Recruitment of hepatocyte nuclear factor 4 into specific intranuclear compartments depends on tyrosine phosphorylation that affects its DNA-binding and transactivation potential.
Hepatocyte nuclear factor 4 (HNF-4) is a prominent member of the family of liver-enriched transcription factors, playing a role in the expression of a large number of liver-specific genes. We report here that HNF-4 is a phosphoprotein and that phosphorylation at tyrosine residue(s) is important for its DNA-binding activity and, consequently, for its transactivation potential both in cell-free systems and in cultured cells. Tyrosine phosphorylation did not affect the transport of HNF-4 from the cytoplasm to the nucleus but had a dramatic effect on its subnuclear localization. HNF-4 was concentrated in distinct nuclear compartments, as evidenced by in situ immunofluorescence and electron microscopy. This compartmentalization disappeared when tyrosine phosphorylation was inhibited by genistein. The correlation between the intranuclear distribution of HNF-4 and its ability to activate endogenous target genes demonstrates a phosphorylation signal-dependent pathway in the regulation of transcription factor activity.
Ktistaki
E
E
Institute of Molecular Biology and Biotechnology, Foundation for Research and Technology, Herakleion Crete, Greece.
Ktistakis
N T
NT
Papadogeorgaki
E
E
Talianidis
I
I
D000818:Animals; D001692:Biological Transport; D002451:Cell Compartmentation / Q000187:drug effects; D002467:Cell Nucleus / Q000378:metabolism* / Q000648:ultrastructure; D002478:Cells, Cultured; D003593:Cytoplasm / Q000378:metabolism; D004247:DNA / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D019084:Fluorescent Antibody Technique, Indirect; D019833:Genistein; D051557:Hepatocyte Nuclear Factor 4; D007529:Isoflavones / Q000494:pharmacology; D010750:Phosphoproteins / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation / Q000187:drug effects; D011485:Protein Binding; D011505:Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors; D011994:Recombinant Proteins / Q000378:metabolism; D015534:Trans-Activators / Q000378:metabolism; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D015533:Transcriptional Activation; D014162:Transfection
D004268:DNA-Binding Proteins; D004791:Enzyme Inhibitors; D051557:Hepatocyte Nuclear Factor 4; D007529:Isoflavones; D010750:Phosphoproteins; D011994:Recombinant Proteins; D015534:Trans-Activators; D014157:Transcription Factors; D004247:DNA; D019833:Genistein; D011505:Protein-Tyrosine Kinases