Inhibition of canonical IKK/NF-kB signaling in Hepatitis B Virus surface antigen transgenic mice drastically increases HCC development due to dysregulated Unfolded Protein Response control

Y Sunami; M Ringelhan; M Lu; N Hüser; E Kokai; F Leithäuser; J Kleeff; S Gul; S Wissel; D Hartmann; RM Schmid; H Friess; C Brunner; P Riedl; R Schirmbeck; P Strnad; M Heikenwälder; T Wirth

doi:10.1055/s-0034-1397179

Zeitschrift für Gastroenterologie, Inhaltsverzeichnis

Inhibition of canonical IKK/NF-kB signaling in Hepatitis B Virus surface antigen transgenic mice drastically increases HCC development due to dysregulated Unfolded Protein Response control

Y Sunami ¹^,², M Ringelhan ³^,⁴^,⁵, M Lu ¹, N Hüser ¹, E Kokai ², F Leithäuser ⁶, J Kleeff ¹, S Gul ², S Wissel ², D Hartmann ¹, RM Schmid ⁵, H Friess ¹, C Brunner ², P Riedl ⁷, R Schirmbeck ⁷, P Strnad ⁸, M Heikenwälder ³^,⁴, T Wirth ²

¹Klinikum rechts der Isar, Technische Universität München, Surgical Clinic and Polyclinic, Munich, Germany
²University of Ulm, Institute of Physiological Chemistry, Ulm, Germany
³Technische Universität München, Institute of Virology, Munich, Germany
⁴Helmholtz Zentrum München, Institute of Virology, Munich, Germany
⁵Klinikum rechts der Isar, Technische Universität München, II. Medical Clinic and Polyclinic, Munich, Germany
⁶University Hospital of Ulm, Institute of Pathology, Ulm, Germany
⁷University Hospital of Ulm, Internal Medicine I, Ulm, Germany
⁸University Hospital of Aachen, Medical Clinic III and IZKF, Aachen, Germany

Abstract

Background and Aims: Hepatitis B Virus (HBV) remains the most common risk factor for hepatocellular carcinoma (HCC). It has been suggested that, in addition to chronic inflammation, HBV viral products directly contribute in HBV-driven hepatocellular carcinogenesis. In patients with low HBV replication, it is proposed that accumulation of HBV surface antigen (HBsAg) in the endoplasmic reticulum (ER) of hepatocytes (referred to as “ground glass hepatocytes”) activates ER stress, directly driving carcinogenesis. In the ER stress response, NF-kB is known to be important for the control of the Unfolded Protein Response (UPR). The role of NF-kB signaling in HCC development has been reported to be on the one hand anti-tumorigenic, due to activation of critical survival signals in hepatocytes. On the other hand, NF-kB has also been identified as a tumor promoter due to its pro-inflammatory function. In this study, we investigate the role of hepatic NF-kB signaling in directly HBV-driven HCC development using mice overexpressing hepatitis B virus surface antigen (HBsAg).

Methods: HBsAg transgenic mice were crossed with animals expressing a dominant-negative mutant of IKK2 (an upstream kinase in canonical NF-kB signaling) under the control of tetracycline-inducible LAP-promoter to achieve inhibition of hepatocellular canonical NF-kB signaling.

Results: The incidence of HBsAg-driven hepatocellular carcinogenesis was dramatically increased at the age of 18 months, when canonical NF-kB signaling was inhibited. However, there was no significant change in inflammatory response such as T-lymphocyte or macrophage infiltration. In addition, MyD88 deficiency did not inhibit HBsAg-induced tumor development in mice. Our data suggest that the role of canonical NF-kB signaling in this model does not rely on changes in the inflammatory response, but disrupts UPR control in HBsAg-driven hepatocellular carcinogenesis. Consistently, in HBsAg mice, a critical UPR regulator BiP/GRP78 was not upregulated when canonical NF-kB system was blocked. Furthermore, ER stress-associated cell death factor CHOP was strongly expressed, pointing to a failure of UPR control. In addition, a massive oval cell reaction (ductular reaction) was induced in HBsAg transgenic mice upon inhibition of canonical NF-kB signaling, indicating extensive liver damage and lost capacity of hepatocytes to contribute to compensatory proliferation.

Conclusion: The role of canonical NF-kB signaling in hepatocellular carcinogenesis depends on the mode of liver damage. In the case of an HBsAg-driven HCC model simulating a direct carcinogenic effect of HBV, NF-kB plays a critical role in controlling the ER stress response. This implies an indispensable role for NF-kB in the control of the UPR and an anti-tumorigenic role in ER stress-related hepatocarcinogenesis.

Corresponding author: Sunami, Yoshiaki

E-Mail: yoshiaki.sunami@tum.de