deSUMOylation of nuclear proteins increases VSG switching in Trypanosome brucei

BERAZATEGUI, M. A.; IRIBARREN, P. A.; DI MARZIO, L. A.; CAZZULO, J. J.; ALVAREZ, V. E.

Les Embiez Island

Workshop; EMBO WORKSHOP: Molecular advances and parasite strategies in host infection; 2018

SUMOylation is a post-translational modification that involves the covalent attachment of theSmall Ubiquitin-like Modifier (SUMO) to a wide-range of target proteins. Modification withSUMO is conserved in eukaryotic organisms and plays important regulatory roles in thefunction of proteins, affecting essential cellular processes such as DNA repair, regulation ofgene expression and stress response, among others. In Trypanosoma brucei, a parasiticprotozoa of medical and economical relevance for being the ethiological agent of sleepingsickness in humans and Nagana in cattle, SUMO is essential for cell cycle progression and isinvolved in the epigenetic control of genes crucial for parasite survival such as those encodingthe variant surface glycoproteins. Particularly In bloodstream parasites (BS) a highlySUMOylated focus that colocalizes with the expression site body (ESB) and with the activevariant surface glycoprotein (VSG) expression site, creates a permissive environment for VSGtranscription.SUMOylation is regulated by a specific enzymatic machinery responsible for SUMOconjugation to its substrates and by a family of SUMO-specific proteases (Ulp/SENPs) whichare responsible for the reversible and dynamic nature of this modification. In spite of therelevant role SUMO proteases play in the process, they have not yet been identified in T.brucei and their role in cellular processes of the parasite is poorly understood. In the presentwork we analysed a set of putative proteins as SUMO proteases in vitro and showed thatTbUlp is an active enzyme capable of processing SUMO precursor, deconjugating SUMOfrom modified substrates and has the ability to process polymeric chains. By using anoverexpression approach, we investigated the effects of deSUMOylation in vivo in BSparasites. Interestingly, parasites that overexpress TbUlp not only showed delocalization ofSUMO and loss of the nuclear highly SUMOylated focus, but also delocalization of RNApolymerase I. Immunofluorescence assays using antibodies against the predominant VSGvariant expressed by the parental cell line, showed and increased number of VSG negativeparasites when TbUlp expression is induced and the appearance of parasites presenting adifferent VSG variant on their surface. All together our data suggests that SUMO proteasesmight play an important role in regulating the antigenic variation process the parasite uses toevade the host immune response.