Autocrine induction of major histocompatibility complex class I antigen expression results from induction of beta interferon in oncogene-transformed BALB/c-3T3 cells

Evidence from transgenic mice that interferon-beta may be involved in the onset of diabetes mellitus

A number of cytokines have been shown to alter the function of pancreatic beta-cells and thus might be involved in the development of type 1 diabetes. Interferon-beta (IFN-beta) expression is induced in epithelial cells by several viruses, and it has been detected in islets of type 1 diabetic patients. Here we show that treatment of isolated mouse islets with this cytokine was able to alter insulin secretion in vitro. To study whether IFN-beta alters beta-cell function in vivo and leads to diabetes, we have developed transgenic mice (C57BL6/SJL) expressing IFN-beta in beta-cells. These mice showed functional alterations in islets and impaired glucose-stimulated insulin secretion. Transgenic animals presented mild hyperglycemia, hypoinsulinemia, hypertriglyceridemia, and altered glucose tolerance test, all features of a prediabetic state. However, they developed overt diabetes, with lymphocytic infiltration of the islets, when treated with low doses of streptozotocin, which did not induce diabetes in control mice. In addition, about 9% of the transgenic mice obtained from the N3 back-cross to outbred albino CD-1 mice spontaneously developed severe hyperglycemia and hypoinsulinemia and showed mononuclear infiltration of the islets. These results suggest that IFN-beta may be involved in the onset of type 1 diabetes when combined with either an additional factor or a susceptible genetic background.

Transfection of IFNalpha in human glioblastoma cells and tumorigenicity in association with induction of PKR and OAS gene expression

Previously these authors and others demonstrated frequent homozygous deletions of the chromosome 9p-localized class I interferon (IFN) gene cluster in glioblastoma tumors and cell lines. To investigate the biological effects of class I IFN gene transfer and constitutive expression in glioblastoma cells devoid of this gene cluster, the authors have developed a stable IFNalpha "transfectant" of the cell line U118. The expression of IFNalpha protein in the U118 transfectant clone is associated with decreased levels of DNA synthesis exhibited by cultures of transfected cells, reduced colony-forming ability in soft agar, and loss of tumorigenicity in athymic nude mice. To address the molecular consequences of constitutive IFNalpha synthesis, they examined the expression of four genes whose transcription has been shown to be responsive to IFN-mediated signal transduction and could be important to the observed antiproliferative and antitumor effects. Northern blot analysis revealed that changes in the levels of messenger (m)RNA for two of these genes, c-myc and mhc class I, are minor. However, mRNAs for oligoadenylate synthetase (OAS) as well as double-stranded RNA-activated protein kinase (PKR), which are not expressed in parental U118 cells, were constitutively expressed in IFNalpha transfectants. These results indicate a differential responsiveness among these four genes to constitutive IFNalpha expression, and suggest that the suppression of U118-transformed phenotypes by IFNalpha transfection may be mediated by the induction of specific IFN response genes thought to have a negative growth-regulatory function.

The effect of H-ras expression on tumorigenicity and immunogenicity of Balb/c 3T3 fibroblasts

In an attempt to define immunological parameters affected by the H-ras oncogene, we have used Balb/c 3T3 cells transfected with either H-ras (98/6), H-ras+v-myc (98/4v) or plasmid only (98/1). We found that while control and oncogene-transfected Balb/c 3T3 cells exhibit similar low sensitivity to lysis by natural killer (NK) cells, H-ras+v-myc-transfected cells could immunize syngeneic Balb/c mice and induce cytotoxic T cells (CTL) with broad specificity, that lysed all types of Balb/c 3T3 cells tested. Immunization of Balb/c mice with 98/4v cells prevented homologous tumor formation and partially inhibited the formation of tumors derived from H-ras-transfected cells. 98/6 cells were not immunogenic in vivo and did not protect the animals from a challenge of 98/6 cells. The results suggested that CTLs but not NK effector cells were important for eliciting in vivo tumor rejection of H-ras+v-myc-transfected cells. In contrast, antigens eliciting the cytotoxic T-cell response, and possibly also the in vivo tumor cell rejection response, were expressed on all cell types tested but were immunogenic only on the surface of 98/4v cells. We further determined major histocompatibility complex (MHC) class-I molecule expression on the outer cell surface and found that H-2K was down-regulated in H-ras-transfected cells. The results support the observation that oncogenes can down-regulate specific MHC antigens, thereby preventing presentation of tumor antigens and allowing tumor escape from immune recognition.

Post-transcriptional downregulation of MHC class I expression in oncogene-transformed cells is reverted by IFN-gamma and TNF-alpha

Transformation of murine NIH3T3 fibroblasts with retroviral vectors carrying the mos, myc and the Ha-ras oncogene, respectively, was associated with a strong reduction of H2 antigen expression in the cell membrane. Analysis of H-2K and beta 2-microglobulin promoter-driven CAT activity in these oncogenic transformants and normal NIH3T3 fibroblasts revealed unchanged promoter activity, suggesting post-transcriptional control of MHC class I expression by these oncogenes. Treatment with IFN-gamma and TNF-alpha caused 2- to 3-fold enhancement of H-2K and beta 2-microglobulin promoter activity, as well as a normalization (TNF-alpha treatment) or enhancement (IFN-gamma treatment) of H2 membrane expression. These data suggest that IFN-gamma as well as TNF-alpha can counteract downregulation of H-2 genes by interference with an oncogene-induced, post-transcriptional block as well as by a direct enhancement of H-2 gene transcription.