RESUMEN

Cell cycle arrest by FoxO transcription factors involves transcriptional repression of cyclin D, although the exact mechanism remains unclear. In this study, we used the BCR-ABL-expressing cell line BV173 as a model system to investigate the mechanisms whereby FoxO3a regulates cyclin D2 expression. Inhibition of BCR-ABL by STI571 results in down-regulation of cyclin D2 expression, activation of FoxO3a activity, and up-regulation of BCL6 expression. Using reporter gene assays, we demonstrate that STI571, FoxO3a, and BCL6 can repress cyclin D2 transcription through a STAT5/BCL6 site located within the cyclin D2 promoter. We propose that BCR-ABL inhibition leads to FoxO3a activation, which in turn induces the expression of BCL6, culminating in the repression of cyclin D2 transcription through this STAT5/BCL6 site. This process was verified by mobility shift and chromatin immunoprecipitation analyses. We find that conditional activation of FoxO3a leads to accumulation of BCL6 and down-regulation of cyclin D2 at protein and mRNA levels. Furthermore, silencing of FoxO3a and BCL6 in BCR-ABL-expressing cells abolishes STI571-mediated effects on cyclin D2. This report establishes the signaling events whereby BCR-ABL signals are relayed to cyclin D2 to mediate cell cycle progression and defines a potential mechanism by which FoxO proteins regulate cyclin D2 expression.

Asunto(s)

Ciclinas/genética , Proteínas de Unión al ADN/metabolismo , Proteínas de Fusión bcr-abl/metabolismo , Proteínas de la Leche/metabolismo , Transactivadores/metabolismo , Factores de Transcripción/metabolismo , Secuencia de Bases , Benzamidas , Sitios de Unión/genética , Línea Celular , Ciclina D2 , Ciclinas/metabolismo , ADN Complementario/genética , Proteínas de Unión al ADN/genética , Proteína Forkhead Box O1 , Factores de Transcripción Forkhead , Proteínas de Fusión bcr-abl/antagonistas & inhibidores , Proteínas de Fusión bcr-abl/genética , Humanos , Mesilato de Imatinib , Proteínas de la Leche/genética , Proteínas Nucleares/metabolismo , Fosforilación , Piperazinas/farmacología , Regiones Promotoras Genéticas , Unión Proteica , Inhibidores de Proteínas Quinasas/farmacología , Proteínas Proto-Oncogénicas c-bcl-6 , Pirimidinas/farmacología , ARN Mensajero/genética , ARN Mensajero/metabolismo , ARN Interferente Pequeño/genética , Factor de Transcripción STAT5 , Transducción de Señal , Transactivadores/genética , Factores de Transcripción/genética , Transcripción Genética/efectos de los fármacos