Tumor promoter phorbol ester reversibly modulates tyrosine dephosphorylatioin/ inactivation of protein kinase FA/GSK-3α in A431 cells

✍ Scribed by Shiaw-Der Yang; Jau-Song Yu; Zin-Der Wen

• Publisher: John Wiley and Sons
• Year: 1994
• Tongue: English
• Weight: 893 KB
• Volume: 56
• Category: Article
• ISSN: 0730-2312
• DOI: 10.1002/jcb.240560416

✦ Synopsis

The signal transduction mechanism of protein kinase FA/GSK-3a by tyrosine phosphorylation in A431 cells was investigated. Kinase FA/GSK-3a was found to exist in a highly tyrosine-phosphorylated/activated state in resting cells but could be tyrosine-dephosphorylated and inactivated to -60% of the control level when cells were acutely treated with 1 p . M tumor promoter phorbol ester (TPA) at 37°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-3a immunoprecipitate kinase assay. Conversely, when cells were chronically treated with 1 pM TPA at 37°C for 24 h and processed under identical conditions, kinase FA/GSK-3a was found to be rephosphorylated on tyrosine residue and reactivated to -130% of the original control level. Taken together, the results provide initial evidence that the phosphotyrosine content and cellular activity of kinase FA/GSK-3a 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-3a in cells, representing a new mode of signal transduction pathway for the regulation of this multisubstrate/multifunctional protein kinase in cells.