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 Mmol/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 UVBinduced apoptosis may explain, in part, the photochemopreventive effects of apigenin. [Cancer Res 2008;68(8):3057-65]

Inhibition of mTOR by apigenin in UVB-irradiated keratinocytes: A new implication of skin cancer prevention

“…UV-induced p53 mutations frequently occur in human skin cancer, in agreement with the critical role of p53 in the elimination of severely damaged cells[39], and keratinocytes with mutated p53 are less prone to UV-induced apoptosis as is evidenced by decreased amounts of sunburn (apoptotic cells) in the epidermis[40, 41]. However, UVB can induce apoptosis in HaCaT human keratinocytes cell line, which bears p53 mutations, suggesting p53-independent apoptosis in response to UVB[17]. Our previous studies uncovered enhanced apoptosis in UVB-irradiated keratinocytes through both the intrinsic and extrinsic apoptotic pathways, and also via a p53-independent pathway[17].…”

“…Apigenin has multiple properties that make it a promising chemopreventive agent[7]. It can inhibit angiogenesis[8, 9], stabilize and enhance the expression of tumor suppressive p53[10, 11], inhibit pro-inflammatory COX-2 expression[12, 13], and cause cell cycle arrest [14, 15] and apoptosis[16, 17] through multiple mechanisms. However, the full scope of apigenin's chemopreventive function is not known.…”

Plant Flavone Apigenin: an Emerging Anticancer Agent

“…This action was attributed to the reduction of endothelial interaction in tumor cells [146]. Topical application of apigenin to mouse skin effectively reduces the incidence and size of skin tumors caused by UVB exposure inducing apoptosis via the intrinsic and extrinsic apoptotic pathways [147]. Exposure of apigenin and luteolin to human keratinocytes inhibited UVA-induced collagenolytic MMP-1 production through interference with Ca(2+)-dependent MAPKs and AP-1 signaling [148].…”

Induction of apoptosis in HPV16 E7 transfected human keratinocyte by ALA-mediated photodynamic therapy

“…The percentages of apoptotic cells were analyzed by CellQuest TM software (BD Biosciences, San Jose CA USA) [18].…”