Abstract 5538: Functional analysis of BAP1, de-ubiquitination enzyme, in intrahepatic cholangiocarcinoma
Authors: Ishii Kentaro , Ishida Masaharu , Ohnuma Shinobu , Kudoh Katsuyoshi , Motoi Fuyuhiko , Naitoh Takeshi , Selaru Florin , Unno Michiaki 
Published: July 2017

BACKGROUND: BRCA associated protein 1 (BAP1) was discovered as a protein associated with the breast cancer susceptibility gene (BRCA), and genetic mutations of BAP1 gene have recently been found in some malignant tumors, such as melanoma, mesothelioma, and renal cell carcinoma. Since the mutations of BAP1 gene resulted in loss of function of this protein and were associated with poor prognoses of the malignancies, BAP1 is now considered as a tumor-suppressor gene. Recent studies have shown that BAP1 mutations were also observed in patients with intrahepatic cholangiocarcinoma (IHCC), which is one of the most aggressive carcinoma with poor prognoses. However, only a few studies have investigated the role of BAP1 mutation on biological function of tumor cells and on clinicopathological features of IHCC. PURPOSE: The purpose of this study was to elucidate the association of BAP1 and IHCC. METHOD: The expression of BAP1 was immunohistochemically analyzed in surgically resected IHCC specimens, and the cases were classified into three groups based on the result of immunostaining concentration; positive or weakly positive or negative. The clinicopathological factors, such as the disease stage of IHCC, curability and overall survival (OS), were compared among the groups. In cell culture analyses, the expression of BAP1 in IHCC cell lines (HuCC-T1 and TFK-1) was down-regulated by Zinc-finger nuclease (ZFN) and siRNA in vitro. Then, cell-proliferation assay, migration assay, invasion assay, and drug-susceptibility test were performed on BAP1 down-regulated cells. RESULTS: The immunohistochemistry of BAP1 on IHCC specimens showed that OS was not significantly changed among three groups. However, the cases with lower expression of BAP1 including weakly positive and negative tended to be advanced in disease stage compared with cases with BAP1 positive. Interestingly, in the patients received postoperative gemcitabine, a standard chemo-drug for cholangiocarcinoma, cases with lower expression of BAP1 showed prolonged survival compared with cases with BAP1 positive. In cell experiments, the knock-down of BAP1 did not affect cell-proliferation of IHCC cells, however, it promoted migration and invasion of IHCC cells. Furthermore, the suppression of BAP1 enhanced chemosensitivity to gemcitabine. CONCLUSIONS: Our study suggested that lower expression of BAP1 was associates with the progression of IHCC and with enhanced chemosensitivity to gemcitabine. BAP1 might be one of the target genes in the treatment of IHCC.

Citation Format: Kentaro Ishii, Masaharu Ishida, Shinobu Ohnuma, Katsuyoshi Kudoh, Fuyuhiko Motoi, Takeshi Naitoh, Florin Selaru, Michiaki Unno. Functional analysis of BAP1, de-ubiquitination enzyme, in intrahepatic cholangiocarcinoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 5538. doi:10.1158/1538-7445.AM2017-5538