Identifying and characterizing casein kinase II in human platelets
CH Hoyt, CJ Oh, JB Beekman, DW Litchfield and KM Lerea
Department of Cell Biology and Anatomy, New York Medical College, Valhalla
10595.
We have recently shown that inhibition of protein phosphatases in platelets
causes increases in protein phosphorylations with a concomitant inhibition
of platelet responses. The burst in protein phosphorylation appears to be
catalyzed by messenger-independent protein kinases. The aim of the present
study was to characterize the presence of broad families of protein kinases
found in platelets. Lysates of control and thrombin-stimulated platelets
were prepared, and proteins were separated on MONO Q fast protein liquid
chromatography. In addition to the presence of histone protein kinase and
tyrosine kinase activities, human platelets contain casein kinase II (CKII)
activity as assessed by phosphorylation of a specific substrate peptide.
Western blot analysis and immunogold electron microscopy studies further
showed the presence of alpha-, alpha'-, and beta- subunits of CKII. The
enzyme appears to be distributed throughout the cytosol and not secreted
after thrombin treatment. Immunoprecipitation studies suggest that at least
some of the holoenzymes exist as an alpha alpha' beta 2 complex. Although
no activation of the enzyme was detected after thrombin treatment, our
results show that CKII is a major messenger-independent protein kinase in
platelets.
Volume 83,
Issue 12,
pp. 3517-3523,
06/15/1994
Copyright © 1994 by The American Society of Hematology
