USP13 regulates cell senescence through mediating MDM2 stability

Lung aging results in altered lung function, reduced lung remodeling and regenerative capacity, and increased susceptibility to acute and chronic lung diseases. The molecular and physiological underlying mechanisms of lung aging remain unclear. Mounting evidence suggests that deubiquitinating enzymes (DUBs) play a critical role in tissue aging and diseases through regulation of cellular signaling pathways. Here we investigate the role of Ubiquitin-Specific Protease 13 (USP13) in cell senescence and lung aging and its underlying mechanisms. Protein levels of USP13 and MDM2 in lung tissues from aged and young mice were compared. Gene silencing and overexpression of USP13 in human cell lines were performed. MDM2 levels were examined by Quantitative Real-Time PCR and Western Blotting analysis. The cell senescence levels of human cells were checked by the β-galactosidase staining. Lung tissues from aged mice showed higher levels of USP13 compared to younger mice. We found a negative correlation between USP13 and MDM2 expression in lung tissues of aged mice. The increased protein levels of MDM2 were detected in lung tissues of USP13 deficient mice. Furthermore, overexpression of USP13 promoted cell senescence. Knockdown of USP13 increased MDM2 levels in lung cells, while overexpression of USP13 reduced it. The degradation of MDM2 caused by USP13 was prevented by the proteasome inhibitor MG132. Furthermore, we showed that USP13 targeted and reduced K63-linked polyubiquitination of MDM2. These results demonstrate that USP13 is involved in the aging signaling pathway in lungs through regulation of MDM2.