title: Tumor promoter phorbol ester reversibly modulates tyrosine dephosphorylation/inactivation of protein kinase FA/GSK-3 alpha in A431 cells.
abstract: The signal transduction mechanism of protein kinase FA/GSK-3 alpha by tyrosine phosphorylation in A431 cells was investigated. Kinase FA/GSK-3 alpha was found to exist in a highly tyrosine-phosphorylated/activated state in resting cells but could be tyrosine-dephosphorylated and inactivated to approximately 60% of the control level when cells were acutely treated with 1 microM tumor promoter phorbol ester (TPA) at 37 degrees C for 30 min, as demonstrated by metabolic 32P-labeling the cells, followed by immunoprecipitation and two-dimensional phosphoamino acid analysis and by immunodetection in an antikinase FA/GSK-3 alpha immunoprecipitate kinase assay. Conversely, when cells were chronically treated with 1 microM TPA at 37 degrees C for 24 h and processed under identical conditions, kinase FA/GSK-3 alpha was found to be rephosphorylated on tyrosine residue and reactivated to approximately 130% of the original control level. Taken together, the results provide initial evidence that the phosphotyrosine content and cellular activity of kinase FA/GSK-3 alpha can be modulated in a reversible manner by short-term and long-term exposure of A431 cells to TPA. Since acute exposure of cells to TPA causes up-regulation of cellular protein kinase C (PKC) activity and prolonged exposure to TPA causes down-regulation of PKC, the results further suggest that the TPA-mediated modulation of PKC may play a role in the regulation of tyrosine phosphorylation and concurrent activation of kinase FA/GSK-3 alpha in cells, representing a new mode of signal transduction pathway for the regulation of this multisubstrate/multifunctional protein kinase in cells.
authors.affiliation: Institute of Biomedical Sciences, National Tsing Hua University, Hsinchu, Taiwan, Republic of China.
authors.forename: S D
authors.initials: SD
authors.lastname: Yang
authors.forename: J S
authors.initials: JS
authors.lastname: Yu
authors.forename: Z D
authors.initials: ZD
authors.lastname: Wen
mesh_terms: D000595:Amino Acid Sequence; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000737:chemistry / Q000378:metabolism*; D002273:Carcinogens; D002294:Carcinoma, Squamous Cell / Q000473:pathology; D004789:Enzyme Activation; D038362:Glycogen Synthase Kinase 3; D006801:Humans; D008969:Molecular Sequence Data; D010703:Phorbol Esters / Q000494:pharmacology*; D010766:Phosphorylation; D011233:Precipitin Tests; D011493:Protein Kinase C / Q000378:metabolism; D011494:Protein Kinases / Q000378:metabolism*; D015398:Signal Transduction; D014407:Tumor Cells, Cultured / Q000378:metabolism; D014443:Tyrosine / Q000737:chemistry / Q000378:metabolism*
chemical_list: D002273:Carcinogens; D010703:Phorbol Esters; D014443:Tyrosine; D011494:Protein Kinases; D011493:Protein Kinase C; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D038362:Glycogen Synthase Kinase 3