p21 promotes gemcitabine tolerance in A549 cells by inhibiting DNA damage and altering the cell cycle.

Gemcitabine is one of the most widely used chemotherapy drugs for advanced malignant tumors, including non-small cell lung cancer. However, the clinical efficacy of gemcitabine is limited due to drug resistance. The aim of the present study was to investigate the role of p21 in gemcitabine-resistant A549 (A549/G+) lung cancer cells. IC50 values were determined using a Cell Counting Kit-8 (CCK-8) assay. mRNA and protein expression levels of genes were measured by reverse transcription-quantitative PCR and western blotting, respectively. The cell cycle distribution and apoptosis rate were analyzed by flow cytometry. DNA damage in cells was evaluated by single-cell gel electrophoresis. The results of western blot analysis and the CCK-8 assay demonstrated that the expression of p21 was higher in A549/G+ cells than in gemcitabine-sensitive cells. Knockdown of p21 expression in gemcitabine-resistant cells sensitized these cells to gemcitabine (with the IC50 decreasing from 84.2 to 26.7 µM). Cell cycle analysis revealed different changes in the cell cycle distribution in A549/G+ cells treated with the same concentration of gemcitabine, and decreased expression of p21 was shown to promote G1 arrest. The apoptosis assay and comet assay results revealed that decreased p21 expression resulted in accumulation of unrepaired DNA double-strand breaks (DSBs) and induction of apoptosis by gemcitabine. The present study demonstrated that knockout of p21 mRNA expression in A549/G+ cells promotes apoptosis and DNA DSB accumulation, accompanied by G1 arrest. These results indicated that p21 is involved in regulating the response of A549 cells to gemcitabine.

MiR-17- 5p/RRM2 regulated gemcitabine resistance in lung cancer A549 cells.

The main objective of this study is to investigate the regulatory roles of the miR-17-5p/RRM2 axis in A549/G+ cells' gemcitabine resistance. The cell viability was determined using CCK8 and clonogenic assays. Gene expression level analysis by RT-qPCR and Western blotting. Cell cycle analysis by flow cytometry. The dual luciferase activity assay was used to verify the target gene of miR-17-5p. In gemcitabine-resistant cell line A549G+, the drug resistance decreased after up-regulation of MiR-17-5p expression. The proportion of cell cycle G1 phase increased, and the S phase decreased. The expression level of cell cycle-related proteins CCNE1, CCNA2, and P21 decreased. The opposite results emerged after the down-regulation of MiR-17-5p expression in gemcitabine-sensitive cell line A549G-. The expression levels of PTEN and PIK3 in A549G+ cells were higher than in A549G-cells, but p-PTEN was lower than that in A549G-. After up-regulating the expression of MiR-17-5p in A549G+, the expression levels of p-PTEN increased, and the expression level of p-AKT decreased. After down-regulating miR-17-5p expression, the opposite results emerged. The dual-luciferase reporter assay and restorative experiments proved that RRM2 is one of the target genes for MiR-17-5p. Our results suggested that the miR-17-5p/RRM2 axis could adjust gemcitabine resistance in A549 cells, and the p-PTEN/PI3K/AKT signal pathway might be involved in this regulatory mechanism.

Chloroquine increases the anti-cancer activity of epirubicin in A549 lung cancer cells.

The present study investigated whether the autophagy inhibitor chloroquine (CQ) can improve the sensitivity of the A549 lung cancer cell line to epirubicin (EPI). The Cell Counting Kit 8 (CCK8) assay was used to determine the EPI IC50 in A549 cells treated for 72 h. A549 cells were treated with Western blot analysis was performed to detect the expression level of the autophagy-associated protein, microtubule associated protein 1 light chain 3 ß (LC3B), and apoptosis-associated proteins such as cleaved caspase-9 and cleaved caspase-3. CCK8, colony formation, wound healing and Transwell assays were performed to analyze cell proliferation, migration and invasion capacity. Reverse transcription-quantitative PCR (RT-qPCR) was used to analyze the mRNA expression levels of LC3B and beclin-1, and the apoptosis rate was analyzed by flow cytometry. The IC50 of EPI was 0.03 µg/ml. The CCK8 results demonstrated that the cell survival rate was lower in CQ + EPI-treated cells when compared with the individual treatment groups. The colony formation results revealed that the number of clones in the EPI + CQ-treated group was reduced compared with EPI or CQ treatment alone. The wound healing assay revealed that migration was reduced in the EPI + CQ-treated group compared with the other treatment groups, and the Transwell results indicated that the number of cells passing through the Matrigel and membrane was lowest in the CQ + EPI treatment group. The mRNA expression levels of LC3B and beclin-1 were increased in the CQ + EPI group by 51.5 and 61.2%, respectively, when compared with the control group. The results indicated that LC3B protein expression was enhanced by EPI in a concentration-dependent manner, and the protein levels of cleaved caspase-3 and cleaved caspase-9 were higher in the combination group than in the EPI alone group. The flow cytometry results demonstrated that the apoptosis rate was highest in the EPI + CQ group. In conclusion, the autophagy inhibitor CQ increased the sensitivity of A549 cells to EPI, and the underlying mechanism of action may be associated with the activation of apoptosis.

Screening miRNAs associated with resistance gemcitabine from exosomes in A549 lung cancer cells.

PURPOSE: To establish a gemcitabine-resistant lung adenocarcinoma cell line, A549/G+, and to screen the differences of miRNA expression in exosomes from A549 and A549/G+ cells. METHODS: A549 cells were exposed in gemcitabine until they were resistant to gemcitabine, and extracted exosomes from A549 and A549/G+. The RNAs from exosomes were subjected to miRNA expression microarray experiments. RESULTS: After 39 weeks of continuous induction, we induced drug resistance in A549 cells. The resistance index was 6. Via GeneChip miRNA 4.0 analysis, there were 446 differential miRNAs between A549 and A549/G+. Target gene prediction and pathway analysis discovered the microRNAs in the intersections may participate in drug resistance. CONCLUSION: These differential miRNAs help to do in-depth research to elucidate the mechanism of resistance to gemcitabine in non-small cell lung cancer.