Beta-catenin And Yes-associated Protein 1 Cooperate In Hepatoblastoma Pathogenesis

Background:Hepatoblastoma(HB),the most common pediatric primary liver neoplasm,show nuclear localization of ?-catenin and yes-associated protein 1(YAP 1)in almost 80%of the cases.Co-expression of constitutively active S127A-YAP1 and ?N90 deletion-mutant-?-catenin(?N90-?-catenin-S127A-YAP 1)causes HB in mice.Heterogeneity in downstream signaling is being identified owing to mutational differences even in b-catenin gene alone.Another type of ?-catenin mutation,S33Y and S45Y point mutations have also been found in liver malignant tumors,but its significance have not yet been elucidated.Objective:In the current study,we aimed to investigate if co-expression of point-mutants of?-catenin(S33Y or S45Y)with S127A-YAP1 led to similar tumors as ?N90-?-catenin-S127 A-YAP 1.Methods:Using sleeping beauty-mediated hydrodynamic tail vein injection(HTVI-SB),we co-expression of point-mutants of ?-catenin(S33Y or S45Y)with S127A-YAP1.According to the plasmid we injected,the group separated into 6 groups:S33Y/S45Y-?-Catenin-?127A-YAP1?dnTCF4-S33Y/S45Y-?-Catenin-S127A-YAP1?dnTEAD2S33Y/S45Y-?-Catenin-S127A-YAP1.The changes of liver in mice after injection were observed,the livers of mice were obtained and analyzed.Result:1.Co-expression of S33Y/S45Y-?-catenin and S127A-YAP1 led to activation of Yap and Wnt signaling and development of HB with 100%mortality by 13 to 14 weeks.Although histologically similar,HB in YAP1-S45Y/S33Y-?-catenin,unlike YAP1-?N90-?-catenin HB were glutamine synthetase(GS)-positive.However,both ?N90-?-catenin and point-mutant-b-catenin comparably induced GS-luciferase reporter in vitro.2.Co-expression with S45/S33Y-?-catenin-S127A-YAP1 of the dominant-negative(dn)TCF4,the surrogate transcription factors,prevented HB development;Co-expression with S45/S33Y-?-catenin-S127A-YAP1 of the dominant-negative(dn)TEAD2,the surrogate transcription factors,also prevented HB development.3.Finally,using a previously reported 16-gene signature,it was shown that YAP 1-?N90-?-catenin HB tumors exhibit genetic similarities with more proliferative,less differentiated,GS-negative HB patient tumors,whereas YAP1-S33Y/S45Y-?-catenin HB exhibit heterogeneity and clustered with both well-differentiated GS-positive and proliferative GS-negative patient tumors.Conclusion:We demonstrate that ?-catenin point mutants can also collaborate with YAP1 in HB development,albeit with distinct molecular profile from the deletion mutant,which may have implications in both biology and therapy.