[HTML][HTML] Differential regulation of gene expression by insulin and IGF-1 receptors correlates with phosphorylation of a single amino acid residue in the forkhead …

J Nakae, V Barr, D Accili - The EMBO journal, 2000 - embopress.org
J Nakae, V Barr, D Accili
The EMBO journal, 2000embopress.org
The transcription factor FKHR is inhibited by phosphorylation in response to insulin and IGF-
1 through Akt kinase. Here we show that FKHR phosphorylation in hepatocytes conforms to
a hierarchical pattern in which phosphorylation of the Akt site at S 253, in the forkhead DNA
binding domain, is a prerequisite for the phosphorylation of two additional potential Akt sites,
T 24 and S 316. Using insulin receptor-deficient hepatocytes, we show that T 24 fails to be
phosphorylated by IGF-1 receptors, suggesting that this residue is targeted by a kinase …
The transcription factor FKHR is inhibited by phosphorylation in response to insulin and IGF-1 through Akt kinase. Here we show that FKHR phosphorylation in hepatocytes conforms to a hierarchical pattern in which phosphorylation of the Akt site at S 253, in the forkhead DNA binding domain, is a prerequisite for the phosphorylation of two additional potential Akt sites, T 24 and S 316. Using insulin receptor-deficient hepatocytes, we show that T 24 fails to be phosphorylated by IGF-1 receptors, suggesting that this residue is targeted by a kinase specifically activated by insulin receptors. Lack of T 24 phosphorylation is associated with the failure of IGF-1 to induce nuclear export of FKHR, and to inhibit expression of a reporter gene under the transcriptional control of the IGF binding protein-1 insulin response element. We propose that site-specific phosphorylation of FKHR is one of the mechanisms by which insulin and IGF-1 receptors exert different effects on gene expression.
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