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Agassandian M, Chen BB, Schuster CC, Houtman JCD, Mallampalli RK. 14-3-3zeta escorts CCTalpha for calcium-activated nuclear import in lung epithelia. FASEB J 2009; 24:1271-83. [PMID: 20007511 DOI: 10.1096/fj.09-136044] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
Integrity of animal biomembranes is critical to preserve normal cellular functions and viability. Phosphatidylcholine, an indispensible membrane component, requires the enzyme CCTalpha for its biosynthesis. Nuclear expression of CCTalpha is needed for expansion of the nuclear membrane network, but mechanisms for CCTalpha nuclear import are unknown. Herein, we show that in epithelia, extracellular Ca(2+) triggers CCTalpha cytoplasmic-nuclear translocation. CCTalpha nuclear import was associated with binding to 14-3-3zeta, a key regulator of protein trafficking. 14-3-3zeta was both sufficient and required for CCTalpha nuclear import. Helix G within the 14-3-3zeta binding groove interacts with a putative molecular signature within the CCTalpha carboxyl-terminal phosphoserine motif (residues 328-343). 14-3-3zeta was critically involved in preserving phosphatidylcholine synthesis and cell viability in a model of Pseudomonas aeruginosa infection where Ca(2+) concentrations increase within epithelia. Thus, 14-3-3zeta controls CCTalpha nuclear import in response to calcium signals, thereby regulating mammalian phospholipid synthesis. Agassandian, M., Chen, B. B., Schuster, C. C., Houtman, J. C. D., Mallampalli, R. K. 14-3-3zeta escorts CCTalpha for calcium-activated nuclear import in lung epithelia.
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Affiliation(s)
- Marianna Agassandian
- Department of Internal Medicine, Roy J. and Lucille A. Carver College of Medicine, The University of Iowa, Iowa City, Iowa, USA
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52
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Zhang Y, Yamada Y, Fan M, Bangaru SD, Lin B, Yang J. The beta subunit of voltage-gated Ca2+ channels interacts with and regulates the activity of a novel isoform of Pax6. J Biol Chem 2009; 285:2527-36. [PMID: 19917615 DOI: 10.1074/jbc.m109.022236] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
Ca(2+) channel beta subunits (Ca(v)betas) are essential for regulating the surface expression and gating of high voltage-activated Ca(2+) channels through their interaction with Ca(2+) channel alpha(1) subunits. In efforts to uncover new interacting partners and new functions for Ca(v)beta, we identified a new splicing isoform of Pax6, a transcription factor crucial for the development of the eye, nose, brain, and pancreas. Pax6 contains two DNA binding domains (paired domain and homeodomain), a glycine-rich linker connecting these two domains and a C-terminal proline-, serine-, and threonine-rich transactivation domain. The protein sequence and function of Pax6 are highly conserved from invertebrate to human. The newly isolated isoform, named Pax6(S), retains the paired domain, linker, and homeodomain of Pax6, but its C terminus is composed of a truncated classic proline, serine, and threonine domain and a unique S tail. Pax6(S) shows a similar level of transcriptional activity in vitro as does Pax6, but only in primates is the protein sequence highly conserved. Its spatial-temporal expression profiles are also different from those of Pax6. These divergences suggest a noncanonical role of Pax6(S) during development. The interaction between Pax6(S) and Ca(v)beta is mainly endowed by the S tail. Co-expression of Pax6(S) with a Ca(2+) channel complex containing the beta(3) subunit in Xenopus oocytes does not affect channel properties. Conversely, however, beta(3) is able to suppress the transcriptional activity of Pax6(S). Furthermore, in the presence of Pax6(S), beta(3) is translocated from the cytoplasm to the nucleus. These results suggest that full-length Ca(v)beta may act directly as a transcription regulator independent of its role in regulating Ca(2+) channel activity.
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Affiliation(s)
- Yun Zhang
- Department of Biological Sciences, Columbia University, New York, New York 10027, USA
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53
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Levy S, Beharier O, Etzion Y, Mor M, Buzaglo L, Shaltiel L, Gheber LA, Kahn J, Muslin AJ, Katz A, Gitler D, Moran A. Molecular basis for zinc transporter 1 action as an endogenous inhibitor of L-type calcium channels. J Biol Chem 2009; 284:32434-43. [PMID: 19767393 DOI: 10.1074/jbc.m109.058842] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
The L-type calcium channel (LTCC) has a variety of physiological roles that are critical for the proper function of many cell types and organs. Recently, a member of the zinc-regulating family of proteins, ZnT-1, was recognized as an endogenous inhibitor of the LTCC, but its mechanism of action has not been elucidated. In the present study, using two-electrode voltage clamp recordings in Xenopus oocytes, we demonstrate that ZnT-1-mediated inhibition of the LTCC critically depends on the presence of the LTCC regulatory beta-subunit. Moreover, the ZnT-1-induced inhibition of the LTCC current is also abolished by excess levels of the beta-subunit. An interaction between ZnT-1 and the beta-subunit, as demonstrated by co-immunoprecipitation and by fluorescence resonance energy transfer, is consistent with this result. Using surface biotinylation and total internal reflection fluorescence microscopy in HEK293 cells, we show a ZnT-1-dependent decrease in the surface expression of the pore-forming alpha(1)-subunit of the LTCC. Similarly, a decrease in the surface expression of the alpha(1)-subunit is observed following up-regulation of the expression of endogenous ZnT-1 in rapidly paced cultured cardiomyocytes. We conclude that ZnT-1-mediated inhibition of the LTCC is mediated through a functional interaction of ZnT-1 with the LTCC beta-subunit and that it involves a decrease in the trafficking of the LTCC alpha(1)-subunit to the surface membrane.
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Affiliation(s)
- Shiri Levy
- Department of Physiology, Faculty of Health Sciences, Ben-Gurion University of the Negev, Beer-Sheva 84101, Israel
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54
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Xu X, Colecraft HM. Engineering proteins for custom inhibition of Ca(V) channels. Physiology (Bethesda) 2009; 24:210-8. [PMID: 19675352 DOI: 10.1152/physiol.00010.2009] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The influx of Ca(2+) ions through voltage-dependent calcium (Ca(V)) channels links electrical signals to physiological responses in all excitable cells. Not surprisingly, blocking Ca(V) channel activity is a powerful method to regulate the function of excitable cells, and this is exploited for both physiological and therapeutic benefit. Nevertheless, the full potential for Ca(V) channel inhibition is not being realized by currently available small-molecule blockers or second-messenger modulators due to limitations in targeting them either to defined groups of cells in an organism or to distinct subcellular regions within a single cell. Here, we review early efforts to engineer protein molecule blockers of Ca(V) channels to fill this crucial niche. This technology would greatly expand the toolbox available to physiologists studying the biology of excitable cells at the cellular and systems level.
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Affiliation(s)
- Xianghua Xu
- Department of Physiology and Cellular Biophysics, College of Physicians and Surgeons, Columbia University, New York, New York, USA
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55
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Taylor JR, Zheng Z, Wang ZM, Payne AM, Messi ML, Delbono O. Increased CaVbeta1A expression with aging contributes to skeletal muscle weakness. Aging Cell 2009; 8:584-94. [PMID: 19663902 DOI: 10.1111/j.1474-9726.2009.00507.x] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
Ca2+ release from the sarcoplasmic reticulum (SR) into the cytosol is a crucial part of excitation-contraction (E-C) coupling. Excitation-contraction uncoupling, a deficit in Ca2+ release from the SR, is thought to be responsible for at least some of the loss in specific force observed in aging skeletal muscle. Excitation-contraction uncoupling may be caused by alterations in expression of the voltage-dependent calcium channel alpha1s (CaV1.1) and beta1a (CaVbeta1a) subunits, both of which are necessary for E-C coupling to occur. While previous studies have found CaV1.1 expression declines in old rodents, CaVbeta1a expression has not been previously examined in aging models. Western blot analysis shows a substantial increase of CaVbeta1a expression over the full lifespan of Friend Virus B (FVB) mice. To examine the specific effects of CaVbeta1a overexpression, a CaVbeta1a-YFP plasmid was electroporated in vivo into young animals. The resulting increase in expression of CaVbeta1a corresponded to decline of CaV1.1 over the same time period. YFP fluorescence, used as a measure of CaVbeta1a-YFP expression in individual fibers, also showed an inverse relationship with charge movement, measured using the whole-cell patch-clamp technique. Specific force was significantly reduced in young CaVbeta1a-YFP electroporated muscle fibers compared with sham-electroporated, age-matched controls. siRNA interference of CaVbeta1a in young muscles reduced charge movement, while charge movement in old was restored to young control levels. These studies imply CaVbeta1a serves as both a positive and negative regulator CaV1.1 expression, and that endogenous overexpression of CaVbeta1a during old age may play a role in the loss of specific force.
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Affiliation(s)
- Jackson R Taylor
- Department of Internal Medicine-Gerontology, Wake Forest University School of Medicine, 1 Medical Center Boulvard, Winston Salem, NC 27157, USA
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56
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Porterfield VM, Mintz EM. Temporal patterns of light-induced immediate-early gene expression in the suprachiasmatic nucleus. Neurosci Lett 2009; 463:70-3. [PMID: 19638298 DOI: 10.1016/j.neulet.2009.07.066] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2009] [Revised: 07/06/2009] [Accepted: 07/23/2009] [Indexed: 12/11/2022]
Abstract
Exposing an animal to light during the normal dark period of its daily cycle induces shifts in the animal's circadian rhythm of activity. These shifts are preceded by an increase in the expression of an array of immediate early genes in the suprachiasmatic nucleus, the location of the primary circadian clock in the brain. For most of these genes, little is known about the physiological significance of their expression in the SCN. In order to characterize the expression of these genes, laser capture microscopy, and real-time PCR were used to measure the time course of expression of immediate-early genes in the SCN after a 30-min light pulse during the early portion of the night. Most of the measured genes show peak expression shortly after the end of the stimulus and then decline back to baseline after 2h. However, a few genes, including Rrad, Egr3, and Jun, show a more sustained elevation in expression. Analysis of the function of light-induced genes in other cellular systems suggests a possible role for these genes in reducing the SCN to subsequent photic stimuli and in protecting the SCN from excitotoxicity.
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57
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Kobayashi MS, Asai S, Ishikawa K, Nishida Y, Nagata T, Takahashi Y. Global profiling of influence of intra-ischemic brain temperature on gene expression in rat brain. ACTA ACUST UNITED AC 2008; 58:171-91. [PMID: 18440647 DOI: 10.1016/j.brainresrev.2008.03.001] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2007] [Revised: 02/08/2008] [Accepted: 03/08/2008] [Indexed: 12/20/2022]
Abstract
Mild to moderate differences in brain temperature are known to greatly affect the outcome of cerebral ischemia. The impact of brain temperature on ischemic disorders has been mainly evaluated through pathological analysis. However, no comprehensive analyses have been conducted at the gene expression level. Using a high-density oligonucleotide microarray, we screened 24000 genes in the hippocampus under hypothermic (32 degrees C), normothermic (37 degrees C), and hyperthermic (39 degrees C) conditions in a rat ischemia-reperfusion model. When the ischemic group at each intra-ischemic brain temperature was compared to a sham-operated control group, genes whose expression levels changed more than three-fold with statistical significance could be detected. In our screening condition, thirty-three genes (some of them novel) were obtained after screening, and extensive functional surveys and literature reviews were subsequently performed. In the hypothermic condition, many neuroprotective factor genes were obtained, whereas cell death- and cell damage-associated genes were detected as the brain temperature increased. At all intra-ischemic brain temperatures, multiple molecular chaperone genes were obtained. The finding that intra-ischemic brain temperature affects the expression level of many genes related to neuroprotection or neurotoxicity coincides with the different pathological outcomes at different brain temperatures, demonstrating the utility of the genetic approach.
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Affiliation(s)
- Megumi Sugahara Kobayashi
- Division of Genomic Epidemiology and Clinical Trials, Advanced Medical Research Center, Nihon University School of Medicine, Oyaguchi-Kami Machi, Itabashi-ku, Tokyo 173-8610, Japan
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58
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Correll RN, Pang C, Niedowicz DM, Finlin BS, Andres DA. The RGK family of GTP-binding proteins: regulators of voltage-dependent calcium channels and cytoskeleton remodeling. Cell Signal 2008; 20:292-300. [PMID: 18042346 PMCID: PMC2254326 DOI: 10.1016/j.cellsig.2007.10.028] [Citation(s) in RCA: 82] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2007] [Accepted: 10/30/2007] [Indexed: 02/05/2023]
Abstract
RGK proteins constitute a novel subfamily of small Ras-related proteins that function as potent inhibitors of voltage-dependent (VDCC) Ca(2+) channels and regulators of actin cytoskeletal dynamics. Within the larger Ras superfamily, RGK proteins have distinct regulatory and structural characteristics, including nonconservative amino acid substitutions within regions known to participate in nucleotide binding and hydrolysis and a C-terminal extension that contains conserved regulatory sites which control both subcellular localization and function. RGK GTPases interact with the VDCC beta-subunit (Ca(V)beta) and inhibit Rho/Rho kinase signaling to regulate VDCC activity and the cytoskeleton respectively. Binding of both calmodulin and 14-3-3 to RGK proteins, and regulation by phosphorylation controls cellular trafficking and the downstream signaling of RGK proteins, suggesting that a complex interplay between interacting protein factors and trafficking contribute to their regulation.
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Affiliation(s)
- Robert N Correll
- Department of Molecular and Cellular Biochemistry, University of Kentucky College of Medicine, Lexington, KY 40536, United States
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59
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Correll RN, Botzet GJ, Satin J, Andres DA, Finlin BS. Analysis of the Rem2 - voltage dependant calcium channel beta subunit interaction and Rem2 interaction with phosphorylated phosphatidylinositide lipids. Cell Signal 2008; 20:400-8. [PMID: 18068949 PMCID: PMC2276613 DOI: 10.1016/j.cellsig.2007.10.029] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2007] [Accepted: 10/30/2007] [Indexed: 11/15/2022]
Abstract
Voltage dependant calcium channels (VDCC) play a critical role in coupling electrical excitability to important physiological events such as secretion by neuronal and endocrine cells. Rem2, a GTPase restricted to neuroendocrine cell types, regulates VDCC activity by a mechanism that involves interaction with the VDCC beta subunit (Ca(V)beta). Mapping studies reveal that Rem2 binds to the guanylate kinase domain (GK) of the Ca(V)beta subunit that also contains the high affinity binding site for the pore forming and voltage sensing VDCC alpha subunit (Ca(V)alpha) interaction domain (AID). Moreover, fine mapping indicates that Rem2 binds to the GK domain in a region distinct from the AID interaction site, and competitive inhibition studies reveal that Rem2 does not disrupt Ca(V)alpha - Ca(V)beta binding. Instead, the Ca(V)beta subunit appears to serve a scaffolding function, simultaneously binding both Rem2 and AID. Previous studies have found that in addition to Ca(V)beta binding, Rem2 must be localized to the plasma membrane to inhibit VDCC function. Plasma membrane localization requires the C-terminus of Rem2 and binding studies indicate that this domain directs phosphorylated phosphatidylinositide (PIP) lipids association. Plasma membrane localization may provide a unique point of regulation since the ability of Rem2 to bind PIP lipids is inhibited by the phosphoserine dependant binding of 14-3-3 proteins. Thus, in addition to Ca(V)beta binding, VDCC blockade by Rem2 is likely to be controlled by both the localized concentration of membrane PIP lipids and direct 14-3-3 binding to the Rem2 C-terminus.
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Affiliation(s)
- Robert N Correll
- Department of Molecular and Cellular Biochemistry, University of Kentucky College of Medicine, 741 S. Limestone, BBSRB, Lexington, KY 40536-0298, U.S.A
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60
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Grueter CE, Abiria SA, Wu Y, Anderson ME, Colbran RJ. Differential regulated interactions of calcium/calmodulin-dependent protein kinase II with isoforms of voltage-gated calcium channel beta subunits. Biochemistry 2008; 47:1760-7. [PMID: 18205403 DOI: 10.1021/bi701755q] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Ca2+/calmodulin-dependent protein kinase II (CaMKII) phosphorylates the beta2a subunit of voltage-gated Ca2+ channels at Thr498 to facilitate cardiac L-type Ca2+ channels. CaMKII colocalizes with beta2a in cardiomyocytes and also binds to a domain in beta2a that contains Thr498 and exhibits an amino acid sequence similarity to the CaMKII autoinhibitory domain and to a CaMKII binding domain in the NMDA receptor NR2B subunit (Grueter, C. E. et al. (2006) Mol. Cell 23, 641). Here, we explore the selectivity of the actions of CaMKII among Ca2+ channel beta subunit isoforms. CaMKII phosphorylates the beta1b, beta2a, beta3, and beta4 isoforms with similar initial rates and final stoichiometries of 6-12 mol of phosphate per mol of protein. However, activated/autophosphorylated CaMKII binds to beta1b and beta2a with a similar apparent affinity but does not bind to beta3 or beta4. Prephosphorylation of beta1b and beta2a by CaMKII substantially reduces the binding of autophosphorylated CaMKII. Residues surrounding Thr498 in beta2a are highly conserved in beta1b but are different in beta3 and beta4. Site-directed mutagenesis of this domain in beta2a showed that Thr498 phosphorylation promotes dissociation of CaMKII-beta2a complexes in vitro and reduces interactions of CaMKII with beta2a in cells. Mutagenesis of Leu493 to Ala substantially reduces CaMKII binding in vitro and in intact cells but does not interfere with beta2a phosphorylation at Thr498. In combination, these data show that phosphorylation dynamically regulates the interactions of specific isoforms of the Ca2+ channel beta subunits with CaMKII.
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Affiliation(s)
- Chad E Grueter
- Department of Molecular Physiology and Biophysics, Vanderbilt University Medical Center, Nashville, Tennessee 37232, USA
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61
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Rem inhibits skeletal muscle EC coupling by reducing the number of functional L-type Ca2+ channels. Biophys J 2008; 94:2631-8. [PMID: 18192376 DOI: 10.1529/biophysj.107.116467] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
In skeletal muscle, the L-type voltage-gated Ca(2+) channel (1,4-dihydropyridine receptor) serves as the voltage sensor for excitation-contraction (EC) coupling. In this study, we examined the effects of Rem, a member of the RGK (Rem, Rem2, Rad, Gem/Kir) family of Ras-related monomeric GTP-binding proteins, on the function of the skeletal muscle L-type Ca(2+) channel. EC coupling was found to be weakened in myotubes expressing Rem tagged with enhanced yellow fluorescent protein (YFP-Rem), as assayed by electrically evoked contractions and myoplasmic Ca(2+) transients. This impaired EC coupling was not a consequence of altered function of the type 1 ryanodine receptor, or of reduced Ca(2+) stores, since the application of 4-chloro-m-cresol, a direct type 1 ryanodine receptor activator, elicited myoplasmic Ca(2+) release in YFP-Rem-expressing myotubes that was not distinguishable from that in control myotubes. However, YFP-Rem reduced the magnitude of L-type Ca(2+) current by approximately 75% and produced a concomitant reduction in membrane-bound charge movements. Thus, our results indicate that Rem negatively regulates skeletal muscle EC coupling by reducing the number of functional L-type Ca(2+) channels in the plasma membrane.
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62
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Correll RN, Pang C, Niedowicz DM, Satin J, Andres DA. Calmodulin binding is dispensable for Rem-mediated Ca2+ channel inhibition. Mol Cell Biochem 2007; 310:103-10. [DOI: 10.1007/s11010-007-9670-8] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2007] [Accepted: 11/22/2007] [Indexed: 10/25/2022]
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63
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Porterfield VM, Piontkivska H, Mintz EM. Identification of novel light-induced genes in the suprachiasmatic nucleus. BMC Neurosci 2007; 8:98. [PMID: 18021443 PMCID: PMC2216081 DOI: 10.1186/1471-2202-8-98] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2007] [Accepted: 11/19/2007] [Indexed: 11/16/2022] Open
Abstract
Background The transmission of information about the photic environment to the circadian clock involves a complex array of neurotransmitters, receptors, and second messenger systems. Exposure of an animal to light during the subjective night initiates rapid transcription of a number of immediate-early genes in the suprachiasmatic nucleus of the hypothalamus. Some of these genes have known roles in entraining the circadian clock, while others have unknown functions. Using laser capture microscopy, microarray analysis, and quantitative real-time PCR, we performed a comprehensive screen for changes in gene expression immediately following a 30 minute light pulse in suprachiasmatic nucleus of mice. Results The results of the microarray screen successfully identified previously known light-induced genes as well as several novel genes that may be important in the circadian clock. Newly identified light-induced genes include early growth response 2, proviral integration site 3, growth-arrest and DNA-damage-inducible 45 beta, and TCDD-inducible poly(ADP-ribose) polymerase. Comparative analysis of promoter sequences revealed the presence of evolutionarily conserved CRE and associated TATA box elements in most of the light-induced genes, while other core clock genes generally lack this combination of promoter elements. Conclusion The photic signalling cascade in the suprachiasmatic nucleus activates an array of immediate-early genes, most of which have unknown functions in the circadian clock. Detected evolutionary conservation of CRE and TATA box elements in promoters of light-induced genes suggest that the functional role of these elements has likely remained the same over evolutionary time across mammalian orders.
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64
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Yang T, Suhail Y, Dalton S, Kernan T, Colecraft HM. Genetically encoded molecules for inducibly inactivating CaV channels. Nat Chem Biol 2007; 3:795-804. [DOI: 10.1038/nchembio.2007.42] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2007] [Accepted: 08/30/2007] [Indexed: 11/09/2022]
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65
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Chen BB, Mallampalli RK. Calmodulin binds and stabilizes the regulatory enzyme, CTP: phosphocholine cytidylyltransferase. J Biol Chem 2007; 282:33494-33506. [PMID: 17804406 DOI: 10.1074/jbc.m706472200] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
CTP:phosphocholine cytidylyltransferase (CCTalpha) is a proteolytically sensitive enzyme essential for production of phosphatidylcholine, the major phospholipid of animal cell membranes. The molecular signals that govern CCTalpha protein stability are unknown. An NH(2)-terminal PEST sequence within CCTalpha did not serve as a degradation signal for the proteinase, calpain. Calmodulin (CaM) stabilized CCTalpha from calpain proteolysis. Adenoviral gene transfer of CaM in cells protected CCTalpha, whereas CaM small interfering RNA accentuated CCTalpha degradation by calpains. CaM bound CCTalpha as revealed by fluorescence resonance energy transfer and two-hybrid analysis. Mapping and site-directed mutagenesis of CCTalpha uncovered a motif (LQERVDKVK) harboring a vital recognition site, Gln(243), whereby CaM directly binds to the enzyme. Mutagenesis of CCTalpha Gln(243) not only resulted in loss of CaM binding but also led to complete calpain resistance in vitro and in vivo. Thus, calpains and CaM both access CCTalpha using a structurally similar molecular signature that profoundly affects CCTalpha levels. These data suggest that CaM, by antagonizing calpain, serves as a novel binding partner for CCTalpha that stabilizes the enzyme under proinflammatory stress.
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Affiliation(s)
- Bill B Chen
- Department of Biochemistry, University of Iowa, Iowa City, Iowa, 52242
| | - Rama K Mallampalli
- Department of Biochemistry, University of Iowa, Iowa City, Iowa, 52242; Department of Internal Medicine, University of Iowa, Iowa City, Iowa, 52242; Department of Veterans Affairs Medical Center and the Roy J. and Lucille A. Carver College of Medicine, University of Iowa, Iowa City, Iowa 52242.
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66
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Correll RN, Pang C, Finlin BS, Dailey AM, Satin J, Andres DA. Plasma membrane targeting is essential for Rem-mediated Ca2+ channel inhibition. J Biol Chem 2007; 282:28431-28440. [PMID: 17686775 PMCID: PMC3063359 DOI: 10.1074/jbc.m706176200] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The small GTPase Rem is a potent negative regulator of high voltage-activated Ca(2+) channels and a known interacting partner for Ca(2+) channel accessory beta subunits. The mechanism for Rem-mediated channel inhibition remains controversial, although it has been proposed that Ca(V)beta association is required. Previous work has shown that a C-terminal truncation of Rem (Rem-(1-265)) displays reduced in vivo binding to membrane-localized beta 2a and lacks channel regulatory function. In this paper, we describe a role for the Rem C terminus in plasma membrane localization through association with phosphatidylinositol lipids. Moreover, Rem-(1-265) can associate with beta 2a in vitro and beta 1b in vivo, suggesting that the C terminus does not directly participate in Ca(V)beta association. Despite demonstrated beta 1b binding, Rem-(1-265) was not capable of regulating a Ca(V)1.2-beta 1b channel complex, indicating that beta subunit binding is not sufficient for channel regulation. However, fusion of the CAAX domain from K-Ras4B or H-Ras to the Rem-(1-265) C terminus restored membrane localization and Ca(2+) channel regulation, suggesting that beta binding and membrane localization are independent events required for channel inhibition.
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Affiliation(s)
| | - Chunyan Pang
- Departments of Molecular and Cellular Biochemistry
| | | | | | - Jonathan Satin
- Departments of Physiology, University of Kentucky College of Medicine, Lexington, Kentucky 40536-0509
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67
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Jarvis SE, Zamponi GW. Trafficking and regulation of neuronal voltage-gated calcium channels. Curr Opin Cell Biol 2007; 19:474-82. [PMID: 17624753 DOI: 10.1016/j.ceb.2007.04.020] [Citation(s) in RCA: 58] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2007] [Accepted: 04/18/2007] [Indexed: 12/17/2022]
Abstract
The importance of voltage-gated calcium channels is underscored by the multitude of intracellular processes that depend on calcium, notably gene regulation and neurotransmission. Given their pivotal roles in calcium (and hence, cellular) homeostasis, voltage-gated calcium channels have been the subject of intense research, much of which has focused on channel regulation. While ongoing research continues to delineate the myriad of interactions that govern calcium channel regulation, an increasing amount of work has focused on the trafficking of voltage-gated calcium channels. This includes the mechanisms by which calcium channels are targeted to the plasma membrane, and, more specifically, to their appropriate loci within a given cell. In addition, we are beginning to gain some insights into the mechanisms by which calcium channels can be removed from the plasma membrane for recycling and/or degradation. Here we highlight recent advances in our understanding of these fundamentally important mechanisms.
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Affiliation(s)
- Scott E Jarvis
- Hotchkiss Brain Institute, Department of Physiology and Biophysics, University of Calgary, 3330 Hospital Dr. NW, Calgary T2N 4N1, Canada
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68
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Yada H, Murata M, Shimoda K, Yuasa S, Kawaguchi H, Ieda M, Adachi T, Murata M, Ogawa S, Fukuda K. Dominant Negative Suppression of Rad Leads to QT Prolongation and Causes Ventricular Arrhythmias via Modulation of L-type Ca
2+
Channels in the Heart. Circ Res 2007; 101:69-77. [PMID: 17525370 DOI: 10.1161/circresaha.106.146399] [Citation(s) in RCA: 62] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Disorders of L-type Ca
2+
channels can cause severe cardiac arrhythmias. A subclass of small GTP-binding proteins, the RGK family, regulates L-type Ca
2+
current (
I
Ca,L
) in heterologous expression systems. Among these proteins, Rad (Ras associated with diabetes) is highly expressed in the heart, although its role in the heart remains unknown. Here we show that overexpression of dominant negative mutant Rad (S105N) led to an increase in
I
Ca,L
and action potential prolongation via upregulation of L-type Ca
2+
channel expression in the plasma membrane of guinea pig ventricular cardiomyocytes. To verify the in vivo physiological role of Rad in the heart, a mouse model of cardiac-specific Rad suppression was created by overexpressing S105N Rad, using the α-myosin heavy chain promoter. Microelectrode studies revealed that action potential duration was significantly prolonged with visible identification of a small plateau phase in S105N Rad transgenic mice, when compared with wild-type littermate mice. Telemetric electrocardiograms on unrestrained mice revealed that S105N Rad transgenic mice had significant QT prolongation and diverse arrhythmias such as sinus node dysfunction, atrioventricular block, and ventricular extrasystoles, whereas no arrhythmias were observed in wild-type mice. Furthermore, administration of epinephrine induced frequent ventricular extrasystoles and ventricular tachycardia in S105N Rad transgenic mice. This study provides novel evidence that the suppression of Rad activity in the heart can induce ventricular tachycardia, suggesting that the Rad-associated signaling pathway may play a role in arrhythmogenesis in diverse cardiac diseases.
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Affiliation(s)
- Hirotaka Yada
- Cardiopulmonary Division, Keio University, 35 Shinanomachi, Shinjuku-ku, Tokyo 160-8582, Japan
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69
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Mahalakshmi RN, Ng MY, Guo K, Qi Z, Hunziker W, Béguin P. Nuclear localization of endogenous RGK proteins and modulation of cell shape remodeling by regulated nuclear transport. Traffic 2007; 8:1164-78. [PMID: 17605760 DOI: 10.1111/j.1600-0854.2007.00599.x] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The members of the RGK small GTP-binding protein family, Kir/Gem, Rad, Rem and Rem2, are multifunctional proteins that regulate voltage-gated calcium channel activity and cell shape remodeling. Calmodulin (CaM) or CaM 14-3-3 are regulators of RGK functions and their association defines the subcellular localization of RGK proteins. Abolition of CaM association results in the accumulation of RGK proteins in the nucleus, whereas 14-3-3 binding maintains them in the cytoplasm. Kir/Gem possesses nuclear localization signals (NLS) that mediate nuclear accumulation through an importin alpha5-dependent pathway (see Mahalakshmi RN, Nagashima K, Ng MY, Inagaki N, Hunziker W, Béguin P. Nuclear transport of Kir/Gem requires specific signals and importin alpha5 and is regulated by Calmodulin and predicted service phosphorylations. Traffic 2007; doi: 10.1111/j.1600-0854.2007.00598.x). Because the extent of nuclear localization depends on the RGK protein and the cell type, the mechanism and regulation of nuclear transport may differ. Here, we extend our analysis to the other RGK members and show that Rem also binds importin alpha5, whereas Rad associates with importins alpha3, alpha5 and beta through three conserved NLS. Predicted phosphorylation of a serine residue within the bipartite NLS affects, as observed for Kir/Gem, nuclear accumulation of Rem, but not that of Rad or Rem2. We also identify an additional regulatory phosphorylation for all RGK proteins that prevents binding of 14-3-3 and thereby interferes with their cytosolic relocalization by 14-3-3. Functionally, nuclear localization of RGK proteins contributes to the suppression of RGK-mediated cell shape remodeling. Importantly, we show that endogenous RGK proteins are localized predominantly in the nucleus of individual cells of the brain cortex 'in situ' as well as in primary hippocampal cells, indicating that transport between the nucleus and their site of action in the cytoplasm (i.e., cytoskeleton, endoplasmic reticulum or plasma membrane) is of physiological relevance for the regulation of RGK protein function.
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Affiliation(s)
- Ramasubbu N Mahalakshmi
- Epithelial Cell Biology Laboratory, Institute of Molecular and Cell Biology, 61 Biopolis Drive, Singapore 138673, Singapore
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70
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Mahalakshmi RN, Nagashima K, Ng MY, Inagaki N, Hunziker W, Béguin P. Nuclear Transport of Kir/Gem Requires Specific Signals and Importin α5 and Is Regulated by Calmodulin and Predicted Serine Phosphorylations. Traffic 2007; 8:1150-63. [PMID: 17605761 DOI: 10.1111/j.1600-0854.2007.00598.x] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Kir/Gem, together with Rad, Rem and Rem2, is a member of the RGK small GTP-binding protein family. These multifunctional proteins regulate voltage-gated calcium channel (VGCC) activity and cell-shape remodeling. Calmodulin and 14-3-3 binding modulate the functions of RGK proteins. Intriguingly, abolishing the binding of calmodulin or calmodulin and 14-3-3 results in nuclear accumulation of RGK proteins. Under certain conditions, the Ca(v)beta3-subunit of VGCCs can be translocated into the nucleus along with the RGK proteins, resulting in channel inactivation. The mechanism by which nuclear localization of RGK proteins is accomplished and regulated, however, is unknown. Here, we identify specific nuclear localization signals (NLS) in Kir/Gem that are both required and sufficient for nuclear transport. Importin alpha5 binds to Kir/Gem, and its depletion using RNA interference impairs nuclear translocation of this RGK protein. Calmodulin and predicted phosphorylations on serine residues within or in the vicinity of a C-terminal bipartite NLS regulate nuclear translocation by interfering with the association between importinalpha5 and Kir/Gem. These predicted phosphorylations, however, do not affect Kir/Gem-mediated calcium channel downregulation but rather, as shown in the accompanying paper (Mahalakshmi RN, Ng MY, Guo K, Qi Z, Hunziker W, Béguin P. Nuclear localization of endogenous RGK proteins and modulation of cell shape remodeling by regulated nuclear transport. Traffic 2007; doi:10.1111/j.1600-0854.2007.00599.x), interfere with cell-shape remodeling.
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Affiliation(s)
- Ramasubbu N Mahalakshmi
- Epithelial Cell Biology Laboratory, Institute of Molecular and Cell Biology, 61 Biopolis Drive, Singapore 138673, Singapore
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71
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Béguin P, Ng YJA, Krause C, Mahalakshmi RN, Ng MY, Hunziker W. RGK small GTP-binding proteins interact with the nucleotide kinase domain of Ca2+-channel beta-subunits via an uncommon effector binding domain. J Biol Chem 2007; 282:11509-20. [PMID: 17303572 DOI: 10.1074/jbc.m606423200] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
RGK proteins (Kir/Gem, Rad, Rem, and Rem2) form a small subfamily of the Ras superfamily. Despite a conserved GTP binding core domain, several differences suggest that structure, mechanism of action, and functional regulation differ from Ras. RGK proteins down-regulate voltage-gated calcium channel activity by binding in a GTP-dependent fashion to the Cavbeta subunits. Mutational analysis combined with homology modeling reveal a novel effector binding mechanism distinct from that of other Ras GTPases. In this model the Switch 1 region acts as an allosteric activator that facilitates electrostatic interactions between Arg-196 in Kir/Gem and Asp-194, -270, and -272 in the nucleotide-kinase (NK) domain of Cavbeta3 and wedging Val-223 and His-225 of Kir/Gem into a hydrophobic pocket in the NK domain. Kir/Gem interacts with a surface on the NK domain that is distinct from the groove where the voltage-gated calcium channel Cavalpha1 subunit binds. A complex composed of the RGK protein and the Cavbeta3 and Cav1.2 subunits could be revealed in vivo using coimmunoprecipitation experiments. Intriguingly, docking of the RGK protein to the NK domain of the Cavbeta subunit is reminiscent of the binding of GMP to guanylate kinase.
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Affiliation(s)
- Pascal Béguin
- Epithelial Cell Biology Laboratory, Institute of Molecular and Cell Biology, 61 Biopolis Drive, Singapore 138673, Republic of Singapore
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72
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Li Y, Wu Y, Zhou Y. Modulation of inactivation properties of CaV2.2 channels by 14-3-3 proteins. Neuron 2006; 51:755-71. [PMID: 16982421 DOI: 10.1016/j.neuron.2006.08.014] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2005] [Revised: 05/08/2006] [Accepted: 08/08/2006] [Indexed: 11/28/2022]
Abstract
Inactivation of presynaptic Ca(V)2.2 channels may play a role in regulating short-term synaptic plasticity. Here, we report a direct modulation of Ca(V)2.2 channel inactivation properties by 14-3-3, a family of signaling proteins involved in a wide range of biological processes. The structural elements critical for 14-3-3 binding and channel modulation lie in the carboxyl tail of the pore-forming alpha(1B) subunit, where we have identified two putative 14-3-3 interaction sites, including a phosphoserine-containing motif that directly binds to 14-3-3 and a second region near the EF hand and IQ domain. In transfected tsA 201 cells, 14-3-3 coexpression dramatically slows open-state inactivation and reduces cumulative inactivation of Ca(V)2.2 channels. In hippocampal neurons, interference with 14-3-3 binding accelerates Ca(V)2.2 channel inactivation and enhances short-term synaptic depression. These results demonstrate that 14-3-3 proteins are important regulators of Ca(V)2.2 channel activities and through this mechanism may contribute to their regulation of synaptic transmission and plasticity.
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MESH Headings
- 14-3-3 Proteins/genetics
- 14-3-3 Proteins/metabolism
- 14-3-3 Proteins/physiology
- Amino Acid Sequence
- Animals
- Binding Sites/genetics
- Binding, Competitive
- Blotting, Western
- Brain/cytology
- Brain/metabolism
- Calcium Channels, L-Type/genetics
- Calcium Channels, L-Type/metabolism
- Calcium Channels, N-Type/genetics
- Calcium Channels, N-Type/metabolism
- Calcium Channels, T-Type/genetics
- Calcium Channels, T-Type/metabolism
- Cell Line
- Cells, Cultured
- Glutathione Transferase/genetics
- Glutathione Transferase/metabolism
- Humans
- Neurons/cytology
- Neurons/metabolism
- Phosphorylation
- Protein Binding
- Protein Subunits/genetics
- Protein Subunits/metabolism
- Rats
- Rats, Sprague-Dawley
- Recombinant Fusion Proteins/genetics
- Recombinant Fusion Proteins/metabolism
- Synaptic Transmission/physiology
- Time Factors
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Affiliation(s)
- Yong Li
- Department of Neurobiology, Evelyn F. McKnight Brain Institute and Civitan International Research Center, School of Medicine, University of Alabama at Birmingham, 35294, USA
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73
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Abstract
Rad (Ras associated with diabetes) is an RGK-family small GTPase that is over-expressed in the skeletal muscle of humans with type II diabetes. Unlike other small GTPases, RGK family members including Rad lack several conserved residues in the GTPase domain. Here, we report the crystal structure of the GTPase domain of human Rad in the GDP-bound form at 1.8 A resolution. The structure revealed unexpected disordered structures of both switches I and II. We showed that the conformational flexibility of both switches is caused by non-conservative substitutions in the G2 and G3 motifs forming the switch cores together with other substitutions in the structural elements interacting with the switches. Glycine-rich sequences of the switches would also contribute to the flexibility. Switch I lacks the conserved phenylalanine that makes non-polar interactions with the guanine base in H-Ras. Instead, water-mediated hydrogen bonding interactions were observed in Rad. The GDP molecule is located at the same position as in H-Ras and adopts a similar conformation as that bound in H-Ras. This similarity seems to be endowed by the conserved hydrogen bonding interactions with the guanine base-recognition loops and the magnesium ion that has a typical octahedral coordination shell identical to that in H-Ras.
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Affiliation(s)
- Arry Yanuar
- Structural Biology Laboratory, Nara Institute of Science and Technology, 8916-5, Takayama, Ikoma, Nara 630-0192, Japan
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74
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Crump SM, Correll RN, Schroder EA, Lester WC, Finlin BS, Andres DA, Satin J. L-type calcium channel alpha-subunit and protein kinase inhibitors modulate Rem-mediated regulation of current. Am J Physiol Heart Circ Physiol 2006; 291:H1959-71. [PMID: 16648185 DOI: 10.1152/ajpheart.00956.2005] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Cardiac voltage-gated L-type Ca channels (Ca(V)) are multiprotein complexes, including accessory subunits such as Ca(V)beta2 that increase current expression. Recently, members of the Rad and Gem/Kir-related family of small GTPases have been shown to decrease current, although the mechanism remains poorly defined. In this study, we evaluated the contribution of the L-type Ca channel alpha-subunit (Ca(V)1.2) to Ca(V)beta2-Rem inhibition of Ca channel current. Specifically, we addressed whether protein kinase A (PKA) modulation of the Ca channel modifies Ca(V)beta2-Rem inhibition of Ca channel current. We first tested the effect of Rem on Ca(V)1.2 in human embryonic kidney 293 (HEK-293) cells using the whole cell patch-clamp configuration. Rem coexpression with Ca(V)1.2 reduces Ba current expression under basal conditions, and Ca(V)beta2a coexpression enhances Rem block of Ca(V)1.2 current. Surprisingly, PKA inhibition by 133 nM H-89 or 50 microM Rp-cAMP-S partially relieved the Rem-mediated inhibition of current activity both with and without Ca(V)beta2a. To test whether the H-89 action was a consequence of the phosphorylation status of Ca(V)1.2, we examined Rem regulation of the PKA-insensitive Ca(V)1.2 serine 1928 (S1928) to alanine mutation (Ca(V)1.2-S1928A). Ca(V)1.2-S1928A current was not inhibited by Rem and when coexpression with Ca(V)beta2a was not completely blocked by Rem coexpression, suggesting that the phosphorylation of S1928 contributes to Rem-mediated Ca channel modulation. As a model for native Ca channel complexes, we tested the ability of Rem overexpression in HIT-T15 cells and embryonic ventricular myocytes to interfere with native current. We find that native current is also sensitive to Rem block and that H-89 pretreatment relieves the ability of Rem to regulate Ca current. We conclude that Rem is capable of regulating L-type current, that release of Rem block is modulated by cellular kinase pathways, and that the Ca(V)1.2 COOH terminus contributes to Rem-dependent channel inhibition.
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Affiliation(s)
- Shawn M Crump
- Dept. of Physiology, MS-508, Univ. of Kentucky College of Medicine, 800 Rose St. Lexington, KY 40536-0298, USA
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