A bipartite activation domain is responsible for the activity of transcription factor HNF1/LFB1 in cells of hepatic and nonhepatic origin.
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.
Toniatti
C
C
I.R.B.M.-Istituto di Ricerche di Biologia Molecolare P. Angeletti, Rome, Italy.
Monaci
P
P
Nicosia
A
A
Cortese
R
R
Ciliberto
G
G
D000595:Amino Acid Sequence; D001483:Base Sequence; D001665:Binding Sites; D004252:DNA Mutational Analysis; D004268:DNA-Binding Proteins / Q000502:physiology; D004848:Epithelium / Q000378:metabolism; D006367:HeLa Cells; D051537:Hepatocyte Nuclear Factor 1; D051538:Hepatocyte Nuclear Factor 1-alpha; D051539:Hepatocyte Nuclear Factor 1-beta; D006801:Humans; D008099:Liver / Q000378:metabolism; D008969:Molecular Sequence Data; D009687:Nuclear Proteins; D009928:Organ Specificity; D011993:Recombinant Fusion Proteins; D013329:Structure-Activity Relationship; D014157:Transcription Factors / Q000737:chemistry*; D014158:Transcription, Genetic / Q000502:physiology; D014407:Tumor Cells, Cultured
D004268:DNA-Binding Proteins; C496487:HNF1A protein, human; C496495:HNF1B protein, human; D051538:Hepatocyte Nuclear Factor 1-alpha; D009687:Nuclear Proteins; D011993:Recombinant Fusion Proteins; D014157:Transcription Factors; D051537:Hepatocyte Nuclear Factor 1; D051539:Hepatocyte Nuclear Factor 1-beta