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Nishad R, Betancourt-Solis M, Dey H, Heidelberger R, McNew JA. Regulation of Syntaxin3B-Mediated Membrane Fusion by T14, Munc18, and Complexin. Biomolecules 2023; 13:1463. [PMID: 37892145 PMCID: PMC10604575 DOI: 10.3390/biom13101463] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2023] [Revised: 09/22/2023] [Accepted: 09/26/2023] [Indexed: 10/29/2023] Open
Abstract
Retinal neurons that form ribbon-style synapses operate over a wide dynamic range, continuously relaying visual information to their downstream targets. The remarkable signaling abilities of these neurons are supported by specialized presynaptic machinery, one component of which is syntaxin3B. Syntaxin3B is an essential t-SNARE protein of photoreceptors and bipolar cells that is required for neurotransmitter release. It has a light-regulated phosphorylation site in its N-terminal domain at T14 that has been proposed to modulate membrane fusion. However, a direct test of the latter has been lacking. Using a well-controlled in vitro fusion assay, we found that a phosphomimetic T14 syntaxin3B mutation leads to a small but significant enhancement of SNARE-mediated membrane fusion following the formation of the t-SNARE complex. While the addition of Munc18a had only a minimal effect on membrane fusion mediated by SNARE complexes containing wild-type syntaxin3B, a more significant enhancement was observed in the presence of Munc18a when the SNARE complexes contained a syntaxin3B T14 phosphomimetic mutant. Finally, we showed that the retinal-specific complexins (Cpx III and Cpx IV) inhibited membrane fusion mediated by syntaxin3B-containing SNARE complexes in a dose-dependent manner. Collectively, our results establish that membrane fusion mediated by syntaxin3B-containing SNARE complexes is regulated by the T14 residue of syntaxin3B, Munc18a, and Cpxs III and IV.
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Affiliation(s)
- Rajkishor Nishad
- Department of BioSciences, Rice University, 6500 Main Street, MS 601, Houston, TX 77005, USA;
| | - Miguel Betancourt-Solis
- Department of BioSciences, Rice University, 6500 Main Street, MS 601, Houston, TX 77005, USA;
- Lonza Biologics, 14905 Kirby Dr, Houston, TX 77047, USA
| | - Himani Dey
- Department of Neurobiology and Anatomy, McGovern Medical School, The University of Texas Health Science Center, Houston (UTHealth Houston), 6431 Fannin Street, Houston, TX 77030, USA;
| | - Ruth Heidelberger
- Department of Neurobiology and Anatomy, McGovern Medical School, The University of Texas Health Science Center, Houston (UTHealth Houston), 6431 Fannin Street, Houston, TX 77030, USA;
| | - James A. McNew
- Department of BioSciences, Rice University, 6500 Main Street, MS 601, Houston, TX 77005, USA;
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2
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Campbell JR, Li H, Wang Y, Kozhemyakin M, Hunt AJ, Liu X, Janz R, Heidelberger R. Phosphorylation of the Retinal Ribbon Synapse Specific t-SNARE Protein Syntaxin3B Is Regulated by Light via a Ca 2 +-Dependent Pathway. Front Cell Neurosci 2020; 14:587072. [PMID: 33192329 PMCID: PMC7606922 DOI: 10.3389/fncel.2020.587072] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2020] [Accepted: 09/11/2020] [Indexed: 12/27/2022] Open
Abstract
Neurotransmitter release at retinal ribbon-style synapses utilizes a specialized t-SNARE protein called syntaxin3B (STX3B). In contrast to other syntaxins, STX3 proteins can be phosphorylated in vitro at T14 by Ca2+/calmodulin-dependent protein kinase II (CaMKII). This modification has the potential to modulate SNARE complex formation required for neurotransmitter release in an activity-dependent manner. To determine the extent to which T14 phosphorylation occurs in vivo in the mammalian retina and characterize the pathway responsible for the in vivo phosphorylation of T14, we utilized quantitative immunofluorescence to measure the levels of STX3 and STX3 phosphorylated at T14 (pSTX3) in the synaptic terminals of mouse retinal photoreceptors and rod bipolar cells (RBCs). Results demonstrate that STX3B phosphorylation at T14 is light-regulated and dependent upon the elevation of intraterminal Ca2+. In rod photoreceptor terminals, the ratio of pSTX3 to STX3 was significantly higher in dark-adapted mice, when rods are active, than in light-exposed mice. By contrast, in RBC terminals, the ratio of pSTX3 to STX3 was higher in light-exposed mice, when these terminals are active, than in dark-adapted mice. These results were recapitulated in the isolated eyecup preparation, but only when Ca2+ was included in the external medium. In the absence of external Ca2+, pSTX3 levels remained low regardless of light/dark exposure. Using the isolated RBC preparation, we next showed that elevation of intraterminal Ca2+ alone was sufficient to increase STX3 phosphorylation at T14. Furthermore, both the non-specific kinase inhibitor staurosporine and the selective CaMKII inhibitor AIP inhibited the Ca2+-dependent increase in the pSTX3/STX3 ratio in isolated RBC terminals, while in parallel experiments, AIP suppressed RBC depolarization-evoked exocytosis, measured using membrane capacitance measurements. Our data support a novel, illumination-regulated modulation of retinal ribbon-style synapse function in which activity-dependent Ca2+ entry drives the phosphorylation of STX3B at T14 by CaMKII, which in turn, modulates the ability to form SNARE complexes required for exocytosis.
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Affiliation(s)
- Joseph R Campbell
- Department of Neurobiology and Anatomy, University of Texas Health Science Center at Houston, Houston, TX, United States
| | - Hongyan Li
- Department of Neurobiology and Anatomy, University of Texas Health Science Center at Houston, Houston, TX, United States
| | - Yanzhao Wang
- Department of Neurobiology and Anatomy, University of Texas Health Science Center at Houston, Houston, TX, United States
| | - Maxim Kozhemyakin
- Department of Neurobiology and Anatomy, University of Texas Health Science Center at Houston, Houston, TX, United States
| | - Albert J Hunt
- Department of Neurobiology and Anatomy, University of Texas Health Science Center at Houston, Houston, TX, United States
| | - Xiaoqin Liu
- Department of Neurobiology and Anatomy, University of Texas Health Science Center at Houston, Houston, TX, United States
| | - Roger Janz
- Department of Neurobiology and Anatomy, University of Texas Health Science Center at Houston, Houston, TX, United States.,MD Anderson Cancer Center UTHealth Graduate School of Biomedical Sciences, Houston, TX, United States
| | - Ruth Heidelberger
- Department of Neurobiology and Anatomy, University of Texas Health Science Center at Houston, Houston, TX, United States.,MD Anderson Cancer Center UTHealth Graduate School of Biomedical Sciences, Houston, TX, United States
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Munc18b is an essential gene in mice whose expression is limiting for secretion by airway epithelial and mast cells. Biochem J 2012; 446:383-94. [PMID: 22694344 PMCID: PMC3430001 DOI: 10.1042/bj20120057] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
Airway mucin secretion and MC (mast cell) degranulation must be tightly controlled for homoeostasis of the lungs and immune system respectively. We found the exocytic protein Munc18b to be highly expressed in mouse airway epithelial cells and MCs, and localized to the apical pole of airway secretory cells. To address its functions, we created a mouse with a severely hypomorphic Munc18b allele such that protein expression in heterozygotes was reduced by ~50%. Homozygous mutant mice were not viable, but heterozygotes showed a ~50% reduction in stimulated release of mucin from epithelial cells and granule contents from MCs. The defect in MCs affected only regulated secretion and not constitutive or transporter-mediated secretion. The severity of passive cutaneous anaphylaxis was also reduced by ~50%, showing that reduction of Munc18b expression results in an attenuation of physiological responses dependent on MC degranulation. The Munc18b promoter is controlled by INR (initiator), Sp1 (specificity protein 1), Ets, CRE (cAMP-response element), GRE (glucocorticoid-response element), GATA and E-box elements in airway epithelial cells; however, protein levels did not change during mucous metaplasia induced by allergic inflammation. Taken together, the results of the present study identify Munc18b as an essential gene that is a limiting component of the exocytic machinery of epithelial cells and MCs.
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Developmental methylation program and concerted expression of Stx11 in mouse tissues. Mamm Genome 2009; 20:131-9. [PMID: 19169743 DOI: 10.1007/s00335-008-9162-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2008] [Accepted: 10/28/2008] [Indexed: 10/21/2022]
Abstract
The human 6q24 region is involved in growth and development, transient neonatal diabetes (TND), cancer, and metabolic dysfunction. To further characterize this region, the developmental status of DNA methylation and expression of Zac1 and Stx11 genes located within the mouse 10A1 region ortholog of human 6q24 were determined. In mice, imprinted Zac1 and Stx11 were highly expressed at the end of fetal development but downregulated at 4 and 11 weeks in brain, pancreas, and heart. Postnatal Zac1 downregulation was independent from promoter methylation of the expressed allele, suggesting the mediation of age-dependent chromatin remodeling. Stx11 nonpromoter CpG island was methylated de novo from E18 to 1 year with tissue-specific kinetics. The high conservation in vertebrates of Stx11 CpG2 is suggestive of an important regulatory function in age-related regional epigenetic state and/or chromatin configuration. Stx11 alleles were unequally expressed in F1 mice tissues, reflecting the influence of cis-regulatory factors on its expression. These data suggest the presence of a methylation domain and a coordinated gene expression pattern in multiple tissues. Methylation variation and allelic regulation of expression may underlie genetic diversity and contribute to disease susceptibility at the 6q24 locus in humans.
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Procino G, Barbieri C, Tamma G, De Benedictis L, Pessin JE, Svelto M, Valenti G. AQP2 exocytosis in the renal collecting duct -- involvement of SNARE isoforms and the regulatory role of Munc18b. J Cell Sci 2008; 121:2097-106. [PMID: 18505797 DOI: 10.1242/jcs.022210] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Vasopressin regulates the fusion of the water channel aquaporin 2 (AQP2) to the apical membrane of the renal collecting-duct principal cells and several lines of evidence indicate that SNARE proteins mediate this process. In this work MCD4 renal cells were used to investigate the functional role of a set of Q- and R-SNAREs, together with that of Munc18b as a negative regulator of the formation of the SNARE complex. Both VAMP2 and VAMP3 were associated with immunoisolated AQP2 vesicles, whereas syntaxin 3 (Stx3), SNAP23 and Munc18 were associated with the apical plasma membrane. Co-immunoprecipitation experiments indicated that Stx3 forms complexes with VAMP2, VAMP3, SNAP23 and Munc18b. Protein knockdown coupled to apical surface biotinylation demonstrated that reduced levels of the R-SNAREs VAMP2 and VAMP3, and the Q-SNAREs Stx3 and SNAP23 strongly inhibited AQP2 fusion at the apical membrane. In addition, knockdown of Munc18b promoted a sevenfold increase of AQP2 fused at the plasma membrane without forskolin stimulation. Taken together these findings propose VAMP2, VAMP3, Stx3 and SNAP23 as the complementary set of SNAREs responsible for AQP2-vesicle fusion into the apical membrane, and Munc18b as a negative regulator of SNARE-complex formation in renal collecting-duct principal cells.
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Affiliation(s)
- Giuseppe Procino
- Department of General and Environmental Physiology, University of Bari, Italy
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Sharma N, Low SH, Misra S, Pallavi B, Weimbs T. Apical targeting of syntaxin 3 is essential for epithelial cell polarity. ACTA ACUST UNITED AC 2006; 173:937-48. [PMID: 16785322 PMCID: PMC2063918 DOI: 10.1083/jcb.200603132] [Citation(s) in RCA: 75] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
In polarized epithelial cells, syntaxin 3 localizes to the apical plasma membrane and is involved in membrane fusion of apical trafficking pathways. We show that syntaxin 3 contains a necessary and sufficient apical targeting signal centered around a conserved FMDE motif. Mutation of any of three critical residues within this motif leads to loss of specific apical targeting. Modeling based on the known structure of syntaxin 1 revealed that these residues are exposed on the surface of a three-helix bundle. Syntaxin 3 targeting does not require binding to Munc18b. Instead, syntaxin 3 recruits Munc18b to the plasma membrane. Expression of mislocalized mutant syntaxin 3 in Madin-Darby canine kidney cells leads to basolateral mistargeting of apical membrane proteins, disturbance of tight junction formation, and loss of ability to form an organized polarized epithelium. These results indicate that SNARE proteins contribute to the overall specificity of membrane trafficking in vivo, and that the polarity of syntaxin 3 is essential for epithelial cell polarization.
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Affiliation(s)
- Nikunj Sharma
- Department of Molecular, Cellular, and Developmental Biology, University of California, Santa Barbara, Santa Barbara, CA 93106, USA
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Ikezumi Y, Kabuki N, Hayakawa H, Matsui T, Gunji T, Uchiyama M. Two patients with arthrogryposis-renal tubular dysfunction-cholestasis syndrome in a Japanese family. Pediatr Int 2006; 48:416-9. [PMID: 16911091 DOI: 10.1111/j.1442-200x.2006.02230.x] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Yohei Ikezumi
- Department of Pediatrics, Niigata University Medical and Dental Hospital, Niigata, Japan.
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Abstract
ROMK potassium channels are present in the cortical collecting duct (CCD) of the kidney and serve as apical exit pathways for K+secretion in this nephron segment. K+secretion in the CCD is regulated by multiple factors. In this study, we show that syntaxin 1A, but not syntaxin 3 or 4, inhibited whole cell ROMK currents in Xenopus laevis oocytes. Syntaxin 1A, but not syntaxin 3 or 4, interacted with the COOH-terminal cytoplasmic domain of ROMK in intro. Coexpression with synaptobrevin 2 reversed inhibition of whole cell ROMK currents by syntaxin 1A. In excised inside-out membranes of oocytes, application of fusion proteins containing the cytoplasmic region of syntaxin 1A to the cytoplasmic face caused a dose-dependent inhibition of ROMK. We further examined regulation of the K+channels in the CCD by syntaxin 1A. Application of botulinum toxin C1 to the excised inside-out membranes of the CCD caused an increase in the activity of K+channels. In contrast, application of toxin B had no effects. These results suggest that syntaxin 1A causes a tonic inhibition of the K+channels in the apical membrane of the CCD. Binding of synaptobrevin 2 to syntaxin 1A during docking and fusion of transport vesicles to the plasma membranes of CCD may lead to activation of these channels.
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Affiliation(s)
- Tie-Jun Sun
- Department of Medicine, Division of Nephrology, University of Texas Southwestern Medical Center, 5323 Harry Hines Blvd., Dallas, TX 75390-8856, USA
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Low SH, Marmorstein LY, Miura M, Li X, Kudo N, Marmorstein AD, Weimbs T. Retinal pigment epithelial cells exhibit unique expression and localization of plasma membrane syntaxins which may contribute to their trafficking phenotype. J Cell Sci 2002; 115:4545-53. [PMID: 12414999 DOI: 10.1242/jcs.00116] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The SNARE membrane fusion machinery controls the fusion of transport vesicles with the apical and basolateral plasma-membrane domains of epithelial cells and is implicated in the specificity of polarized trafficking. To test the hypothesis that differential expression and localization of SNAREs may be a mechanism that contributes to cell-type-specific polarity of different proteins, we studied the expression and distribution of plasma-membrane SNAREs in the retinal pigment epithelium (RPE), an epithelium in which the targeting and steady-state polarity of several plasma membrane proteins differs from most other epithelia. We show here that retinal pigment epithelial cells both in vitro and in vivo differ significantly from MDCK cells and other epithelial cells in their complement of expressed t-SNAREs that are known - or suggested - to be involved in plasma membrane trafficking. Retinal pigment epithelial cells lack expression of the normally apical-specific syntaxin 3. Instead, they express syntaxins 1A and 1B, which are normally restricted to neurons and neuroendocrine cells, on their apical plasma membrane. The polarity of syntaxin 2 is reversed in retinal pigment epithelial cells, and it localizes to a narrow band on the lateral plasma membrane adjacent to the tight junctions. In addition, syntaxin 4 and the v-SNARE endobrevin/VAMP-8 localize to this sub-tight junctional domain, which suggests that this is a region of preferred vesicle exocytosis. Altogether, these data suggest that the unique polarity of many retinal pigment epithelial proteins results from differential expression and distribution of SNAREs at the plasma membrane. We propose that regulation of the expression and subcellular localization of plasma membrane SNAREs may be a general mechanism that contributes to the establishment of distinct sorting phenotypes among epithelial cell types.
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Affiliation(s)
- Seng Hui Low
- Department of Cell Biology, Lerner Research Institute, Cleveland, Ohio 44195, USA
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Kauppi M, Wohlfahrt G, Olkkonen VM. Analysis of the Munc18b-syntaxin binding interface. Use of a mutant Munc18b to dissect the functions of syntaxins 2 and 3. J Biol Chem 2002; 277:43973-9. [PMID: 12198139 DOI: 10.1074/jbc.m208315200] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Munc18b is a mammalian Sec1-related protein that is abundant in epithelial cells and regulates vesicle transport to the apical plasma membrane. We constructed a homology model of Munc18b in complex with syntaxin 3 based on the crystal structure of the neuronal Sec1.syntaxin 1A complex. In this model we identified all residues in the interface between the two proteins that contribute directly to the interaction and mutagenized residues in Munc18b to alter its binding to syntaxins 1A, 2, and 3. The syntaxin-binding properties of the mutants were tested using an in vitro assay and by a co-immunoprecipitation approach employing Munc18b expressed in CHO-K1 cells. Three Munc18b variants, W28S, S42K, and E59K, were generated that are defective in binding to all three syntaxins. A fourth mutant protein, S48D, shows abolishment of syntaxin 3 interaction but binds syntaxin 2 at normal and syntaxin 1A at mildly reduced efficiency. Over-expression of Munc18b S48D inhibited transport of influenza hemagglutinin to the apical surface of Madin-Darby canine kidney II cells, which express syntaxin 2 abundantly, but not of Caco-2 cells, in which syntaxin 3 is the major apical target SNARE (soluble NSF (N-ethylmaleimide sensitive factor) attachment protein receptors). This suggests that, although syntaxin 3 is the main target SNARE operating in exocytic transport to the apical plasma membrane in certain epithelial cell types, syntaxin 2 may play an important role in this trafficking route in others.
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Affiliation(s)
- Maria Kauppi
- Department of Molecular Medicine, National Public Health Institute, Biomedicum, P.O. Box 104, FIN-00251 Helsinki, Finland
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Li X, Low SH, Miura M, Weimbs T. SNARE expression and localization in renal epithelial cells suggest mechanism for variability of trafficking phenotypes. Am J Physiol Renal Physiol 2002; 283:F1111-22. [PMID: 12372788 DOI: 10.1152/ajprenal.00185.2002] [Citation(s) in RCA: 67] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The apical- and basolateral-specific distribution of target soluble N-ethylmaleimide-sensitive factor attachment protein receptors (t-SNAREs) of the syntaxin family appear to be critical for polarity in epithelial cells. To test whether differential SNARE expression and/or subcellular localization may contribute to the known diversity of trafficking phenotypes of epithelial cell types in vivo, we have investigated the distribution of syntaxins 2, 3, and 4 in epithelial cells along the renal tubule. Syntaxins 3 and 4 are restricted to the apical and basolateral domains, respectively, in all cell types, indicating that their mutually exclusive localizations are important for cell polarity. The expression level of syntaxin 3 is highly variable, depending on the cell type, suggesting that it is regulated in concert with the cellular requirement for apical exocytic pathways. While syntaxin 4 localizes all along the basal and lateral plasma membrane domains in vivo, it is restricted to the lateral membrane in Madin-Darby canine kidney (MDCK) cells in two-dimensional monolayer culture. When cultured as cysts in collagen, however, MDCK cells target syntaxin 4 correctly to the basal and lateral membranes. Unexpectedly, the polarity of syntaxin 2 is inverted between different tubule cell types, suggesting a role in establishing plasticity of targeting. The vesicle-associated (v)-SNARE endobrevin is highly expressed in intercalated cells and colocalizes with the H(+)-ATPase in alpha- but not beta-intercalated cells, suggesting its involvement in H(+)-ATPase trafficking in the former cell type. These results suggest that epithelial membrane trafficking phenotypes in vivo are highly variable and that different cell types express or localize SNARE proteins differentially as a mechanism to achieve this variability.
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Affiliation(s)
- Xin Li
- Department of Cell Biology, Lerner Research Institute, and Urological Institute, The Cleveland Clinic, Cleveland, Ohio 44195, USA
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Wada J, Zhang H, Tsuchiyama Y, Hiragushi K, Hida K, Shikata K, Kanwar YS, Makino H. Gene expression profile in streptozotocin-induced diabetic mice kidneys undergoing glomerulosclerosis. Kidney Int 2001; 59:1363-73. [PMID: 11260397 DOI: 10.1046/j.1523-1755.2001.0590041363.x] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
BACKGROUND To elucidate the molecular mechanism of diabetic nephropathy, a high-density DNA filter array was employed to survey the gene expression profile of streptozotocin-induced diabetic CD-1 (ICR) mouse kidneys. METHODS Ten-week-old CD-1 male mice were divided into four groups: (1) control, (2) unilaterally nephrectomized (UX) mice, (3) streptozotocin (STZ)-induced diabetic (STZ) mice, and (4) STZ mice with unilateral renal ablation (STZ-UX). Pathological changes were examined at 24 weeks after the induction. The gene expression profile was compared between the control and STZ mice by a Gene Discovery Array (GDA). RESULTS The glomeruli in UX mouse kidney showed prominent glomerular hypertrophy, while the accumulation of mesangial matrix was minimal. Both STZ and STZ + UX mice had significant glomerular hypertrophy and glomerulosclerosis, and the lesions were not enhanced by renal ablation. By comparison between control and STZ mice, 16 clones that increased in expression with the induction of diabetes and 65 clones that decreased in diabetic kidneys were identified. The 37 known genes were related to glucose and lipid metabolism, ion transport, transcription factors, signaling molecules, and extracellular matrix-related molecules. The genes known to be involved in cell differentiation and organogenesis in various tissues (that is, Unc-18 homolog, POU domain transcription factor 2, lunatic fringe gene homolog, fibrous sheath component 1, Sox-17, fibulin 2, and MRJ) were found to be differentially expressed in the early phase of diabetic kidneys. CONCLUSIONS Hyperglycemia is a major determinant of glomerulosclerosis in STZ-induced diabetic CD-1 mice, and the altered gene expression in the early phase of diabetic kidney may be critical for the development of diabetic nephropathy.
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Affiliation(s)
- J Wada
- Department of Medicine III, Okayama University Medical School, Okayama, Japan.
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Agrawal A, Adachi R, Tuvim M, Yan XT, Teich AH, Dickey BF. Gene structure and promoter function of murine Munc18-2, a nonneuronal exocytic Sec1 homolog. Biochem Biophys Res Commun 2000; 276:817-22. [PMID: 11027553 DOI: 10.1006/bbrc.2000.3513] [Citation(s) in RCA: 8] [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
Sec1 family proteins are regulators of diverse exocytic processes, from yeast to man. Three mammalian homologues, Munc18-1, -2, and -3 have been described. We have studied the structure and expression of the mouse Munc18-2 gene. The Munc18-2 gene comprises 19 exons whose sizes range from 50 to 158 bp, with a total gene size of approximately 11 kb. A single transcript of 2.1 kb is expressed in multiple non-neuronal murine tissues. Munc18-2 has a striking resemblance to Munc18-1 in structure despite only 60% sequence identity, suggesting a recent gene duplication event. Analysis of the region upstream of the transcription start site shows that Munc18-2 has a TATA-less promoter, with a consensus initiator (Inr) sequence at the start of transcription, several Sp1 binding sites, and strong promoter activity in RBL-2H3 mast cells. The region from +5 to -430 is more active than +5 to -800, suggesting upstream repressor elements.
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Affiliation(s)
- A Agrawal
- Department of Internal Medicine, Baylor College of Medicine, Houston, Texas, 77030, USA.
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Riento K, Kauppi M, Keranen S, Olkkonen VM. Munc18-2, a functional partner of syntaxin 3, controls apical membrane trafficking in epithelial cells. J Biol Chem 2000; 275:13476-83. [PMID: 10788461 DOI: 10.1074/jbc.275.18.13476] [Citation(s) in RCA: 64] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The Sec1-related proteins bind to syntaxin family t-SNAREs with high affinity, thus controlling the interaction of syntaxins with their cognate SNARE partners. Munc18-2 is a Sec1 homologue enriched in epithelial cells and forms a complex with syntaxin 3, a t-SNARE localized to the apical plasma membrane. We generated here a set of Munc18-2 point mutants with substitutions in conserved amino acid residues. The mutants displayed a spectrum of different syntaxin binding efficiencies. The in vitro and in vivo binding patterns were highly similar, and the association of the Munc18-2 variants with syntaxin 3 correlated well with their ability to displace SNAP-23 from syntaxin 3 complexes when overexpressed in Caco-2 cells. Even the Munc18-2 mutants that do not detectably bind syntaxin 3 were membrane associated in Caco-2 cells, suggesting that the syntaxin interaction is not the sole determinant of Sec1 protein membrane attachment. Overexpression of the wild-type Munc18-2 was shown to inhibit the apical delivery of influenza virus hemagglutinin (HA). Interestingly, mutants unable to bind syntaxin 3 behaved differently in the HA transport assay. While one of the mutants tested had no effect, one inhibited and one enhanced the apical transport of HA. This implies that Munc18-2 function in apical membrane trafficking involves aspects independent of the syntaxin 3 interaction.
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Affiliation(s)
- K Riento
- Department of Biochemistry, National Public Health Institute (KTL), Mannerheimintie 166, FIN-00300 Helsinki, Finland
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