MENA, BR13 and HSF2 as novel transcriptional targets of the Wnt/β-catenin pathway

Abstract

Wnt/β-catenin signaling pathway plays important roles in embryonic development and carcinogenesis, which makes the pathway and its targets important subjects in developmental biology and cancer research fields. In its inactive form, when the Wnt ligand is not bound to the Frizzled receptor, β-catenin is constantly being phosphorylated by glycogen-synthase kinase 3β (GSK3β) and degraded. When the Wnt ligand binds the receptor, activated pathway leads to inhibition of GSK3β, allowing β-catenin to accumulate and translocate into nucleus, where it activates T-cell factor / lymphoid enhancer factor (Tcf/Lef) family of transcription factors, which regulate expression of developmental and cell cycle-related genes. In this study, which was based on genome-wide differential transcriptome screens, we aimed to identify novel Wnt/β-catenin pathway targets and we focused on three genes, namely MENA (Mammalian enabled homologue), BRI3 (Brain protein I3) and HSF2 (Heat-shock factor 2), since their expression increases significantly upon b-catenin overexpression and because their promoters contain putative Tcf4-binding motifs. In order to test their candidacies of being novel targets of the pathway we employed lithiumtreatment assay to inhibit GSK3β and mimic the pathway activation. We found that the expression of MENA, BRI3 and HSF2 increases upon lithium-treatment. Also, luciferase reporter assay and chromatin immunoprecipitation showed interaction of β-catenin and promoters of MENA, BRI3 and HSF2 genes. Finally, comparative RT-PCR analysis of cancer cell lines and human brain tumors was used to test a possible correlation between MENA and CTNNB1 (β-catenin) expression. Our results strongly suggest that MENA, BRI3 and HSF2 transcription is regulated by the Wnt/β-catenin pathway.