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(Circulation Research. 2003;92:e87.)
© 2003 American Heart Association, Inc.

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Role of the Cytosolic Chaperones Hsp70 and Hsp90 in Maturation of the Cardiac Potassium Channel hERG

Eckhard Ficker, Adrienne T. Dennis, Lu Wang, Arthur M. Brown

From the Rammelkamp Center for Education and Research (E.F., A.T.D., L.W.), MetroHealth Campus, Case Western Reserve University, Cleveland, Ohio; and Department of Physiology and Biophysics (A.M.B.), Case Western Reserve University, Cleveland, Ohio.

Correspondence to Dr Eckhard Ficker, Rammelkamp Center, MetroHealth Medical Center, 2500 MetroHealth Drive, Cleveland, OH 44109. E-mail eficker{at}metrohealth.org

The human ether-a-gogo–related gene (hERG) encodes the subunit of the cardiac potassium current I_Kr. Several mutations in hERG produce trafficking-deficient channels that may cause hereditary long-QT syndrome and sudden cardiac death. Although hERG currents have been studied extensively, little is known about the proteins involved in maturation and trafficking of hERG. Using immunoprecipitations, we show that the cytosolic chaperones heat shock protein (Hsp) 70 and Hsp90, but not Grp94, interact with hERG wild type (WT) during maturation. The specific Hsp90 inhibitor geldanamycin prevents maturation and increases proteasomal degradation of hERG WT, while reducing hERG currents in heterologous expression systems. In ventricular myocytes, inhibition of Hsp90 also decreases I_Kr, whereas geldanamycin had no effect on I_Ks or heterologously expressed Kv2.1 and Kv1.5 currents. Both Hsp90 and Hsp70 interact directly with the core-glycosylated form of hERG WT present in the endoplasmic reticulum but not the fully glycosylated, cell-surface form. For the trafficking-deficient LQT2 mutants, hERG R752W and hERG G601S, interactions with Hsp90 and Hsp70 are increased as both mutants remained tightly associated with Hsp90 and Hsp70 in the endoplasmic reticulum. Incubation at lower temperature for R752W or with the hERG blocker astemizole for G601S dissociates channel-chaperone complexes and restores trafficking. In contrast, nonfunctional but trafficking-competent hERG G628S is released from chaperone complexes during maturation comparable to WT. We conclude that Hsp90 and Hsp70 are crucial for the maturation of hERG WT as well as the retention of trafficking-deficient LQT2 mutants. The full text of this article is available online at http://www.circresaha.org.

Key Words: human ether-a-gogo–related gene • heat shock proteins • chaperones • geldanamycin

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