Directional actin polymerization associated with spotted fever group Rickettsia infection of Vero cells

Abstract

Members of the spotted fever group (SFG) of rickettsiae spread rapidly from cell to cell by an unknown mechanism(s). Staining of Rickeffsia rickettsii-infected Vero cells with rhodamine phalloidin demonstrated unique actin filaments associated with one pole of intracellular rickettsiae. F-actin tails greater than 70 ,m in length were seen extending from rickettsiae. Treatment of infected cells with chloramphenicol eliminated rickettsia-associated F-actin tails, suggesting that de novo protein synthesis of one or more rickettsial proteins is required for tail formation. Rickettsiae were coated with F-actin as early as 15 min postinfection, and tail formation was detected by 30 min. A survey of virulent and avirulent species within the SFG rickettsiae demonstrated that all formed actin tails. Typhus group rickettsiae, which do not spread directly from cell to cell, lacked F-actin tails entirely or exhibited only very short tails. Transmission electron microscopy demonstrated fibrillar material in close association with R. rickeftsii but not Rickeffsia prowazekii. Biochemical evidence that actin polymerization plays a role in movement was provided by showing that transit ofR. rickettsii from infected cells into the cell culture medium was inhibited by treatment of host cells with cytochalasin D. These data suggest that the cell-to-cell transmission of SFG rickettsiae may be aided by induction of actin polymerization in a fashion similar to that described for Shigella flexneri and Listeria monocytogenes.

Chlamydia trachomatis utilizes the host cell microtubule network during early events of infection

“…Intracellular microorganisms of both viral and bacterial origin appear to use polymerization of host cell actin as a mediator of movement within the host cell cytoplasm. These include vaccinia virus (Cudmore et al, 1995), Listeria monocytogenes (Cossart and Kocks, 1994), Shigella flexneri (Goldberg and Sansonetti, 1993) and members of the spotted fever group of rickettsiae (Heinzen et al, 1993). Although chlamydiae are also intracellular pathogens, their life cycle differs markedly from that of the above-mentioned pathogens, because the entire intracellular part of the chlamydial life cycle takes place inside a host cell-derived endosome, whereas vaccinia virus, shigellae, listeriae and rickettsiae all escape from the endosome shortly after endocytosis.…”

Advances in Rickettsia Pathogenicity

“…70 Another key element came from R. typhi analysis. Short and occasional actin tails (<1%) were observed for these TG rickettsiae, 58,59 which were able to move approximately at the same rate as R. rickettsii, at least some of them, while others exhibited rather erratic movements. 71 However, R. typhi genome sequencing confirmed the absence of rickA, 52 thus reinforcing the role for another protein in actin-based motility.…”

“…56,57 The capacity of rickettsiae to use the actin-based motility system for promoting cell-to-cell spreading was evidenced for several SFG rickettsiae including R. conorii, R. rickettsii, R. montanensis, R. parkeri, R. australis, and R. monacensis. [58][59][60] It was long considered that actin-based motility was confined to the SFG rickettsiae. Accordingly, the rickettsial factor susceptible to be responsible for actin polymerization was identified through the comparative analysis of R. conorii (SFG) and R. prowazekii (TG) genomes.…”

“…74 As described for other microbial pathogens, including Listeria monocytogenes and Shigella flexneri, the intracellular actin-based motility is also exploited by rickettsiae to escape the host cell. 10,59,65 The filaments of actin push the rickettsiae to the surface of the host cell, where the host cell membrane is deformed outward and invaginates into the adjacent cell. Disruption of both cell membranes then enables the rickettsia to enter the adjoining cell without being exposed to the extracellular environment.…”

Rickettsial Infections

“…30 The spotted fever group rickettsiae are capable of polymerizing monomeric actin filaments in the cytoplasm at one of their poles. 31,32 The net result of this action is propulsion of rickettsiae through the cytoplasm and penetration of neighboring cells through the cell membranes. This allows rickettsiae to affect short segments of the microvasculature by invading contiguous endothelial cells without being exposed to the intravascular compartment.…”