Background:Hepatoblastoma(HB),the most common pediatric primary liver neoplasm,show nuclear localization of β-catenin and yes-associated protein 1(YAP 1)in almost 80%of the cases.Co-expression of constitutively active S127A-YAP1 and ΔN90 deletion-mutant-β-catenin(ΔN90-β-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 β-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 ofβ-catenin(S33Y or S45Y)with S127A-YAP1 led to similar tumors as ΔN90-β-catenin-S127 A-YAP 1.Methods:Using sleeping beauty-mediated hydrodynamic tail vein injection(HTVI-SB),we co-expression of point-mutants of β-catenin(S33Y or S45Y)with S127A-YAP1.According to the plasmid we injected,the group separated into 6 groups:S33Y/S45Y-β-Catenin-β127A-YAP1、dnTCF4-S33Y/S45Y-β-Catenin-S127A-YAP1、dnTEAD2S33Y/S45Y-β-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-β-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-β-catenin,unlike YAP1-ΔN90-β-catenin HB were glutamine synthetase(GS)-positive.However,both ΔN90-β-catenin and point-mutant-b-catenin comparably induced GS-luciferase reporter in vitro.2.Co-expression with S45/S33Y-β-catenin-S127A-YAP1 of the dominant-negative(dn)TCF4,the surrogate transcription factors,prevented HB development;Co-expression with S45/S33Y-β-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-β-catenin HB tumors exhibit genetic similarities with more proliferative,less differentiated,GS-negative HB patient tumors,whereas YAP1-S33Y/S45Y-β-catenin HB exhibit heterogeneity and clustered with both well-differentiated GS-positive and proliferative GS-negative patient tumors.Conclusion:We demonstrate that β-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. |