Foxp3 overexpression decreases sensitivity to chemotherapy in mouse Lewis lung cancer cells

Chemotherapy is the main strategy for the treatment of lung cancer. However, sensitivity to chemotherapy, one of the main factors affecting the survival rate of patients with lung cancer, is extremely poor. Forkhead box P3 (Foxp3) is the key regulatory gene for the development and function of CD4+CD25+ regulatory T cells (Tregs). Increased levels of Tregs and Foxp3 expression in the peripheral blood and tumour specimens of cancer patients are associated with tumour progression and poor prognosis. In addition, certain studies have suggested that Tregs may be resistant to conventional chemotherapy and thus, enhance tumour immune evasion. Previous studies have demonstrated that Foxp3 is also expressed within tumour cells and that it may mimic the function of Tregs. Currently, the correlation between the tumour cell expression of Foxp3 and sensitivity to chemotherapy is unclear. Therefore, it was hypothesised that Foxp3 causes resistance to chemotherapeutic agents in lung cancer cells and that it may consequently promote the progression of lung cancer. In the current study, the expression of Foxp3 in mouse Lewis lung cancer (LLC) cells was detected using RT-PCR and immunocytochemistry. The overexpression of Foxp3, which was accomplished by the transient transfection of recombinant pcDNA3.1-Foxp3 or empty plasmids into LLC cells, was confirmed by RT-PCR and western blot analysis. The inhibition of cell proliferation was measured using MTT assay. The expression of multidrug resistance protein 1 (mdr1) mRNA and its protein product, P-glycoprotein (P-gp), were detected by RT-PCR and flow cytometry, respectively. The results revealed that Foxp3 was expressed by LLC cells. The inhibitory rate of cell proliferation in Foxp3-overexpressing LLC cells compared with those transfected with an empty plasmid was significantly decreased following adriamycin (ADM) and mitomycin C (MMC) treatment. The IC50 values of ADM and MMC in Foxp3-overexpressing LLC cells were increased. The expression levels of mdr1 mRNA and P-gp were significantly upregulated in Foxp3 overexpressing LLC cells. These results suggest that Foxp3 reduces the sensitivity of LLC cells to ADM and MMC, thus promoting tumour progression, by upregulating the expression of mdr1 mRNA and P-gp.