title: PKA independent and cell type specific activation of the expression of caudal homeobox gene Cdx-2 by cyclic AMP.
abstract: Cdx-2 is a transactivator for the proglucagon gene in pancreatic and intestinal endocrine cells. Cdx-2 is also expressed in differentiated intestinal epithelia of nonendocrine origin. Cdx-2-/- mice are embryonic lethal, while Cdx-2+/- mutants show multiple malfunctions including the formation of intestinal polyps. Within the polyps, the remaining wild type Cdx-2 allele ceases its expression, while the expression of both Cdx-2 and proglucagon in the endocrine cells remains unaltered, indicating that Cdx-2 could be haplo-insufficient for nonendocrine cells, but not for proglucagon producing endocrine cells. We propose that mechanisms underlying Cdx-2 expression and auto-regulation [Xu F, Li H & Jin T (1999), J Biol Chem274, 34310-34316] differ in these two types of cells. We show here that forskolin and cAMP upregulate Cdx-2 expression in proglucagon producing cells, but not in colon cancer cells and primary intestinal cell cultures. It is unlikely that the activation is mainly mediated by PKA, because the activation was observed in a PKA deficient cell line. Co-transfecting a dominant negative Ras expression plasmid substantially repressed the Cdx-2 promoter, in contrast to a previous finding that Ras is a negative factor for Cdx-2 expression in colon cancer cells. Furthermore, forskolin activated ERK1/2 phosphorylation in the endocrine cells, and attenuation of ERK1/2 phosphorylation by its inhibitor is associated with attenuated Cdx-2 expression. Finally, an Epac pathway specific cAMP analogue stimulated both ERK1/2 phosphorylation and Cdx-2 expression. Taken together, our observations suggest that Cdx-2 expression is regulated by the second messenger cAMP, cell-type specifically, via the Epac pathway.
authors.affiliation: Division of Cell and Molecular Biology, Toronto General Research Institute, University Health Network, Toronto, Ontario.
authors.forename: Liang
authors.initials: L
authors.lastname: Chen
authors.forename: Peixiang
authors.initials: P
authors.lastname: Wang
authors.forename: Cristiano F
authors.initials: CF
authors.lastname: Andrade
authors.forename: Ian Y
authors.initials: IY
authors.lastname: Zhao
authors.forename: Philip E
authors.initials: PE
authors.lastname: Dubé
authors.forename: Patricia L
authors.initials: PL
authors.lastname: Brubaker
authors.forename: Mingyao
authors.initials: M
authors.lastname: Liu
authors.forename: Tianru
authors.initials: T
authors.lastname: Jin
mesh_terms: D000818:Animals; D000071616:CDX2 Transcription Factor; D005576:Colforsin / Q000494:pharmacology; D003110:Colonic Neoplasms / Q000378:metabolism / Q000473:pathology; D006224:Cricetinae; D000242:Cyclic AMP / Q000494:pharmacology*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism*; D019858:Enteroendocrine Cells / Q000378:metabolism; D005799:Genes, Dominant; D005934:Glucagon / Q000378:metabolism; D020662:Guanine Nucleotide Exchange Factors / Q000378:metabolism; D018398:Homeodomain Proteins / Q000235:genetics* / Q000378:metabolism*; D006801:Humans; D007413:Intestinal Mucosa / Q000378:metabolism; D007417:Intestinal Polyps / Q000378:metabolism / Q000473:pathology; D007422:Intestines / Q000166:cytology; D007515:Islets of Langerhans / Q000378:metabolism; D051379:Mice; D018345:Mice, Knockout; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D052336:Proglucagon; D011498:Protein Precursors / Q000378:metabolism; D015398:Signal Transduction; D014157:Transcription Factors / Q000235:genetics* / Q000378:metabolism*
chemical_list: D000071616:CDX2 Transcription Factor; C487514:Cdx2 protein, mouse; C482601:Epac protein, mouse; D020662:Guanine Nucleotide Exchange Factors; D018398:Homeodomain Proteins; D011498:Protein Precursors; D014157:Transcription Factors; D005576:Colforsin; D052336:Proglucagon; D005934:Glucagon; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3