BACKGROUND & AIMS
YAP aberrant activation is implicated in intrahepatic cholangiocarcinoma (iCCA). TEAD mediated transcriptional regulation is the primary signaling event downstream of YAP. The role of Wnt/β-Catenin signaling in cholangiocarcinogenesis remains undetermined. Here, we investigated the possible molecular interplay between YAP and β-Catenin cascades in iCCA.
METHODS
Activated Akt (Myr-Akt) was co-expressed with Yap (YapS127A) or Tead2VP16 via hydrodynamic tail vein injection into the mouse livers. Tumor growth was monitored, liver tissues were collected and analyzed using histopathologic and molecular analysis. Yap, β-Catenin, and TEAD interaction in iCCAs was investigated through co-immunoprecipitation. Conditional Ctnnb1 KO mice were utilized to determine β-Catenin function in murine iCCA models. RNA sequencing (RNASeq) was performed to analyze the genes regulated by YAP and/or β-Catenin. Immunostaining of total and non-phosphorylated/activated β-Catenin staining was performed in mouse and human iCCAs.
RESULTS
We discovered that TEAD factors are required for YAP-dependent iCCA development. However, transcriptional activation of TEADs did not fully recapitulate YAP's activities in promoting cholangiocarcinogenesis. Notably, β-Catenin physically interacted with YAP in human and mouse iCCA. Ctnnb1 ablation strongly suppressed human iCCA cell growth and Yap-dependent cholangiocarcinogenesis. Furthermore, RNASeq analysis revealed that YAP/TAZ regulate a set of genes significantly overlapping with those controlled by β-Catenin. Importantly, activated/non-phosphorylated β-Catenin was detected in over 80% of human iCCAs.
CONCLUSION
YAP induces cholangiocarcinogenesis via TEAD-dependent transcriptional activation and interaction with β-Catenin. β-Catenin binds to YAP in iCCA and is required for YAP full transcriptional activity, revealing the functional crosstalk between YAP and β-Catenin pathways in cholangiocarcinogenesis.