title: Enhancement of UVB-induced apoptosis by apigenin in human keratinocytes and organotypic keratinocyte cultures.
abstract: Topical application of the bioflavonoid 4',5,7-trihydroxyflavone (apigenin) to mouse skin effectively reduces the incidence and size of skin tumors caused by UVB exposure. The ability to act as a chemopreventive compound indicates that apigenin treatment alters the molecular events initiated by UVB exposure; however, the effects of apigenin treatment on UVB-irradiated keratinocytes are not fully understood. In the present study, we have used three models of human keratinocytes to study the effect of apigenin treatment on UVB-induced apoptosis: HaCaT human keratinocyte cells, primary keratinocyte cultures isolated from human neonatal foreskin, and human organotypic keratinocyte cultures. Each keratinocyte model was exposed to a moderate dose of UVB (300-1,000 J/m(2)), then treated with apigenin (0-50 micromol/L), and harvested to assess apoptosis by Western blot analysis for poly(ADP)ribose polymerase cleavage, annexin-V staining by flow cytometry, and/or the presence of sunburn cells. Apigenin treatment enhanced UVB-induced apoptosis >2-fold in each of the models tested. When keratinocytes were exposed to UVB, apigenin treatment stimulated changes in Bax localization and increased the release of cytochrome c from the mitochondria compared with UVB exposure alone. Overexpression of the antiapoptotic protein Bcl-2 and expression of a dominant-negative form of Fas-associated death domain led to a reduction in the ability of apigenin to enhance UVB-induced apoptosis. These results suggest that enhancement of UVB-induced apoptosis by apigenin treatment involves both the intrinsic and extrinsic apoptotic pathways. The ability of apigenin to enhance UVB-induced apoptosis may explain, in part, the photochemopreventive effects of apigenin.
authors.affiliation: Department of Pharmacology, Toxicology, and Therapeutics, University of Kansas Medical Center, Kansas City, Kansas, USA.
authors.forename: Adnan O
authors.initials: AO
authors.lastname: Abu-Yousif
authors.forename: Kimberly A
authors.initials: KA
authors.lastname: Smith
authors.forename: Spiro
authors.initials: S
authors.lastname: Getsios
authors.forename: Kathleen J
authors.initials: KJ
authors.lastname: Green
authors.forename: Rukiyah T
authors.initials: RT
authors.lastname: Van Dross
authors.forename: Jill C
authors.initials: JC
authors.lastname: Pelling
mesh_terms: D016588:Anticarcinogenic Agents / Q000494:pharmacology; D047310:Apigenin / Q000494:pharmacology*; D017209:Apoptosis / Q000528:radiation effects*; D018929:Cell Culture Techniques / Q000379:methods; D002478:Cells, Cultured; D047309:Flavones / Q000494:pharmacology; D006801:Humans; D015603:Keratinocytes / Q000166:cytology / Q000187:drug effects / Q000502:physiology* / Q000528:radiation effects; D014466:Ultraviolet Rays
chemical_list: D016588:Anticarcinogenic Agents; D047309:Flavones; D047310:Apigenin