Abstract
Tick-borne spotted fever group (SFG) Rickettsia species must be able to infect both vertebrate and arthropod host cells. The host actin-related protein 2/3 (Arp2/3) complex is important in the invasion process and actin-based motility for several intracellular bacteria, including SFG Rickettsia in Drosophila and mammalian cells. To investigate the role of the tick Arp2/3 complex in tick-Rickettsia interactions, open reading frames of all subunits of the protein including Arp2, Arp3, ARPC1, ARPC2, ARPC3, ARPC4, and ARPC5 were identified from Dermacentor variabilis. Amino acid sequence analysis showed variation (ranging from 25–88%) in percent identity compared to the corresponding subunits of the complex from Drosophila melanogaster, Mus musculus, Homo sapiens, and Saccharomyces cerevisiae. Potential ATP binding sites were identified in D. variabilis (Dv) Arp2 and Arp3 subunits as well as five putative WD (Trp-Asp) motifs which were observed in DvARPC1. Transcriptional profiles of all subunits of the DvArp2/3 complex revealed greater mRNA expression in both Rickettsia-infected and -uninfected ovary compared to midgut and salivary glands. In response to R. montanensis infection of the tick ovary, the mRNA level of only DvARPC4 was significantly upregulated compared to uninfected tissues. Arp2/3 complex inhibition bioassays resulted in a decrease in the ability of R. montanensis to invade tick tissues with a significant difference in the tick ovary, indicating a role for the Arp2/3 complex in rickettsial invasion of tick cells. Characterization of tick-derived molecules associated with rickettsial infection is imperative in order to better comprehend the ecology of tick-borne rickettsial diseases.
Highlights
Ticks serve as both the transmission vectors and reservoir hosts for members of the obligate intracellular spotted fever group (SFG) Rickettsia
Full-length cDNA clones corresponding to the transcript of DvArp2/3 complex subunit genes (DvArp2, DvArp3, DvARPC1, DvARPC2, DvARPC3, DvARPC4, and DvARPC5) from D. variabilis were isolated
The current study provides the molecular and functional characterization of the actinrelated protein 2/3 (Arp2/3) complex from D. variabilis, a competent vector of SFG Rickettsia
Summary
Ticks serve as both the transmission vectors and reservoir hosts for members of the obligate intracellular spotted fever group (SFG) Rickettsia. Horizontal transmission of rickettsiae between ticks can occur via vertebrate hosts; vertical transmission between life cycle stages and transovarial transmission facilitates maintenance of the infection in tick hosts. Some tick species such as the American dog tick, Dermacentor variabilis, are associated with horizontal transmission of pathogenic SFG Rickettsia (e.g. Rickettsia rickettsii) [1], as well as vertical transmission of organisms with limited or no pathogenicity to humans (e.g. Rickettsia montanensis) [2,3,4,5,6]. Despite differences between host molecules associated with rickettsial entry in vertebrate and invertebrate hosts, the actinrelated protein 2/3 (Arp2/3) complex is recognized as a central molecule stimulated during the internalization of SFG Rickettsia into host cells, independent of cell origin
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