Mouse interferons enhance the accumulation of a human HLA RNA and protein in transfected mouse and hamster cells

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.

Hepatic HLA antigen display in chronic hepatitis B virus infection. Relation to hepatic expression of HBV genome/gene products and liver histology

To determine the relationship between hepatitis B virus (HBV) replication and HLA antigen display at a cellular level, the hepatic expression of HLA antigens and HBV genome (HBV-DNA)/gene products (HBsAg/HBcAg) was studied in 24 patients with chronic HBV infection using simultaneously immunohistochemistry and nonisotopic in situ hybridization. The effect of interferon-alpha and interferon-gamma on hepatocyte HLA antigen expression was also evaluated using primary hepatocyte culture in eight patients with chronic HBV infection. HLA class I antigens were detected on hepatocyte membrane in 23 patients (95.8%). Hepatocytes positive for HBcAg and HBV-DNA (cytoplasmic +/- nuclear) were either negative or only faintly positive for HLA class I antigens, while hepatocytes positive for HBsAg showed similar levels of HLA class I antigen expression compared with those hepatocytes with no HBsAg expression. In contrast, hepatocytes adjacent to inflammatory infiltrates, whether positive for HBV-DNA or HBV antigens or not, were always strongly positive for HLA class I antigens. Furthermore, active liver histology (N = 12) was associated with a higher overall level of hepatic HLA class I antigen expression as compared with inactive histology (N = 12, P = 0.003). Both interferon-alpha and interferon-gamma treatment in vitro enhanced hepatocyte HLA class I antigen expression. These data indicate that expression of HLA class I antigens is not enhanced on the membrane of hepatocytes with HBV replication, and this may be one factor that permits the development of viral persistence.

Differential up-regulation of H-2D versus H-2K class I major histocompatibility expression by interferon-gamma: evidence against a trans-acting allele-specific factor

Previous investigation described a unique differential phenotype for the murine T-cell tumor AKR SL3 with regard to augmentation of class I major histocompatibility complex antigen expression by interferon-gamma (IFN-gamma). Dk expression was increased by IFN-gamma as expected, but Kk expression remained at constitutive levels, despite treatment with a range of doses and times of exposure to IFN-gamma. Analysis of somatic cell hybrids obtained by fusion of AKR SL3 with an H-2Kb and Db IFN-gamma augmentable partner tumor argued against the involvement of locus-specific, trans-acting factors as the basis for the nonaugmentable nature of the Kk gene in AKR SL3. Here, we provide evidence against the remaining possibility of an allele-specific, negative-acting factor in AKR SL3. Hybrids were constructed between drug-marked sublines of AKR SL3 and the R1.G1 T-cell tumor which carries IFN-gamma augmentable Kk and Dk genes. The uniform ability of IFN-gamma to cause substantial increases in the expression of Kk in hybrid populations and a large number of hybrid clones from three separate fusions indicated that a trans-acting, negative factor was not present in AKR SL3. Rather, these data coupled with Northern analysis were consistent with cis alterations operating at the level of transcription as the basis for Kk nonaugmentation. These results are discussed with regard to the further study of AKR SL3 to better understand IFN-gamma regulation of class I MHC expression.

IFN-induced modulation of histocompatibility antigens on human cells. Background, mechanisms and perspectives

IFN proteins are a family of lymphokines with anti-viral effects. Several other effects of IFNs have also been described, including enhancement of natural killer (NK) cell activity, enhancement of cytotoxic T-lymphocyte activity, and enhancement of the expression of major histocompatibility complex (MHC) antigens. The latter effects have been characterized as immunomodulatory, whereas the well-known inhibition of growth of malignant cells has been termed anti-proliferative. This review summarizes the current knowledge of the enhancement of MHC products by IFNs. Whereas the basic methodologies for demonstrating the enhancement are simple and reliable, especially when using flow cytometry (FCM), the biological relevance of this reaction is largely unknown. Based on recent findings, however, we have hypothesized that the above-mentioned diverse effects of IFNs are all - in some way or other - related to the classical anti-viral mechanism. This concept proposes that the MHC-enhancing effect of IFNs is a vital part of the immunological defense against virus infections and an integral part of the anti-viral effects of IFN proteins.

Chromosome mapping of biological pathways by fluorescence-activated cell sorting and cell fusion: human interferon gamma receptor as a model system

Human chromosome 6 encodes both the interferon gamma receptor as well as the class I major histocompatibility complex antigens, HLA-A, -B, and -C. However, the presence of chromosome 6 in somatic cell hybrids is insufficient to confer sensitivity to human interferon gamma (Hu-IFN-gamma) as assayed by class I HLA induction; it is necessary for both human chromosomes 6 and 21 to reside in the hybrid to generate a response to Hu-IFN-gamma. Treatment of such a hamster-human hybrid, Q72-18, with Hu-IFN-gamma induces the class I HLA antigens. Q72-18 cells selected by fluorescence-activated cell sorting for the loss of class I HLA induction also lost human chromosome 21. Fusions of such cells to a hybrid that contains only human chromosome 21 reconstitutes HLA antigen induction by Hu-IFN-gamma. Furthermore, fusions of hybrids containing a translocated human chromosome 6q and the HLA-B7 gene to a line containing only human chromosome 21 or a translocated 21q also reconstitutes HLA-B7 mRNA and antigen induction by Hu-IFN-gamma. Thus the segregation of cells on the basis of a biological effect by fluorescence-activated cell sorting and reconstitution by hybrid fusion provides a strategy by which some biological pathways can be mapped at a chromosomal level.

Differential expression of the HLA-B7 and the HLA-A2 gene in transfected mouse L(tk-) cells after stimulation by mouse interferon

Mouse L(tk-) cells were transfected with recombinant genomic clones encoding the human major histocompatibility antigens HLA-A2 or HLA-B7. The exposure of 15 different transfected cell clones to mouse interferon resulted in an up to 2.9-fold enhancement of the HLA-A2 antigen at the cell surface but in an up to 5.5-fold enhancement of the HLA-B7 antigen as shown by quantitative radioimmunoassay with monoclonal antibodies directed against different HLA epitopes. Using the HLA-Bw6 specific monoclonal antibody 2BC4, an even higher increase of the HLA-B7 antigen (up to 12-fold) could be observed. This higher inducibility of an HLA-B versus HLA-A locus gene may reflect distinct regulatory mechanism controlling the expression of HLA class I subregion antigens.

Inhibition of Epstein-Barr virus infection in vitro by recombinant human interferons alpha and gamma

The inhibitory effects of pure recombinant human interferons alpha A and gamma (reIFN-alpha A and -gamma) on Epstein-Barr virus (EBV) infection of a human EBV-negative B cell line, BJAB, and of normal adult B lymphocytes were studied. With pretreatment for 24 h, both types of reIFNs were effective in suppressing the production of EBV specific nuclear antigen (EBNA-1) in BJAB cells 24 h after EBV-infection, as determined by the immunoblotting technique. ReIFN-alpha A was, however, a much more potent inhibitor than reIFN-gamma. With treatment starting 1 h after EBV infection, both types of reIFNs were less effective in the suppression of EBNA production. Neither of the reIFNs showed any inhibitory effect on EBNA production in the latently EBV-infected cell lines, Raji and Daudi. These results suggest that reIFNs act in the early phase of EBV infection. Both types of reIFNs were also effective in inhibiting EBV infection of normal adult B lymphocytes as demonstrated by a reduction both in [3H]thymidine incorporation 6 days after EBV infection and in the total number of proliferating cells 21 days after EBV infection. Again, reIFN-alpha A showed a greater inhibitory effect than reIFN-gamma. We also showed that in BJAB cells, reIFN-alpha A strongly induced (2'-5')oligoadenylate synthetase activity, whereas reIFN-gamma increased the surface expression of HLA class I antigens.

Mx protein: constitutive expression in 3T3 cells transformed with cloned Mx cDNA confers selective resistance to influenza virus

Mx+ mice are much more resistant to influenza virus than Mx- strains. The resistance is mediated by interferon (IFN) alpha/beta. After IFN treatment, Mx+ but not Mx- cells accumulate Mx protein and become specifically resistant to orthomyxoviruses. cDNA encoding Mx protein was cloned and sequenced. Southern analyses indicate that Mx- alleles derive from their Mx+ counterpart by deletions. IFN-treated Mx+ cells contained a 3.5 kb Mx mRNA, while Mx- cells showed only traces of shorter Mx RNA. Mx- cells transformed with Mx cDNA expressed Mx protein constitutively to varying extents; resistance of individual cells to influenza virus correlated with Mx protein expression. Thus, specific resistance to influenza virus in vivo may be attributed to Mx protein expression and is independent of other IFN-mediated effects.

Differential regulation of interferon-induced mRNAs and c-myc mRNA by alpha- and gamma-interferons

The extent and kinetics of induction have been determined for eight mRNAs induced by alpha- and gamma-interferons in HeLa cells. The mRNAs which code for a 2-5A synthetase, metallothionein II, HLA class I antigen and five unknown proteins were induced 2 - greater than 100-fold by alpha-interferons. In the continued presence of alpha-interferon some mRNAs were maintained at the induced levels until at least 40 h, whereas others were induced only transiently. When the effects of alpha- and gamma-interferons were compared, the induced levels and kinetics were very similar for one mRNA (1-8) but were significantly different for the others. One mRNA (6-16) was induced more than 100-fold by alpha-interferon but not significantly by gamma-interferon. Parallel analysis of the level of c-myc mRNA showed it to decrease twofold in response to alpha-interferon, but to increase more than threefold in response to gamma-interferon, despite a more profound inhibition of cell growth by the latter. There must, therefore, be differences in how the levels of different mRNAs are sustained by alpha-interferons and how alpha- and gamma-interferons regulate the levels of the same mRNAs.

Interferon action: transcriptional control of a gene specifying a 56,000-Da protein in Ehrlich ascites tumor cells

The exposure of cells to interferons enhances the accumulation of particular mRNAs and of the corresponding proteins. A cDNA clone (clone 202) complementary to an mRNA (202 mRNA) whose level is enhanced over 12-fold in mouse Ehrlich ascites tumor cells upon exposure to beta-interferon for 10 hr has previously been isolated. The level of this mRNA was also increased in other beta-interferon-responsive mouse cell lines (i.e., L929, L1210S) but not in a line (L1210R) which is not responsive to beta-interferon. The extent of induction in Ehrlich ascites tumor cells depended on the beta-interferon concentration and reached its maximal level between 300 and 1000 units of interferon/ml. Nuclei isolated from Ehrlich ascites tumor cells which had been exposed to beta-interferon produced in vitro more 202 specific RNA than nuclei from control Ehrlich ascites tumor cells: an increase in this production was detectable 2 hr after beginning the exposure of the cells to 1000 units/ml of beta-interferon and the increase reached its maximal level, around 18-fold, after 18 hr exposure. Much, if not all of this increase, appeared to be due to an increase in the rate of synthesis of the RNA and not to a decrease in its rate of turnover. The 202 mRNA was translated in a reticulocyte lysate into a 56,000-Da protein.

Differential effects of recombinant human interferon-alpha A/D on expression of three types of Fc receptors on murine macrophages in vivo and in vitro

Recombinant human interferon-alpha A/D (IFN-alpha A/D) is known to act on murine cells. We studied the in vivo and in vitro effects of pure IFN-alpha A/D on the surface expressions of the three types of murine macrophage Fc receptors (FcRI, II, III). Peritoneal macrophages obtained from BALB/c mice injected 24 h previously with IFN-alpha A/D showed increased expressions of FcRI and FcRII, because an enhanced capacity to bind monoclonal IgG2a- or IgG2b-coated sheep red blood cells was revealed. However, an optimal IFN-alpha A/D dose of a distinct narrow range was required to induce the maximum increase in each type of FcR. Furthermore, the antibody-dependent cellular cytotoxicity mediated by either FcRI or FcRII was also increased with the same optimal dose of IFN-alpha A/D. On the other hand, IFN-alpha A/D did not induce any change in the surface expression of FcRIII, which was demonstrated by the binding of monoclonal IgG3-coated sheep red blood cells. The in vitro treatment of peritoneal macrophages with IFN-alpha A/D also increased the FcRI expression. In contrast with in vivo treatment, however, IFN-alpha A/D treatment in vitro did not bring about any change in the FcRII expression. The FcRIII expression also remained unchanged with IFN-alpha A/D in vitro. Lymphokine-rich mouse spleen cell supernatants which contained natural IFN-gamma again enhanced the FcRI expression, but did not modulate the expressions of FcRII or FcRIII in vitro.

Transcriptional and posttranscriptional regulation of interferon-induced gene expression in human cells

Eighteen cDNAs, cloned from interferon-treated T98G neuroblastoma cells, correspond to seven different mRNAs induced up to 40-fold by interferon. One codes for metallothionein II and another for a class I HLA. The others do not code for proteins of known sequence. In the continued presence of interferon, accumulation of the mRNAs continues for about 1 day but ceases whenever interferon is removed. Once induced, the mRNAs are stable. Synthesis of new proteins is not required for induction. The rate of transcription of one of the genes doubles 5 min after treatment with interferon and reaches a maximum by 60 min. This rate begins to fall after 4-6 hr, reaching the uninduced level by 8-12 hr. Since the mRNA continues to accumulate after 8-12 hr, posttranscriptional events must also play a role in increasing its level.

Assignment of low-molecular-weight human (2', 5')A synthetase to chromosome 11

Human low-molecular-weight (2', 5')A synthetase is induced in certain human X mouse somatic hybrid cell lines when these cells are treated with mouse interferon. We have assigned the gene coding for this interferon-inducible antiviral enzyme to human chromosome 11 by somatic cell genetic techniques (1). Fluorescence-activated cell sorting for cells expressing or lacking 4F2 antigen in two independently derived, chromosome 11-containing hybrid cell lines separated the cells into subpopulations of cells that had retained or segregated chromosome 11, respectively (2). We used these subpopulations to confirm our gene assignment by demonstrating that retention of chromosome 11 was required for expression of human (2', 5')A synthetase.

Chromosomal location of mouse gene 202 which is induced by interferons and specifies a 56.5 kD protein

The 202 gene which specifies a 56.5 kD protein can be induced in Ehrlich ascites tumor cells by treatment with mouse beta interferon. This treatment increases the level of the gene 202-specific mRNA at least 12-fold. For determining the chromosomal location of this gene a 1.5 kb fragment of the gene was hybridized to EcoR1 digested DNA samples from a set of mouse-hamster somatic cell hybrids. Each of the cell hybrids used contained a complete array of hamster chromosomes and one or more mouse chromosomes. The 202 gene fragment hybridized to every DNA sample from cell hybrids containing mouse chromosome 1 (8 hybrids in total) and to none of the DNA samples from hybrids lacking this chromosome (7 hybrids in total). These and other data indicate that the 202 gene is located on mouse chromosome 1.