REGULATION OF THE MESSENGER-RNA EXPRESSION FOR TUMOR-NECROSIS-FACTOR-ALPHA IN RAT-LIVER MACROPHAGES

Kupffer cells are known to produce tumor necrosis factor-a upon stimulation with endotoxin or viruses. This tumor necrosis factor-alpha synthesis is suppressed by prostaglandin E(2) or dexamethasone. Using Northern blotting and reverse transcriptase-polymerase chain reaction, it is demonstrated that endotoxin-induced tumor necrosis factor-a synthesis is blocked by prostaglandin E(2) or dibutyryl 3':5'-cyclic adenosine monophosphate on the transcriptional level. Tumor necrosis factor-alpha itself suppressed endotoxin-evoked tumor necrosis factor-alpha mRNA expression when given in a narrow time interval with lipopolysaccharide. Interleukin-10 of human or mouse origin also inhibited the synthesis of tumor necrosis factor-alpha mRNA and protein when given more than 2 h prior to the endotoxin challenge. The suppressive effect of prostaglandin E(2) lasted for more than 36 h while IL-10 blocked tumor necrosis factor-a production for barely 24 h. Dexamethasone reduced the endotoxin-induced tumor necrosis factor-alpha mRNA formation by approximately 50% only, although it led to nearly complete inhibition of the synthesis of the mature protein. Taken together with reverse transcriptase-polymerase chain reaction data revealing significant amounts of tumor necrosis factor-alpha mRNA in resting Kupffer cells, an additional posttranscriptional regulation of tumor necrosis factor-alpha synthesis has to be assumed. Tumor necrosis factor-alpha mRNA was not induced by interferon-gamma, interleukin-1 beta or interleukin-6 (the latter two cytokines are also synthesized by Kupffer cells), but a 24-h prestimulation of liver macrophages with interferon-gamma or phorbol ester had a modest priming effect. Other substances known to stimulate rat Kupffer cells, such as phorbol ester or calcium ionophore, did not lead to the induction of tumor necrosis factor-alpha or to an alteration of the lipopolysaccharide-induced tumor necrosis factor-alpha mRNA synthesis at 90 min or 24 h after stimulation. Comparison with findings on tumor necrosis factor-alpha mRNA synthesis in some macrophage-related cell lines, monocytes and freshly differentiated macrophages suggests that organ-specific differentiation of resident macrophages leads to;variations in the regulation of tumor necrosis factor-alpha mRNA production. (C) Journal of Hepatology.