Loss of IQGAP3 Erodes Epithelial Identity and Unleashes EMT-Driven Malignant Progression in Cholangiocarcinoma

ABSTRACTBackground:Biliary tract cancer (BTC) is an aggressive malignancy with limited prognostic biomarkers. IQ motif containing GTPase activating protein 3 (IQGAP3) has been implicated in cell-cycle control and epithelial-mesenchymal transition (EMT) across several cancers, although its significance in BTC remains unclear.Methods:We retrospectively analyzed 131 patients who underwent curative resection for intrahepatic, perihilar, or distal cholangiocarcinoma or ampullary carcinoma at a single institution during 2016-2020. IQGAP3 expression was assessed by immunohistochemistry and quantified by QuPath-based H-scores, and associations with clinicopathological variables and survival outcomes were evaluated using Kaplan-Meier and Cox regression analyses. Functional validation was performed in HuCCT1 and TFK-1 cells via shRNA-mediated IQGAP3 knockdown, followed by RNA sequencing and gene set enrichment analysis to identify differentially enriched pathways.Results:High IQGAP3 expression was significantly associated with prolonged overall survival compared with low expression (median 97.6 vs. 64.7 months; hazard ratio 0.50, 95% confidence interval 0.30-0.81; P=0.005), particularly in extrahepatic cholangiocarcinoma. IQGAP3 silencing activated EMT-related transcriptional programs in both cell lines (normalized enrichment score 1.43 and 1.44; P<0.01).Conclusions:Loss of IQGAP3 erodes epithelial identity, unleashing EMT-driven malignant progression in BTC. IQGAP3 thus emerges as a contextual gatekeeper of epithelial fate and a potential therapeutic vulnerability in this disease.