title: The CYP26 inhibitor R115866 potentiates the effects of all-trans retinoic acid on cultured human epidermal keratinocytes.
abstract: BACKGROUND
  All-trans retinoic acid (RA) is known to regulate keratinocyte proliferation and differentiation, and retinoids are used as therapeutic agents in certain dermatological disorders, such as psoriasis and acne. Epidermal expression of the heparin-binding epidermal growth factor-like growth factor (HB-EGF) is induced by RA treatment and HB-EGF is responsible for RA-mediated epidermal hyperplasia in vivo. RA also induces HB-EGF expression in cultured keratinocytes and alters their differentiating phenotype. R115866 is a specific inhibitor of the cytochrome P450 isoform CYP26, which is involved in the metabolic inactivation pathway of RA. Thereby, R115866 is thought to be able to increase the intracellular levels of endogenous RA.
  
  
  OBJECTIVE
  To determine whether or not R115866 potentiates the effect of low concentrations of RA on keratinocytes.
  
  
  METHODS
  We analysed HB-EGF, involucrin and keratin 10 mRNA and protein levels in autocrine human keratinocyte cultures incubated for 18 h with RA or R115866 alone and with RA and R115866 combinations.
  
  
  RESULTS
  RA induced HB-EGF and involucrin expression in a concentration-dependent manner, whereas it inhibited keratin 10 expression. R115866 alone had no effect on the expression of these genes. However, when R115866 was combined with low concentrations of RA, HB-EGF and involucrin expression was induced.
  
  
  CONCLUSIONS
  These results strongly suggest that R115866 potentiates the effects of RA on epidermal keratinocytes when RA is present at low concentrations.
authors.affiliation: Cell and Tissue Laboratory, URPHYM, University of Namur (FUNDP), 61 rue de Bruxelles, B-5000 Namur, Belgium.
authors.forename: S
authors.initials: S
authors.lastname: Giltaire
authors.forename: F
authors.initials: F
authors.lastname: Herphelin
authors.forename: A
authors.initials: A
authors.lastname: Frankart
authors.forename: M
authors.initials: M
authors.lastname: Hérin
authors.forename: P
authors.initials: P
authors.lastname: Stoppie
authors.forename: Y
authors.initials: Y
authors.lastname: Poumay
mesh_terms: D000328:Adult; D052160:Benzothiazoles / Q000494:pharmacology*; D002478:Cells, Cultured; D065607:Cytochrome P-450 Enzyme Inhibitors; D004305:Dose-Response Relationship, Drug; D004357:Drug Synergism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D000078404:Epidermal Cells; D004817:Epidermis / Q000187:drug effects* / Q000378:metabolism; D005786:Gene Expression Regulation / Q000187:drug effects; D066257:Heparin-binding EGF-like Growth Factor; D006801:Humans; D036341:Intercellular Signaling Peptides and Proteins / Q000235:genetics / Q000378:metabolism; D053550:Keratin-10 / Q000235:genetics / Q000378:metabolism; D015603:Keratinocytes / Q000187:drug effects* / Q000378:metabolism; D011498:Protein Precursors / Q000235:genetics / Q000378:metabolism; D014212:Tretinoin / Q000494:pharmacology*; D014230:Triazoles / Q000494:pharmacology*
chemical_list: D052160:Benzothiazoles; D065607:Cytochrome P-450 Enzyme Inhibitors; D004791:Enzyme Inhibitors; C587883:HBEGF protein, human; D066257:Heparin-binding EGF-like Growth Factor; D036341:Intercellular Signaling Peptides and Proteins; C507493:KRT10 protein, human; D011498:Protein Precursors; D014230:Triazoles; D053550:Keratin-10; D014212:Tretinoin; C032253:involucrin; C406527:R 115866