Polyamine-enhanced casein kinase 11 in mouse pancreatic islets

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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 50000, 55000 and 100000. 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 [γ-32P] adenosine 5′-triphosphate (ATP) or [γ-32P] guanosine 5′-triphosphate (GTP) was used as phosphate donors, indicative of the presence of a polyaminestimulated casein kinase 11 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.