Interaction between the Hematopoietic Ets Transcription Factor Spi-B and the Coactivator CREB-binding Protein Associated with Negative Cross-talk with c-Myb

We have previously shown that the hematopoietic Ets transcription factor PU.1 interacts with the transcriptional coactivator CREB-binding protein (CBP). In this study, we further investigated whether Spi-B, another hematopoietic Ets transcription factor, also interacts with CBP. Direct physical interaction of Spi-B with CBP was demonstrated by glutathione Stransferase binding assay. Analysis using several deletion mutants of Spi-B and CBP revealed that the NH 2-terminal region including the activation domain of Spi-B interacted with the region spanning amino acid residues 1283–1915 of CBP in vitro. The interaction of Spi-B with CBP was also observed in vivo. CBP potentiated Spi-B-mediated transcription of the reporter gene driven by the multimerized PU.1/Spi-B binding sites. This transcriptional activation by Spi-B and CBP was inhibited by expression of c-Myb, and the transcriptional activation by c-Myb and CBP was inhibited by expression of Spi-B, suggesting competition for CBP between these two transcription factors. Our results suggest that CBP acts as a transcriptional coactivator of Spi-B and mediates synergistic or antagonistic interactions between other transcription factors.