An mRNA Splice Variant of the AFX Gene with Altered Transcriptional Activity

• Published in: The Journal of biological chemistry 2002-03, Vol.277 (10), p.8068-8075
• Main Authors: Yang, Zhenyu, Whelan, James, Babb, Robert, Bowen, Benjamin R.
• Format: Article
• Language: English
• Subjects: AFX gene; Alternative Splicing; Aminoimidazole Carboxamide - analogs & derivatives; Aminoimidazole Carboxamide - pharmacology; Base Sequence; Blotting, Western; Cell Cycle Proteins; Cell Line; Cloning, Molecular; DNA - metabolism; DNA, Complementary - metabolism; Dose-Response Relationship, Drug; Forkhead Transcription Factors; G6Pase gene; Genes, Reporter; Histidine - chemistry; Humans; Hypoglycemic Agents - pharmacology; IGFBP-1 gene; Insulin - metabolism; Insulin - pharmacology; Molecular Sequence Data; Oligonucleotides - metabolism; PEPCK gene; phosphoenolpyruvate carboxykinase; Phosphorylation; Plasmids - metabolism; Polymerase Chain Reaction; Promoter Regions, Genetic; Protein Binding; Protein Isoforms; Protein-Serine-Threonine Kinases; Proto-Oncogene Proteins - metabolism; Proto-Oncogene Proteins c-akt; Ribonucleotides - pharmacology; RNA, Messenger - metabolism; Signal Transduction; Subcellular Fractions - metabolism; Tissue Distribution; Transcription Factors - chemistry; Transcription Factors - genetics; Transcription, Genetic; Transfection; Vanadates - pharmacology
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M106091200

Several studies indicate that FKHR and AFX, mammalian homologues of the Caenorhabditis elegans forkhead transcription factor DAF-16, function in the insulin signaling pathway. Here we describe the discovery of a novel AFX isoform, which we designated AFXζ, in which the first 16 amino acids of the forkhead domain are not present. PCR analysis showed that this isoform is most abundant in the liver, kidney, and pancreas. In HepG2 cells, overexpressed AFXζ induced reporter gene activity through the insulin-responsive sequences of the phosphoenolpyruvate carboxykinase (PEPCK), IGFBP-1, andG6Pase promoters. AFXζ−mediated stimulation was repressed by insulin treatment, by bisperoxovanadate treatment, and by overexpression of constitutively active protein kinase B (PKB). Insulin treatment and PKB overexpression resulted in phosphorylation of AFXζ. Furthermore, 5-aminoimidazole-4-carboxamide-1-β-d-ribofuranoside (AICAR), an AMP-activated protein kinase activator, repressed AFXζ-dependent reporter activation. Taken together, these findings suggest that AFXζ is a downstream target of both the phosphatidylinositol 3-kinase/PKB insulin signaling pathway and an AMP-activated protein kinase-dependent pathway.