Liver enriched transcription factors and differentiation of hepatocellular carcinoma.

The development of a complex organism relies on the precise temporal and spacial expression of its genome in many different cell types. The unique phenotype of hepatocytes arises from the expression of genes in a liver specific fashion, which is controlled primarily at the level of mRNA synthesis. By analysing DNA sequences implicated in liver specific transcription, it has been possible to identify members of the nuclear proteins, such as the liver enriched transactivating factors, hepatic nuclear factor 1(HNF-1), HNF-3, HNF-4, HNF-6, CCAAT/enhancer binding protein (C/EBP), and D binding protein (DBP), which are key elements in the liver specific transcriptional regulation of genes. Each of these factors is characterised by DNA binding domains that bind to unique DNA sequences (cis-acting factors) in the promoter and enhancer regions of genes expressed in terminally differentiated hepatocytes (such as, albumin, alpha 1-antitrypsin, transthyretin, alpha-fetoprotein). The determination of the tissue distribution of these factors and analysis of their hierarchical relations has led to the hypothesis that the cooperation of liver enriched transcription factors with the ubiquitous transactivating factors is necessary, and possibly even sufficient, for the maintenance of liver specific gene transcription. With the increase in information about transcriptional regulation, it should be possible to evaluate fully the clinicopathological usefulness of transcription factors in the diagnosis and treatment of hepatocellular carcinoma.