Hepatic NOD2 promotes hepatocarcinogenesis via a RIP2-mediated proinflammatory response and a novel nuclear autophagy-mediated DNA damage mechanism

Background: Key hepatic molecules linking gut dysbiosis and hepatocarcinogenesis remain largely unknown. Gut-derived gut microbiota contains pathogen-associated molecular patterns (PAMPs) that may circulate into the liver and, consequently, be recognized by hepatic Pattern Recognition Receptors (PRRs). NOD2, a general intracellular PRR, recognizes muramyl dipeptide (MDP), present in both gram (+) and gram (-) bacteria. Here, we investigated the role of NOD2 as a molecular sensor translating gut dysbiosis signaling into hepatocarcinogenesis.

Methods: NOD2 expression was measured in clinical hepatocellular carcinoma (HCC) samples using qPCR (80 pairs), western blotting (30 pairs) and immunostaining (141 pairs). The role of NOD2 in hepatocarcinogenesis was examined in the hepatocyte-specific Nod2-knockout (NOD2^△hep), Rip2-knockout (Rip2^△hep), Lamin A/C-knockout (Lamn^△hep) and Rip2/Lamin A/C double-knockout (Rip2/Lamn^△hep) mice models of diethylnitrosamine (DEN)/CCl₄-induced HCC.

Results: NOD2 was upregulated and activated in HCC samples, and high NOD2 expression correlated with poor prognosis in HCC patients. Hepatic NOD2 deletion in vivo decreased DEN/CCl₄-induced HCC by reducing the inflammatory response, DNA damage and genomic instability. NOD2 activation increased liver inflammation via RIP2-dependent activation of the MAPK, NF-κB and STAT3 pathways. Notably, a novel RIP2-independent mechanism was discovered, whereby NOD2 activation induces the nuclear Autophagy pathway. We showed that NOD2 undergoes nuclear transport and directly binds to a component of nuclear laminae, lamin A/C, to promote its protein degradation, leading to impaired DNA damage repair and increased genomic instability.

Conclusions: We reveal a novel bridge, Bacterial sensor NOD2, linking gut-derived microbial metabolites to hepatocarcinogenesis via induction of the inflammatory response and nuclear Autophagy. Thus, we propose hepatic NOD2 as a promising therapeutic target against HCC.