The GABAAReceptor γ2 Subunit R43Q Mutation Linked to Childhood Absence Epilepsy and Febrile Seizures Causes Retention of α1β2γ2S Receptors in the Endoplasmic Reticulum

Abstract

The GABA_A receptor γ2 subunit mutation R43Q is an autosomal dominant mutation associated with childhood absence epilepsy and febrile seizures. Previously, we demonstrated that homozygous α1β3γ2L(R43Q) receptor whole-cell currents had reduced amplitude with unaltered time course, suggesting reduced cell surface expression of functional receptors. In human embryonic kidney 293-T cells, we demonstrate that both heterozygous and homozygous α1β2γ2S(R43Q) GABA_A receptor current amplitudes were reduced when receptors were assembled from coexpressed α1, β2, and γ2S subunits and from β2-α1 tandem subunits coexpressed with the γ2L subunit. Using fluorescence confocal microscopy, we demonstrated that mutant receptors containing enhanced yellow fluorescent protein-tagged γ2S subunits had reduced surface expression and were retained in the endoplasmic reticulum. In addition, using biotinylation of surface receptors and immunoblotting, we confirmed that α1β2γ2S(R43Q) receptors had reduced surface expression. These results provide evidence that the γ2S(R43Q) mutation impaired GABA_A receptor function by compromising receptor trafficking and reducing surface expression.