A GABAA Receptor Mutation Linked to Human Epilepsy (γ2R43Q) Impairs Cell Surface Expression of αβγ Receptors*

  1. Feyza Sancar and
  2. Cynthia Czajkowski§
  1. §Department of Physiology and Neuroscience Training Program, University of Wisconsin, Madison, Wisconsin 53706
  1. To whom correspondence should be addressed: Dept. of Physiology, Rm. 197 MSC, University of Wisconsin, 1300 University Ave., Madison WI 53706. Tel.: 608-265-5863; Fax: 608-265-5512; E-mail: czajkowski{at}physiology.wisc.edu.

Abstract

A mutation in the γ2 subunit of the γ-aminobutyric acid (GABA) type A receptor (GABAR), which changes an arginine to a glutamine at position 43 (R43Q), is linked to familial idiopathic epilepsies. We used radioligand binding, immunoblotting, and immunofluorescence techniques to examine the properties of wild-type α1β2γ2 and mutant α1β2γ2R43Q GABARs expressed in HEK 293 cells. The γ2R43Q mutation had no affect on the binding affinity of the benzodiazepine flunitrazepam. However, in cells expressing α1β2γ2R43Q GABARs, the number of binding sites for [3H]flunitrazepam relative to wild-type receptors was decreased 75%. Using surface protein biotinylation, affinity purification, and immunoblotting, we demonstrated that expression of cell surface α1β2γ2R43Q GABARs was decreased. Surface immunostaining of HEK 293 cells expressing α1β2γ2R43Q GABARs confirmed that surface expression of the γ2R43Q subunit was reduced. These data demonstrate that the γ2R43Q mutation impairs expression of cell surface GABARs. A deficit in surface GABAR expression would reduce synaptic inhibition and result in neuronal hyperexcitability, which could explain why families possessing the γ2R43Q subunit have epilepsy.

Footnotes

  • 1 The abbreviations used are: GABA, γ-aminobutyric acid; GABAA, GABA, type A; GABAR, GABAA receptor; BZD, benzodiazepine; WT, wild-type; FNZM, flunitrazepam; PBS, phosphate-buffered saline.

  • * This work was supported by National Institute of Neurological Disorders and Stroke Grant 34727 (to C. C.) and a predoctoral fellowship (to F. S.) from the American Epilepsy Foundation. A portion of this work has been published in abstract form (27). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

    • Received March 26, 2004.
    • Revision received August 20, 2004.
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This Article

  1. The Journal of Biological Chemistry 279, 47034-47039.
  1. All Versions of this Article:
    1. M403388200v1
    2. M403388200v2
    3. 279/45/47034 (most recent)

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