Co-chaperone FKBP38 Promotes HERG Trafficking

Abstract

The Long QT Syndrome is a cardiac disorder associated with ventricular arrhythmias that can lead to syncope and sudden death. One prominent form of the Long QT syndrome has been linked to mutations in the HERG gene (KCNH2) that encodes the voltage-dependent delayed rectifier potassium channel (IKr). In order to search for HERG-interacting proteins important for HERG maturation and trafficking, we conducted a proteomics screen using myc-tagged HERG transfected into cardiac (HL-1) and non-cardiac (human embryonic kidney 293) cell lines. A partial list of putative HERG-interacting proteins includes several known components of the cytosolic chaperone system, including Hsc70 (70-kDa heat shock cognate protein), Hsp90 (90-kDa heat shock protein), Hdj-2, Hop (Hsp-organizing protein), and Bag-2 (BCL-associated athanogene 2). In addition, two membrane-integrated proteins were identified, calnexin and FKBP38 (38-kDa FK506-binding protein, FKBP8). We show that FKBP38 immunoprecipitates and co-localizes with HERG in our cellular system. Importantly, small interfering RNA knock down of FKBP38 causes a reduction of HERG trafficking, and overexpression of FKBP38 is able to partially rescue the LQT2 trafficking mutant F805C. We propose that FKBP38 is a co-chaperone of HERG and contributes via the Hsc70/Hsp90 chaperone system to the trafficking of wild type and mutant HERG potassium channels. The Long QT Syndrome is a cardiac disorder associated with ventricular arrhythmias that can lead to syncope and sudden death. One prominent form of the Long QT syndrome has been linked to mutations in the HERG gene (KCNH2) that encodes the voltage-dependent delayed rectifier potassium channel (IKr). In order to search for HERG-interacting proteins important for HERG maturation and trafficking, we conducted a proteomics screen using myc-tagged HERG transfected into cardiac (HL-1) and non-cardiac (human embryonic kidney 293) cell lines. A partial list of putative HERG-interacting proteins includes several known components of the cytosolic chaperone system, including Hsc70 (70-kDa heat shock cognate protein), Hsp90 (90-kDa heat shock protein), Hdj-2, Hop (Hsp-organizing protein), and Bag-2 (BCL-associated athanogene 2). In addition, two membrane-integrated proteins were identified, calnexin and FKBP38 (38-kDa FK506-binding protein, FKBP8). We show that FKBP38 immunoprecipitates and co-localizes with HERG in our cellular system. Importantly, small interfering RNA knock down of FKBP38 causes a reduction of HERG trafficking, and overexpression of FKBP38 is able to partially rescue the LQT2 trafficking mutant F805C. We propose that FKBP38 is a co-chaperone of HERG and contributes via the Hsc70/Hsp90 chaperone system to the trafficking of wild type and mutant HERG potassium channels. The Long QT Syndrome is a cardiac disorder characterized by a prolongation of the QT interval on the surface electrocardiogram that has been associated with ventricular arrhythmias whose clinical features range from minor dizziness to seizure, syncope, and sudden death. One prominent form of the Long QT syndrome (LQT2) 2The abbreviations used are: LQTS, long QT syndrome; HERG, human ether-a-go-go-related gene; WT, wild type; ER, endoplasmic reticulum; Hsc70, 70-kDa heat shock cognate protein; Hsp90, 90-kDa heat shock protein; CFTR, cystic fibrosis transmembrane conductance regulator; CHIP, C-terminal of Hsp70-interacting protein; Bag-2, BCL-associated athanogene 2; Hop, Hsp-organizing protein; FKBP38, 38-kDa FK506-binding protein; TPR, tetratricopeptide repeat; HA, hemagglutinin; HERG-C, C terminus of HERG; HEK, human embryonic kidney; PBS, phosphate-buffered solution; siRNA, small interfering RNA; AU, arbitrary units. is localized to chromosome 7 (1Curran M.E. Splawski I. Timothy K.W. Vincent G.M. Green E.D. Keating M.T. Cell. 1995; 80: 795-803Abstract Full Text PDF PubMed Scopus (2002) Google Scholar) and has been linked to genetic mutations in the KCNH2 gene that encodes the HERG