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Mol. Cell. Biol., 08 1997, 4208-4219, Vol 17, No. 8
B Viollet, A Kahn and M Raymondjean
Hepatocyte nuclear factor 4 (HNF4), a liver-enriched transcription factor
of the nuclear receptor superfamily, is critical for development and
liver-specific gene expression. Here, we demonstrate that its DNA- binding
activity is modulated posttranslationally by phosphorylation in vivo, ex
vivo, and in vitro. In vivo, HNF4 DNA-binding activity is reduced by
fasting and by inducers of intracellular cyclic AMP (cAMP) accumulation. A
consensus protein kinase A (PKA) phosphorylation site located within the A
box of its DNA-binding domain has been identified, and its role in
phosphorylation-dependent inhibition of HNF4 DNA- binding activity has been
investigated. Mutants of HNF4 in which two potentially phosphorylatable
serines have been replaced by either neutral or charged amino acids were
able to bind DNA in vitro with affinity similar to that of the wild-type
protein. However, phosphorylation by PKA strongly repressed the binding
affinity of the wild-type factor but not that of HNF4 mutants. Accordingly,
in transfection assays, expression vectors for the mutated HNF4 proteins
activated transcription more efficiently than that for the wild-type
protein-when cotransfected with the PKA catalytic subunit expression
vector. Therefore, HNF4 is a direct target of PKA which might be involved
in the transcriptional inhibition of liver genes by cAMP inducers.
Copyright © 1997, American Society for Microbiology
Protein kinase A-dependent phosphorylation modulates DNA-binding activity of hepatocyte nuclear factor 4
Institut Cochin de Genetique Moleculaire, U.129 INSERM, Universite Rene Descartes, Paris, France.
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