DNAJB12 and Hsp70 Facilitate the Conformation Specific Degradation of Arrested N1303K-CFTR Intermediates by ER Associated-Autophagy

Abstract

Proteotoxic stress, intrinsic folding inefficiencies, and disease-related mutations challenge cellular quality control systems tasked with proteome biogenesis and suppressing proteotoxicity. The ER-transmembrane Hsp40 DNAJB12 and Hsp70 cooperate in protein maintenance by triaging nascent membrane proteins for folding versus degradation. N1303K is the second most common CF causing mutation in CFTR, but unlike F508del-CFTR, its biogenic and functional defects are resistant to correction by VX-809. VX-809 stimulates the accumulation of kinetically trapped N1303K-CFTR intermediates that exhibit conformational features of folded CFTR but remain associated with DNAJB12-Hsp70. Stable N1303K-CFTR intermediates are resistant to ERAD and become concentrated in ER-tubules associated with autophagy initiation sites containing WIPI1, FIP200, and LC3. Budding of autophagosomes containing N1303K-CFTR from omegasomes occurs where autolysosomes dock to WIPI1 rings. Mechanisms will be discussed for Hsp40 and Hsp70 action in the sorting of N1303K-CFTR intermediates for secretion versus degradation by ERAD or ERQC-autophagy.