EFFECTS OF HUMAN IMMUNE INTERFERON ON CELL VIABILITY, (2',5')OLIGOADENYLATE SYNTHESIS, AND POLYAMINE-DEPENDENT PROTEIN-PHOSPHORYLATION IN HUMAN-COLON CARCINOMA-CELLS INVITRO

  • 1 January 1984
    • journal article
    • research article
    • Vol. 44  (5) , 2144-2149
Abstract
The growth-inhibitor effect of human immune interferon (IFN-.gamma.) was investigated in human colon carcinoma cell line HT-29. Three-day treatment of HT-29 cells with IFN-.gamma. (10-200 U/ml) resulted in 30-90% growth inhibition and 40-99% reduction in colony formation. Measurement of DNA, RNA and protein synthesis following IFN-.gamma. treatment showed a dose-dependent reduction in all 3 parameters. The associated changes in (2'',5'')oligoadenylate [(2'',5'')oligo(A)] pathway were measured under growth-inhibitory conditions. Upon 1-day exposure to 25-200 U/ml of IFN-.gamma., (2'',5'')oligo(A) synthetase activity was induced 10-15 fold and remained elevated for 3 days, whereas (2'',5'')oligo(A) phosphodiesterase activity remained unchanged. There was no detectable increase in intracellular (2'',5'')oligo(A) levels after IFN-.gamma. treatment and ribosomal RNA degradation was not observed. Accompanying 1-day treatment with IFN-.gamma. (100 U/ml) was an induction of a polyamine-dependent protein kinase, which was double-stranded RNA-independent and phosphorylated endogenous polypeptides with MW of 68,000 and 72,000. A similar exposure of cells to IFN-.gamma. (25-100 U/ml) resulted in 30-70% inhibition of ornithine decarboxylase activity; however, no significant alteration in intracellular polyamine levels was observed. IFN-.gamma.-dependent toxicity is probably not related to (2'',5'')oligo(A) activation of a latent endoribonuclease but is accompanied by protein phosphorylation, which is, in part, stimulated by exogenous polyamines.