Background: Metastasis and relapse of lung cancer are the main cause of disease-related deaths. It’s reported that tumor metastasis and relapse originated from cancer stem cells (CSCs) which possess more potential in proliferation and invasion. In our previous studies, we established a conditional BME-based three-dimensional culture (3D culture) system to mimic the growth environment in vivo and further amplified lung cancer stem cells (LCSCs) in our system. However, the molecular mechanisms of the amplification and development of LCSCs in our 3D culture system are still not very clear.
Methods: We tested the expression of Lin28 and let7 by western blot and qPCR, and constructed A549 cells either knockdown of Lin28 or overexpression of let7, followed by investigating the expression of stemness markers by flow cytometry and qPCR, and stem cell like phenotypes including cell proliferation, colony formation, mammosphere culture, cell apoptosis, migration, invasion and drug resistance in vitro, as well as tumorigenicity in vivo.
Results: Here we observed Lin28A/let-7c was dysregulated in LCSCs both from the 3D culture system and from lung cancer tissues. Further, the abnormal expression of Lin28A/let-7c was correlated with poor survival outcomes. We found over-expression let-7c inhibited the maintenance of LCSC properties, while the results for knockdown of Lin28A showed Lin28A was critical for the enrichment and amplification of LCSCs via MAPK signaling pathway. Importantly, we found that either knockdown of Lin28A or over-expression of let-7c inhibited carcinogenesis and disrupted LCSC expansion in vivo.
Conclusions: Our study uncovered the functions and mechanisms of the "Lin28A/let-7c/MAPK" signaling pathway in promoting the amplification and cancer stemness of LCSCs, which might be a potential therapeutic target for lung cancer therapy by reducing and even eliminating LCSCs in the future.