Elsevier

Cell Calcium

Volume 42, Issues 4–5, October–November 2007, Pages 409-417
Cell Calcium

Neuronal calcium channels: Splicing for optimal performance

https://doi.org/10.1016/j.ceca.2007.04.003Get rights and content

Abstract

Calcium ion channels coordinate an astounding number of cellular functions. Surprisingly, only 10 CaVα1 subunit genes encode the structural cores of all voltage-gated calcium channels. What mechanisms exist to modify the structure of calcium channels and optimize their coupling to the rich spectrum of cellular functions? Growing evidence points to the contribution of post-translational alternative processing of calcium channel RNA as the main mechanism for expanding the functional potential of this important gene family. Alternative splicing of RNA is essential during neuronal development where fine adjustments in protein signaling promote and inhibit cell–cell interactions and underlie axonal guidance. However, attributing a specific functional role to an individual splice isoform or splice site has been difficult. In this regard, studies of ion channels are advantageous because their function can be monitored with precision, allowing even subtle changes in channel activity to be detected. Such studies are especially insightful when coupled with information about isoform expression patterns and cellular localization.

In this paper, we focus on two sites of alternative splicing in the N-type calcium channel CaV2.2 gene. We first describe cassette exon 18a that encodes a 21 amino acid segment in the II–III intracellular loop region of CaV2.2. Here, we show that e18a is upregulated in the nervous system during development. We discuss these new data in light of our previous reports showing that e18a protects the N-type channel from cumulative inactivation. Second, we discuss our published data on exons e37a and e37b, which encode 32 amino acids in the intracellular C-terminus of CaV2.2. These exons are expressed in a mutually exclusive manner. Exon e37a-containing CaV2.2 mRNAs and their resultant channels express at higher density in dorsal root ganglia and, as we showed recently, e37a increases N-type channel sensitivity to G-protein-mediated inhibition, as compared to generic e37b-containing N-type channels.

Section snippets

Alternative splicing in voltage-gated calcium channels

Human, rat, and mouse genomes contain 10 genes that encode CaVα1 subunits. The nervous system expresses nine of these genes. CaVα1 genes are large, spanning 100–800 kb of human genome sequence and containing upwards of 50 exons [1], [2], [3], [4]. The large size of these genes provides ample opportunity for alternative splicing. Based on already known splice sites, the theoretical number of splice isoforms possible from a single CaVα1 subunit exceeds 1000 [3], [4]. Other genes, far smaller than

The CaV2.2 N-type calcium channel

Our interest in the N-type calcium channel stems from its established role in the control of transmitter release from many different types of neurons [25], [26]. The N-type calcium channel is also implicated in synaptogenesis and regulation of gene expression [27], [28]. N-type calcium channels differ functionally across cell types and sub-cellular compartments within a given cell, suggestive of molecular and structural heterogeneity. Differences in N-type channel inactivation, single-channel

Cassette exons in the II–III loops of CaV2 channels

The intracellular loops connecting homologous domains II and III (LII–III) of pore-forming CaVα1 subunits are of special interest. This region supports key cellular functions and links calcium channels to downstream effector proteins. In skeletal muscle, the LII–III of CaV1.1 binds directly to ryanodine receptors on the sarcoplasmic reticulum, an interaction necessary and sufficient for excitation-contraction coupling [51], [52], [53]. In the case of CaV2 calcium channels, II–III loops connect

The C-terminus of CaV2

The C-termini of CaV2 genes coordinate various aspects of calcium channel function, including inactivation, modulation by G-proteins, modulation by calmodulin, and protein-protein interactions that regulate activity and/or target the channel to specific cellular compartments [9], [37], [47], [49], [73], [74], [75], [76]. Alternative splicing in exon 46 of CaV2.2 affects the ability of G-proteins to modulate the N-type calcium channel [49] and alters sub-cellular targeting [47], [73]. Mutually

Conclusions

Our studies of alternative splicing illustrate how investigations of evolutionarily conserved, natural variants of CaV2.2 can uncover critical domains in N-type channels that regulate their activity. The e18a splice site illustrates that alternative splicing of certain exons in CaV2.2 is under developmental control and possibly coordinated with splicing of the homologous site in CaV2.3. Collectively, our studies suggest that N-type channels become less sensitive to inactivation following trains

Acknowledgments

This work was supported by a Howard Hughes Medical Institute Predoctoral Fellowship (A.C.G.) and National Institutes of Health Grants: NS29967 and NS055251 (D.L.)

References (105)

  • L.F. Lareau et al.

    The evolving roles of alternative splicing

    Curr. Opin. Struct. Biol.

    (2004)
  • D. Lipscombe

    Neuronal proteins custom designed by alternative splicing

    Curr. Opin. Neurobiol.

    (2005)
  • C.A. Reid et al.

    Presynaptic Ca2+ channels: a functional patchwork

    Trends Neurosci.

    (2003)
  • K. Dunlap et al.

    Exocytotic Ca2+ channels in mammalian central neurons

    Trends Neurosci.

    (1995)
  • M.R. Plummer et al.

    Elementary properties and pharmacological sensitivities of calcium channels in mammalian peripheral neurons

    Neuron

    (1989)
  • J.C. Poncer et al.

    Either N- or P-type calcium channels mediate GABA release at distinct hippocampal inhibitory synapses

    Neuron

    (1997)
  • D. Walker et al.

    Subunit interaction sites in voltage-dependent Ca2+ channels: role in channel function

    Trends Neurosci.

    (1998)
  • B. Hille et al.

    Multiple G-protein-coupled pathways inhibit N-type Ca channels of neurons

    Life Sci.

    (1995)
  • J. Striessnig

    Targeting voltage-gated Ca2+ channels

    Lancet

    (2001)
  • T. Sakurai et al.

    Immunochemical identification and differential phosphorylation of alternatively spliced forms of the alpha 1A subunit of brain calcium channels

    J. Biol. Chem.

    (1995)
  • C. Leveque et al.

    Purification of the N-type calcium channel associated with syntaxin and synaptotagmin. A complex implicated in synaptic vesicle exocytosis

    J. Biol. Chem.

    (1994)
  • Z.H. Sheng et al.

    Identification of a syntaxin-binding site on N-type calcium channels

    Neuron

    (1994)
  • S. Mochida et al.

    Inhibition of neurotransmission by peptides containing the synaptic protein interaction site of N-type Ca2+ channels

    Neuron

    (1996)
  • M.E. Williams et al.

    Structure and functional characterization of neuronal alpha 1E calcium channel subtypes

    J. Biol. Chem.

    (1994)
  • A. Pereverzev et al.

    Alternate splicing in the cytosolic II–III loop and the carboxy terminus of human E-type voltage-gated Ca(2+) channels: electrophysiological characterization of isoforms

    Mol. Cell. Neurosci.

    (2002)
  • M. Vidovic et al.

    Developmental time course of the sympathetic postganglionic innervation of the rat eye

    Brain Res.

    (1987)
  • A. Maximov et al.

    Association of neuronal calcium channels with modular adaptor proteins

    J. Biol. Chem.

    (1999)
  • H. Hibino et al.

    RIM binding proteins (RBPs) couple Rab3-interacting molecules (RIMs) to voltage-gated Ca(2+) channels

    Neuron

    (2002)
  • H. Liang et al.

    Unified mechanisms of Ca2+ regulation across the Ca2+ channel family

    Neuron

    (2003)
  • L.M. Kerr et al.

    Autoradiographic localization of calcium channels with [125I]omega-conotoxin in rat brain

    Eur. J. Pharmacol.

    (1988)
  • C.A. Maggi et al.

    Neurochemical evidence for the involvement of N-type calcium channels in transmitter secretion from peripheral endings of sensory nerves in guinea pigs

    Neurosci. Lett.

    (1990)
  • C. Kim et al.

    Altered nociceptive response in mice deficient in the alpha(1B) subunit of the voltage-dependent calcium channel

    Mol. Cell Neurosci.

    (2001)
  • H. Saegusa et al.

    Effects of ablation of N- and R-type Ca(2+) channels on pain transmission

    Neurosci. Res.

    (2002)
  • S.S. Bowersox et al.

    Pharmacotherapeutic potential of omega-conotoxin MVIIA (SNX-111), an N-type neuronal calcium channel blocker found in the venom of Conus magus

    Toxicon

    (1998)
  • E.A. Matthews et al.

    Effects of spinally delivered N- and P-type voltage-dependent calcium channel antagonists on dorsal horn neuronal responses in a rat model of neuropathy

    Pain

    (2001)
  • H. Vanegas et al.

    Effects of antagonists to high-threshold calcium channels upon spinal mechanisms of pain, hyperalgesia and allodynia

    Pain

    (2000)
  • G.W. Zamponi et al.

    Splicing it up. A variant of the N-type calcium channel specific for pain

    Neuron

    (2004)
  • M. Diverse-Pierluissi et al.

    Distinct, convergent second messenger pathways modulate neuronal calcium currents

    Neuron

    (1993)
  • S.E. Jarvis et al.

    G protein modulation of N-type calcium channels is facilitated by physical interactions between syntaxin 1A and Gbetagamma

    J. Biol. Chem.

    (2000)
  • D. Lipscombe et al.

    Functional diversity in neuronal voltage-gated calcium channels by alternative splicing of Ca(v)alpha1

    Mol. Neurobiol.

    (2002)
  • D. Lipscombe et al.

    Alternative splicing in voltage gated calcium channels

  • M.C. Emerick et al.

    Profiling the array of Ca(v)3.1 variants from the human T-type calcium channel gene CACNA1G: alternative structures, developmental expression, and biophysical variations

    Proteins

    (2006)
  • E. Bourinet et al.

    Splicing of alpha 1A subunit gene generates phenotypic variants of P- and Q-type calcium channels

    Nat. Neurosci.

    (1999)
  • R.J. Diebold et al.

    Mutually exclusive exon splicing of the cardiac calcium channel alpha 1 subunit gene generates developmentally regulated isoforms in the rat heart

    Proc. Natl. Acad. Sci. U S A

    (1992)
  • S. Kaneko et al.

    Identification and characterization of novel human Ca(v)2,2 (alpha 1B) calcium channel variants lacking the synaptic protein interaction site

    J. Neurosci.

    (2002)
  • Z. Lin et al.

    Alternative splicing of a short cassette exon in alpha1B generates functionally distinct N-type calcium channels in central and peripheral neurons

    J. Neurosci.

    (1999)
  • J.Q. Pan et al.

    Alternative splicing in the cytoplasmic II–III loop of the N-type Ca channel alpha 1B subunit: functional differences are beta subunit-specific

    J. Neurosci.

    (2000)
  • T.W. Soong et al.

    Systematic identification of splice variants in human P/Q-type channel alpha1(2.1) subunits: implications for current density and Ca2+-dependent inactivation

    J. Neurosci.

    (2002)
  • A. Welling et al.

    Alternatively spliced IS6 segments of the alpha 1C gene determine the tissue-specific dihydropyridine sensitivity of cardiac and vascular smooth muscle L-type Ca2+ channels

    Circ. Res.

    (1997)
  • K. Takimoto et al.

    Decreased expression of Kv4.2 and novel Kv4.3 K+ channel subunit mRNAs in ventricles of renovascular hypertensive rats

    Circ. Res.

    (1997)

    • Cited by (0)

    1

    Present address: Department of Biology, Brandeis University, Waltham, MA 02454, United States.

    View full text
    Copyright © 2007 Elsevier Ltd. All rights reserved.