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: Jonathan C Schisler, Per Bo Jensen, David G Taylor, Thomas C Becker, Filip Krag Knop, Shiro Takekawa, Michael German, Gordon C Weir, Danhong Lu, Raghavendra G Mirmira, Christopher B Newgard
• Journal: Proceedings of the National Academy of Sciences of the United States of America (Proc Natl Acad Sci U S A) Vol. 102 Issue 20 Pg. 7297-302 (May 17 2005) ISSN: 0027-8424 [Print] United States
• PMID: 15883383 (Publication Type: Comparative Study, Journal Article, Research Support, N.I.H., Extramural, Research Support, U.S. Gov't, P.H.S.)

Chemical References

• DNA Primers
• Homeobox Protein Nkx-2.2
• Homeodomain Proteins
• Insulin
• Nkx2-2 protein, rat
• Nkx6-1 protein, rat
• RNA, Messenger
• RNA, Small Interfering
• Trans-Activators
• Transcription Factors
• Zebrafish Proteins
• nkx2.2b protein, zebrafish
• pancreatic and duodenal homeobox 1 protein
• Glucagon
• Glucose

Topics

• Adenoviridae
• Animals
• Cell Line
• Chromatin Immunoprecipitation
• DNA Primers
• Genetic Vectors
• Glucagon (genetics, metabolism)
• Glucose (metabolism)
• Homeobox Protein Nkx-2.2
• Homeodomain Proteins (metabolism)
• Insulin (metabolism)
• Insulin Secretion
• Islets of Langerhans (metabolism)
• RNA Interference
• RNA, Messenger (genetics, metabolism)
• RNA, Small Interfering (genetics)
• Rats
• Reverse Transcriptase Polymerase Chain Reaction
• Trans-Activators (metabolism)
• Transcription Factors (metabolism)
• Transfection
• Zebrafish Proteins