Date of Award
Doctor of Philosophy (PhD)
The hyperpolarization activated cyclic nucleotide gated ion channels (HCN) are encoded by 4 isoforms (HCN1-4). These are nonspecific cation channels which mediate the slow inward current Ih. Dysregulation of HCN2 contributes to multiple disease states such as epilepsy, depression and anxiety, and chronic pain. The HCN2 channel is post-translationally modified by the small ubiquitin like modifier (SUMO), where SUMOylation of K669 is associated with an increase in Ih and surface expression. This dissertation work investigates how ion channel SUMOylation regulates hyperexcitability in inflammatory pain. Following complete Freund’s adjuvant (CFA) induced inflammation, there is an increase in HCN2 protein level bilaterally, and a unilateral increase in pain behavior. Interestingly, we observe an increase in HCN2 SUMOylation unilaterally following inflammation suggesting that SUMOylation of HCN2 may play an important role in regulating Ih in inflammation. We examine the molecular mechanisms driving the increase in Ih and surface expression following SUMOylation of K669 in HCN2. Surface expression can be increased by promoting trafficking from the trans-Golgi to the plasma membrane, by reducing channel endocytosis and/or by increasing recycling of the endocytosed channel. Indeed, SUMOylation of HCN2 increases colocalization with the slow recycling marker, Rab11a, and a dominant negative form of Rab11a blocks the SUMO mediated increase in Ih. Together these results suggest a potential mechanism behind the increase in Ih in inflammatory pain. Additionally, investigating the mechanism behind SUMO regulation of another ion channel, Kv4.2, we observe a Rab11a mediated increase in IA. These findings suggest C-terminal SUMOylation of ion channels may represent a general mechanism for regulating the extent of ion channel recycling.
Forster, Lori, "Regulation of the hyperpolarization-activated cyclic nucleotide gated ion channel 2, HCN2, by post-translational SUMOylation." Dissertation, Georgia State University, 2022.
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