Exploring the different roles of SENP3 in neurons

Abstract

SUMOylation is a protein based post-translational modification involving the conjugation of a small protein, SUMO, to lysine residues in substrate proteins to alter their stability, function or activity in a wide range of cellular pathways. The most common SUMO paralogues, SUMO-1-3, are attached to the substrate proteins through a three-step enzymatic cascade and can be removed by SUMO proteases (SPs). The biggest family of SPs are sentrin-specific proteases (SENPs), which include SENP1-3 and SENP5-7. There are multiple SUMO substrates identified in neurons, both in the nucleus, where SUMO is mostly localised, as well as in the cytosol, mitochondria, and plasma membrane.

In my PhD I focused on SENP3, because preliminary data demonstrated that SENP3 interacts with the kainate receptor (KAR) subunit GluK2 and increases the transcription of Rho GTP dissociation inhibitor α (RhoGDIα).

My findings reveal that GluK2 is SUMOylated with SUMO-1 and SUMO-2/3 on K886, and can be deSUMOylated by SENP3. SENP3 interacts with GluK2 even in the absence of SUMOylation, and can also interact with the KAR subunit GluK1, which does not contain a SUMO consensus motif. GluK2 stability may be affected by SENP3 and SUMOylation, although the effect sizes are quite small, suggesting that rather than regulating GluK2 under basal conditions, SENP3-mediated regulation of GluK2 may be primarily activity-dependent.

I began investigating the role of SENP3 and SUMO in regulating RhoGDIα by performing OGD experiments, a cell culture model of ischaemia, in HEK293T cells and neurons. After 2h OGD in HEK293T cells, total SUMOylation, SENP3 and SENP1 are decreased, while RhoGDIα levels do not change. However, RhoGDIα SUMO-2/3ylation is significantly decreased. In neurons, knockdown of RhoGDIα leads to cell death, and this effect cannot be rescued by a non-SUMOylatable RhoGDIα. Finally, I demonstrate that RhoGDIα is expressed ubiquitously in hippocampal neurons and it is important for neurite formation and neuronal complexity.

The data in this work further emphasises a crucial role of the SUMO system in the regulation of extranuclear targets and neuronal activity.

Date of Award	18 Jun 2024
Original language	English
Awarding Institution	University of Bristol
Supervisor	Jonathan G Hanley (Supervisor) & Jeremy M Henley (Supervisor)