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Brd4 is required for recovery from antimicrotubule drug-induced mitotic arrest: preservation of acetylated chromatin.

ABSTRACT: The mammalian bromodomain protein Brd4 interacts with mitotic chromosomes by binding to acetylated histone H3 and H4 and is thought to play a role in epigenetic memory. Mitotic cells are susceptible to antimicrotubule drugs. These drugs activate multiple response pathways and arrest cells at mitosis. We found that Brd4 was rapidly released from chromosomes upon treatment with antimicrotubule drugs, including the reversible agent nocodazole. Yet, when nocodazole was withdrawn, Brd4 was reloaded onto chromosomes, and cells proceeded to complete cell division. However, cells in which a Brd4 allele was disrupted (Brd4+/-), and expressing only half of the normal Brd4 levels, were defective in reloading Brd4 onto chromosomes. Consequently, Brd4+/- cells were impaired in their ability to recover from nocodazole-induced mitotic arrest: a large fraction of +/- cells failed to reach anaphase after drug withdrawal, and those that entered anaphase showed an increased frequency of abnormal chromosomal segregation. The reloading defect observed in Brd4+/- cells coincided with selective hypoacetylation of lysine residues on H3 and H4. The histone deacetylase inhibitor trichostatin A increased global histone acetylation and perturbed nocodazole-induced Brd4 unloading. Brd4 plays an integral part in a cellular response to drug-induced mitotic stress by preserving a properly acetylated chromatin status.

SUBMITTER: Nishiyama A

PROVIDER: S-EPMC1356591 | biostudies-literature | 2006 Feb

REPOSITORIES: biostudies-literature

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Brd4 is required for recovery from antimicrotubule drug-induced mitotic arrest: preservation of acetylated chromatin.

Nishiyama Akira A Dey Anup A Miyazaki Jun-Ichi J Ozato Keiko K

Molecular biology of the cell 20051207 2

The mammalian bromodomain protein Brd4 interacts with mitotic chromosomes by binding to acetylated histone H3 and H4 and is thought to play a role in epigenetic memory. Mitotic cells are susceptible to antimicrotubule drugs. These drugs activate multiple response pathways and arrest cells at mitosis. We found that Brd4 was rapidly released from chromosomes upon treatment with antimicrotubule drugs, including the reversible agent nocodazole. Yet, when nocodazole was withdrawn, Brd4 was reloaded o ...[more]

PMID: 16339075

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Project description:During the human papillomavirus 16 (HPV16) life cycle, the E2 protein binds simultaneously to the viral genome and host chromatin throughout mitosis, ensuring viral genomes reside in daughter cell nuclei following cell division. Previously, we demonstrated that CK2 phosphorylation of E2 on serine 23 promotes interaction with TopBP1, and that this interaction is required for optimum E2 mitotic chromatin association and plasmid segregation function. Others have implicated BRD4 in mediating the plasmid segregation function of E2 and we have demonstrated that there is a TopBP1-BRD4 complex in the cell. We therefore further investigated the role of the E2-BRD4 interaction in mediating E2 association with mitotic chromatin and plasmid segregation function. Using a combination of immunofluorescence and our novel plasmid segregation assay in U2OS and N/Tert-1 cells stably expressing a variety of E2 mutants, we report that direct interaction with the BRD4 carboxyl-terminal motif (CTM) and TopBP1 is required for E2 association with mitotic chromatin and plasmid segregation. We also identify a novel TopBP1-mediated interaction between E2 and the BRD4 extra-terminal domain in vivo. In addition, we demonstrate for the first time that E2 plasmid segregation function occurs in human foreskin keratinocytes immortalized by HPV16. Overall, the results demonstrate that direct interaction with TopBP1 and the BRD4 CTM is required for E2 mitotic chromatin association and plasmid segregation function. Disruption of this complex offers therapeutic options for targeting segregation of viral genomes into daughter cells, potentially combating HPV16 infections and cancers that retain episomal genomes. IMPORTANCE Human papillomavirus 16 (HPV16) is a causative agent in around 3%-4% of all human cancers, and currently, there are no anti-viral therapeutics available for combating this disease burden. In order to identify new therapeutic targets, we must increase our understanding of the HPV16 life cycle. Previously, we demonstrated that an interaction between E2 and the cellular protein TopBP1 mediates the plasmid segregation function of E2, allowing distribution of viral genomes into daughter nuclei following cell division. Here, we demonstrate that E2 interaction with an additional host protein, BRD4, is also essential for E2 segregation function, and that BRD4 exists in a complex with TopBP1. Overall, these results enhance our understanding of a critical part of the HPV16 life cycle and presents several therapeutic targets for disruption of the viral life cycle.

Dataset Information

Brd4 is required for recovery from antimicrotubule drug-induced mitotic arrest: preservation of acetylated chromatin.

Publications

Brd4 is required for recovery from antimicrotubule drug-induced mitotic arrest: preservation of acetylated chromatin.

Similar Datasets

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