Date of Award
Doctor of Philosophy (PhD)
The small ubiquitin-like modifier protein (SUMO) is a 12kD peptide that is post-translationally added to target lysine residues. SUMOylation can dynamically regulate a target’s function and expression by promoting or preventing protein-protein interactions. The nuclear targets of SUMOylation are well studied, while ion channel SUMOylation is still a growing field. SUMO modulates HCN2 and Kv4 currents by regulating their surface expression. HCN2 channels regulate the resting membrane potential in neurons and Kv4 channels regulate action potential repolarization in the myocardium. Altered HCN2 expression is reported in neuronal pathologies, while altered Kv4 expression is reported in cardiac diseases. This work investigated the contribution of ion channel SUMOylation to diseased states, by examining changes in HCN2 SUMOylation during pathological pain. Secondly, this work examined the regulatory mechanisms of ion channel SUMOylation by identifying the Protein Inhibitor of Activated STAT3 (PIAS3) as an E3 SUMO ligase for Kv4 channels.
This work shows that HCN2 expression is bilaterally increased in putative nociceptors following injection of Complete Freud’s Adjuvant. HCN2 SUMOylation exhibited a unilateral increase in putative nociceptors. As HCN2 channels mediate unilateral mechanical hyperalgesia during persistent inflammation, this work indicates that ion channel SUMOylation may underpin pain behaviors during persistent inflammation.
Target SUMOylation is regulated by E3 SUMO ligases; however, none have been identified for ion channels. This work shows that PIAS3 is an E3 SUMO ligase for Kv4 channels. PIAS3 augmented Kv4 SUMOylation in HEK cells and in cultured cardiomyocytes by enhancing SUMOylation at K579. The net effect was an increase in Kv4 currents due to enhanced Rab11a-dependent slow recycling of the channel. PIAS3 required its canonical E3 SUMO ligase properties to mediate these effects. Further, the effects of PIAS3 could be blocked by PKA-mediated phosphorylation of Kv4 channels in HEK cells and in cardiomyocytes, suggesting that the targets of PIAS3 are shaped by their phosphorylation status.
SUMOylation is enhanced in many pathological conditions due to upregulation of the SUMOylation machinery. This work provides insights into the consequences of enhanced SUMOylation of ion channels in diseased states, and importantly, is the first to identify PIAS3 as a regulator for ion channel SUMOylation.
Jansen, Leslie-Anne R., "SUMOylation as a modulator of ion channel function and expression." Dissertation, Georgia State University, 2023.
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