GSE109830
MYR1-dependent effectors are the major drivers of a host cell's early response to Toxoplasma including counteracting MYR1-independent effects
The intracellular parasite Toxoplasma gondii uses a diverse repertoire of effector molecules to manipulate its host cell. The first effectors to be introduced into the host cell derive from rhoptries (ROPs) and are secreted exclusively during invasion. Once the parasite has established a parasitophorous vacuole, a subset of secreted dense granule effector proteins (GRAs) are then translocated across the parasitophorous vacuolar membrane in a MYR1-dependent manner to enter the host cell cytoplasm and nucleus. Translocation of these GRA effectors is also dependent on the activity of Toxoplasma Aspartyl protease 5 (ASP5) which either directly cleaves the effectors or potentiates translocation in some other way. To determine the totality of MYR1-dependent (predominantly GRA) and MYR1-independent (e.g., ROP) host responses as well as the degree of overlap between MYR1- and ASP5-dependent effectors, we analyzed the RNAseq expression profile of human foreskin fibroblasts infected with wild type (RH strain) Toxoplasma gondii tachyzoites, RH?myr1, RH?asp5 and their respective complements. We show that a majority subset of the differentially regulated host gene responses during infection with wild type parasites are modulated in a MYR1-dependent manner. Gene set enrichment analysis of the MYR1-dependent host responses indicates that, among others, there is a clear up-regulation related to E2F transcription factors and the cell cycle and a clear down-regulation in expression related to interferon signaling. The ASP5-dependent host gene responses were less numerous and encompassed fewer gene sets than the MYR1-dependent responses, indicating that translocation and/or activity of a subset of effectors is MYR1- but not ASP5-dependent. Consistent with this, we show that even though MYR1 is normally cleaved by ASP5, such cleavage is not necessary for MYR1's role in translocation. Interestingly, some responses were seen upon infection with RH?myr1 but not RH-WT; these previously “hidden” responses are likely due to the normally counter-balancing action of MYR1-dependent and -independent activities. The host genes and gene sets revealed here to be MYR1-dependent provide new insight into the relative contribution of GRA- vs. ROP-mediated effectors in co-opting host cell functions. Overall design: RNASeq of human foreskin fibroblasts, infected with Toxoplasma, harvested 6 hours post infection. Samples are: Mock infected, infected with a WT RH, RH?myr1,  RH?myr1::MYR1, RH?asp5, RH?asp5::ASP5.