Ligand activation of peroxisome proliferator-activated receptor-beta/delta inhibits cell proliferation in human HaCaT keratinocytes

Mol Pharmacol. 2008 Nov;74(5):1429-42. doi: 10.1124/mol.108.050609. Epub 2008 Aug 7.

Abstract

Although there is strong evidence that ligand activation of peroxisome proliferator-activated receptor (PPAR)-beta/delta induces terminal differentiation and attenuates cell growth, some studies suggest that PPARbeta/delta actually enhances cell proliferation. For example, it was suggested recently that retinoic acid (RA) is a ligand for PPARbeta/delta and potentiates cell proliferation by activating PPARbeta/delta. The present study examined the effect of ligand activation of PPARbeta/delta on cell proliferation, cell cycle kinetics, and target gene expression in human HaCaT keratinocytes using two highly specific PPARbeta/delta ligands [4-[[[2-[3-fluoro-4-(trifluoromethyl)phenyl]-4-methyl-5-thiazolyl]methyl]thio]-2-methylphenoxy acetic acid (GW0742) and 2-methyl-4-((4-methyl-2-(4-trifluoromethylphenyl)-1,3-thiazol-5-yl)-methylsulfanyl)phenoxy-acetic acid (GW501516)] and RA. Both PPARbeta/delta ligands and RA inhibited cell proliferation of HaCaT keratinocytes. GW0742 and GW501516 increased expression of known PPARbeta/delta target genes, whereas RA did not; RA increased the expression of known retinoic acid receptor/retinoid X receptor target genes, whereas GW0742 did not affect these genes. GW0742, GW501516, and RA did not modulate the expression of 3-phosphoinositide-dependent protein kinase or alter protein kinase B phosphorylation. GW0742 and RA increased annexin V staining as quantitatively determined by flow cytometry. The effects of GW0742 and RA were also examined in wild-type and PPARbeta/delta-null primary mouse keratinocytes to determine the specific role of PPARbeta/delta in modulating cell growth. Although inhibition of keratinocyte proliferation by GW0742 was PPARbeta/delta-dependent, inhibition of cell proliferation by RA occurred in both genotypes. Results from these studies demonstrate that ligand activation of PPARbeta/delta inhibits keratinocyte proliferation through PPARbeta/delta-dependent mechanisms. In contrast, the observed inhibition of cell proliferation in mouse and human keratinocytes by RA is mediated by PPARbeta/delta-independent mechanisms and is inconsistent with the notion that RA potentiates cell proliferation by activating PPARbeta/delta.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Annexin A5 / metabolism
  • Blotting, Western
  • Caspase 3 / metabolism
  • Caspase 7 / metabolism
  • Cell Line
  • Cell Proliferation / drug effects*
  • Flow Cytometry
  • Humans
  • Keratinocytes / cytology
  • Keratinocytes / drug effects
  • Ligands
  • PPAR delta / metabolism*
  • PPAR-beta / metabolism*
  • Phosphorylation
  • Polymerase Chain Reaction
  • Thiazoles / metabolism
  • Thiazoles / pharmacology
  • Tretinoin / pharmacology

Substances

  • Annexin A5
  • GW 501516
  • GW0742
  • Ligands
  • PPAR delta
  • PPAR-beta
  • Thiazoles
  • Tretinoin
  • Caspase 3
  • Caspase 7