Abstract
We examined the role of putative trafficking sequences in two GABAA receptor subunits: α4 and δ. These subunits assemble with a β subunit to form a subtype of GABAA receptor involved in generating the “tonic” outward current. Both α4 and δ subunits contain dibasic retention motifs in homologous positions. When basic residues are mutated to alanine in the α4 subunit, surface expression of epitope-tagged δ subunits is increased. When basic residues in homologous regions of the δ subunit are mutated, however, surface expression is reduced. We focused on the mutants that had the maximal effects to increase (in α4) or reduce (in δ) surface expression. The total expression of δ subunits is significantly decreased by the δ mutation, suggesting an effect on subunit maturation. We also examined surface expression of the β2 subunit. Expression of the mutated α4 subunit resulted in increased surface expression of β2 compared with wild-type α4, indicating enhanced forward trafficking. In contrast, mutated δ resulted in decreased surface expression of β2 compared with wild-type δ and to α4 and β2 in the absence of any δ. This observation suggests that the mutated δ incorporates into multimeric receptors and reduces the overall forward trafficking of receptors. These observations indicate that the roles of trafficking motifs are complex, even when located in homologous positions in related subunits. The physiologic properties of receptors containing mutated subunits were not significantly affected, indicating that the mutations in the α4 subunit will be useful to enhance surface expression.
Footnotes
- Received March 17, 2014.
- Accepted April 10, 2014.
This work was supported by the National Institutes of Health National Institute of General Medical Sciences [Grant P01-GM47969]. J.H.S. is the Russell and Mary Shelden Professor of Anesthesiology.
- Copyright © 2014 by The American Society for Pharmacology and Experimental Therapeutics
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