Insulin Inhibits the Activation of Transcription by a C-terminal Fragment of the Forkhead Transcription Factor FKHR

Minoru Tomizawa, Amit Kumar, Valérie Perrot, Jun Nakae, Domenico Accili, Matthew M. Rechler
2000 Journal of Biological Chemistry  
The forkhead rhabdomyosarcoma transcription factor (FKHR) is a promising candidate to be the transcription factor that binds to the insulin response element of the insulin-like growth factor-binding protein-1 (IGF-BP-1) promoter and mediates insulin inhibition of IGF-BP-1 promoter activity. Cotransfection of mouse FKHR increased IGFBP-1 promoter activity 2-3-fold in H4IIE rat hepatoma cells; insulin inhibited FKHR-stimulated promoter activity ϳ70%. A C-terminal fragment of mouse FKHR (residues
more » ... 08 -652) that contains the transcription activation domain fused to a Gal4 DNA binding domain potently stimulated Gal4 promoter activity. Insulin inhibited FKHR fragment-stimulated promoter activity by ϳ70%. Inhibition was abolished by coincubation with the phosphatidylinositol-3 kinase inhibitor, LY294002. The FKHR 208 -652 fragment contains two consensus sites for phosphorylation by protein kinase B (PKB)/Akt, Ser-253 and Ser-316. Neither site is required for insulin inhibition of promoter activity stimulated by the FKHR fragment, and overexpression of Akt does not inhibit FKHR fragment-stimulated Gal4 promoter activity. These results suggest that insulin-and phosphatidylinositol-3 kinase-dependent phosphorylation of another site in the fragment by a kinase different from PKB/Akt inhibits transcription activation by the fragment. Phosphorylation of this site also may be involved in insulin inhibition of transcription activation by full-length FKHR, but only after phosphorylation of Ser-253 by PKB/Akt.
doi:10.1074/jbc.275.10.7289 pmid:10702299 fatcat:zk4leyrtt5b37ojtqw2yxr6kha