Investigation of the molecular mechanisms underlying polarized trafficking of the potassium channels Kv4.2 and Kv1.3 in neurons

UnrestrictedLocalization of voltage-gated potassium channels to specific subcellular compartments in neurons allows them to perform specific functions that modulate the overall electrophysiological properties of neurons. For instance, members of the Shaker family are localized to the axon of cortical pyramidal neurons where they contribute to the propagation of action potentials. Conversely, members of the Shal family of K+ channels are localized to the somatodendritic compartment of cortical pyramidal neurons where they inhibit initiation and propagation of action potentials. My research focuses on molecular mechanisms involved in targeting of these specific voltage-gated potassium channels to different subcellular compartments in neurons. By expressing chimeras between Kv1.4 and Kv4.2, two channels that are targeted to different neuronal compartments, the axon and the dendrites, respectively, as well as deletion mutants of Kv4.2 in cultured slices of rat cortical tissue we were able to identify a sixteen amino acid dileucine-containing motif present on the C-terminus that is necessary and sufficient for the somatodendritic targeting of Kv4.2. This motif is conserved amongst all known members of the Shal family of K+ channels and represents the first evolutionarily conserved dendritic targeting motif to be identified. In addition, I used a similar approach to determine that the highly conserved T1 domain found in Shaker K+ channels is necessary and sufficient for axonal targeting of Kv1.3. To further characterize the mechanisms responsible for the differential targeting of Shal and Shaker channels I used a candidate approach to identify kinesin isoforms that play a role in the transport of Kv1.3 and Kv4.2. By this method the kinesin Kif17 was identified as transporting Kv4.2 and the kinesin Kif5B was identified as transporting Kv1.3.; Overall, this research establishes that like many other neuronal channels and receptors, the targeting of the two distinct voltage-gated K+ channels, Kv4.2 and Kv1.3, is modulated by motifs present on their amino acid sequence; however the mechanisms involved have not been clearlydelineated. Investigating the interaction that these motifs might have with other proteins in the transport pathway, including the kinesins identified, will shed some light on this conundrum