The ErbB3 binding protein Ebp1 interacts with Sin3A to repress E2F1 and AR-mediated transcription

Ectopic expression of ebp1, a member of the PA2G4 family, inhibits the proliferation and induces the differentiation of human breast and prostate cancer cell lines. Ebp1 inhibits transcription of E2F1 and androgen receptor regulated genes such as prostate specific antigen (PSA) through its interactions with histone deacetylases (HDACs). To further understand Ebp1's interactions with other components of the transcriptional repression machinery, we examined the association of Ebp1 with the corepressor Sin3A. Ebp1 interacted with Sin3A both in vitro and in vivo as demonstrated by glutathione S-transferase (GST) pull-down and coimmunoprecipitation analysis. The C-terminal domain of Ebp1, responsible for its ability to repress transcription and arrest cell growth, was necessary and sufficient for binding Sin3A. The C-terminal domain of Sin3A, containing the paired amphipathic domain 4 and the HDAC interacting domain, bound Ebp1. Recombinant Sin3A bound Ebp1 directly, but recombinant HDAC2 failed to bind Ebp1. Chromatin immunoprecipitation (ChIP) and DNA affinity precipitation analysis demonstrated that Ebp1 and Sin3A associate at the PSA and E2F1 promoters. Functionally, Sin3A enhanced the ability of Ebp1 to repress transcription of androgen receptor (AR) and E2F1 regulated genes. These results demonstrate that Ebp1 participates in transcriptional regulation via its interaction with the Sin3-HDAC.