LIPOPOLYSACCHARIDE-INDUCED CHANGE OF PHOSPHORYLATION OF 2 CYTOSOLIC PROTEINS IN HUMAN MONOCYTES IS PREVENTED BY INHIBITORS OF ADP-RIBOSYLATION

Interaction of LPS with human monocytes causes altered phosphate label ing of cytosolic proteins of 36 kDa and 38 kDa (p36/38). This property , determined by in vitro studies, is shared by other monocyte activato rs. Phosphorylated p36/38 are distinct from p38, 42-kDa, and 44-kDa is oforms of mitogen-activated protein kinases expressed in monocytes. Oc cupation of LPS binding sites by a LPS antagonist, the synthetic tetra acylated bisphosphate precursor of Escherichia coli lipid A (also know n as compound 406, lipid IVa, or precursor Ia), prevents LPS-induced c hanges in the phosphate labeling of the two proteins. Abs against CD14 inhibit protein phosphorylation induced by low concentrations of LPS (10 ng/ml), whereas at high concentrations (1 mu g/ml), the Abs fail t o prevent phosphorylation. In addition to phosphorylation, ADP-ribosyl ation of proteins has been implicated in a number of biologic processe s. Here we show that inhibitors of ADP-ribosylation, namely meta-iodob enzylguanidine and nicotinamide, inhibit LPS-initiated altered phospho rylation of p36/38. This loss of phosphate labeling of p36/38 is accom panied by an inhibition of TNF-alpha and IL-6 mRNA and protein product ion. The synthesis of IL-1 is not affected. This suggests that the inh ibitors interfere with specific steps in IL-6 and TNF-alpha production , which are not required for IL-1 synthesis. Taken together, the data indicate that ADP-ribosylation may be involved in LPS-induced alterati on of the phosphorylation state of two cytosolic proteins (p36/38) and that these proteins modulate cellular processes leading to TNF-alpha and IL-6 release.