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 alpha (ID(50)=approx. 10 microM) in a dose-depedent manner, but high doses are required to inhibit A-kinase activity (ID(50)=approx. 90 microM); (ii) the autophosphorylation of CK-I is more sensitive to MTS (ID(50)=approx. 0.2 microM); (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.