The endoplasmic reticulum (ER) is the largest organelle in the eukaryotic cell, consisting of a network of tubules and branches that includes the nuclear envelope and extends throughout the cytoplasm. Its main functions are the synthesis, folding and transport of proteins. When any of these functions is compromised, the unfolded protein response (UPR) is activated, a set of ER-centered signaling cascades aiming to restore homeostasis.
