Jean-François Jeannin

Modulation of Human Colon Tumor-Stromal Interactions by the Endothelin System

Tumor neovascularization is considered to be a critical step in the development of a malignant tumor. Endothelin (ET)-1 is a powerful vasoconstrictor and mitogenic peptide that is produced by many cancer cell lines. The cellular distribution of the ET components was evaluated in human colon tumors and compared to normal colon. There was more of the ET components (preproET-1, endothelin-converting enzyme-1, and ETA and ETB receptors) in adenomas and adenocarcinomas than in the normal colon. There was overproduction of preproET-1 and endothelin-converting enzyme-1 in carcinoma cells and stromal vessels, suggesting that they are a local source of ET-1. ETA receptors were present in stromal myofibroblasts of neoplastic tissue, and there were large amounts of ETB receptors in the endothelium and myofibroblasts. There was also a redistribution of alpha-smooth muscle actin-positive cells in the vascular structures of tumors. An experimental rat model of induced colon cancer treated for 30 days with bosentan, a mixed antagonist of both ET receptors, confirmed the morphological changes observed during the tumor vascularization. Our data suggest that ET-1 and its receptor play a role in colon cancer progression, with ET-1 functioning as a negative modulator of the stromal response.

Post-translational modifications induced by nitric oxide (NO): implication in cancer cells apoptosis.

Post-translational modifications of proteins can regulate the balance between survival and cell death signals. It is increasingly recognized that nitric oxide (NO) and reactive oxygen species (ROS)-induced post-translational modifications could play a role in cell death. This review provides an introduction of current knowledge of NO proteins modifications promoting or inhibiting cell death with special attention in cancer cells.

S-Nitrosylation of the Death Receptor Fas Promotes Fas Ligand-Mediated Apoptosis in Cancer Cells

BACKGROUND & AIMS Fas belongs to the family of tumor necrosis factor receptors which induce apoptosis. Many cancer cells express Fas but do not undergo Fas-mediated apoptosis. Nitric oxide reverses this resistance by increasing levels of Fas at the plasma membrane. We studied the mechanisms by which NO affects Fas function. METHODS Colon and mammary cancer cell lines were incubated with the NO donor glyceryl trinitrate or lipid A; S-nitrosylation of Fas was monitored using the biotin switch assay. Fas constructs that contained mutations at cysteine residues that prevent S-nitrosylation were used to investigate the involvement of S-nitrosylation in Fas-mediated cell death. Apoptosis was monitored according to morphologic criteria. RESULTS NO induced S-nitrosylation of cysteine residues 199 and 304 in the cytoplasmic part of Fas. In cancer cells that overexpressed wild-type Fas, S-nitrosylation induced Fas recruitment to lipid rafts and sensitized the cells to Fas ligand. In cells that expressed a mutant form of Fas in which cysteine 304 was replaced by valine residue, NO-mediated translocation of Fas to lipid rafts was affected and the death-inducing signal complex and synergistic effect of glyceryl trinitrate-Fas ligand were inhibited significantly. These effects were not observed in cells that expressed Fas with a mutation at cysteine 199. CONCLUSIONS We identified post-translational modifications (S-nitrosylation of cysteine residues 199 and 304) in the cytoplasmic domain of Fas. S-nitrosylation at cysteine 304 promotes redistribution of Fas to lipid rafts, formation of the death-inducing signal complex, and induction of cell death.

Cytofluorescence localization of adriamycin in resistant colon cancer cells

SummaryA simple fluorescent microscopic method demonstrated that adriamycin was distributed in two cellular compartments of living rat colon cancer cells. Adriamycin accumulated slowly in cytoplasmic granules, probably lysosomes, where it persisted long after the drug was removed from the medium. On the other hand, adriamycin accumulated rapidly in the nucleus, but was rapidly cleared in adriamycin-free medium. Drug efflux from the nucleus was blocked by sodium azide in glucose-free medium or by verapamil, a calcium-blocking agent.When colon cancer cells were cultivated for 1 day or longer in adriamycin-containing medium no nuclear fluorescence was observed. However, the addition of sodium azide to glucose-free medium or verapamil restores the nuclear fluorescence.The colon cancer cells had low sensitivity to adriamycin, but the addition of verapamil strongly enhanced adriamycin toxicity. Thus adriamycin is permanently cleared from the nucleus of rat colon cancer cells through an energy-dependent efflux mechanism, which is blocked by verapamil. The efficiency of this efflux mechanism is enhanced by exposure of the cell to adriamycin. This mechanism could be involved in the resistance of colon cancer to adriamycin.

Expression of inducible nitric oxide synthase in tumors in relation with their regression induced by lipid A in rats

It is well documented that nitric oxide (NO) is an effector molecule of macrophage‐mediated tumor cell toxicity in vitro; however, little is known about the role of NO in the antitumor immune response in vivo. We have developed a treatment protocol using lipid A. We have investigated the effects of lipid A on inducible NO synthase (NOS II) expression and evolution inside tumors during the course of treatment. Lipid A (OM‐174) treatment induced tumor regression in rats bearing established colon tumors. Furthermore, NO was synthesized and secreted inside the tumors of lipid A‐treated rats, as demonstrated by the increase of NOS II mRNA and NOS II content in the tumors, as well as of NOS II activity and NO production. During treatment, NOS II was localized in tumor cells only. Lipid A had no direct effect on tumor cells in vitro, while the combination of interferon gamma (IFN‐γ) plus interleukin‐1 beta (IL‐1β) induced production of NO by tumor cells which was cytostatic. The content of IFN‐γ and IL‐1β in tumors was enhanced during lipid A treatment; this is in agreement with an indirect effect of lipid A in vivo via the IFN‐γ and IL‐1β pathways. Int. J. Cancer 81:755–760, 1999.

Heat shock enhances transcriptional activation of the murine inducible nitric oxide synthase gene

There is considerable interest in determining the conditions leading to enhanced inducible nitric oxide synthase (iNOS) gene expression and nitric oxide (NO) biosynthesis. Using in vivofootprinting, we demonstrate that heat shock of murine macrophages concurrent with lipopolysaccharide (LPS) treatment stimulated changes in guanine methylation sensitivity at ‐898/9, at a putative partial heat shock element (HSE) and at ‐893/4, a site bordering an E‐box, within the iNOS gene enhancer, suggesting inducible occupation by transcription factors at these regions. LPS treatment accompanied by heat shock provoked increased iNOS gene transcription, increased levels of iNOS protein, and increased production of NO compared with LPS treatment alone. Electrophoretic mobility shift analysis revealed low constitutive levels of specific binding to an E‐box and a partial HSE within the iNOS enhancer. Binding to the E‐box was increased by LPS treatment or by heat shock, achieving a greater increase by a combination of both treatments. The proteins occupying this site were identified as belonging to the USF family of transcription factors. Heat shock or LPS increased binding to the HSE, and the factor responsible for this interaction was identified as heat shock factor‐1 (HSF‐1). Mutations at the HSE revealed the importance of HSF‐1 in the induction of iNOS by LPS. Thus, our data reveal two novel regulatory sites in the murine iNOS gene, one of which is implicated in enhancing iNOS expression via LPS stimulation, and provide the first evidence that heat shock enhances transcription of the iNOS gene. These results could have implications in the host response mechanism to fever‐associated gram‐negative infection.

A repressor in the proximal human inducible nitric oxide synthase promoter modulates transcriptional activation

The human inducible nitric oxide synthase (iNOS or NOSII) gene is regulated through an extended and complex promoter. In this study, the transcriptional regulation of human NOSII is investigated in the human colon cell line HCT‐8R. Stimulation with a cytokine mix (interferon‐γ, interleukin 1‐β, and tumor necrosis factor α) induces NOSII mRNA accumulation, as well as promoter activity in these cells. Several random deletions were performed within the proximal 7 kb of the promoter, which led to the identification of a region, whose deletion provokes a marked increase in transcriptional activity upon cytokine stimulation. Furthermore, this region is shown to repress a viral‐driven luciferase construct, mainly at basal levels. An AP‐1‐like sequence present in this region that is specifically recognized by nuclear proteins is shown to be involved in the repressive effect. This element is capable of repressing a viral promoter, and its deletion augments cytokine‐stimulated transcription. These findings are confirmed in various cell lines and suggest a general mechanism for the control of basal levels of NOSII expression, to avoid unnecessary toxicity under normal conditions.

Antitumor effect of synthetic derivatives of lipid A in an experimental model of colon cancer in the rat

Colon carcinoma is one of the most frequent causes of cancer death in industrialized countries. The patients generally die of the metastases. In a colon cancer rat model, the authors have shown that lipopolysaccharides from Escherichia coli induced the regression of carcinomatosis and cured 20%-30% of the rats. Some synthetic derivatives of lipid A, which are less toxic than lipopolysaccharides, were injected 14 days after the tumor cells. They induced the complete regression of peritoneal carcinomatosis consisting of numerous nodules measuring 1-5 mm in 20%-30% of rats. Only compounds with three or more hydroxymyristic acid residues were effective. In vivo effects were correlated with the capacity to induce the production of interleukin 1 and tumor necrosis factor but not with the capacity to induce macrophage-mediated cytolysis. It is therefore possible to synthesize weakly toxic derivatives of lipopolysaccharides retaining their antitumoral property in vivo.

Arginase Activity is Inhibited by l -NAME, both In Vitro and In Vivo

The present study investigated the ability of the arginine analog L -NAME (Nω-Nitro- L -arginine methyl ester) to modulate the activity of arginase. L -NAME inhibited the activity of arginase in lysates from rat colon cancer cells and liver. It also inhibited the arginase activity of tumor cells in culture. Furthermore, in vivo treatment of rats with L -NAME inhibited arginase activity in tumor nodules and liver, and the effect persisted after treatment ceased. The effect of L -NAME on arginase requires consideration when it is used in vivo in animal models with the aim of inhibiting endothelial NO-synthase, another enzyme using arginine as substrate.

Nitric oxide-induced resistance or sensitization to death in tumor cells.

This report summarizes the present state of our knowledge pertaining to the NO-induced resistance or sensitization of tumor cell death. The effects of NO and its synergy with members of the TNF family, with cytotoxic drugs, and with ionizing radiations have been investigated. The dual effect of NO-induced resistance or sensitization and the underlying molecular mechanisms are discussed.