Abstract 5350: Aberrant activation-induced cytidine deaminase (AID) expression is induced in the process of hepatitis C virus-associated hepatocarcinogenesis
Authors: Kim Soo K. , Marusawa Hiroyuki , Chiba Tsutomu 
Published: May 2015

Activation-induced cytidine deaminase (AID) is a DNA mutator enzyme, which is encoded by Aicda gene. Under physiological condition, AID is essential for somatic hypermutation of immunogloburin genes in activated B lymphocytes and involved in immune diversity. Previous in vitro studies demonstrated that in cultured adult hepatocytes, both the response to chronic inflammation and hepatitis C virus (HCV) infection itself triggers aberrant AID upregulation, and due to the mutagenic activity of AID, nucleotide alterations gradually accumulate in tumor-related genes. In this study, we aimed to obtain a direct evidence of AID expression induced by HCV infection in vivo using human and mice subjects. Immunostaining of human clinical specimen revealed endogenous AID expression was detectable in both the hepatocellular carcinoma (HCC) and the non-tumorous inflamed liver tissues in patients with chronic HCV infection while no AID expression was detected in normal liver tissues without HCV infection. In mice, as endogenous AID expression level of liver is not sufficient to detect by immustaining, we utilized the transgenic mouse (Aicda-cre transgenic mouse), which was generated by inserting the coding sequence of Cre recombinase into the locus of the Aicda gene, crossing with a genetically-marked reporter mouse (Rosa-tdRFP mouse). In this Aicda-cre/Rosa-tdRFP mouse model, AID-expressing cells can be detected as RFP-positive. We injected HCV core antigen-inserted plasmid to the liver of Aicda-cre/Rosa-tdRFP mice by “hydrodynamic tail vein injection” procedure. 14days after injection, RFP-positive hepatocytes were detected in the HCV antibody-labelled liver cells whereas no RFP-positive cells were found in control mice with physiological saline injection, indicating HCV core antigen induced aberrant AID expression in hepatocytes. Next, to examine the effect of constitutive AID expression in hepatic-lineage cells, we established a transplantation model of hepatic progenitor cells derived from AID Tg mice. We enriched hepatic progenitor cells from the E13.5 fetal liver of AID Tg mice and transplanted those cells into recipient mice. HCC developed in 7 of 11 (63.6%) recipient mice receiving enriched hepatic progenitor cells from AID Tg mice. On the other hand, no tumor was found in recipient mice transplanted with hepatic progenitor cells derived from wild-type mice (control). In addition, whole exome sequencing of tumor cells clarified the landscape of the accumulated genetic alterations during tumorigenesis and detected a large number of somatic mutations in each tumor tissue originating from the transplanted hepatic progenitor cells of AID Tg mice. These results suggested aberrant AID production induced by HCV infection could contribute to hepatocarcinogenesis via the accumulation of genetic alterations by its mutagenic activity.

Citation Format: Soo Ki Kim, Hiroyuki Marusawa, Tsutomu Chiba. Aberrant activation-induced cytidine deaminase (AID) expression is induced in the process of hepatitis C virus-associated hepatocarcinogenesis. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 5350. doi:10.1158/1538-7445.AM2014-5350