Isoforms p69 and p100 of 2',5'-oligoadenylate synthetase induced differentially by interferons in vivo and in vitro

Four isoforms of 2',5'-oligoadenylate (2-5A) synthetase have been identified (40, 44, 69, and 100 kD). The 40- and 44-kD enzymes are encoded by the same gene, probably different from the genes encoding the larger isoforms. In this study, induction of the 100- and 69-KD (p100, p69) isoforms in different individuals and in different cell types was investigated after treatment with recombinant human interferons (IFN): IFN-alpha 2, IFN-beta ser, or IFN-gamma. The p69 and p100 isoforms were quantitated in cell extracts on Western blots using specific polyclonal antibodies, or their activity was measured after purification of cell extracts on immunoaffinity columns. The p69 and p100 isoforms were differentially induced in Daudi, fibroblast, and colon adenocarcinoma cells treated with IFNs. Considerable individual variations in both basal and induced levels of p69 and p100 were observed in peripheral blood mononuclear cells from normal donors cultured with IFNs in vitro, and from cancer patients treated with IFN-alpha 2 or with IFN-beta ser. These results demonstrate that the p69 and p100 isoforms are present in vivo in peripheral blood mononuclear cells and their level is increased following IFN administration. Furthermore, both the in vivo and in vitro observations indicate that the expression of these enzymes is specific to each cell type and varies among individuals.