CHOP promotes the transition to chronic integrated stress response signaling with suppression of hepatocyte identity

Abstract

The transcription factor CHOP promotes cell death during ER stress, but it is strongly induced even by moderate stresses that do not result in appreciable cell death. Its role during less severe stresses--especially in intact tissues in vivo--is poorly understood. Here, we both deleted and restored CHOP specifically in hepatocytes and challenged animals with ER stress in vivo. We found that CHOP influenced stress-dependent hepatocyte gene expression through two previously unappreciated mechanisms. It directly suppressed the expression of transcriptional master regulators of hepatocyte identity and metabolism. And more broadly, it exacerbated ER stress through the promotion of protein synthesis, which led to persistent activation of the integrated stress response (ISR) despite dephosphorylation of eIF2. This shift to second-phase ISR signaling was phenocopied by deletion of the protective UPR sensor ATF6, suggesting that it reflects a transition from an acute stress response to a chronic one. Our findings show that CHOP augments the capacity of the ISR and UPR to continue to mount a protective response even after eIF2 phosphorylation has been suppressed. In vivo, where ISR signaling intersects with hepatocyte gene regulatory networks, this transition favors lipid dysregulation, highlighting a pathway through which CHOP impacts tissue function independent of cell death.