Tyrosin dephosphorylation and concurrent inactivation of protein kinase F A /GSK‐3α by genistein in A431 cells

Modulation of protein Kinase F /GSK‐3α by tyrosine phosphorylation in A431 cells was investigated. Kinase F A /GSK‐3α was found to exist in a highly tyrosine‐phosphorylated/activated state in resting cells but could become tyrosine‐dephosphorylated and inactivated down to less than 30% of control values in concentration dependent manner by 50‐400 μM genistein( a Specific tyrosine kinase inhibitor), as demonstrated by metobolic 32 p‐labeling of the cells followed by immunoprecipitation and two‐dimensional phosphoamino acid analysis and byimmunodetection in an antikinase F A /GSK‐3α immunoprecipitate kinase assay. Taken together, the results provide evidence that Kinase F A /GSK‐3α may exist in a highly tyrosine‐phosphorylated/activated state in resting cells which can by tyrosine‐dephosphorylated and nactivated by extracellular stimulus and that tyrosine kinase(s) and /or tyrosine phosphatase(s) may play a role in the modulation of kinse F A /GSK‐3α activity in cells.