Identification and characterization of ΔNp63 as a novel transcriptional target negatively regulated by TAZ in mammary tumorigenesis
Valencia Sama, Ivette
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The transcriptional co-activator with PDZ-binding domain (TAZ) is a key downstream component of the Hippo pathway that plays important roles in animal size control, stem cell renewal, differentiation and tumorigenesis. We and others have previously characterized TAZ as a transcriptional co-activator which regulates cell migration, invasion, proliferation and epithelial-mesenchymal transition (EMT). However, the molecular mechanisms underlying TAZ-mediated phenotypes as well as its implications in tumorigenesis are still not fully addressed. To identify the genes mediating TAZ function, we have performed DNA microarray screenings. Surprisingly, we have identified over 400 genes negatively regulated by TAZ. Further mRNA and protein quantification assays by qRT-PCR and western blot confirmed ΔNp63, a member of the p53 tumor suppressor family, as a significant downregulated target in TAZ-overexpressing MCF10A (MCF10A-TAZ) non-tumorigenic mammary cells. Moreover, luciferase assays have shown that TAZ regulation of the ΔNp63 promoter activity is mainly mediated by the TEA domain (TEAD) family of transcription factors. Interestingly, loss of TEAD abolishes TAZ-induced suppression of ΔNp63. We have further shown that TAZ interacts with other transcription factors, including the thyroid transcriptional factor 1 (TTF-1) to enhance ΔNp63 repression. Surprisingly, TTF-1-mediated repression was also compromised in TEAD-lacking conditions, thus elucidating a novel transcriptional complex for gene suppression. Finally, we have shown that re-introduction of ΔNp63 into MCF10A-TAZ cells partially rescues TAZ-induced cell migration. Together, these findings have identified TAZ as a novel dual modulator of cellular gene expression, arguing against its sole role as a transcriptional co-activator. Future elucidation of the clinical implications of TAZ as a co-repressor of genetic transcription might contribute significantly to our better understanding of the roles of TAZ in breast cancer development, as well as illustrating novel strategies to target this signaling pathway for cancer therapies.