SUMO modification regulates inactivation of the voltage-gated potassium channel Kv1.5

Abstract

The voltage-gated potassium (Kv) channel Kv1.5 mediates the IKur repolarizing current in human atrial myocytes and regulates vascular tone in multiple peripheral vascular beds. Understanding the complex regulation of Kv1.5 function is of substantial interest because it represents a promising pharmacological target for the treatment of atrial fibrillation and hypoxic pulmonary hypertension. Herein we demonstrate that posttranslational modification of Kv1.5 by small ubiquitin-like modifier (SUMO) proteins modulates Kv1.5 function. We have identified two membrane-proximal and highly conserved cytoplasmic sequences in Kv1.5 that conform to established SUMO modification sites in transcription factors. We find that Kv1.5 interacts specifically with the SUMO-conjugating enzyme Ubc9 and is a target for modification by SUMO-1, -2, and -3 in vivo. In addition, purified recombinant Kv1.5 serves as a substrate in a minimal in vitro reconstituted SUMOylation reaction. The SUMO-specific proteases SENP2 and Ulp1 efficiently deconjugate SUMO from Kv1.5 in vivo and in vitro, and disruption of the two identified target motifs results in a loss of the major SUMOconjugated forms of Kv1.5. In whole-cell patch-clamp electrophysiological studies, loss of Kv1.5 SUMOylation, by either disruption of the conjugation sites or expression of the SUMO protease SENP2, leads to a selective Ϸ15-mV hyperpolarizing shift in the voltage dependence of steady-state inactivation. Reversible control of voltage-sensitive channels through SUMOylation constitutes a unique and likely widespread mechanism for adaptive tuning of the electrical excitability of cells.electrical excitability ͉ posttranslational modification ͉ transmembrane protein ͉ ubiquitin-like modifier

Small Ubiquitin-like Modifier (SUMO) Modification Mediates Function of the Inhibitory Domains of Developmental Regulators FOXC1 and FOXC2

“…3). It is important to note that although this suggests preferential conjugation, we have observed a similar pattern for other SUMOylation targets (37), and the detection of modified species is likely to reflect in large part the differential expression of the SUMO isoforms rather than an intrinsic property of FOXC1/C2. To determine the role of the motifs identified by sequence comparison in SUMO modification, we replaced the predicted target Lys residues with Arg, which does not support SUMOylation.…”

Transient ischemia induces massive nuclear accumulation of SUMO2/3-conjugated proteins in spinal cord neurons

“…Furthermore, several SUMO target proteins have important acute effects on neuronal functions. 26 Such proteins include the mRNA-binding protein La, 27 the kainate receptor subunit GluR6 28 and the potassium channel Kv1.5, 29 suggesting a role for SUMO conjugation in ion fluxes and neuronal excitability.…”

Potassium channels in pulmonary arterial hypertension

“…In response to oxidative stress, a sulfenic acid modification has been reported on a cysteine residue present in the C-terminal domain of K V 1.5 that triggers internalisation of K V 1.5, decreases current density, and diverts the channel from the recycling endosome towards degradation [75]. Moreover, tyrosine phosphorylation of K V 1.5 and redox-sensitive K V 1.5 sumoylation were also reported leading to its inactivation [35,73]. Using Xenopus oocytes as a model to study ion channels in a controlled in vivo environment, it was demonstrated that expression of the ubiquitin ligase Nedd4-2 declined K V 1.5 currents by ubiquitinating and thereby reducing K V 1.5 plasma membrane expression [74].…”

“…Protein post-translational modification (PTM) is a highly dynamic and crucial mechanism in which the functional properties of a protein are altered by the covalent addition of a chemical group or protein to its amino-acid residues. Independently of PAH, K V 1.5 has been shown to undergo diverse, reversible or irreversible PTM, including phosphorylation, S-acylation, palmitoylation, sumoylation, ubiquitination and glycosylation, which impact on ion channel expression, channel trafficking to the membrane, stability and activity [35,[70][71][72][73][74]. In response to oxidative stress, a sulfenic acid modification has been reported on a cysteine residue present in the C-terminal domain of K V 1.5 that triggers internalisation of K V 1.5, decreases current density, and diverts the channel from the recycling endosome towards degradation [75].…”