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The tumor suppressor, PTEN/MMAC1, dephosphorylates the lipid second messenger, phosphatidylinositol
1Department of Biological Chemistry, University of Michigan, Ann Arbor, Michigan 48109-0606, USA.
Abstract:
Phosphatidylinositol 3,4,5-trisphosphate (PtdIns(3,4,5)P3) is a key molecule involved in cell growth signaling. We demonstrated that overexpression of PTEN, a putative tumor suppressor, reduced insulin-induced PtdIns(3,4,5)P3 production in human 293 cells without effecting insulin-induced phosphoinositide 3-kinase activation. Further, transfection of the catalytically inactive mutant of PTEN (C124S) caused PtdIns(3,4,5)P3 accumulation in the absence of insulin stimulation. Purified recombinant PTEN catalyzed dephosphorylation of PtdIns(3,4,5)P3, specifically at position 3 on the inositol ring. PTEN also exhibited 3-phosphatase activity toward inositol 1,3,4,5-tetrakisphosphate. Our results raise the possibility that PTEN acts in vivo as a phosphoinositide 3-phosphatase by regulating PtdIns(3,4,5)P3 levels. As expected, the C124S mutant of PTEN was incapable of catalyzing dephosphorylation of PtdIns(3,4,5)P3 consistent with the mechanism observed in protein-tyrosine phosphatase-catalyzed reactions.
Insights
PTEN, a tumor suppressor, regulates cell growth signaling by dephosphorylating phosphatidylinositol 3,4,5-trisphosphate (PtdIns(3,4,5)P3). This study shows PTEN acts as a 3-phosphatase in vivo, controlling PtdIns(3,4,5)P3 levels.
Area of Science:
- Cell Biology
- Biochemistry
- Molecular Signaling
Background:
- Phosphatidylinositol 3,4,5-trisphosphate (PtdIns(3,4,5)P3) is crucial for cell growth signaling pathways.
- PTEN is a known tumor suppressor, but its precise role in PtdIns(3,4,5)P3 regulation requires further elucidation.
Purpose of the Study:
- To investigate the enzymatic activity of PTEN on PtdIns(3,4,5)P3.
- To determine if PTEN functions as a 3-phosphatase in vivo.
Main Methods:
- Overexpression of PTEN and its catalytically inactive mutant (C124S) in human 293 cells.
- Measurement of PtdIns(3,4,5)P3 levels following insulin stimulation.
- Enzymatic assays using purified recombinant PTEN.
Main Results:
- Overexpression of PTEN reduced insulin-induced PtdIns(3,4,5)P3 production without affecting phosphoinositide 3-kinase activation.
- The catalytically inactive PTEN mutant (C124S) led to PtdIns(3,4,5)P3 accumulation.
- Purified PTEN demonstrated specific dephosphorylation of PtdIns(3,4,5)P3 at the 3-position and inositol 1,3,4,5-tetrakisphosphate.
Conclusions:
- PTEN functions as a phosphoinositide 3-phosphatase in vitro.
- PTEN likely regulates PtdIns(3,4,5)P3 levels in vivo, implicating its role in cell growth signaling and tumor suppression.