Caveolin Regulates Kv1.5 Trafficking to Cholesterol-Rich Membrane Microdomains

Abstract

The targeting of ion channels to cholesterol-rich membrane microdomains has emerged as a novel mechanism of ion channel localization. Previously, we reported that Kv1.5, a prominent cardiovascular K ϩ channel ␣-subunit, localizes to caveolar microdomains. However, the mechanisms regulating Kv1.5 targeting and the functional significance of this localization are largely unknown. In this study, we demonstrate a role for caveolin in the trafficking of Kv1.5 to lipid raft microdomains where cholesterol modulates channel function. In cells lacking endogenous caveolin-1 or -3, the association of Kv1.5 with low-density, detergent-resistant membrane fractions requires coexpression with exogenous caveolin, which can form channel-caveolin complexes. Caveolin is not required for cell surface expression, however, and caveolin-trafficking mutants sequester Kv1.5, but not Kv2.1, in intracellular compartments, resulting in a loss of functional cell surface channel. Coexpression with wild type caveolin-1 does not alter Kv1.5 current density; rather, it induces depolarizing shifts in steady-state activation and inactivation. These shifts are analogous to those produced by elevation of membrane cholesterol. Together, these results show that caveolin modulates channel function by regulating trafficking to cholesterol-rich membrane microdomains.

α1-Adrenoreceptors regulate only the caveolae-located subpopulation of cardiac KV4 channels

“…26,27 In our electron micrographs the K V 4.3 channel is always located at the neck of the caveolae, avoiding this hypothetical shortcoming. Recent studies employing electron microscopy reveal that insulin receptors also associate predominantly with the neck, but not the bulb, of caveolae.…”

Clustering and Activity Tuning of Kv1 Channels in Myelinated Hippocampal Axons

“…Interestingly, recent studies show that SLEEPLESS, a GPI-anchored protein in the Ly-6/neurotoxin family, is crucial for sleep in Drosophila, by regulating the expression levels, localization, and activity of Shaker (Drosophila homolog of Kv1 channels) (63,64). Given that lipids can regulate Kv channel activity (65,66), our data raise an intriguing possibility that the GPI-anchored proteins, TAG-1 and SLEEPLESS, may regulate Kv1.2 channel activity by altering lipid composition. However, it is currently too difficult to directly record JXP Kv1 channels under the myelin sheath.…”

Kv1.5 Association Modifies Kv1.3 Traffic and Membrane Localization

“…Because lipid rafts are sensitive to cholesterol-modifying agents, in some experiments, transfected HEK cells were incubated in the presence or the absence of 2% methyl-␤-cyclodextrin (M␤CD) 1 h before raft isolation and confocal microscopy experiments (23,24).…”

“…Raft Isolation and Immunoisolation of Caveolae-Low density, Triton-insoluble complexes were isolated as previously described (23,24,26) from bone marrow-derived macrophages and HEK cells transient transfected with either Kv1.3-YFP or double transfected Kv1.3-YFP/Kv1.5-CFP. The cells were homogenized in 1 ml of 1% Triton X-100, and sucrose was added to a final concentration of 40%.…”

“…Interestingly, both proteins have been located in raft microdomains, and their functions can be influenced by lipidprotein interactions (17,23,24). We report that functional Kv1.3/Kv1.5 heterotetrameric channels exhibit different location and targeting.…”