Critical structural elements and multitarget protein interactions of the transcriptional activator AF-1 of hepatocyte nuclear factor 4.
The nuclear receptor hepatocyte nuclear factor 4 (HNF-4) is an important regulator of several genes involved in diverse metabolic and developmental pathways. Mutations in the HNF-4A gene are responsible for the maturity-onset diabetes of the young type 1. Recently, we showed that the 24 N-terminal residues of HNF-4 function as an acidic transcriptional activator, termed AF-1 (Hadzopoulou-Cladaras, M., Kistanova, E., Evagelopoulou, C., Zeng, S. , Cladaras C., and Ladias, J. A. A. (1997) J. Biol. Chem. 272, 539-550). To identify the critical residues for this activator, we performed an extensive genetic analysis using site-directed mutagenesis. We showed that the aromatic and bulky hydrophobic residues Tyr6, Tyr14, Phe19, Lys10, and Lys17 are essential for AF-1 function. To a lesser degree, five acidic residues are also important for optimal activity. Positional changes of Tyr6 and Tyr14 reduced AF-1 activity, underscoring the importance of primary structure for this activator. Our analysis also indicated that AF-1 is bipartite, consisting of two modules that synergize to activate transcription. More important, AF-1 shares common structural motifs and molecular targets with the activators of the tumor suppressor protein p53 and NF-kappaB-p65, suggesting similar mechanisms of action. Remarkably, AF-1 interacted specifically with multiple transcriptional targets, including the TATA-binding protein; the TATA-binding protein-associated factors TAFII31 and TAFII80; transcription factor IIB; transcription factor IIH-p62; and the coactivators cAMP-responsive element-binding protein-binding protein, ADA2, and PC4. The interaction of AF-1 with proteins that regulate distinct steps of transcription may provide a mechanism for synergistic activation of gene expression by AF-1.
Green
V J
VJ
Gene Regulation Laboratory and Macromolecular Crystallography Unit, Division of Experimental Medicine, Department of Medicine, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, Massachusetts 02115, USA.
Kokkotou
E
E
Ladias
J A
JA
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D051778:Basic Helix-Loop-Helix Leucine Zipper Transcription Factors; D019556:COS Cells; D017931:DNA Primers; D004268:DNA-Binding Proteins; D051557:Hepatocyte Nuclear Factor 4; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D010750:Phosphoproteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D011485:Protein Binding; D051381:Rats; D015534:Trans-Activators / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D014157:Transcription Factors / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
D051778:Basic Helix-Loop-Helix Leucine Zipper Transcription Factors; D017931:DNA Primers; D004268:DNA-Binding Proteins; D051557:Hepatocyte Nuclear Factor 4; C403128:MLX protein, human; D010750:Phosphoproteins; D015534:Trans-Activators; D014157:Transcription Factors