Tumor-suppressor effect of interferon regulatory factor-1 in human hepatocellular carcinoma.

IFN regulatory factor-1 (IRF-1) regulates the IFN system, inhibits cell growth, and has tumor-suppressor activities. p21 is a universal cyclin-dependent kinase inhibitor, the induction of which depends on both p53 and IRF-1 in mouse embryonic fibroblasts. The expression of p21 in hepatocellular carcinomas (HCCs) is regulated by wild-type p53. We examined the expressions of IRF-1 and p21 in 32 HCCs by quantitative reverse transcription-PCR and the mutation p53 gene in 32 HCCs by single-strand conformation polymorphism and direct sequencing. The expression of IRF-1 mRNA in 15 of 32 HCCs was lower than that in adjacent noncancerous tissue. IRF-1 mRNA expression was reduced in 0 of 3 specimens of well-differentiated HCC, 9 of 21 (42%) specimens of moderately differentiated HCC, and 6 of 8 (75%) specimens of poorly differentiated HCC. IRF-1 mRNA expression was significantly lower in tumors with portal thrombus than in those without portal thrombus (P = 0.003). p53 mutations were detected in 7 of 32 HCCS: p21 expression was reduced in 6 of the 7 (86%) HCCs with p53 mutations. In contrast, p21 expression was reduced in 13 of 25 (52%) HCCs with wild-type p53. IRF-1 expression was reduced in 7 of 13 (53%) HCCs with both wild-type p53 and reduced expression of p21. These results suggest that IRF-1 may be a tumor-suppressor gene for HCC and that IRF-1 is related to p21 expression in HCC with wild-type p53.