Abstract 4456: Prevention of MICA shedding from HBV infected hepatocytes to activate NK cells for better clearance of malignant foci and virus-infected cells

Abstract

Abstract Introduction: Hepatocellular carcinoma (HCC) is an important issue to public health of the world. By a genome-wide association study, we previously identified that a single nucleotide polymorphism (SNP) in the promoter region of the MHC class I polypeptide-related sequence A (MICA) gene is significantly associated with the risk of hepatitis-virus-related HCC. MICA is a ligand for NKG2D, a cell receptor of NK cells, which activates NK cells to clear the pathogenic cells expressing MICA such as infected cells or malignant cells as a “danger” signal. However, unexpectedly, the Hepatitis B virus (HBV)-infected patients with risk allele of MICA gene showed higher levels of serum MICA. This suggested that the serum MICA, which is excreted from the infected hepatocytes by a shedding mechanism, may work as a decoy for NK cells and inhibit their activities. Therefore, increasing cellular MICA levels by preventing those shedding and release may contribute to the clearance of the pathogenic cells and the prevention of HCC. In this study, we constructed a convenient MICA shedding assay system and, by a comprehensive screening, we identified several compounds which may prevent MICA shedding from the cells. Methods: We constructed lentivirual vector expressing MICA protein tagged with nano-luciferase (nanoLuc) in its N terminal because N terminal of MICA is excreted from the cells by shedding. We expressed this construct in HBV replicating cells, HepG2.2.15, and after adding compounds, we determined the luciferase activities in the supernatant and cell lysates. Results: We picked up the samples which showed low activities in supernatant with high activities in the cell lysates, indicating low levels of shedding and high levels of remaining cellular MICA. Out of over 1,000 compounds screened, we determined four candidate compounds which efficiently prevented MICA shedding. We confirmed the effects of these compounds in other cell systems infected with HBV. Conclusion: Because these compounds enhanced the expression levels of cellular MICA and decreased its shedding in HBV-replicating human hepatocytes, using these compounds may be favorable during HBV chronic infection to enhance the NK cell-mediated clearance of the pathogenic hepatocytes and to prevent HCC. Citation Format: Motoko Ohno, Motoyuki Otsuka, Takahiro Kishikawa, Takeshi Yoshikawa, Akemi Takata, Kazuhiko Koike. Prevention of MICA shedding from HBV infected hepatocytes to activate NK cells for better clearance of malignant foci and virus-infected cells. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 4456. doi:10.1158/1538-7445.AM2015-4456