma with transthyretin (TTR) to form a ternary RBP-retinol-TTR complex. It is believed that binding to TTR prevents the loss of RBP by filtration in the kidney. At target cells, holo-RBP is recognized by STRA6, a plasma membrane protein that serves a dual role: it mediates uptake of retinol from extracellular RBP into cells, and it functions as a cytokine receptor that, upon binding holo-RBP, triggers a JAK/STAT signaling cascade. We previously showed that STRA6-mediated signaling underlies the ability of RBP to induce insulin resistance. However, the role that TTR, the binding partner of holo-RBP in blood, plays in STRA6-mediated activities remained unknown. Here we show that TTR blocks the ability of holo-RBP to associate with STRA6 and thereby effectively suppresses both STRA6-mediated retinol uptake and STRA6-initiated cell signaling. Consequently, TTR protects mice from RBP-induced insulin resistance, reflected by reduced phosphorylation of insulin receptor and glucose tolerance tests. The data indicate that STRA6 functions only under circumstances where the plasma RBP level exceeds that of TTR and demonstrate that, in addition to preventing the loss of RBP, TTR plays a central role in regulating holo-RBP/STRA6 signaling.
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23
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Cross talk between signaling and vitamin A transport by the retinol-binding protein receptor STRA6. Mol Cell Biol 2012; 32:3164-75. [PMID: 22665496 DOI: 10.1128/mcb.00505-12] [Citation(s) in RCA: 80] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The plasma membrane protein STRA6 transports vitamin A from its blood carrier retinol binding protein (RBP) into cells, and it also functions as a cytokine receptor which activates JAK/STAT signaling. We show here that, unlike other cytokine receptors, phosphorylation of STRA6 is not simply induced upon binding of its extracellular ligand. Instead, activation of the receptor is triggered by STRA6-mediated translocation of retinol from serum RBP to an intracellular acceptor, the retinol-binding protein CRBP-I. The observations also demonstrate that the movement of retinol from RBP to CRBP-I, and thus activation of STRA6, is critically linked to the intracellular metabolism of the vitamin. Furthermore, the data show that STRA6 phosphorylation is required for retinol uptake to proceed. Hence, the observations demonstrate that STRA6 orchestrates a multicomponent "machinery" that couples vitamin A homeostasis and metabolism to activation of a signaling cascade and that, in turn, STRA6 signaling regulates the cellular uptake of the vitamin. STRA6 appears to be a founding member of a new class of proteins that may be termed "cytokine signaling transporters."
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24
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Chen Y, Reese DH. The retinol signaling pathway in mouse pluripotent P19 cells. J Cell Biochem 2012; 112:2865-72. [PMID: 21618588 DOI: 10.1002/jcb.23200] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
atRA (all-trans-retinoic acid), the active metabolite of retinol (vitamin A), is essential for embryogenesis and maintenance of cellular phenotype in adults. Chemicals that interfere with the metabolism of retinol to atRA, therefore, are a human health concern. During development of a screen for disruptors of this signaling pathway, we investigated whether the mouse pluripotent P19 cell metabolizes retinol to atRA and thus can be used in a cell-based screen for disruptors of the pathway. We found that retinol induced the identical pattern of homeobox gene expression as atRA and its precursor, retinal. Retinol was 160-fold less potent than atRA as an inducer, however. In spite of its lower potency, increased Hoxa1 gene expression was detected 30 min after retinol exposure and increased 40-fold by 2 h. Rdh10 and Aldh1a2/Raldh2, which together convert retinol to atRA in the embryo, were the predominant alcohol and aldehyde dehydrogenases expressed in P19 cells. The cell expressed high mRNA levels of retinol binding proteins, Rbp1 and Rbp4, and the 13,14-dihydroretinol saturase, Retsat. It also expressed all Rar and Rxr isotypes, Crabp1&2, the three Cyp26 genes, and both β-carotene-cleaving genes, Bcmo1 and Bco2. The basal expression levels and retinol responsiveness of 25 pathway-related genes were quantitated by RT-qPCR. A test of the Aldh1a2 inhibitor, citral, showed that the disruption of the pathway was easily detected and quantitated showing that the P19 cell provides an in vitro model system for identifying and exploring the mechanism of action of chemicals that interfere with this critical cellular pathway.
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Affiliation(s)
- Yanling Chen
- Division of Molecular Biology, U.S. FDA, Laurel, Maryland 20708, USA
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25
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Berry DC, Noy N. Signaling by vitamin A and retinol-binding protein in regulation of insulin responses and lipid homeostasis. BIOCHIMICA ET BIOPHYSICA ACTA 2012; 1821:168-76. [PMID: 21782034 PMCID: PMC3204314 DOI: 10.1016/j.bbalip.2011.07.002] [Citation(s) in RCA: 62] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/14/2011] [Revised: 05/31/2011] [Accepted: 07/06/2011] [Indexed: 12/25/2022]
Abstract
Vitamin A, retinol, circulates in blood bound to serum retinol binding protein (RBP) and is transported into cells by a membrane protein termed stimulated by retinoic acid 6 (STRA6). It was reported that serum levels of RBP are elevated in obese rodents and humans, and that increased level of RBP in blood causes insulin resistance. A molecular mechanism by which RBP can exert such an effect is suggested by the recent discovery that STRA6 is not only a vitamin A transporter but also functions as a surface signaling receptor. Binding of RBP-ROH to STRA6 induces the phosphorylation of a tyrosine residue in the receptor C-terminus, thereby activating a JAK/STAT signaling cascade. Consequently, in STRA6-expressing cells such as adipocytes, RBP-ROH induces the expression of STAT target genes, including SOCS3, which suppresses insulin signaling, and PPARγ, which enhances lipid accumulation. RBP-retinol thus joins the myriad of cytokines, growth factors and hormones which regulate gene transcription by activating cell surface receptors that signal through activation of Janus kinases and their associated transcription factors STATs. This article is part of a Special Issue entitled Retinoid and Lipid Metabolism.
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Affiliation(s)
- Daniel C Berry
- Department of Pharmacology and Nutrition, Case Western Reserve University School of Medicine, Cleveland, OH 44106-4695, USA
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Spiegler E, Kim YK, Wassef L, Shete V, Quadro L. Maternal-fetal transfer and metabolism of vitamin A and its precursor β-carotene in the developing tissues. BIOCHIMICA ET BIOPHYSICA ACTA 2012; 1821:88-98. [PMID: 21621637 PMCID: PMC3184320 DOI: 10.1016/j.bbalip.2011.05.003] [Citation(s) in RCA: 65] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/01/2011] [Revised: 05/01/2011] [Accepted: 05/12/2011] [Indexed: 11/17/2022]
Abstract
The requirement of the developing mammalian embryo for retinoic acid is well established. Retinoic acid, the active form of vitamin A, can be generated from retinol and retinyl ester obtained from food of animal origin, and from carotenoids, mainly β-carotene, from vegetables and fruits. The mammalian embryo relies on retinol, retinyl ester and β-carotene circulating in the maternal bloodstream for its supply of vitamin A. The maternal-fetal transfer of retinoids and carotenoids, as well as the metabolism of these compounds in the developing tissues are still poorly understood. The existing knowledge in this field has been summarized in this review in reference to our basic understanding of the transport and metabolism of retinoids and carotenoids in adult tissues. The need for future research on the metabolism of these essential lipophilic nutrients during development is highlighted. This article is part of a Special Issue entitled: Retinoid and Lipid Metabolism.
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Affiliation(s)
- Elizabeth Spiegler
- Department of Food Sciences and Rutgers Center for Lipid Research, Rutgers University, New Brunswick, NJ 08901, USA
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Leelawatwattana L, Praphanphoj V, Prapunpoj P. Effect of the N-terminal sequence on the binding affinity of transthyretin for human retinol-binding protein. FEBS J 2011; 278:3337-47. [PMID: 21777382 DOI: 10.1111/j.1742-4658.2011.08249.x] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
During vertebrate evolution, the N-terminal region of transthyretin (TTR) subunit has undergone a change in both length and hydropathy. This was previously shown to change the binding affinity for thyroid hormones (THs). However, it was not known whether this change affects other functions of TTR. In the present study, the effect of these changes on the binding of TTR to retinol-binding protein (RBP) was determined. Two wild-type TTRs from human and Crocodylus porosus, and three chimeric TTRs, including a human chimeric TTR in which its N-terminal sequence was changed to that of C. porosus TTR (croc/huTTR) and two C. porosus chimeric TTRs (hu/crocTTR in which its N-terminal sequence was changed to that of human TTR and xeno/crocTTR in which its N-terminal sequence was changed to that of Xenopus laevis TTR), were analyzed for their binding to human RBP by native-PAGE followed by immunoblotting and a chemilluminescence assay. The K(d) of human TTR was 30.41 ± 2.03 μm, and was similar to that reported for the second binding site, whereas that of crocodile TTR was 2.19 ± 0.24 μm. The binding affinities increased in croc/huTTR (K(d) = 23.57 ± 3.54 μm) and xeno/crocTTR (K(d) = 0.61 ± 0.16 μm) in which their N-termini were longer and more hydrophobic, but decreased in hu/crocTTR (K(d) = 5.03 ± 0.68 μm) in which its N-terminal region was shorter and less hydrophobic. These results suggest an influence of the N-terminal primary structure of TTR on its function as a co-carrier for retinol with RBP.
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Affiliation(s)
- Ladda Leelawatwattana
- Department of Biochemistry, Faculty of Science, Prince of Songkla University, Hat Yai, Songkhla, Thailand
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Hiding in plain sight: uncovering a new function of vitamin A in redox signaling. Biochim Biophys Acta Mol Cell Biol Lipids 2011; 1821:241-7. [PMID: 21763457 DOI: 10.1016/j.bbalip.2011.06.014] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2011] [Revised: 05/27/2011] [Accepted: 06/15/2011] [Indexed: 01/05/2023]
Abstract
The protein kinase Cδ signalosome modulates the generation of acetyl-Coenzyme A from glycolytic sources. This module is composed of four interlinked components: PKCδ, the signal adapter p66Shc, cytochrome c, and vitamin A. It resides in the intermembrane space of mitochondria, and is at the center of a feedback loop that senses upstream the redox balance between oxidized and reduced cytochrome c as a measure of the workload of the respiratory chain, and transmits a forward signal to the pyruvate dehydrogenase complex to adjust the flux of fuel entering the tricarboxylic acid cycle. The novel role of vitamin A as co-activator and potential electron carrier, required for redox activation of PKCδ, is discussed. This article is part of a Special Issue entitled Retinoid and Lipid Metabolism.
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Campos-Sandoval JA, Redondo C, Kinsella GK, Pal A, Jones G, Eyre GS, Hirst SC, Findlay JBC. Fenretinide derivatives act as disrupters of interactions of serum retinol binding protein (sRBP) with transthyretin and the sRBP receptor. J Med Chem 2011; 54:4378-87. [PMID: 21591606 DOI: 10.1021/jm200256g] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
Abstract
Serum retinol binding protein (sRBP) is released from the liver as a complex with transthyretin (TTR), a process under the control of dietary retinol. Elevated levels of sRBP may be involved in inhibiting cellular responses to insulin and in generating first insulin resistance and then type 2 diabetes, offering a new target for therapeutic attack for these conditions. A series of retinoid analogues were synthesized and examined for their binding to sRBP and their ability to disrupt the sRBP-TTR and sRBP-sRBP receptor interactions. A number inhibit the sRBP-TTR and sRBP-sRBP receptor interactions as well as or better than Fenretinide (FEN), presenting a potential novel dual mechanism of action and perhaps offering a new therapeutic intervention against type 2 diabetes and its development. Shortening the chain length of the FEN derivative substantially abolished binding to sRBP, indicating that the strength of the interaction lies in the polyene chain region. Differences in potency against the sRBP-TTR and sRBP-sRBP receptor interactions suggest variant effects of the compounds on the two loops of sRBP guarding the entrance of the binding pocket that are responsible for these two protein-protein interactions.
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Affiliation(s)
- José Angel Campos-Sandoval
- The Marie Curie Laboratory for Membrane Proteins, Department of Biology, National University of Ireland, Maynooth, County Kildare, Ireland
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Abstract
The principles of fluorescence resonance energy transfer have been utilized to develop a high-throughput assay which detects compounds that interfere with interaction between retinol-binding protein (RBP) and transthyretin (TTR). In this assay, the intrinsic fluorescence from the RBP-retinol complex excites a probe molecule which is covalently coupled to TTR. Generation of an emission signal from the TTR probe indicates interaction between RBP-retinol and TTR. Importantly, the inclusion of retinol in the assay allows discrimination of test compounds which bind RBP versus those which bind to TTR. Thus, compounds which bind to RBP must compete with retinol in order to affect RBP-TTR interaction. This feature of the assay will be useful to identify test compounds which are more likely to have an effect in vivo.
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Johnson D, Chen C, Koutalos Y. 2-Hydroxypropyl-beta-cyclodextrin removes all-trans retinol from frog rod photoreceptors in a concentration-dependent manner. J Ocul Pharmacol Ther 2010; 26:245-8. [PMID: 20565310 DOI: 10.1089/jop.2010.0020] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
PURPOSE To determine whether a nonprotein lipophilic carrier, 2-hydroxypropyl-beta-cyclodextrin (HP-beta-CD), can remove all-trans retinol from rod photoreceptor outer segments. All-trans retinol is generated in rod outer segments after light exposure. It is highly insoluble, and its efficient transport across extra- and intracellular aqueous space requires specialized carriers. METHODS Experiments were carried out with isolated frog rod photoreceptor cells. The removal of all-trans retinol by different concentrations of this carrier was measured by imaging its fluorescence in single-rod photoreceptors. RESULTS HP-beta-CD concentrations >0.3 mM significantly increased the rate of all-trans retinol removal. The rate of removal increased linearly with carrier concentration, with a slope of 0.0058 min(-1)/mM. CONCLUSIONS The effectiveness of HP-beta-CD shows that a specialized interaction with the cell membrane is not necessary for the efficient transfer of all-trans retinol between the cell membrane and the carrier. The transfer occurs through a collision-based mechanism, as indicated by the linear increase of the rate of removal with the carrier concentration.
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Affiliation(s)
- Daniel Johnson
- Department of Physics, College of Charleston, Charleston, South Carolina 29425, USA
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Parés X, Farrés J, Kedishvili N, Duester G. Medium- and short-chain dehydrogenase/reductase gene and protein families : Medium-chain and short-chain dehydrogenases/reductases in retinoid metabolism. Cell Mol Life Sci 2008; 65:3936-49. [PMID: 19011747 PMCID: PMC2654207 DOI: 10.1007/s00018-008-8591-3] [Citation(s) in RCA: 120] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
Abstract
Retinoic acid (RA), the most active retinoid, is synthesized in two steps from retinol. The first step, oxidation of retinol to retinaldehyde, is catalyzed by cytosolic alcohol dehydrogenases (ADHs) of the medium-chain dehydrogenase/reductase (MDR) superfamily and microsomal retinol dehydrogenases (RDHs) of the short-chain dehydrogenase/reductase (SDR) superfamily. The second step, oxidation of retinaldehyde to RA, is catalyzed by several aldehyde dehydrogenases. ADH1 and ADH2 are the major MDR enzymes in liver retinol detoxification, while ADH3 (less active) and ADH4 (most active) participate in RA generation in tissues. Several NAD(+)- and NADP(+)-dependent SDRs are retinoid active. Their in vivo contribution has been demonstrated in the visual cycle (RDH5, RDH12), adult retinoid homeostasis (RDH1) and embryogenesis (RDH10). K(m) values for most retinoid-active ADHs and RDHs are close to 1 microM or lower, suggesting that they participate physiologically in retinol/retinaldehyde interconversion. Probably none of these enzymes uses retinoids bound to cellular retinol-binding protein, but only free retinoids. The large number of enzymes involved in the two directions of this step, also including aldo-keto reductases, suggests that retinaldehyde levels are strictly regulated.
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Affiliation(s)
- X Parés
- Department of Biochemistry and Molecular Biology, Universitat Autònoma de Barcelona, Bellaterra, Spain.
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Wolf G. Identification of a Membrane Receptor for Retinol-Binding Protein Functioning in the Cellular Uptake of Retinal. Nutr Rev 2008. [DOI: 10.1111/j.1753-4887.2007.tb00316.x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
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Sjoelund V, Kaltashov IA. Transporter-to-trap conversion: a disulfide bond formation in cellular retinoic acid binding protein I mutant triggered by retinoic acid binding irreversibly locks the ligand inside the protein. Biochemistry 2007; 46:13382-90. [PMID: 17958379 DOI: 10.1021/bi700867c] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Transport proteins must bind their ligands reversibly to enable release at the point of delivery, while irreversible binding is usually associated with the extreme cases of ligand sequestration. Protein conformational dynamics is an important modulator of binding kinetics, as increased flexibility in the regions adjacent to the binding site may facilitate both association and dissociation processes. Ligand entry to, and exit from, the internal binding site of the cellular retinoic acid binding protein I (CRABP I) occurs via a flexible portal region, which functions as a dynamic aperture. We designed and expressed a CRABP I mutant (A35C/T57C), in which a small-scale conformational switch caused by the ligand binding event triggers formation of a disulfide bond in the portal region, thereby arresting structural fluctuations and effectively locking the ligand inside the binding cavity. At the same time, no formation of the disulfide bond is observed in the apo form of the mutant, and most characteristics of the mutant, including protein stability, are very similar to those of the wild-type protein in the absence of retinoic acid. The mutation does not alter the kinetics of retinoic acid binding to the protein, although the disulfide formation makes the binding effectively irreversible, as suggested by the absence of retinoic acid transfer from the holo form of the mutant to lipid vesicles in the absence of a reducing agent. Taken together, these data suggest that the disulfide bond formation in the portal region arrests large-scale structural fluctuations, which are required for retinoic acid release from the protein. The unique properties of the CRABP I mutant described in this work can be used to inspire and guide a design of nanodevices for multiple tasks ranging from sequestering small-molecule toxins in both tissue and circulation to nutrient deprivation of pathogens.
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Affiliation(s)
- Virginie Sjoelund
- Department of Chemistry and Molecular and Cellular Biology Program, University of Massachusetts at Amherst, Amherst, Massachusetts 01003, USA
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Travis GH, Golczak M, Moise AR, Palczewski K. Diseases caused by defects in the visual cycle: retinoids as potential therapeutic agents. Annu Rev Pharmacol Toxicol 2007; 47:469-512. [PMID: 16968212 PMCID: PMC2442882 DOI: 10.1146/annurev.pharmtox.47.120505.105225] [Citation(s) in RCA: 307] [Impact Index Per Article: 18.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Absorption of a photon by an opsin pigment causes isomerization of the chromophore from 11-cis-retinaldehyde to all-trans-retinaldehyde. Regeneration of visual chromophore following light exposure is dependent on an enzyme pathway called the retinoid or visual cycle. Our understanding of this pathway has been greatly facilitated by the identification of disease-causing mutations in the genes coding for visual cycle enzymes. Defects in nearly every step of this pathway are responsible for human-inherited retinal dystrophies. These retinal dystrophies can be divided into two etiologic groups. One involves the impaired synthesis of visual chromophore. The second involves accumulation of cytotoxic products derived from all-trans-retinaldehyde. Gene therapy has been successfully used in animal models of these diseases to rescue the function of enzymes involved in chromophore regeneration, restoring vision. Dystrophies resulting from impaired chromophore synthesis can also be treated by supplementation with a chromophore analog. Dystrophies resulting from the accumulation of toxic pigments can be treated pharmacologically by inhibiting the visual cycle, or limiting the supply of vitamin A to the eyes. Recent progress in both areas provides hope that multiple inherited retinal diseases will soon be treated by pharmaceutical intervention.
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Affiliation(s)
- Gabriel H. Travis
- Department of Ophthalmology, UCLA School of Medicine, Los Angeles, California 90095;
| | - Marcin Golczak
- Department of Pharmacology, Case School of Medicine, Case Western Reserve University, Cleveland, Ohio 44106-4965;
| | - Alexander R. Moise
- Department of Pharmacology, Case School of Medicine, Case Western Reserve University, Cleveland, Ohio 44106-4965;
| | - Krzysztof Palczewski
- Department of Pharmacology, Case School of Medicine, Case Western Reserve University, Cleveland, Ohio 44106-4965;
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Abstract
Vitamins A and E are essential, naturally occurring, fat-soluble nutrients that are involved in several important biological processes such as immunity, protection against tissue damage, reproduction, growth and development. They are extremely important during the early stages of life and must be transferred adequately to the young during gestation and lactation. The present article presents an overview of their biological functions, metabolism and dynamics of transfer to offspring in mammals. Among other topics, the review focuses on the biochemical aspects of their intestinal absorption, blood transport, tissue uptake, storage and catabolism. It also describes their different roles as well as their use as preventive and therapeutic agents. Finally, the mechanisms involved in their transfer during gestation and lactation are discussed.
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Affiliation(s)
- C Debier
- Institut des Sciences de la Vie, Unité de Biochimie de la Nutrition, Université catholique de Louvain, Croix du Sud 2/8, B-1348 Louvain-la-Neuve, Belgium.
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Campochiaro PA. Seeing the light: New insights into the molecular pathogenesis of retinal diseases. J Cell Physiol 2007; 213:348-54. [PMID: 17654481 DOI: 10.1002/jcp.21213] [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] [Indexed: 11/07/2022]
Abstract
In the past, most treatments for retinal diseases have been empirical. Steroids and/or laser photocoagulation and/or surgery have been tried for almost every condition with little or no understanding of the underlying disease. Over the past several years vision researchers have uncovered molecular components of processes, such as visual transduction and the visual cycle, that are critical for visual function, and identified other molecules that lead to dysfunction and disease processes such as neovascularization and macular edema. It is becoming clear that dysregulation of certain molecules can have major effects on retinal structure and function. Studies in animal models have suggested that inhibiting or augmenting levels of a single molecule can have major effects in complex disease processes. Although several molecules probably contribute to neovascularization and excessive vascular permeability in the eye, blockade of vascular endothelial growth factor (VEGF) has remarkable beneficial effects in animal models that have now been proven to apply to human diseases in clinical trials. Intraocular injection of VEGF antagonists has revolutionized the treatment of choroidal neovascularization (CNV) and macular edema and serves as a model of targeted ocular pharmacotherapy. Significant progress elucidating the molecular pathogenesis of several disease processes in the eye may soon lead to new treatments following the lead of VEGF antagonists. Initial treatments that provide benefit from frequent intraocular injections are likely to be followed by sustained delivery of drugs and/or prolonged protein delivery by gene transfer. The eye has entered the era of molecular therapy.
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Affiliation(s)
- Peter A Campochiaro
- Department of Ophthalmology, Johns Hopkins University School of Medicine, Baltimore, Maryland 21287-9277, USA.
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Gallego O, Belyaeva O, Porté S, Ruiz F, Stetsenko A, Shabrova E, Kostereva N, Farrés J, Parés X, Kedishvili N. Comparative functional analysis of human medium-chain dehydrogenases, short-chain dehydrogenases/reductases and aldo-keto reductases with retinoids. Biochem J 2006; 399:101-9. [PMID: 16787387 PMCID: PMC1570161 DOI: 10.1042/bj20051988] [Citation(s) in RCA: 103] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Retinoic acid biosynthesis in vertebrates occurs in two consecutive steps: the oxidation of retinol to retinaldehyde followed by the oxidation of retinaldehyde to retinoic acid. Enzymes of the MDR (medium-chain dehydrogenase/reductase), SDR (short-chain dehydrogenase/reductase) and AKR (aldo-keto reductase) superfamilies have been reported to catalyse the conversion between retinol and retinaldehyde. Estimation of the relative contribution of enzymes of each type was difficult since kinetics were performed with different methodologies, but SDRs would supposedly play a major role because of their low K(m) values, and because they were found to be active with retinol bound to CRBPI (cellular retinol binding protein type I). In the present study we employed detergent-free assays and HPLC-based methodology to characterize side-by-side the retinoid-converting activities of human MDR [ADH (alcohol dehydrogenase) 1B2 and ADH4), SDR (RoDH (retinol dehydrogenase)-4 and RDH11] and AKR (AKR1B1 and AKR1B10) enzymes. Our results demonstrate that none of the enzymes, including the SDR members, are active with CRBPI-bound retinoids, which questions the previously suggested role of CRBPI as a retinol supplier in the retinoic acid synthesis pathway. The members of all three superfamilies exhibit similar and low K(m) values for retinoids (0.12-1.1 microM), whilst they strongly differ in their kcat values, which range from 0.35 min(-1) for AKR1B1 to 302 min(-1) for ADH4. ADHs appear to be more effective retinol dehydrogenases than SDRs because of their higher kcat values, whereas RDH11 and AKR1B10 are efficient retinaldehyde reductases. Cell culture studies support a role for RoDH-4 as a retinol dehydrogenase and for AKR1B1 as a retinaldehyde reductase in vivo.
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Affiliation(s)
- Oriol Gallego
- *Department of Biochemistry and Molecular Biology, Universitat Autònoma de Barcelona, E-08193 Bellaterra, Barcelona, Spain
| | - Olga V. Belyaeva
- †Department of Biochemistry and Molecular Genetics, Schools of Medicine and Dentistry, University of Alabama at Birmingham, Birmingham, AL 35294, U.S.A
| | - Sergio Porté
- *Department of Biochemistry and Molecular Biology, Universitat Autònoma de Barcelona, E-08193 Bellaterra, Barcelona, Spain
| | - F. Xavier Ruiz
- *Department of Biochemistry and Molecular Biology, Universitat Autònoma de Barcelona, E-08193 Bellaterra, Barcelona, Spain
| | - Anton V. Stetsenko
- †Department of Biochemistry and Molecular Genetics, Schools of Medicine and Dentistry, University of Alabama at Birmingham, Birmingham, AL 35294, U.S.A
| | - Elena V. Shabrova
- †Department of Biochemistry and Molecular Genetics, Schools of Medicine and Dentistry, University of Alabama at Birmingham, Birmingham, AL 35294, U.S.A
| | - Natalia V. Kostereva
- †Department of Biochemistry and Molecular Genetics, Schools of Medicine and Dentistry, University of Alabama at Birmingham, Birmingham, AL 35294, U.S.A
| | - Jaume Farrés
- *Department of Biochemistry and Molecular Biology, Universitat Autònoma de Barcelona, E-08193 Bellaterra, Barcelona, Spain
| | - Xavier Parés
- *Department of Biochemistry and Molecular Biology, Universitat Autònoma de Barcelona, E-08193 Bellaterra, Barcelona, Spain
| | - Natalia Y. Kedishvili
- †Department of Biochemistry and Molecular Genetics, Schools of Medicine and Dentistry, University of Alabama at Birmingham, Birmingham, AL 35294, U.S.A
- To whom correspondence should be addressed (email )
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Sankaranarayanan S, Suárez M, Taren D, Genaro-Wolf D, Duncan B, Shrestha K, Shrestha N, Rosales FJ. The concentration of free holo-retinol binding protein is higher in vitamin A-sufficient than in deficient Nepalese women in late pregnancy. J Nutr 2005; 135:2817-22. [PMID: 16317126 DOI: 10.1093/jn/135.12.2817] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Free holo-retinol binding protein (RBP) [i.e., unbound to transthyretin (TTR)] plays a role in transporting vitamin A across the placenta during pregnancy. In a cross-sectional study of clinically healthy urban women, we assessed the association among clinical and biochemical factors on estimated concentrations of free holo-RBP during the last trimester of pregnancy. Serum samples obtained from a subsample of women (n = 259), who had participated in the Night Vision Threshold Test study in Nepal, were analyzed for determinations of retinol by HPLC, and RBP, TTR, and alpha-1 acid glycoprotein by radial immunodiffusion. Free holo-RBP concentrations were calculated using dissociation constants for free holo- and apo-RBP. Among these women, 30% were vitamin A deficient based on either the RBP:TTR index < or = 0.36 or serum retinol < 1.05 micromol/L. Using stepwise regression analyses, the RBP:TTR index explained 75% of the variance in free holo-RBP concentrations, whereas retinol explained only 14%. Women were classified as vitamin A sufficient (n = 185) or deficient (n = 74) using the RBP:TTR index and were stratified into 3 gestational groups (I: 24-28 wk, II: 29-33 wk, III: >33 wk). Concentrations of free holo-RBP were higher in vitamin A-sufficient women than in vitamin A-deficient women (mean +/- SEM, 48.1 +/- 1.2 vs. 27.6 +/- 0.8 nmol/L; P < 0.001), and in a 3 x 2 factorial analysis, the interaction between gestational group and vitamin A status was significant. These results demonstrate that the RBP:TTR index is a useful proxy for free holo-RBP concentration and that vitamin A status affects its distribution.
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Affiliation(s)
- Sandhya Sankaranarayanan
- The Huck Institutes of the Life Sciences, The Pennsylvania State University, University Park, PA, USA
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40
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Hinterhuber G, Cauza K, Brugger K, Dingelmaier-Hovorka R, Horvat R, Wolff K, Foedinger D. RPE65 of Retinal Pigment Epithelium, A Putative Receptor Molecule for Plasma Retinol-Binding Protein, is Expressed in Human Keratinocytes. J Invest Dermatol 2004; 122:406-13. [PMID: 15009723 DOI: 10.1046/j.0022-202x.2004.22216.x] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Retinoids are important modulators for cell growth and differentiation of normal skin. In plasma, retinol is transported coupled to plasma retinol-binding protein. In this study, we investigated gene and protein expression of RPE65, a putative receptor for plasma retinol-binding protein in human epidermal keratinocytes. We performed real-time PCR analysis to evaluate expression of RPE65 mRNA in proliferating and differentiating keratinocytes. Immunoblotting with anti-RPE65 antibody shows distinct reactivity to a 61-kDa protein. Indirect immunofluorescence on normal human epidermis reveals cell surface labeling of keratinocytes. Laser scan microscopy exhibits colocalization of plasma retinol-binding protein and RPE65 on cultured keratinocytes. Internalization experiments with [3H]retinoic acid-retinol-binding protein complex in the presence and absence of excess of retinol-binding protein indicates receptor-dependent uptake of retinoids. We further show isolation of RPE65 protein by affinity chromatography from lysates of keratinocytes using a retinol-binding protein-matrix gel column. In summary, we demonstrate mRNA and protein expression of RPE65 in epidermal keratinocytes. Colocalization of plasma retinol-binding protein with RPE65 and affinity binding suggest a direct interaction of RPE65 with plasma retinol-binding protein in cultured human keratinocytes that might be involved in retinoid uptake of keratinocytes.
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Affiliation(s)
- Gabriele Hinterhuber
- Department of Dermatology, Division of General Dermatology, University of Vienna, School of Medicine, Vienna, Austria.
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41
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Lubzens E, Lissauer L, Levavi-Sivan B, Avarre JC, Sammar M. Carotenoid and retinoid transport to fish oocytes and eggs: what is the role of retinol binding protein? Mol Aspects Med 2003; 24:441-57. [PMID: 14585315 DOI: 10.1016/s0098-2997(03)00040-2] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Fish eggs contain carotenoids, retinals (retinal and dehydroretinal) and retinols (retinol, dehydroretinol and retinyl-esters) that are utilized during embryonic development, after fertilization. The carotenoids (mainly astaxanthins) are transported in the plasma by the low density lipoproteins, high density lipoproteins, and very high density lipoproteins (VHDL) and were found to be associated also with serum albumin. Retinals were found to be associated vitellogenin (VTG), a component of the plasma VHDL fraction that is internalized by oocytes during vitellogenesis. However, the transport of retinols and retinyl-esters that were located in the oil droplet fraction of homogenized eggs, has yet to be elucidated. Retinols are more abundant in freshwater fish eggs than in eggs of marine fish species. Since retinol is transported in the plasma of vertebrates in association with retinol binding protein (RBP), recent studies on the molecular characterization and expression sites of RBP, could contribute to determining the involvement of RBP in transporting retinol to developing oocytes in vertebrates.Recently, results from our laboratory show that RBP mRNA levels in the liver and RBP plasma levels did not significantly change with the onset and during vitellogenesis in the Rainbow trout. These results were in contrast with a dramatic elevation in the mRNA levels of VTG in the liver and an increase in VTG plasma levels that was observed in the same females. Moreover, 17beta-estradiol treatment of immature fish, resulted in relatively lower mRNA levels of RBP in the liver, concomitantly with an increase in the level of VTG transcripts and the appearance of VTG in the plasma of treated fish. In addition, RBP was localized in the cytosol of ovulated oocytes. These results for Rainbow trout are similar to those reported for the chicken but differ from those of Xenopus, where an increase in RBP mRNA was reported in the liver and higher levels of retinal and retinol were found in the plasma of 17beta-estradiol treated animals. The results, reported here for the first time in Rainbow trout, showing RBP transcripts in the ovary, oviduct (the ovarian tissue adjacent to the gonopore) and oocytes, suggest a modulating role for RBP in follicular development, as has been suggested for the bovine ovary.
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Affiliation(s)
- E Lubzens
- Israel Oceanographic and Limnological Research, P.O. Box 8030, Tel-Shikmona, 31080 Haifa, Israel.
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42
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Fortuna VA, Martucci RB, Trugo LC, Borojevic R. Hepatic stellate cells uptake of retinol associated with retinol-binding protein or with bovine serum albumin. J Cell Biochem 2003; 90:792-805. [PMID: 14587034 DOI: 10.1002/jcb.10703] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
Retinol is stored in liver, and the dynamic balance between its accumulation and mobilization is regulated by hepatic stellate cells (HSC). Representing less than 1% total liver protein, HSC can reach a very high intracellular retinoid (vitamin-A and its metabolites) concentration, which elicits their conversion from the myofibroblast to the fat-storing lipocyte phenotype. Circulating retinol is associated with plasma retinol-binding protein (RBP) or bovine serum albumin (BSA). Here we have used the in vitro model of GRX cells to compare incorporation and metabolism of BSA versus RBP associated [(3)H]retinol in HSC. We have found that lipocytes, but not myofibroblasts, expressed a high-affinity membrane receptor for RBP-retinol complex (KD = 4.93 nM), and both cell types expressed a low-affinity one (KD = 234 nM). The RBP-retinol complex, but not the BSA-delivered retinol, could be dislodged from membranes by treatments that specifically disturb protein-protein interactions (high RBP concentrations). Under both conditions, treatments that disturb the membrane lipid layer (detergent, cyclodextrin) released the membrane-bound retinol. RBP-delivered retinol was found in cytosol, microsomal fraction and, as retinyl esters, in lipid droplets, while albumin-delivered retinol was mainly associated with membranes. Disturbing the clathrin-mediated endocytosis did not interfere with retinol uptake. Retinol derived from the holo-RBP complex was differentially incorporated in lipocytes and preferentially reached esterification sites close to lipid droplets through a specific intracellular traffic route. This direct influx pathway facilitates the retinol uptake into HSC against the concentration gradients, and possibly protects cell membranes from undesirable and potentially noxious high retinol concentrations.
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Affiliation(s)
- Vitor A Fortuna
- Departamento de Histologia e Embriologia, Instituto de Ciências Biomédicas, Universidade Federal do Rio de Janeiro, 21941-970 Cidade Universitária, Rio de Janeiro, Brazil
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Sammar M, Babin PJ, Durliat M, Meiri I, Zchori I, Elizur A, Lubzens E. Retinol binding protein in rainbow trout: molecular properties and mRNA expression in tissues. Gen Comp Endocrinol 2001; 123:51-61. [PMID: 11551117 DOI: 10.1006/gcen.2001.7636] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Retinoids are important regulatory signaling molecules during embryonic development. The molecular properties of rainbow trout (Oncorhynchus mykiss) retinol-binding protein (rtRBP), the specific retinol carrier in vertebrate plasma, were studied to elucidate its role in transporting retinols to developing fish oocytes. A 954-nucleotide rtRBP cDNA was cloned from the liver coding for a 176-amino-acid (aa) mature protein, with an estimated molecular mass of 20,267 Da. The nucleotide sequence suggests a putative 16-aa signal peptide and shows all the aa residues that were previously identified as critical for the retinol binding pocket. Five of the eight amino acid residues that are associated with the interaction of RBP and transthyretin in mammalian and non-mammalian species are conserved. The deduced aa sequence of rtRBP shows 60-66% identity with zebrafish, chicken, mouse, rat, horse, bovine, and human RBPs and 56% identity with Xenopus RBP. Northern blot analysis revealed a approximately 1.1-kb hepatic mRNA transcript. RBP is highly expressed in the liver, but low levels were also detected in the spleen, kidney, ovary, and brain. In the rainbow trout, 17beta-estradiol treatment led to a decrease in the RBP mRNA signal relative to that of the controls. The efficacy of the 17beta-estradiol treatment was verified by an induction of vitellogenin (VTG) mRNA expression in the liver and occurrence of VTG in the plasma.
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Affiliation(s)
- M Sammar
- Israel Oceanographic and Limnological Research, Haifa
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Budhu A, Gillilan R, Noy N. Localization of the RAR interaction domain of cellular retinoic acid binding protein-II. J Mol Biol 2001; 305:939-49. [PMID: 11162104 DOI: 10.1006/jmbi.2000.4340] [Citation(s) in RCA: 71] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The pleiotropic effects of retinoic acid (RA) in mammalian cells are mediated by two classes of proteins: the retinoic acid receptors (RAR), and cellular retinoic acid binding proteins (CRABP-I and CRABP-II). The high conservation across species and the differential expression patterns of the two CRABPs suggest that they serve distinct biological functions. We previously showed that CRABP-II, but not CRABP-I, delivers RA to RAR through direct protein-protein interactions between the binding protein and the receptor. "Channeling" of RA between CRABP-II and RAR markedly facilitates the formation of the holo-receptor and, as a consequence, enhances the transcriptional activity of RAR in cells. Here, we localize the region of CRABP-II that mediates the interactions of this protein with RAR. Comparison between the electrostatic surface potential of CRABP-I and II revealed the presence of a sole region displaying a dramatic potential change between the two isoforms. Examination of the underlying model revealed that the change stemmed from CRABP-I/CRABP-II substitution of three spatially aligned residues E75Q, K81P, and E102 K, located on a protrusion above the entrance to the ligand binding pocket of the protein. Substituting the corresponding CRABP-II residues onto CRABP-I conferred upon this protein the ability to channel RA to RAR and to enhance the transcriptional activity of RAR in cells. Conversely, converting these amino acid residues in CRABP-II to the homologous CRABP-I residues resulted in loss of the ability of CRABP-II to interact with RAR and to augment the receptor's activity. The data demonstrate that the surface region of CRABP-II containing residues Gln75, Pro81, and Lys102 is necessary and sufficient for mediating the interactions of this protein with RAR, facilitating the formation of the holo-receptor, and enhancing the transcriptional activity of RA.
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Affiliation(s)
- A Budhu
- Division of Nutritional Sciences, Cornell Theory Center, Cornell University, Ithaca, NY 14853, USA
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45
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Abstract
Transthyretin (TTR, formerly called prealbumin), one of the transporters of the hormone thyroxine and the lipocalin retinol-binding protein (RBP), the specific carrier of the vitamin, are known to form, under physiological conditions, a macromolecular complex that is believed to play an important physiological role: prevention of glomerular filtration of the low molecular weight RBP in the kidneys. The physiological significance of complex formation is discussed first, followed by a brief description of the three-dimensional structure of the two participating proteins. The two X-ray models of the complex available are subsequently discussed and compared and finally the non-crystallographic evidence that supports these models is reviewed.
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Affiliation(s)
- H L Monaco
- Biocrystallography Laboratory, Department of Science and Technology, University of Verona, Strada Le Grazie 15, 37134 Verona, Italy
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46
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Newcomer ME, Ong DE. Plasma retinol binding protein: structure and function of the prototypic lipocalin. BIOCHIMICA ET BIOPHYSICA ACTA 2000; 1482:57-64. [PMID: 11058747 DOI: 10.1016/s0167-4838(00)00150-3] [Citation(s) in RCA: 135] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
In terms of both structure and biological function, retinol binding protein (RBP) is one of the best characterized members of the lipocalin superfamily. The molecular interactions in which RBP participates are described herein.
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Affiliation(s)
- M E Newcomer
- Biochemistry Department, Vanderbilt University School of Medicine, Nashville, TN 37232-0146, USA.
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47
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Marabotti A, Balestreri L, Cozzini P, Mozzarelli A, Kellogg GE, Abraham DJ. HINT predictive analysis of binding between retinol binding protein and hydrophobic ligands. Bioorg Med Chem Lett 2000; 10:2129-32. [PMID: 10999486 DOI: 10.1016/s0960-894x(00)00414-5] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
The interaction between the retinol binding protein and four ligands was evaluated using HINT, a software based on experimental LogP values of individual atoms. A satisfactory correlation was found between the HINT scores and the experimental dissociation constants of three of the ligands, fenretinide, N-ethylretinamide and all-trans retinol, despite their hydrophobic nature. A prediction is made for the binding affinity of the fourth ligand, axerophtene, not yet determined in solution.
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Affiliation(s)
- A Marabotti
- Institute of Biochemical Sciences, University of Parma, Italy
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Dong D, Ruuska SE, Levinthal DJ, Noy N. Distinct roles for cellular retinoic acid-binding proteins I and II in regulating signaling by retinoic acid. J Biol Chem 1999; 274:23695-8. [PMID: 10446126 DOI: 10.1074/jbc.274.34.23695] [Citation(s) in RCA: 272] [Impact Index Per Article: 10.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The pleiotropic effects of retinoic acid (RA) in mammalian cells are mediated by two classes of proteins: the retinoic acid receptors (RAR) and cellular retinoic acid-binding proteins (CRABP-I and CRABP-II). Here we show that expression of CRABP-II, but not CRABP-I, markedly enhanced RAR-mediated transcriptional activation of a reporter gene in COS-7 cells. The equilibrium dissociation constants of complexes of CRABP-I or CRABP-II with RA were found to differ by 2-fold. It is thus unlikely that the distinct effects of the two proteins on transactivation stem from differential ligand-binding affinities. The mechanisms by which RA transfers from the CRABPs to RAR were thus investigated directly. The rate constant for movement of RA from CRABP-II, but not from CRABP-I, to RAR strongly depended on the concentration of the acceptor. The data suggest that transfer of RA from CRABP-I to RAR involves dissociation of the ligand from the binding protein, followed by association with the receptor. In contrast, movement of RA from CRABP-II to the receptor is facilitated by a mechanism that involves direct interactions between CRABP-II and RAR. These findings reveal a striking functional difference between CRABP-I and CRABP-II, and point at a novel mechanism by which the transcriptional activity of RA can be regulated by CRABP-II.
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Affiliation(s)
- D Dong
- Cornell University, Division of Nutritional Sciences, Savage Hall, Ithaca, New York 14853, USA
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Tosetti F, Campelli F, Levi G. Studies on the cellular uptake of retinol binding protein and retinol. Exp Cell Res 1999; 250:423-33. [PMID: 10413596 DOI: 10.1006/excr.1999.4520] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The uptake and release of (125)I-RBP and of holoRBP labeled with [(3)H]retinol ((3)H-ROH) were studied in two cell lines which synthesize and secrete RBP, the HepG2 hepatocarcinoma cell line and the Caki-1 kidney adenocarcinoma cell line, and in HeLa cells that do not express the endogenous RBP gene. In all three cell lines a part of endocytosed (125)I-RBP is recycled to the extracellular medium and part is degraded. Nonspecific endocytosis of (125)I-RBP was estimated to be approximately 10% of total endocytosed (125)I-RBP. In HepG2 cells the (3)H-ROH from the [(3)H]retinol-RBP complex ((3)H-ROH-RBP) is recycled bound to RBP into serum-free chase medium. This (3)H-ROH recycling is blocked in HepG2 cells by cyclohexymide and by brefeldin A, an inhibitor of protein export from the main secretory route, and is absent in HeLa cells, which do not synthesize RBP. These data suggest that at least part of retinol taken up from exogenous holoRBP is delivered to newly synthesized RBP. (3)H-ROH recycled by HeLa cells is bound to serum albumin, as is a portion of that recycled by HepG2 cells. Transfer of (3)H-ROH from RBP to serum albumin does not occur in the absence of cells. We conclude that RBP is endocytosed through a specific pathway and that the RBP-associated retinol is transferred to newly synthesized RBP or to serum albumin.
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Affiliation(s)
- F Tosetti
- Molecular Biology Laboratory, National Cancer Institute (I.S.T.) -Advanced Biotechnology Center (ABC-CBA), Largo Rosanna Benzi 10, Genoa, 16132, Italy.
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Herr FM, Li E, Weinberg RB, Cook VR, Storch J. Differential mechanisms of retinoid transfer from cellular retinol binding proteins types I and II to phospholipid membranes. J Biol Chem 1999; 274:9556-63. [PMID: 10092641 DOI: 10.1074/jbc.274.14.9556] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Cellular retinol-binding proteins types I and II (CRBP-I and CRBP-II) are known to differentially facilitate retinoid metabolism by several membrane-associated enzymes. The mechanism of ligand transfer to phospholipid small unilamellar vesicles was compared in order to determine whether differences in ligand trafficking properties could underlie these functional differences. Unidirectional transfer of retinol from the CRBPs to membranes was monitored by following the increase in intrinsic protein fluorescence that occurs upon ligand dissociation. The results showed that ligand transfer of retinol from CRBP-I was >5-fold faster than transfer from CRBP-II. For both proteins, transfer of the other naturally occurring retinoid, retinaldehyde, was 4-5-fold faster than transfer of retinol. Rates of ligand transfer from CRBP-I to small unilamellar vesicles increased with increasing concentration of acceptor membrane and with the incorporation of the anionic lipids cardiolipin or phosphatidylserine into membranes. In contrast, transfer from CRBP-II was unaffected by either membrane concentration or composition. Preincubation of anionic vesicles with CRBP-I was able to prevent cytochrome c, a peripheral membrane protein, from binding, whereas CRBP-II was ineffective. In addition, monolayer exclusion experiments demonstrated differences in the rate and magnitude of the CRBP interactions with phospholipid membranes. These results suggest that the mechanisms of ligand transfer from CRBP-I and CRBP-II to membranes are markedly different as follows: transfer from CRBP-I may involve and require effective collisional interactions with membranes, whereas a diffusional process primarily mediates transfer from CRBP-II. These differences may help account for their distinct functional roles in the modulation of intracellular retinoid metabolism.
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Affiliation(s)
- F M Herr
- Department of Nutritional Sciences, Rutgers University, Cook College, New Brunswick, New Jersey 08901, USA
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