Role of ADP-ribosylation in activated monocytes/macrophages.

Stimulating monocytes/macrophages with bacterial lipopolysaccharide (LPS) results in TNF-alpha, IL-1, IL-6 and nitrite (NO2-) formation. Inhibitors of poly(ADP-ribose)polymerase inhibit release of these mediators by preventing mRNA expression indicating that ADP-ribosylation plays a crucial role in the synthesis of these mediators. Furthermore we present evidence that ADP-ribosylation is involved in modifying cellular proteins. In murine macrophages a 33 kDa cytosolic protein could be identified that in response to LPS changed its state of ADP-ribosylation, and in human monocytes we showed that the inhibitor nicotinamide prevents LPS induced phosphorylation of two cytosolic proteins of 36 kDa and 38 kDa (p36/38) LPS. Taken together these data indicate that protein modification by ADP-ribosylation may control cellular processes involved in distinct steps of monocyte/macrophage activation.