title: Palmitoylation of the β4-subunit regulates surface expression of large conductance calcium-activated potassium channel splice variants.
abstract: Regulatory β-subunits of large conductance calcium- and voltage-activated potassium (BK) channels play an important role in generating functional diversity and control of cell surface expression of the pore forming α-subunits. However, in contrast to α-subunits, the role of reversible post-translational modification of intracellular residues on β-subunit function is largely unknown. Here we demonstrate that the human β4-subunit is S-acylated (palmitoylated) on a juxtamembrane cysteine residue (Cys-193) in the intracellular C terminus of the regulatory β-subunit. β4-Subunit palmitoylation is important for cell surface expression and endoplasmic reticulum (ER) exit of the β4-subunit alone. Importantly, palmitoylated β4-subunits promote the ER exit and surface expression of the pore-forming α-subunit, whereas β4-subunits that cannot be palmitoylated do not increase ER exit or surface expression of α-subunits. Strikingly, however, this palmitoylation- and β4-dependent enhancement of α-subunit surface expression was only observed in α-subunits that contain a putative trafficking motif (… REVEDEC) at the very C terminus of the α-subunit. Engineering this trafficking motif to other C-terminal α-subunit splice variants results in α-subunits with reduced surface expression that can be rescued by palmitoylated, but not depalmitoylated, β4-subunits. Our data reveal a novel mechanism by which palmitoylated β4-subunit controls surface expression of BK channels through masking of a trafficking motif in the C terminus of the α-subunit. As palmitoylation is dynamic, this mechanism would allow precise control of specific splice variants to the cell surface. Our data provide new insights into how complex interplay between the repertoire of post-transcriptional and post-translational mechanisms controls cell surface expression of BK channels.
authors.affiliation: Centre for Integrative Physiology, College of Medicine and Veterinary Medicine, University of Edinburgh, Edinburgh EH8 9XD, Scotland, United Kingdom.
authors.forename: Lie
authors.initials: L
authors.lastname: Chen
authors.forename: Danlei
authors.initials: D
authors.lastname: Bi
authors.forename: Lijun
authors.initials: L
authors.lastname: Tian
authors.forename: Heather
authors.initials: H
authors.lastname: McClafferty
authors.forename: Franziska
authors.initials: F
authors.lastname: Steeb
authors.forename: Peter
authors.initials: P
authors.lastname: Ruth
authors.forename: Hans Guenther
authors.initials: HG
authors.lastname: Knaus
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Shipston
mesh_terms: D020816:Amino Acid Motifs; D000818:Animals; D004721:Endoplasmic Reticulum / Q000235:genetics / Q000378:metabolism*; D005786:Gene Expression Regulation / Q000502:physiology*; D057809:HEK293 Cells; D006801:Humans; D051036:Large-Conductance Calcium-Activated Potassium Channels / Q000096:biosynthesis* / Q000235:genetics; D054878:Lipoylation / Q000502:physiology*; D020033:Protein Isoforms / Q000096:biosynthesis / Q000235:genetics; D011499:Protein Processing, Post-Translational / Q000502:physiology*; D021122:Protein Subunits / Q000235:genetics / Q000378:metabolism*; D021381:Protein Transport / Q000502:physiology
chemical_list: D051036:Large-Conductance Calcium-Activated Potassium Channels; D020033:Protein Isoforms; D021122:Protein Subunits
keywords: Ion Channels; Membrane Transport; Potassium Channels; Protein Palmitoylation; S-Acylation; Signal Transduction