UVA and UVB radiation differentially regulate vascular endothelial growth factor expression in keratinocyte-derived...

Vascular endothelial growth factor (VEGF) is a central regulator of neoangiogenesis in inflammatory and neoplastic conditions. Ultraviolet irradiation is one of the mainstays of dermatological therapy for various inflammatory skin diseases. In the present study we have compared the effects of UV irradiation on the production of VEGF by keratinocytes (KC) and by the KC-derived cell lines A431 and HaCaT. Irradiation of A431 and HaCaT cells with both UVA (10 J/cm2 and 20 J/cm2) and UVB (8 mJ/cm2 and 16 mJ/cm2) led to strong upregulation of VEGF mRNA and protein. Induction of VEGF by UVA and UVB in these cells was mediated by different pathways, i.e. the generation of free radicals and the secretion of (a) soluble factor(s), respectively. Unlike KC-derived cell lines, no increase in VEGF production was observed in KC in primary culture after irradiation with the same UV doses. Increasing the irradiation dose in these cells of UVA to 40 J/cm2 led to a marked decrease in soluble VEGF, whereas doses as high as 32 mJ/cm2 UVB only minimally affected VEGF levels. Reduction of VEGF production by KC might contribute to the effect of UVA irradiation in inflammatory skin diseases. The differential response of primary KC and autonomously growing KC-derived cell lines to the induction of VEGF by UV light could favor neoangiogenesis in the vicinity of epidermal tumor cells in vivo, thereby endowing them with a growth advantage over normal cells.