A Gro/TLE-NuRD Corepressor Complex Facilitates Tbx20-Dependent Transcriptional Repression

The cardiac transcription factor
Tbx20 has a critical role in the
proper morphogenetic development of the vertebrate heart, and its
misregulation has been implicated in human congenital heart disease.
Although it is established that Tbx20 exerts its function in the embryonic
heart through positive and negative regulation of distinct gene programs,
it is unclear how Tbx20 mediates proper transcriptional regulation
of its target genes. Here, using a combinatorial proteomic and bioinformatic
approach, we present the first characterization of Tbx20 transcriptional
protein complexes. We have systematically investigated Tbx20 protein–protein
interactions by immunoaffinity purification of tagged Tbx20 followed
by proteomic analysis using GeLC-MS/MS, gene ontology classification,
and functional network analysis. We demonstrate that Tbx20 is associated
with a chromatin remodeling network composed of TLE/Groucho corepressors,
members of the Nucleosome Remodeling and Deacetylase (NuRD) complex,
the chromatin remodeling ATPases RUVBL1/RUVBL2, and the T-box repressor
Tbx18. We determined that the interaction with TLE corepressors is
mediated via an eh1 binding motif in Tbx20. Moreover, we demonstrated
that ablation of this motif results in a failure to properly assemble
the repression network and disrupts Tbx20 function in vivo. Importantly, we validated Tbx20–TLE interactions in the
mouse embryonic heart, and identified developmental genes regulated
by Tbx20–TLE binding, thereby confirming a primary role for
a Tbx20-TLE repressor complex in embryonic heart development. Together,
these studies suggest a model in which Tbx20 associates with a Gro/TLE-NuRD
repressor complex to prevent inappropriate gene activation within
the forming heart.