TBX1 functions as a tumor suppressor in thyroid cancer through inhibiting the activities of PI3K/AKT and MAPK/ERK pathways.

BACKGROUND: TBX1 is a member of the T-box family of transcription factors characterized by a conserved DNA binding domain termed T-box. TBX1 has been reported to be downregulated in mouse skin tumors, and negatively regulated tumor cell growth; however, its role and exact mechanism in human cancers including thyroid cancer remain totally unknown.

METHODS: Quantitative RT-PCR (qRT-PCR) and western blot assays were performed to evaluate the expression of investigated genes. Methylation-specific PCR (MSP) and pyrosequencing were used to analyze TBX1 promoter methylation. The biological functions of TBX1 in thyroid cancer cells were determine by a series of in vitro and in vivo experiments. Chromatin immunoprecipitation Sequencing (ChIP-Seq) and dual-luciferase reporter assays were used to identify its downstream targets.

RESULTS: We demonstrated that TBX1 was frequently downregulated by promoter methylation in both papillary thyroid cancers (PTCs) and thyroid cancer cell lines. Ectopic expression of TBX1 in thyroid cancer cells dramatically inhibited cell viability, colony formation and tumorigenic potential in nude mice, and induced cell cycle arrest and apoptosis through modulating a panel of cell cycle- and apoptosis-related genes. In addition, ectopic expression of TBX1 significantly decreased migration and invasion potential of thyroid cancer cells through inhibiting the process of epithelial-mesenchymal transition (EMT) and the expression of matrix metalloproteinases (MMPs). On the other hand, TBX1 knockdown markedly promoted thyroid cancer cell viability and invasiveness. Mechanistically, TBX1 exerted its tumor suppressor function in thyroid cancer cells through inhibiting phosphorylation of AKT at Ser473 and ERK via regulating its downstream targets such as RNF41, PARK2 and PHLPP2.

CONCLUSIONS: Our data show that TBX1 is frequently inactivated by promoter methylation, and functions as a potential tumor suppressor in thyroid cancer through inhibiting the activities of PI3K/AKT and MAPK/ERK signaling pathways.