Metformin mediated reversal of epithelial to mesenchymal transition is triggered by epigenetic changes in E-cadherin promoter

Epithelial-mesenchymal transition (EMT) is one of the key biological phenomena behind cancer and metastasis. Clinical studies suggest that patients undergoing metformin therapy are less predisposed to cancer but the underlying mechanism is far from clear. Given that metformin also acts as TGF-beta inhibitor, we sought to explore whether and how metformin could modulate EMT in a cancer like microenvironment. Our data using human cell lines revealed that metformin induced a distinct change from stromal-shaped mesenchymal cells to cuboidal-shaped epithelial cells with upregulation of epithelial markers and mitigation of their invasive property. One of the key regulatory pathways, which intersect tumorigenesis and metformin activity, is AMPK. We demonstrated that metformin attenuates ERK signaling by activating AMPK pathway leading to suppression of Snail and Slug resulting in upregulation of crucial tumor suppressor gene E-cadherin. ChIP assay confirmed insufficient binding of repressors like Slug to the E-cadherin promoter. Further, our data revealed reduction in HDAC activity prompting hypomethylation of E-cadherin promoter thus reflecting an epigenetic modification. To expand the translational significance of the study we verified these findings in diabetic patients undergoing metformin treatment. To our knowledge this is the first report representing an inverse relationship of AMPK and ERK signaling axis in promoting mesenchymal to epithelial transition (MET) via reexpression of E-cadherin upon metformin treatment thus rationalizing lower incidence of cancer in metforminadministered patients. Metformin promotes reversal of the epithelial-mesenchymal transition. Metformin attenuates ERK signaling by activating AMP kinase. Metformin induces hypomethylation of the E-cadherin gene promoter. Epigenetic modification of the E-cadherin promoter was observed in leukocytes from diabetic subjects. These findings provide a potential basis for decreased cancer incidence in metformin-treated subjects.