BAP1 Downregulates NRF2 Target Genes and Exerts Anti-Tumorigenic Effects by Deubiquitinating KEAP1 in Lung Adenocarcinoma

KELCH-ECH-associated protein 1 (KEAP1) is an adaptor protein of Cullin 3 (CUL3) E3 ubiquitin ligase that targets a redox sensitive transcription factor, NF-E2-related factor 2 (NRF2). BRCA1-associated protein 1 (BAP1) is a tumor suppressor and deubiquitinase whose mutations increase the risk of several types of familial cancers. In the present study, we have identified that BAP1 deubiquitinates KEAP1 by binding to the BTB domain. Lentiviral transduction of BAP1 decreased the expression of NRF2 target genes, suppressed the migration and invasion, and sensitized cisplatin-induced apoptosis in human lung adenocarcinoma (LUAD) A549 cells. Examination of the lung tissues in Kras(G12D/+) mice demonstrated that the level of Bap1 and Keap1 mRNAs progressively decreases during lung tumor progression, and it is correlated with NRF2 activation and the inhibition of oxidative stress. Supporting this observation, lentiviral transduction of BAP1 decreased the growth of A549 xenografts in athymic nude mice. Transcriptome analysis of human lung tissues showed that the levels of Bap1 mRNA are significantly higher in normal samples than LUAD samples. Moreover, the expression of Bap1 mRNA is associated with a better survival of LUAD patients. Together, our study demonstrates that KEAP1 deubiquitination by BAP1 is novel tumor suppressive mechanism of LUAD.