Transcriptional Repression by Blimp-1 (PRDI-BF1) Involves Recruitment of Histone Deacetylase

Abstract

B-lymphocyte-induced maturation protein (Blimp-1) is a transcriptional repressor that is considered to be a master regulator of terminal B-cell development because it is sufficient to trigger differentiation in the BCL₁-cell model. Transcription of the c-myc gene is repressed by Blimp-1 during B-cell differentiation. In this study, we have explored the mechanism by which Blimp-1 represses transcription by using Gal4-fusion protein assays and assays in which Blimp-1 represses the natural c-mycpromoter. The results show that Blimp-1 represses the c-mycpromoter by an active mechanism that is independent of the adjacently bound activator YY1. Blimp-1 contains two regions that independently associate with histone deacetylase (HDAC) and endogenous Blimp-1 in nuclear extracts binds in vitro to the c-myc Blimp-1 site in a complex containing HDAC. The functional importance of recruiting HDAC for Blimp-1-dependent repression of c-myctranscription is supported by two experiments. First, the HDAC inhibitor tricostatin A inhibits Blimp-1-dependent repression in cotransfection assays. Second, a chromatin immunoprecipitation assay shows that expression of Blimp-1 causes deacetylation of histone H3 associated with the c-myc promoter, and this deacetylation depends on the Blimp-1 binding site in the c-myc promoter.

ACKNOWLEDGMENTS

We are grateful to Gerald Siu and Xiaoming Zou for critically reading the manuscript and to Dimitrios Thanos and members of the Calame laboratory for many helpful discussions. We thank Wen-Ming Yang and Edward Seto for HDAC2 cDNA, Christian Hassig and Stuart Schrieber for HDAC1 cDNA, and Leila Alland and Ron DePinho for testing the interaction between Blimp-1 and mSin3. We are grateful to D. Thanos and T. Maniatis and members of their laboratories for advice on the ChIP assay and to S. Ghosh and members of his lab for advice on EMSA protocol.

This work was supported by USPHS grant RO1 AI 43576 to K.C.