Combining VCP Inhibition and SAHA Treatment Additively Enhances the Folding, Trafficking, and Function of Epilepsy-Associated GABAA Receptors [Membrane Biology]
November 18th, 2014 by Han, D.-Y., Di, X.-J., Fu, Y.-L., Mu, T.-W.
Gamma-aminobutyric acid type A (GABAA) receptors are the primary inhibitory ion channels in the mammalian central nervous system. The A322D mutation in the α1 subunit results in its excessive endoplasmic reticulum-associated degradation (ERAD) at the expense of plasma membrane trafficking, leading to autosomal dominant juvenile myoclonic epilepsy. Presumably, VCP/p97 extracts misfolded subunits from the ER membrane to the cytosolic proteasome for degradation. Here, we showed that inhibiting VCP using Eeyarestatin I reduces the ERAD of the α1(A322D) subunit without an apparent effect on its dynamin-1 dependent endocytosis, and this treatment enhances its trafficking. Furthermore, co-application of Eeyarestatin I and SAHA (suberanilohydroxamic acid), a known small molecule that promotes chaperone-assisted folding, yields an additive restoration of surface expression of α1(A322D) subunits in HEK293 cells and neuronal SH-SY5Y cells. Consequently, this combination significantly increases GABA-induced chloride currents in whole-cell patch clamping experiments than either chemical compound alone in HEK293 cells. Our findings suggest that VCP inhibition without stress induction together with folding enhancement represents a new strategy to restore proteostasis of misfolding-prone GABAA receptors, and thus a potential remedy for idiopathic epilepsy.