Mechanism Of MicroRAN-545Inhibiting Lung Cancer Cell Proliferation

MicroRNAs (miRNAs) are a class of small noncoding RNA of about22nt long. MiRNAs can inhibit mRNA translation or cause mRNA degradation by binding with their3’UTR. An increasing number of studies have shown that miRNAs are involved in biological process such as cell proliferation, differentiation and apoptosis; therefore aberrant expression of miRNAs may cause cancer.Lung cancer causes a leading death rate among all types of cancers and accumulating studies have proved that tumor proliferation and progression are relative to miRNAs. Considering that hundreds of miRNAs exist in human genome, we decided to perform a miRNA profile in tumor tissue and normal lung tissue. We found that31miRNAs are underexpressed. To further study the function of these miRNAs in lung cancer cell proliferation, we performed a further screen and transfected these miRNAs into A549and H460cells, and found that miR-545could significantly inhibit cell proliferation. We studied the mechanism with EdU incorporation assay and found miR-545could suppress DNA synthesis. We assumed that miR-545might affect cell cycle. We then found miR-545caused cell cycle arrest at G0/G1phase. Additionally, we found miRNA causes A549cell apoptosis.Furthermore, we studied the mechanism by which miR-545caused cell cycle arrest. We used Targetscan, an online program, to predict target genes of miR-545, and found cyclin D1and CDK4as candidates. We found miR-545could suppress cyclin D1and CDK4expression, whereas inhibition of miR-545promoted cyclin D1and CDK4expression in HFL1cells. Our dual-luciferase assay showed that miR-545suppressed cyclin D1and CDK4by binding to their3’UTR. This proved that cyclin D1and CDK4were direct targets of miR-545. We used siRNAs to inhibit cyclin D1and CDK4expression, this caused the inhibition of cell proliferation, cell cycle at G1phase and cell apoptosis. This suggested that miR-545supressed cell proliferation by inhibiting cyclin D1and CDK4expression.In addition, we found CpG islands in the promoter region of miR-545, which indicated that miR-545expression might be regulated by promoter methylation. but our study did not proved miR-545expression be modulated by promoter methylation.