title: PPAR gamma is an important transcription factor in 1 alpha,25-dihydroxyvitamin D3-induced involucrin expression.
abstract: BACKGROUND
  1 alpha,25-Dihydroxyvitamin D3 (1 alpha,25(OH)2D3), the active form of vitamin D, suppresses keratinocyte proliferation, promotes keratinocyte differentiation, and induces involucrin expression. Peroxisome proliferation-activated receptors (PPARs) are ligand-activated transcription factors. It has been reported that PPARs stimulate keratinocyte differentiation and regulate the expression of differentiation molecules.
  
  
  OBJECTIVE
  Keratinocytes treated with 1 alpha,25(OH)2D3 induced PPAR gamma, which was followed by increased involucrin expression. In this study, we investigated whether PPAR gamma is involved in the 1 alpha,25(OH)2D3-induced involucrin expression in human keratinocytes.
  
  
  METHODS
  Subconfluent keratinocytes were treated with 10(-7)M 1 alpha,25(OH)2D3 for the indicated times, and PPAR and involucrin mRNA expression were determined by real-time RT-PCR. The levels of PPARs, involucrin, p38, and phospho-p38 proteins were assayed by Western blotting, and the DNA binding activities of PPAR gamma and AP-1 were investigated by electrophoretic mobility shift assays (EMSA). To examine the role of PPAR gamma in 1 alpha,25(OH)2D3 responses, recombinant adenovirus carrying a dominant-negative form of PPAR gamma (Axdn-PPAR gamma) was constructed and transfected into keratinocytes. The p38 inhibitor SB203580 was added to the cultures to evaluate the involvement of p38 in involucrin expression.
  
  
  RESULTS
  1 alpha,25(OH)2D3 induced PPAR gamma expression and stimulated PPAR gamma activity. The introduction of dn-PPAR gamma inhibited the expression of involucrin mRNA and protein induced by 1 alpha,25(OH)2D3, and suppressed AP-1 DNA binding activity. 1 alpha,25(OH)2D3 also triggered the phosphorylation of p38, which contributes to involucrin induction. Moreover, dn-PPAR gamma prevented the 1 alpha,25(OH)2D3-induced phosphorylation of p38.
  
  
  CONCLUSIONS
  These results suggest that PPAR gamma regulates involucrin expression by controlling the AP-1 signal and p38 activation in 1 alpha,25(OH)2D3-induced keratinocyte differentiation.
authors: Department of Dermatology, Ehime University School of Medicine, Ehime, Japan.
authors: Xiuju
authors: X
authors: Dai
authors: Koji
authors: K
authors: Sayama
authors: Yuji
authors: Y
authors: Shirakata
authors: Sho
authors: S
authors: Tokumaru
authors: Lujun
authors: L
authors: Yang
authors: Mikiko
authors: M
authors: Tohyama
authors: Satoshi
authors: S
authors: Hirakawa
authors: Yasushi
authors: Y
authors: Hanakawa
authors: Koji
authors: K
authors: Hashimoto
mesh_terms: D002117:Calcitriol / Q000494:pharmacology*; D002478:Cells, Cultured; D005786:Gene Expression Regulation; D006801:Humans; D015603:Keratinocytes / Q000378:metabolism*; D047495:PPAR gamma / Q000502:physiology*; D011498:Protein Precursors / Q000235:genetics*; D018808:Transcription Factor AP-1 / Q000235:genetics; D015533:Transcriptional Activation; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism
chemical_list: D047495:PPAR gamma; D011498:Protein Precursors; D018808:Transcription Factor AP-1; C032253:involucrin; D048051:p38 Mitogen-Activated Protein Kinases; D002117:Calcitriol