Molecular foundations of interferon action

Synthesis and properties of 5,6-dichlorobenzimidazole 2'----5'- and 3'----5'-nucleotide dimers and trimers

5,6-Dichloro-1-beta-D-ribofuranosylbenzimidazole (2), synthesised by the fusion method, was used for the synthesis of 2'----5'- and 3'----5'-linked di- and tri-meric oligonucleotides. The protecting groups used were p-methoxytrityl for HO-5', tert-butyldimethylsilyl for HO-2',3', and 2,5-dichlorophenyl and 2-(4-nitrophenyl)ethyl for the phosphate group. The internucleotidic linkages were established by the phosphotriester approach to give the fully protected 2'----5' dimers (15, 17, and 18) and trimers (27 and 28), as well as the 3'----5' dimers (22 and 23) and trimers (31 and 32). Deprotection involved a sequence of steps to afford the corresponding free oligonucleotides 21, 26, 30, and 33 isolated as the triethylammonium salts in good yields. The new compounds were characterised by elemental analysis and by u.v. and 1H-n.m.r. spectroscopy.

Age-related differences in the induction of 2-5A synthetase and 2-5A dependent binding protein activities by interferon in guinea pig peritoneal macrophages

2-5A synthetase and binding protein activities in peritoneal macrophages have been compared between young (6 month) and old (22-24 month) guinea pigs. Enzyme activities are lower in aged animals with a 17% and a 31% reduction in synthetase and binding protein activities, respectively. In addition, the response to the addition of mouse fibroblast interferon by macrophages from these two age groups is also substantially different. Whereas addition of interferon to young guinea pig macrophages elicits a 3.8- and a 1.7-fold increase in the synthetase and binding protein activities, only a marginal elevation in these two enzyme activities is found with interferon-treated old guinea pig macrophages. Analysis by thin layer chromatography demonstrates a marked difference in the relative distribution of the various oligomeric forms of 2-5A synthesized by young or old guinea pig macrophages. The binding protein in old animals appears to be significantly more thermolabile than the corresponding activity from young animals. The altered response to interferon and the difference in enzymatic properties in aged animals may represent part of the mechanisms involved in the progressive loss of the adaptative ability of an organism to environmental changes during senescence.

Some properties of 2-5A binding/nucleolytic activities in gel filtered rabbit reticulocyte lysates

Rabbit reticulocyte lysates, gel filtered on Sephadex G-25 with or without ATP (or its analogs), were preincubated at 37 degrees C and their subsequent binding to p3A4,3'-[32P]pCp was studied. Lysates filtered without ATP or in the presence of 0.1 mM 8-bromo-ATP, 1,N6-etheno-ATP, or ITP showed a time-dependent decrease in binding activity. This decrease was completely prevented when lysates were filtered with 0.1 mM ATP, 2'-deoxy-ATP, beta-gamma-methylene-ATP, or ATP-gamma-S. The stability of binding provided by ATP or 2'-deoxy-ATP analogs corresponds to a more active 2-5A dependent endonucleolytic (RNAase L) activity based on studies using [3H] viral mRNA. Chromatography on heparin-agarose showed that ATP-supplemented gel-filtered reticulocyte lysates had a different p3A4,3'-[32P]pCp binding activity elution-profile than lysates gel-filtered in the absence of ATP. Covalent cross-linking of periodate-oxidized p3A4,3'-[32P]pC to gel-filtered lysates, preincubated at 0 degree C or 37 degrees C for 30 min, showed the following results: all lysates gave a major cross-linking of the radioactive ligand to an 80 000 dalton polypeptide, regardless of the temperature of preincubation, lysates gel-filtered without ATP, with 0.1 mM ITP, or beta-gamma-methylene-ATP, showed a significant reduction in the cross-linking of the 80 000 dalton protein, after preincubation at 37 degrees C for 30 min. This decrease was accompanied by an increase in the labeling of two smaller polypeptides.

Effects of K+ concentration on inhibition of protein synthesis by trimer and tetramer triphosphates of 2',5'-oligoadenylates in rabbit reticulocyte lysates

The inhibition of protein synthesis by trimer or tetramer triphosphates of 2',5'-oligoadenylates (2-5A) in rabbit reticulocyte lysates is dependent on the concentration of K+ in the assay mixture. Based on studies using mRNA-dependent rabbit reticulocyte lysates and the degradation of [3H] polyadenylated mRNA, the greater inhibitory effects of trimer or tetramer triphosphates at the higher K+ is shown to be due to a more active 2-5A-dependent endoribonuclease (RNase L).

A sensitive immunoenzymometric assay for 2',5'-oligoadenylate. Detection of elevated 2',5'-oligoadenylate synthetase in human peripheral mononuclear cells

A competition immunoenzymometric assay for 2',5'-oligoadenylate was developed and employed to measure the interferon-inducible enzyme 2',5'-oligoadenylate synthetase in cell extracts. Microtiter plates coated with a novel conjugate of p5'A2'p5'A2'p5'A and N-(2-aminoethyl)-carbamylmethylated-Ficoll (AECM-Ficoll) bound rabbit polyclonal or mouse monoclonal antibody directed against 2',5'-oligoadenylate. Binding was inhibited by soluble 2',5'-oligoadenylate. Estimates of 2',5'-oligoadenylate concentrations based on inhibition of antibody binding compared favorably with those obtained using a protein synthesis inhibition assay. Low concentrations of 2',5'-oligoadenylate synthesized in vitro by extracts of human peripheral mononuclear cells were conveniently estimated using less than or equal to 10(6) cells. Virtually identical results were obtained when either total extract or synthetase bound to poly(I) . poly(C)-agarose was used for the in vitro incubation. When peripheral mononuclear cells were incubated in vitro with interferon, the normally low levels of 2',5'-oligo(A) synthetase rose dramatically. The assay was employed to measure synthetase levels in peripheral mononuclear cells isolated from patients with systemic lupus erythematosus. Some of these patients were found to have elevated levels of 2',5'-oligoadenylate synthetase.

Effect of temperature on ppp(A2'p)nA binding protein activities in rabbit reticulocyte lysates and other mammalian extracts

Lysates of rabbit reticulocytes and other mammalian cells are known to contain an activity which binds with high specificity ppp(A2'p)3A,3'-[32P]pCp. The binding activity shows a marked dependence on preincubation of lysates at different temperatures (4 degrees C - 45 degrees C). For example, binding was increased 50% by preincubation of rabbit reticulocyte lysates at 37 degrees C for 60 minutes. An identical preincubation of mouse brain extracts results in a greater than 90% loss of binding activity. Fractionation of rabbit reticulocyte lysates into the postribosomal supernatant (PRS) and the ribosomal salt wash (RSW), followed by heparin-agarose column chromatography, showed that with the PRS fraction, most of the binding activity is eluted with 600 mM KCl. With the RSW fraction, more than 50% of the binding activity is eluted with 250 mM KCl. These data suggest that multiple ppp(A2'p)nA binding protein activities exist in mammalian cells.