HC class I expression can be up-regulated by interferons (IFN) and other cytokines. Both IFNalpha and IFNgamma have been shown to exert their effects via a recently discovered signalling pathway by inducing tyrosine phosphorylation of their receptors. Receptors for interferons and other cytokines signal through the action of associated protein tyrosine kinases of the JAK family (Janus kinase) and latent cytoplasmic transcriptional activators from the STAT family (signal transducers and activators of transcription). Here we report a gastric adenocarcinoma cell line, AGS, that is defective in its response to either IFNalpha or IFNgamma. AGS cells display selective alterations only in MHC class I inducibility and not in constitutive MHC class I expression. In nuclear extracts of AGS cells, no binding activity to interferon-responsive elements (GAS/ISRE) was observed. We found that AGS cells showed an extremely low level of STAT1 expression, which may be responsible for the absence of biological response to IFN. Because STAT1-deficient cells are highly sensitive to infection by virus, the absence of these proteins may also contribute to the tumor phenotype, giving the tumor a selective advantage, by inhibiting cell growth suppression mediated by IFN and abetting escape from the T cell antitumor response.

Thirty-five mitochondrial (mt) DNAs from Spain that harbor the mutation A3243G in association with either MELAS (mitochondrial myopathy, encephalopathy, lactic acidosis, and strokelike episodes) syndrome or a wide array of disease phenotypes (ranging from diabetes and deafness to a mixture of chronic progressive external ophthalmoplegic symptoms and strokelike episodes) were studied by use of high-resolution restriction fragment length polymorphism analysis and control-region sequencing. A total of 34 different haplotypes were found, indicating that all instances of the A3243G mutation are probably due to independent mutational events. Haplotypes were distributed into 13 haplogroups whose frequencies were close to those of the general Spanish population. Moreover, there was no statistically significant difference in haplogroup distribution between patients with MELAS and those with disease phenotypes other than MELAS. Overall, these data indicate that the A3243G mutation harbors all the evolutionary features expected from a severely deleterious mtDNA mutation under strong negative selection, and they reveal that European mtDNA backgrounds do not play a substantial role in modulating the mutation's phenotypic expression.

Maintenance therapy with newer NAs, after discontinuation of HBIG prophylaxis, was safe and effective, with a low rate of serological recurrence and no evident clinical, biochemical, or virological consequences.

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The gef gene has cell-killing functions in Escherichia coli. To evaluate the feasibility of using this gene as a new strategy for cancer therapy, we transfected it in MCF-7 cells derived from breast cancer (MCF-7TG). The gef gene was cloned in a pMAMneo vector under the control of a mouse mammary tumour virus promoter, inducible by dexamethasone (Dex), and was transfected with liposomes. After selection and induction, expression of the gef gene was confirmed by reverse transcription -polymerase chain reactions (RT -PCR) and Western blot. Cell viability was determined with a haemocytometre and the sulphorodamine B colorimetric assay, and the cell cycle was studied by propidium iodide (PI) staining. Annexin V-FITC and PI assays were used to evaluate apoptosis, which was confirmed by electron microscopy. In comparison with MCF-7 parental cells and MCF-7 cells transfected with an empty vector, MCF-7TG cells induced with Dex showed a significant decrease in proliferation rate, which was associated with evidence of apoptosis. Morphological findings confirmed apoptosis and showed a typical pattern of mitochondrial dilation. Furthermore, the cell cycle was characterised by premature progression from G 1 to S phase and G 2 delay. Our results show that the gef gene was able to decrease proliferation in a breast cancer cell line, and induce apoptosis. These findings suggest that the gef gene is a potential candidate for tumour therapy.

Progressive tumor growth may be associated with suppression of the immune response. Many different mechanisms may contribute to immune evasion. We investigated some of these mechanisms in melanoma cells lines generated from two patients. These cell lines show a complex pattern of altered HLA expression; however, the resulting phenotype did not satisfactorily explain the simultaneous evasion of T and NK cell cytotoxicity. Two additional alterations have now been detected in these melanoma cell lines: (1) resistance to FAS-induced apoptosis caused by defective FAS gene expression, and (2) constitutive expression of immunosuppressive cytokines. Our results show that several of the major mechanisms for immune evasion may coexist in a single tumor. This suggests that tumor progression may give rise to an extremely resistant phenotype, which may be an impediment to some immunotherapeutic strategies. We hypothesize that the simultaneous presence of several mechanisms involved in tumor immune evasion must be the result of progressive selection of characteristics that are advantageous for tumor survival in a competent host. Our findings do not support the possibility that FASL expression is a common mechanism of evasion of immune response in melanoma cells.

Alpha/beta and gamma type interferons (IFN), act through distinct cell surface receptors and induce transcription of an overlapping sets of genes. MHC class I genes are inducible by both type of interferons. We have analyzed a gastric tumor cell line, AGS, which was completely defective in MHC class I response to interferon-alpha and gamma. Northern blot analysis demonstrated that the lack of IFN response was related with the absence of up-regulation of specific HLA class I mRNA. Electrophoretic mobility shift assays in various tumor cell lines after IFN-alpha and IFN-gamma treatment showed differential binding of the transcriptional factors to MHC class I regulatory elements. Comparison of kappa-B binding activity showed that IFN-alpha and IFN-gamma induced opposite changes in NF-kappa B binding activity in AGS cells, indicating that the absence of MHC class I response in AGS appears to be independent of kappa-B activity. In contrast, there were remarkable differences in the level of transcriptional factor binding to an interferon-responsive sequence element (IRSE), between AGS and other interferon-responsive tumor cell lines. This result suggests that the low level of transcriptional factor binding to IRSE in AGS cells was responsible of the lack of induction of MHC class I antigens. In this context, overlapping factors in the signal transduction pathway of both type I and II interferons may be involved in the non-responsiveness of this gastric carcinoma tumor cell line.