scholarly journals Interaction of Bovine Papillomavirus E2 Protein with Brd4 Stabilizes Its Association with Chromatin

2005 ◽  
Vol 79 (14) ◽  
pp. 8920-8932 ◽  
Author(s):  
Maria G. McPhillips ◽  
Keiko Ozato ◽  
Alison A. McBride
Keyword(s):  
Cell Types ◽  
Bovine Papillomavirus ◽  
Chromosomal Protein ◽  
Transactivation Domain ◽  
Mitotic Chromosomes ◽  
E2 Protein ◽  
Viral Genomes ◽  
Protein Protein Interaction ◽  
Binding Function ◽  
Interphase Cells

ABSTRACT The bovine papillomavirus E2 protein maintains and segregates the viral extrachromosomal genomes by tethering them to cellular mitotic chromosomes. E2 interacts with a cellular bromodomain protein, Brd4, to mediate the segregation of viral genomes into daughter cells. Brd4 binds acetylated histones and has been observed to diffusely coat mitotic chromosomes in several cell types. In this study, we show that in mitotic C127 cells, Brd4 diffusely coated the condensed chromosomes. However, in the presence of the E2 protein, E2 and Brd4 colocalized in punctate dots that were randomly distributed over the chromosomes. A similar pattern of E2 and Brd4 colocalization on mitotic chromosomes was observed in CV-1 cells, whereas only a faint chromosomal coating of Brd4 was detected in the absence of the E2 protein. Therefore, the viral E2 protein relocalizes and/or stabilizes the association of Brd4 with chromosomes in mitotic cells. The colocalization of E2 and Brd4 was also observed in interphase cells, indicating that this protein-protein interaction persists throughout the cell cycle. The interaction of E2 with Brd4 greatly stabilized the association of Brd4 with interphase chromatin. In both mitotic and interphase cells, this stabilization required a transcriptionally competent transactivation domain, but not the DNA binding function of the E2 protein. Thus, the E2 protein modulates the chromatin association of Brd4 during both interphase and mitosis. This study demonstrates that the segregation of papillomavirus genomes is not simply due to the passive hitchhiking of the E2/genome complex with a convenient cellular chromosomal protein.

scholarly journals Dimerization of the Papillomavirus E2 Protein Is Required for Efficient Mitotic Chromosome Association and Brd4 Binding

2008 ◽  
Vol 82 (15) ◽  
pp. 7298-7305 ◽  
Author(s):  
Juan Cardenas-Mora ◽  
Jonathan E. Spindler ◽  
Moon Kyoo Jang ◽  
Alison A. McBride
Keyword(s):  
Dna Binding ◽  
Fluorescent Protein ◽  
Binding Domain ◽  
Bovine Papillomavirus ◽  
Dna Binding Domain ◽  
Transactivation Domain ◽  
Mitotic Chromosomes ◽  
Dimerization Domain ◽  
E2 Protein ◽  
Binding Function

ABSTRACT The E2 proteins of several papillomaviruses link the viral genome to mitotic chromosomes to ensure retention and the efficient partitioning of genomes into daughter cells following cell division. Bovine papillomavirus type 1 E2 binds to chromosomes in a complex with Brd4, a cellular bromodomain protein. Interaction with Brd4 is also important for E2-mediated transcriptional regulation. The transactivation domain of E2 is crucial for interaction with the Brd4 protein; proteins lacking or mutated in this domain do not interact with Brd4. However, we found that the C-terminal DNA binding/dimerization domain of E2 is also required for efficient binding to Brd4. Mutations that eliminated the DNA binding function of E2 had no effect on the ability of E2 to interact with Brd4, but an E2 protein with a mutation that disrupted C-terminal dimerization bound Brd4 with greatly reduced efficiency. Furthermore, E2 proteins in which the C-terminal domains were replaced with the dimeric DNA binding domain of EBNA-1 or Gal4 bound efficiently to the Brd4 protein, but the replacement of the E2 C-terminal domain with a monomeric red fluorescent protein did not rescue efficient Brd4 binding. Thus, E2 bound to Brd4 most efficiently as a dimer. To prove this finding further, the E2 DNA binding domain was replaced with an FKBP12-derived domain in which dimerization was regulated by a bivalent ligand. This fusion protein bound Brd4 efficiently only in the presence of the ligand, confirming that a dimer of E2 was required. Correspondingly, E2 proteins that could dimerize were able to bind to mitotic chromosomes much more efficiently than monomeric E2 polypeptides.

Bovine Papillomavirus Type 1 Genomes and the E2 Transactivator Protein Are Closely Associated with Mitotic Chromatin

1998 ◽  
Vol 72 (3) ◽  
pp. 2079-2088 ◽  
Author(s):  
Mario H. Skiadopoulos ◽  
Alison A. McBride
Keyword(s):  
Bovine Papillomavirus ◽  
Transactivation Domain ◽  
Mitotic Chromosomes ◽  
Viral Genomes ◽  
Binding Function ◽  
Dividing Cells ◽  
Transactivator Protein ◽  
Episomal Maintenance ◽  
Mitotic Chromatin

ABSTRACT The bovine papillomavirus type 1 E2 transactivator protein is required for viral transcriptional regulation and DNA replication and may be important for long-term episomal maintenance of viral genomes within replicating cells (M. Piirsoo, E. Ustav, T. Mandel, A. Stenlund, and M. Ustav, EMBO J. 15:1–11, 1996). We have evidence that, in contrast to most other transcriptional transactivators, the E2 transactivator protein is associated with mitotic chromosomes in dividing cells. The shorter E2-TR and E8/E2 repressor proteins do not bind to mitotic chromatin, and the N-terminal transactivation domain of the E2 protein is necessary for the association. However, the DNA binding function of E2 is not required. We have found that bovine papillomavirus type 1 genomes are also associated with mitotic chromosomes, and we propose a model in which E2-bound viral genomes are transiently associated with cellular chromosomes during mitosis to ensure that viral genomes are segregated to daughter cells in approximately equal numbers.

scholarly journals Conditional Mutations in the Mitotic Chromosome Binding Function of the Bovine Papillomavirus Type 1 E2 Protein

2005 ◽  
Vol 79 (3) ◽  
pp. 1500-1509 ◽  
Author(s):  
Peng-Sheng Zheng ◽  
Jane Brokaw ◽  
Alison A. McBride
Keyword(s):  
Amino Acid ◽  
Bovine Papillomavirus ◽  
Transactivation Domain ◽  
Mitotic Chromosomes ◽  
E2 Protein ◽  
Binding Function ◽  
Acid Domain ◽  
Necessary And Sufficient ◽  
Amino Acid Domain

ABSTRACT The papillomavirus E2 protein is required for viral transcriptional regulation, DNA replication and genome segregation. We have previously shown that the E2 transactivator protein and BPV1 genomes are associated with mitotic chromosomes; E2 links the genomes to cellular chromosomes to ensure efficient segregation to daughter nuclei. The transactivation domain of the E2 protein is necessary and sufficient for association of the E2 protein with mitotic chromosomes. To determine which residues of this 200-amino-acid domain are important for chromosomal interaction, E2 proteins with amino acid substitutions in each conserved residue of the transactivation domain were tested for their ability to associate with mitotic chromosomes. Chromatin binding was assessed by using immunofluorescence on both spread and directly fixed mitotic chromosomes. E2 proteins defective in the transactivation and replication functions were unable to associate with chromosomes, and those that were competent in these functions were attached to mitotic chromosomes. However, several mutated proteins that were defective for chromosomal interaction could associate with chromosomes after treatment with agents that promote protein folding or when cells were incubated at lower temperatures. These results indicate that precise folding of the E2 transactivation domain is crucial for its interaction with mitotic chromosomes and that this association can be modulated.

scholarly journals The Human Papillomavirus Type 8 E2 Tethering Protein Targets the Ribosomal DNA Loci of Host Mitotic Chromosomes

2008 ◽  
Vol 83 (2) ◽  
pp. 640-650 ◽  
Author(s):  
Atasi Poddar ◽  
Shawna C. Reed ◽  
Maria G. McPhillips ◽  
Jonathan E. Spindler ◽  
Alison A. McBride
Keyword(s):  
Human Papillomavirus ◽  
Ribosomal Dna ◽  
Cellular Protein ◽  
Bovine Papillomavirus ◽  
Mitotic Chromosomes ◽  
Protein Targets ◽  
E2 Protein ◽  
Viral Genomes ◽  
Wide Range ◽  
Polymerase I

ABSTRACT For many papillomaviruses, the viral protein E2 tethers the viral genome to the host mitotic chromosomes to ensure persistent, long-term maintenance of the genome during cell division. Our previous studies of E2 proteins from different genera of papillomaviruses have shown that they bind to different regions of the host chromosomes during mitosis. For example, bovine papillomavirus type 1 (BPV-1) E2 binds to all chromosomes as small speckles in complex with the cellular protein Brd4. In contrast, the human papillomavirus type 8 (HPV-8) E2 protein binds as large speckles at the pericentromeric regions of chromosomes. Here we show that these speckles do not contain Brd4, and unlike that of BPV-1, the N-terminal Brd4-interacting domain of HPV-8 E2 is not required for chromosome binding. In contrast to BPV-1 E2, the HPV-8 E2 protein targets the short arms of acrocentric mitotic chromosomes. Furthermore, the E2 protein interacts with the repeated ribosomal DNA genes found in this location and colocalizes with UBF, the RNA polymerase I transcription factor. Therefore, HPV-8 E2 genome tethering occurs by a Brd4-independent mechanism through a novel interaction with specific regions of mitotic chromosomes. Thus, a wide range of viruses have adopted the strategy of linking their genomes to host chromosomes, but individual viruses use different chromosomal targets. Characterization of these targets will enable the development of antiviral therapies to eliminate the viral genomes from infected cells.

scholarly journals Association of Bovine Papillomavirus E2 Protein with Nuclear Structures In Vivo

2005 ◽  
Vol 79 (16) ◽  
pp. 10528-10539 ◽  
Author(s):  
Reet Kurg ◽  
Kristiina Sild ◽  
Aigi Ilves ◽  
Mari Sepp ◽  
Mart Ustav
Keyword(s):  
Cellular Protein ◽  
Micrococcal Nuclease ◽  
Viral Gene ◽  
Genome Replication ◽  
Bovine Papillomavirus ◽  
Transactivation Domain ◽  
Proliferating Cells ◽  
E2 Protein ◽  
Nuclear Structures

ABSTRACT Papillomaviruses are small DNA viruses which have the capacity to establish a persistent infection in mammalian epithelial cells. The papillomavirus E2 protein is a central coordinator of viral gene expression, genome replication, and maintenance. We have investigated the distribution of bovine papillomavirus E2 protein in nuclei of proliferating cells and found that E2 is associated with cellular chromatin. This distribution does not change during the entire cell cycle. The N-terminal transactivation domain, but not the C-terminal DNA-binding domain, of the E2 protein is responsible for this association. The majority of the full-length E2 protein can only be detected in chromatin-enriched fractions but not as a free protein in the nucleus. Limited micrococcal nuclease digestion revealed that the E2 protein partitioned to different chromatin regions. A fraction of the E2 protein was located at nuclear sites that are resistant against nuclease attack, whereas the remaining E2 resided on compact chromatin accessible to micrococcal nuclease. These data suggest that there are two pools of E2 in the cell nucleus: one that localizes on transcriptionally inactive compact chromatin and the other, which compartmentalizes to transcriptionally active nuclear structures of the cell. Our data also suggest that E2 associates with chromatin through cellular protein(s), which in turn is released from chromatin at 0.4 M salt.

scholarly journals Dynamic Localization of the Human Papillomavirus Type 11 Origin Binding Protein E2 through Mitosis While in Association with the Spindle Apparatus

2006 ◽  
Vol 80 (10) ◽  
pp. 4792-4800 ◽  
Author(s):  
Luan D. Dao ◽  
Aaron Duffy ◽  
Brian A. Van Tine ◽  
Shwu-Yuan Wu ◽  
Cheng-Ming Chiang ◽  
...  
Keyword(s):  
Human Papillomavirus ◽  
Binding Protein ◽  
Cellular Protein ◽  
Bovine Papillomavirus ◽  
Mitotic Spindles ◽  
Mitotic Chromosomes ◽  
Mitotic Apparatus ◽  
Viral Origin ◽  
E2 Protein ◽  
Origin Binding Protein

ABSTRACT Papillomaviral DNA replicates as extrachromosomal plasmids in squamous epithelium. Viral DNA must segregate equitably into daughter cells to persist in dividing basal/parabasal cells. We have previously reported that the viral origin binding protein E2 of human papillomavirus types 11 (HPV-11), 16, and 18 colocalized with the mitotic spindles. In this study, we show the localization of the HPV-11 E2 protein to be dynamic. It colocalized with the mitotic spindles during prophase and metaphase. At anaphase, it began to migrate to the central spindle microtubules, where it remained through telophase and cytokinesis. It was additionally observed in the midbody at cytokinesis. A peptide spanning residues 285 to 308 in the carboxyl-terminal domain of HPV-11 E2 (E2C) is necessary and sufficient to confer localization on the mitotic spindles. This region is conserved in HPV-11, -16, and -18 and bovine papillomavirus type 4 (BPV-4) E2 and is also required for the respective E2C to colocalize with the mitotic spindles. The E2 protein of bovine papillomavirus type 1 is tethered to the mitotic chromosomes via the cellular protein Brd4. However, the HPV-11 E2 protein did not associate with Brd4 during mitosis. Lastly, a chimeric BPV-1 E2C containing the spindle localization domain from HPV-11 E2C gained the ability to localize to the mitotic spindles, whereas the reciprocal chimera lost the ability. We conclude that this region of HPV E2C is critical for localization with the mitotic apparatus, enabling the HPV DNA to sustain persistent infections.

scholarly journals High- and Low-mobility Populations of HP1 in Heterochromatin of Mammalian Cells

2004 ◽  
Vol 15 (6) ◽  
pp. 2819-2833 ◽  
Author(s):  
Lars Schmiedeberg ◽  
Klaus Weisshart ◽  
Stephan Diekmann ◽  
Gabriele Meyer zu Hoerste ◽  
Peter Hemmerich
Keyword(s):  
Mammalian Cells ◽  
Constitutive Heterochromatin ◽  
Chromatin Condensation ◽  
Cell Types ◽  
Correlation Spectroscopy ◽  
Chromosomal Protein ◽  
Mitotic Chromosomes ◽  
Heterochromatin Protein 1 ◽  
Stable Conformation ◽  
Fluorescence Correlation

Heterochromatin protein 1 (HP1) is a conserved nonhistone chromosomal protein with functions in euchromatin and heterochromatin. Here we investigated the diffusional behaviors of HP1 isoforms in mammalian cells. Using fluorescence correlation spectroscopy (FCS) and fluorescence recovery after photobleaching (FRAP) we found that in interphase cells most HP1 molecules (50–80%) are highly mobile (recovery halftime: t1/2 ≈ 0.9 s; diffusion coefficient: D ≈ 0.6–0.7 μm2 s-1). Twenty to 40% of HP1 molecules appear to be incorporated into stable, slow-moving oligomeric complexes (t1/2 ≈ 10 s), and constitutive heterochromatin of all mammalian cell types analyzed contain 5–7% of very slow HP1 molecules. The amount of very slow HP1 molecules correlated with the chromatin condensation state, mounting to more than 44% in condensed chromatin of transcriptionally silent cells. During mitosis 8–14% of GFP-HP1α, but not the other isoforms, are very slow within pericentromeric heterochromatin, indicating an isoform-specific function of HP1α in heterochromatin of mitotic chromosomes. These data suggest that mobile as well as very slow populations of HP1 may function in concert to maintain a stable conformation of constitutive heterochromatin throughout the cell cycle.

scholarly journals Effect of Bovine Papillomavirus E2 Protein-Specific Monoclonal Antibodies on Papillomavirus DNA Replication

1999 ◽  
Vol 73 (6) ◽  
pp. 4670-4677 ◽  
Author(s):  
Reet Kurg ◽  
Jüri Parik ◽  
Erkki Juronen ◽  
Tiina Sedman ◽  
Aare Abroi ◽  
...  
Keyword(s):  
Monoclonal Antibodies ◽  
Intramolecular Interactions ◽  
Hinge Region ◽  
Bovine Papillomavirus ◽  
Dependent Manner ◽  
Transactivation Domain ◽  
Dimerization Domain ◽  
Fab Fragment ◽  
Concentration Dependent Manner ◽  
E2 Protein

ABSTRACT The bovine papillomavirus type 1 (BPV-1) E2 protein is the master regulator of papillomavirus replication and transcription. We have raised a panel of monoclonal antibodies (MAbs) against the BPV-1 E2 protein and used them to probe the structure and function of the protein. Five MAbs reacted with linear epitopes, and four MAbs recognized conformation-dependent epitopes which mapped within the C-terminal DNA-binding and dimerization domain. MAb 1E2 was able to recognize the replication- and transactivation-defective but not the competent conformation of the transactivation domain of the E2 protein. MAb 5H4 prevented efficiently the formation of E2-DNA as well as E2-dependent E1-E2-origin complexes and also dissociated preformed complexes in a concentration-dependent manner. Cotransfection of several MAbs with the BPV-1 minimal origin plasmid pUCAlu into CHO4.15 cells resulted in a dose-dependent inhibition of replication. Inhibition of replication by MAb 5H4 and the Fab′ fragment of 5H4 correlated with their ability to dissociate the E2 protein from the DNA. MAb 3F12 and MAbs 1H10 and 1E4, directed against the hinge region, were also capable of inhibiting BPV-1 origin replication in CHO4.15 cells. However, the Fab′ fragments of 1H10 and 3F12 had no effect in the transient replication assay. These data suggest that MAbs directed against the hinge region sterically hinder the inter- or intramolecular interactions required for the replication activity of the E2 protein.

scholarly journals The Mitotic Chromosome Binding Activity of the Papillomavirus E2 Protein Correlates with Interaction with the Cellular Chromosomal Protein, Brd4

2005 ◽  
Vol 79 (8) ◽  
pp. 4806-4818 ◽  
Author(s):  
Michael K. Baxter ◽  
Maria G. McPhillips ◽  
Keiko Ozato ◽  
Alison A. McBride
Keyword(s):  
Transcriptional Activation ◽  
Transcriptional Repression ◽  
Mitotic Chromosome ◽  
Structural Model ◽  
Binding Activity ◽  
Chromosomal Protein ◽  
Transactivation Domain ◽  
Mitotic Chromosomes ◽  
Functional Region ◽  
Chromosome Binding

ABSTRACT The papillomavirus transcriptional activator, E2, is involved in key functions of the viral life cycle. These include transcriptional regulation, viral DNA replication, and viral genome segregation. The transactivation domain of E2 is required for each of these functions. To identify the regions of the domain that mediate binding to mitotic chromosomes, a panel of mutations has been generated and their effect on various E2 functions has been analyzed. A structural model of the bovine papillomavirus type 1 (BPV1) E2 transactivation domain was generated based on its homology with the solved structure of the human papillomavirus type 16 (HPV16) domain. This model was used to identify distinct surfaces of the domain to be targeted by point mutation to further delineate the functional region of the transactivation domain responsible for mitotic chromosome association. The mutated E2 proteins were assessed for mitotic chromosome binding and, in addition, transcriptional activation and transcriptional repression activities. Mutation of amino acids R37 and I73, which are located on a surface of the domain that in HPV16 E2 is reported to mediate self-interaction, completely eliminated mitotic chromosome binding. Mitotic chromosome binding activity was found to correlate well with the ability to interact with the cellular chromosomal associated factor Brd4, which has recently been proposed to mediate the association between BPV1 E2 and mitotic chromosomes.

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