Alternative splicing determines sensitivity of murine calcium-activated potassium channels to glucocorticoids

• Published in: The Journal of physiology 2001-11, Vol.537 (1), p.57-68
• Main Authors: Tian, Lijun, Hammond, Martin S. L., Florance, Hannah, Antoni, Ferenc A., Shipston, Michael J.
• Format: Article
• Language: English
• Subjects: Alternative Splicing; Animals; Cell Line; Cyclic AMP-Dependent Protein Kinases - physiology; Dexamethasone - pharmacology; Glucocorticoids - pharmacology; Humans; Large-Conductance Calcium-Activated Potassium Channel alpha Subunits; Large-Conductance Calcium-Activated Potassium Channels; Mice; Original; Phosphoprotein Phosphatases - physiology; Potassium Channel Blockers; Potassium Channels - chemistry; Potassium Channels - drug effects; Potassium Channels - metabolism; Potassium Channels, Calcium-Activated - drug effects; Potassium Channels, Calcium-Activated - genetics; Protein Biosynthesis; Protein Isoforms - metabolism; Protein Phosphatase 1; Protein Phosphatase 2; Protein Structure, Tertiary - physiology; Receptors, Glucocorticoid - metabolism; RNA, Messenger - biosynthesis
• ISSN: 0022-3751; 1469-7793
• DOI: 10.1111/j.1469-7793.2001.0057k.x

Large-conductance Ca 2+ - and voltage-activated potassium (BK) channels are important regulators of cellular excitability. Here, we present a patch-clamp electrophysiological analysis of splice-variant-specific regulation by the synthetic glucocorticoid dexamethasone (DEX) of BK channels consisting of cloned STREX or ZERO α-subunit variants expressed in human embryonic kidney (HEK 293) cells. STREX channels in isolated membrane patches were inhibited by protein kinase A (PKA) and this was blocked on pre-treatment of intact cells with DEX (100 n m ) for 2 h. The effect of DEX required the synthesis of new mRNA and protein. Furthermore, it required protein phosphatase 2A (PP2A)-like activity intimately associated with the channels, as it was blocked by 10 n m okadaic acid but not by the specific protein phosphatase-1 inhibitor peptide PPI−2. ZERO variant channels that lack the STREX insert were activated by PKA but were not influenced by DEX. ZERO channels containing a mutant STREX domain (S4 STREX A) were also activated by PKA. Importantly, DEX blocked PKA activation of S4 STREX A channels in a PP2A-dependent manner. Taken together, the STREX domain is crucial for glucocorticoid regulation of BK channels through a PP2A-type enzyme. Moreover, glucocorticoids appear to induce a generic set of proteins in different types of cells, the actions of which depend on the expression of cell-specific targets.