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.

CXCL1 Inhibits Airway Smooth Muscle Cell Migration through the Decoy Receptor Duffy Antigen Receptor for Chemokines

“…6A), supporting a possible role for HSP90 in CXCL1-mediated ASMC migration inhibition. However, there are two isoforms of HSP90, HSP90a and HSP90b (47,48), which are known to differentially regulate cellular processes (49). When we examined the mRNA expression of HSP90a and HSP90b in ASMCs in response to 4 ng/ml of CXCL1, we found a significant increase in the mRNA expression of HSP90a, but not HSP90b, after 30 and 60 min of stimulation (Supplemental Fig.…”

Bag1 Co-chaperone Promotes TRC8 E3 Ligase-dependent Degradation of Misfolded Human Ether a Go-Go-related Gene (hERG) Potassium Channels

“…There is surprisingly little known about the ERAD of these channels. CHIP and Hsc70/Hsp70 have been implicated in the degradation of cardiac KCNA5/Kv1.5 channels and KCNQ4/Kv7.4 in auditory sensory neurons (55,56). Whether TRC8 contributes to the degradation of these and related channels remains to be determined.…”

The endosomal trafficking factors CORVET and ESCRT suppress plasma membrane residence of the renal outer medullary potassium channel (ROMK)

“…In addition to CFTR and hERG, the impact of cellular quality control mechanisms in the regulation of other disease-associated ion channels has also been investigated (11,20,(22)(23)(24)(25)(26)(27)(28)(29). However, the rules that govern the quality control of diverse ion channels remain poorly defined.…”