CtBP1 Mediates Hypoxia-Induced Sarcomatoid Transformation in Hepatocellular Carcinoma

BACKGROUND: Sarcomatoid hepatocellular carcinoma (sHCC), a highly aggressive subtype of hepatocellular carcinoma (HCC), mostly transforms from classical hepatocellular carcinoma (cHCC). The study intended to explore the role of C-terminal binding protein 1 (CtBP1) in sarcomatoid transformation of hepatocellular carcinoma. METHODS: Western blotting and/or immunohistochemistry were used to confirm the expression of CtBP1 and other proteins in HCC cells, xenografts and clinical tissue samples. CtBP1 shRNA-expressing lentivirus was used to infect HepG2 cells to construct CtBP1 knockdown cells. Cell migration was determined by scratch wound assays and Transwell assays. Immunofluorescence was used to label the a-tubulin cytoskeleton to evaluate cell morphology. HepG2 cells were inoculated subcutaneously in nude mice to construct xenografts and beneath the liver capsule to evaluate in vivo metastasis. RESULTS: Compared to that in the cHCC area, CtBP1 expression was significantly upregulated in the sHCC area, as shown by immunohistochemistry. HE staining showed that cells in the sHCC area were spindle-shaped, while those in the cHCC area were polygonal. Immunohistochemically, the epithelial markers pancytokeratin (CK) and E-cadherin were partially or completely lost, while the expression of the mesenchymal marker vimentin was upregulated in the sHCC area. Moreover, HepG2, an HCC cell line with high expression of CtBP1, autonomously underwent sarcomatoid transformation, showing a sarcomatoid morphology and phenotype. HIF1a expression was upregulated in epithelial cells adjacent to the sHCC area. Hypoxia upregulated CtBP1 protein expression and induced an EMT phenotype with increased migration and a spindle-shaped morphology in HepG2 cells. Knockdown of CtBP1 partially reversed the EMT phenotype induced by hypoxia. Silencing CtBP1 completely blocked the sarcomatoid transformation of subcutaneous xenografts and decreased lung metastasis in subcapsular xenografts of the liver in nude mice. CONCLUSION: CtBP1 plays a key role in hypoxia-induced EMT and sarcomatoid transformation in HCC and could be a candidate target for the management of sHCC.