Epithelial-mesenchymal transition (EMT) was shown to confer tumor cells with abilities essential for metastasis, including migratory phenotype, invasiveness, resistance to apoptosis, evading immune surveillance, and tumor stem cell traits. Therefore, inhibition of EMT can be an important therapeutic strategy to inhibit tumor metastasis. Here, we show that activation of peroxisome proliferator-activated receptor γ (PPAR-γ) inhibits transforming growth factor β (TGF-β)-induced EMT in lung cancer cells and prevents metastasis by antagonizing Smad3 function. Activation of PPAR-γ by synthetic ligands (troglitazone and rosiglitazone) or by a constitutively active form of PPAR-γ prevents TGF-β–induced loss of E-cadherin expression and inhibits the induction of mesenchymal markers (vimentin, N-cadherin, fibronectin) and matrix metalloproteases. Consistently, activation of PPAR-γ also inhibited EMT-induced migration and invasion of lung cancer cells. Furthermore, effects of PPAR-γ ligands were attenuated by siRNA-mediated knockdown of PPAR-γ, indicating that the ligand-induced responses are PPAR-γ dependent. Selective knockdown of Smad2 and Smad3 by siRNA showed that TGF-β–induced EMT is Smad3 dependent in lung cancer cells. Activation of PPAR-γ inhibits TGF-β–induced Smad transcriptional activity but had no effect on the phosphorylation or nuclear translocation of Smads. Consistently, PPAR-γ activation prevented TGF-β–induced transcriptional repression of E-cadherin promoter and inhibited transcriptional activation of N-cadherin promoter. Finally, treatment of mice with troglitazone or knockdown of Smad3 in tumor cells significantly inhibited TGF-β–induced experimental metastasis in SCID-Beige mice. Together, with the low toxicity profile of PPAR-γ ligands, our data show that these ligands may serve as potential therapeutic agents to inhibit metastasis. Mol Cancer Ther; 9(12); 3221–32. ©2010 AACR.

Peroxisome proliferator-activated receptors (PPARs) are nuclear transcription factors that play central roles in metabolism and inflammation. Although a variety of compounds have been shown to activate PPARs, identification of physiologically relevant ligands has proven difficult. In silico studies of lipid derivatives reported here identify specific 5-lipoxygenase products as candidate physiologically relevant PPAR-alpha activators. Subsequent studies show both in vitro and in a murine model of inflammation that 5-lipoxygenase stimulation induces PPAR-alpha signaling and that this results specifically from production of the inflammatory mediator and chemoattractant leukotriene B(4) (LTB(4)). Activation of PPAR-alpha is a direct effect of intracellularly generated LTB(4) binding to the nuclear receptor and not of secreted LTB(4) acting via its cell-surface receptors. Activation of PPAR-alpha reduces secretion of LTB(4) by stimulating degradation of this fatty acid derivative. We also show that the LTB(4) precursors leukotriene A(4) (LTA(4)) and 5-hydroperoxyeicosatetrenoic acid (5-HPETE) activate PPAR-alpha but have no significant endogenous effect independent of conversion to LTB(4). We conclude that LTB(4) is a physiologically relevant PPAR-alpha activator in cells of the immune system. This, together with previous findings, demonstrates that different types of lipids serve as endogenous PPAR-alpha ligands, with the relevant ligand varying between functionally different cell types. Our results also support the suggestion that regulation of inflammation may involve balancing proinflammatory effects of LTB(4), exerted through cell-surface receptors, and anti-inflammatory effects exerted through PPAR-alpha activation.

Idiopathic pulmonary fibrosis (IPF) is a progressive and typically fatal lung disease for which no effective therapy has been identified. The disease is characterized by excessive collagen deposition, possibly in response to dysregulated wound healing. Mediators normally involved in would healing induce proliferation of fibroblasts and their differentiation to myofibroblasts that actively secrete collagen. Curcumin, a polyphenolic compound from turmeric, has been shown to exert a variety of biological effects. Effects on IPF and associated cell types remain unclear, however. We accordingly tested the ability of curcumin to inhibit proliferation and differentiation to myofibroblasts by human lung fibroblasts, including those from IPF patients. To further examine the potential usefulness of curcumin in IPF, we examined its ability to reduce fibrosis in bleomycin-treated mice. We show that curcumin effectively reduces profibrotic effects in both normal and IPF fibroblasts in vitro and that this reduction is accompanied by inhibition of key steps in the transforming growth factor-β (TGF-β) signaling pathway. In vivo, oral curcumin treatment showed no effect on important measures of bleomycin-induced injury in mice, whereas intraperitoneal curcumin administration effectively inhibited inflammation and collagen deposition along with a trend toward improved survival. Intraperitoneal curcumin reduced fibrotic progression even when administered after the acute bleomycin-induced inflammation had subsided. These results encourage further research on alternative formulations and routes of administration for this potentially attractive IPF therapy.

Neutrophils (polymorphonuclear leukocytes [PMNs]) are critical to the immune response, including clearance of infectious pathogens. Sepsis is associated with impaired PMN function, including chemotaxis. PMNs express peroxisome proliferator-activated receptor-γ (PPAR-γ), a ligand-activated nuclear transcription factor involved in immune and inflammatory regulation. The role of PPAR-γ in PMN responses, however, is not well characterized. We report that freshly isolated human PMNs constitutively express PPAR-γ, which is up-regulated by the sepsis-induced cytokines TNF-α and IL-4. PMN chemotactic responses to formylmethionyl-leucyl-phenylalanine (fMLP) and IL-8 were dose-dependently inhibited by treatment with the PPAR-γ ligands troglitazone and 15-deoxy-Δ12,14-prostaglandin J2 (15d-PGJ2) and by transfection of PMN-like HL-60 cells with a constitutively active PPAR-γ construct. Inhibition of chemotaxis by PPAR-γ ligands correlated with decreases in extracellular signal-regulated kinase-1 and -2 activation, actin polymerization, and adherence to a fibrinogen substrate. Furthermore, PMN expression of PPAR-γ was increased in sepsis patients and mice with either of 2 models of sepsis. Finally, treatment with the PPAR-γ antagonist GW9662 significantly reversed the inhibition of PMN chemotaxis and increased peritoneal PMN recruitment in murine sepsis. This study indicates that PPAR-γ activation is involved in PMN chemotactic responses in vitro and may play a role in the migration of these cells in vivo.

Critically ill patients are commonly treated with high levels of oxygen, hyperoxia, for prolonged periods of time. Unfortunately, extended exposure to hyperoxia can exacerbate respiratory failure and lead to a high mortality rate. Mitochondrial A-kinase anchoring protein (Akap) has been shown to regulate mitochondrial function. It has been reported that, under hypoxic conditions, Akap121 undergoes proteolytic degradation and promotes cardiac injury. However, the role of Akap1 in hyperoxia-induced acute lung injury (ALI) is largely unknown. To address this gap in our understanding of Akap1, we exposed wild-type ( wt) and Akap1^−/−mice to 100% oxygen for 48 h, a time point associated with lung damage in the murine model of ALI. We found that under hyperoxia, Akap1^−/−mice display increased levels of proinflammatory cytokines, immune cell infiltration, and protein leakage in lungs, as well as increased alveolar capillary permeability compared with wt controls. Further analysis revealed that Akap1 deletion enhances lung NF-κB p65 activity as assessed by immunoblotting and DNA-binding assay and mitochondrial autophagy-related markers, PINK1 and Parkin. Ultrastructural analysis using electron microscopy revealed that Akap1 deletion was associated with remarkably aberrant mitochondria and lamellar bodies in type II alveolar epithelial cells. Taken together, these results demonstrate that Akap1 genetic deletion increases the severity of hyperoxia-induced acute lung injury in mice.