1
|
Welch MA, Jansen LAR, Baro DJ. SUMOylation of the Kv4.2 Ternary Complex Increases Surface Expression and Current Amplitude by Reducing Internalization in HEK 293 Cells. Front Mol Neurosci 2021; 14:757278. [PMID: 34795560 PMCID: PMC8593141 DOI: 10.3389/fnmol.2021.757278] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2021] [Accepted: 10/05/2021] [Indexed: 11/29/2022] Open
Abstract
Kv4 α-subunits exist as ternary complexes (TC) with potassium channel interacting proteins (KChIP) and dipeptidyl peptidase-like proteins (DPLP); multiple ancillary proteins also interact with the α-subunits throughout the channel’s lifetime. Dynamic regulation of Kv4.2 protein interactions adapts the transient potassium current, IA, mediated by Kv4 α-subunits. Small ubiquitin-like modifier (SUMO) is an 11 kD peptide post-translationally added to lysine (K) residues to regulate protein–protein interactions. We previously demonstrated that when expressed in human embryonic kidney (HEK) cells, Kv4.2 can be SUMOylated at two K residues, K437 and K579. SUMOylation at K437 increased surface expression of electrically silent channels while SUMOylation at K579 reduced IA maximal conductance (Gmax) without altering surface expression. KChIP and DPLP subunits are known to modify the pattern of Kv4.2 post-translational decorations and/or their effects. In this study, co-expressing Kv4.2 with KChIP2a and DPP10c altered the effects of enhanced Kv4.2 SUMOylation. First, the effect of enhanced SUMOylation was the same for a TC containing either the wild-type Kv4.2 or the mutant K437R Kv4.2, suggesting that either the experimental manipulation no longer enhanced K437 SUMOylation or K437 SUMOylation no longer influenced Kv4.2 surface expression. Second, instead of decreasing IA Gmax, enhanced SUMOylation at K579 now produced a significant ∼37–70% increase in IA maximum conductance (Gmax) and a significant ∼30–50% increase in Kv4.2g surface expression that was accompanied by a 65% reduction in TC internalization. Blocking clathrin-mediated endocytosis (CME) in HEK cells expressing the Kv4.2 TC mimicked and occluded the effect of SUMO on IA Gmax; however, the amount of Kv4.2 associated with the major adaptor for constitutive CME, adaptor protein 2 (AP2), was not SUMO dependent. Thus, SUMOylation reduced Kv4.2 internalization by acting downstream of Kv4.2 recruitment into clathrin-coated pits. In sum, the two major findings of this study are: SUMOylation of Kv4.2 at K579 regulates TC internalization most likely by promoting channel recycling. Additionally, there is a reciprocity between Kv4.2 SUMOylation and the Kv4.2 interactome such that SUMOylation regulates the interactome and the interactome influences the pattern and effect of SUMOylation.
Collapse
Affiliation(s)
- Meghyn A Welch
- Department of Biology, Georgia State University, Atlanta, GA, United States
| | | | - Deborah J Baro
- Department of Biology, Georgia State University, Atlanta, GA, United States.,Neuroscience Institute, Georgia State University, Atlanta, GA, United States
| |
Collapse
|
2
|
Oláh VJ, Lukacsovich D, Winterer J, Arszovszki A, Lőrincz A, Nusser Z, Földy C, Szabadics J. Functional specification of CCK+ interneurons by alternative isoforms of Kv4.3 auxiliary subunits. eLife 2020; 9:58515. [PMID: 32490811 PMCID: PMC7269670 DOI: 10.7554/elife.58515] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2020] [Accepted: 05/20/2020] [Indexed: 01/18/2023] Open
Abstract
CCK-expressing interneurons (CCK+INs) are crucial for controlling hippocampal activity. We found two firing phenotypes of CCK+INs in rat hippocampal CA3 area; either possessing a previously undetected membrane potential-dependent firing or regular firing phenotype, due to different low-voltage-activated potassium currents. These different excitability properties destine the two types for distinct functions, because the former is essentially silenced during realistic 8–15 Hz oscillations. By contrast, the general intrinsic excitability, morphology and gene-profiles of the two types were surprisingly similar. Even the expression of Kv4.3 channels were comparable, despite evidences showing that Kv4.3-mediated currents underlie the distinct firing properties. Instead, the firing phenotypes were correlated with the presence of distinct isoforms of Kv4 auxiliary subunits (KChIP1 vs. KChIP4e and DPP6S). Our results reveal the underlying mechanisms of two previously unknown types of CCK+INs and demonstrate that alternative splicing of few genes, which may be viewed as a minor change in the cells’ whole transcriptome, can determine cell-type identity.
Collapse
Affiliation(s)
- Viktor János Oláh
- Laboratory of Cellular Neuropharmacology, Institute of Experimental Medicine, Budapest, Hungary.,János Szentágothai School of Neurosciences, Semmelweis University, Budapest, Hungary
| | - David Lukacsovich
- Laboratory of Neural Connectivity, Brain Research Institute, University of Zurich, Zurich, Switzerland
| | - Jochen Winterer
- Laboratory of Neural Connectivity, Brain Research Institute, University of Zurich, Zurich, Switzerland
| | - Antónia Arszovszki
- Laboratory of Cellular Neuropharmacology, Institute of Experimental Medicine, Budapest, Hungary
| | - Andrea Lőrincz
- Laboratory of Cellular Neurophysiology, Institute of Experimental Medicine, Budapest, Hungary
| | - Zoltan Nusser
- Laboratory of Cellular Neurophysiology, Institute of Experimental Medicine, Budapest, Hungary
| | - Csaba Földy
- Laboratory of Neural Connectivity, Brain Research Institute, University of Zurich, Zurich, Switzerland
| | - János Szabadics
- Laboratory of Cellular Neuropharmacology, Institute of Experimental Medicine, Budapest, Hungary
| |
Collapse
|
3
|
Welch MA, Forster LA, Atlas SI, Baro DJ. SUMOylating Two Distinct Sites on the A-type Potassium Channel, Kv4.2, Increases Surface Expression and Decreases Current Amplitude. Front Mol Neurosci 2019; 12:144. [PMID: 31213982 PMCID: PMC6554448 DOI: 10.3389/fnmol.2019.00144] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2018] [Accepted: 05/17/2019] [Indexed: 12/15/2022] Open
Abstract
Post-translational conjugation of Small Ubiquitin-like Modifier (SUMO) peptides to lysine (K) residues on target proteins alters their interactions. SUMOylation of a target protein can either promote its interaction with other proteins that possess SUMO binding domains, or it can prevent target protein interactions that normally occur in the absence of SUMOylation. One subclass of voltage-gated potassium channels that mediates an A-type current, IA, exists as a ternary complex comprising Kv4 pore-forming subunits, Kv channel interacting proteins (KChIP) and transmembrane dipeptidyl peptidase like proteins (DPPL). SUMOylation could potentially regulate intra- and/or intermolecular interactions within the complex. This study began to test this hypothesis and showed that Kv4.2 channels were SUMOylated in the rat brain and in human embryonic kidney (HEK) cells expressing a GFP-tagged mouse Kv4.2 channel (Kv4.2g). Prediction software identified two putative SUMOylation sites in the Kv4.2 C-terminus at K437 and K579. These sites were conserved across mouse, rat, and human Kv4.2 channels and across mouse Kv4 isoforms. Increasing Kv4.2g SUMOylation at each site by ~30% produced a significant ~22%–50% decrease in IA Gmax, and a ~70%–95% increase in channel surface expression. Site-directed mutagenesis of Kv4.2g showed that K437 SUMOylation regulated channel surface expression, while K579 SUMOylation controlled IA Gmax. The K579R mutation mimicked and occluded the SUMOylation-mediated decrease in IA Gmax, suggesting that SUMOylation at K579 blocked an intra- or inter-protein interaction involving K579. The K437R mutation did not obviously alter channel surface expression or biophysical properties, but it did block the SUMOylation-mediated increase in channel surface expression. Interestingly, enhancing K437 SUMOylation in the K579R mutant roughly doubled channel surface expression, but produced no change in IA Gmax, suggesting that the newly inserted channels were electrically silent. This is the first report that Kv4.2 channels are SUMOylated and that SUMOylation can independently regulate Kv4.2 surface expression and IA Gmax in opposing directions. The next step will be to determine if/how SUMOylation affects Kv4 interactions within the ternary complex.
Collapse
Affiliation(s)
- Meghyn A Welch
- Department of Biology, Georgia State University, Atlanta, GA, United States
| | - Lori A Forster
- Neuroscience Institute, Georgia State University, Atlanta, GA, United States
| | - Selin I Atlas
- Department of Biology, Georgia State University, Atlanta, GA, United States
| | - Deborah J Baro
- Department of Biology, Georgia State University, Atlanta, GA, United States.,Neuroscience Institute, Georgia State University, Atlanta, GA, United States
| |
Collapse
|
4
|
Long-Term Potentiation at the Mossy Fiber-Granule Cell Relay Invokes Postsynaptic Second-Messenger Regulation of Kv4 Channels. J Neurosci 2017; 36:11196-11207. [PMID: 27807163 DOI: 10.1523/jneurosci.2051-16.2016] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2016] [Accepted: 09/12/2016] [Indexed: 11/21/2022] Open
Abstract
Mossy fiber afferents to cerebellar granule cells form the primary synaptic relay into cerebellum, providing an ideal site to process signal inputs differentially. Mossy fiber input is known to exhibit a long-term potentiation (LTP) of synaptic efficacy through a combination of presynaptic and postsynaptic mechanisms. However, the specific postsynaptic mechanisms contributing to LTP of mossy fiber input is unknown. The current study tested the hypothesis that LTP induces a change in intrinsic membrane excitability of rat cerebellar granule cells through modification of Kv4 A-type potassium channels. We found that theta-burst stimulation of mossy fiber input in lobule 9 granule cells lowered the current threshold to spike and increases the gain of spike firing by 2- to 3-fold. The change in postsynaptic excitability was traced to hyperpolarizing shifts in both the half-inactivation and half-activation potentials of Kv4 that occurred upon coactivating NMDAR and group I metabotropic glutamatergic receptors. The effects of theta-burst stimulation on Kv4 channel control of the gain of spike firing depended on a signaling cascade leading to extracellular signal-related kinase activation. Under physiological conditions, LTP of synaptically evoked spike output was expressed preferentially for short bursts characteristic of sensory input, helping to shape signal processing at the mossy fiber-granule cell relay. SIGNIFICANCE STATEMENT Cerebellar granule cells receive mossy fiber inputs that convey information on different sensory modalities and feedback from descending cortical projections. Recent work suggests that signal processing across multiple cerebellar lobules is controlled differentially by postsynaptic ionic mechanisms at the level of granule cells. We found that long-term potentiation (LTP) of mossy fiber input invoked a large increase in granule cell excitability by modifying the biophysical properties of Kv4 channels through a specific signaling cascade. LTP of granule cell output became evident in response to bursts of mossy fiber input, revealing that Kv4 control of intrinsic excitability is modified to respond most effectively to patterns of afferent input that are characteristic of physiological sensory patterns.
Collapse
|
5
|
Cheng CF, Wang WC, Huang CY, Du PH, Yang JH, Tsaur ML. Coexpression of auxiliary subunits KChIP and DPPL in potassium channel Kv4-positive nociceptors and pain-modulating spinal interneurons. J Comp Neurol 2015; 524:846-73. [PMID: 26239200 DOI: 10.1002/cne.23876] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2015] [Revised: 07/30/2015] [Accepted: 07/31/2015] [Indexed: 12/21/2022]
Abstract
Subthreshold A-type K(+) currents (ISA s) have been recorded from the somata of nociceptors and spinal lamina II excitatory interneurons, which sense and modulate pain, respectively. Kv4 channels are responsible for the somatodendritic ISA s. Accumulative evidence suggests that neuronal Kv4 channels are ternary complexes including pore-forming Kv4 subunits and two types of auxiliary subunits: K(+) channel-interacting proteins (KChIPs) and dipeptidyl peptidase-like proteins (DPPLs). Previous reports have shown Kv4.3 in a subset of nonpeptidergic nociceptors and Kv4.2/Kv4.3 in certain spinal lamina II excitatory interneurons. However, whether and which KChIP and DPPL are coexpressed with Kv4 in these ISA -expressing pain-related neurons is unknown. In this study we mapped the protein distribution of KChIP1, KChIP2, KChIP3, DPP6, and DPP10 in adult rat dorsal root ganglion (DRG) and spinal cord by immunohistochemistry. In the DRG, we found colocalization of KChIP1, KChIP2, and DPP10 in the somatic surface and cytoplasm of Kv4.3(+) nociceptors. KChIP3 appears in most Aβ and Aδ sensory neurons as well as a small population of peptidergic nociceptors, whereas DPP6 is absent in sensory neurons. In the spinal cord, KChIP1 is coexpressed with Kv4.3 in the cell bodies of a subset of lamina II excitatory interneurons, while KChIP1, KChIP2, and DPP6 are colocalized with Kv4.2 and Kv4.3 in their dendrites. Within the dorsal horn, besides KChIP3 in the inner lamina II and lamina III, we detected DPP10 in most projection neurons, which transmit pain signal to brain. The results suggest the existence of Kv4/KChIP/DPPL ternary complexes in ISA -expressing nociceptors and pain-modulating spinal interneurons.
Collapse
Affiliation(s)
- Chau-Fu Cheng
- Institute of Neuroscience, Brain Research Center, National Yang-Ming University, Taipei, Taiwan
| | - Wan-Chen Wang
- Institute of Neuroscience, Brain Research Center, National Yang-Ming University, Taipei, Taiwan
| | - Chia-Yi Huang
- Institute of Neuroscience, Brain Research Center, National Yang-Ming University, Taipei, Taiwan
| | - Po-Hau Du
- Institute of Neuroscience, Brain Research Center, National Yang-Ming University, Taipei, Taiwan
| | - Jung-Hui Yang
- Institute of Neuroscience, Brain Research Center, National Yang-Ming University, Taipei, Taiwan
| | - Meei-Ling Tsaur
- Institute of Neuroscience, Brain Research Center, National Yang-Ming University, Taipei, Taiwan
| |
Collapse
|
6
|
Kitazawa M, Kubo Y, Nakajo K. Kv4.2 and accessory dipeptidyl peptidase-like protein 10 (DPP10) subunit preferentially form a 4:2 (Kv4.2:DPP10) channel complex. J Biol Chem 2015. [PMID: 26209633 DOI: 10.1074/jbc.m115.646794] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Kv4 is a member of the voltage-gated K(+) channel family and forms a complex with various accessory subunits. Dipeptidyl aminopeptidase-like protein (DPP) is one of the auxiliary subunits for the Kv4 channel. Although DPP has been well characterized and is known to increase the current amplitude and accelerate the inactivation and recovery from inactivation of Kv4 current, it remains to be determined how many DPPs bind to one Kv4 channel. To examine whether the expression level of DPP changes the biophysical properties of Kv4, we expressed Kv4.2 and DPP10 in different ratios in Xenopus oocytes and analyzed the currents under two-electrode voltage clamp. The current amplitude and the speed of recovery from inactivation of Kv4.2 changed depending on the co-expression level of DPP10. This raised the possibility that the stoichiometry of the Kv4.2-DPP10 complex is variable and affects the biophysical properties of Kv4.2. We next determined the stoichiometry of DPP10 alone by subunit counting using single-molecule imaging. Approximately 70% of the DPP10 formed dimers in the plasma membrane, and the rest existed as monomers in the absence of Kv4.2. We next determined the stoichiometry of the Kv4.2-DPP10 complex; Kv4.2-mCherry and mEGFP-DPP10 were co-expressed in different ratios and the stoichiometries of Kv4.2-DPP10 complexes were evaluated by the subunit counting method. The stoichiometry of the Kv4.2-DPP10 complex was variable depending on the relative expression level of each subunit, with a preference for 4:2 stoichiometry. This preference may come from the bulky dimeric structure of the extracellular domain of DPP10.
Collapse
Affiliation(s)
- Masahiro Kitazawa
- From the Division of Biophysics and Neurobiology, Department of Molecular Physiology, National Institute for Physiological Sciences, Okazaki, Aichi 444-8585, Japan and the Department of Physiological Sciences, Graduate University for Advanced Studies (SOKENDAI), Hayama, Kanagawa 240-0155, Japan
| | - Yoshihiro Kubo
- From the Division of Biophysics and Neurobiology, Department of Molecular Physiology, National Institute for Physiological Sciences, Okazaki, Aichi 444-8585, Japan and the Department of Physiological Sciences, Graduate University for Advanced Studies (SOKENDAI), Hayama, Kanagawa 240-0155, Japan
| | - Koichi Nakajo
- From the Division of Biophysics and Neurobiology, Department of Molecular Physiology, National Institute for Physiological Sciences, Okazaki, Aichi 444-8585, Japan and the Department of Physiological Sciences, Graduate University for Advanced Studies (SOKENDAI), Hayama, Kanagawa 240-0155, Japan
| |
Collapse
|
7
|
Interaction of the scorpion toxin discrepin with Kv4.3 channels and A-type K+ channels in cerebellum granular cells. Biochim Biophys Acta Gen Subj 2014; 1840:2744-51. [DOI: 10.1016/j.bbagen.2014.05.009] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2013] [Revised: 05/01/2014] [Accepted: 05/12/2014] [Indexed: 12/13/2022]
|
8
|
The expression pattern of a Cav3-Kv4 complex differentially regulates spike output in cerebellar granule cells. J Neurosci 2014; 34:8800-12. [PMID: 24966380 DOI: 10.1523/jneurosci.0981-14.2014] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
The cerebellum receives sensory information by mossy fiber input from a multitude of sources that require differential signal processing. A compartmentalization of function begins with the segregation of mossy fibers across 10 distinct lobules over the rostrocaudal axis, with tactile receptor afferents prevalent in anterior lobules and vestibular input in caudal lobules. However, it is unclear how these unique signals might be differentially processed at the circuit level across the cerebellum. As granule cells receive mossy fiber input, they represent a key stage at which postsynaptic mechanisms could influence signal processing. Granule cells express an A-type current mediated by Kv4 potassium channels that modify the latency and frequency of spike output. The current study examined the potential for a Cav3 calcium-Kv4 channel complex to regulate the response of granule cells to mossy fiber input in lobules 2 and 9 of the rat cerebellum. Similar A-type currents were recorded in both regions, but the Cav3 calcium current was expressed at a substantially higher density in lobule 9 cells, acting to increase A-type current availability through its influence on Kv4 voltage for inactivation. The difference in excitability imparted by Cav3-Kv4 interactions proves to allow lobule 2 granule cells to respond more effectively to tactile stimulus-like burst input and lobule 9 cells to slow shifts in input frequency characteristic of vestibular input. The expression pattern of Cav3 channels and its control of Kv4 availability thus provides a novel means of processing widely different forms of sensory input across cerebellar lobules.
Collapse
|
9
|
Kv4 channels underlie A-currents with highly variable inactivation time courses but homogeneous other gating properties in the nucleus tractus solitarii. Pflugers Arch 2014; 467:789-803. [PMID: 24872163 DOI: 10.1007/s00424-014-1533-z] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2013] [Revised: 04/18/2014] [Accepted: 05/08/2014] [Indexed: 10/25/2022]
Abstract
In the nucleus of the tractus solitarii (NTS), a large proportion of neurones express transient A-type potassium currents (I KA) having deep influence on the fidelity of the synaptic transmission of the visceral primary afferent inputs to second-order neurones. Up to now, the strong impact of I KA within the NTS was considered to result exclusively from its variation in amplitude, and its molecular correlate(s) remained unknown. In order to identify which Kv channels underlie I KA in NTS neurones, the gating properties and the pharmacology of this current were determined using whole cell patch clamp recordings in slices. Complementary information was brought by immunohistochemistry. Strikingly, two neurone subpopulations characterized by fast or slow inactivation time courses (respectively about 50 and 200 ms) were discriminated. Both characteristics matched those of the Kv4 channel subfamily. The other gating properties, also matching the Kv4 channel ones, were homogeneous through the NTS. The activation and inactivation occurred at membrane potentials around the threshold for generating action potentials, and the time course of recovery from inactivation was rapid. Pharmacologically, I KA in NTS neurones was found to be resistant to tetraethylammonium (TEA), sea anemone toxin blood-depressing substance (BDS) and dendrotoxin (DTX), whereas Androctonus mauretanicus mauretanicus toxin 3 (AmmTX3), a scorpion toxin of the α-KTX 15 family that has been shown to block all the members of the Kv4 family, inhibited 80 % of I KA irrespectively of its inactivation time course. Finally, immunohistochemistry data suggested that, among the Kv4 channel subfamily, Kv4.3 is the prevalent subunit expressed in the NTS.
Collapse
|
10
|
Jerng HH, Pfaffinger PJ. Modulatory mechanisms and multiple functions of somatodendritic A-type K (+) channel auxiliary subunits. Front Cell Neurosci 2014; 8:82. [PMID: 24723849 PMCID: PMC3973911 DOI: 10.3389/fncel.2014.00082] [Citation(s) in RCA: 54] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2014] [Accepted: 03/03/2014] [Indexed: 12/13/2022] Open
Abstract
Auxiliary subunits are non-conducting, modulatory components of the multi-protein ion channel complexes that underlie normal neuronal signaling. They interact with the pore-forming α-subunits to modulate surface distribution, ion conductance, and channel gating properties. For the somatodendritic subthreshold A-type potassium (ISA) channel based on Kv4 α-subunits, two types of auxiliary subunits have been extensively studied: Kv channel-interacting proteins (KChIPs) and dipeptidyl peptidase-like proteins (DPLPs). KChIPs are cytoplasmic calcium-binding proteins that interact with intracellular portions of the Kv4 subunits, whereas DPLPs are type II transmembrane proteins that associate with the Kv4 channel core. Both KChIPs and DPLPs genes contain multiple start sites that are used by various neuronal populations to drive the differential expression of functionally distinct N-terminal variants. In turn, these N-terminal variants generate tremendous functional diversity across the nervous system. Here, we focus our review on (1) the molecular mechanism underlying the unique properties of different N-terminal variants, (2) the shaping of native ISA properties by the concerted actions of KChIPs and DPLP variants, and (3) the surprising ways that KChIPs and DPLPs coordinate the activity of multiple channels to fine-tune neuronal excitability. Unlocking the unique contributions of different auxiliary subunit N-terminal variants may provide an important opportunity to develop novel targeted therapeutics to treat numerous neurological disorders.
Collapse
Affiliation(s)
- Henry H. Jerng
- Department of Neuroscience, Baylor College of MedicineHouston, TX, USA
| | | |
Collapse
|
11
|
Jerng HH, Pfaffinger PJ. S-glutathionylation of an auxiliary subunit confers redox sensitivity to Kv4 channel inactivation. PLoS One 2014; 9:e93315. [PMID: 24675763 PMCID: PMC3968176 DOI: 10.1371/journal.pone.0093315] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2013] [Accepted: 03/04/2014] [Indexed: 12/24/2022] Open
Abstract
Reactive oxygen species (ROS) regulate ion channels, modulate neuronal excitability, and contribute to the etiology of neurodegenerative disorders. ROS differentially suppress fast "ball-and-chain" N-type inactivation of cloned Kv1 and Kv3 potassium channels but not of Kv4 channels, likely due to a lack of reactive cysteines in Kv4 N-termini. Recently, we discovered that N-type inactivation of Kv4 channel complexes can be independently conferred by certain N-terminal variants of Kv4 auxiliary subunits (DPP6a, DPP10a). Here, we report that both DPP6a and DPP10a, like Kv subunits with redox-sensitive N-type inactivation, contain a highly conserved cysteine in their N-termini (Cys-13). To test if N-type inactivation mediated by DPP6a or DPP10a is redox sensitive, Xenopus oocyte recordings were performed to examine the effects of two common oxidants, tert-butyl hydroperoxide (tBHP) and diamide. Both oxidants markedly modulate DPP6a- or DPP10a-conferred N-type inactivation of Kv4 channels, slowing the overall inactivation and increasing the peak current. These functional effects are fully reversed by the reducing agent dithiothreitol (DTT) and appear to be due to a selective modulation of the N-type inactivation mediated by these auxiliary subunits. Mutation of DPP6a Cys-13 to serine eliminated the tBHP or diamide effects, confirming the importance of Cys-13 to the oxidative regulation. Biochemical studies designed to elucidate the underlying molecular mechanism show no evidence of protein-protein disulfide linkage formation following cysteine oxidation. Instead, using a biotinylated glutathione (BioGEE) reagent, we discovered that oxidation by tBHP or diamide leads to S-glutathionylation of Cys-13, suggesting that S-glutathionylation underlies the regulation of fast N-type inactivation by redox. In conclusion, our studies suggest that Kv4-based A-type current in neurons may show differential redox sensitivity depending on whether DPP6a or DPP10a is highly expressed, and that the S-glutathionylation mechanism may play a previously unappreciated role in mediating excitability changes and neuropathologies associated with ROS.
Collapse
Affiliation(s)
- Henry H. Jerng
- Department of Neuroscience, Baylor College of Medicine, Houston, Texas, United States of America
| | - Paul J. Pfaffinger
- Department of Neuroscience, Baylor College of Medicine, Houston, Texas, United States of America
| |
Collapse
|
12
|
Pfaffinger PJ. A conserved pre-block interaction motif regulates potassium channel activation and N-type inactivation. PLoS One 2013; 8:e79891. [PMID: 24236164 PMCID: PMC3827413 DOI: 10.1371/journal.pone.0079891] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2013] [Accepted: 10/06/2013] [Indexed: 02/02/2023] Open
Abstract
N-type inactivation occurs when the N-terminus of a potassium channel binds into the open pore of the channel. This study examined the relationship between activation and steady state inactivation for mutations affecting the N-type inactivation properties of the Aplysia potassium channel AKv1 expressed in Xenopus oocytes. The results show that the traditional single-step model for N-type inactivation fails to properly account for the observed relationship between steady state channel activation and inactivation curves. We find that the midpoint of the steady state inactivation curve depends in part on a secondary interaction between the channel core and a region of the N-terminus just proximal to the pore blocking peptide that we call the Inactivation Proximal (IP) region. The IP interaction with the channel core produces a negative shift in the activation and inactivation curves, without blocking the pore. A tripeptide motif in the IP region was identified in a large number of different N-type inactivation domains most likely reflecting convergent evolution in addition to direct descent. Point mutating a conserved hydrophobic residue in this motif eliminates the gating voltage shift, accelerates recovery from inactivation and decreases the amount of pore block produced during inactivation. The IP interaction we have identified likely stabilizes the open state and positions the pore blocking region of the N-terminus at the internal opening to the transmembrane pore by forming a Pre-Block (P state) interaction with residues lining the side window vestibule of the channel.
Collapse
Affiliation(s)
- Paul J. Pfaffinger
- Department of Neuroscience, Baylor College of Medicine, Houston, Texas, United States of America
- * E-mail:
| |
Collapse
|
13
|
Abstract
Dipeptidyl Peptidase-like Protein 6 (DPP6) is widely expressed in the brain where it co-assembles with Kv4 channels and KChIP auxiliary subunits to regulate the amplitude and functional properties of the somatodendritic A-current, ISA. Here we show that in cerebellar granule (CG) cells DPP6 also regulates resting membrane potential and input resistance by increasing the amplitude of the IK(SO) resting membrane current. Pharmacological analysis shows that DPP6 acts through the control of a channel with properties matching the K2P channel TASK-3. Heterologous expression and co-immunoprecipitation shows that DPP6 co-expression with TASK-3 results in the formation of a protein complex that enhances resting membrane potassium conductance. The co-regulation of resting and voltage-gated channels by DPP6 produces coordinate shifts in resting membrane potential and A-current gating that optimize the sensitivity of ISA inactivation gating to subthreshold fluctuations in resting membrane potential.
Collapse
|
14
|
Witzel K, Fischer P, Bähring R. Hippocampal A-type current and Kv4.2 channel modulation by the sulfonylurea compound NS5806. Neuropharmacology 2012; 63:1389-403. [PMID: 22964468 DOI: 10.1016/j.neuropharm.2012.08.017] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2012] [Revised: 08/16/2012] [Accepted: 08/18/2012] [Indexed: 12/24/2022]
Abstract
We examined the effects of the sulfonylurea compound NS5806 on neuronal A-type channel function. Using whole-cell patch-clamp we studied the effects of NS5806 on the somatodendritic A-type current (I(SA)) in cultured hippocampal neurons and the currents mediated by Kv4.2 channels coexpressed with different auxiliary β-subunits, including both Kv channel interacting proteins (KChIPs) and dipeptidyl aminopeptidase-related proteins (DPPs), in HEK 293 cells. The amplitude of the I(SA) component in hippocampal neurons was reduced in the presence of 20 μM NS5806. I(SA) decay kinetics were slowed and the recovery kinetics accelerated, but the voltage dependence of steady-state inactivation was shifted to more negative potentials by NS5806. The peak amplitudes of currents mediated by ternary Kv4.2 channel complexes, associated with DPP6-S (short splice-variant) and either KChIP2, KChIP3 or KChIP4, were potentiated and their macroscopic inactivation slowed by NS5806, whereas the currents mediated by binary Kv4.2 channels, associated only with DPP6-S, were suppressed, and the NS5806-mediated slowing of macroscopic inactivation was less pronounced. Neither potentiation nor suppression and no effect on current decay kinetics in the presence of NS5806 were observed for Kv4.2 channels associated with KChIP3 and the N-type inactivation-conferring DPP6a splice-variant. For all recombinant channel complexes, NS5806 slowed the recovery from inactivation and shifted the voltage dependence of steady-state inactivation to more negative potentials. Our results demonstrate the activity of NS5806 on native I(SA) and possible molecular correlates in the form of recombinant Kv4.2 channels complexed with different KChIPs and DPPs, and they shed some light on the mechanism of NS5806 action.
Collapse
Affiliation(s)
- Katrin Witzel
- Institut für Zelluläre und Integrative Physiologie, Zentrum für Experimentelle Medizin, Universitätsklinikum Hamburg-Eppendorf, Martinistr. 52, 20246 Hamburg, Germany
| | | | | |
Collapse
|