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 stimul ation with endotoxin or viruses. This tumor necrosis factor-alpha synt hesis is suppressed by prostaglandin E(2) or dexamethasone. Using Nort hern blotting and reverse transcriptase-polymerase chain reaction, it is demonstrated that endotoxin-induced tumor necrosis factor-a synthes is is blocked by prostaglandin E(2) or dibutyryl 3':5'-cyclic adenosin e monophosphate on the transcriptional level. Tumor necrosis factor-al pha itself suppressed endotoxin-evoked tumor necrosis factor-alpha mRN A expression when given in a narrow time interval with lipopolysacchar ide. Interleukin-10 of human or mouse origin also inhibited the synthe sis of tumor necrosis factor-alpha mRNA and protein when given more th an 2 h prior to the endotoxin challenge. The suppressive effect of pro staglandin E(2) lasted for more than 36 h while IL-10 blocked tumor ne crosis factor-a production for barely 24 h. Dexamethasone reduced the endotoxin-induced tumor necrosis factor-alpha mRNA formation by approx imately 50% only, although it led to nearly complete inhibition of the synthesis of the mature protein. Taken together with reverse transcri ptase-polymerase chain reaction data revealing significant amounts of tumor necrosis factor-alpha mRNA in resting Kupffer cells, an addition al posttranscriptional regulation of tumor necrosis factor-alpha synth esis has to be assumed. Tumor necrosis factor-alpha mRNA was not induc ed by interferon-gamma, interleukin-1 beta or interleukin-6 (the latte r two cytokines are also synthesized by Kupffer cells), but a 24-h pre stimulation of liver macrophages with interferon-gamma or phorbol este r had a modest priming effect. Other substances known to stimulate rat Kupffer cells, such as phorbol ester or calcium ionophore, did not le ad to the induction of tumor necrosis factor-alpha or to an alteration of the lipopolysaccharide-induced tumor necrosis factor-alpha mRNA sy nthesis at 90 min or 24 h after stimulation. Comparison with findings on tumor necrosis factor-alpha mRNA synthesis in some macrophage-relat ed cell lines, monocytes and freshly differentiated macrophages sugges ts that organ-specific differentiation of resident macrophages leads t o;variations in the regulation of tumor necrosis factor-alpha mRNA pro duction. (C) Journal of Hepatology.