Effects of human immune interferon on cell viability, (2',5')oligoadenylate synthesis, and polyamine-dependent
Abstract:
The growth-inhibitory 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 to 200 units/ml) resulted in 30 to 90% growth inhibition and 40 to 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 to 200 units/ml of IFN-gamma, (2',5')oligo(A) synthetase activity was induced 10- to 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 units/ml) was an induction of a polyamine-dependent protein kinase, which was double-stranded RNA-independent and phosphorylated endogenous polypeptides with molecular weights of 68,000 and 72,000. A similar exposure of cells to IFN-gamma (25 to 100 units/ml) resulted in 30 to 70% inhibition of ornithine decarboxylase activity; however, no significant alteration in intracellular polyamine levels was observed. These data suggest that IFN-gamma-dependent toxicity is 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.
Insights
Human immune interferon (IFN-gamma) significantly inhibits HT-29 colon cancer cell growth and DNA, RNA, and protein synthesis. This toxicity is linked to protein phosphorylation, not the (2
Area of Science:
- Molecular Biology
- Cancer Research
- Immunology
Background:
- Human immune interferon (IFN-gamma) is known to possess antiproliferative properties.
- The molecular mechanisms underlying IFN-gamma's effects on cancer cells require further elucidation.
- The HT-29 human colon carcinoma cell line serves as a model for studying cancer cell responses.
Purpose of the Study:
- To investigate the growth-inhibitory effects of IFN-gamma on the HT-29 colon carcinoma cell line.
- To explore the impact of IFN-gamma on cellular synthesis pathways (DNA, RNA, protein).
- To examine the role of the (2',5')oligoadenylate [(2',5')oligo(A)] pathway and protein phosphorylation in IFN-gamma-induced toxicity.
Main Methods:
- HT-29 cells were treated with varying concentrations of IFN-gamma.
- Cell growth, colony formation, and synthesis of DNA, RNA, and protein were measured.
- Activities of (2',5')oligo(A) synthetase and phosphodiesterase were assessed.
- Intracellular (2',5')oligo(A) levels, ribosomal RNA degradation, and protein kinase activity were analyzed.
- Ornithine decarboxylase activity and intracellular polyamine levels were evaluated.
Main Results:
- IFN-gamma treatment caused significant dose-dependent inhibition of HT-29 cell growth (30-90%) and colony formation (40-99%).
- DNA, RNA, and protein synthesis were reduced in a dose-dependent manner following IFN-gamma exposure.
- (2',5')oligo(A) synthetase activity was induced by IFN-gamma, but intracellular (2',5')oligo(A) levels and ribosomal RNA degradation remained unchanged.
- A polyamine-dependent protein kinase was induced, phosphorylating 68,000 and 72,000 molecular weight proteins.
- Ornithine decarboxylase activity was inhibited by IFN-gamma, without significant changes in intracellular polyamine levels.
Conclusions:
- IFN-gamma exhibits potent growth-inhibitory effects on HT-29 colon carcinoma cells.
- The observed toxicity is associated with induced protein phosphorylation rather than activation of the (2',5')oligo(A) pathway.
- Exogenous polyamines may play a role in stimulating the observed protein phosphorylation.
