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Theses

Les déterminants moléculaires et cellulaires de la mutation humaine R482X de la sous-unité Cavb4 impliqués dans l'épilepsie

Abstract : High voltage-activated (HVA) calcium channels are hetero-multimeric complexes
that translate electrical signals into Ca2+ influx, a secondary messenger that mediates
essential neuronal processes such as neurotransmitter release and neuronal excitability.
HVA calcium channels are composed of four subunits: Cavα1 subunit, the pore forming
of the channel and the auxiliary subunits Cavβ, Cavα2δ and Cavγ. The Cavß subunit has
focused much of the interest owing to its regulatory functions within the complex. By
masking an endoplasmic retention signal on the Cavα1 subunit, Cavß subunit targets the
mature calcium channel to the plasma membrane and contributes to the increase in
number of functional calcium currents. In humans, pathologic mutations have been
identified in CACNAB4 that produce epileptic phenotype. One of these mutations is a
premature termination mutation (R482X). Mutations produced minor biophysical effects
on calcium channels in spite of their preponderant pathological phenotypes, which tend to
indicate that cellular functions other than channel regulation may be responsible for the
predominant neurological effects of the R482X mutation.
My thesis focuses on the molecular and cellular determinants of the Cavb4 mutant
(R482X) inducing the human neurological phenotype. Studies were realized in
hippocampal neurons which are particularly implicated in epilepsy. A translocation of
endogenous Cavß4, from the cytoplasm to the nucleus is observed during neuronal
differentiation and synaptogenesis. This translocation is conditioned by the native
structural conformation of Cavß4 subunit; carboxy-terminal deletion inhibits the nuclear
localization of the mutant. The 38 amino acids deletion disturbs the structure of Cavß4 by
altering the intramolecular interaction between the two conserved domains in Cavß4
subunit. In hippocampal neurons, this structural distortion prevents the nuclear
localization of the mutant Cavß4. In order to identify the impact of the nuclear localization
of the Cavß4 subunit on transcriptional regulation, a study on gene expression generated
by microarray is realized. Profiles of gene expression revealed a differential gene
regulation between wild-type and mutant Cavß4. Cavß4 subunit seems to have a repressive
action on gene regulation; on the other hand, the lack of nuclear localization of the
mutant reverses this repressive impact. Among the specific transcripts differentially
expressed, some genes are primordial keys in neuronal activities, thus alterations in the
regulation of these genes could be involved in neuronal diseases. Since no NLS
consensus sequence has been identified on Cavß4, two-hybrid assay was realized in order
to identify partners responsible of the Cavß4 nuclear targeting. A specific protein holding
a NLS sequence interacts specifically with Cavß4 subunit, but not with the mutant, and is
able to target Cavß4 to the nucleus. The other protein which specifically interacts with the
WT Cavß4 sequesters Cavß4 in the cytoplasm.
Finally, the lack in nuclear targeting of the R482X mutant due to the structural
distortion appears to alter the transcriptional gene regulation which is maybe implicated
in the epileptic phenotype of patients holding the mutation.
Document type :
Theses
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https://tel.archives-ouvertes.fr/tel-00171896
Contributor : Abir Tadmouri <>
Submitted on : Thursday, September 13, 2007 - 3:29:40 PM
Last modification on : Friday, November 6, 2020 - 3:45:55 AM
Long-term archiving on: : Monday, September 24, 2012 - 12:26:38 PM

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  • HAL Id : tel-00171896, version 1

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Citation

Abir Tadmouri. Les déterminants moléculaires et cellulaires de la mutation humaine R482X de la sous-unité Cavb4 impliqués dans l'épilepsie. Neurosciences [q-bio.NC]. Université Joseph-Fourier - Grenoble I, 2007. Français. ⟨tel-00171896⟩

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