Differential activity of the 30-kD and the 100-kD forms of 2'-5'An synthetase induced by recombinant human interferon-alpha and interferon-gamma.

Two molecular weight variants of the interferon (IFN)-induced intracellular enzyme 2',5'-oligoadenylate (2-5A) synthetase have been described recently; a 100-kD (cytoplasmic) and a 30-kD (intranuclear) form of the enzyme. The 30-kD form has been located primarily in the nucleus, while the 100-kD enzyme was found mainly in the cytoplasm. We examined 2-5A synthetase activity in extracts of human melanoma (Hs294t) cells treated with either recombinant (r) IFN-alpha A or rIFN-gamma to determine the differential regulation of these enzyme subtypes by treatment with the two types of IFN. Cells were treated (continuous exposure) with doses of rIFN-alpha A (1,000 U/ml) or rIFN-gamma (5,000 U/ml), each of which reduced the number of viable cells to 50% of control values (ED50) by day 3 of treatment. At equieffective doses, the maximal increase in 2-5A synthetase occurred at 48 h for both rIFN-alpha A and rIFN-gamma continuous exposure. The maximal 2-5A intracellular activities at 48 h were 800 +/- 40 and 160 +/- 15 nmoles/mg protein for rIFN-alpha A and rIFN-gamma treatment, respectively. High-performance gel permeation chromatography of cell lysates resolved the 2-5A activity into both 100-kD and 30-kD fractions. At 48 h after treatment with rIFN-alpha A, the activity of the 30-kD synthetase was approximately twofold greater than that of the 100-kD enzyme. In contrast, the activity of both 30- and 100-kD enzymes were equivalent 48 h after treatment with rIFN-gamma.(ABSTRACT TRUNCATED AT 250 WORDS)