Chromatin bound bacterial effector AnkA recruits HDAC1 and modifies host gene expression

Control of host epigenetics is becoming evident as a mechanism by which symbionts and pathogens survive. <em>Anaplasma phagocytophilum</em>, an obligate intracellular bacterium, downregulates multiple host defense genes where histone deacetylase 1 (HDAC1) binds and histone 3 is deacetylated at their promoters, including the NADPH oxidase component, <em>CYBB</em>. How HDAC1 is targeted to defense gene promoters is unknown. Ankyrin A (AnkA), an <em>A. phagocytophilum</em> T4SS effector, enters the granulocyte nucleus, binds stretches of AT-rich DNA and alters transcription of antimicrobial defense genes, including downregulation of <em>CYBB</em>. Here we found AnkA binds to a predicted matrix attachment region in the proximal <em>CYBB</em> promoter. Using the <em>CYBB</em> promoter as a model of <em>cis</em>-gene silencing, we interrogated the mechanism of AnkA-mediated <em>CYBB</em> repression. The N-terminus of AnkA was critical for nuclear localization, the central ANK repeats and C-terminus were important for DNA binding, and most promoter activity localized to the central ANK repeats. Furthermore, a direct interaction between AnkA and HDAC1 was detected at the <em>CYBB</em> promoter, and was critical for AnkA-mediated <em>CYBB</em> repression. This novel microbial manipulation of host chromatin and gene expression provides important evidence of the direct effects that prokaryotic nuclear effectors can exert over host transcription and function.