Unfolded proteins in the mitochondria activate HRI and shut-down of mitochondrial protein translation

Mitochondrial unfolded protein response (UPR ^mt ) is triggered through eIF2α phosphorylation in mammal. However, the mechanisms of UPR ^mt activation and the influence on mitochondrial protein translation through eIF2α phosphorylation remain unclear. In this study, we confirmed that UPR ^mt was a rapid and specific stress response through eIF2α phosphorylation with pharmacological induction, along with the protein expression of eIF2α phosphorylation, ATF4, and CHOP. Meanwhile, with the up-regulation of some chaperones, cytochrome P450 enzymes, and DDIT4 determined by RNA-Seq and ribosome profiling, eIF2α phosphorylation is essential for expressing ATF4 and CHOP, then ATF4 traffics into the nucleus and initiates CHOP expression. In addition, the generation of ROS and mitochondrial morphology was unchanged under GTPP induced UPR ^mt . Furthermore, we unraveled the mechanism that HRI kinase mediates UPR ^mt induced with mitochondrial unfolded proteins by CRISPR-Cas9 technology and mitochondrial recruitment of HRI and interaction with other proteins. Meanwhile, we confirmed that mitochondrial protein translation and the number of mitochondrial protein imports were inhibited through eIF2α phosphorylation with the accumulation of mitochondrial unfolded protein. These findings provide the molecular mechanism of UPR ^mt and the impact on cellular protein translation, which will offer a novel insights into the functional research of UPR ^mt , including its implications for human diseases and pathobiology.