Phosphorylation of protein phosphatase inhibitor-1 by protein kinase C

Bogachan Sahin, Hongjun Shu, Joseph Fernandez, Ali El-Armouche, Jeffery D. Molkentin, Angus C. Nairn, James A. Bibb

Research output: Contribution to journalArticle

18 Scopus citations

Abstract

Inhibitor-1 becomes a potent inhibitor of protein phosphatase 1 when phosphorylated by cAMP-dependent protein kinase at Thr35. Moreover, Ser67 of inhibitor-1 serves as a substrate for cyclin-dependent kinase 5 in the brain. Here, we report that dephosphoinhibitor-1 but not phospho-Ser67 inhibitor-1 was efficiently phosphorylated by protein kinase C at Ser65 in vitro. In contrast, Ser67 phosphorylation by cyclin-dependent kinase 5 was unaffected by phospho-Ser 65. Protein kinase C activation in striatal tissue resulted in the concomitant phosphorylation of inhibitor-1 at Ser65 and Ser 67, but not Ser65 alone. Selective pharmacological inhibition of protein phosphatase activity suggested that phospho-Ser 65 inhibitor-1 is dephosphorylated by protein phosphatase 1 in the striatum. In vitro studies confirmed these findings and suggested that phospho-Ser67 protects phospho-Ser65 inhibitor-1 from dephosphorylation by protein phosphatase 1 in vivo. Activation of group I metabotropic glutamate receptors resulted in the up-regulation of diphospho-Ser65/Ser67 inhibitor-1 in this tissue. In contrast, the activation of N-methyl-D-aspartate-type ionotropic glutamate receptors opposed increases in striatal diphospho-Ser65/Ser 67 inhibitor-1 levels. Phosphomimetic mutation of Ser65 and/or Ser67 did not convert inhibitor-1 into a protein phosphatase 1 inhibitor. On the other hand, in vitro and in vivo studies suggested that diphospho-Ser65/Ser67 inhibitor-1 is a poor substrate for cAMP-dependent protein kinase. These observations extend earlier studies regarding the function of phospho-Ser67 and underscore the possibility that phosphorylation in this region of inhibitor-1 by multiple protein kinases may serve as an integrative signaling mechanism that governs the responsiveness of inhibitor-1 to cAMP-dependent protein kinase activation.

Original languageEnglish (US)
Pages (from-to)24322-24335
Number of pages14
JournalJournal of Biological Chemistry
Volume281
Issue number34
DOIs
StatePublished - Aug 25 2006

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology

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    Sahin, B., Shu, H., Fernandez, J., El-Armouche, A., Molkentin, J. D., Nairn, A. C., & Bibb, J. A. (2006). Phosphorylation of protein phosphatase inhibitor-1 by protein kinase C. Journal of Biological Chemistry, 281(34), 24322-24335. https://doi.org/10.1074/jbc.M603282200