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

LORENA CORIA; ANDREU SAURA; VANINA E. ALVAREZ; LUCIA DI MARZIO; JULIANA CASSATARO; PAULA A. IRIBARREN; MARÍA AGUSTINA BERAZATEGUI; MIGUEL NAVARRO

Woods Hole

Congreso; Eight Kinetoplastid Molecular Cell Biology Meeting; 2019

Marine Biological Laboratory (MBL)

SUMOylation is a post-translational modification conserved in eukaryotic organisms involving the covalent attachment of the Small UbiquitinlikeMOdifier (SUMO) to internal lysine residues within target proteins. This modifier usually alters the interaction surface of its substrates, leadingto changes in their biological activity, stability or subcellular localization, among other possible outputs. SUMO can be attached as a singlemoiety or as SUMO polymers in case there are internal acceptor sites in SUMO itself. These chains are important for proteasomal degradation aswell as for the formation of subnuclear structures such as the synaptonemal complex in Saccharomyces cerevisiae or promyelocytic leukemianuclear bodies in mammals.Interestingly, SUMO has been linked to T. brucei antigenic variation, a process where the major surface antigenic protein is replaced by a differentvariant with certain frequency as a strategy to elude the specific immune response of the host. TbSUMO was found to be enriched in a particularregion of the nucleus of bloodstream parasites, colocalizing with the RNA polymerase I at the expression-site body (ESB) within the active variantsurface glycoprotein (VSG) expression site. This highly SUMOylated focus (HSF) creates a permissive environment for VSG transcription.In this work, we have examined the role of SUMO chain formation in bloodstream parasites. Using a bacterial strain engineered to produceSUMOylated proteins we confirmed the ability of TbSUMO to form polymers and determined the type of linkage using site-directed mutationalanalysis. By generating transgenic cell lines unable to form chains, we concluded that SUMO polymerization is not essential for normal growthin vitro. However, using a mouse model of infection remarkable differences between wild-type (WT) and SUMO chain mutant parasites could beobserved. While infections with monomorphic parasites caused an unremitting parasitemia and death within 5 to 6 days, chain mutant parasiteswere able to establish successful infections displaying relapsing and remitting waves of parasitemia and prolonged host survival, resemblingthe infection pattern observed with pleomorphic parasites. This behavior was not due to differences in VSG expression, as judged by qPCR,FACS and WB, but might be related with the differentiation process as SUMO chain mutants displayed an increased differentiation kinetics frombloodstream to procyclic forms induced by cis-aconitate treatment. Furthermore, mRNA levels of the stumpy markers PAD1 and PAD2 wereindeed increased in most SUMO chain mutant samples relative to WT, when parasitemia was at maximum. Taking together these results suggestthat parasites with stumpy-like characteristics might be present in mice infected with monomorphic SUMO chain mutants being poli-SUMOylation involved as a negative regulator of parasite differentiation in vivo.