title: Expression of 25-hydroxyvitamin D3-24-hydroxylase mRNA in cultured human keratinocytes.
abstract: It is well documented that 1 alpha,25-dihydroxyvitamin D3 (1 alpha,25[OH]2D3), the most active vitamin D metabolite, inhibits epidermal keratinocyte proliferation and promotes differentiation. 1 alpha,25(OH)2D3 can be produced in keratinocytes from 25-hydroxyvitamin D3 by the enzyme 25-hydroxyvitamin D3-1 alpha-hydroxylase (1-OHase). Hydroxylation of 1 alpha,25(OH)2D3 by 25-hydroxyvitamin D3-24-hydroxylase (24-OHase), the first step in the catabolic pathway of 1 alpha,25(OH)2D3 could significantly reduce the intracellular concentration of 1 alpha,25(OH)2D3. Therefore, the expression of 24-OHase could have a critical regulatory role in 1 alpha,25(OH)2D3-dependent gene expression. As a first step to examine this possibility, the steady state level of 24-OHase mRNA in cultured human keratinocytes (CHK) was investigated. 24-OHase mRNA was not detected in control CHK. 1 alpha,25(OH)2D3 caused a dose- and time-dependent increase in 24-OHase mRNA level. The highest accumulation of 24-OHase mRNA was observed in CHK treated with 0.1-1 microM 1 alpha,25(OH)2D3. The level of 24-OHase mRNA reached a plateau 12-24 hr after 1 alpha,25(OH)2D3 treatment. 1 beta,25-dihydroxyvitamin D3, the stereoisomer of 1 alpha,25(OH)2D3, failed to induce 24-OHase mRNA expression significantly. In addition to 24-OHase mRNA, a 1.0-kb mRNA hybridized strongly with both rat and human 24-OHase cDNA probes. The origin of this 1.0-kb message is unknown at present, however, it was regulated by 1 alpha,25(OH)2D3. These results demonstrate that 1 alpha,25(OH)2D3 up-regulates the expression of 24-OHase mRNA, and this may be an important first step in the initiation of catabolism of 1 alpha,25(OH)2D3 in human keratinocytes.
authors.affiliation: Department of Medicine, Boston University Medical Center, Massachusetts.
authors.forename: M L
authors.initials: ML
authors.lastname: Chen
authors.forename: G
authors.initials: G
authors.lastname: Heinrich
authors.forename: Y I
authors.initials: YI
authors.lastname: Ohyama
authors.forename: K
authors.initials: K
authors.lastname: Okuda
authors.forename: J L
authors.initials: JL
authors.lastname: Omdahl
authors.forename: T C
authors.initials: TC
authors.lastname: Chen
authors.forename: M F
authors.initials: MF
authors.lastname: Holick
mesh_terms: D002117:Calcitriol / Q000494:pharmacology*; D002478:Cells, Cultured; D003577:Cytochrome P-450 Enzyme System; D004790:Enzyme Induction / Q000187:drug effects; D015870:Gene Expression / Q000187:drug effects; D006801:Humans; D066298:In Vitro Techniques; D015603:Keratinocytes / Q000378:metabolism*; D008297:Male; D012333:RNA, Messenger / Q000235:genetics; D013250:Steroid Hydroxylases / Q000235:genetics*; D065668:Vitamin D3 24-Hydroxylase
chemical_list: D012333:RNA, Messenger; D003577:Cytochrome P-450 Enzyme System; D013250:Steroid Hydroxylases; D065668:Vitamin D3 24-Hydroxylase; D002117:Calcitriol