The S. pombe Translation Initiation Factor eIF4G Is Sumoylated and Associates with the SUMO Protease Ulp2

Abstract

SUMO is a small post-translational modifier, that is attached to lysine residues in target proteins. It acts by altering protein-protein interactions, protein localisation and protein activity. SUMO chains can also act as substrates for ubiquitination, resulting in proteasome-mediated degradation of the target protein. SUMO is removed from target proteins by one of a number of specific proteases. The processes of sumoylation and desumoylation have well documented roles in DNA metabolism and in the maintenance of chromatin structure. To further analyse the role of this modification, we have purified protein complexes containing the S. pombe SUMO protease, Ulp2. These complexes contain proteins required for ribosome biogenesis, RNA stability and protein synthesis. Here we have focussed on two translation initiation factors that we identified as co-purifying with Ulp2, eIF4G and eIF3h. We demonstrate that eIF4G, but not eIF3h, is sumoylated. This modification is increased under conditions that produce cytoplasmic stress granules. Consistent with this we observe partial co-localisation of eIF4G and SUMO in stressed cells. Using HeLa cells, we demonstrate that human eIF4GI is also sumoylated; in vitro studies indicate that human eIF4GI is modified on K1368 and K1588, that are located in the C-terminal eIF4A- and Mnk-binding sites respectively.

Sumoylation of eIF4A2 affects stress granule formation

“…The translation initiation factor eIF4F consists of three proteins: eIF4A, eIF4E and eIF4G. We and others have previously demonstrated that both mammalian eIF4E and eIF4G are sumoylated ( Xu et al, 2010 ; Jongjitwimol et al, 2014 ). We therefore wished to determine whether eIF4A is also modified by SUMO.…”

“…We have previously demonstrated that fission yeast and mammalian eIF4G are sumoylated ( Jongjitwimol et al, 2014 ), and have identified two sumoylation sites in the C-terminus of human eIF4G. Our initial studies suggest that sumoylation might have a role in regulating protein synthesis in response to stress.…”

Pli1PIAS1 SUMO Ligase Protected by the Nuclear Pore-associated SUMO Protease Ulp1SENP1/2

“…Both Ulp1 and Ulp2 desumoylate a subset of SUMO conjugates, with specificity likely driven in large part by their spatial separation (12). Ulp1 localizes to the nuclear rim by associating with nuclear pores, whereas Ulp2 is nucleoplasmic (12)(13)(14)(15)(16)(17)(18). In higher eukaryotes, SENP1/2 localize to nuclear pores like Ulp1 (19 -21), and SENP6/7, like Ulp2, are nucleoplasmic (22,23).…”

High Confidence Fission Yeast SUMO Conjugates Identified by Tandem Denaturing Affinity Purification

“…Although not validated herein, we recently showed that as in other species fission yeast Top1 is a bona fide SUMO conjugate 37 . In addition, the translation initiation factor eIF4G was recently independently found to be SUMOylated 38 .…”