RESUMO
During metazoan development, the Wnt/Wingless signal transduction pathway is activated repetitively to direct cell proliferation, fate specification, differentiation and apoptosis. Distinct outcomes are elicited by Wnt stimulation in different cellular contexts; however, mechanisms that confer context specificity to Wnt signaling responses remain largely unknown. Starting with an unbiased forward genetic screen in Drosophila, we recently uncovered a novel mechanism by which the cell-specific co-factor Earthbound 1 (Ebd1), and its human homolog jerky, promote interaction between the Wnt pathway transcriptional co-activators ß-catenin/Armadillo and TCF to facilitate context-dependent Wnt signaling responses. Here, through the same genetic screen, we find an unanticipated requirement for Erect Wing (Ewg), the fly homolog of the human sequence-specific DNA-binding transcriptional activator nuclear respiratory factor 1 (NRF1), in promoting contextual regulation of Wingless signaling. Ewg and Ebd1 functionally interact with the Armadillo-TCF complex and mediate the same context-dependent Wingless signaling responses. In addition, Ewg and Ebd1 have similar cell-specific expression profiles, bind to each other directly and also associate with chromatin at shared genomic sites. Furthermore, recruitment of Ebd1 to chromatin is abolished in the absence of Ewg. Our findings provide in vivo evidence that recruitment of a cell-specific co-factor complex to specific chromatin sites, coupled with its ability to facilitate Armadillo-TCF interaction and transcriptional activity, promotes contextual regulation of Wnt/Wingless signaling responses.
Assuntos
Proteínas do Domínio Armadillo/metabolismo , Proteína B de Centrômero/metabolismo , Cromatina/metabolismo , Proteínas de Drosophila/metabolismo , Proteínas de Drosophila/fisiologia , Neuropeptídeos/fisiologia , Fatores de Transcrição/metabolismo , Fatores de Transcrição/fisiologia , Via de Sinalização Wnt/fisiologia , Proteína Wnt1/fisiologia , Proteínas Adaptadoras de Transdução de Sinal/genética , Proteínas Adaptadoras de Transdução de Sinal/metabolismo , Animais , Animais Geneticamente Modificados , Proteínas do Domínio Armadillo/genética , Proteína B de Centrômero/genética , Drosophila/embriologia , Drosophila/genética , Proteínas de Drosophila/genética , Embrião não Mamífero , Células HEK293 , Humanos , Neuropeptídeos/genética , Neuropeptídeos/metabolismo , Especificidade de Órgãos/genética , Ligação Proteica/fisiologia , Fatores de Transcrição TCF/genética , Fatores de Transcrição TCF/metabolismo , Fatores de Transcrição/genética , Via de Sinalização Wnt/genética , Proteína Wnt1/genética , Proteína Wnt1/metabolismoRESUMO
Wnt/Wingless signal transduction directs fundamental developmental processes, and upon hyperactivation triggers colorectal adenoma/carcinoma formation. Responses to Wnt stimulation are cell specific and diverse; yet, how cell context modulates Wnt signalling outcome remains obscure. In a Drosophila genetic screen for components that promote Wingless signalling, we identified Earthbound 1 (Ebd1), a novel member in a protein family containing Centromere Binding Protein B (CENPB)-type DNA binding domains. Ebd1 is expressed in only a subset of Wingless responsive cell types, and is required for only a limited number of Wingless-dependent processes. In addition, Ebd1 shares sequence similarity and can be functionally replaced with the human CENPB domain protein Jerky, previously implicated in juvenile myoclonic epilepsy development. Both Jerky and Ebd1 interact directly with the Wnt/Wingless pathway transcriptional co-activators ß-catenin/Armadillo and T-cell factor (TCF). In colon carcinoma cells, Jerky facilitates Wnt signalling by promoting association of ß-catenin with TCF and recruitment of ß-catenin to chromatin. These findings indicate that tissue-restricted transcriptional co-activators facilitate cell-specific Wnt/Wingless signalling responses by modulating ß-catenin-TCF activity.
