SUMO chain mutants promote oscillating parasitemia and extended host survival during T. brucei infection in mice

IRIBARREN, P. A.; CORIA, L.; DI MARZIO, L. A.; BERAZATEGUI, M. A.; SAURA, A.; CASSATARO, J.; NAVARRO, M.; ALVAREZ, V. E.

Woodshole

Congreso; Eight Kinetoplastid Molecular Cell Biology Meeting; 2019

Marine Biological Laboratory Woods Hole, Massachusetts, USA

SUMOylation is a post-translational modification conserved in eukaryoticorganisms involving the covalent attachment of the Small Ubiquitin-likeMOdifier (SUMO) to internal lysine residues within target proteins. Thismodifier usually alters the interaction surface of its substrates, leading tochanges in their biological activity, stability or subcellular localization, amongother possible outputs. SUMO can be attached as a single moiety or asSUMO polymers in case there are internal acceptor sites in SUMO itself.These chains are important for proteasomal degradation as well as for theformation of subnuclear structures such as the synaptonemal complex inSaccharomyces cerevisiae or promyelocytic leukemia nuclear bodies inmammals.Interestingly, SUMO has been linked to T. brucei antigenicvariation, a process where the major surface antigenic protein is replaced bya different variant with certain frequency as a strategy to elude the specificimmune response of the host. TbSUMO was found to be enriched in aparticular region of the nucleus of bloodstream parasites, colocalizing withthe RNA polymerase I at the expression-site body (ESB) within the activevariant surface glycoprotein (VSG) expression site. This highly SUMOylatedfocus (HSF) creates a permissive environment for VSG transcription.In thiswork, we have examined the role of SUMO chain formation in bloodstreamparasites. Using a bacterial strain engineered to produce SUMOylatedproteins we confirmed the ability of TbSUMO to form polymers anddetermined the type of linkage using site-directed mutational analysis. Bygenerating transgenic cell lines unable to form chains, we concluded thatSUMO polymerization is not essential for normal growth in vitro. However,using a mouse model of infection remarkable differences between wild-type(WT) and SUMO chain mutant parasites could be observed. While infectionswith monomorphic parasites caused an unremitting parasitemia and deathwithin 5 to 6 days, chain mutant parasites were able to establish successfulinfections displaying relapsing and remitting waves of parasitemia andprolonged host survival, resembling the infection pattern observed withpleomorphic parasites. This behavior was not due to differences in VSGexpression, as judged by qPCR, FACS and WB, but might be related with thedifferentiation process as SUMO chain mutants displayed an increaseddifferentiation kinetics from bloodstream to procyclic forms induced by cisaconitatetreatment. Furthermore, mRNA levels of the stumpy markers PAD1and PAD2 were indeed increased in most SUMO chain mutant samplesrelative to WT, when parasitemia was at maximum. Taking together theseresults suggest that parasites with stumpy-like characteristics might bepresent in mice infected with monomorphic SUMO chain mutants being poliSUMOylationinvolved as a negative regulator of parasite differentiation invivo.