Nkx2.2 activates the ghrelin promoter in pancreatic islet cells.
Nkx2.2 is an essential regulator of pancreatic endocrine differentiation. Nkx2.2-null mice are completely devoid of beta-ells and have a large reduction of alpha- and PP cells. In the place of these islet populations, there is a corresponding increase in the ghrelin-positive epsilon-cells. Molecular studies have indicated that Nkx2.2 functions as an activator and repressor to regulate islet cell fate decisions. To determine whether Nkx2.2 is solely important for islet cell fate decisions or also has the capability to control ghrelin at the promoter level, we studied the transcriptional regulation of the ghrelin promoter within the pancreas, in vitro and in vivo. These studies demonstrate that both of the previously identified transcriptional start sites in the ghrelin promoter are active within the embryonic pancreas; however, the long transcript is preferentially up-regulated in the Nkx2.2-null pancreas. We also show that the promoter region between -619 and -488 bp upstream of the translational start site is necessary for repression of ghrelin in alphaTC1 and betaTC6 cells. Surprisingly, we also show that Nkx2.2 is able to bind to and activate the ghrelin promoter in several cell lines that do or do not express endogenous ghrelin. Together, these results suggest that the up-regulation of ghrelin expression in the Nkx2.2-null mice is not due to loss of repression of the ghrelin promoter in the nonghrelin islet populations. Furthermore, Nkx2.2 may contribute to the activation of ghrelin in mature islet epsilon-cells.
Hill
Jonathon T
JT
Department of Genetics and Development, Columbia University, New York, New York 10032, USA.
Chao
Christina S
CS
Anderson
Keith R
KR
Kaufman
Fernanda
F
Johnson
Christopher W
CW
Sussel
Lori
L
D000818:Animals; D000831:Animals, Newborn; D019556:COS Cells; D045744:Cell Line, Tumor; D002522:Chlorocebus aethiops; D047369:Chromatin Immunoprecipitation; D016384:Consensus Sequence; D004268:DNA-Binding Proteins / Q000172:deficiency / Q000235:genetics / Q000378:metabolism; D024202:Electrophoretic Mobility Shift Assay; D004622:Embryo, Mammalian; D005786:Gene Expression Regulation; D054439:Ghrelin / Q000235:genetics*; D000090322:Homeobox Protein Nkx-2.2; D018398:Homeodomain Proteins / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D007515:Islets of Langerhans / Q000378:metabolism*; D051379:Mice; D008822:Mice, Transgenic; D041681:NIH 3T3 Cells; D009687:Nuclear Proteins; D010179:Pancreas / Q000378:metabolism; D011401:Promoter Regions, Genetic; D012333:RNA, Messenger / Q000378:metabolism; D016415:Sequence Alignment; D014157:Transcription Factors / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D029961:Zebrafish Proteins
D004268:DNA-Binding Proteins; D054439:Ghrelin; D000090322:Homeobox Protein Nkx-2.2; D018398:Homeodomain Proteins; C000715631:NKX2-2 protein, human; C000715627:Nkx2-2 protein, mouse; D009687:Nuclear Proteins; D012333:RNA, Messenger; D014157:Transcription Factors; D029961:Zebrafish Proteins; C000715630:nkx2.2b protein, zebrafish