IRF-1 and p65 mediate upregulation of constitutive HLA-A antigen expression by hepatocellular carcinoma cells.

Malignant transformation of hepatocytes is frequently associated with upregulation of HLA-A expression. Currently there is no information available regarding the mechanisms underlying this phenotypic change. We investigated HLA-A expression in 165 paraffin embedded tissues and 21 fresh tissues from liver cancer patients. Utilizing truncated HLA-A promoter-reporter constructs and gel-shift assay we had identified the regulatory elements and transcription factors required for HLA-A upregulation. 54% of the paraffin embedded tissues showed increased HLA-A expression in their cancerous part. 43% of the fresh liver cancer tissues had increased HLA-A complex expression with the HLA-A heavy chain gene demonstrating the highest level of upregulation (62%). Enhanced HLA-A expression in the liver cell lines QGY7701 and BEL7402 was found to be mediated by binding of interferon regulatory factor 1 (IRF-1) to interferon stimulated response element, and of nuclear transcription factor p65 binding to enhancer A element in the HLA-A promoter of these cell lines. The in vivo relevance of these findings was indicated by the association of the enhanced expression of IRF-1 and accumulation of nuclear p65 with HLA-A upregulation in 8 of the 21 liver cancer lesions investigated. Our results indicated that HLA-A upregulation in liver cancer was mediated by both increased nuclear aggregation of transcription factor p65 and upregulation of transcription factor IRF-1.