Abstract 269: DACH1 (Dachshund homolog 1) attenuates forkhead signaling through recruiting transcription elongation regulator 1 (TCERG1)

Abstract

Abstract The Drosophila Dachshund (Dac) gene, cloned as a dominant inhibitor of the hyperactive growth factor mutant, ellipse, encodes a key component of the Retinal Determination Gene Network (RDGN) that governs cell fate. DACH1 (Dachshund homolog 1) regulates gene expression either indirectly as a co-integrator or through direct DNA binding. CAST identified a DACH1 DNA-binding sequence which resembles the FOX (Forkhead Box containing protein) binding site. Genome-wide in-silico promoter analysis of DACH1 binding sites identified gene clusters populating cellular pathways associated with the cell cycle and growth factor signaling. ChIP-Seq mapped DACH1 binding sites to corresponding gene clusters predicted in silico and identified as weight matrix resembling the CAST-defined sequence. DACH1 antagonized FOXM1 target gene expression, promoter occupancy in the context of local chromatin, and contact-independent growth. Further studies were conducted to understand, at a higher level of resolution, the mechanisms governing DACH1-mediated transcriptional repression via DNA-sequence specific binding. DACH1 repressed, while FOX proteins enhanced, both DRE and FOXA responsive element-driven gene expression. Reduced DACH1 expression using a shRNA approach enhanced FOX protein activity. As DACH1 antagonized FOX target gene expression and attenuated FOX signaling, we sought to identify limiting co-integrator proteins governing DACH1 signaling. Proteomic analysis identified transcription elongation regulator 1 (TCERG1) as the transcriptional co-regulator of DACH1 activity. The FF2 domain of TCERG1 was required for DACH1 binding, and the deletion of FF2 abolished DACH1 trans-repression function. The carboxyl terminus of DACH1 was necessary and sufficient for TCERG1 binding. Thus, DACH1 represses gene transcription through direct DNA binding to the promoter region of target genes by recruiting the transcriptional co-regulator, TCERG1. Attenuation of FOX function by the cell fate determination pathway has broad implications given the diverse role of FOX proteins in cellular biology and tumorigenesis. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 269. doi:10.1158/1538-7445.AM2011-269