The ß-catenin-target Fascin-1, altering hepatocyte differentiation, is a new marker of immature cells in hepatoblastomas

BACKGROUND & AIMS ß-catenin is a well-known effector of the Wnt pathway and a key player in cadherin-mediated cell adhesion. Oncogenic mutations of ß-catenin are highly frequent in pediatric liver primary tumors. Those mutations are mostly heterozygous allowing the co-expression of wild-type (WT) and mutated ß-catenins in tumor cells. We investigated the interplay between WT and mutated ß-catenins in liver tumor cells, and searched for new actors of the ß-catenin pathway. METHODS Using an RNAi strategy in ß-catenin-mutated hepatoblastoma (HB) cells, we dissociated the structural and transcriptional activities of β-catenin, carried mainly by, respectively, WT and mutated proteins. Their impact was characterized using transcriptomic and functional analyses. We studied mice that develop liver tumors upon activation of ß-catenin in hepatocytes (APCKO and ß-cateninΔexon3 mice). We made use of transcriptomic data from mouse and human HB specimens and analyzed samples by immunohistochemistry. RESULTS We highlighted an antagonist role of WT and mutated ß-catenins on hepatocyte differentiation as attested by alteration of hepatocyte markers expression and bile canaliculi formation. We characterized Fascin-1 as a target of ß-catenin involved in hepatocyte differentiation. Using mouse models that allow the formation of two phenotypically distinct tumors (differentiated or undifferentiated), we found that Fascin-1 expression is higher in undifferentiated tumors. Finally, we found that Fascin-1 is a specific marker of the embryonal component in human HBs. CONCLUSIONS In mice and human, Fascin-1 expression is linked to loss of differentiation and polarity of hepatocytes. Thus, we highlighted Fascin-1 as a new player in the modulation of hepatocyte differentiation associated to ß-catenin pathway alteration in the liver. Data Transparency Statement study materials will be made available to other researchers upon request. ### Competing Interest Statement The authors have declared no competing interest. * BC : bile canaliculus CFDA : 5-carboxyfluorescein diacetate HB : hepatoblastoma HCC : hepatocellular carcinoma HNF4a : hepatocyte nuclear factor-4 alpha KD : knock-down STED : stimulated emission depletion WT : wild-type