Ultrastructural localization of interferon receptors on the surfaces of cultured cells and erythrocytes

Corrections for mRNA extraction and sample normalization errors find increased mRNA levels may compensate for cancer haplo-insufficiency

The relative mRNA levels of differentially expressed (DE) and housekeeping (HK) genes of six aneuploid cancer lines with large-scale genomic changes identified by SNP/SKY analysis were compared with similar genes in diploid cells. The aneuploid cancer lines had heterogeneous genomic landscapes with subdiploid, diploid, and supradiploid regions and higher overall gene copy numbers compared with diploid cells. The mRNA levels of the haploid, diploid, and triploid HK genes were found to be higher after correction of easily identifiable mRNA measurement errors. Surprisingly, diploid and aneuploid HK gene mRNA levels were the same by standard expression array analyses, despite the higher copy numbers of the cancer cell HK genes. This paradoxical result proved to be due to inaccurate inputs of true intra-cellular mRNAs for analysis. These errors were corrected by analyzing the expression intensities of DE and HK genes in mRNAs extracted from equal cell numbers (50:50) of intact cancer cell and lymphocyte mixtures. Correction for both mRNA extraction/sample normalization errors and total gene copy numbers found the SUIT-2 and PC-3 cell lines' cancer genes both had ∼50% higher mRNA levels per single allele than lymphocyte gene alleles. These increased mRNA levels for single transcribed cancer alleles may restore functional mRNA levels to cancer genes rendered haplo-insufficient by the genetic instability of cancer. © 2013 Wiley Periodicals, Inc.

Interferon receptors and their role in interferon action

Interferon (IFN) proteins interact with cells through specific cell surface receptors, some of which have been purified and cloned. The alpha-IFNs and beta-IFN bind to a common receptor (type I), whereas gamma-IFN binds to a separate receptor (type II). Both types of high-affinity receptors have been demonstrated on a variety of receptors and the ways in which IFNs may affect cellular physiology and gene expression is discussed.

Rat interferon enhances the expression of acetylcholine receptors in rat myotubes in culture

Interferon enhances alpha-bungarotoxin binding on 5-day-old rat myotubes. The increase is time- and dose-dependent. KD for alpha-bungarotoxin remains unchanged in the presence and in the absence of interferon, while the maximum number of binding sites is dramatically affected by interferon. Cycloheximide inhibits the effect of interferon, which suggests that the enhancement of alpha-bungarotoxin binding depends on protein synthesis.

Interferon pretreatment enhances the sensitivity of Vero cells to Clostridium perfringens type A enterotoxin

Treatment of Vero (African green monkey kidney) cells with interferon (IFN) before the addition of Clostridium perfringens type A enterotoxin (CPE) significantly increased the sensitivity of these cells to CPE. IFN pretreatment caused a subsequent two- to four-fold increase in CPE-induced membrane permeability alterations and also decreased the time of CPE treatment required before the onset of permeability alterations and morphologic damage. Enhancement of CPE activity was dependent on the amount of IFN added during pretreatment and on the duration of IFN pretreatment incubations. Potentiation of CPE activity was observed following pretreatment of Vero cells with natural human IFN-alpha or IFN-gamma or Roferon recombinant human IFN-alpha. However, pretreatment with mouse IFN did not affect CPE activity. IFN pretreatment did not grossly enlarge the size of the functional hole produced in plasma membranes by CPE. IFN pretreatment of Vero cells slightly increased CPE specific binding, but this effect occurred kinetically after the enhancement of CPE toxicity. These results suggest that IFN pretreatment enhances the action of CPE on IFN pretreated Vero cells by increasing the sensitivity of these cells to the action of CPE rather than by increasing CPE specific binding or by directly activating the CPE molecule. Additional studies are required to further clarify the mechanism by which IFN sensitized Vero cells to CPE.

Evidence that divalent cations bind to diphtheria toxin: an ESR approach

We have used electron spin resonance (ESR) techniques to study the binding of divalent cations to diphtheria toxin (DT). Addition of DT to Mn(II) solution at a stoichiometry of 2:1 (DT:Mn) induces a 79% loss in the intensity of the ESR spectrum of Mn(II) suggesting a strong binding of Mn(II) to DT. Inclusion of Ca(II) at a ratio of 1:2:1 (Ca:DT:Mn) in the reaction mixture restores the intensity of the Mn(II) signal to 64%. This indicates that Ca(II) and Mn(II) share same binding site(s) in DT. The results presented in this communication suggest that DT is a Ca(II) binding protein.

Lanthanide ion enhancement of interferon binding to cells

Pretreatment of purified [125I]-labeled human and mouse beta interferons (IFN) with lanthanum chloride (LaCl3) enhanced 20-30 fold the binding of the [125I]-IFNs to human A549 and mouse L cells at 0 degree C and also enhanced antiviral activity in homologous cells. Although lanthanides enhanced cross-species binding of both human and mouse [125I]-IFNs, there was no increase in cross-species antiviral activity. Unlabeled IFN not treated with LaCl3 did not compete with [125I]-IFN treated with LaCl3 for cellular receptors. However, unlabeled IFN treated with LaCl3 did compete with LaCl3-treated [125I]-IFN. These results suggest that lanthanide treated IFNs do not bind to the same receptors as native IFNs.

The interferon receptors

Early studies on the mode of action of interferons have indicated that a receptor system on the cell surface is involved in its action. The first direct evidence to a high-affinity binding site was found only after pure interferon was available. Two different receptors, one specific for interferons-alpha and beta, and the other for interferon-gamma were recognized. A correlation between affinity to the receptor and specific activity was established. Cross-linked complexes of labeled interferons with their receptors were visualized on gel electrophoresis and even partially purified. Internalization of interferons after binding to the receptor was reported. The role of gangliosides as helpers of interferon binding was recently investigated. Fragments of interferons which still retained binding capacity were described and helped in elucidating the binding site on the interferon molecule.

Sensitivity to alpha/beta-interferon is independent of N-linked complex-type oligosaccharides on cell-surface-membrane glycoproteins

The extent of involvement of carbohydrate structures in the mechanism of action of alpha and beta-interferon (IFN-alpha, IFN-beta) is undefined. In this report we examine the role of complex-type N-linked oligosaccharides in the response to these interferons. The response of mouse leukemia L 1210S cells, grown in the presence of swainsonine, an inhibitor of Golgi mannosidase II [Tulsiani, D. R. P., Harris, T. M. and Touster, O. (1982) J. Biol. Chem. 257, 7936-7939; Elbein A. D., Solf, R., Dorling, P. R. and Vosbeck, K. (1981) Proc. Natl Acad. Sci. USA 78, 7393-7397], to mouse IFN-alpha/beta, both with respect to antiviral and antigrowth effects, remains intact in spite of the total absence of complex-type N-linked oligosaccharides. Also, there is no difference in the response to human IFN-beta of a parental Chinese hamster ovary cell line and a mutant lacking beta-N-acetylglucosaminyltransferase I and therefore unable to synthesize complex-type N-linked oligosaccharides [Stanley, P., Callibot, V. and Siminovitch, L. (1975) Cell 6, 121-128]. These results are significant in permitting the conclusion that the carbohydrate-specific binding of IFN-alpha and IFN-beta to gangliosides cannot be due to a similarity of the ganglioside carbohydrate to that of a glycoprotein containing a complex-type N-liked oligosaccharide.

Diphtheria toxin induces leakage of acidic liposomes

Diphtheria toxin (DT) induces the leakage of dipalmitoylphosphatidic acid (DPPA) membranes but not neutral dipalmitoylphosphatidylcholine (DPPC) membranes. Cholesterol incorporated into liposomes enhances the membrane leakage induced by DT in acidic DPPA membranes but not in neutral DPPC membranes. Membrane leakage was determined by assaying the release of TEMPOcholine, a cationic spin probe from the multilamellar vesicles by using electron spin resonance methods. The effect of DT on membrane leakage is noticeable at 3 micrograms/ml concentrations, and reaches a plateau of about 20% leakage at 20 micrograms/ml. This saturation phenomenon led to the postulation that DT binds to the first shell of DPPA membranes and induces the leakage of TEMPOcholine limited to this layer of DPPA multimellar vesicles.

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.

Human interferon alpha enters cells by receptor-mediated endocytosis

A small number of Escherichia coli-derived human interferon alpha A molecules (up to approximately 800/cell) bind specifically to high-affinity cell surface receptors on bovine kidney cells at 4 degrees. When the cells are subsequently warmed to 37 degrees, the amount of surface-bound interferon alpha (IFN-alpha) as recognized by a radiolabeled monoclonal antibody rapidly decreases. Using 125I-IFN-alpha and treatment of cells with acetic acid/sodium chloride to remove surface-bound IFN, a similar decrease of surface-bound IFN and a corresponding increase in intracellular radiolabeled material is observed following the temperature shift. An analysis of the trichloroacetic acid precipitability of the radiolabeled material in the medium, removed by acid treatment or internalized, shows that IFN is degraded intracellularly and that its degradation products are then released into the medium. The process of uptake, degradation, and release of degraded material can be inhibited by the lysosomotropic agent chloroquine. A stable conjugate of IFN with 5-nm colloidal gold was prepared without a detectable loss of antiviral activity. As shown by transmission electron microscopy, the conjugate, bound to cells at 4 degrees, was found in clathrin-coated pits and later in receptosomes following a temperature shift to 37 degrees. Morphometric quantitation showed that an excess of native IFN added during binding of the conjugate in the cold reduced the appearance of conjugate in receptosomes by 80%. These studies demonstrate that at least a portion of receptor-bound IFN enters cells by receptor-mediated endocytosis.

Ultrastructural distribution of interferon receptor sites on mouse L fibroblasts grown in suspension: ganglioside blockade of ligand binding

Murine beta-interferon (IFN) receptors on L929 cells grown in suspension culture were visualized by indirect immunoferritin electron microscopy. Ferritin label on these cells was associated primarily with the coated areas and coated pits of the membrane, in contrast to previous observations with L929 cells grown in a monolayer, which did not reveal such coated areas or pits but showed ferritin label distributed randomly on the cell membrane (Kushnaryov et al., Infect. Immun. 36:811-821, 1982). On about 15% of the cell sections from suspension-grown cells, the ferritin label was found outside coated membrane areas. These findings suggest that different cell populations exist with respect to the localization and possibly the affinity of IFN receptors. In the same experiment, exogenously added gangliosides blocked the binding to cell surfaces not only of 125I-labeled IFN but also of unlabeled IFN as revealed by an immunospecific ferritin labeling technique, providing direct evidence that gangliosides interfere with the binding of IFN to specific receptor sites on the surface of mouse L929 cells. These studies establish that the binding of IFN to cell membranes, depending on cell growth conditions, can involve coated areas and coated pits, to which certain hormones and toxins have been shown to bind.