Negative Autoregulation of GTF2IRD1 in Williams-Beuren Syndrome via a Novel DNA Binding Mechanism

Abstract

The GTF2IRD1 gene is of principal interest to the study of Williams-Beuren syndrome (WBS). This neurodevelopmental disorder results from the hemizygous deletion of a region of chromosome 7q11.23 containing 28 genes including GTF2IRD1. WBS is thought to be caused by haploinsufficiency of certain dosage-sensitive genes within the deleted region, and the feature of supravalvular aortic stenosis (SVAS) has been attributed to reduced elastin caused by deletion of ELN. Human genetic mapping data have implicated two related genes GTF2IRD1 and GTF2I in the cause of some the key features of WBS, including craniofacial dysmorphology, hypersociability, and visuospatial deficits. Mice with mutations of the Gtf2ird1 allele show evidence of craniofacial abnormalities and behavioral changes. Here we show the existence of a negative autoregulatory mechanism that controls the level of GTF2IRD1 transcription via direct binding of the GTF2IRD1 protein to a highly conserved region of the GTF2IRD1 promoter containing an array of three binding sites. The affinity for this protein-DNA interaction is critically dependent upon multiple interactions between separate domains of the protein and at least two of the DNA binding sites. This autoregulatory mechanism leads to dosage compensation of GTF2IRD1 transcription in WBS patients. The GTF2IRD1 promoter represents the first established in vivo gene target of the GTF2IRD1 protein, and we use it to model its DNA interaction capabilities. Williams-Beuren syndrome (WBS)4 is a relatively rare disorder with an estimated incidence of 1:7,500 -1:20,000 (1). In 95% of cases, this deletion is 1.5 Mb long and results from illegitimate recombination during meiosis between two blocks of low copy repeats (LCRs) that flank the deletion domain (2, 3). To explain the causes of WBS in molecular terms, it is first necessary to identify the genes that underpin each of the disorders. The only symptom that fulfills this to date is SVAS. Haploinsufficiency of elastin due to loss of the ELN gene leads to narrowing of the large elastic aorta and may also affect the pulmonary, coronary, and carotid arteries (4). Accumulating evidence from patients with atypical hemizygous deletions within the critical region indicate that the many of the remaining symptoms, in particular the craniofacial abnormalities, the visuospatial construction deficit and the hypersociability, can be attributed to two genes at the telomeric end of the deletion region, GTF2IRD1 and GTF2I (5-7). These genes share sequence homology and are adjacent, indicating that they have arisen by duplication and divergence from a common ancestor. Functional evidence suggests that these genes encode nuclear proteins with DNA binding capabilities and are widely considered to be transcription factors with specific gene targets (8, 9).The first reported gene product of GTF2IRD1 was Mus-TRD1, which was isolated in a yeast one-hybrid screen for proteins that could bind to a DNA enhancer element present in the TNNI1 gene (10). Human, mouse, and Xenopus orthologs o...

The nuclear localization pattern and interaction partners of GTF2IRD1 demonstrate a role in chromatin regulation

“…The GTF2IRD1 upstream region (GUR) contains three GGATTA binding sites and EMSA studies have shown that all three are required to achieve high-affinity GTF2IRD1 binding (Palmer et al 2010). This may explain why GTF2IRD1 was readily isolated from the artificial triplicated bait constructs of the original yeast one-hybrid assays.…”

The role of GTF2IRD1 in the auditory pathology of Williams–Beuren Syndrome

“…23,24 Both lines were maintained on a C57BL/6J background and homozygous Gtf2ird1 tm1Hrd and wild-type siblings were produced in the same litters from heterozygous parents and housed together in identical conditions. The Gtf2ird1 tm1Hrd line was used to assess hearing capacity and heterozygous and homozygous mutant mice are hereinafter referred to as Gtf2ird1 − /+ and Gtf2ird1 −/− , respectively.…”

GTF2IRD2from the Williams-Beuren critical region encodes a mobile element-derived fusion protein that antagonizes the action of its related family members

“…Gtf2ird1 is expressed strongly during skeletal muscle development, but is downregulated in mature muscle (Palmer et al, 2007). Studies on Gtf2ird1 knockout mice (Palmer et al, 2010;Howard et al, 2012) have so far failed to reveal fiber type changes, which may reflect very low levels of adult expression. By contrast, Gtf2i mRNA is relatively abundant in adult skeletal muscle tissue (Roy et al, 1997) and therefore TFII-I is the best candidate for such a role.…”

“…Conservation of the RDs between orthologs or between family members is much higher than any other regions of the protein, suggesting that these domains constitute an essential functional element. Some of the RDs within GTF2IRD1 have been shown to have sequencespecific DNA binding properties (Polly et al, 2003;Vullhorst and Buonanno, 2005) and GTF2IRD1 protein can bind to its own promoter region via simultaneous usage of two RDs making contact with two independent DNA binding sites in the GTF2IRD1 promoter (Palmer et al, 2010). RD2 of TFII-I has also been associated with sequence-specific DNA binding properties (Cheriyath and Roy, 2001;Roy, 2001).…”

“…To examine GTF2IRD2 function, we considered using the assays that have been previously applied to GTF2IRD1 and TFII-I, but most are based on specific assumptions concerning known gene targets and known mechanisms of transcriptional regulation (Manzano-Winkler et al, 1996;Kim et al, 1998;Tantin et al, 2004;Tapia-Páez et al, 2008), the nature and sequence specificity of DNA binding (O'Mahoney et al, 1998;Bayarsaihan and Ruddle, 2000;Calvo et al, 2001;Ring et al, 2002;Polly et al, 2003;Vullhorst and Buonanno, 2003;Vullhorst and Buonanno, 2005;Palmer et al, 2010) or specifically identified protein-protein interactions (Roy et al, 1993;Novina et al, 1999;Casteel et al, 2002;Sacristán et al, 2004;Jiang et al, 2005;Caraveo et al, 2006). In this case, it was not possible to make specific assumptions about mechanism of GTF2IRD2 action based on sequence similarity alone as the protein has diverged significantly.…”