Calmodulin stimulates polyamine-responsive protein kinase in the absence of Ca 2+

Abstract

A cyclic nucleotide-independent, polyamine-responsive protein kinase from the cytosol of Morris hepatoma 3924A, which phosphorylated heat-stable endogenous substrates and casein in the presence of polyamines (Criss, W.E., Yamamoto, M., Takai, Y., Nishizuka, Y. and Morris, H.P. (1978) Cancer Res. 38, 3540–3545) was observed to be stimulated by an endogenous protein activator. This protein activator was identified to be calmodulin. the polyamine-responsive protein kinase was also stimulated by purified calmodulin, but only in the presence of polyamines such as polylysine. This action of cadmodulin did not require Ca 2+ for activation of the enzyme; and activation occured in the presence of EGTA. DNA and RNA inhibited the polyamine-responsive protein kinase, either in the presence or absence of Ca 2+. Purified calmodulin, in the presence of cyclic AMP or cyclic GMP, did not activate the protein kinase. Therefore, polyamines such as polylysine are an absolute requirement for this expression of calmodulin action. The increased enzyme activity by calmodulin was accompanied with an increased V max and with no changes in the F m (ATP). High levels of cation, up to 100 mM Mg 2+, did not effect the action of cadmodulin. These results indicate that tumor cytosolic polyamine-responsive protein kinase is regulated by calmodulin, the latter being increased in the tumor tissue.