Vectorial release of carcinoembryonic antigen induced by IFN-gamma in human colon cancer cells cultured in serum-free medium

All-trans retinoic acid induces XAF1 expression through an interferon regulatory factor-1 element in colon cancer

BACKGROUND & AIMS

X-linked inhibitor of apoptosis protein (XIAP)-associated factor 1 (XAF1) is a novel tumor suppressor and interferon (IFN)-stimulated gene. All-trans retinoic acid (ATRA) exerts an antiproliferative effect on tumor cells through up-regulation of IFN regulatory factor 1 (IRF-1) and the downstream IFN-stimulated genes. The aim of this study was to determine the effect and mechanism of ATRA on XAF1 expression and the role of XAF1 in ATRA-induced growth inhibition in colon cancer.

METHODS

Gene expression is detected by reverse-transcription polymerase chain reaction and immunoblotting. The transcription activity of XAF1 promoter is examined by luciferase reporter assay. The activity of IFN regulatory factor binding element (IRF-E) is assessed by electrophoretic mobility shift assay and chromatin immunoprecipitation assay. Cell growth is evaluated by both in vitro and in vivo in nude mice xenografts.

RESULTS

IFN-alfa stimulates XAF1 promoter activity in the colon cancer cells Lovo and SW1116 dose-dependently. An IRF-1 binding element (IRF-E-XAF1) is found in the -30 to -38 nucleotide region upstream of the ATG initiator codon of the XAF1 gene. Site-directed mutagenesis of IRF-E-XAF1 abrogates native and IFN-induced promoter activity and binding capacity. ATRA induces XAF1 expression both in vitro and in vivo through interaction with IRF-E-XAF1. Overexpression of XAF1 increases cell susceptibility to ATRA-induced growth suppression both in vitro and in vivo. Furthermore, the effect of ATRA on XAF1 expression is independent of the promoter methylation and the subcellular distribution of XIAP.

CONCLUSIONS

XAF1 participates in ATRA-induced growth suppression through IRF-1-mediated transcriptional regulation.

Interferon-gamma-induced differentiation and apoptosis of HT29 cells: dissociation of (glucosyl)ceramide signaling

Recently, (glyco)sphingolipids (SL) like ceramide (Cer) and glucosylceramide (GlcCer) have been shown to be involved in signaling pathways leading to differentiation and apoptosis in several cell types, including the colon adenocarcinoma cell line HT29. Intracellular levels of Cer can be modulated by ligands such as interferon-gamma (IFN gamma). In the present study we show that IFN gamma, depending on its concentration, has both differentiation- and apoptosis-inducing effects on HT29 cells. Since both phenomena have been related to SL-mediated signaling in other cell types, we next examined whether IFN gamma was able to induce changes in the SL levels of HT29 cells. Remarkably, no significant changes in these levels could be revealed, implying that SL are not involved in IFN gamma-induced differentiation and/or apoptosis of HT29 cells. This observation provides evidence for the hypothesis that SL-mediated signaling pathways might be more cell type specific than is generally assumed.

Intracellular localisation of suramin, an anticancer drug, in human colon adenocarcinoma cells: a study by quantitative autoradiography

Suramin is a polysulphonated naphthylurea currently investigated for the treatment of advanced malignancy. In the present study, we have analysed the uptake and the intracellular localisation of tritiated suramin in human colon adenocarcinoma cells (HT-29-D4), using quantitative autoradiographic techniques at the optical and electron microscopy levels. Our results show that the drug is able to enter both undifferentiated and differentiated HT-29-D4 cells. The process of suramin uptake is time-dependent, and significantly inhibited by the presence of the suramin-binding protein serum albumin in the culture medium of HT-29-D4 cells. Autoradiographic analysis revealed two distinct patterns of intracellular localisation of tritiated suramin labelling, according to the presence or absence of serum albumin. Indeed, in the absence of serum albumin, the labelling of free suramin was distributed over the nucleus, the Golgi apparatus and the mitochondria, while it was restricted to the lysosomal system when suramin was complexed with albumin. These data show that a serum factor, i.e. albumin, influences the biological activity of suramin by determining its intracellular localisation. The presence of suramin in a given compartment may account for specific effects of the drug including mitochondrial hypertrophy, altered gene expression and lysosomal perturbation.

Virus infection of polarized epithelial cells

This chapter focuses on the interaction of viruses with epithelial cells. The role of specific pathways of virus entry and release in the pathogenesis of viral infection is examined together with the mechanisms utilized by viruses to circumvent the epithelial barrier. Polarized epithelial cells in culture, which can be grown on permeable supports, provide excellent systems for investigating the events in virus entry and release at the cellular level, and much information is being obtained using such systems. Much remains to be learned about the precise routes by which many viruses traverse the epithelial barrier to initiate their natural infection processes, although important information has been obtained in some systems. Another area of great interest for future investigation is the process of virus entry and release from other polarized cell types, including neuronal cells.

Inhibition of human immunodeficiency virus infection in human colon epithelial cells by recombinant interferon-gamma

Pretreatment of human colon epithelial cells HT29 by recombinant gamma interferon (IFN)-gamma was found to protect the cells from infection with various isolates of human immunodeficiency virus (HIV)-1 and HIV-2, as assessed by co-cultivation with human T lymphoblastoid cells and gene amplification by polymerase chain reaction technique. Additionally, IFN-gamma induced a dose-dependent inhibition of HIV-1 and HIV-2 production in chronically infected HT29 cells. In situ hybridization studies demonstrated that IFN-treated cells were still able to synthesize viral messenger ribonucleic acid. However, the expression of the p24 product of the gag gene was markedly decreased after IFN treatment as demonstrated by radio-immunoprecipitation assay. Taken together, these data suggested that the cytokine acted at the post-translational level by inhibiting the processing of structural viral proteins. It is concluded from this study that IFN-gamma has a potent anti-HIV effect on epithelial gastrointestinal cells.