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J. Biol. Chem., Vol. 282, Issue 41, 29777-29784, October 12, 2007

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Direct Protein Kinase C-dependent Phosphorylation Regulates the Cell Surface Stability and Activity of the Potassium Chloride Cotransporter KCC2^*

Henry H. C. Lee¹, Joshua A. Walker, Jeffery R. Williams, Richard J. Goodier, John A. Payne, and Stephen J. Moss^¶2

From the Department of Neuroscience, School of Medicine, University of Pennsylvania, Pennsylvania 19104, Department of Physiology and Membrane Biology, University of California, Davis, California 95616-8644, and ^¶Department of Pharmacology, University College London, WC1E 6BT, United Kingdom

The potassium chloride cotransporter KCC2 plays a major role in the maintenance of transmembrane chloride potential in mature neurons; thus KCC2 activity is critical for hyperpolarizing membrane currents generated upon the activation of -aminobutyric acid type A and glycine (Gly) receptors that underlie fast synaptic inhibition in the adult central nervous system. However, to date an understanding of the cellular mechanism that neurons use to modulate the functional expression of KCC2 remains rudimentary. Using Escherichia coli expression coupled with in vitro kinase assays, we first established that protein kinase C (PKC) can directly phosphorylate serine 940 (Ser⁹⁴⁰) within the C-terminal cytoplasmic domain of KCC2. We further demonstrated that Ser⁹⁴⁰ is the major site for PKC-dependent phosphorylation for full-length KCC2 molecules when expressed in HEK-293 cells. Phosphorylation of Ser⁹⁴⁰ increased the cell surface stability of KCC2 in this system by decreasing its rate of internalization from the plasma membrane. Coincident phosphorylation of Ser⁹⁴⁰ increased the rate of ion transport by KCC2. It was further evident that phosphorylation of endogenous KCC2 in cultured hippocampal neurons is regulated by PKC-dependent activity. Moreover, in keeping with our recombinant studies, enhancing PKC-dependent phosphorylation increased the targeting of KCC2 to the neuronal cell surface. Our studies thus suggest that PKC-dependent phosphorylation of KCC2 may play a central role in modulating both the functional expression of this critical transporter in the brain and the strength of synaptic inhibition.

Received for publication, June 20, 2007 , and in revised form, July 26, 2007.

^* This work was supported in part National Institutes of Health/NINDS Grants NS-036296 (to J. A. P.) and NS-047478 and NS-048045 (to S. J. M.). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement"in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

¹ Recipient of a predoctoral fellowship from the Epilepsy Foundation of America.

² To whom correspondence should be addressed: Dept. of Neuroscience, University of Pennsylvania, 215 Stemmler Hall, 3450 Hamilton Walk, Philadelphia, PA 19104. Tel.: 215-898-3420; E-mail: sjmoss{at}mail.med.upenn.edu.

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