Ubiquitin-Mediated Response to Microsporidia and Virus Infection in C. elegans

Abstract

Microsporidia comprise a phylum of over 1400 species of obligate intracellular pathogens that can infect almost all animals, but little is known about the host response to these parasites. Here we use the whole-animal host C. elegans to show an in vivo role for ubiquitin-mediated response to the microsporidian species Nematocida parisii, as well to the Orsay virus, another natural intracellular pathogen of C. elegans. We analyze gene expression of C. elegans in response to N. parisii, and find that it is similar to response to viral infection. Notably, we find an upregulation of SCF ubiquitin ligase components, such as the cullin ortholog cul-6, which we show is important for ubiquitin targeting of N. parisii cells in the intestine. We show that ubiquitylation components, the proteasome, and the autophagy pathway are all important for defense against N. parisii infection. We also find that SCF ligase components like cul-6 promote defense against viral infection, where they have a more robust role than against N. parisii infection. This difference may be due to suppression of the host ubiquitylation system by N. parisii: when N. parisii is crippled by anti-microsporidia drugs, the host can more effectively target pathogen cells for ubiquitylation. Intriguingly, inhibition of the ubiquitin-proteasome system (UPS) increases expression of infection-upregulated SCF ligase components, indicating that a trigger for transcriptional response to intracellular infection by N. parisii and virus may be perturbation of the UPS. Altogether, our results demonstrate an in vivo role for ubiquitin-mediated defense against microsporidian and viral infections in C. elegans.

Caenorhabditis elegans as an Emerging Model for Virus-Host Interactions

“…These observations suggest that DRH-1 might function as a sensor of viral RNA, analogous to RIG-I, but instead trigger an RNAi response (26). Others have argued that [17,28,43]). Virus infection and replication leads to the production of viral dsRNA that triggers the antiviral RNAi pathway.…”

“…These fungal-related pathogens have been recovered from wild-caught nematodes, and one species, Nematocida parisii, causes a lethal intestinal infection in C. elegans (12). Examination of transcriptional responses to N. parisii infection identified a set of differentially regulated genes (DEGs) that shared a large degree of overlap with DEGs found after OV infection but little overlap with DEGs observed after infections with extracellular pathogens (43,44). This suggested that there might be a unique host response to intracellular pathogens.…”

“…This suggested that there might be a unique host response to intracellular pathogens. Many of the DEGs that were upregulated encode ubiquitylation-related machinery, in particular members of Skp1-Cull-F-box (SCF) class of multisubunit E3 ubiquitin ligases (43). Furthermore, RNAi knockdown of core SCF ligase components such as CUL-6 promoted N. parisii and OV infection (43).…”

“…Many of the DEGs that were upregulated encode ubiquitylation-related machinery, in particular members of Skp1-Cull-F-box (SCF) class of multisubunit E3 ubiquitin ligases (43). Furthermore, RNAi knockdown of core SCF ligase components such as CUL-6 promoted N. parisii and OV infection (43). These studies suggest that C. elegans responds to intracellular infection by upregulation of core SCF ligase components such as CUL-6 as well as F-box proteins that modulate SCF ligase complex target specificity.…”

Antimicrobial effectors in the nematode Caenorhabditis elegans : an outgroup to the Arthropoda

“…Knock-down of lgg-1 and atg-18 (encoding the homolog of human WIPI1) by RNAi resulted in increased bacterial load, indicating that autophagy is required for controlling N. parisii infection. In addition, examination of transgenic worms carrying a translational GFP reporter for LGG-1 revealed that the autophagy machinery is targeted to N. parisii cells [42]. (iii) Infection with the extracellular pathogen S. aureus also activates the expression of several autophagy genes and this activation is dependent on the bHLH transcription factor HLH-30, which is required for the expression of 80% of the transcriptional C. elegans response to S. aureus, including AMP genes [23].…”