Endocytic SNAREs are involved in optimalCoxiella burnetiivacuole development

Abstract

SummaryCoxiella burnetii is a Gram-negative intracellular bacterium. As previously described, both the endocytic and the autophagic pathways contribute to the maturation of Coxiella replicative vacuoles (CRVs). The large CRVs share the properties of both phagolysosomal and autophagolysosomal compartments. Vamp3, Vamp7 and Vamp8 are v-SNAREs involved in the endocytic pathway which participate mainly in the fusion between endosomes and lysosomes. In the present study we observed that Vamp7 interacts with C. burnetii at different infection times (1 h-48 h p.i.). We have determined that a truncated mutant of Vamp7 (Vamp7 NT) and a siRNA against this SNARE protein affects the optimal development of CRVs, suggesting that Vamp7 mediates fusion events that are required for the biogenesis of CRVs. Indeed, we have observed that overexpression of Vamp7 NT inhibited the heterotypic fusion with lysosomes and the homotypic fusion between individual Coxiella phagosomes and CRVs. Moreover, we have detected in the vacuole membrane, at different infection times, the Vamp7 partners (Vti1a and Vti1b). Interestingly, treatment with chloramphenicol reduced the colocalization between C. burnetii and Vamp7, Vti1a or Vti1b, indicating that the recruitment of these SNAREs proteins is a bacteria-driven process that favours the CRV biogenesis, likely by facilitating the interaction with the endolysosomal compartment.

Coxiella burnetii Effector Proteins That Localize to the Parasitophorous Vacuole Membrane Promote Intracellular Replication

“…Moreover, C. burnetii also requires membrane components from autophagic and secretory compartments for PV expansion (10-12, 15, 61). Several SNARE proteins, including syntaxin-8, syntaxin-17, and vesicle-associated membrane protein 7 (VAMP7), localize to the PV membrane, with syntaxin-17 and VAMP7 having demonstrated roles in vacuole expansion (11,15). Coxiella researchers are just beginning to investigate the molecular mechanisms that control PV fusogenicity, a process that likely involves the activities of multiple Rab GTPases, SNARE proteins, and Dot/ Icm effectors (11,(14)(15)(16).…”

“…In response to vacuole acidification, C. burnetii becomes metabolically active, resulting in the synthesis of bacterial proteins required for PV maturation (8,9). PV biogenesis involves fusion of the vacuole with vesicles originating from endocytic, autophagic, and secretory pathways through processes regulated by multiple host factors, including Rab GTPases and soluble N-ethylmaleimide-sensitive factor attachment protein receptors (SNAREs) (10)(11)(12)(13)(14)(15).…”

Space: A Final Frontier for Vacuolar Pathogens

“…For example, the CCV is considered a promiscuous subcellular compartment, as fusion with host endosomal, lysosomal and secretory pathways has been observed (36–38). The core machinery that orchestrates docking and fusion of synaptic vesicles mediates membrane fusion events in a wide variety of membrane trafficking pathways (39).…”

The Effector Cig57 Hijacks FCHO-Mediated Vesicular Trafficking to Facilitate Intracellular Replication of Coxiella burnetii

“…The retromer trafficking process, required for retrograde transport from endosomes to the trans -Golgi network [21], has been shown to contribute to the maturation of the CCV with retromer subunits VPS35 and VPS29 and sorting nexins all required for expansion of the CCV [22]. In addition, v-SNAREs VAMP3, VAMP7 and VAMP8 are found on the CCV membrane and have been shown, via siRNA experiments, to aide fusion events with vesicles in the endolysosomal pathway [23]. The autophagic SNARE, syntaxin-17, is required for the homotypic fusion of CCVs [22, 23].…”