Elevated expression of protein casein kinase II (CKII) stimulated basal phospholipase D (PLD) activity as well as PMA-induced PLD activation in human U87 astroglioma cells. Moreover, CKII-selective inhibitor, emodin and apigenin suppressed PMA-induced PLD activation in a dose-dependent manner as well as basal PLD activity, suggesting the involvement of CKII in the activation of both PLD1 and PLD2. CKII was associated with PLD1 and PLD2 in co-transfection experiments. Furthermore, CKII induced serine/threonine phosphorylation of PLD2 in vivo, and the multiple regions of PLD2 were phosphorylated by CKII in vitro kinase assay using glutathione S-transferase-PLD2 fusion protein fragments. Elevated expression of CKII or PLD increased cell proliferation but pretreatment of cells with 1-butanol suppressed CKII-induced cell proliferation. These results suggest that CKII is involved in proliferation of U87 cells at least in part, through stimulation of PLD activity.
1-Butanol/pharmacology ; Astrocytoma/*enzymology/metabolism/pathology ; Blotting, Western ; Casein Kinase II/analysis/*pharmacology ; Cell Line, Tumor ; Cell Proliferation/drug effects ; Dose-Response Relationship, Drug ; Enzyme Activation ; Enzyme Inhibitors/pharmacology ; Glutathione Transferase/metabolism ; Humans ; Kinetics ; Phospholipase D/genetics/*metabolism ; Phosphorylation/drug effects ; Precipitin Tests ; Recombinant Fusion Proteins/metabolism ; Research Support, Non-U.S. Gov't ; Tetradecanoylphorbol Acetate/pharmacology