Increased levels of (2'-5')oligo(A) polymerase activity in human lymphoblastoid cells treated with glucocorticoids.

An enzymatic activity that synthesizes (2'-5')-oligo(A) from ATP is induced in animal cells treated with interferon. This activity, designated (2'-5')A polymerase, is also elevated in human lymphoblastoid Daudi and Raji cells treated with hydrocortisone. The polymerase activity increases significantly after 24 hr of treatment and declines when hydrocortisone is removed from the culture medium. The product of the enzyme prepared from hydrocortisone-treated cells is indistinguishable from (2'-5')oligo(A) synthesized with polymerase of interferon-treated cells either by an endonuclease activation assay or by chromatographic analysis. The increase in (2'-5')A polymerase is not mediated by secretion of interferon by hydrocortisone-treated cells; less than 1 unit of interferon per ml is present in the culture medium during treatment with this glucocorticoid hormone. Moreover, this increase is related to the concentration of hydrocortisone in the culture medium and is inhibited by the addition of cortexolone. This steroid interferes with the interaction between glucocorticoid hormones and their receptor. Cortexolone has no effect, however, on the induction of (2'-5')A polymerase by interferon. The synthetic glucocorticoid dexamethasone also increases the polymerase activity. Experiments with inhibitors show that such an increase requires RNA and protein synthesis.