Exploring the connection between SUMO conjugation and the splicing process

MAMMI, PABLO; POZZI, BERTA; BRAGADO, LAUREANO; SREBROW, ANABELLA

Cold Spring Harbor

Conferencia; 40 years of mRNA Splicing: From Discovery to Therapeutics; 2017

Cold Spring Harbor Laboratory

Few years ago our laboratory found that the splicing auxiliary factor SRSF1, a member of the SR family of proteins, functions as a regulator of SUMO conjugation, both in vitro and in living cells. We demonstrated that SRSF1 displays certain characteristics of SUMO E3 ligases and also affects the activity of a well-known member of this latter group, PIAS1. The process known as SUMO conjugation or ?SUMOylation? is a reversible post-translational modification consisting of the covalent attachment of a SUMO (small ubiquitin-related modifier) peptide to a lysine residue in the target protein, by an enzymatic cascade that resembles the ubiquitin pathway. SUMO conjugation has gained a prominent role as a regulator of a great variety of cellular processes including transcription, DNA repair, chromatin organization, nucleo-cytoplasmic transport, and genome stability. On the contrary, there is extremely scarce information about its involvement in pre-mRNA processing and in particular during the splicing process. This is indeed curious considering that RNA metabolism-related proteins have been revealed as the most represented group among SUMO conjugation substrates by proteomic studies. Based on the aforementioned, we decided to explore a possible connection between the SUMO conjugation pathway and the splicing machinery. We have recently shown that different spliceosomal protein components are present in a SUMOylated state within assembled spliceosomes throughout in vitro splicing reactions. Remarkably, SUMOylation of several of these proteins is regulated by SRSF1 in cultured cells. We have also demonstrated that SUMO conjugation influences splicing efficiency and that SUMOylation of the U4/U6 component, hPrp3-90K, is involved in tri-snRNP formation and/or tri-snRNP recruitment to active spliceosomes. Currently, we are further exploring the mechanisms by which SRSF1 is able to stimulate SUMO conjugation. Using a broad set of SRSF1 mutants, we are analyzing the sub-cellular or sub-nuclear localization where this function is exerted. Moreover, we are trying to characterize both cellular components as well as cellular conditions that modulate SRSF1 activity along the SUMO pathway.