title: Inhibition of PTEN and activation of Akt by menadione.
abstract: Menadione (vitamin K(3)) has been shown to activate Erk in several cell lines. This effect has been shown to be due to the activation of EGF receptors (EGFR) as a result of inhibition of some protein tyrosine phosphatases. In the present study, we examined the effects of menadione on Akt in Chinese hamster ovary cells. The phosphorylation of Akt by menadione was not inhibited by AG1478, an inhibitor of EGFR. Menadione inhibited the lipid phosphatase activity of PTEN in a cell-free system. In an intact cell system, menadione inhibited the effect of transfected PTEN on Akt. Thus, one mechanism of its action was considered the accelerated activation of Akt through inhibition of PTEN. This was not the sole mechanism responsible for the EGFR-independent activation of Akt, because menadione attenuated the rate of Akt dephosphorylation even in PTEN-null PC3 cells. The decelerated inactivation of Akt, probably through inhibition of some tyrosine phosphatases, was considered another mechanism of its action.
authors.affiliation: Division of Molecular Medical Science, Graduate School of Biomedical Sciences, Hiroshima University, Minami-ku, Hiroshima 734-8553, Japan.
authors.forename: Kyoko
authors.initials: K
authors.lastname: Yoshikawa
authors.forename: Kiyomi
authors.initials: K
authors.lastname: Nigorikawa
authors.forename: Mariko
authors.initials: M
authors.lastname: Tsukamoto
authors.forename: Namiko
authors.initials: N
authors.lastname: Tamura
authors.forename: Kaoru
authors.initials: K
authors.lastname: Hazeki
authors.forename: Osamu
authors.initials: O
authors.lastname: Hazeki
mesh_terms: D000818:Animals; D016466:CHO Cells; D006224:Cricetinae; D003412:Cricetulus; D004305:Dose-Response Relationship, Drug; D004789:Enzyme Activation / Q000187:drug effects; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D051059:PTEN Phosphohydrolase / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010766:Phosphorylation; D051057:Proto-Oncogene Proteins c-akt / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects*; D013997:Time Factors; D014162:Transfection; D024483:Vitamin K 3 / Q000494:pharmacology*; D014815:Vitamins / Q000494:pharmacology*; D020687:cdc25 Phosphatases / Q000037:antagonists & inhibitors / Q000378:metabolism
chemical_list: D014815:Vitamins; D024483:Vitamin K 3; D019869:Phosphatidylinositol 3-Kinases; D051057:Proto-Oncogene Proteins c-akt; D048049:Extracellular Signal-Regulated MAP Kinases; D020687:cdc25 Phosphatases; D051059:PTEN Phosphohydrolase