Induction of Endoplasmic Reticulum-Plasma Membrane Contacts is a Non-Conducting Function of the Kv2.1 Voltage-Gated Potassium Channel

Abstract

The voltage-gated potassium channel Kv2.1 localizes to micron diameter clusters on the soma of hippocampal pyramidal neurons and transfected HEK 293 cells. Channels localized to clusters are largely unable to flux K+ suggesting Kv2.1 possesses an auxiliary, non-conducting function. We present evidence that one non-conducting function of Kv2.1 is to induce the formation of endoplasmic reticulum (ER)-plasma membrane (PM) contacts. In HEK 293 cells, the cortical ER (cER) as observed by TIRF microscopy typically consists of a meshwork of tubules. Expression of Kv2.1 induced the enlargement of cER tubules into micron diameter sheets, mirroring the clustered localization of the channel. An ultrastructural analysis using thin-section electron microscopy and immuno-gold labeling indicated that cER is brought into close apposition to the PM (<30nm) opposite dense immuno-gold labeling for Kv2.1. The close apposition of cER observed opposite Kv2.1 immuno-gold was accompanied by thinning of the cER lumen. ER-PM contacts are typically demonstrated to be anchored by proteins which reside in the ER membrane and extend into the cytoplasm to bind anionic lipid species which reside in the inner leaflet of the PM. These data suggest that the integral PM protein Kv2.1 functions to direct the formation of ER-PM contacts through interactions with unknown lipids or proteins in the ER.