title: The Pathogen-Occupied Vacuoles of Anaplasma phagocytophilum and Anaplasma marginale Interact with the Endoplasmic Reticulum.
abstract: The genus Anaplasma consists of tick-transmitted obligate intracellular bacteria that invade white or red blood cells to cause debilitating and potentially fatal infections. A. phagocytophilum, a human and veterinary pathogen, infects neutrophils to cause granulocytic anaplasmosis. A. marginale invades bovine erythrocytes. Evidence suggests that both species may also infect endothelial cells in vivo. In mammalian and arthropod host cells, A. phagocytophilum and A. marginale reside in host cell derived pathogen-occupied vacuoles (POVs). While it was recently demonstrated that the A. phagocytophilum-occupied vacuole (ApV) intercepts membrane traffic from the trans-Golgi network, it is unclear if it or the A. marginale-occupied vacuole (AmV) interacts with other secretory organelles. Here, we demonstrate that the ApV and AmV extensively interact with the host endoplasmic reticulum (ER) in endothelial, myeloid, and/or tick cells. ER lumen markers, calreticulin, and protein disulfide isomerase, and the ER membrane marker, derlin-1, were pronouncedly recruited to the peripheries of both POVs. ApV association with the ER initiated early and continued throughout the infection cycle. Both the ApV and AmV interacted with the rough ER and smooth ER. However, only derlin-1-positive rough ER derived vesicles were delivered into the ApV lumen where they localized with intravacuolar bacteria. Transmission electron microscopy identified multiple ER-POV membrane contact sites on the cytosolic faces of both species' vacuoles that corresponded to areas on the vacuoles' lumenal faces where intravacuolar Anaplasma organisms closely associated. A. phagocytophilum is known to hijack Rab10, a GTPase that regulates ER dynamics and morphology. Yet, ApV-ER interactions were unhindered in cells in which Rab10 had been knocked down, demonstrating that the GTPase is dispensable for the bacterium to parasitize the ER. These data establish the ApV and AmV as pathogen-host interfaces that directly engage the ER in vertebrate and invertebrate host cells and evidence the conservation of ER parasitism between two Anaplasma species.
authors.affiliation: Department of Microbiology and Immunology, Virginia Commonwealth University School of Medicine Richmond, VA, USA.
authors.forename: Hilary K
authors.initials: HK
authors.lastname: Truchan
authors.affiliation: Department of Microbiology and Immunology, Virginia Commonwealth University School of Medicine Richmond, VA, USA.
authors.forename: Chelsea L
authors.initials: CL
authors.lastname: Cockburn
authors.affiliation: Department of Microbiology and Immunology, Virginia Commonwealth University School of Medicine Richmond, VA, USA.
authors.forename: Kathryn S
authors.initials: KS
authors.lastname: Hebert
authors.affiliation: Program in Vector Borne Diseases, Department of Veterinary Microbiology and Pathology, Washington State UniversityPullman, WA, USA; The Paul G. Allen School for Global Animal Health, Washington State UniversityPullman, WA, USA.
authors.forename: Forgivemore
authors.initials: F
authors.lastname: Magunda
authors.affiliation: Program in Vector Borne Diseases, Department of Veterinary Microbiology and Pathology, Washington State UniversityPullman, WA, USA; Animal Disease Research Unit, Agricultural Research Service, U. S. Department of AgriculturePullman, WA, USA.
authors.forename: Susan M
authors.initials: SM
authors.lastname: Noh
authors.affiliation: Department of Microbiology and Immunology, Virginia Commonwealth University School of Medicine Richmond, VA, USA.
authors.forename: Jason A
authors.initials: JA
authors.lastname: Carlyon
mesh_terms: D042322:Anaplasma marginale / Q000276:immunology / Q000472:pathogenicity*; D041081:Anaplasma phagocytophilum / Q000276:immunology / Q000472:pathogenicity*; D000712:Anaplasmosis / Q000382:microbiology / Q000473:pathology*; D000818:Animals; D037282:Calreticulin / Q000378:metabolism; D045744:Cell Line, Tumor; D004721:Endoplasmic Reticulum / Q000382:microbiology / Q000473:pathology*; D042783:Endothelial Cells / Q000382:microbiology; D057809:HEK293 Cells; D018922:HL-60 Cells; D054884:Host-Pathogen Interactions / Q000276:immunology; D006801:Humans; D018884:Ixodes / Q000382:microbiology; D008565:Membrane Proteins / Q000378:metabolism; D046529:Microscopy, Electron, Transmission; D022423:Myeloid Cells / Q000382:microbiology; D019704:Protein Disulfide-Isomerases / Q000378:metabolism; D021381:Protein Transport; D034622:RNA Interference; D034741:RNA, Small Interfering; D014617:Vacuoles / Q000382:microbiology*; D020691:rab GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism
chemical_list: D037282:Calreticulin; C487709:DERL1 protein, human; D008565:Membrane Proteins; D034741:RNA, Small Interfering; C538901:Rab10 protein, human; D020691:rab GTP-Binding Proteins; D019704:Protein Disulfide-Isomerases
keywords: Anaplasmataceae; Rab; Rickettsia; endoplasmic reticulum; intracellular bacteria; pathogen synapse