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Role of Cdx-2 in insulin and proglucagon gene expression: a study using the RIN-1056A cell line with an inducible gene expression system.

Abstract
Although the homeobox gene Cdx-2 was initially isolated from the pancreatic beta cell line HIT-T15, no examination of its role in regulating endogenous insulin gene expression has been reported. To explore further the role of Cdx-2 in regulating both insulin and proglucagon gene expression, we established an ecdysone-inducible Cdx-2 expression system. This report describes a study using the rat insulinoma cell line RIN-1056A, which abundantly expresses both insulin and proglucagon (glu), and relatively high amounts of endogenous Cdx-2. Following the introduction of the inducible Cdx-2 expression system into this cell line and the antibiotic selection procedure, we obtained novel cell lines that displayed dramatically reduced expression of endogenous Cdx-2, in the absence of the inducer. These novel cell lines did not express detectable amounts of glu mRNA or the glucagon hormone, while their insulin expression was not substantially affected. In the presence of the inducer, however, transfected Cdx-2 expression was dramatically increased, accompanied by stimulation of endogenous Cdx-2 expression. More importantly, activated Cdx-2 expression was accompanied by elevated insulin mRNA expression, and insulin synthesis. Cdx-2 bound to the insulin gene promoter enhancer elements, and stimulated the expression of a luciferase reporter gene driven by these enhancer elements. Furthermore, Cdx-2 and insulin gene expressions in the wild-type RIN-1056A cells were stimulated by forskolin treatment, and forskolin-mediated activation on insulin gene expression was attenuated in the absence of Cdx-2. We suggest that Cdx-2 may mediate the second messenger cAMP in regulating insulin gene transcription.
AuthorsYi Zhao, Tao Liu, Nina Zhang, Fenghua Yi, Qinghua Wang, Ivan George Fantus, Tianru Jin
JournalThe Journal of endocrinology (J Endocrinol) Vol. 186 Issue 1 Pg. 179-92 (Jul 2005) ISSN: 0022-0795 [Print] England
PMID16002547 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)
Chemical References
  • CDX2 Transcription Factor
  • Homeodomain Proteins
  • Insulin
  • Protein Precursors
  • RNA, Messenger
  • Trans-Activators
  • Proglucagon
  • Glucagon
Topics
  • Animals
  • Blotting, Northern (methods)
  • Blotting, Western (methods)
  • CDX2 Transcription Factor
  • Cell Line
  • Clone Cells
  • Cricetinae
  • Electrophoretic Mobility Shift Assay (methods)
  • Gene Expression
  • Glucagon (genetics)
  • Homeodomain Proteins (physiology)
  • Immunoblotting (methods)
  • Insulin (genetics)
  • Pancreas (metabolism)
  • Proglucagon
  • Protein Precursors (genetics)
  • RNA, Messenger (analysis, metabolism)
  • Rats
  • Trans-Activators (physiology)

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