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Activation of human monocyte-derived macrophages by interferon gamma is accompanied by increase of poly(ADP-ribose)
G Berton1, C Sorio, C Laudanna
1Institute of General Pathology, University of Verona, Italy.
Abstract:
We have investigated poly(ADP-ribosyl)ation processes in human monocyte-derived macrophages and the effect of the activating cytokine, interferon gamma (IFN-gamma) on these processes. IFN-gamma was shown to increase the activity of poly(ADP-ribose) polymerase in human macrophages. A 2-3-fold enhancement of poly(ADP-ribose) polymerase activity was observed after 3-4 h of incubation with IFN-gamma, whose effects were dose-dependent and maximal at 20-50 U/ml. Staining with anti-poly(ADP-ribose) antibodies and purification of ADP-ribosylated nuclear proteins by affinity chromatography over boronate agarose showed that enhancement of poly(ADP-ribose) polymerase activity by IFN-gamma was accompanied by accumulation of poly(ADP-ribose) polymers in nuclear proteins. The effects of IFN-gamma on poly(ADP-ribose) polymerase activity were not due to an enhanced accumulation of the message for the enzyme, indicating that the activation of the enzyme activity was due to post-transcriptional modifications. IFN-gamma was shown to induce DNA strand breaks in human macrophages. This phenomenon followed the same time-course and was evident with the same doses of IFN-gamma that increased poly(ADP-ribose) polymerase activity. Since poly(ADP-ribose) polymerase is known to require DNA nicks for its activity, the capability of IFN-gamma to induce DNA strand breaks can explain its effects on poly(ADP-ribosyl)ation processes.
Insights
Interferon gamma (IFN-gamma) activates poly(ADP-ribosyl)ation in human macrophages by inducing DNA strand breaks. This post-transcriptional modification enhances poly(ADP-ribose) polymerase activity, leading to polymer accumulation.
Area of Science:
- Immunology
- Molecular Biology
- Cellular Biology
Background:
- Poly(ADP-ribosyl)ation is a crucial post-translational modification involved in DNA repair and gene regulation.
- Interferon gamma (IFN-gamma) is a key cytokine in immune responses, modulating macrophage functions.
- The precise mechanisms by which IFN-gamma influences poly(ADP-ribosyl)ation in macrophages are not fully understood.
Purpose of the Study:
- To investigate the effects of IFN-gamma on poly(ADP-ribosyl)ation processes in human monocyte-derived macrophages.
- To elucidate the relationship between IFN-gamma, poly(ADP-ribose) polymerase activity, and DNA integrity.
Main Methods:
- Human monocyte-derived macrophages were treated with varying doses and durations of IFN-gamma.
- Poly(ADP-ribose) polymerase activity was measured.
- Poly(ADP-ribose) polymer accumulation was assessed using anti-poly(ADP-ribose) antibodies and affinity chromatography.
- DNA strand breaks were detected.
Main Results:
- IFN-gamma significantly increased poly(ADP-ribose) polymerase activity in a dose-dependent manner (maximal at 20-50 U/ml) after 3-4 hours of incubation.
- This enhanced activity correlated with increased poly(ADP-ribose) polymer accumulation in nuclear proteins.
- The observed effects were independent of changes in the enzyme's messenger RNA levels, suggesting post-transcriptional regulation.
- IFN-gamma treatment induced DNA strand breaks in macrophages, mirroring the time-course and dosage of poly(ADP-ribose) polymerase activation.
Conclusions:
- IFN-gamma activates poly(ADP-ribosyl)ation in human macrophages.
- The induction of DNA strand breaks by IFN-gamma is the likely mechanism driving the observed increase in poly(ADP-ribose) polymerase activity.
- These findings highlight a novel role for IFN-gamma in modulating DNA repair pathways via post-transcriptional regulation of poly(ADP-ribosyl)ation.