Modulation of UVB-induced and basal cyclooxygenase-2 (COX-2) expression by apigenin in mouse keratinocytes: role of USF transcription factors.
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.
Van Dross
Rukiyah T
RT
Department of Pharmacology and Toxicology, Leo Jenkins Cancer Center, East Carolina University, Greenville, North Carolina 27834, USA.
Hong
Xiaoman
X
Essengue
Suzanne
S
Fischer
Susan M
SM
Pelling
Jill C
JC
D000818:Animals; D047310:Apigenin / Q000494:pharmacology*; D002460:Cell Line; D051546:Cyclooxygenase 2 / Q000096:biosynthesis*; D004790:Enzyme Induction / Q000187:drug effects / Q000528:radiation effects; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects / Q000528:radiation effects; D015603:Keratinocytes / Q000201:enzymology* / Q000528:radiation effects; D051379:Mice; D015398:Signal Transduction / Q000187:drug effects / Q000528:radiation effects; D014466:Ultraviolet Rays; D051720:Upstream Stimulatory Factors / Q000378:metabolism*
D051720:Upstream Stimulatory Factors; D047310:Apigenin; D051546:Cyclooxygenase 2