Pdx-1 is not sufficient for repression of proglucagon gene transcription in islet or enteroendocrine cells.
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 alpha- vs. beta-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 alphaTC-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 alphaTC-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 alphaTC-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.
Flock
Grace
G
Department of Medicine, Toronto General Hospital, Banting and Best Diabetes Centre, University of Toronto, Toronto, Ontario, Canada.
Cao
Xiemin
X
Drucker
Daniel J
DJ
D000818:Animals; D002460:Cell Line; D004702:Endocrine Glands / Q000166:cytology / Q000378:metabolism*; D005934:Glucagon / Q000037:antagonists & inhibitors* / Q000235:genetics* / Q000378:metabolism; D052216:Glucagon-Like Peptide 1; D018398:Homeodomain Proteins / Q000378:metabolism / Q000502:physiology*; D007413:Intestinal Mucosa / Q000378:metabolism*; D007422:Intestines / Q000166:cytology; D007515:Islets of Langerhans / Q000166:cytology / Q000378:metabolism*; D051379:Mice; D010446:Peptide Fragments / Q000378:metabolism; D052336:Proglucagon; D011498:Protein Precursors / Q000037:antagonists & inhibitors* / Q000235:genetics* / Q000378:metabolism; D015534:Trans-Activators / Q000378:metabolism / Q000502:physiology*; D014158:Transcription, Genetic / Q000502:physiology*; D014161:Transduction, Genetic
D018398:Homeodomain Proteins; D010446:Peptide Fragments; D011498:Protein Precursors; D015534:Trans-Activators; C084010:pancreatic and duodenal homeobox 1 protein; D052336:Proglucagon; D052216:Glucagon-Like Peptide 1; D005934:Glucagon