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Buck TM, Jordan R, Lyons-Weiler J, Adelman JL, Needham PG, Kleyman TR, Brodsky JL. Expression of three topologically distinct membrane proteins elicits unique stress response pathways in the yeast Saccharomyces cerevisiae. Physiol Genomics 2015; 47:198-214. [PMID: 25759377 DOI: 10.1152/physiolgenomics.00101.2014] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/10/2014] [Accepted: 03/04/2015] [Indexed: 01/11/2023] Open
Abstract
Misfolded membrane proteins are retained in the endoplasmic reticulum (ER) and are subject to ER-associated degradation, which clears the secretory pathway of potentially toxic species. While the transcriptional response to environmental stressors has been extensively studied, limited data exist describing the cellular response to misfolded membrane proteins. To this end, we expressed and then compared the transcriptional profiles elicited by the synthesis of three ER retained, misfolded ion channels: The α-subunit of the epithelial sodium channel, ENaC, the cystic fibrosis transmembrane conductance regulator, CFTR, and an inwardly rectifying potassium channel, Kir2.1, which vary in their mass, membrane topologies, and quaternary structures. To examine transcriptional profiles in a null background, the proteins were expressed in yeast, which was previously used to examine the degradation requirements for each substrate. Surprisingly, the proteins failed to induce a canonical unfolded protein response or heat shock response, although messages encoding several cytosolic and ER lumenal protein folding factors rose when αENaC or CFTR was expressed. In contrast, the levels of these genes were unaltered by Kir2.1 expression; instead, the yeast iron regulon was activated. Nevertheless, a significant number of genes that respond to various environmental stressors were upregulated by all three substrates, and compared with previous microarray data we deduced the existence of a group of genes that reflect a novel misfolded membrane protein response. These data indicate that aberrant proteins in the ER elicit profound yet unique cellular responses.
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Affiliation(s)
- Teresa M Buck
- Department of Biological Sciences, University of Pittsburgh, Pittsburgh, Pennsylvania
| | - Rick Jordan
- GPCL Bioinformatics Analysis Core, University of Pittsburgh, Pittsburgh, Pennsylvania; and
| | - James Lyons-Weiler
- GPCL Bioinformatics Analysis Core, University of Pittsburgh, Pittsburgh, Pennsylvania; and
| | - Joshua L Adelman
- Department of Biological Sciences, University of Pittsburgh, Pittsburgh, Pennsylvania
| | - Patrick G Needham
- Department of Biological Sciences, University of Pittsburgh, Pittsburgh, Pennsylvania
| | - Thomas R Kleyman
- Department of Medicine, Renal-Electrolyte Division, University of Pittsburgh, Pittsburgh, Pennsylvania
| | - Jeffrey L Brodsky
- Department of Biological Sciences, University of Pittsburgh, Pittsburgh, Pennsylvania;
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Kolb AR, Needham PG, Rothenberg C, Guerriero CJ, Welling PA, Brodsky JL. ESCRT regulates surface expression of the Kir2.1 potassium channel. Mol Biol Cell 2013; 25:276-89. [PMID: 24227888 PMCID: PMC3890348 DOI: 10.1091/mbc.e13-07-0394] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
The Kir2.1 potassium channel is targeted by endoplasmic reticulum–associated degradation in yeast. To identify other Kir2.1 quality control factors, a novel yeast screen was performed. ESCRT components were among the strongest hits from the screen. Consistent with these data, ESCRT also regulates Kir2.1 stability in human cells. Protein quality control (PQC) is required to ensure cellular health. PQC is recognized for targeting the destruction of defective polypeptides, whereas regulated protein degradation mechanisms modulate the concentration of specific proteins in concert with physiological demands. For example, ion channel levels are physiologically regulated within tight limits, but a system-wide approach to define which degradative systems are involved is lacking. We focus on the Kir2.1 potassium channel because altered Kir2.1 levels lead to human disease and Kir2.1 restores growth on low-potassium medium in yeast mutated for endogenous potassium channels. Using this system, first we find that Kir2.1 is targeted for endoplasmic reticulum–associated degradation (ERAD). Next a synthetic gene array identifies nonessential genes that negatively regulate Kir2.1. The most prominent gene family that emerges from this effort encodes members of endosomal sorting complex required for transport (ESCRT). ERAD and ESCRT also mediate Kir2.1 degradation in human cells, with ESCRT playing a more prominent role. Thus multiple proteolytic pathways control Kir2.1 levels at the plasma membrane.
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Affiliation(s)
- Alexander R Kolb
- Department of Biological Sciences, University of Pittsburgh, Pittsburgh, PA 15261 Department of Physiology, University of Maryland School of Medicine, Baltimore, MD 21201
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Sandow S, Grayson TH. 'Altered' mesenteric artery SK(Ca) : functional implications? Br J Pharmacol 2011; 163:1115-7; author reply 1118-21. [PMID: 21707589 DOI: 10.1111/j.1476-5381.2011.01262.x] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
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Inhibition of lysosomal degradation rescues pentamidine-mediated decreases of KIR2.1 ion channel expression but not that of Kv11.1. Eur J Pharmacol 2011; 652:96-103. [DOI: 10.1016/j.ejphar.2010.10.093] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2010] [Revised: 10/13/2010] [Accepted: 10/29/2010] [Indexed: 11/19/2022]
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Schwalbe RA, Corey MJ, Cartwright TA. Novel Kv3 glycoforms differentially expressed in adult mammalian brain contain sialylated N-glycans. Biochem Cell Biol 2009; 86:21-30. [PMID: 18364742 DOI: 10.1139/o07-152] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
The N-glycan pool of mammalian brain contains remarkably high levels of sialylated N-glycans. This study provides the first evidence that voltage-gated K+ channels Kv3.1, Kv3.3, and Kv3.4, possess distinct sialylated N-glycan structures throughout the central nervous system of the adult rat. Electrophoretic migration patterns of Kv3.1, Kv3.3, and Kv3.4 glycoproteins from spinal cord, hypothalamus, thalamus, cerebral cortex, hippocampus, and cerebellum membranes digested with glycosidases were used to identify the various glycoforms. Differences in the migration of Kv3 proteins were attributed to the desialylated N-glycans. Expression levels of the Kv3 proteins were highest in cerebellum, whereas those of Kv3.1 and Kv3.3 were much lower in the other 5 regions. The lowest level of Kv3.1 was expressed in the hypothalamus, whereas the lowest levels of Kv3.3 were expressed in both thalamus and hypothalamus. The other regions expressed intermediate levels of Kv3.3, with spinal cord expressing the highest. The expression level of Kv3.4 in the hippocampus was slightly lower than that in cerebellum, and was closely followed by the other 4 regions, with spinal cord expressing the lowest level. We suggest that novel Kv3 glycoforms may endow differences in channel function and expression among regions throughout the central nervous system.
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Affiliation(s)
- Ruth A Schwalbe
- Department of Biochemistry and Molecular Biology, Brody School of Medicine, East Carolina University, 600 Moye Boulevard, Greenville, NC 27834, USA.
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Atypical sialylated N-glycan structures are attached to neuronal voltage-gated potassium channels. Biosci Rep 2009; 29:301-13. [DOI: 10.1042/bsr20080149] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023] Open
Abstract
Mammalian brains contain relatively high amounts of common and uncommon sialylated N-glycan structures. Sialic acid linkages were identified for voltage-gated potassium channels, Kv3.1, 3.3, 3.4, 1.1, 1.2 and 1.4, by evaluating their electrophoretic migration patterns in adult rat brain membranes digested with various glycosidases. Additionally, their electrophoretic migration patterns were compared with those of NCAM (neural cell adhesion molecule), transferrin and the Kv3.1 protein heterologously expressed in B35 neuroblastoma cells. Metabolic labelling of the carbohydrates combined with glycosidase digestion reactions were utilized to show that the N-glycan of recombinant Kv3.1 protein was capped with an oligo/poly-sialyl unit. All three brain Kv3 glycoproteins, like NCAM, were terminated with α2,3-linked sialyl residues, as well as atypical α2,8-linked sialyl residues. Additionally, at least one of their antennae was terminated with an oligo/poly-sialyl unit, similar to recombinant Kv3.1 and NCAM. In contrast, brain Kv1 glycoproteins consisted of sialyl residues with α2,8-linkage, as well as sialyl residues linked to internal carbohydrate residues of the carbohydrate chains of the N-glycans. This type of linkage was also supported for Kv3 glycoproteins. To date, such a sialyl linkage has only been identified in gangliosides, not N-linked glycoproteins. We conclude that all six Kv channels (voltage-gated K+ channels) contribute to the α2,8-linked sialylated N-glycan pool in mammalian brain and furthermore that their N-glycan structures contain branched sialyl residues. Identification of these novel and unique sialylated N-glycan structures implicate a connection between potassium channel activity and atypical sialylated N-glycans in modulating and fine-tuning the excitable properties of neurons in the nervous system.
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Cartwright TA, Corey MJ, Schwalbe RA. Complex oligosaccharides are N-linked to Kv3 voltage-gated K+ channels in rat brain. Biochim Biophys Acta Gen Subj 2006; 1770:666-71. [PMID: 17197096 DOI: 10.1016/j.bbagen.2006.11.013] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2006] [Revised: 11/14/2006] [Accepted: 11/27/2006] [Indexed: 11/17/2022]
Abstract
Neuronal Kv3 voltage-gated K(+) channels have two absolutely conserved N-glycosylation sites. Here, it is shown that Kv3.1, 3.3, and 3.4 channels are N-glycosylated in rat brain. Digestion of total brain membranes with peptide N glycosidase F (PNGase F) produced faster migrating immunobands than those of undigested membranes. Additionally, partial PNGase F digests showed that both sites are occupied by oligosaccharides. Neuraminidase treatment produced a smaller immunoband shift relative to PNGase F treatment. These results indicate that both sites are highly available and occupied by N-linked oligosaccharides for Kv3.1, 3.3, and 3.4 in rat brain, and furthermore that at least one oligosaccharide is of complex type. Additionally, these results point to an extracytoplasmic S1-S2 linker in Kv3 proteins expressed in native membranes. We suggest that N-glycosylation processing of Kv3 channels is critical for the expression of K(+) currents at the surface of neurons, and perhaps contributes to the pathophysiology of congenital disorders of glycosylation.
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Affiliation(s)
- Tara A Cartwright
- Department of Biochemistry and Molecular Biology, Brody School of Medicine at East Carolina University, 600 Moye Boulevard, Greenville, NC 27834, USA
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Brooks NL, Corey MJ, Schwalbe RA. Characterization of N-glycosylation consensus sequences in the Kv3.1 channel. FEBS J 2006; 273:3287-300. [PMID: 16792699 DOI: 10.1111/j.1742-4658.2006.05339.x] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
N-Glycosylation is a cotranslational and post-translational process of proteins that may influence protein folding, maturation, stability, trafficking, and consequently cell surface expression of functional channels. Here we have characterized two consensus N-glycosylation sequences of a voltage-gated K+ channel (Kv3.1). Glycosylation of Kv3.1 protein from rat brain and infected Sf9 cells was demonstrated by an electrophoretic mobility shift assay. Digestion of total brain membranes with peptide N glycosidase F (PNGase F) produced a much faster-migrating Kv3.1 immunoband than that of undigested brain membranes. To demonstrate N-glycosylation of wild-type Kv3.1 in Sf9 cells, cells were treated with tunicamycin. Also, partially purified proteins were digested with either PNGase F or endoglycosidase H. Attachment of simple-type oligosaccharides at positions 220 and 229 was directly shown by single (N229Q and N220Q) and double (N220Q/N229Q) Kv3.1 mutants. Functional measurements and membrane fractionation of infected Sf9 cells showed that unglycosylated Kv3.1s were transported to the plasma membrane. Unitary conductance of N220Q/N229Q was similar to that of the wild-type Kv3.1. However, whole cell currents of N220Q/N229Q channels had slower activation rates, and a slight positive shift in voltage dependence compared to wild-type Kv3.1. The voltage dependence of channel activation for N229Q and N220Q was much like that for N220Q/N229Q. These results demonstrate that the S1-S2 linker is topologically extracellular, and that N-glycosylation influences the opening of the voltage-dependent gate of Kv3.1. We suggest that occupancy of the sites is critical for folding and maturation of the functional Kv3.1 at the cell surface.
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Affiliation(s)
- Natasha L Brooks
- Department of Biochemistry and Molecular Biology, Brody School of Medicine, East Carolina University, Greenville, NC 27834, USA
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Bogdanov M, Zhang W, Xie J, Dowhan W. Transmembrane protein topology mapping by the substituted cysteine accessibility method (SCAM(TM)): application to lipid-specific membrane protein topogenesis. Methods 2005; 36:148-71. [PMID: 15894490 PMCID: PMC4104023 DOI: 10.1016/j.ymeth.2004.11.002] [Citation(s) in RCA: 126] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2004] [Revised: 11/15/2004] [Accepted: 11/15/2004] [Indexed: 01/03/2023] Open
Abstract
We provide an overview of lipid-dependent polytopic membrane protein topogenesis, with particular emphasis on Escherichia coli strains genetically altered in their lipid composition and strategies for experimentally determining the transmembrane organization of proteins. A variety of reagents and experimental strategies are described including the use of lipid mutants and thiol-specific chemical reagents to study lipid-dependent and host-specific membrane protein topogenesis by substituted cysteine site-directed chemical labeling. Employing strains in which lipid composition can be controlled temporally during membrane protein synthesis and assembly provides a means to observe dynamic changes in protein topology as a function of membrane lipid composition.
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Affiliation(s)
- Mikhail Bogdanov
- Department of Biochemistry and Molecular Biology, University of Texas-Houston, Medical School, Houston, TX 77030, USA
| | - Wei Zhang
- Department of Biochemistry and Molecular Biology, University of Texas-Houston, Medical School, Houston, TX 77030, USA
| | - Jun Xie
- Department of Biochemistry and Molecular Biology, University of Texas-Houston, Medical School, Houston, TX 77030, USA
| | - William Dowhan
- Department of Biochemistry and Molecular Biology, University of Texas-Houston, Medical School, Houston, TX 77030, USA
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Ricardo Pérez Riera A, Ferreira C, Dubner SJ, Schapachnik E. Andersen syndrome: the newest variant of the hereditary-familial long QT syndrome. Ann Noninvasive Electrocardiol 2004; 9:175-9. [PMID: 15084216 PMCID: PMC6932481 DOI: 10.1111/j.1542-474x.2004.92552.x] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
Abstract
Andersen's Syndrome is a rare disease, hereditary with autosomal dominant transmission, of the ion channels of the sarcolemmal membranes of the cardiac and skeletal muscles (channelopathy), which affects chromosome 17 of the KCNJ2 gene, responsible for encoding the outward potassium delayed rectifier current KIR2.1, resulting in a loss or suppression of the function of this channel.
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Malinowska DH, Sherry AM, Tewari KP, Cuppoletti J. Gastric parietal cell secretory membrane contains PKA- and acid-activated Kir2.1 K+ channels. Am J Physiol Cell Physiol 2003; 286:C495-506. [PMID: 14602583 DOI: 10.1152/ajpcell.00386.2003] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
Abstract
Our objective was to identify and localize a K+ channel involved in gastric HCl secretion at the parietal cell secretory membrane and to characterize and compare the functional properties of native and recombinant gastric K+ channels. RT-PCR showed that mRNA for Kir2.1 was abundant in rabbit gastric mucosa with lesser amounts of Kir4.1 and Kir7.1, relative to beta-actin. Kir2.1 mRNA was localized to parietal cells of rabbit gastric glands by in situ RT-PCR. Resting and stimulated gastric vesicles contained Kir2.1 by Western blot analysis at approximately 50 kDa as observed with in vitro translation. Immunoconfocal microscopy showed that Kir2.1 was present in parietal cells, where it colocalized with H+ -K+ -ATPase and ClC-2 Cl- channels. Function of native K+ channels in rabbit resting and stimulated gastric mucosal vesicles was studied by reconstitution into planar lipid bilayers. Native gastric K+ channels exhibited a linear current-voltage relationship and a single-channel slope conductance of approximately 11 pS in 400 mM K2SO4. Channel open probability (Po) in stimulated vesicles was high, and that of resting vesicles was low. Reduction of extracellular pH plus PKA treatment increased resting channel Po to approximately 0.5 as measured in stimulated vesicles. Full-length rabbit Kir2.1 was cloned. When stably expressed in Chinese hamster ovary (CHO) cells, it was activated by reduced extracellular pH and forskolin/IBMX with no effects observed in nontransfected CHO cells. Cation selectivity was K+ = Rb+ >> Na+ = Cs+ = Li+ = NMDG+. These findings strongly suggest that the Kir2.1 K+ channel may be involved in regulated gastric acid secretion at the parietal cell secretory membrane.
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Affiliation(s)
- Danuta H Malinowska
- Department of Molecular and Cellular Physiology, University of Cincinnati College of Medicine, Cincinnati, Ohio 45267-0576, USA.
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Schwalbe RA, Wingo CS, Xia SL. Mutations in the putative pore-forming segment favor short-lived wild-type Kir2.1 pore conformations. Biochemistry 2002; 41:12457-66. [PMID: 12369836 DOI: 10.1021/bi026304a] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
We have characterized single and double mutations in the M1-M2 segment of an inwardly rectifying K(+) channel, Kir2.1, using the cell-attached configuration of the patch-clamp technique. These mutations generated novel N-glycosylation sites at positions 128, 140, 143, and 147. Previously, we showed that these mutants were glycosylated, functional, and at the cell surface, which indicated that the putative pore-forming segment, including the invariant G(Y/F)G sequence of K(+) channels, was extracellular [Schwalbe, R. A., Rudin, A., Xia, S.-L., and Wingo, C. S. (2002) J. Biol. Chem. 277, 24382-24389]. In this study, three conductance states, corresponding to the main open state and two subconductance states, were identified in WT Kir2.1 channels expressed in infected Sf9 cells. Kir2.1 channels with mutations in the M1-M2 linker had at least one distinguishable conductance state of WT channels. In addition, these mutations altered the transitions, duration, and frequency of the defined populations of permeating and nonpermeating states. Of note, S128N had permeation rates similar to those of WT Kir2.1, but the total duration of the lower subconductance state was 3-5 times longer. Mutations in the signature sequence, I143N/Y145T, produced channels with permeation rates similar to those of the main open state and lower subconductance state of WT Kir2.1; however, the frequencies of these states were substantially different. These results demonstrate a novel functional role of the M1-M2 segment in regulating the transitions of the Kir2.1 channel and therefore suggest that this segment is a critical structural determinant in adjustments of pore conformations. Additionally, our results indicate that these mutants are correctly folded and thus further substantiate that the M1-M2 segment, including the G(Y/F)G sequence, is topologically extracellular.
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Affiliation(s)
- Ruth A Schwalbe
- Nephrology Section, Department of Veterans Affairs Medical Center, Division of Nephrology, Hypertension, and Transplantation, University of Florida, Gainesville, Florida 32610, USA.
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