PPARdelta promotes wound healing by up-regulating TGF-beta1-dependent or -independent expression of extracellular matrix proteins.

Although the peroxisome proliferator-activated receptor (PPAR) delta has been implicated in the wound healing process, its exact role and mechanism of action have not been fully elucidated. Our previous findings showed that PPARdelta induces the expression of the transforming growth factor (TGF)-beta1, which has been implicated in the deposit of extracellular matrix proteins. Here, we demonstrate that administration of GW501516, a specific PPARdelta ligand, significantly promoted wound closure in the experimental mouse and had a profound effect on the expression of collagen types I and III, alpha-smooth muscle actin, pSmad3 and TGF-beta1, which play a pivotal role in wound healing processes. Activation of PPARdelta increased migration of human epidermal keratinocytes and dermal fibroblasts in in vitro scrape-wounding assays. Addition of a specific ALK5 receptor inhibitor SB431542 significantly suppressed GW501516-induced migration of human keratinocytes and fibroblasts. In these cells, activated PPARdelta also induced the expression of collagen types I and III and fibronectin in a TGF-beta1-dependent or -independent manner. The effect of PPARdelta on the expression of type III collagen was dually regulated by the direct binding of PPARdelta and Smad3 to a direct repeat-1 site and a Smad-binding element, respectively, of the type III gene promoter. Taken together, these results demonstrated that PPARdelta plays an important role in skin wound healing in vivo and that it functions by accelerating extracellular matrix-mediated cellular interactions in a process mediated by the TGF-beta1/Smad3 signaling-dependent or - independent pathway.

Identification of ADP-ribosylation factor 4 as a suppressor of N-(4-hydroxyphenyl)retinamide-induced cell death.

Yeast-based functional screening for inhibitors of Bcl-2-associated X protein (Bax)-induced cell death in yeast identified ADP-ribosylation factor 4 (ARF4) as a novel anti-apoptotic gene in human glioblastoma-derived U373MG cells. Yeast or U373MG cells that overexpressed ARF4 exhibited reduced reactive oxygen species (ROS) generation in response to Bax or N-(4-hydroxyphenyl)retinamide (4-HPR), respectively, which suggests that ROS play a role in the inhibition of cell death by ARF4. The 4-HPR-mediated phosphorylation of c-JUN N-terminal kinase, p38, and extracellular signal-regulated kinase was markedly suppressed in U373MG cells that stably expressed ARF4. Stable ARF4 transfectants were also refractory to 4-HPR-induced mitochondrial translocation of Bax, release of mitochondrial cytochrome c, and activation of caspase-3. Our results suggest that ARF4 participates in the regulation of glioblastoma apoptosis through the inhibition of stress-mediated apoptotic signals.

Down-regulation of aldose reductase renders J774A.1 cells more susceptible to acrolein- or hydrogen peroxide-induced cell death.

Aldose reductase (AR) is abundantly expressed in a variety of cell lineages and has been implicated in the cellular response against oxidative stress. However, the exact functional role of AR against oxidative stress remains relatively unclear. This study investigated the role of AR in acrolein- or hydrogen peroxide-induced apoptosis using the J774.A.1 macrophage cell line. Ablation of AR with a small interference RNA or inhibition of AR activity significantly enhanced the acrolein- or hydrogen peroxide-induced generation of reactive oxygen species and aldehydes, leading to increased apoptotic cell death. Blockade of AR activity in J774A.1 cells markedly augmented the acrolein- or hydrogen peroxide-induced translocation of Bax to mitochondria along with reduced Bcl-2 and increased release of cytochrome c from the mitochodria. Taken together, these findings indicate that AR plays an important role in the cellular response against oxidative stress, by sequestering the reactive molecules generated in cells exposed to toxic substances.

Nrf2 regulates curcumin-induced aldose reductase expression indirectly via nuclear factor-kappaB.

The osmotic response element (ORE) differs from the nuclear factor-kappaB (NF-kappaB) binding sequence by a single base pair; therefore, we investigated the involvement of NF-kappaB in the induction of aldose reductase (AR) by curcumin. Curcumin, an herb-derived polyphenolic compound, elicited an increase in the expression and promoter activity of the AR gene in a nuclear factor-erythroid 2-related factor 2 (Nrf2)-dependent manner. Small interfering RNA (siRNA) against p65 or BAY11-7082, an inhibitor of NF-kappaB, significantly suppressed the curcumin and/or Nrf2-induced increase in expression levels and promoter activity of the AR gene. BAY11-7082 or siRNA against p65 also attenuated the curcumin-induced increase in the promoter activity of the wild type AR-ORE(wt) gene, but not that of the mutated AR-ORE(mt), indicating that the ORE is essential for the response to NF-kappaB. The expression of p65, the promoter activity and DNA binding activity of NF-kappaB were enhanced in the presence of curcumin in cells that were transfected with Nrf2 compared to those treated with curcumin alone. Cells that had been preincubated with curcumin demonstrated resistance to reactive oxygen species-induced cell damage through the suppressive effects in the generation of reactive aldehydes. These effects were significantly attenuated in the presence of BAY11-7082, indicating the involvement of NF-kappaB in the cellular response of AR to oxidative stress and toxic aldehydes.

Phorbol ester potentiates the growth inhibitory effects of troglitazone via up-regulation of PPARgamma in A549 cells.

The activation of peroxisome proliferator-activated receptor gamma (PPARgamma) has been shown to induce growth arrest and differentiation of various cancer cells. In the current study, we investigated the effect of 12-O-tetradecanoylphorbol-13-acetate (TPA) on the expression of PPARgamma and proliferation of A549 cells. TPA elicited a dose- and time-dependent increase in PPARgamma mRNA and protein levels. PPARgamma expression in response to TPA was attenuated by pretreatment with bisindolylmaleimide I, N-acetyl-L-cysteine (NAC) and PD98059. TPA-induced protein kinase C (PKC) activation was linked to the generation of reactive oxygen species (ROS), both of which were indispensable for PPARgamma expression in A549 cells. Pretreatment with bisindolylmaleimide I or NAC blocked TPA-induced phosphorylation of extracellular signal-regulated kinase (ERK), suggesting that ERK-mediated signaling is also involved in the induction of PPARgamma. Furthermore, the growth inhibitory effect of troglitazone was significantly potentiated by prolonged incubation with TPA and was attenuated in the presence of GW9662, a specific inhibitor of PPARgamma. These effects were associated with an induction of cell cycle arrest at G0/G1 phase, which was accompanied by the induction of p21Waf1/Cip1 expression and decreased cyclin D1 expression. Taken together, these observations indicate that TPA synergizes with PPARgamma ligand to inhibit cell growth through up-regulation of PPARgamma expression.