ERdj4 and ERdj5 Are Required for Endoplasmic Reticulum-associated Protein Degradation of Misfolded Surfactant Protein C

Abstract

Mutations in the SFTPC gene associated with interstitial lung disease in human patients result in misfolding, endoplasmic reticulum (ER) retention, and degradation of the encoded surfactant protein C (SP-C) proprotein. In this study, genes specifically induced in response to transient expression of two disease-associated mutations were identified by microarray analyses. Immunoglobulin heavy chain binding protein (BiP) and two heat shock protein 40 family members, endoplasmic reticulum-localized DnaJ homologues ERdj4 and ERdj5, were significantly elevated and exhibited prolonged and specific association with the misfolded proprotein; in contrast, ERdj3 interacted with BiP, but it did not associate with either wild-type or mutant SP-C. Misfolded SP-C, ERdj4, and ERdj5 coprecipitated with p97/VCP indicating that the cochaperones remain associated with the misfolded proprotein until it is dislocated to the cytosol. Knockdown of ERdj4 and ERdj5 expression increased ER retention and inhibited degradation of misfolded SP-C, but it had little effect on the wild-type protein. Transient expression of ERdj4 and ERdj5 in X-box binding protein 1 ؊/؊ mouse embryonic fibroblasts substantially restored rapid degradation of mutant SP-C proprotein, whereas transfection of HPD mutants failed to rescue SP-C endoplasmic reticulum-associated protein degradation. ERdj4 and ERdj5 promote turnover of misfolded SP-C and this activity is dependent on their ability to stimulate BiP ATPase activity.

A Novel ER J-protein DNAJB12 Accelerates ER-associated Degradation of Membrane Proteins Including CFTR

“…1D). In contrast to the other characterized mammalian ER-localized J-proteins all of which have a J-domain on the luminal side (Chevaliar et al, 2000;Kurisu et al, 2003;Hosoda et al, 2003;Dong et al, 2008;Jin et al, 2009;Zahedi et al, 2009), DNAJB12 has its J-domain in the cytosol (Fig. 1D).…”

Protein Folding and Quality Control in the ER

“…ERdj4 and ERdj5 are reported to enhance the ERAD of misfolded proteins. ERdj5 was shown to interact with EDEM (ER degradation-enhancing a-mannosidaselike protein), and overexpressed ERdj4 and ERdj5 interact with p97, a component of the ERAD machinery (Dong et al 2008;Ushioda et al 2008;Ushioda and Nagata 2011) (see also later section). ERdj6, designated p58 IPK , was initially reported to negatively regulate PKR and PERK phosphorylation in the cytosol (Gale et al 1998;Yan et al 2002).…”

Genotoxic stress/p53-induced DNAJB9 inhibits the pro-apoptotic function of p53

“…21 The primary location of DNAJB9 is the ER, where it binds to BiP/GRP78, the major Hsp70 in the ER, and stimulates the ATPase activity of BiP. 19 Although it has been recently proposed that DNAJB9 is involved in the ER-associated degradation of misfolded proteins, 26 the cellular function of DNAJB9 is largely unknown. We here found a novel function of DNAJB9 under genotoxic conditions: DNAJB9 is induced by p53 and inhibits the proapoptotic function of p53 (Figures 1-3).…”