Structurally diverse peroxisome proliferator-activated receptor agonists induce apoptosis in human uro-epithelial cells by a receptor-independent mechanism involving store-operated calcium channels

Peroxisome proliferator-activated receptor β/δ and γ agonists differentially affect prostaglandin E2 and cytokine synthesis and nutrient transporter expression in porcine trophoblast cells during implantation

Peroxisome proliferator-activated receptors (PPARs) belong to the nuclear receptor family of ligand-dependent transcription factors. PPARs have been shown to be important regulators of female reproductive functions, including conceptus development and placenta formation. This study examines the effect of PPARβ/δ and PPARγ agonists and antagonists on (1) the synthesis of prostaglandin (PG) E2, interleukin (IL) 6, interferon (IFN) γ, and tumor necrosis factor (TNF) α and (2) the mRNA expression of genes encoding nutrient transporters and/or binding proteins in Day 15 conceptus trophoblast cells. The study also examines whether PPAR agonist-modulated IL6, IFNγ, and TNFα secretion is mediated via mitogen-activated protein kinase (MAPK) pathways. Trophoblast cells were exposed to L-165,041 (a PPARβ/δ agonist) or rosiglitazone (a PPARγ agonist) in the presence or absence of GSK3787 (a PPARβ/δ antagonist) or GW9662 (a PPARγ antagonist) or in the presence or absence of U0126 (a MAPK inhibitor). Rosiglitazone stimulated PGE synthase and IFNG mRNA expression in trophoblast cells and enhanced PGE2 concentrations in the incubation medium. Moreover, cells treated with rosiglitazone exhibited increased abundance of the solute carrier organic anion transporter family member 2A1 (SLCO2A1, a PG transporter) and of fatty acid binding protein (FABP) 5 transcripts. All these effects were abolished by the addition of GW9662, which indicates that the action of rosiglitazone is PPARγ-dependent in the studied cells. L-165,041 inhibited TNFα synthesis and decreased the mRNA expression of FABP3 and IL6 in trophoblast cells. However, this effect was not abolished by the addition of GSK3787 into the incubation medium, suggesting that L-165,041 action is independent of PPARβ/δ. The inhibitory effect of L-165,041 on TNFα concentration and the stimulatory effect of rosiglitazone on IFNγ accumulation in the medium were not observed in the presence of the MAPK inhibitor, suggesting that the action of both agonists may be mediated by MAPKs. In conclusion, PPARβ/δ and PPARγ agonists are differentially involved in the trophoblast expression of genes related to conceptus development and implantation in pigs. Furthermore, L-165,041 and rosiglitazone may have PPAR-dependent and -independent effects in conceptus trophoblast cells.

Ketamine-Induced Apoptosis in Normal Human Urothelial Cells: A Direct, N-Methyl-d-Aspartate Receptor-Independent Pathway Characterized by Mitochondrial Stress

Recreational abuse of ketamine has been associated with the emergence of a new bladder pain syndrome, ketamine-induced cystitis, characterized by chronic inflammation and urothelial ulceration. We investigated the direct effects of ketamine on normal human urothelium maintained in organ culture or as finite cell lines in vitro. Exposure of urothelium to ketamine resulted in apoptosis, with cytochrome c release from mitochondria and significant subsequent caspase 9 and 3/7 activation. The anesthetic mode-of-action for ketamine is mediated primarily through N-methyl d-aspartate receptor (NMDAR) antagonism; however, normal (nonimmortalized) human urothelial cells were unresponsive to NMDAR agonists or antagonists, and no expression of NMDAR transcript was detected. Exposure to noncytotoxic concentrations of ketamine (≤1 mmol/L) induced rapid release of ATP, which activated purinergic P2Y receptors and stimulated the inositol trisphosphate receptor to provoke transient release of calcium from the endoplasmic reticulum into the cytosol. Ketamine concentrations >1 mmol/L were cytotoxic and provoked a larger-amplitude increase in cytosolic Ca(2+) concentration that was unresolved. The sustained elevation in cytosolic Ca(2+) concentration was associated with pathological mitochondrial oxygen consumption and ATP deficiency. Damage to the urinary barrier initiates bladder pain and, in ketamine-induced cystitis, loss of urothelium from large areas of the bladder wall is a reported feature. This study offers first evidence for a mechanism of direct toxicity of ketamine to urothelial cells by activating the intrinsic apoptotic pathway.

Effect of pioglitazone on the fructose-induced abdominal adipose tissue dysfunction

Aim. To test the potential role of PPARγ in the endocrine abdominal tissue dysfunction induced by feeding normal rats with a fructose rich diet (FRD) during three weeks. Methodology. Adult normal male rats received a standard commercial diet (CD) or FRD, (10% in drinking water) without or with pioglitazone (PIO) (i.p. 0.25 mg/Kg BW/day; CD-PIO and FRD-PIO). Thereafter, we measured circulating metabolic, endocrine, and oxidative stress (OS) markers, abdominal adipose tissue (AAT) mass, leptin (LEP) and plasminogen activator inhibitor-1 (PAI-1) tissue content/expression, and leptin release by isolated adipocytes incubated with different concentrations of insulin. Results. Plasma glucose, insulin, triglyceride, TBARS, LEP, and PAI-1 levels were higher in FRD rats; PIO coadministration fully prevented all these increments. AAT adipocytes from FRD rats were larger, secreted a higher amount of LEP, and displayed decreased sensitivity to insulin stimulation; these effects were significantly ameliorated by PIO. Whereas AAT LEP and PAI-1 (mRNA) concentrations increased significantly in FRD rats, those of insulin-receptor-substrate- (IRS-) 1 and IRS-2 were reduced. PIO coadministration prevented FRD effects on LEP, PAI-1, and IRS-2 (fully) and IRS-1 (partially) mRNAs in AAT. Conclusion. PPARγ would play a relevant role in the development of the FRD-induced metabolic-endocrine dysfunction.

EGR1 expression: a calcium and ERK1/2 mediated PPARγ-independent event involved in the antiproliferative effect of 15-deoxy-Δ12,14-prostaglandin J2 and thiazolidinediones in breast cancer cells

Our aim was to get new information about the Peroxisome Proliferator Activated Receptor gamma (PPARγ)-independent pathway involved in the antiproliferative action of PPARγ ligands in breast cancer cells. We investigated the effects of Troglitazone (TGZ), Ciglitazone (CGZ), Rosiglitazone (RGZ) and, 15-deoxy-Δ12,14-prostaglandin J2 (15d-PGJ(2)) on the hormone-dependent breast cancer cell line MCF7. The early transcription factor EGR1 (Early Growth Response gene 1) mRNA and protein levels peaked after 3h of incubation with 25μM TGZ, CGZ or 15d-PGJ(2) and then gradually decreased. RGZ, the most potent activator of PPARγ, did not show this effect. The PPARγ antagonist GW 9662 did not block EGR1 mRNA induction which also still occurred in case of PPARγ silencing as well as in case of treatment with the PPARγ-inactive compound Δ2-TGZ. EGR1 mRNA induction required ERK1/2 phosphorylation which was not blocked by EGF Receptor (EGFR) inhibition. The ERK1/2 pathway was also involved in Δ2-TGZ-induced EGR1 mRNA expression in the hormone-independent breast cancer cell line MDA-MB-231. Using the fluorescent dye Fura2, we showed in MCF7 that TGZ or Δ2-TGZ induced an immediate increase in cytosolic calcium which was required for ERK1/2 phosphorylation and EGR1 mRNA induction as demonstrated by calcium chelation experiments. Furthermore, in MCF7 transfected with siRNA targeting EGR1, Δ2-TGZ inhibited less efficiently cell proliferation.

Differential regulation of growth-promoting signalling pathways by E-cadherin

BACKGROUND

Despite the well-documented association between loss of E-cadherin and carcinogenesis, as well as the link between restoration of its expression and suppression of proliferation in carcinoma cells, the ability of E-cadherin to modulate growth-promoting cell signalling in normal epithelial cells is less well understood and frequently contradictory. The potential for E-cadherin to co-ordinate different proliferation-associated signalling pathways has yet to be fully explored.

METHODOLOGY/PRINCIPAL FINDINGS

Using a normal human urothelial (NHU) cell culture system and following a calcium-switch approach, we demonstrate that the stability of NHU cell-cell contacts differentially regulates the Epidermal Growth Factor Receptor (EGFR)/Extracellular Signal-Regulated Kinase (ERK) and Phosphatidylinositol 3-Kinase (PI3-K)/AKT pathways. We show that stable cell contacts down-modulate the EGFR/ERK pathway, whilst inducing PI3-K/AKT activity, which transiently enhances cell growth at low density. Functional inactivation of E-cadherin interferes with the capacity of NHU cells to form stable calcium-mediated contacts, attenuates E-cadherin-mediated PI3-K/AKT induction and enhances NHU cell proliferation by allowing de-repression of the EGFR/ERK pathway and constitutive activation of β-catenin-TCF signalling.

CONCLUSIONS/SIGNIFICANCE

Our findings provide evidence that E-cadherin can differentially and concurrently regulate specific growth-related signalling pathways in a context-specific fashion, with direct, functional consequences for cell proliferation and population growth. Our observations not only reveal a novel, complex role for E-cadherin in normal epithelial cell homeostasis and tissue regeneration, but also provide the basis for a more complete understanding of the consequences of E-cadherin loss on malignant transformation.