A bipartite activation domain is responsible for the activity of transcription factor HNF1/LFB1 in cells of hepatic and nonhepatic origin.

ABSTRACT

HNF1/LFB1 is a transcription factor that controls the expression of several liver-specific genes. Previous in vitro experiments allowed us to identify two different regions in the carboxy-terminal portion of the protein responsible for most of the transcription activation potential the first, ADI, between amino acids 546 and 628 and the second, ADII, between amino acids 281 and 318. To characterize the molecular anatomy of HNF1/LFB1 better, we have analyzed its trans-activating properties in vivo. Several HNF1/LFB1 deletion mutants were tested for their ability to induce transcription from HNF1/LFB1-dependent synthetic promoters in cells of hepatic and nonhepatic origin. These last recipient cells provide an HNF1/LFB1-deficient environment that is useful for a precise quantification of the recombinant protein. Our results confirm the importance of ADI and indicate that no activating property can be assigned to ADII in vivo. Moreover, a novel glutamine/proline-rich activation domain (ADIII) has been identified between amino acids 440 and 506. These findings are confirmed by domain-swapping experiments, carried out with the heterologous GAL4 DNA-binding domain, which also show that the activity of each individual activation domain is influenced by combining adjacent HNF1/LFB1 sequences. The data presented indicate that HNF1/LFB1 transcription activating potential relies on a complex structure and also provide important clues to understanding the different functions exerted by transcription factors of this family.