deSUMOylation of nuclear proteins increases VSG switching in Trypanosoma brucei

PAULA A. IRIBARREN; VANINA E. ALVAREZ; MARÍA A. BERAZATEGUI; JUAN J. CAZZULO; LUCÍA A. DI MARZIO

Les Embiez Island

Workshop; Molecular advances and parasite strategies in host infection; 2018

European Molecular Biology Organization (EMBO)

SUMOylation is a post-translational modification that involves the covalent attachment of the Small Ubiquitin-like Modifier (SUMO) to a wide-range of target proteins. Modification with SUMO is conserved in eukaryotic organisms and plays important regulatory roles in the function of proteins, affecting essential cellular processes such as DNA repair, regulation of gene expression and stress response, among others. In Trypanosoma brucei, a parasitic protozoa of medical and economical relevance for being the ethiological agent of sleeping sickness in humans and Nagana in cattle, SUMO is essential for cell cycle progression and is involved in the epigenetic control of genes crucial for parasite survival such as those encoding the variant surface glycoproteins. Particularly in bloodstream parasites (BS) a highly SUMOylated focus that colocalizes with the expression site body (ESB) and with the active variant surface glycoprotein (VSG) expression site, creates a permissive environment for VSG transcription.SUMOylation is regulated by a specific enzymatic machinery responsible for SUMOconjugation to its substrates and by a family of SUMO-specific proteases (Ulp/SENPs) which are responsible for the reversible and dynamic nature of this modification. In spite of the relevant 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 present work we analysed a set of putative proteins as SUMO proteases in vitro and showed that TbUlp is an active enzyme capable of processing SUMO precursor, deconjugating SUMO from modified substrates and has the ability to process polymeric chains. By using anoverexpression approach, we investigated the effects of deSUMOylation in vivo in BS parasites. Interestingly, parasites that overexpress TbUlp not only showed delocalization of SUMO and loss of the nuclear highly SUMOylated focus, but also delocalization of RNA polymerase I. Immunofluorescence assays using antibodies against the predominant VSG variant expressed by the parental cell line, showed and increased number of VSG negative parasites when TbUlp expression is induced and the appearance of parasites presenting a different VSG variant on their surface. All together our data suggests that SUMO proteases might play an important role in regulating the antigenic variation process the parasite uses to evade the host immune response.