Toxoplasma gondii Infection Specifically Increases the Levels of Key Host MicroRNAs

Abstract

BackgroundThe apicomplexan parasite Toxoplasma gondii can infect and replicate in virtually any nucleated cell in many species of warm-blooded animals; thus, it has evolved the ability to exploit well-conserved biological processes common to its diverse hosts. Here we have investigated whether Toxoplasma modulates the levels of host microRNAs (miRNAs) during infection.Methodology/Principal FindingsUsing microarray profiling and a combination of conventional molecular approaches we report that Toxoplasma specifically modulates the expression of important host microRNAs during infection. We show that both the primary transcripts for miR-17∼92 and miR-106b∼25 and the pivotal miRNAs that are derived from miR-17∼92 display increased abundance in Toxoplasma-infected primary human cells; a Toxoplasma-dependent up-regulation of the miR-17∼92 promoter is at least partly responsible for this increase. The abundance of mature miR-17 family members, which are derived from these two miRNA clusters, remains unchanged in host cells infected with the closely related apicomplexan Neospora caninum; thus, the Toxoplasma-induced increase in their abundance is a highly directed process rather than a general host response to infection.Conclusions/SignificanceAltered levels of miR-17∼92 and miR-106b∼25 are known to play crucial roles in mammalian cell regulation and have been implicated in numerous hyperproliferative diseases although the mechanisms driving their altered expression are unknown. Hence, in addition to the implications of these findings on the host-pathogen interaction, Toxoplasma may represent a powerful probe for understanding the normal mechanisms that regulate the levels of key host miRNAs.

Use of two novel approaches to discriminate between closely related host microRNAs that are manipulated by Toxoplasma gondii during infection

“…2C), we did not observe the nontemplated primer-extension products in any reaction performed on total RNA. Based on our previous observation that pri-miR-106a-363 is undetectable in uninfected HFFs or in HFFs infected with Toxoplasma (Zeiner et al 2010) and on the results presented in Figure 2D, we conclude that miR-106a-363 is likely not affected by Toxoplasma infection. In contrast, based on our observation that primiR-17-92 is significantly increased in Toxoplasma-infected HFFs and that the mature miR-18 and miR-19 members derived from pri-miR-17-92 are also increased (Zeiner et al 2010), and upon the results of Figure 2D, it appears that a contributor to the rise in miR-17 family levels is miR-17, itself.…”

“…Previously, we concluded that one or both of these loci are affected by Toxoplasma infection but could not determine which. Although the primary transcript (pri-) for miR-17-92 increased in abundance in Toxoplasmainfected cells, we were unable to detect pri-miR-106a-363 (Zeiner et al 2010), precluding any conclusion on its contribution to the increased levels of mature miR-17 family members; this leaves open the possibilities that pri-miR106a-363 transcription peaks at time points not examined and/or that pri-miR-106a-363 is so rapidly processed into mature miRNAs that it is not present at levels high enough to be detected.…”

“…Pathogens can alter host miRNA levels as we previously demonstrated with the obligate, intracellular parasite Toxoplasma gondii; this protozoan specifically increases the expression of host miR-17 family members in primary human cells (Zeiner et al 2010). In that study, however, we were unable to distinguish between the individual mature miR-17 family members using conventional methods because of their nearly identical sequences.…”

The mammalian microRNA response to bacterial infections

“…34,35 The let-7 family is commonly downregulated by infection with several of these parasites, namely Cryptosporidium, 30,31 Plasmodium 32 and Toxoplasma. 33 However, the above studies also suggest that the expression of most miRNAs is altered in a parasite specific manner.…”

“…[27][28][29] Several studies have explored the impact of apicomplexan parasites, many of which cause serious diseases in humans, on host microRNA expression during infection. Interestingly, modulation of host microRNA profiles was observed upon infection with several parasites, including Cryptosporidium parvum, 30,31 Plasmodium chabaudii, 32 Toxoplasma gondii 33 and Eimeria papillata. 34,35 The let-7 family is commonly downregulated by infection with several of these parasites, namely Cryptosporidium, 30,31 Plasmodium 32 and Toxoplasma.…”