title: Inhibition of TPA-induced cyclooxygenase-2 (COX-2) expression by apigenin through downregulation of Akt signal transduction in human keratinocytes.
abstract: Apigenin is a nonmutagenic bioflavonoid that has been shown to be an inhibitor of mouse skin carcinogenesis induced by the two-stage regimen of initiation and promotion with dimethylbenzanthracene (DMBA) and 12-O-tetradecanoylphorbol-13-acetate (TPA). These DMBA/TPA-induced squamous cell carcinomas overexpress cyclooxygenase-2 (COX-2). Cyclooxygenases are key enzymes required for prostaglandin (PG) synthesis, converting the arachidonic acid (AA) released by phospholipase A2 into prostaglandins. A large body of evidence indicates that the inducible form of cyclooxygenase, COX-2, is involved in tumor promotion and carcinogenesis in a wide variety of tissue types, including colon, breast, lung, and skin. In the present study, we have determined that apigenin inhibited the TPA-induced increase in COX-2 protein and mRNA in the human keratinocyte cell line; HaCaT. The induction of COX-2 elicited by TPA correlated with increased activation of Akt kinase and cell treatment with the PI3 kinase inhibitor, LY294002, blocked TPA induction of COX-2. In cells treated with TPA and apigenin, the inhibition of COX-2 expression correlated with inhibition of Akt kinase activation. Apigenin-mediated inhibition of TPA-induced COX-2 expression was reversed by transient transfection with constitutively active Akt (CA-Akt). Chemical inhibitors of MEK (PD98059), p38 (SB202190), but not JNK (SP600125) blocked TPA induction of COX-2 although apigenin did not inhibit TPA-mediated COX-2 expression through these pathways. The TPA-induced release of AA from HaCaT cells was also inhibited by cell treatment with apigenin. These data show that apigenin inhibits TPA-mediated COX-2 expression by blocking signal transduction of Akt and that apigenin also blocks AA release, which may contribute to its chemopreventive activity.
authors.affiliation: Department of Pathology and Laboratory Medicine, University of Kansas Medical Center, Kansas City, KS 66160, USA
authors.forename: Rukiyah T
authors.initials: RT
authors.lastname: Van Dross
authors.forename: Xiaoman
authors.initials: X
authors.lastname: Hong
authors.forename: Jill C
authors.initials: JC
authors.lastname: Pelling
mesh_terms: D047310:Apigenin / Q000494:pharmacology*; D002460:Cell Line; D051546:Cyclooxygenase 2; D015232:Dinoprostone / Q000378:metabolism; D015536:Down-Regulation; D004789:Enzyme Activation; D006801:Humans; D015603:Keratinocytes / Q000187:drug effects* / Q000378:metabolism; D008565:Membrane Proteins; D011451:Prostaglandin-Endoperoxide Synthases / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt; D017382:Reactive Oxygen Species / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*; D014162:Transfection
chemical_list: D008565:Membrane Proteins; D011518:Proto-Oncogene Proteins; D017382:Reactive Oxygen Species; D047310:Apigenin; D051546:Cyclooxygenase 2; C496540:PTGS2 protein, human; D011451:Prostaglandin-Endoperoxide Synthases; C494918:AKT1 protein, human; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt; D015232:Dinoprostone; D013755:Tetradecanoylphorbol Acetate