Jinsei Jung^1,2,*, Jiyoon Kim^1,*, Shin Hye Roh¹, Ikhyun Jun¹, Robert D. Sampson¹, Heon Yung Gee^1,3, Jae Young Choi² & Min Goo Lee<sup>1

1</sup>Department of Pharmacology and Brain Korea 21 Project for Medical Sciences, Yonsei University College of Medicine, Seoul 120-752, Republic of Korea. ²Department of Otorhinolaryngology, Yonsei University College of Medicine, Seoul 120-752, Republic of Korea. ³Division of Nephrology, Department of Medicine, Boston Children’s Hospital and Harvard Medical School, Boston, Massachusetts 02115, USA. ^* These authors contributed equally to this work.

Correspondence and requests for materials should be addressed to M.G.L.

Abstract
Mutations in SLC26A4, which encodes pendrin, are responsible for hearing loss with an enlarged vestibular aqueduct and Pendred syndrome. The most prevalent mutation in East Asia is p.H723R (His723Arg), which leads to defects in protein folding and cell-surface expression. Here we show that H723R-pendrin can be rescued to the cell surface by an HSP70 co-chaperone DNAJC14-dependent unconventional trafficking pathway. Blockade of ER-to-Golgi transport or activation of ER stress signals induced Golgi-independent cell-surface expression of H723R-pendrin and restored its cell-surface Cl/^-/HCO₃^- exchange activity. Proteomic and short interfering RNA screenings with subsequent molecular analyses showed that Hsc70 and DNAJC14 are required for the unconventional trafficking of H723R-pendrin. Moreover, DNAJC14 upregulation was able to induce the unconventional cell-surface expression of H723R-pendrin. These results indicate that Hsc70 and DNAJC14 play central roles in ER stress-associated unconventional protein secretion and are potential therapeutic targets for diseases such as Pendred syndrome, which arise from transport defects of misfolded proteins.