Membrane Trafficking at Kv2.1 Induced Endoplasmic Reticulum/Plasma Membrane Contact Sites

Abstract

Kv2.1 is the most abundantly expressed and widely distributed voltage-gated K+ channel in mammals. In addition to regulating neuronal electrical activity, we have previously reported that a non-conducting, majority population of Kv2.1 forms micron-sized endoplasmic reticulum/plasma membrane (ER/PM) contact sites in HEK cells, neurons, and cardiac myocytes. As originally shown by the Lotan group, another non-conducting function of Kv2.1 is to enhance exocytosis in neuroendocrine cells via interaction with syntaxin. Interestingly, Kv2.1 remodels the cortical ER by binding ER resident VAPs (VAMP Associated Protein) which were originally identified as being necessary for neurotransmitter release in Aplysia. We have previously demonstrated that ER/PM junctions in non-transfected, Kv2.1-free, HEK cells are trafficking hubs,providing platforms for the delivery and retrieval of transferrin receptors, ion channels and viral coat proteins. Thus an obvious question is how the presence of Kv2.1 alters the functions associated with ER/PM junctions. This presentation will summarize our progress in determining how Kv2.1 at the ER/PM contact site influences both exo and endocytosis. Exocytosis of recycling transferrin receptors becomes sensitive to thapsigargin, i.e. ER-Ca2+, in the presence of Kv2.1. Clathrin-coated pit (CCP) behavior adjacent to the Kv2.1-induced ER/PM contact site is also changed, for in the presence of Kv2.1 both CCP lifetime and mobility are reduced. Kv2.1-induced ER/PM contact sites also remodel the diffusion landscape of the cell surface, concentrating membrane proteins in the immediate vicinity which could in turn enhance CCP/cargo interactions. Perhaps related toboth membrane protein trafficking and diffusion, ER Ca2+ homeostasis is altered when Kv2.1 is present at the ER/PM contact site. Importantly, many of the Kv2.1 influences on membrane biology just described are due to specific Kv2.1 domains and not just close apposition of the ER and PM.