Mechanism of interferon uptake in parental and somatic monkey-mouse hybrid cells

Historical developments in the research of interferon receptors

Interferons (IFNs) were discovered 50 years ago independently by Isaacs and Lindemann and by Nagata and Kojima. When it was later realized that IFNs are active at very low concentrations, research began to determine how their powerful effects were generated from such a small initial signal. It has since been established that interferons, as well as all other cytokines, employ cell surface receptors to translate their presence in the serum to a potent cellular response to a viral infection. These receptor complexes are composed of multiple distinct glycosylated transmembrane polypeptides, a number of protein tyrosine kinases, and interact transiently with a large variety of other proteins including transcription factors, phosphatases, signaling repressors, and adaptor proteins coupling the receptor to alternative signaling pathways. Three major receptor complexes exist that are exclusive to each of three major classes of interferon. Even though the effects of each major class of interferon vary physiologically, each receptor complex interacts with its ligand in similar ways and activates similar signaling cascades. In this mini-review, we take a historical perspective at the major events in the characterization of interferon receptors, discussing interesting results that still need to be explained.

Somatic cell mapping of the bovine interferon-alpha receptor

The bovine interferon-alpha receptor (BoIFN-alpha R) mediates the activity of bovine IFN-alpha s and IFN-beta. In addition, human IFN-alpha s have uniformly high biological activity on bovine cells. A 32P-labeled derivative of human recombinant IFN-alpha A (HuIFN-alpha A-P1) binds well and can form a characteristic 130-kDa complex on bovine cells, but not on hamster cells. We have, therefore, analyzed the binding and covalent crosslinking of [32P]HuIFN-alpha A-P1 to a panel of bovine-hamster somatic cell hybrids. Binding to several bovine-hamster hybrid cell lines was strong (about 30-50% of that seen with bovine MDBK cells) and specific. The binding correlated uniquely with bovine syntenic group U10. In several of the hybrid lines, the ability of human IFN-alpha B to enhance the expression of endogenous MHC class I molecules correlated with the binding results. We thus conclude that the bovine IFN-alpha R structural gene (locus designation IFNAR) localizes to syntenic group U10. This group includes a number of other genes whose homologs map to human Chromosome (Chr) 21.

Sublocalization on chromosome 21 of human interferon-alpha receptor gene and the gene for an interferon-gamma response protein

The cellular responses to alpha and beta interferons (IFN-alpha and -beta) are mediated through the IFN-alpha/beta (type I) receptor, while the response to IFN-gamma is mediated through the IFN-gamma (type II) receptor. The receptors for IFN-alpha/beta and IFN-gamma are encoded by genes on human chromosomes 21 and 6q, respectively. The presence of chromosome 21q confers both ligand binding and responsiveness to human IFN-alpha/beta, whereas chromosome 6q confers binding of Hu-IFN-gamma, but not cellular responsiveness on somatic cell hybrids. Chromosome 6q (i.e., the Hu-IFN-gamma receptor gene) and chromosome 21q are both necessary for the cellular response of somatic cell hybrids (from fibroblasts) to Hu-IFN-gamma. It is conceivable that the factor mediating activity through the IFN-gamma receptor is, in fact, the IFN-alpha receptor, or that the two genes are distinct but part of an "interferon response" region. Here we more precisely localize on human chromosome 21 the genes for the IFN-alpha receptor and for the factor(s) mediating the action of IFN-gamma through the chromosome 6-encoded receptor. Hamster-human somatic cell hybrids containing various fragments of human chromosome 21 were used. The presence of the human IFN-alpha/beta receptor was determined by binding 32P-labeled human IFN-alpha to cells, covalently cross-linking the [32P]IFN-alpha-receptor complex, and analyzing it by SDS-polyacrylamide gel electrophoresis. The presence of the IFN-gamma receptor-related factor mediating cellular responsiveness was determined by HLA induction in hybrid cells containing the IFN-gamma receptor (chromosome 6q), a transfected copy of the human HLA-B7 gene, and various portions of chromosome 21. In all hybrids examined, the two genes cosegregate. Specifically, both genes are localized to the region of chromosome 21 containing the markers D21S58, D21S65, and GART and appear to be proximal to D21S58. The implications for IFN action are discussed.

Regulation of cell growth by interferon

Interferons can regulate growth and differentiation in a wide range of cell types. These mechanisms are currently being examined. Interferons inhibit the growth of tumour cells and are thus potential anti-cancer agents. They can also inhibit normal cell growth in vitro, and stimulate tumour cell growth in vitro. They may also be involved in some autoimmune diseases. This review examines the effect of interferons on cell proliferation, function, and growth, focusing primarily on in vitro cell systems.

Interferon--present and future prospects

The interferons are a group of proteins that have inspired a new era of investigation into biological modification. The interferons are now divided into subgroups characterized by chemical means and correspond to different biological responses which can be observed in terms of the inducer used, and the timing of the response. Identified originally as antiviral agents when homologous cell systems were treated prior to infection, new studies have extended these observations to place the interferons in a central role as a strong force in the regulation of immunologic responses. A marriage of interferonology and cell immunology is enlarging both our understanding of the action of these proteins and our ability to follow the course of an illness and eventually to control its outcome . Genetic engineering has provided a way to process quantities of interferon and provided the molecular sequence of all three classes of IFN including a model of the active site for IFN-alpha. The offshot of the technology developed to study the intracellular processes after interferon treatment have already led to increased sensitivity to detect virally treated diseases. Both the variety of the interferon inducers and the scope of parasites in which it can exert its influence provide a frontier of biological investigation which has at the root of its nature the very secret of life. In addition to cellular phenomena, the positive effects on tumor-bearing organisms and the ill effects on infant animals highlight the potential power of the interferons.

Protective effect of interferon on target cells exposed to cellular cytotoxicity

In order to explore by immunological methods the interferon-induced cell membrane modulation, the effect of interferon in parental and monkey-mouse hybrid cells was studied in the presence of sensitized lymphocytes from isologous mice. After primary immunization to the hybrids, both parental interferons increased the lymphocyte-induced specific cytotoxicity in the same hybrid cells used as targets. In addition, a significnt increase of spontaneous lysis due to the two interferons was observed. In contrast, after secondary sensitization, in spite of the higher specific cytotoxicity induced by the lymphocytes, the same interferon preparation significantly protected the cells. These results are probably related to a greater number of sensitized effector cells after secondary sensitizationn. It is likely that, although interferon increases the affinity of sensitized T lymphocytes for the target cell membrane, in case of unsuccessful encounters, the target cells become resistant to new hits. Interferon could augment the number of such immune cells.

Human leukocyte interferon: relationship between molecular structure and species specificity

Human leukocyte interferon can be separated into two classes of subspecies by polynucleotide-agarose affinity chromatography; 30-40% of the molecular species have the polynucleotide-binding property and 60-70% lack affinity for the polynucleotide ligand. When analyzed on sodium dodecyl sulfate/polyacrylamide gel electrophoresis, the former class of interferon has a slower mobility corresponding to the migration of a polypeptide of 21,000 daltons, while the latter class has a faster mobility corresponding to a polypeptide of 13,500-15,000 daltons. By analogy to the behavior of other interferons and a class of nucleotidyl transferases on the polynucleotide-agarose chromatography, we suggest that the human leukocyte interferon having the polynucleotide-binding site is in a possibly "native" conformation and the loss of affinity for polynucleotide results from a degradative alteration of the native molecules. Moreover, the alteration of interferon is accompanied by an increase in heterospecific activity on bovine cells. It is suggested that the polypeptide domain responsible for species specificity may be closely related to the polynucleotide binding area. The modified interferon molecule, however, still conserves its antiviral activity. The simplicity and the high capacity of polynucleotide-agarose chromatography make this a powerful technique for the purification of interferon. The easy separation of these two classes of human leukocyte interferon makes the purification procedures more rational and will facilitate the preparation of both subspecies to a high degree of molecular homogeneity.

Isolation, preliminary characterization, and interferon antagonistic effect of a mammalian lectin-like substance

We have isolated from mouse costal cartilage a tissue antagonist of interferon (TAI) which accelerates the decay of an established antiviral state. The effect is reminiscent of substances previously isolated from the basement membrane of human amnion. Since we have recently shown that phytohemagglutinin can mimic the biological effect of TAI, we have explored the possibility that TAI could be an animal lectin-like material. First, TAI agglutinates mouse cells; second, this cell agglutination is inhibited by some sugars. Preliminary characterization indicates that the active molecule is a protein. After Sephadex G-100 gel filtration, TAI is found in a peak of 150,000 molecular weight. When purified by isoelectric focusing, this peak shows maximal activities corresponding to an isoelectric point of pH 8.8 TAI binds to polysaccharide residues of the cell membrane which could be its primary site of action, comparable to phytohemagglutinin.

Presence of human chromosome 21 alone is sufficient for hybrid cell sensitivity to human interferon

Human/mouse somatic cell hybrids with chromosome 21 as the only detectable human genetic material were sensitive to both human leukocyte and fibroblast interferons. The presence of additional human chromosomes decreased the amount of interferon needed to attain a given level of virus resistance. Decreased cytopathic effects, decreased virus yields, and the appearance of a specific phosphorylated protein associated with interferon treatment were all observed in hybrids maintaining only human chromosome 21. The phosphorylated protein found in extracts of these human interferon-treated hybrid cells was of mouse origin.

Chromosomal localization of human genes governing the interferon-induced antiviral state

Interferon sensitivity of different normal and aneusomic human cells and of different mouse-human hybrids cells has been compared. G21 trisomic cells are more sensitive than diploid cells; whereas, on the contrary, triploid cells are normal in their human interferon sensitivity. Among other aneusomic cell lines tested, E16 trisomic cells are significantly less sensitive. These data are in favor of the hypotheses that the G21 chromosome carries genetic information for structural proteins involved in the receptor system for interferon, that there is a regulatory mechanism governing the antiviral state, and that the E16 chromosome is a possible candidate for carrying information for such a depressive regulatory mechanism. None of the chromosome abnormalities studies are involved with interferon synthesis.

Antiviral effect of interferon covalently bound to sepharose

Interferon, covalently bound to Sepharose 4B activated by cyanogen bromide, induces the antiviral state in sensitive cells. The antiviral effect is neutralized by antiserum specific to interferon and is recovered thereafter when the antibody is detached from the interferon by treatment at low pH. Binding interferon to Sepharose increases the stability of the molecule. It is likely that the interferon molecule acts on the cell receptor without being detached from the beads. However, the data do not exclude the possibility of a small loss of interferon, or fragments of it, after contact with the cell.