Keiko Dawid, Ph.D.
Section on Molecular Genetics of Immunity
Gene Regulation in Innate Immunity
Macrophages and dendritic cells (DC) respond to pathogen stimuli and produce cytokines including interferons (IFNs), IL-1, IL-6, and TNF-alpha to impart anti-viral and anti-microbial status to the host. Our goal is to study molecular pathways that direct the development and function of macrophages and DCs. Our long-term interest has been the role of a transcription factor IRF8 in innate immunity. IRF8 is expressed in M_ and DC at high levels and is required for production of both type I and type II IFNs. IRF8 and related transcription factors including IRF3 and IRF7 are post-translationally modified by ubiquitin and small ubiquitin-like molecules (SUMO). SUMO modification of these factors almost always results in transcriptional repression. SUMO–mediated repression likely represents an important mechanism to limit overproduction of inflammatory cytokines.
Transcriptionally active genes are embedded in chromatin that is dynamically exchanged, whereas silenced genes are surrounded by more stable chromatin. The chromatin environment influences transcriptional processes and controls epigenetic regulation. We are interested in BRD4, a chromatin-binding protein associated with transcribed genes. We are also interested in histone H3.3, the variant histone that is selectively associated with actively expressed genes. BRD4 is a 200 kDa nuclear protein carrying two tandem bromodomains through which it binds to acetylated chromatin. BRD4 also interacts with the elongation factor P-TEFb and regulates transcription of many genes, including those induced by external stimuli. BRD4 is implicated in transcriptional memory across cell division because it stays on condensed chromosomes during mitosis and affects gene expression in the daughter cells. Despite close structural similarity with the standard H3.1 and H3.2, histone H3.3 has an extraordinary property, in that it is incorporated into nucleosomes and DNA only in actively transcribed genes. In contrast, H3.1, H3.2, and other standard core histones are incorporated into nucleosomes during DNA replication. The difference between H3.3 and H3.1/2 reflects distinct chromatin activities during replication and transcription. Although there is mounting recognition of the importance of transcription-coupled histone incorporation, the process and its physiological significance is still shrouded in mystery. Our goal is to elucidate the activity of BRD4 and histone H3.3 in the context of transcriptional activation and epigenetic memory.
Dr. Keiko Ozato received her Ph.D. in Developmental Biology from Kyoto University, Japan in 1973. Then, she trained at the Carnegie Institution of Washington, Johns Hopkins University, and NCI as a postdoctoral associate. Dr. Ozato came to NICHD in 1981 to launch an independent research group in molecular immunology and received tenure in 1987. All along, her research has focused on transcriptional gene regulation in innate immunity. Her laboratory isolated and reported IRF8 in 1990, a transcription factor critical for host resistance against pathogens in macrophages and dendritic cells. Her group demonstrated that IF8 is central to the induction of proinflammatory cytokines and autophagy regulation in these cells. With the longstanding interest in the role of chromatin in gene regulation, the Ozato lab later reported BRD4, a bromodomain protein that binds to acetylated histones. Their subsequent study showed that BRD4 recruits the elongation factor P-TEFb (CyclinT/CDk9 complex) and regulates many cellular and viral genes. They also showed that BRD4 remains on chromosomes during mitosis and plays a role in regulating transcription relevant to epigenetic memory. Extending the chromatin angle, the Ozato lab also studies transcription-coupled histone exchange focusing on the replacement histone H3.3. Dr. Ozato has been active in the research community and has published 330 papers, to date, in scientific journals. The current goal of the laboratory is to study the activities of these proteins in vivo using newly constructed mouse models.
Yoshida Y, Yoshimi R, Yoshii H, Kim D, Dey A, Xiong H, Munasinghe J, Yazawa I, O'Donovan MJ, Maximova OA, Sharma S, Zhu J, Wang H, Morse HC 3rd, Ozato K. The transcription factor IRF8 activates integrin-mediated TGF-β signaling and promotes neuroinflammation. Immunity. 2014;40(2):187-98.
Kurotaki D, Yamamoto M, Nishiyama A, Uno K, Ban T, Ichino M, Sasaki H, Matsunaga S, Yoshinari M, Ryo A, Nakazawa M, Ozato K, Tamura T. IRF8 inhibits C/EBPα activity to restrain mononuclear phagocyte progenitors from differentiating into neutrophils. Nat Commun. 2014;5:4978.
Kanno T, Kanno Y, LeRoy G, Campos E, Sun HW, Brooks SR, Vahedi G, Heightman TD, Garcia BA, Reinberg D, Siebenlist U, O'Shea JJ, Ozato K. BRD4 assists elongation of both coding and enhancer RNAs by interacting with acetylated histones. Nat Struct Mol Biol. 2014;21(12):1047-57.
Gupta M, Shin DM, Ramakrishna L, Goussetis DJ, Platanias LC, Xiong H, Morse HC 3rd, Ozato K. IRF8 directs stress-induced autophagy in macrophages and promotes clearance of Listeria monocytogenes. Nat Commun. 2015;6:6379.
Liang Q, Deng H, Li X, Wu X, Tang Q, Chang TH, Peng H, Rauscher FJ 3rd, Ozato K, Zhu F. Tripartite motif-containing protein 28 is a small ubiquitin-related modifier E3 ligase and negative regulator of IFN regulatory factor 7. J Immunol. 2011;187(9):4754-63.
Related Scientific Focus Areas
Genetics and Genomics
Molecular Biology and Biochemistry
This page was last updated on October 19th, 2017