Analysis of genes responding to ultraviolet B irradiation of HaCaT keratinocytes using a cDNA microarray

Background; Ultraviolet (UV) B irradiation causes many important biological changes in skin, which lead to pathophysiological alterations of the homeostatic environment. Objectives: To gain more insight into the molecular events provoked by UVB irradiation, we performed cDNA microarray analysis. Methods: Immortalized HaCaT keratinocytes were irradiated with a high cytotoxic dose of UVB (50 mJ cm^-2), and total RNA was isolated. Fluorescently labelled probes were prepared by reverse transcription and were hybridized with cDNA microarray slides made using 840 cDNA clones. Results: Time-course cDNA microarray analysis revealed the global gene expression profile after UVB exposure. Of 840 genes tested, 192 genes showed changes in their expression levels at one or more of four time points. The genes were clustered into four groups according to their expression patterns in a self-organizing maps analysis. Classification of these genes into nine functional categories revealed that UVB irradiation affected several biological processes. The genes that were first upregulated and then returned to normal levels included several genes related to the inhibition of cell growth and the proteasome pathway. Conversely, the expressions of many genes involved in the cytoskeleton, signal transduction, metabolism and transcription were first downregulated or unchanged and then upregulated later, reflecting the recovery of UVB-damaged cellular activities. Conclusions: These results demonstrate the complexity of the transcriptional profile of the UVB response, and provide a basis for the global characterization of UV-regulated gene expression.