Monoubiquitinated proteins decorate the Anaplasma phagocytophilum-occupied vacuolar membrane

An emerging theme among vacuole-adapted bacterial pathogens is the ability to hijack ubiquitin machinery to modulate host cellular processes and secure pathogen survival. Mono- and polyubiquitination differentially dictate the subcellular localization, activity, and fate of protein substrates. Monoubiquitination directs membrane traffic from the plasma membrane to the endosome and has been shown to promote autophagy. Anaplasma phagocytophilum is an obligate intracellular bacterium that replicates within a host cell-derived vacuole that co-opts membrane traffic and numerous other host cell processes. Here, we show that monoubiquitinated proteins decorate the A. phagocytophilum-occupied vacuolar membrane (AVM) during infection of promyelocytic HL-60 cell, endothelial RF/6A cells, and to a lesser extent, embryonic tick ISE6 cells. Monoubiquitinated proteins are present on the AVM upon its formation and continue to accumulate throughout infection. Tetracycline-mediated inhibition of de novo bacterial protein synthesis promotes the loss of ubiquitinated proteins from the AVM. This effect is reversible, as removal of tetracycline restores AVM ubiquitination to pretreatment levels. These results demonstrate a novel mechanism by which A. phagocytophilum remodels the composition of its host cell-derived vacuolar membrane and present the first example of a Rickettsiales pathogen co-opting ubiquitin during intracellular residence.