Gamma-Synuclein As A Potential Novel Prognostic Marker Promoting Tumor Cell Migration In Biliary Tract Carcinoma

577 Background: Biliary tract carcinoma (BTC) is a highly malignant tumor, but the detailed pathological mechanism of its development and progression remain ill-defined. Gamma-synuclein (SNCG) promotes invasive behavior in pancreatic cancer and a range of other cancers, and SNCG expression is reportedly a prognostic factor. However, the role of SNCG in BTC remains unknown. Consequently, we investigated the clinicopathological significance and function of SNCG in BTC. Methods: Using surgically resected BTC specimens from 149 patients with adenocarcinoma [extrahepatic cholangiocarcinoma (ECC) (n =98); intrahepatic cholangiocarcinoma (ICC) (n =51)], we immunohistochemically evaluated SNCG positivity and checked for correlations with clinicopathological factors and outcomes. Furthermore, cell lines with high expressions of SNCG were selected from 17 BTC cell lines by using immunohistochemistry and qPCR. Cell proliferation and migration assays were then performed in the presence and absence of SNCG (silenced using). Results: SNCG expression was found in 32 of 149 (21.4%) BTC patients. SNCG expression was significantly correlated with poorly differentiated tumor ( P = 0.001) and lymph node metastases ( P = 0.001). SNCG positivity was also correlated with poorly differentiated tumor in both ECC and ICC ( P = 0.008 and P = 0.03, respectively), but was correlated with lymph node metastases only in ECC ( P = 0.003). Multivariate analyses identified SNCG expression as an independent prognostic factor of poor overall survival ( P = 0.008) and poor recurrence-free survival (RFS) ( P = 0.006). SNCG expression in both ECC and ICC was significantly associated with poor prognosis in univariate analysis, and multivariate analysis identified SNCG as an independent prognostic factor of poor RFS for ECC (P = 0.03). High SNCG expression was found in 3 BTC cell lines (NCC-BD1, NCC-BD3, and NCC-CC6-1). Functional analysis revealed that SNCG silencing by siRNA suppressed cell migration significantly in NCC-BD1 and NCC-CC6-1 and downregulated cell proliferation in NCC-CC6-1. Conclusions: Our results suggest that SNCG may promote tumor cell activity and is potentially a novel prognostic marker in BTC.