DNAJB12 and DNJB14 are non-redundant Hsp40 redox chaperones involved in endoplasmic reticulum protein reflux
Aline Dias da Purificação1, Victor Debbas1, Leonardo Yuji Tanaka1
1Laboratorio de Biologia Vascular, LIM-64 (Biologia Cardiovascular Translacional), Instituto do Coracao (InCor), Hospital das Clinicas HCFMUSP, Faculdade de Medicina, Universidade de Sao Paulo, Sao Paulo, SP, Brazil.
Background:
The endoplasmic reticulum (ER) transmembrane chaperones DNAJB12(B12) and DNAJB14(B14) are cofactors that cooperate with cytosolic Heat Shock-70 protein (HSC70) facilitating folding/degradation of nascent membrane proteins and supporting the ER-membrane penetration of viral particles. Here, we assessed structural/functional features of B12/B14 with respect to their regulation by ER stress and their involvement in ER stress-mediated protein reflux.
Methods:
We investigated the effect of Unfolded Protein Response(UPR)-eliciting drugs on the expression/regulation of B12-B14 and their roles in ER-to-cytosol translocation of Protein Disulfide Isomerase-A1(PDI).
Results:
We show that B12 and B14 are similar but do not seem redundant. They share predicted structural features and show high homology of their cytosolic J-domains, while their ER-lumen DUF1977 domains are quite dissimilar. Interactome analysis suggested that B12/B14 associate with different biological processes. UPR activation did not significantly impact on B12 gene expression, while B14 transcripts were up-regulated. Meanwhile, B12 and B14 (33.4 kDa isoform) protein levels were degraded by the proteasome upon acute reductive challenge. Also, B12 degradation was impaired upon sulfenic-acid trapping by dimedone. We originally report that knockdown of B12/B14 and their cytosolic partner SGTA in ER-stressed cells significantly impaired the amount of the ER redox-chaperone PDI in a cytosolic-enriched fraction. Additionally, B12 but not B14 overexpression increased PDI relocalization in non-stressed cells.
Conclusions And General Significance:
Our findings reveal that B12/B14 regulation involves thiol redox processes that may impact on their stability and possibly on physiological effects. Furthermore, we provide novel evidence that these proteins are involved in UPR-induced ER protein reflux.
Related Concept Videos
Export of Misfolded Proteins out of the ER
Regulation of the Unfolded Protein Response
Molecular Chaperones and Protein Folding
The...
The Unfolded Protein Response
Bacterial Protein Maturation
Protein Folding Quality Check in the RER


