Characterization of (−)-Matairesinol as a Potent Inhibitor of Casein Kinase I in Vitro

The inhibitory effects of (−)-matairesinol (MTS) isolated from Thujopsis dolabrata var. hondai on the activities of four distinct Ser/Thr-protein kinases [two casein kinases (CK-I and CK-II), A-kinase and C-kinase] were determined in vitro. It was found that (i) MTS inhibits the activities of CK-I and C-kinase α (ID50=approx. 10 μM) in a dose-depedent manner, but high doses are required to inhibit A-kinase activity (ID50=approx. 90 μM); (ii) the autophosphorylation of CK-I is more sensitive to MTS (ID50=approx. 0.2 μM); (iii) MTS inhibits CK-I activity in a manner similar to that observed with CK-I-7 (a CK-I inhibitor); and (iv) the compound inhibits CK-I activity by affecting ATP binding in a mixed type manner. These results indicate that MTS is a potent CK-I inhibitor in vitro.