Anaplasma regulation of host granulocyte function

University Of Maryland Baltimore, Baltimore MD

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Abstract

DESCRIPTION (provided by applicant): Human granulocytic anaplasmosis (HGA) is an emerging tick-borne disease caused by Anaplasma phagocytophilum, an obligate intracellular bacterium of neutrophils. A. phagocytophilum infection impairs neutrophil function by transcriptional reprogramming, where the reprogrammed neutrophil promotes inflammatory recruitment of new neutrophils, tissue injury, ineffective regulation of inflammation, and poor antimicrobial responses. We studied altered neutrophil function with A. phagocytophilum infection and focused on how the nuclear effector protein AnkA, when delivered into the host cell where it binds to promoters of genes regulated with infection, induces epigenetic chromatin remodeling and transcriptional reprogramming. The granulocyte transcriptome with A. phagocytophilum infection shows a number of differentially transcribed genes that promote infection [3-6]. Given the meager genomic resources of A. phagocytophilum, it is difficult to explain the extent of host transcriptional change and functional reprogramming by individual translocated effector proteins. This implies that the bacterium exerts influence over global gene transcription, including chromatin and histone remodeling, perhaps by targeting conserved mechanisms of transcriptional regulation such as in cellular differentiation and neoplasia. AnkA has properties that suggest function as a matrix attachment region-binding protein that could regulate access of chromosomal territories to transcriptional modifiers, a new paradigm in bacteria-host interactions. We hypothesize that AnkA binds to promoters of some transcriptionally regulated genes and modifies or recruits modifiers of epigenetic chromatin marks or transcription factors. In addition, we hypothesize that A. phagocytophilum reprograms the global neutrophil transcriptome by altering the epigenome through AnkAs action on nuclear matrix, chromatin, and transcriptional apparatus recruitment. We propose the following aims: 1. To identify AnkA binding sites in the CYBB promoter and to define AnkA domains or motifs involved in CYBB promoter binding and transcriptional activity. 2. To determine whether AnkA affects host gene transcription through direct action at the CYBB promoter or through recruitment of chromatin remodeling or transcription factors. 3. To determine whether AnkA functions as a matrix attachment region-binding protein that tethers DNA to nuclear matrix, regulates DNA loopscape, and permits docking of other chromatin modifiers in global transcriptional regulation. The effects that bacteria have over cellular transcription are increasingly recognized. Testing these hypotheses will provide evidence of a potentially powerful mechanism for prokaryotic control over eukaryotes. The long- term goals are to develop a mechanistic understanding of how bacteria with intimate host cell associations circumvent host functions. This information could allow rational preventions and therapies for HGA, but could also span biology and medicine, since such molecules could be engineered as epigenetic tools or therapies.