Identification of a protein kinase C (PKC) activator, daphnoretin, that suppresses hepatitis B virus gene expression in human hepatoma cells.
We examined the antiviral activity of a crude extract prepared from a Chinese medicinal herb Wikstroemia indica C.A. Mey. One active component, daphnoretin (7-hydroxyl-6-methoxy-3,7'-dicoumarylether), was identified, which showed strong suppressive effects on the expression of the hepatitis B surface antigen (HBsAg) in human hepatoma Hep3B cells. To examine the signaling pathway of daphnoretin on the Hep3B cells, we pretreated Hep3B cells with 12-O-tetradecanoylphorbol-13-O-acetate (200 nM) for 24 hr to down-regulate intracellular protein kinase C (PKC) levels and found that the PKC-down-regulated Hep3B cells did not respond at all to daphnoretin. Furthermore, daphnoretin induced translocation of PKC from the cytosol to the membrane and down-regulated intracellular PKC levels in the Hep3B cells, indicating that it may directly activate PKC. This hypothesis was supported by the observation that daphnoretin directly competed with [3H]phorbol dibutyrate for the binding of PKC in the whole cell and activated purified PKC activity in vitro. Our results demonstrated that daphnoretin, with a structure distinct from phorbol ester, is a PKC activator and has suppressive effects on HBsAg gene expression in human hepatoma cells.
Chen
H C
HC
Institute of Biochemistry, National Yang-Ming University, Taipei, Taiwan, R.O.C.
Chou
C K
CK
Kuo
Y H
YH
Yeh
S F
SF
D000972:Antineoplastic Agents, Phytogenic / Q000494:pharmacology*; D002478:Cells, Cultured; D003374:Coumarins / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D015870:Gene Expression / Q000187:drug effects*; D006515:Hepatitis B virus / Q000187:drug effects*; D006801:Humans; D008099:Liver / Q000187:drug effects*; D011493:Protein Kinase C / Q000187:drug effects*
D000972:Antineoplastic Agents, Phytogenic; D003374:Coumarins; C035316:daphnoretin; D011493:Protein Kinase C