title: Nkx6.2 synergizes with Cdx-2 in stimulating proglucagon gene expression.
abstract: OBJECTIVE
  To investigate whether the transactivator of the proglucagon gene (Gcg), Cdx-2, synergizes with other transcription factors in stimulating Gcg expression and the trans-differentiation of Gcg-expressing cells.
  
  
  METHODS
  We conducted affinity chromatography to identify proteins that interact with Cdx-2, using GST-tagged Cdx-2 against cell lysates from pancreatic InR1-G9 and intestinal GLUTag cell lines. This was followed by a mass-spectrometry analysis. From a potential Cdx-2 interaction protein identified, we examined its expression in pancreatic and gut endocrine cells, confirmed its interaction with Cdx-2 by GST-pull down and determined its effect in provoking Gcg expression in cell lines that do not express endogenous Gcg.
  
  
  RESULTS
  We identified 18 potential Cdx-2 interacting proteins. One of them is Nkx6.2. This homeodomain (HD) protein is expressed in pancreatic α and intestinal endocrine L cells but not in insulin producing cell lines, including In111. Nkx6.2, but not Nkx6.1, was shown to interact with Cdx-2, detected by GST-pull down. Furthermore, Nkx6.2 was found to synergize with Cdx-2 in provoking Gcg expression when they were ectopically expressed in the In111 cell line. Finally, when Cdx-2 and Nkx6.2 were co-transfected into the undifferentiated rat intestinal IEC-6 cell line, it produced detectable amount of Gcg mRNA.
  
  
  CONCLUSIONS
  Cdx-2 recruits Nkx6.2 in exerting its effect in stimulating Gcg expression. Our observations further support the notion that multiple HD proteins, including Cdx-2 and Nkx6.2, are involved in the regulation of Gcg expression and the genesis of Gcg-producing cells.
authors.affiliation: Pei-Xiang Wang, Zhi-Wen Yu, Tian-Ru Jin, Department of Nutrition, School of Public Health, Sun Yat-sen University, Guangzhou 510080, Guangdong Province, China.
authors.forename: Pei-Xiang
authors.initials: PX
authors.lastname: Wang
authors.forename: Zhi-Wen
authors.initials: ZW
authors.lastname: Yu
authors.forename: Steven
authors.initials: S
authors.lastname: Wong
authors.forename: Tian-Ru
authors.initials: TR
authors.lastname: Jin