RNF5 promotes acute lung injury through HSPA5 ER-to-cytosol translocation and resultant PERK activation.

Acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) are severe conditions lacking specific pharmacological treatments. Endoplasmic reticulum (ER) stress plays a pivotal role in their pathophysiology, yet the precise regulatory mechanisms remain elusive. In this study, we identify the E3 ubiquitin ligase ring finger protein 5 (RNF5) as a critical driver of ALI/ARDS. RNF5 is markedly upregulated in response to ALI and significantly exacerbates lung injury by stabilizing HSPA5 (heat shock protein family A member 5), a master regulator of the unfolded protein response (UPR). Notably, in vivo Rnf5 ablation effectively attenuated pulmonary edema, inflammatory cell infiltration, and apoptosis, whereas lung-specific Rnf5 overexpression worsened inflammation and cell death in mice. Mechanistically, RNF5 interacts with HSPA5 and competitively blocks its binding to PERK, facilitating PERK release. Furthermore, RNF5 promotes the retro-translocation of HSPA5 from the ER lumen to the cytosol. In the cytosol, RNF5 mediates the K6- and K63-linked polyubiquitination of HSPA5, enhancing its thermal stability and preventing its re-entry into the ER. This spatial sequestration sustains the persistent dissociation of the PERK-HSPA5 complex, leading to the hyperactivation of the pro-apoptotic and pro-inflammatory PERK-eIF2α-CHOP signaling cascade. The ability of RNF5 to promote ALI is strictly dependent on its E3 ligase activity. In conclusion, our findings uncover a compartment-specific regulatory mechanism of HSPA5, suggesting that the RNF5-HSPA5-PERK axis represents a promising therapeutic target for ALI/ARDS.