Modulation of UVB-induced and basal cyclooxygenase-2 (COX-2) expression by apigenin in mouse keratinocytes: role of USF transcription factors

Mol Carcinog. 2007 Apr;46(4):303-14. doi: 10.1002/mc.20281.


Apigenin is a bioflavonoid with chemopreventive activity against UV- or chemically-induced mouse skin tumors. To further explore the mechanism of apigenin's chemopreventive activity, we determined whether apigenin inhibited UVB-mediated induction of cyclooxygenase-2 (COX-2) expression in mouse and human keratinocytes. Apigenin suppressed the UVB-induced increase in COX-2 protein and mRNA in mouse and human keratinocyte cell lines. UVB radiation of keratinocytes transfected with a mouse COX-2 promoter/luciferase reporter plasmid resulted in a threefold increase in transcription from the promoter, and apigenin inhibited the UV-induced promoter activity at doses of 5-50 microM. Transient transfections with COX-2 promoter deletion constructs and COX-2 promoter constructs containing mutations in specific enhancer elements indicated that the effects of UVB required intact Ebox and ATF/CRE response elements. Electrophoretic mobility shift assays with supershifting antibodies were used to identify USF-1, USF-2, and CREB as proteins binding to the ATF/CRE-Ebox responsive element of the COX-2 promoter. Keratinocytes co-transfected with the COX-2 luciferase reporter and a USF-2 expression vector, alone or in combination with a USF-1 expression vector, exhibited enhanced promoter activity in both UVB-irradiated and nonirradiated cultures. However, COX-2 promoter activity was inhibited in keratinocytes co-transfected with USF-1 alone. Finally, we present data showing that the suppressive effect of apigenin on COX-2 expression could be reversed by co-expression of USF-1 and USF-2. These results suggest that one pathway by which apigenin inhibits COX-2 expression is through modulation of USF transcriptional activity.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Animals
  • Apigenin / pharmacology*
  • Cell Line
  • Cyclooxygenase 2 / biosynthesis*
  • Enzyme Induction / drug effects
  • Enzyme Induction / radiation effects
  • Gene Expression Regulation, Enzymologic* / drug effects
  • Gene Expression Regulation, Enzymologic* / radiation effects
  • Keratinocytes / enzymology*
  • Keratinocytes / radiation effects
  • Mice
  • Signal Transduction / drug effects
  • Signal Transduction / radiation effects
  • Ultraviolet Rays
  • Upstream Stimulatory Factors / metabolism*


  • Upstream Stimulatory Factors
  • Apigenin
  • Cyclooxygenase 2