miRNA let-7a-3 overexpression in lung cancer cell line A549

MicroRNAs (miRNAs) are small non-coding RNAs that repress their target mRNAs by complementary base pairing and induction of the RNAi pathway. It has been shown that miRNA expression can be regulated by DNA methylation and it has been suggested that altered miRNA gene methylation might contribute to human tumorigenesis. In this study, we show that the human let-7a-3 gene on chromosome 22q13.31 is associated with a CpG island. Let-7a-3 belongs to the archetypal let-7 miRNA gene family DNA methylation and was found to be methylated by the DNA methyltransferases DNMT1 and DNMT3B. The gene was heavily methylated in normal human tissues, but hypomethylated in some human lung adenocarcinomas. Let-7a-3 hypomethylation facilitated epigenetic reactivation of the gene and elevated expression of let-7a-3 in a human lung cancer cell line resulted in enhanced tumor phenotypes and oncogenic changes in transcription profiles. Keywords: genetic modification Gene expression analysis comprised 4 microarray hybridizations: 4 let-7a-3 transfected cell culture replicates and 4 parental cell culture replicates (controls). Each let-7a-3 expressing replicate was hybridized against a control replicate of the same cell line including a dye swap design. Rawdata gpr files were processed using software ArrayMagic (Buness et al. 2005) including VSN normalization available on Bioconductor open source software platform. Differentially expressed genes between let-7a-3 transfected and control cell lines were analyzed by LIMMA (Wettenhall and Smyth, 2004) considering biological replicates and dye swap design.