Translocational attenuation regulated by PERK-SRP14 axis is a novel protective mechanism of UPR

Slowing down protein synthesis, increasing protein folding capability, and enhancing misfolded protein degradation are the main mechanisms of unfolded protein response (UPR) to lessen ER stress. It has also been shown that substrate-specific translocational attenuation may be another protective measure during ER stress. Nevertheless, the underlying mechanism is still obscure. Through a multi-omics analysis, we found the protein SRP14, a subunit of SRP, was markedly decreased in ER-stressed cells. Given its critical function in the selective translocation of proteins, we investigated the mechanisms of SRP14 down-regulation and its role in ER stress. It was found that UPR, mainly the activation of PERK, induced SRP14 ubiquitination and proteasomal degradation. Furthermore, enforced expression of SRP14 in stressed cells augmented the substrate's translocation, aggravated ER stress, and reduced cell viability. Taken together, these results suggest the specific translocational attenuation regulated by the PERK-SRP14 axis is a protective measure to mitigate ER stress. To investigate the effects of ER stress induced by HRD1 knockdown on gene expression, we constructed a LoVo cell line that expresses a Tet-On shRNA against HRD1. After exposure to doxycycline (Dox) for 0, 3, and 5 days to induce HRD1 knockdown, the cells were harvested and processed for RNA-Seq.