Phosphorylation-mediated activation of ubiquitin-specific protease-14 regulates lipopolysaccharide-induced immunoproteasome activation

Severe bacterial infection is a major cause of global mortality and morbidity. Acute respiratory distress syndrome (ARDS) is a devastating complication of severe sepsis. Dysfunction of protein homeostasis in the immune system has been known to contribute to the pathogenesis of systemic inflammation. Immunoproteasome driven by inflammation has been shown to be involved in the pathophysiology of lung inflammatory diseases such as ARDS, asthma, chronic obstructive pulmonary disease (COPD), and idiopathic pulmonary fibrosis (IPF). Ubiquitin-specific protease-14 (USP14) is a deubiquitinating enzyme associated with 19S proteasome. The effect of 19S associated deubiquitinating enzymes on immunoproteasome formation has not been reported. Here, we found that phosphorylation and activation of USP14 modulates LPS-induced immunoproteasome formation and activation. LPS increased immunoproteasome formation, which was attenuated by downregulation or inhibition of USP14. PKCδ-mediated phosphorylation of USP14 on serine residues increased USP14 activation and promoted immunoproteasome production. Inhibition of USP14 by an inhibitor (IU1) or overexpression of phospho-deficient USP14 mutants significantly diminished LPS-induced USP14 activation and inflammatory responses. Further, intratracheal administration of LPS in mice induced phosphorylation and activation of USP14, immunoproteasome formation and activity in lungs. IU1 administration ameliorated severity of LPS- and sepsis-induced lung injury. This study reveals that the pro-inflammatory effect of USP14 is partly through upregulation of immunoproteasome. This work was supported by the US National Institutes of Health R01HL151513 and R01HL167846 to Jing Zhao. R01HL157164 and R01HL169203 to Yutong Zhao. This abstract was presented at the American Physiology Summit 2025 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.