Insulin promoter factor-1 gene mutation linked to early-onset type 2 diabetes mellitus directs expression of a dominant negative isoprotein.

Abstract

The homeodomain transcription factor insulin promoter factor-1 (IPF-1) is required for development of the pancreas and also mediates glucose-responsive stimulation of insulin gene transcription. Earlier we described a human subject with pancreatic agenesis attributable to homozygosity for a cytosine deletion in codon 63 of the IPF-1 gene (Pro63fsdelC). Pro63fsdelC resulted in the premature truncation of an IPF-1 protein which lacked the homeodomain required for DNA binding and nuclear localization. Subsequently, we linked the heterozygous state of this mutation with type 2 diabetes mellitus in the extended family of the pancreatic agenesis proband. In the course of expressing the mutant IPF-1 protein in eukaryotic cells, we detected a second IPF-1 isoform, recognized by COOH-but not NH 2 -terminal-specific antisera. This isoform localizes to the nucleus and retains DNA-binding functions. We provide evidence that internal translation initiating at an out-of-frame AUG accounts for the appearance of this protein. The reading frame crosses over to the wild-type IPF-1 reading frame at the site of the point deletion just carboxy proximal to the transactivation domain. Thus, the single mutated allele results in the translation of two IPF-1 isoproteins, one of which consists of the NH 2 -terminal transactivation domain and is sequestered in the cytoplasm and the second of which contains the COOH-terminal DNA-binding domain, but lacks the transactivation domain. Further, the COOH-terminal mutant IPF-1 isoform does not activate transcription and inhibits the transactivation functions of wild-type IPF-1. This circumstance suggests that the mechanism of diabetes in these individuals may be due not only to reduced gene dosage, but also to a dominant negative inhibition of transcription of the insulin gene and other ␤ cell-specific genes regulated by the mutant IPF-1. ( J. Clin. Invest. 1998. 102: 232-241.)

A feat of metabolic proportions: Pdx1 orchestrates islet development and function in the maintenance of glucose homeostasis

“…Pdx1 haploinsufficiency does not appear to physically or functionally impinge upon pancreas development in Pdx1+/− mice [12,13], however, such mice exhibit strikingly impaired glucose tolerance and glucose-stimulated insulin secretion with age [56,57]. Similarly impaired β cell function in the setting of Pdx1 deficiency has been observed in several other animal models (rat, fish, and sand rat [58][59][60][61][62]), as well as in humans with single allelic mutations in Ipf1 (where the development of impaired glucose responsiveness and frank diabetes occurs) [17][18][19][20][21]. The sand rat (Psammomys obesus) is a particularly an interesting case, as Pdx1 is not normally found in islets from these animals; however, gene transfer experiments show that repletion of Pdx1 in these islets greatly enhances insulin content and glucose-stimulated insulin transcription [62].…”

“…Pdx1 also appears to be crucial for the function of the mature β cell. Heterozygous missense and frameshift mutations of the Ipf1 gene in humans (while not impairing pancreas formation) result in defective insulin secretion and the development of a form of diabetes known as maturity onset diabetes of the young 4 (MODY4) [17][18][19][20][21]. Similarly, studies of animal models of insulin resistance suggest that the down regulation of pdx1 expression in the β cell may underlie the pathogenesis of β cell failure and type 2 diabetes [22][23][24].…”

Two conserved domains in PCIF1 mediate interaction with pancreatic transcription factor PDX‐1

“…Expression vectors were full length mouse PDX-1, mouse PDX-1(1-210), pGBKT7-PDX-1(144-283) and GST-PDX-1(206-283) [12], rat PDX-1 [13], human PDX-1 [14], zebrafish PDX-1 [15], Flag-PCIF1 [12], Gal-4 PDX-1 [6], Gal-4 BCL6 POZ and Gal-4 PLZF POZ [16], human PDX-1 wild-type and E224K [3] and GST-TRAF and GST-POZ [17]. Reporters were the PDX-1-responsive somatostatin promoter reporter (TAAT) 5 -65 SMS-CAT [13] and the Gal4 responsive reporters G51bCAT [12] and Gal4SV40Luc.…”

“…Primary Abbreviations: PDX-1, pancreas and duodenum homeobox-1; MODY, maturity onset diabetes of youth; PCIF1, PDX-1 C-terminus interacting factor; MIN6, mouse insulinoma cell line 6; TRAF, TNF-receptor associated factor domain; POZ, poxvirus and zinc finger domain; BTB, broad-complex, tramtrack, and bric-a-brac domain; HDAC, histone deacetylase; PCR, polymerase chain reaction antisera were: HDAC3 (mouse, gift from M. Lazar) and HDAC3 (Santa Cruz #sc-11417); HDAC2 (Santa Cruz #sc-7899); SMRT (mouse, gift from Mitch Lazar) and SMRT (ABR, # PA1-842). PCIF1 and PDX-1 antisera were previously described [12,14].…”

Oligonucleotide Microarray Analysis Reveals PDX1 as an Essential Regulator of Mitochondrial Metabolism in Rat Islets

“…The susceptibility for type 2 diabetes is inherited, but single diabetes genes have only been identified in about 5% of cases. Mutations in one of these genes, the homeodomain transcription factor ipf1 (also known as, pdx1, idx1, or stf1), have been associated with a rare form of maturity onset diabetes of the young (MODY4) 1 as well as predisposing individuals to late onset type 2 diabetes (1-5). Furthermore, homozygous null mutations in the ipf1 gene result in pancreas agenesis indicating that this transcription factor is indispensable for both pancreas development and subsequent ␤-cell function (6,7).…”