A molecular switch for specific stimulation of the BKCa channel by cGMP and cAMP kinase.
The cGMP and the cAMP pathways control smooth muscle tone by regulation of BK(Ca) (BK) channel activity. BK channels show considerable diversity and plasticity in their regulation by cyclic nucleotide-dependent protein kinases. The underlying molecular mechanisms are unclear but may involve expression of splice variants of the BK channel alpha subunit. Three isoforms, BK(A), BK(B), and BK(C), which were cloned from tracheal smooth muscle, differed only in their C terminus. When expressed in HEK293 cells, cGMP kinase (cGK) but not cAMP kinase (cAK) stimulated the activity of BK(A) and BK(B) by shifting the voltage dependence of the channel to more negative potentials. In contrast, BK(C) was exclusively stimulated by cAK. BK(C) lacks a C-terminal tandem phosphorylation motif for protein kinase C (PKC) with Ser(1151) and Ser(1154). Mutation of this motif in BK(A) switched channel regulation from cGK to cAK. Furthermore, inhibition of PKC in excised patches from cells expressing BK(A) abolished the stimulatory effect of cGK but allowed channel stimulation by cAK. cAK and cGK phosphorylated the channel at different sites. Thus, phosphorylation/dephosphorylation by PKC determines whether the BK channel is stimulated by cGK or cAK. The molecular mechanisms may be relevant for smooth muscle relaxation by cAMP and cGMP.
Zhou
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Abteilung Pharmakologie für Pharmazeuten, Universitätsklinikum Hamburg-Eppendorf, Martinistr. 52, D-20246 Hamburg, Germany.
Arntz
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C
Kamm
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Motejlek
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K
Sausbier
U
U
Wang
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GX
Ruth
P
P
Korth
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M
D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002417:Cattle; D002460:Cell Line; D003001:Cloning, Molecular; D000242:Cyclic AMP / Q000378:metabolism; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism*; D006152:Cyclic GMP / Q000378:metabolism*; D004594:Electrophysiology; D004789:Enzyme Activation; D006801:Humans; D051037:Large-Conductance Calcium-Activated Potassium Channel alpha Subunits; D051036:Large-Conductance Calcium-Activated Potassium Channels; D008954:Models, Biological; D008969:Molecular Sequence Data; D009130:Muscle, Smooth / Q000378:metabolism; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D010766:Phosphorylation; D015221:Potassium Channels / Q000737:chemistry* / Q000378:metabolism*; D024681:Potassium Channels, Calcium-Activated; D011485:Protein Binding; D020033:Protein Isoforms; D011493:Protein Kinase C / Q000737:chemistry / Q000378:metabolism; D017434:Protein Structure, Tertiary; D017386:Sequence Homology, Amino Acid; D012689:Sequence Homology, Nucleic Acid; D012694:Serine / Q000737:chemistry; D014132:Trachea / Q000378:metabolism
D051037:Large-Conductance Calcium-Activated Potassium Channel alpha Subunits; D051036:Large-Conductance Calcium-Activated Potassium Channels; D015221:Potassium Channels; D024681:Potassium Channels, Calcium-Activated; D020033:Protein Isoforms; D012694:Serine; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases; D011493:Protein Kinase C; D006152:Cyclic GMP