RESUMO
Genetic analysis of TP63 indicates that ΔNp63 isoforms are required for preservation of self-renewing capacity in the stem cell compartments of diverse epithelial structures; however, the underlying cellular and molecular mechanisms remain incompletely defined. Cellular quiescence is a common feature of adult stem cells that may account for their ability to retain long-term replicative capacity while simultaneously limiting cellular division. Similarly, quiescence within tumor stem cell populations may represent a mechanism by which these populations evade cytotoxic therapy and initiate tumor recurrence. Here, we present evidence that ΔNp63α, the predominant TP63 isoform in the regenerative compartment of diverse epithelial structuresm, promotes cellular quiescence via activation of Notch signaling. In HC11 cells, ectopic ΔNp63α mediates a proliferative arrest in the 2N state coincident with reduced RNA synthesis characteristic of cellular quiescence. Additionally, ΔNp63α and other quiescence-inducing stimuli enhanced expression of Notch3 in HC11s and breast cancer cell lines, and ectopic expression of the Notch3 intracellular domain (N3 (ICD) ) was sufficient to cause accumulation in G 0/G 1 and increased expression of two genes associated with quiescence, Hes1 and Mxi1. Pharmacologic inhibition of Notch signaling or shRNA-mediated suppression of Notch3 were sufficient to bypass quiescence induced by ΔNp63α and other quiescence-inducing stimuli. These studies identify a novel mechanism by which ΔNp63α preserves long-term replicative capacity by promoting cellular quiescence and identify the Notch signaling pathway as a mediator of multiple quiescence-inducing stimuli, including ΔNp63α expression.
Assuntos
Pontos de Checagem do Ciclo Celular , Fosfoproteínas/metabolismo , Receptores Notch/metabolismo , Transativadores/metabolismo , Adenoviridae/genética , Adenoviridae/metabolismo , Células-Tronco Adultas/citologia , Células-Tronco Adultas/metabolismo , Animais , Apoptose , Fatores de Transcrição Hélice-Alça-Hélice Básicos/genética , Fatores de Transcrição Hélice-Alça-Hélice Básicos/metabolismo , Linhagem Celular Tumoral , Proliferação de Células , Clonagem Molecular , Replicação do DNA , Feminino , Citometria de Fluxo , Células HEK293 , Proteínas de Homeodomínio/genética , Proteínas de Homeodomínio/metabolismo , Humanos , Lentivirus/genética , Lentivirus/metabolismo , Camundongos , Fosfoproteínas/genética , RNA Mensageiro/genética , RNA Mensageiro/metabolismo , RNA Interferente Pequeno/genética , RNA Interferente Pequeno/metabolismo , Receptor Notch3 , Receptores Notch/genética , Transdução de Sinais , Transativadores/genética , Fatores de Transcrição HES-1 , Ativação Transcricional , TransfecçãoRESUMO
The evolutionarily conserved Wnt/Wingless signal transduction pathway directs cell proliferation, cell fate, and cell death during development in metazoans and is inappropriately activated in several types of cancer. The majority of colorectal carcinomas contain truncating mutations in the adenomatous polyposis coli (APC) tumor suppressor, a negative regulator of Wnt/Wingless signaling. Here, we demonstrate that Drosophila Apc homologs also have an activating role in both physiological and ectopic Wingless signaling. The Apc amino terminus is important for its activating function, whereas the beta-catenin binding sites are dispensable. Apc likely promotes Wingless transduction through down-regulation of Axin, a negative regulator of Wingless signaling. Given the evolutionary conservation of APC in Wnt signal transduction, an activating role may also be present in vertebrates with relevance to development and cancer.
