The Role And Possible Mechanisms Of MiR-125b In Drug Resistance Of Gastric Cancer Cell Lines

Drug resistance constitutes a major obstacle to successful chemotherapy in cancer patients. In many cases, chemotherapies fail because of drug resistance of cancer cells either intrinsic or acquired after an initial round of treatment. It is believed that most of clinical observed drug resistance of cancer patients belongs to acquired resistance. The genetic disorders mainly lie in intrinsic drug resistance of cancer cells, while acquired drug resistance of cancer cells is closely related to epigenetic abnormality of genes. Epigenetics abnormality does not involve DNA sequence changes, which through DNA methylation, histone modifications and the non-coding RNA regulation, playing an important role in modulating drug resistance of cancer cellsmicroRNAs (miRNAs) are short non-coding RNA molecules, which post-transcriptionally regulate genes expression and play crucial roles in diverse biological processes, such as development, differentiation, apoptosis and proliferation. Recent studies suggested that the acquisition of drug resistance by cancer cells might be modulated via the changes in miRNAs levels. Emerging evidence has shown that knock-down or re-expression of specific miRNAs by synthetic anti-sense oligonucleotides or miRNAs precusors or mimics could modulate drug resistance of cancer cells.Recently, the research on gastric cancer drug resistance related miRNAs was few. Studies showed that miR-15b,miR-16,miR-181b and miR-497 was downregulated in human gastric drug resistant cell line SGC-7901/VCR, upregulation of these above miRNAs could modulate the drug resistance phenotype via targeting the antiapoptotic BCL2. Here we further investigated the possible role of miRNAs in the development of drug resistance in human gastric cancer cell line SGC-7901/VCR.Methods:1. Using miRNAs microarray analysis combined with miRNA qRT-PCR to detect and verify miR-125b expression level between drug resistant and parental gastric and lung cancer cell line.2. Using in vitro drug sensitivity assay to detect the drug resistance phenotype changes of cancer cells via exogenous overexpression of miR-125b through transient transfection of the corresponding miRNA mimic.3. Using dual-luciferase activity assay to verify the target genes of miR-125b. Using Western blot analysis and apoptosis assay to elucidate the mechanism of miR-125b on modulating drug resistance.Results:1. miR-125b was downregulated in drug resistant cells SGC-7901/VCR which was concurrent with the upregulation of BCL2, MCL1 protein, compared with the parental gastric cancer cell line SGC-7901, respectively.2. Overexpression of miR-125b sensitized SGC7901/VCR cells to anticancer drugs.3. BCL2 and MCL1 were the direct target genes of miR-125b.4. Enforced miR-125b expression reduced BCL2 and MCL1 protein level and sensitized SGC7901/VCR to VCR-induced apoptosis.ConclusionOur findings first suggested that miR-125b could play a role in gastric cancer cell lines at least in part by modulation of apoptosis via targeting BCL2 and MCL1.