title: Myotonia congenita mutation enhances the degradation of human CLC-1 chloride channels.
abstract: Myotonia congenita is a hereditary muscle disorder caused by mutations in the human voltage-gated chloride (Cl(-)) channel CLC-1. Myotonia congenita can be inherited in an autosomal recessive (Becker type) or dominant (Thomsen type) fashion. One hypothesis for myotonia congenita is that the inheritance pattern of the disease is determined by the functional consequence of the mutation on the gating of CLC-1 channels. Several disease-related mutations, however, have been shown to yield functional CLC-1 channels with no detectable gating defects. In this study, we have functionally and biochemically characterized a myotonia mutant: A531V. Despite a gating property similar to that of wild-type (WT) channels, the mutant CLC-1 channel displayed a diminished whole-cell current density and a reduction in the total protein expression level. Our biochemical analyses further demonstrated that the reduced expression of A531V can be largely attributed to an enhanced proteasomal degradation as well as a defect in protein trafficking to surface membranes. Moreover, the A531V mutant protein also appeared to be associated with excessive endosomal-lysosomal degradation. Neither the reduced protein expression nor the diminished current density was rescued by incubating A531V-expressing cells at 27°C. These results demonstrate that the molecular pathophysiology of A531V does not involve anomalous channel gating, but rather a disruption of the balance between the synthesis and degradation of the CLC-1 channel protein.
authors: Department of Physiology, College of Medicine, National Taiwan University, Taipei, Taiwan.
authors: Ting-Ting
authors: TT
authors: Lee
authors: Xiao-Dong
authors: XD
authors: Zhang
authors: Chao-Chin
authors: CC
authors: Chuang
authors: Jing-Jer
authors: JJ
authors: Chen
authors: Yi-An
authors: YA
authors: Chen
authors: Shu-Ching
authors: SC
authors: Chen
authors: Tsung-Yu
authors: TY
authors: Chen
authors: Chih-Yung
authors: CY
authors: Tang
mesh_terms: D000818:Animals; D019556:COS Cells; D002462:Cell Membrane / Q000378:metabolism; D018118:Chloride Channels / Q000096:biosynthesis / Q000235:genetics* / Q000378:metabolism*; D002522:Chlorocebus aethiops; D055724:Electrophysiological Phenomena; D011992:Endosomes / Q000378:metabolism; D005786:Gene Expression Regulation / Q000235:genetics; D057809:HEK293 Cells; D006801:Humans; D008247:Lysosomes / Q000378:metabolism; D009154:Mutation; D009224:Myotonia Congenita / Q000235:genetics*; D059748:Proteolysis; D013696:Temperature
chemical_list: C086321:CLC-1 channel; D018118:Chloride Channels