title: Distinct roles of molecular chaperones HSP90α and HSP90β in the biogenesis of KCNQ4 channels.
abstract: Loss-of-function mutations in the KCNQ4 channel cause DFNA2, a subtype of autosomal dominant non-syndromic deafness that is characterized by progressive sensorineural hearing loss. Previous studies have demonstrated that the majority of the pathogenic KCNQ4 mutations lead to trafficking deficiency and loss of KCNQ4 currents. Over the last two decades, various strategies have been developed to rescue trafficking deficiency of pathogenic mutants; the most exciting advances have been made by manipulating activities of molecular chaperones involved in the biogenesis and quality control of the target protein. However, such strategies have not been established for KCNQ4 mutants and little is known about the molecular chaperones governing the KCNQ4 biogenesis. To identify KCNQ4-associated molecular chaperones, a proteomic approach was used in this study. As a result, two major molecular chaperones, HSP70 and HSP90, were identified and then confirmed by reciprocal co-immunoprecipitation assays, suggesting that the HSP90 chaperone pathway might be involved in the KCNQ4 biogenesis. Manipulating chaperone expression further revealed that two different isoforms of HSP90, the inducible HSP90α and the constitutive HSP90β, had opposite effects on the cellular level of the KCNQ4 channel; that HSP40, HSP70, and HOP, three key components of the HSP90 chaperone pathway, were crucial in facilitating KCNQ4 biogenesis. In contrast, CHIP, a major E3 ubiquitin ligase, had an opposite effect. Collectively, our data suggest that HSP90α and HSP90β play key roles in controlling KCNQ4 homeostasis via the HSP40-HSP70-HOP-HSP90 chaperone pathway and the ubiquitin-proteasome pathway. Most importantly, we found that over-expression of HSP90β significantly improved cell surface expression of the trafficking-deficient, pathogenic KCNQ4 mutants L274H and W276S. KCNQ4 surface expression was restored by HSP90β in cells mimicking heterozygous conditions of the DFNA2 patients, even though it was not sufficient to rescue the function of KCNQ4 channels.
authors: Department of Otolaryngology, University of California Davis, Davis, California, United States of America.
authors: Yanhong
authors: Y
authors: Gao
authors: Sergey
authors: S
authors: Yechikov
authors: Ana E
authors: AE
authors: Vazquez
authors: Dongyang
authors: D
authors: Chen
authors: Liping
authors: L
authors: Nie
mesh_terms: D002462:Cell Membrane / Q000378:metabolism; D057809:HEK293 Cells; D050956:HSP40 Heat-Shock Proteins / Q000378:metabolism; D018840:HSP70 Heat-Shock Proteins / Q000378:metabolism; D018841:HSP90 Heat-Shock Proteins / Q000502:physiology*; D006319:Hearing Loss, Sensorineural / Q000235:genetics; D018398:Homeodomain Proteins / Q000378:metabolism; D006706:Homeostasis; D006801:Humans; D015640:Ion Channel Gating; D051656:KCNQ Potassium Channels / Q000096:biosynthesis* / Q000235:genetics; D008564:Membrane Potentials; D020125:Mutation, Missense; D021381:Protein Transport; D059748:Proteolysis; D025521:Tumor Suppressor Proteins / Q000378:metabolism; D044767:Ubiquitin-Protein Ligases / Q000378:metabolism
chemical_list: C494647:DNAJB1 protein, human; C476884:HOPX protein, human; D050956:HSP40 Heat-Shock Proteins; D018840:HSP70 Heat-Shock Proteins; D018841:HSP90 Heat-Shock Proteins; C533585:HSP90AA2P protein, human; C493165:HSP90AB1 protein, human; D018398:Homeodomain Proteins; D051656:KCNQ Potassium Channels; C117367:KCNQ4 protein, human; D025521:Tumor Suppressor Proteins; C467728:STUB1 protein, human; D044767:Ubiquitin-Protein Ligases