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.
Department of Medicine, Toronto General Hospital, Banting and Best Diabetes Centre, University of Toronto, Toronto, Ontario, Canada.
Grace
G
Flock
Xiemin
X
Cao
Daniel J
DJ
Drucker
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