ATF4 and injury: Qian et al. reported that the protein kinase r-like endoplasmic reticulum kinase (PERK), activating transcription factor 4 (ATF4), and the C/EBP homologous protein (CHOP) expressions were increased and Fe2+ concentrations were elevated in rats with ischemia/reperfusion lung injury, suggesting that this injury may trigger iron-dependent cell death by activating the endoplasmic reticulum.