Regulation of Smad signaling through a differential recruitment of coactivators and corepressors by ZEB proteins

Balancing signals derived from the TGFβ family is crucial for regulating cell proliferation and differentiation, and in establishing the embryonic axis during development. TGFβ/BMP signaling leads to the activation and nuclear translocation of Smad proteins, which activate transcription of specific target genes by recruiting P/CAF and p300. The two members of the ZEB family of zinc finger factors (ZEB-1/δEF1 and ZEB-2/SIP1) regulate TGFβ/BMP signaling in opposite ways: ZEB-1/δEF1 synergizes with Smadmediated transcriptional activation, while ZEB-2/SIP1 represses it. Here we report that these antagonistic effects by the ZEB proteins arise from the differential recruitment of transcriptional coactivators (p300 and P/CAF) and corepressors (CtBP) to the Smads. Thus, while ZEB-1/δEF1 binds to p300 and promotes the formation of a p300-Smad transcriptional complex, ZEB-2/SIP1 acts as a repressor by recruiting CtBP. This model of regulation by ZEB proteins also functions in vivo, where they have opposing effects on the regulation of TGFβ family-dependent genes during Xenopus development.