DNA methylation and not H3K4 trimethylation dictates the expression status of miR-152 gene which inhibits migration of breast cancer cells via DNMT1/CDH1 loop.

MicroRNAs (miRNA) are small non-coding RNAs which targets most protein-coding transcripts (mRNA) and destroy them. Thus miRNA controls the abundance of those specific proteins and impact on developmental, physiological and pathological processes. Dysregulation of miRNA function thus may lead to various clinicopathological complications, including breast cancer. Silencing of miR-152 gene due to promoter DNA methylation alter the expression pattern of several other genes. E-cadherin (CDH1) forms the core of adherent junctions between surrounding epithelial cells, link with actin cytoskeleton and affects cell signaling. CDH1 gene is down regulated by promoter DNA methylation during cancer progression. In this investigation, we attempt to elucidate the correlation of miR-152 and CDH1 function, as it is well known that the loss of CDH1 function is one of the major reasons for cancer metastasis and aggressiveness of spreading. For the first time we have shown that loss of CDH1 expression is directly proportional to the loss of miR-152 function in breast cancer cells. mRNA and protein expression profile of DNMT1 implicate that miR-152 targets DNMT1 mRNA and inhibits its protein expression. Tracing the molecular marks on DNA and histone 3 for understanding the mechanism of gene regulation by ChIP analyses leads to a paradoxical result that shows DNA methylation adjacent to active histone marking (enrichment of H3K4me3) silence miR-152 gene. Further experiments revealed that DNMT1 plays crucial role for regulation of miR-152 gene. When DNMT1 protein function is blocked miR-152 expression prevails and destroys the mRNA of DNMT1; this molecular regulatory mechanism is creating a cyclic feedback loop, which is now focused as DNMT1/miR-152 switch for on/off of DNMT1 target genes. We discovered modulation of CDH1 gene expression by DNMT1/miR-152 switches. We have demonstrated further that DNMT1 down regulation mediated upregulation of CDH1 (hereafter, DNMT1/CDH1 loop) in presence of ectopic-excess of miR-152 prevents migration of cancer cells. Our data provides novel insights into the regulation mechanism of miRNA and mRNA/protein coding genes and enhances the amplitude of cancer epigenome.