Abstract
Although protein phosphatases appear to be highly controlled in intact cells, relatively little is known about the physiological regulation of their activity. DARPP-32, a dopamine- and cAMP-regulated phosphoprotein of apparent M(r) 32,000, is phosphorylated in vitro by casein kinase I, casein kinase II, and cAMP-dependent protein kinase on sites phosphorylated in vivo. DARPP-32 phosphorylated on Thr-34 by cAMP-dependent protein kinase is a potent inhibitor of protein phosphatase 1 and an excellent substrate for calcineurin, a Ca2+/calmodulin-dependent protein phosphatase. Here we provide evidence, using both purified proteins and brain slices, that phosphorylation of DARPP-32 on Ser-137 by casein kinase I inhibits the dephosphorylation of Thr-34 by calcineurin. This inhibition occurs only when phospho-Ser-137 and phospho-Thr-34 are located on the same DARPP-32 molecule and is not dependent on the mode of activation of calcineurin. The results demonstrate that the inhibition is due to a modification in the properties of the substrate which alters its dephosphorylation rate. Thus, casein kinase I may play a physiological role in striatonigral neurons as a modulator of the regulation of protein phosphatase 1 via DARPP-32.
Publication types
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Research Support, Non-U.S. Gov't
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Research Support, U.S. Gov't, P.H.S.
MeSH terms
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Amino Acid Sequence
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Animals
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Calcineurin
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Calcium / pharmacology
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Calmodulin / pharmacology
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Calmodulin-Binding Proteins / antagonists & inhibitors
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Calmodulin-Binding Proteins / metabolism*
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Casein Kinases
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Cattle
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Cyclic AMP / metabolism*
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Cyclic AMP-Dependent Protein Kinases / metabolism*
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Dopamine / metabolism*
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Dopamine and cAMP-Regulated Phosphoprotein 32
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Kinetics
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Manganese / pharmacology
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Muscle, Skeletal / enzymology
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Myocardium / enzymology
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Nerve Tissue Proteins / metabolism*
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Phosphoprotein Phosphatases / antagonists & inhibitors
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Phosphoprotein Phosphatases / metabolism*
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Phosphoproteins / metabolism
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Phosphorylation
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Phosphoserine / analysis
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Phosphothreonine / analysis
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Protein Kinases / metabolism*
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Protein Phosphatase 1
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Rabbits
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Rats
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Recombinant Proteins / metabolism
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Serine*
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Substantia Nigra / metabolism
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Threonine*
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Thymus Gland / enzymology
Substances
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Calmodulin
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Calmodulin-Binding Proteins
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Dopamine and cAMP-Regulated Phosphoprotein 32
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Nerve Tissue Proteins
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Phosphoproteins
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Recombinant Proteins
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Phosphothreonine
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Phosphoserine
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Threonine
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Manganese
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Serine
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Cyclic AMP
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Protein Kinases
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Casein Kinases
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Cyclic AMP-Dependent Protein Kinases
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Calcineurin
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Phosphoprotein Phosphatases
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Protein Phosphatase 1
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Calcium
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Dopamine