Inhibition of TPA-induced cyclooxygenase-2 (COX-2) expression by apigenin through downregulation of Akt signal transduction in human keratinocytes

Mol Carcinog. 2005 Oct;44(2):83-91. doi: 10.1002/mc.20123.


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.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Apigenin / pharmacology*
  • Cell Line
  • Cyclooxygenase 2
  • Dinoprostone / metabolism
  • Down-Regulation
  • Enzyme Activation
  • Humans
  • Keratinocytes / drug effects*
  • Keratinocytes / metabolism
  • Membrane Proteins
  • Prostaglandin-Endoperoxide Synthases / metabolism*
  • Protein-Serine-Threonine Kinases / metabolism*
  • Proto-Oncogene Proteins / metabolism*
  • Proto-Oncogene Proteins c-akt
  • Reactive Oxygen Species / metabolism
  • Signal Transduction / drug effects
  • Tetradecanoylphorbol Acetate / pharmacology*
  • Transfection


  • Membrane Proteins
  • Proto-Oncogene Proteins
  • Reactive Oxygen Species
  • Apigenin
  • Cyclooxygenase 2
  • PTGS2 protein, human
  • Prostaglandin-Endoperoxide Synthases
  • AKT1 protein, human
  • Protein-Serine-Threonine Kinases
  • Proto-Oncogene Proteins c-akt
  • Dinoprostone
  • Tetradecanoylphorbol Acetate