Cell-specific expression of glucose-dependent-insulinotropic polypeptide is regulated by the transcription factor PDX-1.
Glucose-dependent insulinotropic polypeptide (GIP) is a potent stimulator of insulin secretion and comprises an important component of the enteroinsular axis. GIP is synthesized in enteroendocrine K-cells located principally in the upper small intestine. The homeobox-containing gene PDX-1 is also expressed in the small intestine and plays a critical role in pancreatic development and in the expression of pancreatic-specific genes. Previous studies determined that the transcription factors GATA-4 and ISL-1 are important for GIP expression. In this study, we demonstrate that PDX-1 is also involved in regulating GIP expression in K-cells. Using immunohistochemistry, we verified the expression of PDX-1 protein in the nucleus of GIP-expressing mouse K-cells and evaluated the expression of PDX-1, serotonin, and GIP in wild-type and PDX-1(-/-) mice at 18.5 d after conception. Although we demonstrated a 97.8% reduction in the number of GIP-expressing cells in PDX-1(-/-) mice; there was no statistical difference in the number of serotonin-positive cells. Additionally, PDX-1 transcripts and protein were detected in a GIP-expressing neuroendocrine cell line, STC-1. Electromobility shift assays using STC-1 nuclear extracts demonstrated the specific binding of PDX-1 protein to a specific regulatory region in the GIP promoter. Using chromatin immunoprecipitation analysis, we demonstrated binding of PDX-1 to this same region of the GIP promoter in intact cells. Lastly, overexpression of PDX-1 in transient transfection assays led to a specific increase in the activity of GIP/Luc reporter constructs. The results of these studies indicate that the transcription factor PDX-1 plays a critical role in the cell-specific expression of the GIP gene.
Jepeal
Lisa I
LI
Section of Gastroenterology, Boston University School of Medicine and Boston Medical Center, Boston, Massachusetts 02118, USA.
Fujitani
Yoshio
Y
Boylan
Michael O
MO
Wilson
Cherrell N
CN
Wright
Christopher V
CV
Wolfe
M Michael
MM
D000818:Animals; D002460:Cell Line; D005749:Gastric Inhibitory Polypeptide / Q000235:genetics / Q000378:metabolism*; D018398:Homeodomain Proteins / Q000502:physiology*; D007150:Immunohistochemistry; D007421:Intestine, Small / Q000166:cytology / Q000378:metabolism; D051379:Mice; D018345:Mice, Knockout; D009490:Neurosecretory Systems / Q000166:cytology / Q000378:metabolism; D011401:Promoter Regions, Genetic / Q000502:physiology; D017434:Protein Structure, Tertiary / Q000502:physiology; D051381:Rats; D015534:Trans-Activators / Q000172:deficiency / Q000502:physiology*
D018398:Homeodomain Proteins; D015534:Trans-Activators; C084010:pancreatic and duodenal homeobox 1 protein; D005749:Gastric Inhibitory Polypeptide