| Abstract: | This report describes the activity of a novel phospholipid-stimulated protein kinase from mouse DA-1 leukemic cells. The kinase was activated by phosphatidylglycerol or phosphatidylinositol. Phospholipid-stimulated protein phosphorylation occurred in the presence of Mn2+ or Mg2+; kinase activity was greater with Mg2+ than with Mn2+ from 4 to 10 mM, although at lower divalent cation concentrations Mn2+ was preferred. A Mr 75,500-77,000 endogenous protein doublet and a Mr 42,000 endogenous protein were phosphorylated in whole cell extracts under these conditions. These substrates contrasted with those identified under protein kinase C conditions. Of the exogenous proteins tested, phospholipid-stimulated phosphorylation was highest with histone H2B followed by other histones. In addition to DA-1 cells, phospholipid-stimulated protein kinase also was detected in high levels in normal mouse spleen, marrow, and kidney but not detectable in brain extracts. The phosphatidylglycerol-stimulated kinase was separated from protein kinase C by anion-exchange chromatography on DEAE-Sephacel, from which it eluted at 0.2 to 0.3 M NaCl. Physiological dissociation of the two types of kinase activity was demonstrated by down regulation of protein kinase C over 24 h by phorbol 12-myristate 13-acetic acid. Under these conditions phosphatidylglycerol kinase activity and subcellular distribution were unaffected. Thus, phosphatidylglycerol-stimulated kinase was detectable in both normal and malignant cells and contrasted with, and was separable from, protein kinase C in numerous respects. Phosphatidylglycerol-stimulated protein kinase basic biochemistry and physiological roles are topics worthy of further investigation. |
