title: The Nkx6.1 homeodomain transcription factor suppresses glucagon expression and regulates glucose-stimulated insulin secretion in islet beta cells.
abstract: We have previously described rat insulinoma INS-1-derived cell lines with robust or poor glucose-stimulated insulin secretion (GSIS). In the current study, we have further resolved these lines into three classes: class 1, glucose-unresponsive/glucagon-expressing; class 2, glucose-unresponsive/glucagon-negative; and class 3, glucose-responsive/glucagon-negative. The transcription factor Nkx2.2 was expressed with relative abundance of 3.3, 1.0, and 1.0 in class 1, class 2, and class 3 cells, respectively, whereas Nkx6.1 expression had the opposite trend: 1.0, 2.6, and 6.4 in class 1, class 2, and class 3 cells, respectively. In class 1 cells, overexpressed Nkx6.1 suppressed glucagon expression but did not affect the levels of several other prominent beta cell transcription factors. RNA interference (RNAi)-mediated suppression of Nkx6.1 in class 3 cells resulted in a doubling of glucagon mRNA, with no effect on Pdx1 levels, whereas suppression of Pdx1 in class 3 cells caused a 12-fold increase in glucagon transcript levels, demonstrating independent effects of Nkx6.1 and Pdx1 on glucagon expression in beta cell lines. RNAi-mediated suppression of Nkx6.1 expression in class 3 cells also caused a decrease in GSIS from 13.9- to 3.7-fold, whereas suppression of Pdx1 reduced absolute amounts of insulin secretion without affecting fold response. Finally, RNAi-mediated suppression of Nkx6.1 mRNA in primary rat islets was accompanied by a significant decrease in GSIS relative to control cells. In sum, our studies have revealed roles for Nkx6.1 in suppression of glucagon expression and control of GSIS in islet beta cells.
authors.affiliation: Department of Pharmacology, Sarah W. Stedman Nutrition and Metabolism Center, Durham, NC 27704, USA.
authors.forename: Jonathan C
authors.initials: JC
authors.lastname: Schisler
authors.forename: Per Bo
authors.initials: PB
authors.lastname: Jensen
authors.forename: David G
authors.initials: DG
authors.lastname: Taylor
authors.forename: Thomas C
authors.initials: TC
authors.lastname: Becker
authors.forename: Filip Krag
authors.initials: FK
authors.lastname: Knop
authors.forename: Shiro
authors.initials: S
authors.lastname: Takekawa
authors.forename: Michael
authors.initials: M
authors.lastname: German
authors.forename: Gordon C
authors.initials: GC
authors.lastname: Weir
authors.forename: Danhong
authors.initials: D
authors.lastname: Lu
authors.forename: Raghavendra G
authors.initials: RG
authors.lastname: Mirmira
authors.forename: Christopher B
authors.initials: CB
authors.lastname: Newgard
mesh_terms: D000256:Adenoviridae; D000818:Animals; D002460:Cell Line; D047369:Chromatin Immunoprecipitation; D017931:DNA Primers; D005822:Genetic Vectors; D005934:Glucagon / Q000235:genetics / Q000378:metabolism*; D005947:Glucose / Q000378:metabolism; D000090322:Homeobox Protein Nkx-2.2; D018398:Homeodomain Proteins / Q000378:metabolism*; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D007515:Islets of Langerhans / Q000378:metabolism*; D034622:RNA Interference; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism*; D034741:RNA, Small Interfering / Q000235:genetics; D051381:Rats; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015534:Trans-Activators / Q000378:metabolism*; D014157:Transcription Factors / Q000378:metabolism*; D014162:Transfection; D029961:Zebrafish Proteins
chemical_list: D017931:DNA Primers; D000090322:Homeobox Protein Nkx-2.2; D018398:Homeodomain Proteins; D007328:Insulin; C000715628:Nkx2-2 protein, rat; C491327:Nkx6-1 protein, rat; D012333:RNA, Messenger; D034741:RNA, Small Interfering; D015534:Trans-Activators; D014157:Transcription Factors; D029961:Zebrafish Proteins; C000715630:nkx2.2b protein, zebrafish; C084010:pancreatic and duodenal homeobox 1 protein; D005934:Glucagon; D005947:Glucose