Pdx-1 Is Not Sufficient for Repression of Proglucagon Gene Transcription in Islet or Enteroendocrine Cells

• Published in: Endocrinology (Philadelphia) 2005-01, Vol.146 (1), p.441-449
• Main Authors: Flock, Grace, Cao, Xiemin, Drucker, Daniel J
• Format: Article
• Language: English
• Subjects: Animals; Beta cells; Biological and medical sciences; Cell Line; Endocrine Glands - cytology; Endocrine Glands - metabolism; Extinction; Fundamental and applied biological sciences. Psychology; Gene expression; Gene silencing; Glucagon; Glucagon - antagonists & inhibitors; Glucagon - genetics; Glucagon - metabolism; Glucagon-Like Peptide 1; Homeodomain Proteins - metabolism; Homeodomain Proteins - physiology; Intestines - cytology; Intestines - metabolism; Islets of Langerhans - cytology; Islets of Langerhans - metabolism; Mice; Nuclear transport; Pdx-1 protein; Peptide Fragments - metabolism; Phenotypes; Proglucagon; Protein Precursors - antagonists & inhibitors; Protein Precursors - genetics; Protein Precursors - metabolism; Trans-Activators - metabolism; Trans-Activators - physiology; Transcription, Genetic - physiology; Transduction, Genetic; Translocation; Vertebrates: endocrinology; Western blotting
• ISSN: 0013-7227; 1945-7170
• DOI: 10.1210/en.2004-0495

Pdx-1 plays a key role in the development of the pancreas and the control of islet gene transcription and has also been proposed as a dominant regulator of the α- vs. β-cell phenotype via extinction of proglucagon expression. To ascertain the relationship between Pdx-1 and proglucagon gene expression, we examined the effect of enhanced pdx-1 expression on proglucagon gene expression in murine islet αTC-1 and GLUTag enteroendocrine cells. Although adenoviral transduction increased the levels of pdx-1 mRNA transcripts and nuclear Pdx-1 protein, overexpression of pdx-1 did not repress endogenous proglucagon gene expression in αTC-1 or GLUTag cells or murine islets. Immunohistochemical analysis of cells transduced with Ad-pdx-1 demonstrated multiple individual islet or enteroendocrine cells exhibiting both nuclear Pdx-1 and cytoplasmic glucagon-like peptide-1 immunopositivity. The failure of pdx-1 to inhibit endogenous proglucagon gene expression was not attributable to defects in Pdx-1 nuclear translocation or DNA binding as demonstrated using Western blotting and EMSA analyses. Furthermore, Ad-pdx-1 transduction did not repress proglucagon promoter activity in αTC-1 or GLUTag cells. Taken together, these findings demonstrate that pdx-1 alone is not sufficient for specification of the hormonal phenotype or extinction of proglucagon gene expression in islet or enteroendocrine cells.