title: SUMOylation of the Hyperpolarization-Activated Cyclic Nucleotide-Gated Channel 2 Increases Surface Expression and the Maximal Conductance of the Hyperpolarization-Activated Current.
abstract: Small Ubiquitin-like Modifier (SUMO) is a ∼10 kDa peptide that can be post-translationally added to a lysine (K) on a target protein to facilitate protein-protein interactions. Recent studies have found that SUMOylation can be regulated in an activity-dependent manner and that ion channel SUMOylation can alter the biophysical properties and surface expression of the channel. Hyperpolarization-activated cyclic nucleotide-gated (HCN) channel surface expression can be regulated in an activity-dependent manner through unknown processes. We hypothesized that SUMOylation might influence the surface expression of HCN2 channels. In this manuscript, we show that HCN2 channels are SUMOylated in the mouse brain. Baseline levels of SUMOylation were also observed for a GFP-tagged HCN2 channel stably expressed in Human embryonic kidney (Hek) cells. Elevating GFP-HCN2 channel SUMOylation above baseline in Hek cells led to an increase in surface expression that augmented the hyperpolarization-activated current (Ih) mediated by these channels. Increased SUMOylation did not alterIhvoltage-dependence or kinetics of activation. There are five predicted intracellular SUMOylation sites on HCN2. Site-directed mutagenesis indicated that more than one K on the GFP-HCN2 channel was SUMOylated. Enhancing SUMOylation at one of the five predicted sites, K669, led to the increase in surface expression andIhGmax. The role of SUMOylation at additional sites is currently unknown. The SUMOylation site at K669 is also conserved in HCN1 channels. Aberrant SUMOylation has been linked to neurological diseases that also display alterations in HCN1 and HCN2 channel expression, such as seizures and Parkinson's disease. This work is the first report that HCN channels can be SUMOylated and that this can regulate surface expression andIh.
authors.affiliation: Department of Biology, Georgia State University Atlanta, GA, USA.
authors.forename: Anna R
authors.initials: AR
authors.lastname: Parker
authors.affiliation: Department of Biology, Georgia State University Atlanta, GA, USA.
authors.forename: Meghyn A
authors.initials: MA
authors.lastname: Welch
authors.affiliation: Neuroscience Institute, Georgia State University Atlanta, GA, USA.
authors.forename: Lori A
authors.initials: LA
authors.lastname: Forster
authors.affiliation: Department of Biology, Georgia State University Atlanta, GA, USA.
authors.forename: Sarah M
authors.initials: SM
authors.lastname: Tasneem
authors.affiliation: Department of Biology, Georgia State University Atlanta, GA, USA.
authors.forename: Janhavi A
authors.initials: JA
authors.lastname: Dubhashi
authors.affiliation: Department of Biology, Georgia State UniversityAtlanta, GA, USA; Neuroscience Institute, Georgia State UniversityAtlanta, GA, USA.
authors.forename: Deborah J
authors.initials: DJ
authors.lastname: Baro
keywords: HCN; SUMO; cyclic nucleotide binding domain; hyperpolarization-activated cyclic nucleotide-gated channel; ion channel; trafficking