Kaempferol is a potent inhibitor of recombinant human protein kinase CK2 holoenzyme in vitro / 中国药理学与毒理学杂志

ABSTRACT

AIM In order to search inhibitors of protein kinase CK2, we observed the inhibitory effects of kaempferol on recombinant human protein kinase CK2 holoenzyme and its kinetics in vitro. METHODSCloning, prokaryotic expression and purification of human protein kinase CK2 α' and β subunits by gene engineering, the two subunits were mixed at equal molar ratio to reconstitute CK2 holoenzyme and identify its biological properties. The CK2 activity was assayed by detecting incorporation of 32P of [γ-32P]ATP into the substrate. The inhibitory effect of kaempferol on CK2 was assayed in the presence of different concentrations of kaempferol. Kinetic analysis of kaempferol-induced inhibition was carried out in the condition that casein concentration was fixed at 2 g·L-1 and ATP was changed at various concentrations(10, 20, 40, 80 μmol·L-1), or ATP was fixed at 10 μmol·L-1 and casein was changed at different concentrations (1, 2, 4, 8 g·L-1). RESULTS Kaempferol was shown to strongly inhibit the holoenzyme activity of recombinant human protein kinase CK2 with IC50 of 1.9 μmol·L-1, which was more effective than chrysin, morin and genistein which are both known as CK2 special inhibitors. Kinetic studies of kaempferol on recombinant human CK2 showed that kaempferol acted as a noncompetitive inhibitor with substrate ATP(Ki=1.1 μmol·L-1) and casein (Ki=3.1 μmol·L-1). CONCLUSIONKaempferol is a novel potent inhibitor of protein kinase CK2 in vitro. Discussions indicate that flavonoid inhibitors of CK2 may adopt different orientations in theactive site of CK2 and that these are determined by the number and position of their hydroxyl groups.