A gamma 2(R43Q) mutation, linked to epilepsy in humans, alters GABAA receptor assembly and modifies subunit composition on the cell surface.
Journal of Biological Chemistry. 2006-11-30; 282(6): 3819-3828
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1. J Biol Chem. 2007 Feb 9;282(6):3819-28. Epub 2006 Dec 5.
A gamma 2(R43Q) mutation, linked to epilepsy in humans, alters GABAA receptor
assembly and modifies subunit composition on the cell surface.
Frugier G(1), Coussen F, Giraud MF, Odessa MF, Emerit MB, Boué-Grabot E, Garret
(1)Laboratoire de Neurophysiologie, CNRS-UMR 5543, Université de Bordeaux II,
33076 Bordeaux, France.
Genetic defects leading to epilepsy have been identified in gamma2 GABA(A)
receptor subunit. A gamma2(R43Q) substitution is linked to childhood absence
epilepsy and febrile seizure, and a gamma2(K289M) mutation is associated with
generalized epilepsy with febrile seizures plus. To understand the effect of
these mutations, surface targeting of GABA(A) receptors was analyzed by
subunit-specific immunofluorescent labeling of living cells. We first transfected
hippocampal neurons in culture with recombinant gamma2 constructs and showed that
the gamma 2(R43Q) mutation prevented surface expression of the subunit, unlike
gamma2(K289M) substitution. Several gamma2-subunit constructs, bearing point
mutations within the Arg-43 domain, were expressed in COS-7 cells with alpha3-
and beta3-subunits. R43Q and R43A substitutions dramatically reduced surface
expression of the gamma2-subunit, whereas R43K, P44A, and D39A substitutions had
a lesser, but still significant, impact and K289M substitution had no effect.
Whereas the mutant gamma2(R43Q) was retained within intracellular compartments,
alphabeta complexes were still targeted at the cell membrane.
Coimmunoprecipitation experiments showed that gamma2(R43Q) was able to associate
with alpha3- or beta3-subunits, although the stoichiometry of the complex with
alpha3 was altered. Our data show that gamma2(R43Q) is not a dominant negative
and that the mutation leads to a modification of GABA(A) receptor subunit
composition on the cell surface that impairs the synaptic targeting in neurons.
This study reveals an involvement of the gamma2-Arg-43 domain in the control of
receptor assembly that may be relevant to the effect of the heterozygous
gamma2(R43Q) mutation leading to childhood absence epilepsy and febrile seizure.
PMID: 17148443 [Indexed for MEDLINE]