Expression profiling of vitamin D treated primary human keratinocytes

Vitamin D has attracted much attention by its ability to stop cell proliferation and induce differentiation, which became of particular interest for the treatment of cancer and psoriasis. We performed an expression profile of 12 hours and 24 hours 1α,25‐dihydroxyvitamin D 3 (1α,25(OH) 2 D 3 ) treated primary human keratinocytes, to determine the changes in gene expression induced by the steroid in order to improve our understanding of the biological activity of 1α,25(OH) 2 D 3 . This we expect to be useful for establishing a test system for vitamin D analogs or might open new therapeutic targets or uses for the hormone. For the filter array experiments a non‐redundant set of 2135 sequence verified EST clones was used. The normalized raw data of 2 filters per time point were combined and subjected to SAM analysis to further increase the statistical significance. 86 positive and 50 negative genes were identified after 12 h. The numbers went down to 43 positive and 1 negative gene after 24 h of treatment. Fifteen genes are up‐regulated over a longer period of time (12 h and 24 h). Results were verified by real‐time PCR and/or Northern blots. Targets identified are involved in intracellular signaling, transcription, cell cycle, metabolism, cellular growth, constitution of the extracellular matrix or the cytoskeleton and apoptosis, immune responses, and DNA repair, respectively. Expression profiles showed an initial stop of proliferation and induction of differentiation, and resumed proliferation after prolonged incubation, most likely due to degradation of the hormone. J. Cell. Biochem. 100: 574–592, 2007. © 2006 Wiley‐Liss, Inc.