Induction and nuclear overexpression of CHOP in AECII is an eminent feature in IPF lungs and is detected together with other ER stress markers, such as activating transcription factor-4 (ATF4) [PRKR-like endoplasmic reticulum kinase (PERK) pathway], p50ATF6 [activating transcription factor-6 (ATF6) pathway], and spliced x-box-binding protein-1 (XBP1) [inositol-requiring protein-1α (IRE1α) pathway], as well as caspase-3 activation [8]. Here, ATF4 is linked to idiopathic pulmonary fibrosis.