C-Terminal Binding Protein Is a Transcriptional Repressor That Interacts with a Specific Class of Vertebrate Polycomb Proteins
| Autor: | Richard George Antonius Bernardus Sewalt, Arie P. Otte, M. J. Gunster, David P. E. Satijn, J. van der Vlag |
|---|---|
| Rok vydání: | 1999 |
| Předmět: |
DNA
Complementary animal structures genetic structures Recombinant Fusion Proteins Ubiquitin-Protein Ligases Xenopus Polyhomeotic Molecular Sequence Data Polycomb-Group Proteins HL-60 Cells macromolecular substances Biology Posterior Sex Combs DNA-binding protein Antibodies Ligases CTBP1 Genes Reporter Tumor Cells Cultured Animals Humans Amino Acid Sequence Enhancer Molecular Biology Cell Nucleus Genetics Binding Sites Base Sequence Sequence Homology Amino Acid General transcription factor fungi Cell Biology Phosphoproteins DNA Dynamics and Chromosome Structure Chromatin DNA-Binding Proteins Repressor Proteins Alcohol Oxidoreductases K562 Cells Homeotic gene Dimerization HeLa Cells |
| Zdroj: | Molecular and Cellular Biology. 19:777-787 |
| ISSN: | 1098-5549 |
| DOI: | 10.1128/mcb.19.1.777 |
| Popis: | In Drosophila the Polycomb (Pc) group (PcG) genes have been identified as being part of a cellular memory system that is responsible for the stable and heritable repression of gene expression (3, 16). The PcG genes are required for maintenance of the repressed state of certain homeotic genes. Mutations in PcG genes result in derepression of these homeotic genes, which leads to homeotic transformations. In recent years vertebrate homologs of PcG genes have been identified and characterized. Mutations in these vertebrate PcG genes also lead to homeotic transformations, indicating that the vertebrate PcG genes have a function similar to that of their Drosophila homologs (reviewed in references 8 and 24). Despite the extensive knowledge concerning the identity of Drosophila and vertebrate PcG genes, the molecular mechanism of how PcG proteins achieve inheritably stable transcriptional repression of target genes is not understood. Several models in which the PcG proteins can package target genes in a heterochromatin-like conformation or induce modifications of the nucleosomal organization have been considered (16). It also is not understood how PcG proteins interfere with transcription regulation. In theory, the PcG proteins might directly interact with enhancer proteins, with proteins of the basal transcription machinery, or with proteins that modify chromatin structure, such as histone deacetylases. Insight into the molecular mechanisms underlying PcG action comes from observations indicating that PcG proteins function as large multimeric complexes. In Drosophila, several PcG proteins share 60 to 100 sites on polytene chromosomes of the salivary gland (18, 28), and coimmunoprecipitation experiments have shown that the Pc protein is present in a large protein complex that also includes the PcG protein Polyhomeotic (Ph) (6). The vertebrate PcG proteins also form multimeric protein complexes. Recently, we have shown that there are at least two distinct human PcG protein complexes (25). On the one hand, there is a complex which consists of human Pc 2 (HPC2), a human Pc homolog; a human homolog of the murine Pc protein M33 (21); HPH1 and HPH2, human homologs of the Drosophila PcG protein Ph; and BMI1, a human homolog of the Drosophila PcG protein Posterior sex combs (1, 9). This complex also contains the RING1 protein (20). All of these proteins coimmunoprecipitate with each other and colocalize in large nuclear domains termed PcG domains (9, 20, 21). On the other hand, Enx1/EZH2 and EED, mammalian homologs of the Drosophila PcG proteins Enhancer of zeste and Extra sex combs, respectively, appear to be part of a distinct PcG complex. Enx1/EZH2 and EED coimmunoprecipitate and colocalize with each other but not with the above-mentioned PcG proteins (25, 27). To identify additional proteins that interact with the PcG complex, we screened two-hybrid cDNA libraries with vertebrate Pc homologs as targets. We found that a Xenopus homolog of C-terminal binding protein 1 (XCtBP1) (22) interacts with Xenopus Pc (XPc) (19) and that human CtBP2 (11) interacts with HPC2 (21). The CtBP1 protein has previously been identified as a protein that binds to the extreme C terminus of the adenovirus type 2 and 5 (Ad2/5) E1A protein, and CtBP1 attenuates transcriptional activation and tumorigenesis mediated by the E1A protein (2, 22, 26). We show that the CtBP proteins coimmunoprecipitate with HPC2, that the CtBP proteins partially colocalize in nuclear domains with HPC2, and, finally, that CtBP is able to repress gene activity. These findings are of particular interest since the recently identified Drosophila homolog of CtBP is able to interact with the Drosophila pair-rule segmentation protein Hairy (17) and the gap segmentation protein Knirps and the zinc finger protein Snail (14). Remarkably, all of these Drosophila CtBP-interacting proteins are, like HPC2 and XPc, repressors of gene activity. Our data suggest that HPC2-mediated repression involves an association with corepressors such as CtBP. |
| Databáze: | OpenAIRE |
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