An NF-kappaB- and IKK-Independent Function of NEMO Prevents Hepatocarcinogenesis by Suppressing Compensatory Liver...

The IκBKinase (IKK) complex represents a central signaling nexus in the TNF-dependent activation of the pro-inflammatory NF-κB pathway. However, recent studies suggested that the distinct IKK subunits (IKK, IKK, and NEMO) might withhold additional NF-κB-independent functions in inflammation and cancer. Here, we generated mice lacking all three IKK subunits in liver parenchymal cells (LPC) (IKK//NEMO^LPC-KO) and compared their phenotype with mice lacking both catalytic subunits (IKK/^LPC-KO), allowing to functionally dissect putative I-κB-Kinase-independent functions of the regulatory subunit NEMO. We show that the additional deletion of NEMO rescues IKK/^LPC-KO mice from lethal cholestasis and biliary ductopenia by triggering LPC apoptosis and inducing a strong compensatory proliferation of LPC including cholangiocytes. Beyond this beneficial effect, we show that increased hepatocyte cell-death and compensatory proliferation inhibit the activation of LPC-necroptosis but trigger spontaneous hepatocarcinogenesis in IKK//NEMO^LPC-KO mice. Collectively, our data show that free NEMO molecules unbound to the catalytic IKK subunits control LPC programmed cell death pathways and proliferation, cholestasis and hepatocarcinogenesis independently of an IKK-related function. These findings support the idea of different functional levels at which NEMO controls inflammation and cancer in the liver.