Phosphorylation of phosphatase inhibitor-2 at centrosomes during mitosis.

Journal Article (Journal Article)

Inhibitor-2 (I-2) is a regulator of protein phosphatase type-1 (PP1), known to be phosphorylated in vitro by multiple kinases. In particular Thr72 is a Thr-Pro phosphorylation site conserved from yeast to human, but there is no evidence that this phosphorylation responds to any physiological signals. Here, we used electrophoretic mobility shift and immunoblotting with a site-specific phospho-Thr72 antibody to establish Thr72 phosphorylation in HeLa cells and show a 25-fold increase in phosphorylation during mitosis. Mass spectrometry demonstrated I-2 in actively growing HeLa cells was also phosphorylated at three other sites, Ser120, Ser121, and an additional Ser located between residues 70 and 90. In vitro kinase assays using recombinant I-2 as a substrate showed that the Thr72 kinase(s) was activated during mitosis, and sensitivity to kinase inhibitors indicated that the principal I-2 Thr72 kinase was not GSK3 but instead a member of the cyclin-dependent protein kinase family. Immunocytochemistry confirmed Thr72 phosphorylation of I-2 during mitosis, with peak intensity at prophase, and revealed subcellular concentration of the phospho-Thr72 I-2 at centrosomes. Together, the data show dynamic changes in I-2 phosphorylation during mitosis and localization of phosphorylated I-2 at centrosomes, suggesting involvement in mammalian cell division.

Full Text

Duke Authors

Cited Authors

  • Leach, C; Shenolikar, S; Brautigan, DL

Published Date

  • July 11, 2003

Published In

Volume / Issue

  • 278 / 28

Start / End Page

  • 26015 - 26020

PubMed ID

  • 12697755

International Standard Serial Number (ISSN)

  • 0021-9258

Digital Object Identifier (DOI)

  • 10.1074/jbc.M300782200


  • eng

Conference Location

  • United States