Direct identification of PTEN phosphorylation sites.

Abstract	The PTEN tumor suppressor gene encodes a phosphatidylinositol 3'-phosphatase that is inactivated in a high percentage of human tumors, particularly glioblastoma, melanoma, and prostate and endometrial carcinoma. Previous studies showed that PTEN is a seryl phosphoprotein and a substrate of protein kinase CK2 (CK2). However, the sites in PTEN that are phosphorylated in vivo have not been identified directly, nor has the effect of phosphorylation on PTEN catalytic activity been reported. We used mass spectrometric methods to identify Ser(370) and Ser(385) as in vivo phosphorylation sites of PTEN. These sites also are phosphorylated by CK2 in vitro, and phosphorylation inhibits PTEN activity towards its substrate, PIP3. We also identify a novel in vivo phosphorylation site, Thr(366). Following transient over-expression, a fraction of CK2 and PTEN co-immunoprecipitate. Moreover, pharmacological inhibition of CK2 activity leads to decreased Akt activation in PTEN+/+ but not PTEN-/- fibroblasts. Our results contrast with previous assignments of PTEN phosphorylation sites based solely on mutagenesis approaches, suggest that CK2 is a physiologically relevant PTEN kinase, and raise the possibility that CK2-mediated inhibition of PTEN plays a role in oncogenesis.
Authors	Susan J Miller, David Y Lou, David C Seldin, William S Lane, Benjamin G Neel
Journal	FEBS letters (FEBS Lett) Vol. 528 Issue 1-3 Pg. 145-53 (Sep 25 2002) ISSN: 0014-5793 [Print] England
PMID	12297295 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't, Research Support, U.S. Gov't, P.H.S.)
Chemical References	Proto-Oncogene Proteins Recombinant Fusion Proteins Tumor Suppressor Proteins Serine AKT1 protein, human Casein Kinase II Protein Serine-Threonine Kinases Proto-Oncogene Proteins c-akt Phosphoric Monoester Hydrolases PTEN Phosphohydrolase PTEN protein, human
Topics	Binding Sites Casein Kinase II Female Genes, Tumor Suppressor Humans Male Mass Spectrometry PTEN Phosphohydrolase Phosphoric Monoester Hydrolases (chemistry, genetics, metabolism) Phosphorylation Protein Serine-Threonine Kinases (metabolism) Proto-Oncogene Proteins (metabolism) Proto-Oncogene Proteins c-akt Recombinant Fusion Proteins (chemistry, genetics, metabolism) Serine (chemistry) Tumor Cells, Cultured Tumor Suppressor Proteins (chemistry, genetics, metabolism)

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