Polyamine-enhanced casein kinase II in mouse pancreatic islets

Abstract

The occurrence of polyamine-stimulated protein kinase (casein kinase II) in cytosol of mouse pancreatic islets was investigated. Islet protein phosphorylation was enhanced by spermidine, spermine, lysine-rich histone and polylysine; the major endogenous substrates in the cytosol were three proteins of Mr 50,000, 55,000 and 100,000. Cadaverine and putrescine were without effects. A Mr 100,000 protein is a major substrate for Ca2+-calmodulin-dependent protein kinase, and Mr 50,000 and 55,000 proteins are substrates for cyclic adenosine 3',5'-cyclic monophosphate (AMP) dependent protein kinase in mouse islets. However, neither cyclic-AMP-dependent protein kinase inhibitor nor trifluoperazine inhibited polyamine-enhanced protein phosphorylation. Both basal and polyamine-enhanced protein phosphorylation patterns were identical when either [gamma-32P] adenosine 5'-triphosphate (ATP) or [gamma-32P] guanosine 5'-triphosphate (GTP) was used as phosphate donors, indicative of the presence of a polyamine-stimulated casein kinase II in pancreatic islets. It is suggested that polyamines and polyamine-enhanced casein kinase II activity may have an important role in regulation of protein phosphorylation in pancreatic islets.