Protective role of FBXL19 in Streptococcus pneumoniae-induced lung injury in pneumonia immature mice.

OBJECTIVE: Streptococcus pneumoniae (Spn) is a common pathogen for pediatric pneumonia and leads to severe lung injury. This study is conducted to analyze the role of F-box and leucine rich repeat protein 19 (FBXL19) in Spn-induced lung injury in immature mice.

METHODS: Immature mice were infected with Spn to record the survival rates and bacterial loads in bronchoalveolar lavage fluid. Levels of FBXL19 and FOXM1 in lung tissues were determined via real-time quantitative polymerase chain reaction or Western blotting. After the interference of FBXL19, its impacts on lung inflammatory injury were appraised by the lung wet/dry weight ratio, myeloperoxidase activity, hematoxylin and eosin staining, and enzyme-linked immunosorbent assay. The binding of FBXL19 to forkhead box M1 (FOXM1) in mouse lung epithelial cells was determined. After MG132 treatment, the protein and ubiquitination levels of FOXM1 were measured. The functional rescue experiments were performed to analyze the role of FOXM1 in FBXL19-regulated lung injury.

RESULTS: FBXL19 was downregulated while FOXM1 was upregulated in lung tissues of Spn-infected immature mice. Overexpression of FBXL19 reduced the degree of lung injury and inflammation. FBXL19 can bind to FOXM1 to reduce its protein level via ubiquitination degradation. MG132 reduced the ubiquitination and increased the protein level of FOXM1. Overexpression of FOXM1 reversed the protective role of FBXL19 overexpression in lung injury of Spn immature mice.

CONCLUSION: FBXL19 was downregulated by Spn and FBXL19 overexpression alleviated lung injury by inducing ubiquitination and degradation of FOXM1 in Spn immature mice.