Background: TTF-1 inhibits lung cancer progression via HMGA2 down-regulation. Results: TTF-1 up-regulates miR-33a, which in turn directly represses HMGA2. Conclusion:The signaling axis of TTF-1 to HMGA2, important in controlling lung cancer metastasis, is mediated by miR-33a. Significance: This study explains the mechanism of HMGA2 suppression by TTF-1.

Through both gain- and loss-of-TTF-1 expression strategies, we show that TTF-1 positively regulates vascular endothelial growth factor (VEGF) and that the VEGF promoter element contains multiple TTF-1-responsive sequences. The major signaling receptor for VEGF, i.e VEGFR2, also appears to be under a direct and positive regulation of TTF-1. The TTF-1-dependent upregulation of VEGF was moderately sensitive to rapamycin, implicating a partial involvement of mammalian target of rapamycin (mTOR). However, hypoxia did not further increase the secreted VEGF level of the TTF-1+ lung cancer cells. The TTF-1-induced VEGF upregulation occurs in both compartments (exosomes and exosome-depleted media (EDM)) of the conditioned media. Surprisingly, the EDM of TTF-1+ lung cancer cells (designated EDM-TTF-1+) displayed an anti-angiogenic activity in the endothelial cell tube formation assay. Mechanistic studies suggest that the increased granulocyte-macrophage colony-stimulating factor (GM-CSF) level in the EDM-TTF-1+ conferred the antiangiogenic activities. In human lung cancer, the expression of TTF-1 and GM-CSF exhibits a statistically significant and positive correlation. In summary, this study provides evidence that TTF-1 may reprogram lung cancer secreted proteome into an antiangiogenic state, offering a novel basis to account for the long-standing observation of favorable prognosis associated with TTF-1+ lung adenocarcinomas.