Ultraviolet-A-induced transactivation of the vascular endothelial growth factor gene in HaCaT keratinocytes is conveyed by activator protein-2 transcription factor

Ultraviolet-A radiation represents a significant proportion of the ultravio let solar spectrum that was recently shown to affect gene expression of epi dermal keratinocytes by molecular mechanisms distinct from ultraviolet-B ra diation. As ultraviolet-A either alone or in combination with ultraviolet-B may contribute to photocarcinogenesis, we aimed to explore the biologic ef fects of ultraviolet-A radiation on vascular endothelial growth factor gene expression by the immortalized keratinocyte cell line HaCaT. As keratinocy te-derived vascular endothelial growth factor not only provides the major c utaneous angiogenic activity but may also augment the malignant phenotype o f tumor cells, we studied the molecular mechanisms of ultraviolet-A-induced vascular endothelial growth factor expression in HaCaT cells, serving as a transformed preneoplastic epithelial cell line. Whereas ultraviolet-B-medi ated vascular endothelial growth factor expression has been previously indi cated to be conveyed by indirect mechanisms, ultraviolet-A rapidly induced vascular endothelial growth factor mRNA expression in a fashion comparable to that seen with the transforming growth factor alpha, representing a dire ct and potent activator of vascular endothelial growth factor gene transcri ption. Ultraviolet-A was found to readily induce vascular endothelial growt h factor promoter-based reporter gene constructs through a consensus elemen t for activator protein-2 transcription factor. The critical role of activa tor protein-2 was substantiated by demonstration of ultraviolet-A-induced a ctivator-protein-2-dependent nuclear DNA binding activity to this site, and by inhibition of ultraviolet-A-mediated vascular endothelial growth factor gene transcription through insertion of a critical mutation within the act ivator protein-2 sequence. Together, our data further elucidate photobiolog ic aspects of ultraviolet-A-induced gene expression by characterizing mecha nisms of vascular endothelial growth factor upregulation at the molecular l evel. In addition, our experiments support the concept of a more general im portance of activator protein-2 in ultra- violet-A-mediated responses by ke ratinocytes or keratinocyte-derived cell lines.