Positive contribution of ERdj5/JPDI to endoplasmic reticulum protein quality control in the salivary gland

In eukaryotic cells, most membrane and secretory proteins are modified post-translationally in the ER (endoplasmic reticulum) for correct folding and assembly. Disulfide-bond formation is one of the important modifications affecting folding and is catalysed by the PDI (protein disulfide isomerase) family proteins. ERdj5 [also known as JPDI (J-domain-containing PDI-Iike protein)] is a member of the PDI family proteins and has been reported to act as a reductase in ERAD (ER-associated degradation). However, the role of ERdj5 at the whole-body level remains unclear. Therefore in the present study we generated ER(ERdj5-knockout mice {the mouse gene of ERdj5 is known as Dnajc10 [DnaJ (Hsp40) homologue, Subfamily C, member 10]} and analysed them. Although ERdj5-knockout mice were viable and healthy, the ER stress response was activated in the salivary gland of the knockout mice more than that of control mice. Furthermore, in ERdj5-knockout cells. the expression of exogenous ERdj5 mitigated the ER stress Caused by overproduction of alpha-amylase. which is one of the most abundant proteins in saliva and has five intramolecular disulfide bonds. This effect was dependent on the thioredoxin-like motif's of ERdj5. Thus we suggest that ERdj5 contributes to ER protein quality control in the salivary gland.