TGF-β1 exposure induces epithelial to mesenchymal transition both in CSCs and non-CSCs of the A549 cell line, leading to an increase of migration ability in the CD133(+) A549 cell fraction

Metastasis is the leading cause of death by cancer. Non-small-cell lung cancer (NSCLC) represents nearly 85% of primary malignant lung tumours. Recent researches have demonstrated that epithelial-to-mesenchymal transition (EMT) plays a key role in the early process of metastasis of cancer cells. Transforming growth factor-β1 (TGF-β1) is the major inductor of EMT. The aim of this study is to investigate TGF-β1's effect on cancer stem cells (CSCs) identified as cells positive for CD133, side population (SP) and non-cancer stem cells (non-CSCs) identified as cells negative for CD133, and SP in the A549 cell line. We demonstrate that TGF-β1 induces EMT in both CSC and non-CSC A549 sublines, upregulating the expression of mesenchymal markers such as vimentin and Slug, and downregulating levels of epithelial markers such as e-cadherin and cytokeratins. CSC and non-CSC A549 sublines undergoing EMT show a strong migration and strong levels of MMP9 except for the CD133(−) cell fraction. OCT4 levels are strongly upregulated in all cell fractions except CD133(−) cells. On the contrary, wound size reveals that TGF-β1 enhances motility in wild-type A549 as well as CD133(+) and SP(+) cells. For CD133(−) and SP(−) cells, TGF-β1 exposure does not change the motility. Finally, assessment of growth kinetics reveals major colony-forming efficiency in CD133(+) A549 cells. In particular, SP(+) and SP(−) A549 cells show more efficiency to form colonies than untreated corresponding cells, while for CD133(−) cells no change in colony number was observable after TGF-β1 exposure. We conclude that it is possible to highlight different cell subpopulations with different grades of stemness. Each population seems to be involved in different biological mechanisms such as stemness maintenance, tumorigenicity, invasion and migration.