Polyamines stimulate the activity of glycogen synthase (casein) kinase-1 from bovine kidney and different rat tissues

Previous studies have established that casein kinase-2 (CK-2) is stimulated by polyamines. In this study it is shown that glycogen synthase (casein) kinase-1 (CK-1) can be activated similarly. Using casein as the substrate, bovine kidney CK-1 was stimulated 7-, 2-, and 0.5-fold by spermine, spermidine, and putrescine, respectively. Half-maximal activation of CK-1 by these polyamines was observed at 0.25, 0.70, and 0.50 mM, respectively. CK-1 was optimally activated by spermine at low ionic strength and low Mg2+ concentrations (1-3 mM). Using phosvitin as the substrate, CK-1 was stimulated at low concentrations (0-0.8 mM) and inhibited at higher concentrations of spermine. By contrast CK-2 was inhibited at all concentrations of spermine when phosvitin was used as substrate. Using calcineurin (not a substrate for CK-2) as a substrate, CK-1 from bovine kidney or from three rat tissues (liver, kidney, and testis) was stimulated greater than 2-fold by spermine. It is further shown that heparin inhibits CK-1 and this inhibition can be reversed by spermine. The Vmax of CK-1 for both casein and ATP is increased by spermine while the Km remains unchanged by the polyamine. These studies indicate that CK-1, like CK-2, is a heparin-inhibited and polyamine-activated protein kinase. The results also suggest that CK-1 may be activated by spermine in vivo.