title: Ligand activation of peroxisome proliferator-activated receptor-beta/delta inhibits cell proliferation in human HaCaT keratinocytes.
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.
authors.affiliation: Department of Veterinary and Biomedical Sciences, The Pennsylvania State University, 312 Life Science Building, University Park, PA 16802, USA.
authors.forename: Michael G
authors.initials: MG
authors.lastname: Borland
authors.forename: Jennifer E
authors.initials: JE
authors.lastname: Foreman
authors.forename: Elizabeth E
authors.initials: EE
authors.lastname: Girroir
authors.forename: Reza
authors.initials: R
authors.lastname: Zolfaghari
authors.forename: Arun K
authors.initials: AK
authors.lastname: Sharma
authors.forename: Shantu
authors.initials: S
authors.lastname: Amin
authors.forename: Frank J
authors.initials: FJ
authors.lastname: Gonzalez
authors.forename: A Catharine
authors.initials: AC
authors.lastname: Ross
authors.forename: Jeffrey M
authors.initials: JM
authors.lastname: Peters
mesh_terms: D017304:Annexin A5 / Q000378:metabolism; D015153:Blotting, Western; D053148:Caspase 3 / Q000378:metabolism; D053179:Caspase 7 / Q000378:metabolism; D002460:Cell Line; D049109:Cell Proliferation / Q000187:drug effects*; D005434:Flow Cytometry; D006801:Humans; D015603:Keratinocytes / Q000166:cytology / Q000187:drug effects; D008024:Ligands; D047494:PPAR delta / Q000378:metabolism*; D048068:PPAR-beta / Q000378:metabolism*; D010766:Phosphorylation; D016133:Polymerase Chain Reaction; D013844:Thiazoles / Q000378:metabolism / Q000494:pharmacology; D014212:Tretinoin / Q000494:pharmacology; D010636:Phenols; D013438:Sulfhydryl Compounds
chemical_list: D017304:Annexin A5; D053148:Caspase 3; D053179:Caspase 7; D008024:Ligands; D047494:PPAR delta; D048068:PPAR-beta; D013844:Thiazoles; D014212:Tretinoin; C425931:GW 501516; C479979:(4-(((2-(3-fluoro-4-(trifluoromethyl)phenyl)-4-methyl-1,3-thiazol-5-yl)methyl)sulfanyl)-2-methylphenoxy)acetic acid; D010636:Phenols; D013438:Sulfhydryl Compounds