Corresponding author:

ur na l o f C el l S ci en ce A cc ep te d m an us cr ip t JCS Advance Online Article. Posted on 23 April 2015 While junctions between cortical endoplasmic reticulum (cER) and the plasma membrane (PM) are a subtle but ubiquitous feature in mammalian cells very little is known about the functions and molecular interactions associated with neuronal ER/PM junctions. Here we report that Kv2.1, the primary delayed-rectifier K+ channel in the mammalian brain, induces the formation of ER/PM junctions. Kv2.1 localizes to dense, cell-surface clusters that contain non-conducting channels, suggesting a function unrelated to membrane potential regulation. Accordingly, Kv2.1 clusters function as membrane trafficking hubs, providing platforms for delivery and retrieval of multiple membrane proteins. Using both total internal reflection fluorescence and electron microscopy we demonstrate that the clustered Kv2.1 plays a direct structural role in the induction of stable ER/PM junctions in both transfected HEK 293 cells and cultured hippocampal neurons. Glutamate exposure results in a loss of Kv2.1 clusters in neurons and subsequent retraction of the cER from the PM. We propose Kv2.1-induced ER/PM junctions represent a new macromolecular plasma membrane complex that is sensitive to excitotoxic insult and functions as a scaffolding site for both membrane trafficking and Ca2+ signaling. Jo ur na l o f C el l S ci en ce A cc ep te d m an us cr ip