ACTIVATION OF MAP2-KINASE IN B-LYMPHOCYTES BY CALCIUM IONOPHORES

The role of increases in intracellular calcium levels on tyrosine phos phorylation in human B lymphocytes was studied. Stimulation of normal, resting B lymphocytes or B lymphoblastoid cells with the calcium iono phores ionomycin or A23187 induced the tyrosine phosphorylation and th e enzymatic activation of microtubule-associated protein-2 kinase (MAP 2-K). Treatment of these cells with PMA induced tyrosine phosphorylati on of a protein with the identical mobility, as well as the enzymatic activation of MAP2-K. Stimulation of these cells with ionomycin also r esulted in increased ribosomal S6 kinase activity. Activation of MAP2- K in B lymphocytes by calcium ionophore was rapid (detectable within 1 min), transient (returning to background levels by 45 min), and depen dent on extracellular calcium. These results demonstrate that transmem brane calcium flux induced by calcium ionophore results in the tyrosin e phosphorylation and enzymatic activation of MAP2-K in human B cells.