The lncRNA H19-derived miR-675 promotes liver necroptosis by targeting FADD

Chronic inflammation is closely linked to cancer formation. Many molecular pathways are involved in the inflammatory response and some of these including microRNAs, have been connected to liver cancer development. The H19 derived microRNA-675 (miR-675) has been implicated as both tumor promoter and tumor suppressor and plays a role in liver inflammation, which is not yet fully understood. We found that miR-675 promotes cell death in human hepatocellular carcinoma (HCC) cell lines. We show that FADD, a mediator of cell death signaling, is targeted and down regulated by miR-675. Importantly, we found a negative correlation between miR-675 and FADD expression in mouse models of HCC and in human samples. We demonstrate in a mouse model of liver inflammation that over expression of miR-675 represses FADD expression and promotes necrosis. We confirm both in vitro and in vivo that this necrotic cell death is necroptosis which can be inhibited by the necroptosis specific inhibitor Nec-1/Nec-1s.We show that necroptosis induced by miR-675 expression, is mediated by p-MLKL in lipopolysaccharide (LPS) induced liver inflammation. Furthermore, miR-675 enhanced MLKL binding to RIP3, key signaling molecules in necroptosis and inhibited cleaved caspase-8 & 3, suggesting that miR-675 may induce a “shift” from apoptotic cellular cascades to a necroptotic cellular pathway. In conclusion, down regulation of FADD by miR-675 promotes liver necroptosis in response to inflammatory signals. We propose that this regulation cascade could stimulate and enhance the inflammatory response in the liver, making miR-675 an important regulator in liver inflammation and potentially also in HCC.