The distal enhancer implicated in the developmental regulation of the tyrosine aminotransferase gene is bound by liver-specific and ubiquitous factors.
Tyrosine aminotransferase gene expression is confined to parenchymal cells of the liver, is inducible by glucocorticoids and glucagon, and is repressed by insulin. Three enhancers control this tissue-specific and hormone-dependent activity, one of which, located at -11 kb, is implicated in establishing an active expression domain. We have studied in detail this important regulatory element and have identified a 221-bp fragment containing critical enhancer sequences which stimulated the heterologous thymidine kinase promoter more than 100-fold in hepatoma cells. Within this region, we have characterized two essential liver-specific enhancer domains, one of which was bound by proteins of the hepatocyte nuclear factor 3 (HNF3) family. Analyses with the dedifferentiated hepatoma cell line HTC suggested that HNF3 alpha and/or -gamma, but not HNF3 beta, are involved in activating the tyrosine aminotransferase gene via the -11-kb enhancer. Genomic footprinting and in vitro protein-DNA binding studies documented cell-type-specific binding of ubiquitous factors to the second essential enhancer domain, which by itself stimulated the thymidine kinase promoter preferentially in hepatoma cells. These results will allow further characterization of the role of these enhancer sequences in developmental activation of the tyrosine aminotransferase gene.
Nitsch
D
D
Division Molecular Biology of the Cell I, German Cancer Research Center, Heidelberg.
Schütz
G
G
D000818:Animals; D001483:Base Sequence; D002460:Cell Line; D004252:DNA Mutational Analysis; D004268:DNA-Binding Proteins / Q000378:metabolism; D004742:Enhancer Elements, Genetic; D015971:Gene Expression Regulation, Enzymologic; D051541:Hepatocyte Nuclear Factor 3-alpha; D051542:Hepatocyte Nuclear Factor 3-beta; D008099:Liver / Q000201:enzymology*; D008113:Liver Neoplasms / Q000235:genetics; D008114:Liver Neoplasms, Experimental / Q000235:genetics; D008969:Molecular Sequence Data; D009687:Nuclear Proteins / Q000378:metabolism; D009838:Oligodeoxyribonucleotides / Q000737:chemistry; D017354:Point Mutation; D051381:Rats; D012045:Regulatory Sequences, Nucleic Acid; D015183:Restriction Mapping; D017384:Sequence Deletion; D014157:Transcription Factors; D014444:Tyrosine Transaminase / Q000235:genetics*
D004268:DNA-Binding Proteins; C496501:Foxa1 protein, rat; C496504:Foxa2 protein, rat; D051541:Hepatocyte Nuclear Factor 3-alpha; D009687:Nuclear Proteins; D009838:Oligodeoxyribonucleotides; D014157:Transcription Factors; D051542:Hepatocyte Nuclear Factor 3-beta; D014444:Tyrosine Transaminase