Molecular Determinant for Specific Ca/Ba Selectivity Profiles of Low and High Threshold Ca2+ Channels

Voltage-gated Ca2+ channels (VGCC) play a key role in many physiological functions by their high selectivity for Ca2+ over other divalent and monovalent cations in physiological situations. Divalent/monovalent selection is shared by all VGCC and is satisfactorily explained by the existence, within the pore, of a set of four conserved glutamate/aspartate residues (EEEE locus) coordinating Ca2+ ions. This locus however does not explain either the choice of Ca2+ among other divalent cations or the specific conductances encountered in the different VGCC. Our systematic analysis of high- and low-threshold VGCC currents in the presence of Ca2+ and Ba2+ reveals highly specific selectivity profiles. Sequence analysis, molecular modeling, and mutational studies identify a set of nonconserved charged residues responsible for these profiles. In HVA (high voltage activated) channels, mutations of this set modify divalent cation selectivity and channel conductance without change in divalent/monovalent selection, activation, inactivation, and kinetics properties. The CaV2.1 selectivity profile is transferred to CaV2.3 when exchanging their residues at this location. Numerical simulations suggest modification in an external Ca2+ binding site in the channel pore directly involved in the choice of Ca2+, among other divalent physiological cations, as the main permeant cation for VGCC. In LVA (low voltage activated) channels, this locus (called DCS for divalent cation selectivity) also influences divalent cation selection, but our results suggest the existence of additional determinants to fully recapitulate all the differences encountered among LVA channels. These data therefore attribute to the DCS a unique role in the specific shaping of the Ca2+ influx between the different HVA channels

Cav2.1 C‐terminal fragments produced in Xenopus laevis oocytes do not modify the channel expression and functional properties

International audienceThe sequence and genomic organization of the CACNA1A gene that encodes the Cav2.1 subunit of both P and Q type Ca2+ channels are well conserved in mammals. In human, rat and mouse CACNA1A, the use of an alternative acceptor site at the exon 46‐47 boundary results in the expression of a long Cav2.1 splice variant. In transfected cells, the long isoform of human Cav2.1 produces a C‐terminal fragment, but it is not known whether this fragment affects Cav2.1 expression or functional properties. Here, we cloned the long isoform of rat Cav2.1 (Cav2.1(e47)) and identified a novel variant with a shorter C‐terminus (Cav2.1(e47s)) that differs from those previously described in the rat and mouse. When expressed in Xenopus laevis oocytes, Cav2.1(e47) and Cav2.1(e47s) displayed similar functional properties as the short isoform (Cav2.1). We show that Cav2.1 isoforms produced short (CT1) and long (CT1(e47)) C‐terminal fragments that interacted in vivo with the auxiliary Cavβ4a subunit. Overexpression of the C‐terminal fragments did not affect Cav2.1 expression and functional properties. Furthermore, the functional properties of a Cav2.1 mutant without the C‐terminal Cavβ4 binding domain (Cav2.1ΔCT2) were similar to those of Cav2.1, and were not influenced by the co‐expression of the missing fragments (CT2 or CT2(e47)). Our results exclude a functional role of the C‐terminal fragments in Cav2.1 biophysical properties in an expression system widely used to study this channel

Regulation by protein kinase-C of putative P-type Ca channels expressed in Xenopus oocytes from cerebellar mRNA

AbstractXenopus oocytes injected with rat cerebellar mRNA expressed functional voltage-dependent Ca channels detected as an inward Ba current (IBa). The pharmacological resistance to dihydropyridines and ω-conotoxin together with the blockade obtained with Agelenopsis aperta venom suggest that these channels could be somehow assimilated to P-type Ca channels. The precise nature of the transplanted Ca channels was assessed by hybrid-arrest experiments using a specific oligonucleotide antisense-derivated from the recently cloned α1-subunit of P channels (BI-1 clone). In addition, we demonstrate that exogenous Ca channel activity was enhanced by two different PKC activators (a phorbol ester and a structural analog to diacylglycerol). The general electrophysiological and pharmacological properties of the stimulated Ca channels remain unchanged. This potentiation induced by PKC activators is antagonized by a PKC inhibitor (staurosporine) and by a monoclonal antibody directed against PKC. It is concluded that P-type Ca channels are potentially regulated by PKC phosphorylation and the functional relevance of this intracellular pathway is discussed

Targeting TMEM176B Enhances Antitumor Immunity and Augments the Efficacy of Immune Checkpoint Blockers by Unleashing Inflammasome Activation.

Although immune checkpoint blockers have yielded significant clinical benefits in patients with different malignancies, the efficacy of these therapies is still limited. Here, we show that disruption of transmembrane protein 176B (TMEM176B) contributes to CD8+ T cell-mediated tumor growth inhibition by unleashing inflammasome activation. Lack of Tmem176b enhances the antitumor activity of anti-CTLA-4 antibodies through mechanisms involving caspase-1/IL-1β activation. Accordingly, patients responding to checkpoint blockade therapies display an activated inflammasome signature. Finally, we identify BayK8644 as a potent TMEM176B inhibitor that promotes CD8+ T cell-mediated tumor control and reinforces the antitumor activity of both anti-CTLA-4 and anti-PD-1 antibodies. Thus, pharmacologic de-repression of the inflammasome by targeting TMEM176B may enhance the therapeutic efficacy of immune checkpoint blockers.Uruguay INNOVA 2, Fondo Maria Viñas and Clemente Estable from ANII, as well as grants from CABBIO, PEDECIBA, ECOS-SUD and FOCEM (MERCOSUR Structural Convergence Fund), COF 03/11 to MH, The Harry J Lloyd Foundation to MRG and the Instituto Nacional del Cancer to YDM, Agencia de Promoción Científica y Tecnológica to GAR and MRG, Fundación Bunge & Born and Fundación Sales to GA

Caracterisation et regulation du courant calcique cardiaque des cellules isolees de rat et de grenouille : utilisation des molecules photosensibles

SIGLECNRS T Bordereau / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Reply to "Rigor, reproducibility and in vitro CSF assays: The devil in the details"

International audienc

Les canaux calciques neuronaux (bases moléculaires de l'inactivation et implication dans l'ataxie spino-cérébelleuse)

MONTPELLIER-BU Médecine (341722104) / SudocMONTPELLIER-BU Médecine UPM (341722108) / SudocPARIS-BIUM (751062103) / SudocPARIS-BIUP (751062107) / SudocSudocFranceF

Régulations des canaux calciques activés par le voltage de type P/Q par le calcium et les protéines G

MONTPELLIER-BU Médecine UPM (341722108) / SudocPARIS-BIUP (751062107) / SudocMONTPELLIER-BU Médecine (341722104) / SudocSudocFranceF

Two sets of amino acids of the domain I of Cav2.3 Ca(2+) channels contribute to their high sensitivity to extracellular protons.

International audienceExtracellular acidification decreases Ca(2+) current amplitude and produces a depolarizing shift in the activation potential (Va) of voltage-gated Ca(2+) channels (VGCC). These effects are common to all VGCC, but differences exist between Ca(2+) channel types and the underlying molecular mechanisms remain largely unknown. We report here that the changes in current amplitude induced by extracellular acidification or alkalinisation are more important for Cav2.3 R type than for Cav2.1 P/Q-type Ca(2+) channels. This difference results from a higher shift of Va combined with a modification of channel conductance. Although involved in the sensitivity of channel conductance to extracellular protons, neither the EEEE locus nor the divalent cation selectivity locus could explain the specificity of the pH effects. We show that this specificity involves two separate sets of amino acids within domain I of the Cavα subunit. Residues of the voltage sensor domain and residues in the pore domain mediate the effects of extracellular protons on Va and on channel conductance, respectively. These new insights are important for elucidating the molecular mechanisms that control VGCC gating and conductance and for understanding the role of extracellular protons in other channels or membrane-tethered enzymes with similar pore and/or voltage sensor domains