genes encoding ER chaperones and enzymatic activities, thus enhancing folding and maturation of secretory proteins. UPR targets also allow unfolded proteins to be extracted from the ER, and subsequently degraded in the cytosol (a process called ER-associated degradation) (Vembar and Brodsky, 2008). Additionally, a transient reduction in translation relieves ER protein load (Harding et al., 2001). If these adaptive UPR outputs are successful, the decline in unfolded proteins causes UPR signaling to wane as homeostasis is restored (Merksamer et al., 2008).
