P2X7 Receptor Promotes Mouse Mammary Cancer Cell Invasiveness and Tumour Progression, and Is a Target for Anticancer Treatment.

The P2X7 receptor is an ATP-gated cation channel with a still ambiguous role in cancer progression, proposed to be either pro- or anti-cancerous, depending on the cancer or cell type in the tumour. Its role in mammary cancer progression is not yet defined. Here, we show that P2X7 receptor is functional in highly aggressive mammary cancer cells, and induces a change in cell morphology with fast F-actin reorganization and formation of filopodia, and promotes cancer cell invasiveness through both 2- and 3-dimensional extracellular matrices in vitro. Furthermore, P2X7 receptor sustains Cdc42 activity and the acquisition of a mesenchymal phenotype. In an immunocompetent mouse mammary cancer model, we reveal that the expression of P2X7 receptor in cancer cells, but not in the host mice, promotes tumour growth and metastasis development, which were reduced by treatment with specific P2X7 antagonists. Our results demonstrate that P2X7 receptor drives mammary tumour progression and represents a pertinent target for mammary cancer treatment.

Suppression of PPARß, and DHA treatment, inhibit NaV1.5 and NHE-1 pro-invasive activities.

Peroxisome proliferator-activated receptor ß (PPARß) and NaV1.5 voltage-gated sodium channels have independently been shown to regulate human breast cancer cell invasiveness. The n-3 polyunsaturated docosahexaenoic acid (DHA, 22:6n-3), a natural ligand of PPAR, is effective in increasing survival and chemotherapy efficacy in breast cancer patient with metastasis. DHA reduces breast cancer cell invasiveness and it also inhibits PPARß expression. We have shown previously that NaV1.5 promotes MDA-MB-231 breast cancer cells invasiveness by potentiating the activity of Na(+)/H(+) exchanger type 1 (NHE-1), the major regulator of H(+) efflux in these cells. We report here that DHA inhibited NaV1.5 current and NHE-1 activity in human breast cancer cells, and in turn reduced NaV1.5-dependent cancer cell invasiveness. For the first time, we show that antagonizing PPARß, or inhibiting its expression, reduced NaV1.5 mRNA and protein expression and NaV1.5 current, as well as NHE-1 activity and cell invasiveness. Consistent with these results, the DHA-induced reduction of both NaV1.5 expression and NHE-1 activity was abolished in cancer cells knocked-down for the expression of PPARß (shPPARß). This demonstrates a direct link between the inhibition of PPARß expression and the inhibition of Nav1.5/NHE-1 activities and breast cancer cell invasiveness. This study provides new mechanistic data advocating for the use of natural fatty acids such as DHA to block the development of breast cancer metastases.

Disturbances in cholesterol, bile acid and glucose metabolism in peroxisomal 3-ketoacylCoA thiolase B deficient mice fed diets containing high or low fat contents.

The peroxisomal 3-ketoacyl-CoA thiolase B (ThB) catalyzes the thiolytic cleavage of straight chain 3-ketoacyl-CoAs. Up to now, the ability of ThB to interfere with lipid metabolism was studied in mice fed a laboratory chow enriched or not with the synthetic agonist Wy14,643, a pharmacological activator of the nuclear hormone receptor PPARα. The aim of the present study was therefore to determine whether ThB could play a role in obesity and lipid metabolism when mice are chronically fed a synthetic High Fat Diet (HFD) or a Low Fat Diet (LFD) as a control diet. To investigate this possibility, wild-type (WT) mice and mice deficient for Thb (Thb(-/-)) were subjected to either a synthetic LFD or a HFD for 25 weeks, and their responses were compared. First, when fed a normal regulatory laboratory chow, Thb(-/-) mice displayed growth retardation as well as a severe reduction in the plasma level of Growth Hormone (GH) and Insulin Growth Factor-I (IGF-I), suggesting alterations in the GH/IGF-1 pathway. When fed the synthetic diets, the corrected energy intake to body mass was significantly higher in Thb(-/-) mice, yet those mice were protected from HFD-induced adiposity. Importantly, Thb(-/-) mice also suffered from hypoglycemia, exhibited reduction in liver glycogen stores and circulating insulin levels under the LFD and the HFD. Thb deficiency was also associated with higher levels of plasma HDL (High Density Lipoproteins) cholesterol and increased liver content of cholesterol under both the LFD and the HFD. As shown by the plasma lathosterol to cholesterol ratio, a surrogate marker for cholesterol biosynthesis, whole body cholesterol de novo synthesis was increased in Thb(-/-) mice. By comparing liver RNA from WT mice and Thb(-/-) mice using oligonucleotide microarray and RT-qPCR, a coordinated decrease in the expression of critical cholesterol synthesizing genes and an increased expression of genes involved in bile acid synthesis (Cyp7a1, Cyp17a1, Akr1d1) were observed in Thb(-/-) mice. In parallel, the elevation of the lathosterol to cholesterol ratio as well as the increased expression of cholesterol synthesizing genes were observed in the kidney of Thb(-/-) mice fed the LFD and the HFD. Overall, the data indicate that ThB is not fully interchangeable with the thiolase A isoform. The present study also reveals that modulating the expression of the peroxisomal ThB enzyme can largely reverberate not only throughout fatty acid metabolism but also cholesterol, bile acid and glucose metabolism.

PPARß mRNA expression, reduced by n-3 PUFA diet in mammary tumor, controls breast cancer cell growth.

The effect of numerous anticancer drugs on breast cancer cell lines and rodent mammary tumors can be enhanced by a treatment with long-chain n-3 polyunsaturated fatty acids (n-3 PUFA) such as docosahexaenoic acid (DHA, 22:6n-3) which is a natural ligand of peroxisome proliferator-activated receptors (PPAR). In order to identify the PPAR regulating breast cancer cell growth, we tested the impact of siRNA, selected to suppress PPARα, PPARß or PPARγ mRNA in MDA-MB-231 and MCF-7 breast cancer cell lines. The siPPARß was the most effective to inhibit breast cancer cell growth in both cell lines. Using PPARα, PPARß and PPARγ pharmacological antagonists, we showed that PPARß regulated DHA-induced inhibition of growth in MDA-MB-231 and MCF-7 cells. In addition, the expressions of all 3 PPAR mRNA were co-regulated in both cell lines, upon treatments with siRNA or PPAR antagonists. PPAR mRNA expression was also examined in the NitrosoMethylUrea (NMU)-induced rat mammary tumor model. The expressions of PPARα and PPARß mRNAs were correlated in the control group but not in the n-3 PUFA group in which the expression of PPARß mRNA was reduced. Although PPARα expression was also increased in the n-3 PUFA-enriched diet group under docetaxel treatment, it is only the expression of PPARß mRNA that correlated with the regression of mammary tumors: those that most regressed displayed the lowest PPARß mRNA expression. Altogether, these data identify PPARß as an important player capable of modulating other PPAR mRNA expressions, under DHA diet, for inhibiting breast cancer cell growth and mammary tumor growth.

Anthraquinone emodin inhibits human cancer cell invasiveness by antagonizing P2X7 receptors.

The adenosine 5'-triphosphate (ATP)-gated Ca(2+)-permeable channel P2X7 receptor (P2X7R) is strongly upregulated in many tumors and cancer cells, and has an important role in cancer cell invasion associated with metastases. Emodin (1,3,8-trihydroxy-6-methylanthraquinone) is an anthraquinone derivative originally isolated from Rheum officinale Baill known for decades to possess anticancer properties. In this study, we examined the effects of emodin on P2X7R-dependent Ca(2+) signaling, extracellular matrix degradation, and in vitro and in vivo cancer cell invasiveness using highly aggressive human cancer cells. Inclusion of emodin at doses ≤10 µM in cell culture had no or very mild effect on the cell viability. ATP elicited increases in intracellular Ca(2+) concentration were reduced by 35 and 60% by 1 and 10 µM emodin, respectively. Emodin specifically inhibited P2X7R-mediated currents with an IC50 of 3 µM and did not inhibit the currents mediated by the other human P2X receptors heterologously expressed in human embryonic kidney (HEK293T) cells. ATP-induced increase in gelatinolytic activity, in cancer cell invasiveness in vitro and in cell morphology changes were prevented by 1 µM emodin. Furthermore, such ATP-evoked effects and inhibition by emodin were almost completely ablated in cancer cells transfected with P2X7R-specific small interfering RNA (siRNA) but not with scrambled siRNA. Finally, the in vivo invasiveness of the P2X7R-positive MDA-MB-435s breast cancer cells, assessed using a zebrafish model of micrometastases, was suppressed by 40 and 50% by 1 and 10 µM emodin. Taken together, these results provide consistent evidence to indicate that emodin inhibits human cancer cell invasiveness by specifically antagonizing the P2X7R.

PPARα/HNF4α interplay on diversified responsive elements. Relevance in the regulation of liver peroxisomal fatty acid catabolism.

In mammals, the liver is the major organ of fatty acid catabolism. This pathway is involved in both mitochondria and peroxisome. While mitochondria breaks down fatty acids with short, medium and long carbon chains, peroxisomes are involved in the catabolism of very long and branched chain fatty acids, which are degraded by three enzymes: acyl-CoA oxidase, multifunctional enzyme and thiolase enzyme. The active pathway results mainly from a tight transcriptional control of these gene-encoding enzymes. Two major nuclear receptors that are highly expressed in this organ are involved in this control, e.g. PPARα (peroxisome proliferator-activated receptor, α isoform) and HNF4α (hepatic nuclear factor 4, α isotype). Both are key regulators of liver lipid metabolism. While numerous papers have reported on the role of PPARα in liver lipid homeostasis, less is known on the implication of HNF4α in this metabolism. Moreover, very few studies have taken an interest in the important question of the implication of these two receptors and most particularly their crosstalk. This review therefore presents the current knowledge on the PPARα/HNF4α interplay in diversified DNA responsive elements and its relevance in the regulation fatty acid catabolism. It presents a review of the properties of the nuclear receptors PPARα and HNF4α, then the genes regulated by HNF4α and PPARα, particularly the peroxisomal enzyme target genes. To conclude, the consequences of the regulation of these genes in the liver by PPARα and HNF4α will be analyzed. The current data indicate the requirement of PPARα and HNF4α for regulation in the liver of peroxisomal and mitochondrial fatty acid ß-oxidation, cholesterol and bile acid metabolism, lipoprotein metabolism and consequently the prevention of liver steatosis. However, several questions remain unsolved. To show the interplay of PPARα and HNF4α in the regulation of liver fatty acid metabolism, different strategies are proposed.