Real–Time Quantitative Reverse Transcriptase-Polymerase Chain Reaction (RT–PCR) Analysis of the Vitamin D Pathway in UV Irradiated Keratinocytes
Humans have developed many mechanisms for detecting and responding to solar ultraviolet (UV) and visible radiation. The primary UV responses are localized to the skin because of its direct interface with sunlight. There is a complex underlying network of response pathways initiated through hormonal and other biologic systems in the skin after UV irradiation which augment gene expression. It is well established that, during exposure to sunlight, the UVB portion (290–315nm) of the solar spectrum is responsible for the photolysis of epidermal and dermal stores of 7–dehydrocholesterol [provitamin D3] to previtamin D3 (1). Once formed, it is then isomerized by a thermally induced mechanism to vitamin D3 (1). Vitamin D3 a biologically inert form, enters the circulation and requires two successive hydroxylations before becoming biologically active. It is first hydroxylated in the liver by the vitamin D–25–hydroxylase [25–OHase] to form 25–hydroxyvitamin D3 [25(OH)D3] and then in the kidney to its biologically active form 1α,25–dihydroxyvitamin D3 [1α,25(OH)2D3] by the 25–hydroxyvitamin D3 1α–hydroxylase [1α–OHase] or to 24,25–dihydroxyvitamin D3 [24,25(OH)2D3], a catabolic metabolite, by 25–hydroxyvitamin D3 24–hydroxylase [24OHase] (2). Once formed, 1α,25(OH)2D3 acts on its target tissues by interacting with a specific nuclear receptor, the vitamin D receptor (VDR), to bring about its biological effects on gene transcription (3).
KeywordsNormal Human Keratinocytes Specific Nuclear Receptor Nonirradiated Cell Augment Gene Expression Catabolic Metabolite
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