A cellular response to environmental insults that cause disruptions in PROTEIN FOLDING
and/or accumulation of defectively folded protein in the ENDOPLASMIC RETICULUM. It
consists of a group of regulatory cascades that are triggered as a response to altered
levels of calcium and/or the redox state of the endoplasmic reticulum. Persistent
activation of the unfolded protein response leads to the induction of APOPTOSIS