Hepatocyte nuclear factor-4 is a novel downstream target of insulin via FKHR as a signal-regulated transcriptional inhibitor.
Previous studies have shown that FKHR, a member of the forkhead family of transcription factors, acts as a DNA binding-independent cofactor of nuclear receptors, including estrogen, retinoid, and thyroid hormone receptors, in addition to the original function as a DNA binding transcription factor that redistributes from the nucleus to the cytoplasm by insulin-induced phosphorylation. Here, we demonstrated the physical interaction of FKHR with hepatocyte nuclear factor (HNF)-4, a member of steroid/thyroid nuclear receptor superfamily, and the repression of HNF-4 transactivation by FKHR. FKHR interacted with the DNA binding domain of HNF-4 and inhibited HNF-4 binding to the cognate DNA. Furthermore, the binding affinity of HNF-4 with phosphorylated FKHR significantly decreased in comparison to that with unphosphorylated FKHR. Therefore, a phosphorylation of FKHR by insulin followed by its dissociation from HNF-4 and the redistribution of FKHR from the nucleus to the cytoplasm would expect to induce the transcriptional activation of HNF-4 by facilitating to the access of HNF-4 to its DNA element. Indeed, most intriguingly, insulin stimulation reversed the repression of HNF-4 transcriptional activity by phosphorylation-sensitive (wild-type) FKHR, but not by phosphorylation-deficient FKHR. These results suggest that insulin regulates the transcriptional activity of HNF-4 via FKHR as a signal-regulated transcriptional inhibitor.
Hirota
Keiko
K
Center of Tsukuba Advanced Research Alliance, Institute of Applied Biochemistry, University of Tsukuba, Tsukuba, Ibaraki 305-8577, Japan.
Daitoku
Hiroaki
H
Matsuzaki
Hitomi
H
Araya
Natsumi
N
Yamagata
Kazuyuki
K
Asada
Sachie
S
Sugaya
Takeshi
T
Fukamizu
Akiyoshi
A
D051778:Basic Helix-Loop-Helix Leucine Zipper Transcription Factors; D003001:Cloning, Molecular; D004268:DNA-Binding Proteins / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D000071161:Forkhead Box Protein O1; D051858:Forkhead Transcription Factors; D005786:Gene Expression Regulation; D051557:Hepatocyte Nuclear Factor 4; D006801:Humans; D007328:Insulin / Q000494:pharmacology / Q000502:physiology*; D016296:Mutagenesis; D010750:Phosphoproteins / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation; D011485:Protein Binding; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D017384:Sequence Deletion; D014157:Transcription Factors / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic; D015533:Transcriptional Activation; D014162:Transfection; D014407:Tumor Cells, Cultured
D051778:Basic Helix-Loop-Helix Leucine Zipper Transcription Factors; D004268:DNA-Binding Proteins; C085126:FOXO1 protein, human; D000071161:Forkhead Box Protein O1; D051858:Forkhead Transcription Factors; D051557:Hepatocyte Nuclear Factor 4; D007328:Insulin; C403128:MLX protein, human; D010750:Phosphoproteins; D011993:Recombinant Fusion Proteins; D014157:Transcription Factors