The caudal-related homeodomain protein Cdx-2/3 regulates glucagon gene expression in islet cells.
Glucagon gene transcription in the endocrine pancreas is regulated by at least four cis-acting DNA control elements. We showed previously that G1 is critical for alpha cell-specific expression. G1 contains three AT-rich sequences important for promoter function, which represent candidate binding sites for homeodomain transcription factors. Performing reverse transcription-polymerase chain reaction amplifications with degenerate oligonucleotide primers homologous to the Antennapedia homeobox, cDNA clones corresponding to the caudal-related gene cdx-2/3 were predominantly obtained from glucagon-producing cells and primary non-beta cells. From RNase protection and polymerase chain reaction analyses, cdx-2/3 turned out to be the only caudal-related gene that is expressed at significant levels in cells of the endocrine pancreas. Cdx-2/3 binds with high affinity to an AT-rich motif of G1, which matches the consensus binding site of caudal-related proteins. In the glucagon-producing hamster cell line InR1G9, Cdx-2/3 is a subunit of complex B3 formed on G1. Alternative splicing generates two cdx-2/3 transcripts in islet cells, coding for a full-length protein and an amino-terminally truncated isoform. Although both isoforms bind G1 with similar affinity, only the full-length Cdx-2/3 A protein activates glucagon gene transcription in non-glucagon-producing cells, transcriptional activation being dose-dependent. We therefore conclude that the caudal-related gene cdx-2/3 is implicated in the transcriptional control of glucagon gene expression in the alpha cells of the islets of Langerhans.
Clinical Diabetology, Department of Medicine, Centre Médical Universitaire, 1 rue Michel Servet, CH-1211 Geneva 4, Switzerland. Laser@cmu.unige.ch
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Laser
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Meda
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Philippe
D017398:Alternative Splicing; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D006224:Cricetinae; D005786:Gene Expression Regulation / Q000502:physiology*; D005801:Genes, Homeobox; D005934:Glucagon / Q000235:genetics*; D018398:Homeodomain Proteins / Q000502:physiology*; D007515:Islets of Langerhans / Q000166:cytology / Q000378:metabolism*; D008647:Mesocricetus; D008969:Molecular Sequence Data; D009838:Oligodeoxyribonucleotides; D011401:Promoter Regions, Genetic; D012333:RNA, Messenger / Q000235:genetics; D051381:Rats; D015533:Transcriptional Activation
D018398:Homeodomain Proteins; D009838:Oligodeoxyribonucleotides; D012333:RNA, Messenger; D005934:Glucagon