Nur77 promotes cigarette smoke-induced autophagic cell death by increasing the dissociation of Bcl2 from Beclin-1

Chronic obstructive pulmonary disease (COPD) is characterized by partially reversible airflow limitation and persistent alveolar destruction, and autophagy is involved in the pathogenesis of cigarette smoke (CS)-induced COPD. Nuclear receptor 77 (Nur77) participates in a number of biological processes, including apoptosis, autophagy and in disease pathogenesis; however, the role of Nur77 in COPD remains unknown. Thus, in this study, we aimed to elucidate the role of Nur77 in COPD. We report that CS promotes Nur77 expression and nuclear export in vivo and in vitro, which increases cigarette smoke extract (CSE)-induced autophagy. In addition, we found that lung tissues, human bronchial epithelial (HBE) cells and A549 cells exposed to CS or CSE expressed lower levels of LC3 and Beclin-1 and contained fewer autophagosomes following Nur77 knockdown with siRNA-Nur77. Moreover, a co-immunoprecipitation assay demonstrated that CSE promoted autophagy, partly by accelerating the interaction between Nur77 and Bcl2, in turn leading to the increased dissociation of Bcl2 from Beclin-1; by contrast, leptomycin B (LMB) suppressed the dissociation of Bcl2 from Beclin-1. Taken together, the findings of this study demonstrate that Nur77 is involved in the CSE-induced autophagic death of lung cells, and that this process is partially dependent on the increased interaction between Nur77 and Bcl2, and on the dissociation of Bcl2 from Beclin-1. This study illustrates the role of Nur77 in bronchial and alveolar destruction following exposure to CS.