Lung CSC-derived exosomal miR-210-3p contributes to a pro-metastatic phenotype in lung cancer by targeting FGFRL1

Lung cancer has the highest mortality rate among human cancers, and the majority of deaths can be attributed to metastatic spread. Lung cancer stem cells (CSCs) are a component of the tumour microenvironment that contributes to this process. Exosomes are small membrane vesicles secreted by all types of cells that mediate cell interactions, including cancer metastasis. Here, we show that lung CSC-derived exosomes promote the migration and invasion of lung cancer cells, up-regulate expression levels of N-cadherin, vimentin, MMP-9 and MMP-1, and down-regulate E-cadherin expression. Moreover, we verified that these exosomes contribute to a pro-metastatic phenotype in lung cancer cells via miR-210-3p transfer. The results of bioinformatics analysis and dual-luciferase reporter assays further indicated that miR-210-3p may bind to fibroblast growth factor receptor-like 1 (FGFRL1); silencing FGFRL1 enhanced the metastatic ability of lung cancer cells, whereas overexpressing FGFRL1 suppressed metastasis. Taken together, our results provide new insights into a potential molecular mechanism whereby lung CSC-derived exosomal miR-210-3p targets FGFRL1 to promote lung cancer metastasis. FGFRL1 may be a promising therapeutic target in lung cancer.

Role of YAP in lung cancer resistance to cisplatin

Yes-associated protein (YAP) serves a critical role in the initiation and progression of a variety of types of cancer via modulating the expression of genes involved in cell proliferation and the downregulation of apoptosis. Recent studies have suggested that YAP is responsible for the development of drug resistance and cancer metastasis and recurrence. However, the association between YAP and chemoresistance in lung cancer, particularly in lung cancer stem cells (LCSCs) remains largely unknown. In the current study, lung cancer cell spheres were established using the A549 cell line, which demonstrated stem cell properties. It was revealed that YAP was overexpressed in lung cancer spheres compared with normal A549 adherent cells and was associated with enhanced cisplatin (CDDP) resistance. Knockdown of YAP effectively sensitized the adherent A549 and tumor spheres to CDDP treatment and resulted in enhanced cell death. These results suggest that YAP serves a critical role in LCSCs drug resistance and YAP targeting could become a promising adjuvant to current the chemotherapy for lung cancer.

Isolation, cultivation and identification of human lung adenocarcinoma stem cells

Recently, an increasing number of studies have demonstrated that lung cancer is a stem cell disease. However, ideal cell surface markers for isolating stem cells in lung cancer are yet to be identified. In the present study, a cell population with a cluster of differentiation (CD)133⁺ phenotype was successfully isolated from a single cell suspension of lung adenocarcinoma tissue using magnetic-activated cell sorting (MACS) and enriched in a serum-free culture. In comparison to CD133^- cells, the CD133⁺ cells exhibited an enhanced capacity for self-renewal and differentiation, and a greater potential for in vivo tumor formation, in non-obese diabetic/severe combined immunodeficient (NOD/SCID) mice. Tumors could be induced in NOD/SCID mice by the transplantation of 10² stem-like cells per mouse. The results of the present study demonstrated that CD133 may serve as a specific cell surface marker for lung adenocarcinoma stem cells, and that MACS combined with serum-free culture is an effective method for isolating and enriching lung cancer stem cells.

IL-6 enriched lung cancer stem-like cell population by inhibition of cell cycle regulators via DNMT1 upregulation

Tumors are influenced by a microenvironment rich in inflammatory cytokines, growth factors and chemokines, which may promote tumor growth. Interleukin-6 (IL-6) is a multifunctional cytokine and known as a regulator of immune and inflammation responses. IL-6 has also been reported to be associated with tumor progression and chemoresistance in different types of cancers. In our study, we demonstrated that IL-6 enriches the properties of lung cancer stem-like cells in A549 lung cancer cells cultured in spheroid medium. IL-6 also promotes sphere formation and stem-like properties of A549 cells by enhancing cell proliferation. Methylation-specific polymerase chain reaction (PCR) was performed and revealed that IL-6 increased methylation of p53 and p21 in A549 cancer cells. Western blot analysis and quantitative real-time PCR demonstrated that IL-6 increased the expression of DNA methyltransferase 1 (DNMT1) in A549 cells cultured in spheroid medium, but not the expression of DNMT3a or DNMT3b. Knockdown of DNMT1 eliminated IL-6-mediated hypermethylation of cell cycle regulators and enrichment of lung cancer stem-like properties. In conclusion, our study, for the first time, shows that the IL-6/JAK2/STAT3 pathway upregulates DNMT1 and enhances cancer initiation and lung cancer stem cell (CSC) proliferation by downregulation of p53 and p21 resulting from DNA hypermethylation. Upon blockage of the IL-6/JAK2/STAT3 pathway and inhibition of DNMT1, the proliferation of lung CSCs was reduced and their formation of spheres and ability to initiate tumor growth were decreased. These data suggest that targeting of the IL-6/JAK2/STAT3 signaling pathway and DNMT1 may become important strategies for treating lung cancer.