抄録
The inhibitory effects of galloyl pedunculagin (GP) and eugeniin on the phosphorylation of histone H2B by cAMP-dependent protein kinase (A-kinase) and autophosphorylation of its β-regulatory subunit (A-kinase β) were examined in vitro. It was found that (i) GP (ID50=approx. 50nM) effectively inhibits the activity of A-kinase (heterodimer), but high doses are required to inhibit the activities of the α-catalytic subunit (ID50=approx. 0.25μM) and casein kinase II (CK-II, ID50=approx. 0.6μM); (ii) GP inhibits the autophosphorylation of A-kinase β in a dose-dependent manner with an ID50 of approx. 6.6nM, which is about 30-fold lower than that observed with CK-IIβ; and (iii) GP reduces the suppressive effect of the β-subunit on the activity of the α-subunit. In addition, purified bovine heart A-kinase precipitates when incubated with excess GP at pH 5.0. A similar precipitation of A-kinase was observed with eugeniin. These results show that the direct binding of GP to the β-subunit prevents the physiological interaction between the β-and α-subunits of A-kinase in vitro. This conclusion is presumably consistent with the binding affinity of proline-rich proteins with tannins, since A-kinase β contains a proline-rich domain that interacts with GP or eugeniin. Therefore, GP will serve as a powerful inhibitor for in vitro and in vivo cellular studies of A-kinase β-mediated signal transduction.
