SIRT7 promotes thyroid tumorigenesis through phosphorylation and activation of Akt and p70S6K1 via DBC1/SIRT1 axis

SIRT7 is an NAD+-dependent histone/non-histone deacetylase, which is highly expressed in different types of cancer including thyroid cancer; however, its biological function in thyroid cancer is still undiscovered. In this study, we found that SIRT7 expression was elevated in papillary thyroid cancers (PTCs), and demonstrated that SIRT7 knockdown dramatically inhibited the proliferation, colony formation, migration and invasion of thyroid cancer cells, and induced thyroid cancer cell cycle arrest and apoptosis. Conversely, SIRT7 re-expression markedly enhanced thyroid cancer cell growth, invasiveness and tumorigenic potential in nude mice. Further studies revealed that SIRT7 exerted an oncogenic function in thyroid tumorigenesis by phosphorylation of Akt and p70S6K1. Mechanistically, SIRT7 binds to the promoter of deleted in breast cancer-1 (DBC1), an endogenous inhibitor of SIRT1, and represses its transcription via deacetylation of H3K18Ac. This results in enhanced interactions between SIRT1 and Akt or p70S6K1, thereby promoting deacetylation and subsequent phosphorylation of Akt and p70S6K1 through a SIRT1-dependent manner. Altogether, our results show that DBC1 is a downstream target of SIRT7, and first uncover that SIRT7 promotes thyroid tumorigenesis through phosphorylation and activation of Akt and p70S6K1 via the modulation of DBC1/SIRT1 axis.