Functional implications of kv1.3 spatial organization

Resumen

Kv1.3 is a voltage-gated potassium channel mainly expressed at the plasma membrane and at the inner mitochondrial membrane of different cell types. A dual role for the channel has been suggested: Plasma membrane channel is linked to proliferation and activation while mitochondrial channel controls apoptosis. In this thesis, we analyse in depth the duality of Kv1.3 function. We show that Kv1.3 orchestrates cellular physiology in a way even more complex than expected. The thesis is structured in two parts: Plasma membrane Kv1.3 and Mitochondrial Kv1.3. Each part contains three contributions addressed to the understanding of Kv1.3 traffic and physiological implications of its localization. In the first part (Plasma membrane Kv1.3), we describe the caveolin-binding domain (CBD) of Kv1.3 as the determinant for the lipid raft targeting of the channel in cells expressing caveolin (Contribution I). The caveolar localization of the channel is required for proper insulin signalling in adipocytes. In these cells, Kv1.3 controls glucose uptake and insulin resistance. Kv1.3 is a target of Insulin Receptor activation via its localization at caveolae (Contribution II). Finally, we focus on the mechanisms of membrane arrangement of Kv1.3 in systems with limited Caveolin expression, such as lymphocytes, where the expression of Kv1.3 at the plasma membrane is also crucial. In this context, Kv1.3 palmitoylation resulted to be important for the Kv1.3 organization at the immunological synapse. This is the first time that Kv1.3 lipidation is reported and that Kv1.3 is visualized at the immunological synapse platform. Thus, our work expands our knowledge to define better therapeutic strategies in autoimmune diseases, where Kv1.3 is aberrantly expressed at the immunological synapse (Contribution III). In the second part (Mitochondrial Kv1.3), we first identify caveolin interaction as regulator of Kv1.3 pro-apoptotic activity. Kv1.3/Caveolin axis is an important regulator of cell apoptosis, with important consequences for chemotherapy resistance (Contribution IV). We also describe, for the first time, the mechanisms of Kv1.3 mitochondrial targeting, which involve an unconventional TIM/TOM pathway. We identify cytosolic chaperones as key regulators of Kv1.3 mitochondrial import and show how transmembrane domains cooperate to mediate such process (Contribution V). Finally, we show, for the first time, that mitochondrial Kv1.3 can also regulate proliferation through the control of mitochondrial fusion/fission equilibrium. This is a novel finding because reveals a novel function for mitochondrial Kv1.3 beyond apoptosis. At the same time, puzzle out Kv1.3 as an important component of the mitochondrial fusion/fission machinery (ContributionVI). In conclusion, this thesis includes novel and relevant findings about Kv1.3 function linked to its localization in the cell