The characterisation of the human Wolfram syndrome gene promoter demonstrating regulation by Sp1 and Sp3 transcription factors

WFS1 protein expression correlates with clinical progression of optic atrophy in patients with Wolfram syndrome

BACKGROUND

Wolfram syndrome (WFS) is a rare disorder characterised by childhood-onset diabetes mellitus and progressive optic atrophy. Most patients have variants in the WFS1 gene. We undertook functional studies of WFS1 variants and correlated these with WFS1 protein expression and phenotype.

METHODS

9 patients with a clinical diagnosis of WFS were studied with quantitative PCR for markers of endoplasmic reticulum (ER) stress and immunoblotting of fibroblast protein extracts for WFS1 protein expression. Luciferase reporter assay was used to assess ATF-6 dependent unfolded protein response (UPR) activation.

RESULTS

6 patients with compound heterozygous nonsense mutations in WFS1 had no detectable WFS1 protein expression; 3 patients with missense variants had 4%, 45% and 48% WFS1 protein expression. One of these also had an OPA1 mutation and was reclassified as autosomal dominant optic atrophy-plus syndrome. There were no correlations between ER stress marker mRNA and WFS1 protein expression. ERSE-luciferase reporter indicated activation of the ATF6 branch of UPR in two patients tested. Patients with partial WFS1 expression showed milder visual acuity impairment (asymptomatic or colour blind only), compared with those with absent expression (registered severe vision impaired) (p=0.04). These differences remained after adjusting for duration of optic atrophy.

CONCLUSIONS

Patients with WFS who have partial WFS1 protein expression present with milder visual impairment. This suggests a protective effect of partial WFS1 protein expression on the severity and perhaps progression of vision impairment and that therapies to increase residual WFS1 protein expression may be beneficial.

Differential promoter activity by nucleotide substitution at a type 2 diabetes genome-wide association study signal upstream of the wolframin gene

BACKGROUND

Functional knowledge of most genetic variants identified from genome-wide association studies (GWAS) for type 2 diabetes (T2D) is limited. A recent T2D GWAS revealed an association signal (rs4689388) upstream of the gene encoding Wolfram syndrome 1 (WFS1) whose intrinsic nucleotide variants had been previously associated with T2D in several candidate gene analyses. The aim of the present study was to identify functional variants of the GWAS signal.

METHODS

Promoter activity of luciferase reporter constructs was compared with haplotypes including variants composing a linkage disequilibrium block in the vicinity of rs4689388 in HEK293 and HepG2 cells.

RESULTS

Promoter activity was highest with the most frequent haplotype (H1; ATCGT) and lowest with second most frequent haplotype (H2; GATCG), whose nucleotide alleles were all complementary to those of H1. Further analysis with artificial haplotypes revealed differential transcriptional activity by nucleotide substitution of rs4320200, rs13107806, or rs13127445 (P < 0.05). This concurred with changes in predicted transcription factor binding site by their allele substitutions.

CONCLUSIONS

The previously reported GWAS signal for T2D may be identified by the differential promoter activity of rs4320200, rs13107806, and rs13127445 in the promoter of WFS1 by nucleotide substitution.

Identification and characterization of the minimal promoter of Mipu1: the role of GC boxes in the regulation of basal transcription

Mipu1, a novel gene encoding a KRAB/C2H2 zinc finger protein, was first reported to be up-regulated in myocardial ischemia-reperfusion injury, functioning to protect cells against oxidative stress. To map the promoter region of the gene and to understand its regulation, we identified the transcription start site and revealed that the 1366-bp fragment upstream of the transcription start site possesses promoter activity. Deletion constructs of the 5'-flanking region of Mipu1 lead to the identification of a minimal promoter, in which neither a TATA box nor a CAAT box was detected. Two GC boxes were found; however, they are the specific binding sites for Sp1-family transcription factors. Mutations in these GC boxes resulted in the total loss of Mipu1 minimal promoter activity. Finally, WP631, an Sp1-family-specific inhibitor, was found to decrease the promoter activity in a dose-dependent manner, indicating that the GC boxes are essential for the activity of the Mipu1 minimal promoter activity.

Sodium-potassium ATPase 1 subunit is a molecular partner of Wolframin, an endoplasmic reticulum protein involved in ER stress

Wolfram syndrome, an autosomal recessive disorder characterized by diabetes mellitus and optic atrophy, is caused by mutations in the WFS1 gene encoding an endoplasmic reticulum (ER) membrane protein, Wolframin. Although its precise functions are unknown, Wolframin deficiency increases ER stress, impairs cell cycle progression and affects calcium homeostasis. To gain further insight into its function and identify molecular partners, we used the WFS1-C-terminal domain as bait in a yeast two-hybrid screen with a human brain cDNA library. Na+/K+ ATPase beta1 subunit was identified as an interacting clone. We mapped the interaction to the WFS1 C-terminal and transmembrane domains, but not the N-terminal domain. Our mapping data suggest that the interaction most likely occurs in the ER. We confirmed the interaction by co-immunoprecipitation in mammalian cells and with endogenous proteins in JEG3 placental cells, neuroblastoma SKNAS and pancreatic MIN6 beta cells. Na+/K+ ATPase beta1 subunit expression was reduced in plasma membrane fractions of human WFS1 mutant fibroblasts and WFS1 knockdown MIN6 pancreatic beta-cells compared with wild-type cells; Na+/K+ ATPase alpha1 subunit expression was also reduced in WFS-depleted MIN6 beta cells. Induction of ER stress in wild-type cells only partly accounted for the reduced Na+/K+ ATPase beta1 subunit expression observed. We conclude that the interaction may be important for Na+/K+ ATPase beta1 subunit maturation; loss of this interaction may contribute to the pathology seen in Wolfram syndrome via reductions in sodium pump alpha1 and beta1 subunit expression in pancreatic beta-cells.