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[FOXC1 Knockdown Reverses Gefitinib Resistance in Non-small Cell Lung Cancer].

BACKGROUND
Lung cancer is the malignant tumor with the highest incidence and mortality in China, among which Non-small cell lung cancer (NSCLC) accounts for about 80%. Epidermal growth factor receptor-tyrosine kinase inhibitor (EGFR-TKI) targeted therapy has been playing an important role in treatment of NSCLC. However, unavoidable therapeutic resistance significantly limits the clinical efficacy of EGFR-TKI. As a key member of the forkhead box protein family, FOXC1 is aberrantly expressed in NSCLC and involved in NSCLC progression. The aim of this work is to investigate the effect and potential mechanism of FOXC1 on gefitinib resistance in NSCLC.


METHODS
Western blot was performed to assess the expression of FOXC1 protein in HCC827/GR cells. Immunohistochemistry (IHC) assays were performed in human NSCLC tissues with gefitinib resistance. HCC827/GR cells were transfected with shRNA specifically targeting FOXC1 mRNA and stable cell lines were established. The effects of FOXC1 on cell viability and apoptosis were analyzed using MTT assays and flow cytometry. Self-renewal ability was determined by mammosphere-formation analysis. Quantitative real-time PCR (RT-qPCR) and Western blot were employed to detect the expression of SOX2, Nanog, OCT4 and CD133. Flow cytometry analysis were further used to detect the level of CD133. IHC assays were used to detect the levels of SOX2 and CD133 in NSCLC tissues with genfitiinb resistance. Correlations of the expressions of FOXC1, CD133 and SOX2 with each other in lung adenocarcinoma samples were analyzed based on The Cancer Genome Atlas (TCGA) database.


RESULTS
The expression of FOXC1 is significantly increased in HCC827/GR cells compared with HCC827 cells (P<0.05). IHC results showed FOXC1 was highly expressed in NSCLC tissues with gefitinib resisitance. Knockdown of FOXC1 significantly increased the sensitivity of HCC827/GR cells to gefitinib. The cell viability was decreased and the apoptosis was promoted (P<0.05). Moreover, FOXC1 knockdown apparently inhibited the expression of SOX2 and CD133, and decreased the mammosphere-formation capacity in HCC827/GR cells. In NSCLC tissues with gefitinib resistance, the expressions of SOX2 and CD133 were significantly higher compared with gefitinib-sensitive tissues (P<0.01). Meanwhile, the expressions of FOXC1, CD133 and SOX2 with each other were positively correlated (P<0.05).


CONCLUSIONS
FOXC1 could increase gefitinib resitance in NSCLC, by which mechanism is related to the regulation of cancer stem cell properties.