A SUMOylation-dependent pathway regulates SIRT1 transcription and lung cancer metastasis.

BACKGROUND Epithelial-to-mesenchymal transition (EMT) plays a pivotal role in lung cancer metastasis. The class III deacetylase sirtuin 1 (SIRT1) possesses both pro- and anticarcinogenic properties. The role of SIRT1 in lung cancer EMT is largely undefined. METHODS The effect of SIRT1 on migration of lung cancer cells was evaluated by wound healing assay in vitro and metastasis assay in nude mice in vivo. Protein expression in human lung cancers and cultured lung cancer cells was assessed by western blotting and immunohistochemistry. Interaction between protein and DNA was measured by chromatin immunoprecipitation assay. SIRT1 promoter activity was determined by reporter assay. RESULTS SIRT1 activation antagonized migration of lung cancer cells by suppressing EMT in vitro. Activation of SIRT1 by resveratrol also statistically significantly hampered (by 68.33%; P < .001, two-sided test) lung cancer cell metastasis in vivo. Hypoxia repressed SIRT1 transcription through promoting the competition between Sp1 and HIC1 on the SIRT1 proximal promoter in a SUMOylation-dependent manner. Disruption of SUMOylation by targeting either Ubc9 or PIASy restored SIRT1 expression in and favored an epithelial-like phenotype of cancer cells, thereby preventing metastasis. Decreased SIRT1 combined with elevated PIASy expression was implicated in more-invasive types of lung cancers in humans. CONCLUSIONS We have identified a novel pathway that links SIRT1 down-regulation to hypoxia-induced EMT in lung cancer cells and may shed light on the development of novel antitumor therapeutics.