1
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Enhancing transient protein expression in HEK-293 cells by briefly exposing the culture to DMSO. J Neurosci Methods 2020; 350:109058. [PMID: 33359979 DOI: 10.1016/j.jneumeth.2020.109058] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2020] [Revised: 12/17/2020] [Accepted: 12/20/2020] [Indexed: 12/11/2022]
Abstract
BACKGROUND Transient expression of proteins in mammalian cells is a key technique for many functional and structural studies of human and higher eukaryotic genes as well as for the production of recombinant protein therapeutics. Maximizing the expression efficiency to achieve a higher expression yield is desirable and may be even critical when, for instance, an expressed protein must be characterized at the single-cell level. NEW METHODS Our goal was to develop a simple method by which protein expression yield in human embryonic kidney (HEK)-293 cells could be enhanced with a brief treatment of dimethyl sulfoxide (DMSO) solution. RESULTS By expressing green fluorescent protein (GFP) as a reporter protein using the calcium phosphate transfection method and imaging a large population of cells, we found that a 5-min exposure of 10 % DMSO to HEK-293 cells, 4 h after transfection of the protein of interest, leads to ∼1.6-fold increase in the expression yield without causing any appreciable cytotoxicity. By expressing an α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) and separately a kainate receptor in HEK-293 cells and measuring glutamate-induced whole-cell current response, we also found that such a brief DMSO treatment did not affect channel activity. CONCLUSION This method is simple, efficient and inexpensive to use for enhancing transient transfection yield in HEK-293 cells.
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2
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Wen W, Lin CY, Niu L. R/G editing in GluA2R flop modulates the functional difference between GluA1 flip and flop variants in GluA1/2R heteromeric channels. Sci Rep 2017; 7:13654. [PMID: 29057893 PMCID: PMC5651858 DOI: 10.1038/s41598-017-13233-2] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2017] [Accepted: 09/20/2017] [Indexed: 12/12/2022] Open
Abstract
In α-amino-3-hydroxy-5-methyl-4-isoxazole-propionate (AMPA) receptors, RNA editing and alternative splicing generate sequence variants, and those variants, as in GluA2-4 AMPA receptor subunits, generally show different properties. Yet, earlier studies have shown that the alternatively spliced, flip and flop variants of GluA1 AMPA receptor subunit exhibit no functional difference in homomeric channel form. Using a laser-pulse photolysis technique, combined with whole-cell recording, we measured the rate of channel opening, among other kinetic properties, for a series of AMPA channels with different arginine/glycine (R/G) editing and flip/flop status. We find that R/G editing in the GluA2 subunit modulates the channel properties in both homomeric (GluA2Q) and complex (GluA2Q/2R and GluA1/2R) channel forms. However, R/G editing is only effective in flop channels. Specifically, editing at the R/G site on the GluA2R flop isoform accelerates the rate of channel opening and desensitization for GluA1/2R channels more pronouncedly with the GluA1 being in the flop form than in the flip form; yet R/G editing has no effect on either channel-closing rate or EC50. Our results suggest R/G editing via GluA2R serve as a regulatory mechanism to modulate the function of GluA2R-containing, native receptors involved in fast excitatory synaptic transmission.
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Affiliation(s)
- Wei Wen
- Department of Chemistry, and Center for Neuroscience Research, University at Albany, SUNY, Albany, New York, 12222, United States
| | - Chi-Yen Lin
- Department of Chemistry, and Center for Neuroscience Research, University at Albany, SUNY, Albany, New York, 12222, United States
| | - Li Niu
- Department of Chemistry, and Center for Neuroscience Research, University at Albany, SUNY, Albany, New York, 12222, United States.
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3
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Inoue R, Hirohashi Y, Kitamura H, Nishida S, Murai A, Takaya A, Yamamoto E, Matsuki M, Tanaka T, Kubo T, Nakatsugawa M, Kanaseki T, Tsukahara T, Sato N, Masumori N, Torigoe T. GRIK2 has a role in the maintenance of urothelial carcinoma stem-like cells, and its expression is associated with poorer prognosis. Oncotarget 2017; 8:28826-28839. [PMID: 28418868 PMCID: PMC5438695 DOI: 10.18632/oncotarget.16259] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2016] [Accepted: 02/20/2017] [Indexed: 01/16/2023] Open
Abstract
Cancer stem-like cells (CSCs)/cancer-initiating cells (CICs) are small sub-population of cancer cells that are endowed with higher tumor-initiating ability, self-renewal ability and differentiation ability. CSCs/CICs could be isolated as high aldehyde dehydrogenase 1 activity cells (ALDH1high) from various cancer samples. In this study, we isolated urothelial carcinoma CSCs/CICs as ALDHhigh cells and investigated the molecular aspects. ALDH1high cells showed greater sphere-forming ability and higher tumor-initiating ability in immune-deficient mice than those of ALDH1low cells, indicating that CSCs/CICs were enriched in ALDH1high cells. cDNA microarray analysis revealed that an ionotropic glutamate receptor glutamate receptor, ionotropic, kainate 2 (GRIK2) was expressed in ALDH1high cells at a higher level than that in ALDH1low cells. GRIK2 gene knockdown by siRNAs decreased the sphere-forming ability and invasion ability, whereas GRIK2 overexpression increased the sphere-forming ability, invasion ability and tumorigenicity, indicating that GRIK2 has a role in the maintenance of CSCs/CICs. Immunohistochemical staining revealed that higher levels of GRIK2 and ALDH1 expression were related to poorer prognosis in urinary tract carcinoma cases. The findings indicate that GRIK2 has a role in the maintenance of urothelial CSCs/CICs and that GRIK2 and ALDH1 can be prognosis prediction markers for urinary tract carcinomas.
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Affiliation(s)
- Ryuta Inoue
- Department of Pathology, Sapporo Medical University School of Medicine, Chuo-Ku, Sapporo 060-8556, Japan
- Department of Urology, Sapporo Medical University School of Medicine, Chuo-Ku, Sapporo 060-8556, Japan
| | - Yoshihiko Hirohashi
- Department of Pathology, Sapporo Medical University School of Medicine, Chuo-Ku, Sapporo 060-8556, Japan
| | - Hiroshi Kitamura
- Department of Urology, Graduate School of Medicine and Pharmaceutical Science for Research, University of Toyama, Toyama-Shi 930-0194, Japan
| | - Sachiyo Nishida
- Department of Pathology, Sapporo Medical University School of Medicine, Chuo-Ku, Sapporo 060-8556, Japan
- Department of Urology, Sapporo Medical University School of Medicine, Chuo-Ku, Sapporo 060-8556, Japan
| | - Aiko Murai
- Department of Pathology, Sapporo Medical University School of Medicine, Chuo-Ku, Sapporo 060-8556, Japan
| | - Akari Takaya
- Department of Pathology, Sapporo Medical University School of Medicine, Chuo-Ku, Sapporo 060-8556, Japan
| | - Eri Yamamoto
- Department of Pathology, Sapporo Medical University School of Medicine, Chuo-Ku, Sapporo 060-8556, Japan
| | - Masahiro Matsuki
- Department of Pathology, Sapporo Medical University School of Medicine, Chuo-Ku, Sapporo 060-8556, Japan
- Department of Urology, Sapporo Medical University School of Medicine, Chuo-Ku, Sapporo 060-8556, Japan
| | - Toshiaki Tanaka
- Department of Urology, Sapporo Medical University School of Medicine, Chuo-Ku, Sapporo 060-8556, Japan
| | - Terufumi Kubo
- Department of Pathology, Sapporo Medical University School of Medicine, Chuo-Ku, Sapporo 060-8556, Japan
| | - Munehide Nakatsugawa
- Department of Pathology, Sapporo Medical University School of Medicine, Chuo-Ku, Sapporo 060-8556, Japan
| | - Takayuki Kanaseki
- Department of Pathology, Sapporo Medical University School of Medicine, Chuo-Ku, Sapporo 060-8556, Japan
| | - Tomohide Tsukahara
- Department of Pathology, Sapporo Medical University School of Medicine, Chuo-Ku, Sapporo 060-8556, Japan
| | - Noriyuki Sato
- Department of Pathology, Sapporo Medical University School of Medicine, Chuo-Ku, Sapporo 060-8556, Japan
| | - Naoya Masumori
- Department of Urology, Sapporo Medical University School of Medicine, Chuo-Ku, Sapporo 060-8556, Japan
| | - Toshihiko Torigoe
- Department of Pathology, Sapporo Medical University School of Medicine, Chuo-Ku, Sapporo 060-8556, Japan
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4
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Wu A, Wang C, Niu L. Mechanism of inhibition of the GluA1 AMPA receptor channel opening by the 2,3-benzodiazepine compound GYKI 52466 and a N-methyl-carbamoyl derivative. Biochemistry 2014; 53:3033-41. [PMID: 24738995 PMCID: PMC4025570 DOI: 10.1021/bi5002079] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
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2,3-Benzodiazepine derivatives, also
known as GYKI compounds, represent
a group of the most promising synthetic inhibitors of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic
acid (AMPA) receptors. Here we investigate the mechanism of inhibition
of the GluA1 channel opening and the site of inhibition by GYKI 52466
and its N-3 methyl-carbamoyl derivative, which we term as BDZ-f. GluA1 is a key AMPA receptor subunit involved in the
brain function. Excessive activity and elevated expression of GluA1,
however, has been implicated in a number of neurological disorders.
Using a laser-pulse photolysis technique, which provides ∼60
μs resolution, we measured the effect of these inhibitors on
the rate of GluA1 channel opening and the amplitude of the glutamate-induced
whole-cell current. We found that both compounds inhibit GluA1 channel
noncompetitively. Addition of an N-3 methyl-carbamoyl group to the
diazepine ring with the azomethine feature (i.e., GYKI 52466) improves
the potency of the resulting compound or BDZ-f without
changing the site of binding. This site, which we previously termed
as the “M” site on the GluA2 AMPA receptor subunit,
therefore favorably accommodates an N-3 acylating group. On the basis
of the magnitude of the inhibition constants for the same inhibitors
but different receptors, the “M” sites on GluA1 and
GuA2 are different. Overall, the “M” site or the binding
environment on GluA2 accommodates the same compounds better, or the
same inhibitors show stronger potency on GluA2, as we have reported
previously [Wang et al. (2011) 50, 7284−729321751782]. However, acylating
the N-3 position to occupy the N-3 side pocket of the “M”
site can significantly narrow the difference and improve the potency
of a resulting compound on GluA1.
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Affiliation(s)
- Andrew Wu
- Department of Chemistry, and Center for Neuroscience Research, University at Albany, SUNY , Albany, New York 12222, United States
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5
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Reiner A, Isacoff EY. Tethered ligands reveal glutamate receptor desensitization depends on subunit occupancy. Nat Chem Biol 2014; 10:273-80. [PMID: 24561661 PMCID: PMC4041372 DOI: 10.1038/nchembio.1458] [Citation(s) in RCA: 50] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2013] [Accepted: 12/30/2013] [Indexed: 12/11/2022]
Abstract
Cell signaling is often mediated by the binding of multiple ligands to multisubunit receptors. The probabilistic nature and sometimes slow rate of binding encountered with diffusible ligands can impede attempts to determine how the ligand occupancy controls signaling in such protein complexes. We describe a solution to this problem that uses a photoswitched tethered ligand as a 'ligand clamp' to induce rapid and stable binding and unbinding at defined subsets of subunits. We applied the approach to study gating in ionotropic glutamate receptors (iGluRs), ligand-gated ion channels that mediate excitatory neurotransmission and plasticity at glutamatergic synapses in the brain. We probed gating in two kainate-type iGluRs, GluK2 homotetramers and GluK2-GluK5 heterotetramers. Ultrafast (submillisecond) photoswitching of an azobenzene-based ligand on specific subunits provided a real-time measure of gating and revealed that partially occupied receptors can activate without desensitizing. The findings have implications for signaling by locally released and spillover glutamate.
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Affiliation(s)
- Andreas Reiner
- Department of Molecular and Cell Biology and Helen Wills Neuroscience Institute, University of California Berkeley, Berkeley, California 94720
| | - Ehud Y. Isacoff
- Department of Molecular and Cell Biology and Helen Wills Neuroscience Institute, University of California Berkeley, Berkeley, California 94720
- Physical Bioscience Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720
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6
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Wang C, Han Y, Wu A, Sólyom S, Niu L. Mechanism and site of inhibition of AMPA receptors: pairing a thiadiazole with a 2,3-benzodiazepine scaffold. ACS Chem Neurosci 2014; 5:138-47. [PMID: 24313227 DOI: 10.1021/cn400193u] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
Abstract
2,3-Benzodiazepine compounds are synthesized as drug candidates for treatment of various neurological disorders involving excessive activity of AMPA receptors. Here we report that pairing a thiadiazole moiety with a 2,3-benzodiazepine scaffold via the N-3 position yields an inhibitor type with >28-fold better potency and selectivity on AMPA receptors than the 2,3-benzodiazepine scaffold alone. Using whole-cell recording, we characterized two thiadiazolyl compounds, that is, one contains a 1,3,4-thiadiazole moiety and the other contains a 1,2,4-thiadiazole-3-one moiety. These compounds exhibit potent, equal inhibition of both the closed-channel and the open-channel conformations of all four homomeric AMPA receptor channels and two GluA2R-containing complex AMPA receptor channels. Furthermore, these compounds bind to the same receptor site as GYKI 52466 does, a site we previously termed as the "M" site. A thiadiazole moiety is thought to occupy more fully the side pocket of the receptor site or the "M" site, thereby generating a stronger, multivalent interaction between the inhibitor and the receptor binding site. We suggest that, as a heterocycle, a thiadiazole can be further modified chemically to produce a new class of even more potent, noncompetitive inhibitors of AMPA receptors.
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Affiliation(s)
- Congzhou Wang
- Department of Chemistry, and Center for Neuroscience Research, University at Albany, SUNY, Albany, New York 12222, United States
| | - Yan Han
- Department of Chemistry, and Center for Neuroscience Research, University at Albany, SUNY, Albany, New York 12222, United States
| | - Andrew Wu
- Department of Chemistry, and Center for Neuroscience Research, University at Albany, SUNY, Albany, New York 12222, United States
| | - Sándor Sólyom
- CF Pharma Pharmaceutical Manufacturing Co., Ltd, H-1097 Budapest, Kén
utca 5, Hungary
| | - Li Niu
- Department of Chemistry, and Center for Neuroscience Research, University at Albany, SUNY, Albany, New York 12222, United States
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7
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Amperometric resolution of a prespike stammer and evoked phases of fast release from retinal bipolar cells. J Neurosci 2013; 33:8144-58. [PMID: 23658155 DOI: 10.1523/jneurosci.5062-12.2013] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
The neurotransmitter glutamate is used by most neurons in the brain to activate a multitude of different types of glutamate receptors and transporters involved in fast and relatively slower signaling. Synaptic ribbons are large presynaptic structures found in neurons involved in vision, balance, and hearing, which use a large number of glutamate-filled synaptic vesicles to meet their signaling demands. To directly measure synaptic vesicle release events, the ribbon-type presynaptic terminals of goldfish retinal bipolar cells were coaxed to release a false transmitter that could be monitored with amperometry by placing the carbon fiber directly on the larger synaptic terminal. Spontaneous secretion events formed a unimodal charge distribution, but single spike properties were heterogeneous. Larger events rose exponentially without interruption (τ ∼ 30 μs), and smaller events exhibited a stammer in their rising phase that is interpreted as a brief pause in pore dilation, a characteristic commonly associated with large dense core granule fusion pores. These events were entirely Ca(2+)-dependent. Holding the cells at -60 mV halted spontaneous release; and when the voltage was stepped to >-40 mV, secretion ensued. When stepping the voltage to 0 mV, novel kinetic phases of vesicle recruitment were revealed. Approximately 14 vesicles were released per ribbon in two kinetic phases with time constants of 1.5 and 16 ms, which are proposed to represent different primed states within the population of docked vesicles.
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8
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Qu Y, Dang S, Hou P. Gene methylation in gastric cancer. Clin Chim Acta 2013; 424:53-65. [PMID: 23669186 DOI: 10.1016/j.cca.2013.05.002] [Citation(s) in RCA: 257] [Impact Index Per Article: 23.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2013] [Revised: 05/03/2013] [Accepted: 05/03/2013] [Indexed: 02/07/2023]
Abstract
Gastric cancer is one of the most common malignancies and remains the second leading cause of cancer-related death worldwide. Over 70% of new cases and deaths occur in developing countries. In the early years of the molecular biology revolution, cancer research mainly focuses on genetic alterations, including gastric cancer. Epigenetic mechanisms are essential for normal development and maintenance of tissue-specific gene expression patterns in mammals. Disruption of epigenetic processes can lead to altered gene function and malignant cellular transformation. Recent advancements in the rapidly evolving field of cancer epigenetics have shown extensive reprogramming of every component of the epigenetic machinery in cancer, including DNA methylation, histone modifications, nucleosome positioning, noncoding RNAs, and microRNAs. Aberrant DNA methylation in the promoter regions of gene, which leads to inactivation of tumor suppressor and other cancer-related genes in cancer cells, is the most well-defined epigenetic hallmark in gastric cancer. The advantages of gene methylation as a target for detection and diagnosis of cancer in biopsy specimens and non-invasive body fluids such as serum and gastric washes have led to many studies of application in gastric cancer. This review focuses on the most common and important phenomenon of epigenetics, DNA methylation, in gastric cancer and illustrates the impact epigenetics has had on this field.
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Key Words
- 5-hmC
- 5-hydroxymethylcytosine
- 5-mC
- 5-methylcytosine
- ADAM metallopeptidase domain 23
- ADAM metallopeptidase with thrombospondin type 1 motif, 9
- ADAM23
- ADAMTS9
- AML
- APC
- ARID1A
- AT motif-binding factor 1
- AT rich interactive domain 1A (SWI-like)
- ATBF1
- Acute myelocytic leukemia
- Adenomatosis polyposis coli
- B-cell translocation gene 4
- BCL2/adenovirus E1B 19kDa interacting protein 3
- BMP-2
- BNIP3
- BS
- BTG4
- Biomarkers
- Bisulfite sequencing
- Bone morphogenetic protein 2
- C-MET
- CACNA1G
- CACNA2D3
- CD44
- CD44 molecule (Indian blood group)
- CDH1
- CDK4
- CDK6
- CDKN1C
- CDKN2A
- CDX2
- CGI
- CHD5
- CHFR
- CKLF-like MARVEL transmembrane domain containing 3
- CMTM3
- CNS
- CRBP1
- Cadherin 1 or E-cadherin
- Calcium channel, voltage-dependent, T type, alpha 1G subunit
- Calcium channel, voltage-dependent, alpha 2/delta subunit 3
- Caudal type homeobox 2
- Central nervous system
- Checkpoint with forkhead and ring finger domains, E3 ubiquitin protein ligase
- Chromodomain helicase DNA binding protein 5
- Chromosome 2 open reading frame 40
- Clinical outcomes
- CpG islands
- Cyclin-dependent kinase 4
- Cyclin-dependent kinase 6
- Cyclin-dependent kinase inhibitor 1A
- Cyclin-dependent kinase inhibitor 1B
- Cyclin-dependent kinase inhibitor 1C
- Cyclin-dependent kinase inhibitor 2A
- Cyclin-dependent kinase inhibitor 2B
- DAB2 interacting protein
- DACT1
- DAPK
- DNA
- DNA methylatransferases
- DNA mismatch repair
- DNMT
- Dapper, antagonist of beta-catenin, homolog 1 (Xenopus laevis)
- Death-associated protein kinase
- Deoxyribose Nucleic Acid
- Dickkopf 3 homolog (Xenopus laevis)
- Dkk-3
- EBV
- ECRG4
- EDNRB
- EGCG
- ERBB4
- Endothelin receptor type B
- Epigallocatechin gallate
- Epigenetics
- Epstein–Barr Virus
- FDA
- FLNc
- Filamin C
- Food and Drug Administration
- GC
- GDNF
- GI endoscopy
- GPX3
- GRIK2
- GSTP1
- Gastric cancer
- Gene methylation
- Glutamate receptor, ionotropic, kainate 2
- Glutathione S-transferase pi 1
- Glutathione peroxidase 3 (plasma)
- H. pylori
- HACE1
- HAI-2/SPINT2
- HECT domain and ankyrin repeat containing E3 ubiquitin protein ligase 1
- HGFA
- HLTF
- HOXA1
- HOXA10
- HRAS-like suppressor
- HRASLS
- Helicase-like transcription factor
- Helicobacter pylori
- Homeobox A1
- Homeobox A10
- Homeobox D10
- HoxD10
- IGF-1
- IGF-1R
- IGFBP3
- IL-1β
- ITGA4
- Insulin-like growth factor 1 (somatomedin C)
- Insulin-like growth factor I receptor
- Insulin-like growth factor binding protein 3
- Integrin, alpha 4 (antigen CD49D, alpha 4 subunit of VLA-4 receptor)
- Interleukin 1, beta
- KL
- KRAS
- Klotho
- LL3
- LMP2A
- LOX
- LRP1B
- Low density lipoprotein receptor-related protein 1B
- Lysyl oxidase
- MAPK
- MBPs
- MDS
- MGMT
- MINT25
- MLF1
- MLL
- MMR
- MSI
- MSP
- Matrix metallopeptidase 24 (membrane-inserted)
- Met proto-oncogene (hepatocyte growth factor receptor)
- Methyl-CpG binding proteins
- Methylation-specific PCR
- Microsatellite instability
- Myeloid leukemia factor 1
- Myeloid/lymphoid or mixed-lineage leukemia (trithorax homolog, Drosophila)
- Myeloid/lymphoid or mixed-lineage leukemia 3
- NDRG family member 2
- NDRG2
- NPR1
- NR3C1
- Natriuretic peptide receptor A/guanylate cyclase A
- Notch 1
- Nuclear receptor subfamily 3, group C, member 1 (glucocorticoid receptor)
- O-6-methylguanine-DNA methyltransferase
- PCDH10
- PCDH17
- PI3K/Akt
- PIK3CA
- PR domain containing 5
- PRDM5
- PTCH1
- Patched 1
- Phosphatidylethanolamine binding protein 1
- Protein tyrosine phosphatase, non-receptor type 6
- Protocadherin 10
- Protocadherin 17
- Q-MSP
- Quantitative methylation-specific PCR
- RAR-related orphan receptor A
- RARRES1
- RARß
- RAS/RAF/MEK/ERK
- RASSF1A
- RASSF2
- RBP1
- RKIP
- RORA
- ROS
- RUNX3
- Ras association (RalGDS/AF-6) domain family member 1
- Ras association (RalGDS/AF-6) domain family member 2
- Rb
- Retinoic acid receptor responder (tazarotene induced) 1
- Retinoic acid receptor, beta
- Retinol binding protein 1, cellular
- Runt-related transcription factor 3
- S-adenosylmethionine
- SAM
- SFRP2
- SFRP5
- SHP1
- SOCS-1
- STAT3
- SYK
- Secreted frizzled-related protein 2
- Secreted frizzled-related protein 5
- Serine peptidase inhibitor, Kunitz type, 2
- Spleen tyrosine kinase
- Suppressor of cytokine signaling 1
- TCF4
- TET
- TFPI2
- TGF-β
- TIMP metallopeptidase inhibitor 3
- TIMP3
- TNM
- TP73
- TSP1
- Thrombospondin 1
- Tissue factor pathway inhibitor 2
- Transcription factor 4
- Tumor Node Metastasis
- Tumor protein p73
- V-erb-a erythroblastic leukemia viral oncogene homolog 4
- ZFP82 zinc finger protein
- ZIC1
- ZNF545
- Zinc finger protein of the cerebellum 1
- gastrointestinal endoscopy
- glial cell derived neurotrophic factor
- hDAB2IP
- hMLH1
- hepatocyte growth factor activator
- latent membrane protein
- mutL homolog 1
- myelodysplastic syndromes
- p15
- p16
- p21
- p27
- p53
- p73
- phosphatidylinositol-4,5-bisphosphate 3-kinase, catalytic subunit alpha
- phosphoinositide 3-kinase (PI3K)/Akt
- reactive oxygen species
- retinoblastoma
- signal transducer and activator of transcription-3
- ten-eleven translocation
- transforming growth factor-β
- tumor protein p53
- tumor protein p73
- v-Ki-ras2 Kirsten rat sarcoma viral oncogene homolog
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Affiliation(s)
- Yiping Qu
- Department of Endocrinology, The First Affiliated Hospital of Xi'an Jiaotong University School of Medicine, Xi'an 710061, People's Republic of China
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9
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Han Y, Wang C, Park JS, Niu L. Channel-opening kinetic mechanism of wild-type GluK1 kainate receptors and a C-terminal mutant. Biochemistry 2012; 51:761-8. [PMID: 22191429 DOI: 10.1021/bi201446z] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
GluK1 is a kainate receptor subunit in the ionotropic glutamate receptor family and can form functional channels when expressed, for instance, in HEK-293 cells. However, the channel-opening mechanism of GluK1 is poorly understood. One major challenge to studying the GluK1 channel is its apparent low level of surface expression, which results in a low whole-cell current response even to a saturating concentration of agonist. A low level of surface expression is thought to be contributed by an endoplasmic reticulum (ER) retention signal sequence. When this sequence motif is present as in the C-terminus of wild-type GluK1-2b, the receptor is significantly retained in the ER. Conversely, when this sequence is either lacking, as in wild-type GluK1-2a (i.e., a different alternatively spliced isoform at the C-terminus), or disrupted, as in a GluK1-2b mutant (i.e., R896A, R897A, R900A, and K901A), there is a higher level of surface expression and a greater whole-cell current response. Here we characterize the channel-opening kinetic mechanism for these three GluK1 receptors expressed in HEK-293 cells by using a laser-pulse photolysis technique. Our results show that wild-type GluK1-2a, wild-type GluK1-2b, and the GluK1-2b mutant have identical channel opening and channel closing rate constants. These results indicate that the amino acid sequence near or within the C-terminal ER retention signal sequence, which affects receptor trafficking and/or expression, does not affect channel gating properties. Furthermore, as compared with the GluK2 kainate receptor, the GluK1 channel is faster to open, close, and desensitize by at least 2-fold, yet the EC(50) value of GluK1 is similar to that of GluK2.
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Affiliation(s)
- Yan Han
- Department of Chemistry and Center for Neuroscience Research, University at Albany, SUNY, Albany, New York 12222, United States
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10
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Wang C, Sheng Z, Niu L. Mechanism of inhibition of the GluA2 AMPA receptor channel opening: consequences of adding an N-3 methylcarbamoyl group to the diazepine ring of 2,3-benzodiazepine derivatives. Biochemistry 2011; 50:7284-93. [PMID: 21751782 PMCID: PMC3170730 DOI: 10.1021/bi2007977] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
2,3-Benzodiazepine derivatives are AMPA receptor inhibitors, and they are potential drugs for treating some neurological diseases caused by excessive activity of AMPA receptors. Using a laser-pulse photolysis and rapid solution flow techniques, we characterized the mechanism of action of a 2,3-benzodiazepine derivative, termed BDZ-f, by measuring its inhibitory effect on the channel-opening and channel-closing rate constants as well as the whole-cell current amplitude of the homomeric GluA2Q AMPA receptor channels. We also investigated whether BDZ-f competes with GYKI 52466 for binding to the same site on GluA2Q(flip). GYKI 52466 is the prototypic 2,3-benzodiazepine compound, and BDZ-f is the N-3 methylcarbamoyl derivative. We found that BDZ-f is a noncompetitive inhibitor with a slight preference for the closed-channel state of both the flip and the flop variants of GluA2Q. Similar to other 2,3-benzodiazepine compounds that we have previously characterized, BDZ-f inhibits GluA2Q(flip) by forming an initial, loose intermediate that is partially conducting; however, this intermediate rapidly isomerizes into a tighter, fully inhibitory receptor-inhibitor complex. BDZ-f binds to the same noncompetitive site as GYKI 52466 does. Together, our results show that the addition of an N-3 methylcarbamoyl group to the diazepine ring with the azomethine feature (i.e., GYKI 52466) is what makes BDZ-f more potent and more selective toward the closed-channel conformation than the original GYKI 52466. Our results have useful implications for the structure-activity relationship of the 2,3-benzodiazepine series.
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Affiliation(s)
- Congzhou Wang
- Department of Chemistry, and Center for Neuroscience Research, University at Albany, SUNY, Albany, NY 12222, USA
| | | | - Li Niu
- Department of Chemistry, and Center for Neuroscience Research, University at Albany, SUNY, Albany, NY 12222, USA
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11
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Park JS, Wang C, Han Y, Huang Z, Niu L. Potent and selective inhibition of a single alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor subunit by an RNA aptamer. J Biol Chem 2011; 286:15608-17. [PMID: 21402710 DOI: 10.1074/jbc.m111.229559] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
Inhibitors of AMPA-type glutamate ion channels are useful as biochemical probes for structure-function studies and as drug candidates for a number of neurological disorders and diseases. Here, we describe the identification of an RNA inhibitor or aptamer by an in vitro evolution approach and a characterization of its mechanism of inhibition on the sites of interaction by equilibrium binding and on the receptor channel opening rate by a laser-pulse photolysis technique. Our results show that the aptamer is a noncompetitive inhibitor that selectively inhibits the GluA2Q(flip) AMPA receptor subunit without any effect on other AMPA receptor subunits or kainate or NMDA receptors. On the GluA2 subunit, this aptamer preferentially inhibits the flip variant. Furthermore, the aptamer preferentially inhibits the closed-channel state of GluA2Q(flip) with a K(I) = 1.5 μM or by ∼15-fold over the open-channel state. The potency and selectivity of this aptamer rival those of small molecule inhibitors. Together, these properties make this aptamer a promising candidate for the development of water-soluble, highly potent, and GluA2 subunit-selective drugs.
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Affiliation(s)
- Jae-Seon Park
- Department of Chemistry and Center for Neuroscience Research, University at Albany, State University of New York, Albany, New York 12222, USA
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12
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Han Y, Wang C, Park JS, Niu L. Channel-opening kinetic mechanism for human wild-type GluK2 and the M867I mutant kainate receptor. Biochemistry 2010; 49:9207-16. [PMID: 20863077 PMCID: PMC2988652 DOI: 10.1021/bi100819v] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
GluK2 is a kainate receptor subunit that is alternatively spliced at the C-terminus. Previous studies implicated GluK2 in autism. In particular, the methionine-to-isoleucine replacement at amino acid residue 867 (M867I) that can only occur in the longest isoform of the human GluK2 (hGluK2), as the disease (autism) mutation, is thought to cause gain-of-function. However, the kinetic properties of the wild-type hGluK2 and the functional consequence of this gain-of-function mutation at the molecular level are not well understood. To investigate whether the M867I mutation affects the channel properties of the human GluK2 kainate receptor, we have systematically characterized the rate and the equilibrium constants pertinent to channel opening and channel desensitization for this mutant and the wild-type hGluK2 receptor, along with the wild-type rat GluK2 kainate receptor (rGluK2) as the control. Our results show that the M867I mutation does not affect either the rate or the equilibrium constants of the channel opening but does slow down the channel desensitization rate by ~1.6-fold at saturating glutamate concentrations. It is possible that a consequence of this mutation on the desensitization rate is linked to facilitating the receptor trafficking and membrane expression, given the close proximity of M867 to the forward trafficking motif in the C-terminal sequence. By comparing the kinetic data of the wild-type human and rat GluK2 receptors, we also find that the human GluK2 has a ~3-fold smaller channel-opening rate constant but an identical channel-closing rate constant and thus a channel-opening probability of 0.85 vs 0.96 for rGluK2. Furthermore, the intrinsic equilibrium dissociation constant K(1) for hGluK2, like the EC(50) value, is ~2-fold lower than rGluK2. Our results therefore suggest that the human GluK2 is relatively a slowly activating channel but more sensitive to glutamate, as compared to the rat ortholog, despite the fact that the human and rat forms share 99% sequence homology.
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Affiliation(s)
- Yan Han
- Department of Chemistry and Center for Neuroscience Research, University at Albany, SUNY, Albany, New York 12222
| | - Congzhou Wang
- Department of Chemistry and Center for Neuroscience Research, University at Albany, SUNY, Albany, New York 12222
| | - Jae Seon Park
- Department of Chemistry and Center for Neuroscience Research, University at Albany, SUNY, Albany, New York 12222
| | - Li Niu
- Department of Chemistry and Center for Neuroscience Research, University at Albany, SUNY, Albany, New York 12222
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13
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Abstract
Advances in optics, genetics, and chemistry have enabled the investigation of brain function at all levels, from intracellular signals to single synapses, whole cells, circuits, and behavior. Until recent years, these research tools have been utilized in an observational capacity: imaging neural activity with fluorescent reporters, for example, or correlating aberrant neural activity with loss-of-function and gain-of-function pharmacological or genetic manipulations. However, optics, genetics, and chemistry have now combined to yield a new strategy: using light to drive and halt neuronal activity with molecular specificity and millisecond precision. Photostimulation of neurons is noninvasive, has unmatched spatial and temporal resolution, and can be targeted to specific classes of neurons. The optical methods developed to date encompass a broad array of strategies, including photorelease of caged neurotransmitters, engineered light-gated receptors and channels, and naturally light-sensitive ion channels and pumps. In this review, we describe photostimulation methods, their applications, and opportunities for further advancement.
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Affiliation(s)
- Stephanie Szobota
- Department of Molecular and Cell Biology, University of California, Berkeley, California 94720, USA
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14
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Wu CS, Lu YJ, Li HP, Hsueh C, Lu CY, Leu YW, Liu HP, Lin KH, Hui-Ming Huang T, Chang YS. Glutamate receptor, ionotropic, kainate 2 silencing by DNA hypermethylation possesses tumor suppressor function in gastric cancer. Int J Cancer 2010; 126:2542-52. [PMID: 19824040 DOI: 10.1002/ijc.24958] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Aberrant DNA methylation is considered a major mechanism for silencing tumor suppressor genes in gastric cancer. We used CpG microarray and differential methylation hybridization strategies to identify potential tumor suppressor genes and recovered glutamate receptor, ionotropic, kainate 2 (GRIK2) as a novel epigenetic target in gastric cancer. Additional experiments showed that the promoter region of GRIK2 was hypermethylated in 3 of the 4 tested gastric cancer cell lines, and its expression was restored by treatment of cells with the DNA methylation inhibitor, 5'-aza-dC. In clinical samples, the GRIK2 promoter was differentially hypermethylated in tumor tissues compared with adjacent normal tissues (p < 0.001), and this methylation was inversely correlated with the expression level of GRIK2 mRNA (r = -0.44). Functional studies further showed that GRIK2-expressing gastric cancer cell lines showed decreased colony formation and cell migration. Taken together, these results suggest that GRIK2 may play a tumor-suppressor role in gastric cancer. Future studies are warranted to examine whether DNA hypermethylation of the GRIK2 promoter can be used as a potential tumor marker for gastric cancer.
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Affiliation(s)
- Chi-Sheng Wu
- Graduate Institute of Biomedical Sciences, Chang Gung University, Taoyuan, Taiwan
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15
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Huang Z, Pei W, Han Y, Jayaseelan S, Shekhtman A, Shi H, Niu L. One RNA aptamer sequence, two structures: a collaborating pair that inhibits AMPA receptors. Nucleic Acids Res 2009; 37:4022-32. [PMID: 19417060 PMCID: PMC2709572 DOI: 10.1093/nar/gkp284] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
RNA is ideally suited for in vitro evolution experiments, because a single RNA molecule possesses both genotypic (replicable sequence) and phenotypic (selectable shape) properties. Using systematic evolution of ligands by exponential enrichment (SELEX), we found a single 58-nt aptamer sequence that assumes two structures with different functions, both of which are required to inhibit the GluR2 AMPA receptor channel. Yet, the two structures, once formed during transcription, appear to be incapable of interconverting through unfolding and refolding, presumably due to their extraordinary structural stability. Thus, our results suggest more broadly that natural RNA molecules can evolve to acquire alternative structures and associated functions. Such divergence of RNA phenotype may precede gene duplication at the genome level.
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Affiliation(s)
- Zhen Huang
- Department of Chemistry and Center for Neuroscience Research and Department of Biological Sciences, University at Albany, SUNY, Albany, NY 12222, USA
| | - Weimin Pei
- Department of Chemistry and Center for Neuroscience Research and Department of Biological Sciences, University at Albany, SUNY, Albany, NY 12222, USA
| | - Yan Han
- Department of Chemistry and Center for Neuroscience Research and Department of Biological Sciences, University at Albany, SUNY, Albany, NY 12222, USA
| | - Sabarinath Jayaseelan
- Department of Chemistry and Center for Neuroscience Research and Department of Biological Sciences, University at Albany, SUNY, Albany, NY 12222, USA
| | - Alexander Shekhtman
- Department of Chemistry and Center for Neuroscience Research and Department of Biological Sciences, University at Albany, SUNY, Albany, NY 12222, USA
| | - Hua Shi
- Department of Chemistry and Center for Neuroscience Research and Department of Biological Sciences, University at Albany, SUNY, Albany, NY 12222, USA
| | - Li Niu
- Department of Chemistry and Center for Neuroscience Research and Department of Biological Sciences, University at Albany, SUNY, Albany, NY 12222, USA
- *To whom correspondence should be addressed. Tel: +1 518 591 8819; Fax: +1 518 591 8820;
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16
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Du M, Rambhadran A, Jayaraman V. Luminescence resonance energy transfer investigation of conformational changes in the ligand binding domain of a kainate receptor. J Biol Chem 2008; 283:27074-8. [PMID: 18658129 PMCID: PMC2556009 DOI: 10.1074/jbc.m805040200] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2008] [Revised: 07/23/2008] [Indexed: 11/06/2022] Open
Abstract
The apo state structure of the isolated ligand binding domain of the GluR6 subunit and the conformational changes induced by agonist binding to this protein have been investigated by luminescence resonance energy transfer (LRET) measurements. The LRET-based distances show that agonist binding induces cleft closure, and the extent of cleft closure is proportional to the extent of activation over a wide range of activations, thus establishing that the cleft closure conformational change is one of the mechanisms by which the agonist mediates receptor activation. The LRET distances also provide insight into the apo state structure, for which there is currently no crystal structure available. The distance change between the glutamate-bound state and the apo state is similar to that observed between the glutamate-bound and antagonist UBP-310-bound form of the GluR5 ligand binding domain, indicating that the cleft for the apo state of the GluR6 ligand binding domain should be similar to the UBP-310-bound form of GluR5. This observation implies that te apo state of GluR6 undergoes a cleft closure of 29-30 degrees upon binding full agonists, one of the largest observed in the glutamate receptor family.
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Affiliation(s)
- Mei Du
- Center for Membrane Biology, Department of Biochemistry and Molecular Biology, University of Texas Health Science Center, Houston, Texas 77030, USA
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17
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Zhang Y, Nayeem N, Green T. Mutations to the kainate receptor subunit GluR6 binding pocket that selectively affect domoate binding. Mol Pharmacol 2008; 74:1163-9. [PMID: 18664604 DOI: 10.1124/mol.108.048819] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2023] Open
Abstract
Kainate receptor responses to domoate are characterized by large steady-state currents and slow deactivation kinetics. To improve our understanding of these responses, we mutated residues at the mouth of the agonist binding pocket of GluR6 using whole-cell electrophysiology to characterize the effects of the mutants. We identified two residues where mutations had significant ligand-specific effects. One, Met691, forms a hydrogen bond that seems to facilitate domoate binding by affecting the main-chain conformation. We found that mutation of Met691 to alanine significantly attenuated responses to domoate but had no effect on responses to glutamate, confirming the importance of this main-chain interaction in GluR6. The second residue, Val685, is located at the mouth of the binding pocket, adjacent to the domoate side-arm. Mutation of Val685 to glutamine increased the rate of decay from steady-state responses to domoate by more than 50-fold but had no effect on the rate or extent of desensitization or on the kinetics of responses to either glutamate or kainate. The V685Q mutant also significantly reduced the potencies of both glutamate (peak) and domoate (peak and steady-state). Empirical analysis using a basic kinetic model indicated that the V685Q phenotype could be fully explained by faster ligand dissociation. The V685Q mutant accelerated receptor deactivation without affecting either desensitization or gating, making it a potentially useful tool for further dissection of ligand binding and gating in kainate receptors.
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MESH Headings
- Alanine/metabolism
- Amino Acid Substitution/genetics
- Animals
- Binding Sites
- Cell Line
- Dose-Response Relationship, Drug
- Electrophysiology
- Glutamic Acid/metabolism
- Glutamic Acid/pharmacology
- Glutamine/metabolism
- Humans
- Hydrogen Bonding
- Kainic Acid/analogs & derivatives
- Kainic Acid/chemistry
- Kainic Acid/metabolism
- Kainic Acid/pharmacology
- Kidney/cytology
- Kinetics
- Models, Molecular
- Protein Conformation
- Protein Structure, Secondary
- Protein Structure, Tertiary
- Rats
- Receptors, AMPA/agonists
- Receptors, AMPA/chemistry
- Receptors, AMPA/metabolism
- Receptors, Kainic Acid/agonists
- Receptors, Kainic Acid/chemistry
- Receptors, Kainic Acid/genetics
- Receptors, Kainic Acid/metabolism
- Recombinant Proteins/chemistry
- Recombinant Proteins/metabolism
- Transfection
- GluK2 Kainate Receptor
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Affiliation(s)
- Yihong Zhang
- Department of Pharmacology, School of Biomedical Sciences, University of Liverpool, Ashton Street, Liverpool L69 3GE, UK
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18
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19
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Gorostiza P, Isacoff E. Optical switches and triggers for the manipulation of ion channels and pores. MOLECULAR BIOSYSTEMS 2007; 3:686-704. [PMID: 17882331 DOI: 10.1039/b710287a] [Citation(s) in RCA: 63] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Like fluorescence sensing techniques, methods to manipulate proteins with light have produced great advances in recent years. Ion channels have been one of the principal protein targets of photoswitched manipulation. In combination with fluorescence detection of cell signaling, this has enabled non-invasive, all-optical experiments on cell and tissue function, both in vitro and in vivo. Optical manipulation of channels has also provided insights into the mechanism of channel function. Optical control elements can be classified according to their molecular reversibility as non-reversible phototriggers where light breaks a chemical bond (e.g. caged ligands) and as photoswitches that reversibly photoisomerize. Synthetic photoswitches constitute nanoscale actuators that can alter channel function using three different strategies. These include (1) nanotoggles, which are tethered photoswitchable ligands that either activate channels (agonists) or inhibit them (blockers or antagonists), (2) nanokeys, which are untethered (freely diffusing) photoswitchable ligands, and (3) nanotweezers, which are photoswitchable crosslinkers. The properties of such photoswitches are discussed here, with a focus on tethered photoswitchable ligands. The recent literature on optical manipulation of ion channels is reviewed for the different channel families, with special emphasis on the understanding of ligand binding and gating processes, applications in nanobiotechnology, and with attention to future prospects in the field.
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Affiliation(s)
- Pau Gorostiza
- Department of Molecular and Cell Biology, University of California, Berkeley, CA 94720, USA
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20
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Abstract
Biologically active compounds which are light-responsive offer experimental possibilities which are otherwise very difficult to achieve. Since light can be manipulated very precisely, for example, with lasers and microscopes rapid jumps in concentration of the active form of molecules are possible with exact control of the area, time, and dosage. The development of such strategies started in the 1970s. This review summarizes new developments of the last five years and deals with "small molecules", proteins, and nucleic acids which can either be irreversibly activated with light (these compounds are referred to as "caged compounds") or reversibly switched between an active and an inactive state.
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Affiliation(s)
- Günter Mayer
- Kekulé-Institut für Organische Chemie und Biochemie, Rheinische Friedrich-Wilhelms-Universität Bonn, Gerhard-Domagk-Strasse 1, 53121 Bonn, Germany.
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21
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Kornreich BG, Niu L, Roberson MS, Oswald RE. Identification of C-terminal domain residues involved in protein kinase A-mediated potentiation of kainate receptor subtype 6. Neuroscience 2007; 146:1158-68. [PMID: 17379418 PMCID: PMC2700767 DOI: 10.1016/j.neuroscience.2007.02.012] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2006] [Revised: 02/07/2007] [Accepted: 02/07/2007] [Indexed: 11/18/2022]
Abstract
Glutamate receptors are the major excitatory receptors in the vertebrate CNS and have been implicated in a number of physiological and pathological processes. Previous work has shown that glutamate receptor function may be modulated by protein kinase A (PKA)-mediated phosphorylation, although the molecular mechanism of this potentiation has remained unclear. We have investigated the phosphorylation of specific amino acid residues in the C-terminal cytoplasmic domain of the rat kainate receptor subtype 6 (GluR6) as a possible mechanism for regulation of receptor function. The C-terminal tail of rat GluR6 can be phosphorylated by PKA on serine residues as demonstrated using [gamma-32P]ATP kinase assays. Whole cell recordings of transiently transfected human embryonic kidney (HEK) 293 cells showed that phosphorylation by PKA potentiates whole cell currents in wildtype GluR6 and that removal of the cytoplasmic C-terminal domain abolishes this potentiation. This suggested that the C-terminal domain may contain residue(s) involved in the PKA-mediated potentiation. Single mutations of each serine residue in the C-terminal domain (S815A, S825A, S828A, and S837A) and a truncation after position 855, which removes all threonines (T856, T864, and T875) from the domain, do not abolish PKA potentiation. However, the S825A/S837A mutation, but no other double mutation, abolishes potentiation. These results demonstrate that phosphorylation of the C-terminal tail of GluR6 by PKA leads to potentiation of whole cell response, and the combination of S825 and S837 in the C-terminal domain is a vital component of the mechanism of GluR6 potentiation by PKA.
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Affiliation(s)
| | - Li Niu
- Dept of Molecular Medicine, Cornell University, Ithaca, NY 14853
- Dept of Chemistry, Center of Biochemistry & Biophysics, SUNY Albany, Albany, NY 12222
| | - Mark S. Roberson
- Dept of Biomedical Sciences, Cornell University, Ithaca, NY 14853
| | - Robert E. Oswald
- Dept of Molecular Medicine, Cornell University, Ithaca, NY 14853
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22
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23
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Grewer C, Rauen T. Electrogenic glutamate transporters in the CNS: molecular mechanism, pre-steady-state kinetics, and their impact on synaptic signaling. J Membr Biol 2005; 203:1-20. [PMID: 15834685 PMCID: PMC2389879 DOI: 10.1007/s00232-004-0731-6] [Citation(s) in RCA: 107] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2004] [Accepted: 12/06/2004] [Indexed: 12/12/2022]
Abstract
Glutamate is the major excitatory neurotransmitter in the mammalian CNS. The spatiotemporal profile of the glutamate concentration in the synapse is critical for excitatory synaptic signalling. The control of this spatiotemporal concentration profile requires the presence of large numbers of synaptically localized glutamate transporters that remove pre-synaptically released glutamate by uptake into neurons and adjacent glia cells. These glutamate transporters are electrogenic and utilize energy stored in the transmembrane potential and the Na+/K+-ion concentration gradients to accumulate glutamate in the cell. This review focuses on the kinetic and electrogenic properties of glutamate transporters, as well as on the molecular mechanism of transport. Recent results are discussed that demonstrate the multistep nature of the transporter reaction cycle. Results from pre-steady-state kinetic experiments suggest that at least four of the individual transporter reaction steps are electrogenic, including reactions associated with the glutamate-dependent transporter halfcycle. Furthermore, the kinetic similarities and differences between some of the glutamate transporter subtypes and splice variants are discussed. A molecular mechanism of glutamate transport is presented that accounts for most of the available kinetic data. Finally, we discuss how synaptic glutamate transporters impact on glutamate receptor activity and how transporters may shape excitatory synaptic transmission.
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Affiliation(s)
- C Grewer
- Department of Physiology and Biophysics, University of Miami School of Medicine, Miami, FL 33136, USA.
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24
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Maier W, Corrie JET, Papageorgiou G, Laube B, Grewer C. Comparative analysis of inhibitory effects of caged ligands for the NMDA receptor. J Neurosci Methods 2005; 142:1-9. [PMID: 15652611 DOI: 10.1016/j.jneumeth.2004.07.006] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2004] [Revised: 06/08/2004] [Accepted: 07/01/2004] [Indexed: 11/26/2022]
Abstract
Photolytic release of neurotransmitters from caged precursors is a useful method to study synaptic processes with high temporal and spatial resolution. At present, the two most widely used classes of caged precursors for studies on glutamate receptors are based on derivatives of the 2-nitrobenzyl caging group (alpha-carboxy-2-nitrobenzyl, CNB) and the nitroindoline caging group (7-nitroindoline, NI, and 4-methoxy-7-nitroindoline, MNI). Besides NI- and MNI-caged amino acids being thermally more stable than the CNB-caged amino acids, there have been no other major advantages reported of using compounds from either of these two classes. Here, we show inhibitory effects of CNB-glutamate and a number of other CNB-caged agonists on N-methyl-D-aspartate (NMDA) receptors at non-saturating concentrations of the co-agonist glycine. In contrast, NI- and MNI-glutamate and most other NI-/MNI-caged agonists that we tested were inert under these conditions. Furthermore, we demonstrate that carboxynitroindoline-caged glycine (CNI-glycine), which was previously found to inhibit glycine receptors, has no such effect on NMDA receptors. Together, these findings underline the usefulness of NI- and MNI-caged ligands and show that CNB-caged compounds should be avoided in studies involving NMDA receptors.
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Affiliation(s)
- Wolfgang Maier
- Max-Planck-Institute for Brain Research, Deutschordenstr. 46, D-60528 Frankfurt, Germany
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25
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Huang Z, Li G, Pei W, Sosa LA, Niu L. Enhancing protein expression in single HEK 293 cells. J Neurosci Methods 2005; 142:159-66. [PMID: 15652630 DOI: 10.1016/j.jneumeth.2004.09.009] [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] [Received: 06/02/2004] [Revised: 09/07/2004] [Accepted: 09/17/2004] [Indexed: 11/29/2022]
Abstract
Recombinant proteins are routinely expressed in heterologous expression systems such as human embryonic kidney 293 (HEK 293) cells. The efficiency of the expression is critical when the expressed protein must be characterized at the single-cell level. Here we describe a simple method by which the protein expression efficiency in single HEK 293 cells is enhanced by coexpressing simian virus 40 large T antigen (TAg), a powerful oncoprotein. Using the GluR2 ionotropic glutamate receptor as an example, we found that the receptor expression in single HEK 293S cells increased approximately seven-fold. The ratio of the plasmid amount of TAg to that of the receptor was optimized at 1:10, while the receptor function was unaffected in the presence of TAg. We further used fluorescence imaging from a population of cells as an independent detection method and found a similar increase in expression of green fluorescent protein (GFP) by TAg coexpression. This method is thus applicable for enhancing the expression of both membrane and soluble proteins at the single-cell level. More importantly, the function of a protein can be studied directly in intact cells, a feature particularly useful for studying membrane proteins.
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Affiliation(s)
- Zhen Huang
- Department of Chemistry, Center for Neuroscience Research, University at Albany, SUNY, Albany, NY 12222, USA
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26
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Abstract
Opening of a ligand-gated ion channel is the step at which the binding of a neurotransmitter is transduced into the electrical signal by allowing ions to flow through the transmembrane channel, thereby altering the postsynaptic membrane potential. We report the kinetics for the opening of the GluR1Qflip channel, an alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor subunit of the ionotropic glutamate receptors. Using a laser-pulse photolysis technique that permits glutamate to be liberated photolytically from gamma-O-(alpha-carboxy-2-nitrobenzyl)glutamate (caged glutamate) with a time constant of approximately 30 micros, we show that, after the binding of glutamate, the channel opened with a rate constant of (2.9 +/- 0.2) x 10(4) s(-1) and closed with a rate constant of (2.1 +/- 0.1) x 10(3) s(-1). The observed shortest rise time (20-80% of the receptor current response), i.e. the fastest time by which the GluR1Qflip channel can open, was predicted to be 35 micros. This value is three times shorter than those previously reported. The minimal kinetic mechanism for channel opening consists of binding of two glutamate molecules, with the channel-opening probability being 0.93 +/- 0.10. These findings identify GluR1Qflip as one of the temporally efficient receptors that transduce the binding of chemical signals (i.e. glutamate) into an electrical impulse.
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Affiliation(s)
- Gang Li
- Department of Chemistry and the Center for Neuroscience Research, State University of New York, Albany, New York 12222, USA
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