Inhibition of interferon action by cytochalasin B, colchicine, and vinblastine

Identification of an adenine-nucleotide-binding site on interferon alpha2

Using 32P-labeled 2-azidoadenosine 5'-triphosphate (2N3ATP) and 8-azidoadenosine 5'-triphosphate (8N3ATP), we have identified a site on human interferon alpha2 (IFN-alpha2) that binds adenine nucleotides. The results from saturation and competition experiments demonstrated the specificity of the nucleotide interaction. Half-maximal saturation of IFN-alpha2 was observed at 10 microM 2N3ATP or 35 microM 8N3ATP. ATP effectively decreased photoinsertion of both photoaffinity analogs of ATP. Photoinsertion of 8N3ATP was enhanced by MgCl2, independent of the ionic strength, and exhibited an optimum pH between 7.0 and 7.5. Immobilized-Al3+ affinity chromatography and HPLC were used to purify the modified peptides from IFN-alpha2 that had been photolabeled with 8N3ATP and digested with trypsin or chymotrypsin. Overlapping-sequence analysis localized the sites of photoinsertion to the region corresponding to Lys121-Tyr135 in the amino acid sequence of IFN-alpha2, which almost perfectly overlaps a nuclear-localization signal (R120KYFQRITLYLKEKKY135).

Cytoskeletal modulation of plasma membrane events induced by interferon-alpha

Cytochalasin B, a drug that alters microfilament structure, was found to modulate interferon-alpha (IFN-alpha)-induced changes in ion fluxes, in motional freedom of spin probes, and lateral diffusion of surface antigens. These changes occur in Daudi cells inherently sensitive to the antiproliferative signal of IFN-alpha, but not in insensitive cells, and were associated with the antiproliferative signal previously. The biophysical effects of cytochalasin B were detected by flow cytometric quantitation of membrane potential using an oxonol dye, by electron spin resonance (ESR) spectrometry, and by measurements of fluorescence recovery after photobleaching (FRAP) of surface antigens using a laser-interactive cell imaging system. Cytochalasin B treatment increased an IFN-alpha-induced membrane potential shift by -5 mV. The motional freedom of 5-doxyl-stearic acid changed from 0.67 to 0.63, as expressed by the order parameter, S, with IFN-alpha treatment and was prevented by cytochalasin B. Changes in the lateral diffusion of surface antigens induced by IFN-alpha treatment, D = 5.3 x 10(-10) without treatment and D = 7.8 x 10(-10) cm2/s with treatment, was blocked by cytochalasin B. In contrast, the microtubule stabilizers taxol and D2O and the microtubule depolymerizing colcemid were ineffective at dose levels sufficient to cause the characteristic cell physiological alterations of these agents. These results implicate microfilaments but not the microtubule system in transduction of the antiproliferative signal by IFN-alpha in Daudi cells.

Butyric monosaccharide ester-induced cell differentiation and anti-tumor activity in mice. Importance of their prolonged biological effect for clinical applications in cancer therapy

The interest of butyric salts is based on their capacity to promote differentiation of malignant cells and inhibition of tumor development. The phenotypic modifications are rapidly reversible and require the continuous presence of butyric salts in the target area, which raises problems for therapeutic applications. We show here that the covalent binding of n-butyric acid on natural polyhydroxylated compounds such as monosaccharides, especially 3- or 6-O-butanoyl-1,2-O-isopropylidene-alpha-D-glucofuranose, retains the majority of the biological properties of n-butyric acid. The delayed degradation of these covalent compounds is associated with an improved maintenance of cell differentiation and anti-tumor protection in mice. These butyric complexes thus seem potentially useful for therapeutic applications.

Cytoskeletal association of human alpha-interferon-receptor complexes in interferon-sensitive and -resistant lymphoblastoid cells

Human Daudi lymphoblastoid cells, which are highly sensitive to the antiproliferative action of human leukocyte alpha-interferon (IFN-alpha), and IFN-resistant and IFN-sensitive Daudi subclones (Cl2 and Cl1, respectively), contain 2300 (Kd = 20 X 10(-12) M), 3000 (Kd = 45 X 10(-12) M), and 3700 (Kd = 52 X 10(-12) M) IFN-alpha binding sites per cell, respectively. Thus, these IFN-sensitive and IFN-resistant cells have similar numbers of high-affinity IFN-alpha receptors. IFN-receptor complexes that are insoluble in Triton X-100 accumulate in IFN-sensitive but not in IFN-resistant cells. The ligand-induced accumulation of Triton-insoluble complexes in IFN-sensitive cells was inhibited by cytochalasin B. This suggests that the solubility change of IFN-receptor complexes results from their interaction with the cytoskeletal matrix. The dissociation of IFN-alpha from IFN-sensitive and IFN-resistant cells can be resolved into fast and slow components. IFN-alpha dissociates more slowly from IFN-sensitive cells than from IFN-resistant cells. Very slow dissociation of IFN-alpha from Triton-insoluble complexes correlates with this difference. These observations suggest that IFN-receptor complexes become coupled to the cytoskeletal matrix in IFN-sensitive but not in IFN-resistant cells, and that such interaction is an important element in the mechanism of the antiproliferative action of IFN-alpha on Daudi cells.

Effect of glucose on antiviral activity of interferon

Glucose was found to impair the antiviral activity of rabbit interferon (IFN) in RK-13 cells. This impairment was dependent on the glucose concentration: A pronounced impairment was observed at the concentration of 30 mg of glucose/ml, the maximum concentration which produced neither morphological changes of cells nor diminution of overall macromolecular synthesis. Maximal impairment was seen when glucose was added to the IFN-treated RK-13 cells early during the development of antiviral activity. Furthermore, glucose decreased the extent of induction of 2',5'-oligoadenylate synthetase by IFN. Of six different monosaccharides examined, only fructose had the same anti-IFN effect as glucose.

Antitumor therapy based on the use of an immune modulator, arginine butyrate and interferon

The analysis of the likely physiological role of interferon during pregnancy and antitumor protection can be employed in developing a new strategy in antitumor therapy. Indeed, pretreatment of the patients with a potent immune stimulation compensates to some extent interferon's immune repressive effects. Through the modulation of the cytoskeleton, interferon enhances macrophage activity. Moreover, butyrate by its own effect on the malignant phenotype increases interferon sensitivity in a number of malignant cells. All of these substances should be used at the lowest possible concentration delivered as closely as possible to the target area.

Enhancement of basophil chemotaxis in vitro by virus-induced interferon

It is well established that viral infections may precipitate or worsen attacks of bronchial asthma. Furthermore, in symptomatic atopic subjects, the local accumulation of basophils and the production of a basophil chemotactic factor have been reported. We have investigated the effect of cell-free supernates from viral stimulated cultures of human mononuclear cells on the in vitro migration of human basophils. Our results show the presence of a factor in these culture supernates that enhances the migration of basophils toward two separate chemoattractants, a peptide from C5 and a lymphokine. The enhancing activity, while affecting basophil migration, did not change the response of monocytes. The enhancing activity resembled viral-induced interferon when (a) pH 2 stability, (b) heat resistance, (c) trypsin sensitivity, and (d) species-specificity were compared. Finally, the enhancing activity for basophil chemotaxis and the interferon titer were highly correlated in preparations with a 10(4)-fold difference in interferon specific activity. Our studies show that viral-induced interferon can augment the in vitro chemotactic response of basophils. Because mediators present in basophils may be involved in the pathogenesis of immediate hypersensitivity, the modulation of basophil movement by interferon suggests a possible mechanism for the association between viral infections and atopic disorders.

Inhibitory effect of interferon on cellular DNA synthesis: modulation by pure mitogenic factors

Quiescent Swiss 3T3 cells can be stimulated to synthesize DNA by combinations of polypeptide hormones, retinoids and tubulin-disrupting agents. Low doses of mouse interferon are effective in inhibiting DNA synthesis induced by one, two or three factors. When more growth factors are added DNA synthesis is not further stimulated, although the dose response curve for interferon is shifted dramatically to the right. Even when added before the mitogenic stimulus, up to 2000 units of interferon have no effect on DNA synthesis stimulated by five factors. A change in the dose-response curve for interferon as an antiviral agent is also observed when the mitogenic stimulation is increased, but the effect is less dramatic than that observed on its function as an inhibitor or DNA synthesis.

Effect of sodium butyrate on the antiviral and anticellular action of interferon in normal and MSV-transformed cells

Sodium butyrate enhances the antiviral and anticellular action of interferon in MSV-transformed cells but has no such effect in normal cells. The increased sensitivity could be mediated at least partially by the butyrate-induced elaboration of the microtubule and microfilament network.

Enhancement of antiviral protection against encephalomyocarditis virus by a combination of isoprinosine and interferon

The antiviral effect of interferon against encephalomyocarditis (EMC) virus infection in mice was enhanced by isoprinosine. However, the enhancement was only obtained when both interferon and the virus were inoculated into the peritoneum; the inoculation route of isoprinosone did not modify significantly the final results. In addition, the time sequence of injections was of great importance; generally the injection of isoprinosine had to precede that of interferon by a few hours.