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Camarena V, Sant DW, Huff TC, Mustafi S, Muir RK, Aron AT, Chang CJ, Renslo AR, Monje PV, Wang G. cAMP signaling regulates DNA hydroxymethylation by augmenting the intracellular labile ferrous iron pool. eLife 2017; 6:29750. [PMID: 29239726 PMCID: PMC5745079 DOI: 10.7554/elife.29750] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2017] [Accepted: 12/13/2017] [Indexed: 12/11/2022] Open
Abstract
It is widely accepted that cAMP regulates gene transcription principally by activating the protein kinase A (PKA)-targeted transcription factors. Here, we show that cAMP enhances the generation of 5-hydroxymethylcytosine (5hmC) in multiple cell types. 5hmC is converted from 5-methylcytosine (5mC) by Tet methylcytosine dioxygenases, for which Fe(II) is an essential cofactor. The promotion of 5hmC was mediated by a prompt increase of the intracellular labile Fe(II) pool (LIP). cAMP enhanced the acidification of endosomes for Fe(II) release to the LIP likely through RapGEF2. The effect of cAMP on Fe(II) and 5hmC was confirmed by adenylate cyclase activators, phosphodiesterase inhibitors, and most notably by stimulation of G protein-coupled receptors (GPCR). The transcriptomic changes caused by cAMP occurred in concert with 5hmC elevation in differentially transcribed genes. Collectively, these data show a previously unrecognized regulation of gene transcription by GPCR-cAMP signaling through augmentation of the intracellular labile Fe(II) pool and DNA hydroxymethylation.
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Affiliation(s)
- Vladimir Camarena
- John P. Hussman Institute for Human Genomics, University of Miami Miller School of Medicine, Miami, United States.,Dr. John T. Macdonald Foundation Department of Human Genetics, University of Miami Miller School of Medicine, Miami, United States
| | - David W Sant
- John P. Hussman Institute for Human Genomics, University of Miami Miller School of Medicine, Miami, United States.,Dr. John T. Macdonald Foundation Department of Human Genetics, University of Miami Miller School of Medicine, Miami, United States
| | - Tyler C Huff
- John P. Hussman Institute for Human Genomics, University of Miami Miller School of Medicine, Miami, United States.,Dr. John T. Macdonald Foundation Department of Human Genetics, University of Miami Miller School of Medicine, Miami, United States
| | - Sushmita Mustafi
- John P. Hussman Institute for Human Genomics, University of Miami Miller School of Medicine, Miami, United States.,Dr. John T. Macdonald Foundation Department of Human Genetics, University of Miami Miller School of Medicine, Miami, United States
| | - Ryan K Muir
- Department of Pharmaceutical Chemistry, University of California, San Francisco, San Francisco, United States
| | - Allegra T Aron
- Department of Chemistry, University of California, Berkeley, Berkeley, United States
| | - Christopher J Chang
- Department of Chemistry, University of California, Berkeley, Berkeley, United States.,Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, United States.,Howard Hughes Medical Institute, University of California, Berkeley, Berkeley, United States
| | - Adam R Renslo
- Department of Pharmaceutical Chemistry, University of California, San Francisco, San Francisco, United States
| | - Paula V Monje
- The Miami Project to Cure Paralysis, University of Miami Miller School of Medicine, Miami, United States.,Department of Neurological Surgery, University of Miami Miller School of Medicine, Miami, United States
| | - Gaofeng Wang
- John P. Hussman Institute for Human Genomics, University of Miami Miller School of Medicine, Miami, United States.,Dr. John T. Macdonald Foundation Department of Human Genetics, University of Miami Miller School of Medicine, Miami, United States.,Dr. Nasser Ibrahim Al-Rashid Orbital Vision Research Center, Bascom Palmer Eye Institute, University of Miami Miller School of Medicine, Miami, United States.,Sylvester Comprehensive Cancer Center, University of Miami Miller School of Medicine, Miami, United States
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Liu J, Lu W, Reigada D, Nguyen J, Laties AM, Mitchell CH. Restoration of lysosomal pH in RPE cells from cultured human and ABCA4(-/-) mice: pharmacologic approaches and functional recovery. Invest Ophthalmol Vis Sci 2008; 49:772-80. [PMID: 18235027 DOI: 10.1167/iovs.07-0675] [Citation(s) in RCA: 100] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
PURPOSE Degradation of engulfed material is primarily mediated by lysosomal enzymes that function optimally within a narrow range of acidic pH values. RPE cells are responsible for daily degradation of photoreceptor outer segments and are thus particularly susceptible to perturbations in lysosomal pH. The authors hypothesized that elevated lysosomal pH levels could slow enzyme activity and encourage accumulation of partially digested material. Consequently, treatment to lower perturbed lysosomal pH levels may enhance degradative activity. METHODS A high-throughput screening assay was developed to quantify the lysosomal pH of fresh mouse and cultured ARPE-19 cells. The effect of lysosomal pH on outer segment clearance was determined. RESULTS Lysosomal pH is elevated in RPE cells from ABCA4 knockout mice and in cultured human ARPE-19 cells exposed to N-retinylidene-N-retinylethanolamine (A2E), tamoxifen, or chloroquine. The lysosomal pH of fresh RPE cells from ABCA4(-/-) mice and of chemically compromised RPE cells was reacidified by elevating intracellular cAMP directly. Compromised lysosomal pH was also restored by stimulating A(2A) adenosine or beta-adrenergic receptors, consistent with G(s)-protein coupling of these receptors. Restoring lysosomal pH with these treatments enhanced photoreceptor outer segment clearance, demonstrating functional relevance consistent with an enhancement of degradative enzyme activity. CONCLUSIONS Elevation of lysosomal pH in RPE cells interferes with the degradation of outer segments and may contribute to the pathologies associated with A2E. Pharmacologic elevation of cAMP can restore an acid pH and improve degradative function.
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Affiliation(s)
- Ji Liu
- Department of Physiology, University of Pennsylvania, Philadelphia, PA 19104-6085, USA
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El Hage T, Merlen C, Fabrega S, Authier F. Role of receptor-mediated endocytosis, endosomal acidification and cathepsin D in cholera toxin cytotoxicity. FEBS J 2007; 274:2614-29. [PMID: 17451437 DOI: 10.1111/j.1742-4658.2007.05797.x] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Using the in situ liver model system, we have recently shown that, after cholera toxin binding to hepatic cells, cholera toxin accumulates in a low-density endosomal compartment, and then undergoes endosomal proteolysis by the aspartic acid protease cathepsin-D [Merlen C, Fayol-Messaoudi D, Fabrega S, El Hage T, Servin A, Authier F (2005) FEBS J272, 4385-4397]. Here, we have used a subcellular fractionation approach to address the in vivo compartmentalization and cytotoxic action of cholera toxin in rat liver parenchyma. Following administration of a saturating dose of cholera toxin to rats, rapid endocytosis of both cholera toxin subunits was observed, coincident with massive internalization of both the 45 kDa and 47 kDa Gsalpha proteins. These events coincided with the endosomal recruitment of ADP-ribosylation factor proteins, especially ADP-ribosylation factor-6, with a time course identical to that of toxin and the A subunit of the stimulatory G protein (Gsalpha) translocation. After an initial lag phase of 30 min, these constituents were linked to NAD-dependent ADP-ribosylation of endogenous Gsalpha, with maximum accumulation observed at 30-60 min postinjection. Assessment of the subsequent postendosomal fate of internalized Gsalpha revealed sustained endolysosomal transfer of the two Gsalpha isoforms. Concomitantly, cholera toxin increased in vivo endosome acidification rates driven by the ATP-dependent H(+)-ATPase pump and in vitro vacuolar acidification in hepatoma HepG2 cells. The vacuolar H(+)-ATPase inhibitor bafilomycin and the cathepsin D inhibitor pepstatin A partially inhibited, both in vivo and in vitro, the cAMP response to cholera toxin. This cathepsin D-dependent action of cholera toxin under the control of endosomal acidity was confirmed using cellular systems in which modification of the expression levels of cathepsin D, either by transfection of the cathepsin D gene or small interfering RNA, was followed by parallel changes in the cytotoxic response to cholera toxin. Thus, in hepatic cells, a unique endocytic pathway was revealed following cholera toxin administration, with regulation specificity most probably occurring at the locus of the endosome and implicating endosomal proteases, such as cathepsin D, as well as organelle acidification.
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Affiliation(s)
- Tatiana El Hage
- INSERM, U756; and Université Paris-Sud, Faculté de Pharmacie, Châtenay, Malabry, France
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Merlen C, Fayol-Messaoudi D, Fabrega S, El Hage T, Servin A, Authier F. Proteolytic activation of internalized cholera toxin within hepatic endosomes by cathepsin D. FEBS J 2005; 272:4385-97. [PMID: 16128808 DOI: 10.1111/j.1742-4658.2005.04851.x] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
We have defined the in vivo and in vitro metabolic fate of internalized cholera toxin (CT) in the endosomal apparatus of rat liver. In vivo, CT was internalized and accumulated in endosomes where it underwent degradation in a pH-dependent manner. In vitro proteolysis of CT using an endosomal lysate required an acidic pH and was sensitive to pepstatin A, an inhibitor of aspartic acid proteases. By nondenaturating immunoprecipitation, the acidic CT-degrading activity was attributed to the luminal form of endosomal cathepsin D. The rate of toxin hydrolysis using an endosomal lysate or pure cathepsin D was found to be high for native CT and free CT-B subunit, and low for free CT-A subunit. On the basis of IC(50) values, competition studies revealed that CT-A and CT-B subunits share a common binding site on the cathepsin D enzyme, with native CT and free CT-B subunit displaying the highest affinity for the protease. By immunofluorescence, partial colocalization of internalized CT with cathepsin D was confirmed at early times of endocytosis in both hepatoma HepG2 and intestinal Caco-2 cells. Hydrolysates of CT generated at low pH by bovine cathepsin D displayed ADP-ribosyltransferase activity towards exogenous Gsalpha protein suggesting that CT cytotoxicity, at least in part, may be related to proteolytic events within endocytic vesicles. Together, these data identify the endocytic apparatus as a critical subcellular site for the accumulation and proteolytic degradation of endocytosed CT, and define endosomal cathepsin D an enzyme potentially responsible for CT cytotoxic activation.
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Affiliation(s)
- Clémence Merlen
- Institut National de la Santé et de la Recherche Médicale U510, Faculté de Pharmacie Paris XI, Châtenay-Malabry, France
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Van Dyke RW. Effect of cholera toxin and cyclic adenosine monophosphate on fluid-phase endocytosis, distribution, and trafficking of endosomes in rat liver. Hepatology 2000; 32:1357-69. [PMID: 11093743 DOI: 10.1053/jhep.2000.19790] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
In prior studies, we showed that cholera (CTX) and pertussis toxins (PTX) increase rat liver endosome acidification. This study was performed to characterize the effects of these toxins and cyclic adenosine monophosphate (cAMP) on endosome ion transport, fluid-phase endocytosis (FPE), and endosome trafficking in liver. In control liver, more mature populations of endosomes acidified progressively more slowly, but both toxins and cAMP caused retention of an early endosome acidification profile in maturing endosomes. CTX caused a density shift in endosomes, and all agents increased net FPE at time points from 5 to 60 minutes. By confocal microscopy, fluorescent dextrans first appeared in small vesicles at the hepatocyte sinusoidal membrane and trafficked rapidly to the pericanalicular area, near lysosomes and the trans-Golgi network (TGN). Prolonged exposure to these agents caused redistribution of many labeled vesicles to the perinuclear region, colocalized with markers of both early (EEA1 and transferrin receptor) and late (LAMP1) endosomes. We conclude that cAMP is the common agent that disrupted normal maturation and trafficking of endosomes and increased net FPE, in part via decreased diacytosis.
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Affiliation(s)
- R W Van Dyke
- Department of Medicine, University of Michigan Medical School and Veterans' Administration Hospital, Ann Arbor, MI 48109-0682, USA.
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Van Dyke RW, Ervin LL, Lewis MR, Wang X. Effect of cholera toxin on rat liver lysosome acidification. Biochem Biophys Res Commun 2000; 274:717-21. [PMID: 10924342 DOI: 10.1006/bbrc.2000.3196] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
We have shown that cholera toxin and cAMP greatly increase both acidification rates of liver endosomes and the liver and endosome content of fluid-phase endocytosis probes. In this study lysosomes were purified from control and cholera toxin-treated livers that were pulsed with fluorescein conjugated dextran and chased overnight. Cholera toxin-treated livers weighed less, contained less protein and exhibited higher contents of lysosomal marker enzymes, consistent with the catabolic effects of this agent. By contrast to its effects on endosomes, cholera toxin had no consistent or significant effect on lysosome acidification rates, steady-state internal pH or potassium content, proton leak rates or fluorescein-dextran content. We conclude that cholera toxin and cAMP predominantly alter earlier steps of endocytosis but may also increase transfer of probes from lysosomes to bile.
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Affiliation(s)
- R W Van Dyke
- Department of Medicine, University of Michigan Medical School and Veterans' Administration Hospital, Ann Arbor, Michigan, 48109-0682, USA
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Tanaka Y, Nakano H, Ishikawa F, Yoshida M, Gyotoku Y, Kakiuchi T. Cholera toxin increases intracellular pH in B lymphoma cells and decreases their antigen-presenting ability. Eur J Immunol 1999; 29:1561-70. [PMID: 10359110 DOI: 10.1002/(sici)1521-4141(199905)29:05<1561::aid-immu1561>3.0.co;2-z] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Cholera toxin (CT) can function as a potent adjuvant in the mucosal immune response. However, we have found that treatment of A20-HL murine B lymphoma cells with CT severely inhibits the presentation of ovalbumin (OVA) to cells of the T cell clone 42-6A specific for OVA(323-339)/I-Ad, whereas it does not affect the presentation of OVA(323-339) peptide. CT treatment did not affect the expression of B7-1, B7-2, ICAM-1, LFA-1 or MHC class II on, or the internalization of OVA into A20-HL cells. In CT-treated A20-HL cells, degradation of OVA was decreased, and intracellular pH was raised to a level approximately equivalent to that in CH3NH2-treated cells. Treatment with CH3NH2 is known to raise the pH in endocytic structures and thus inhibits antigen processing. Treatment of A20-HL cells with dibutyryl-cAMP similarly increased intracellular pH. The increase in intracellular pH following CT treatment was inhibited by a cAMP inhibitor, 2',3'-dideoxyadenosine. These results strongly suggest that CT treatment of A20-HL cells inhibits their antigen-presenting cell function by triggering the cAMP cascade, increasing intracellular pH, and reducing the degradation of OVA.
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Affiliation(s)
- Y Tanaka
- Department of Immunology, Toho University School of Medicine, Tokyo, Japan
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Ellinger I, Klapper H, Fuchs R. Fluid-phase marker transport in rat liver: free-flow electrophoresis separates distinct endosome subpopulations. Electrophoresis 1998; 19:1154-61. [PMID: 9662178 DOI: 10.1002/elps.1150190716] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Free-flow electrophoresis (FFE) was used to investigate the intracellular compartments involved in fluid-phase marker, fluoresceine isothiocyanate (FITC)-dextran, transport in the isolated perfused rat liver. One to 2 min after uptake at 37 degrees C, FITC-dextran was found in endosomes with the same electrophoretic mobility as early sorting endosomes labeled either by the hepatocyte-specific marker asialoorosomucoid (ASOR) or by transferrin that enters all liver cells. Labeling at low temperature (16 degrees C) blocked transport of ASOR and dextran in early endosomes. With increasing internalization time (3-13 min) at 37 degrees C, FITC-dextran-labeled compartments co-localized with late, ASOR-containing endosomes. Since localization of FITC-dextran in late transcytotic compartments was not observed upon FFE separation, it is concluded that the majority of internalized markers is directed to lysosomes. The FITC-label did not account for the predominant lysosomal targeting of the dextran, since [3H]dextran-labeled endosomes exhibited an identical FFE pattern. Taken together, these data indicate that the fluid-phase marker dextran is transported through intracellular compartments with identical characteristics as endosome subcompartments of the receptor-mediated lysosomal route.
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Affiliation(s)
- I Ellinger
- Department of General and Experimental Pathology, University of Vienna, Austria
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