Date of Award

8-10-2021

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biology

First Advisor

Deborah Baro

Second Advisor

Chun Jiang

Third Advisor

Aaron Roseberry

Abstract

The family of voltage-gated Kv4 ion channels (Kv4.1-3) mediates the transient A-type potassium currents, IA, and is an important regulator of neuronal signaling. Aberrations in Kv4 channel expression and/or function are associated with several disease states, including chronic pain, epilepsy, Alzheimer’s disease, Huntington’s disease and major depressive disorder. Kv4 channels exist as ternary complexes with potassium channel interacting proteins and dipeptidyl peptidase-like proteins. Multiple ancillary proteins also associate with the Kv4 ternary complex throughout its lifetime. Little is known about the regulation of protein-protein interactions within Kv4 macromolecular complexes. Small ubiquitin-like modifier (SUMO) is a peptide that is post-translationally conjugated to lysine (K) residues on target proteins. This post-translational modification dynamically regulates protein-protein interactions. It can either promote or prevent a given interaction. This dissertation research investigated if/how post-translational SUMOylation moderated Kv4.2 protein-protein interactions to tune IA. Kv4.2 has several putative SUMOylation sites. Two conserved sites were examined in this work: K437 and K579. SUMOylating K579 increased IA when Kv4.2 existed in the ternary complex but decreased IA when Kv4.2 was expressed alone. Studies to identify the mechanism indicated that K579 SUMOylation increased IA by promoting ternary complex recycling after endocytosis, most likely by blocking an interaction with a ubiquitin ligase and thereby reducing a ubiquitin lysosome sorting signal. In contrast, when Kv4 was not incorporated into a ternary complex, K579 SUMOylation blocked an unknown protein-protein interaction that altered channel gating to reduce IA. SUMOylation at the second site, K437, had no effect when Kv4.2 was incorporated into the ternary complex, but increased the insertion of electrically silent channels when Kv4.2 was expressed alone. The mechanism underpinning increased surface expression was not examined. These dissertation findings were the first to demonstrate that Kv4.2 can be SUMOylated to regulate IA, that SUMOylation modulates Kv4.2 internalization and that the effect of SUMOylation depends upon the available interactome.

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