RESUMO
Ligand-bound nuclear receptors (NR) activate transcription of the target genes. This activation is coupled with histone modifications and chromatin remodeling through the function of various coregulators. However, the nature of the dependence of a NR coregulator action on the presence of the chromatin environment at the target genes is unclear. To address this issue, we have developed a modified position effect variegation experimental model system that includes an androgen-dependent reporter transgene inserted into either a pericentric heterochromatin region or a euchromatic region of Drosophila chromosome. Human androgen receptor (AR) and its constitutively active truncation mutant (AR AF-1) were transcriptionally functional in both chromosomal regions. Predictably, the level of AR-induced transactivation was lower in the pericentric heterochromatin. In genetic screening for AR AF-1 coregulators, Drosophila CREB binding protein (dCBP) was found to corepress AR transactivation at the pericentric region whereas it led to coactivation in the euchromatic area. Mutations of Sir2 acetylation sites or deletion of the CBP acetyltransferase domain abrogated dCBP corepressive action for AR at heterochromatic areas in vivo. Such a CBP corepressor function for AR was observed in the transcriptionally silent promoter of an AR target gene in cultured mammalian cells. Thus, our findings suggest that the action of NR coregulators may depend on the state of chromatin at the target loci.
Assuntos
Proteína de Ligação a CREB/metabolismo , Efeitos da Posição Cromossômica/genética , Drosophila melanogaster/genética , Heterocromatina/metabolismo , Modelos Genéticos , Receptores Androgênicos/genética , Ativação Transcricional/genética , Acetilação , Sequência de Aminoácidos , Animais , Proteína de Ligação a CREB/química , Domínio Catalítico , Linhagem Celular Tumoral , Sequência Conservada , Proteínas de Drosophila/química , Eucromatina/metabolismo , Histona Desacetilases/química , Histonas/metabolismo , Humanos , Lisina/metabolismo , Metilação , Dados de Sequência Molecular , Regiões Promotoras Genéticas/genética , Receptores Androgênicos/química , Receptores Androgênicos/metabolismo , Proteínas Repressoras/metabolismo , Sirtuínas/químicaRESUMO
Wnt and estrogen signaling represent important regulatory pathways, each controlling a wide range of biological processes. While an increasing number of observations suggest potential convergence between these pathways, no direct evidence of their functional interaction has been reported. Using human colon and breast cancer cells, we found that estrogen receptor (ER) alpha- and beta-catenin precipitated within the same immunocomplexes, reciprocally enhanced the transactivation of cognate reporter genes, and were reciprocally recruited to cognate response elements in the promoters of endogenous target genes. Using transgenic Drosophila that ectopically expressed human ERalpha alone or together with metabolically stable beta-catenin/Armadillo mutants, we demonstrated genetic interaction between these signal transducers in vivo. Thus, we present here the first direct evidence of cross-talk between Wnt and estrogen signaling pathways via functional interaction between beta-catenin and ERalpha.
