The endoplasmic reticulum (ER) is the site for folding of membrane and secreted
proteins in the cell. Physiological or pathological processes that disturb protein folding in the
ER cause ER stress and activate a set of signaling pathways termed the unfolded protein
response (UPR). The UPR leads to transcriptional activation of genes encoding ER-resident
chaperones, oxidoreductases, and ER-associated degradation (ERAD) components.