Ligand activation of peroxisome proliferator-activated receptor-β/δ(PPARβ/δ) inhibits cell growth of human N/TERT-1 keratinocytes

Abstract

The functional role of peroxisome proliferator-activated receptor-β (PPARβ; also referred to as PPARδ) in epidermal cell growth remains controversial. Recent evidence suggests that ligand activation of PPARβ/δ increases cell growth and inhibits apoptosis in epidermal cells. In contrast, other reports suggest that ligand activation of PPARβ/δ leads to the induction of terminal differentiation and inhibition of cell growth. In the present study, the effect of the highly specific PPARβ/δ ligand GW0742 on cell growth was examined using a human keratinocyte cell line (N/ TERT-1) and mouse primary keratinocytes. Ligand activation of PPARβ/δ with GW0742 prevented cell cycle progression from G1 to S phase and attenuated cell proliferation in N/TERT-1 cells. Despite specifically activating PPARβ/δ as revealed by target gene induction, no changes in PTEN, PDK and ILK expression or downstream phosphorylation of Akt were found in either N/TERT-1 cells or primary keratinocytes. Further, altered cell growth resulting from serum withdrawal and the induction of caspase-3 activity by ultraviolet radiation were unchanged in the absence of PPARβ/δ expression and/or the presence of GW0742. While no changes in the expression of mRNAs encoding cell cycle control proteins were found in response to GW0742, a significant decrease in the level of ERK phosphorylation was observed. Results from these studies demonstrate that ligand activation of PPARβ/δ does not lead to an anti-apoptotic effect in either human or mouse keratinocytes, but rather, leads to inhibition of cell growth likely through the induction of terminal differentiation.

Peroxisome proliferator-activated receptor-β/δ (PPARβ/δ) ligands inhibit growth of UACC903 and MCF7 human cancer cell lines

“…These observations are consistent with recent findings made in other human cancer cell lines (Hollingshead et al 2007a), as well as numerous reports linking PPARβ/δ with inducing terminal differentiation and/or inhibiting cell growth (Ali et al 2005;Aung et al 2006;Burdick et al 2007;Fukumoto et al 2005;Hollingshead et al 2007a;Kim et al 2004;Kim et al 2006;Kim et al 2005;Man et al 2007;Marin et al 2006;Martinasso et al 2006;Matthiessen et al 2005;Michalik et al 2001;Müller-Brüsselbach et al 2007;Nadra et al 2006;Ou et al 2007;Peters et al 2000;Planavila et al 2005;Schmuth et al 2004;Tan et al 2001;Teunissen et al 2007;Varnat et al 2006;Westergaard et al 2001). The relatively modest activation of PPARβ/δ in both UACC903 and MCF7 cells as shown by increased mRNA encoding ANGPTL4 shows that these cells are not highly responsive to PPARβ/δ ligands as compared to other cells such as keratinocytes.…”

“…Anti-inflammatory activity of PPARβ/δ and/or PPARβ/δ ligands has been shown in a number of different models including immune cells, colon epithelium, macrophages, cardiomyocytes, keratinocytes, myoblasts, endothelial cells, nerve tissue and hepatocytes Graham et al 2005;Hollingshead et al 2007b;Jakobsen et al 2006;Kim et al 2006;Nagasawa et al 2006;Peters et al 2000;Polak et al 2005;Rival et al 2002;Schmuth et al 2004;Welch et al 2003;Woo et al 2006). There is also strong evidence that ligand activation of PPARβ/δ promotes terminal differentiation in intestinal epithelium, breast and colon cancer cell lines, trophoblasts and primary keratinocytes (Aung et al 2006;Burdick et al 2007;Kim et al 2006;Marin et al 2006;Nadra et al 2006;Schmuth et al 2004;Tan et al 2001;Varnat et al 2006;Westergaard et al 2001). Evidence from a large number of independent laboratories also shows that cell growth is inhibited by PPARβ/δ and its ligands in colonocytes, keratincytes, cardiomyocytes, fibroblasts, endothelial cells and a variety of cancer cell lines (Ali et al 2005;Aung et al 2006;Burdick et al 2007;Fukumoto et al 2005;Hollingshead et al 2007a;Kim et al 2004;Kim et al 2006;Kim et al 2005;Man et al 2007;Marin et al 2006;Martinasso et al 2006;Matthiessen et al 2005;Michalik et al 2001;Müller-Brüsselbach et al 2007;Nadra et al 2006;O...…”

“…There is also strong evidence that ligand activation of PPARβ/δ promotes terminal differentiation in intestinal epithelium, breast and colon cancer cell lines, trophoblasts and primary keratinocytes (Aung et al 2006;Burdick et al 2007;Kim et al 2006;Marin et al 2006;Nadra et al 2006;Schmuth et al 2004;Tan et al 2001;Varnat et al 2006;Westergaard et al 2001). Evidence from a large number of independent laboratories also shows that cell growth is inhibited by PPARβ/δ and its ligands in colonocytes, keratincytes, cardiomyocytes, fibroblasts, endothelial cells and a variety of cancer cell lines (Ali et al 2005;Aung et al 2006;Burdick et al 2007;Fukumoto et al 2005;Hollingshead et al 2007a;Kim et al 2004;Kim et al 2006;Kim et al 2005;Man et al 2007;Marin et al 2006;Martinasso et al 2006;Matthiessen et al 2005;Michalik et al 2001;Müller-Brüsselbach et al 2007;Nadra et al 2006;Ou et al 2007;Peters et al 2000;Planavila et al 2005;Schmuth et al 2004;Tan et al 2001;Teunissen et al 2007;Varnat et al 2006;Westergaard et al 2001). Given the potential of PPARβ/δ ligands as therapeutic agents, it is of great importance to determine the effect of ligand activation of PPARβ/δ on cell growth in vitro and in vivo.…”

Peroxisome proliferator-activated receptor-β/δ protects against chemically induced liver toxicity in mice

“…[9][10][11]21,24,35,41,[52][53][54][55][56][57][58][59][60][61][62] It is possible that PPAR␤/␦-dependent regulation of kinase signaling as found in skin cells, 24 is also critical in liver cells, and thus protects against enhanced cell proliferation. This putative PPAR␤/␦-dependent process could ultimately contribute to preventing liver cancer, as PPAR␤/␦-dependent regulation of cell proliferation is known to influence skin and colon cancer.…”

Activation of Peroxisome Proliferator–Activated Receptor β/δ Inhibits Lipopolysaccharide-Induced Cytokine Production in Adipocytes by Lowering Nuclear Factor-κB Activity via Extracellular Signal–Related Kinase 1/2

“…The involvement of PPAR␤/␦ in ERK1/2 regulation has been previously reported in other cell types. In fact, Burdick et al (39) recently reported that the PPAR␤/␦ agonist GW0742 reduces phospho-ERK1/2 levels in human keratinocytes. In addition, phospho-ERK1/2 levels are higher in the skin of PPAR␤/␦-null mice treated with 12-O-tetradecanoylphorbol-13-acetate than in the skin of wild-type animals (40).…”