FBXW7 regulates epithelial barrier impairment in human bronchial epithelial cells in vitro by targeting apoptosis signal-regulating kinase1 via the p38 pathway

Bronchial asthma is a common chronic inflammatory disease characterized by airway hyperresponsiveness (AHR), inflammatory cell infiltration, and airway remodeling. F-box/WD repeat-containing protein 7 (FBXW7), an E3 ubiquitin ligase, is required for various endothelial functions, such as cell migration, inflammation, and endothelial integrity. This study aimed to investigate the role of FBXW7 in lipopolysaccharide (LPS)-induced epithelial barrier impairment in bronchial epithelial cells in vitro. By using lentivirus-based technology, FBXW7 was overexpressed or silenced (24 h) in human bronchial epithelial (16HBE) cells, which were treated with LPS or not (24 h). Immunoprecipitation (IP) detection and Western blot analysis were used to evaluate the interaction of target proteins. Cell permeability was measured using transepithelial electrical resistance and FITC dextran flux (48 h). IL-1 beta, IL-18 and TNF-alpha in cell supernatants were measured using ELISA (48 h). The results showed that LPS stimulation suppressed FBXW7 expression in a time- and dose-dependent manner. LPS exposure decreased cell proliferation, elevated IL-1 beta, IL-18 and TNF-alpha, increased epithelial permeability, and p38 phosphorylation. These LPS-induced changes were partly compromised by FBXW7 overexpression. Similar to LPS stimulation, FBXW7 knockdown increased epithelial permeability and levels of inflammatory cytokines and p38 phosphorylation, which were, in part, blocked by apoptosis signal-regulating kinase (ASK) 1 knockdown or p38 pathway inhibition. IP and Western blot analysis showed that FBXW7 interacted with ASK1. ASK1 expression was inversely associated with FBXW7 expression. FBXW7 overexpression markedly enhanced ASK1 ubiquitination. These data revealed that FBXW7 counter against inflammation and protects epithelial barrier integrity in bronchial epithelial cells by promoting ubiquitination-mediated degradation of ASK1 via the p38 pathway.