Physalin A regulates the Nrf2 pathway through ERK and p38 for induction of detoxifying enzymes

BACKGROUND: Physalin A isolated from Physalis alkekengi var. franchetii has been known to have many pharmacological properties. However, its effect through the Nrf2 pathway has not yet been elucidated. In the present study, we determined the effects of physalin A on cancer chemoprevention via the Nrf2 pathway. METHODS: Experiments were performed in Hepa-1c1c7 and HepG2 cells. The quinone reductase (QR) activity assay was used to assess the activity of physalin A and other compounds isolated from P. alkekengi. The antioxidant response element (ARE) reporter assay was used to determine physalin A induced transcription of Nrf2 target genes, whereas the oligonucleotide pull-down assay was used to investigate Nrf2 binding to the AREs post physalin A treatment. Real-time PCR and western blotting were performed to determine the expression of Nrf2 target genes. Immunocytochemistry was used to determine Nrf2 localization after treatment with physalin A. Kinase inhibitors were used to test the involvement of Nrf2-targeting kinases and the role of ERK and p38 phosphorylation was confirmed using western blotting. RESULTS: Physalin A significantly induced QR activity. As an upstream effector of QR, Nrf2 induced genes containing the ARE, which encode various antioxidants and detoxification enzymes. We observed that physalin A increased the expression of Nrf2 and its target genes in HepG2 cells. Moreover, we observed that physalin A-induced Nrf2 activation was regulated by ERK and p38 kinase in HepG2 cells. CONCLUSIONS: Taken together, we showed that physalin A increased detoxifying enzyme expression via activation of Nrf2 and its target genes. These results imply that physalin A could be a potential chemopreventive agent for liver diseases, as well as cancer.