CYTOKINE INDUCTION OF INTERFERON REGULATORY FACTOR-I IN HEPATOCYTES

Background. Interferon regulatory factor-1 (IRF-1) is a transcriptiona l factor originally cloned from fibroblasts that activates interferons and certain interferon-responsive genes. Because IRF-1 is an ''early- immediate'' nuclear protein, it can function acutely after trauma or s eptic stimuli. We have identified IRF-1 expression in hepatocytes in v ivo in sepsis. The purpose of this study was to characterize the cytok ine signals that up-regulate IRF-1 messenger RNA (mRNA) in cultured he patocytes. Methods. Rat hepatocytes were isolated by in situ collagena se perfusion and stimulated in vitro with cytokines. IRF-1 mRNA levels were determined by Northern blot hybridization with a DNA probe for h epatocyte IRF-1 generated with reverse transcription polymerase chain reaction with custom-designed oligonucleotide primers based on the kno wn sequence for T-cell IRF-1. Results. Northern blot of hepatocyte RNA showed a single IRF-1 mRNA band at -2.4 Kb. The mRNA levels were mark edly up-regulated (vs control hepatocytes) 2 hours after in vitro stim ulation with the cytokines interferon-gamma (17-fold), tumor necrosis factor-a (3-fold), and interleukin-1beta (2-fold). Lipopolysaccharide had no direct effect. Conclusions. The results showed that IRF-1 is up -regulated in hepatocytes primarily in response to interferon-gamma an d to a lesser extent after tumor necrosis factor-a or interleukin-1bet a stimulation. This suggests that IRF-1 plays a role in regulating liv er gene expression in sepsis; however, the specific genes controlled b y IRF-1 remain to be determined.