NEMO Prevents Steatohepatitis and Hepatocellular Carcinoma by Inhibiting RIPK1 Kinase Activity-Mediated Hepatocyte Apoptosis.
Bottom Line: Mice lacking NEMO in liver parenchymal cells (LPC) spontaneously develop steatohepatitis and hepatocellular carcinoma (HCC) suggesting that NF-κB prevents liver disease and cancer.Here, we show that complete NF-κB inhibition by combined LPC-specific ablation of RelA, c-Rel, and RelB did not phenocopy NEMO deficiency, but constitutively active IKK2-mediated NF-κB activation prevented hepatocellular damage and HCC in NEMO(LPC-KO) mice.Knock-in expression of kinase inactive receptor-interacting protein kinase 1 (RIPK1) prevented hepatocyte apoptosis and HCC, while RIPK1 ablation induced TNFR1-associated death domain protein (TRADD)-dependent hepatocyte apoptosis and liver tumors in NEMO(LPC-KO) mice, revealing distinct kinase-dependent and scaffolding functions of RIPK1.
Affiliation: Institute for Genetics, University of Cologne, 50674 Cologne, Germany; Cologne Excellence Cluster on Cellular Stress Responses in Aging-Associated Diseases (CECAD), University of Cologne, 50931 Cologne, Germany; Center for Molecular Medicine (CMMC), University of Cologne, 50931, Cologne, Germany.Show MeSH
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Mentions: Although NF-κB inhibition alone was not sufficient to cause liver tumors, impairment of NF-κB could contribute to the liver pathology of NEMOLPC-KO mice when combined with the loss of NF-κB-independent NEMO functions. To address this possibility, we examined whether enforced NF-κB activation in NEMO-deficient hepatocytes induced by the overexpression of a constitutively active IKK2 (IKK2ca) transgene (Sasaki et al., 2006) could rescue the liver phenotype of NEMOLPC-KO mice. Heterozygous expression of the R26-StopFL-IKK2ca transgene in NEMOLPC-KO;IKK2caLPC mice resulted in ∼5-fold increased IKK2 protein levels in the liver compared to endogenous IKK2 levels correlating with nuclear accumulation of RelA in hepatocytes (Figures 3A and S3A). Strikingly, serum ALT levels as well as hepatocyte apoptosis and proliferation, myeloid cell and HSC activation, and fibrosis were drastically reduced in 8-week-old NEMOLPC-KO;IKK2caLPC mice compared to NEMOLPC-KO (Figures 3B, 3C, and S3B, compare with Figures 1E and S1). Furthermore, NEMOLPC-KO;IKK2caLPC mice examined at the age of 12–16 months did not show macroscopically visible liver nodules and had markedly lower LW/BW ratio compared to NEMOLPC-KO mice (Figures 4A–4D). Histological analysis confirmed the lack of dysplastic nodules in livers from NEMOLPC-KO;IKK2caLPC mice (Figures 4E and S4A). Therefore, overexpression of IKK2ca prevented chronic hepatocellular damage and the development of HCC in NEMOLPC-KO mice.
Affiliation: Institute for Genetics, University of Cologne, 50674 Cologne, Germany; Cologne Excellence Cluster on Cellular Stress Responses in Aging-Associated Diseases (CECAD), University of Cologne, 50931 Cologne, Germany; Center for Molecular Medicine (CMMC), University of Cologne, 50931, Cologne, Germany.