UV-A radiation produces
cataract in animals, enhances photoaging of the lens and skin and increases the
phototoxicity of drugs. However, the nature of genes that are activated or repressed after cellular exposure to UV-A radiation remains enigmatic. Because lens epithelial cells exposed to UV-A radiation undergo apoptosis 4 h after exposure to the stress, we sought to establish the change in gene expression in cells by UV-A radiation using gene expression profiling using
complementary DNA microarrays containing about 12 000 genes. We identified 78 genes abnormally expressed in UV-A-irradiated cells (showing >2.5-fold change at P < 0.05). These genes are implicated in various biological processes, including signal transduction and
nucleic acid binding, and genes encoding
enzymes. A majority of the genes were downregulated. Our analysis revealed that the expression of genes for the
transcription factors ATF-3 and Pilot increased four-fold, whereas the gene for the apoptosis regulator NAPOR-1 decreased five-fold. These changes were confirmed by real-time quantitative
reverse transcriptase-polymerase chain reaction. The
calpain large
polypeptide 3 (CANP3) gene also increased nine-fold after UV-A radiation. In addition, peroxisomal biogenesis
factor 7,
glucocorticoid receptor-alpha and
tumor-associated
calcium signal transducer genes decreased three- to eight-fold. Western blot analysis further confirmed the increase in
protein expression of ATF-3 and CANP3 and decreased expression of
glucocorticoid receptor-alpha in the irradiated cells. Surprisingly, most of these genes had not been previously shown to be modulated by UV-A radiation. Our results show that human lens epithelial cells respond to a single dose of UV-A radiation by enhancing or suppressing functionally similar sets of genes, some of which have opposing functions, around the time at which apoptosis occurs. These studies support the intriguing concept that activation of competing pathways favoring either cell survival or death is a means to coordinate the response of cells to UV-A stress.