Interferon regulatory factor-1 (IRF-1) is a transcriptional 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 septic stimuli. We have identified IRF-1 expression in hepatocytes in vivo in sepsis. The purpose of this study was to characterize the cytokine signals that up-regulate IRF-1 messenger RNA (mRNA) in cultured hepatocytes.Rat hepatocytes were isolated by in situ collagenase perfusion and stimulated in vitro with cytokines. IRF-1 mRNA levels were determined by Northern blot hybridization with a DNA probe for hepatocyte IRF-1 generated with reverse transcription polymerase chain reaction with custom-designed oligonucleotide primers based on the known sequence for T-cell IRF-1.Northern blot of hepatocyte RNA showed a single IRF-1 mRNA band at approximately 2.4 Kb. The mRNA levels were markedly up-regulated (vs control hepatocytes) 2 hours after in vitro stimulation with the cytokines interferon-gamma (17-fold), tumor necrosis factor-alpha (3-fold), and interleukin-1 beta (2-fold). Lipopolysaccharide had no direct effect.The results showed that IRF-1 is up-regulated in hepatocytes primarily in response to interferon-gamma and to a lesser extent after tumor necrosis factor-alpha or interleukin-1 beta stimulation. This suggests that IRF-1 plays a role in regulating liver gene expression in sepsis; however, the specific genes controlled by IRF-1 remain to be determined.