Functional analyses of the mutation nt-128 T→G in the hepatocyte nuclear factor-1α promoter region in Chinese diabetes pedigrees

Analysis of the promoter regions of disease-causing genes in maturity-onset diabetes of the young patients

Maturity-onset diabetes of the young (MODY) is a form of monogenic diabetes caused by the variants in MODY-related genes. In addition to coding variants, variants in the promoter region of MODY-related genes can cause the disease as well. In this study, we screened the promoter regions of the most common MODY-related genes GCK, HNF1A, HNF4A and HNF1B in our cohort of 29 MODY patients. We identified one genetic variant in the HNF1A gene, a 7 bp insertion c.-154-160insTGGGGGT, and three variants in the GCK gene, -282C>T; -194A>G; 402C>G appearing as set. Chloramphenicol acetyltransferase (CAT) assay was performed to test the effect of the 7 bp insertion and the variant set on the activity of the reporter gene in HepG2 and RIN-5F cell, respectively, where a decreasing trend was observed for both variants. In silico analysis and electrophoretic mobility shift assay showed that the 7 bp insertion did not create the binding site for new transcriptional factors, but gave rise to additional binding sites for the existing ones. Results from our study indicated that the 7 bp insertion in the HNF1A gene could be associated with the patient's diabetes. As for the GCK variant set, it is probably not associated with diabetes in patients, but it may modify the fasting glucose level by causing small elevation in variant set carriers. We have presented two promoter variants in MODY-related genes. Variant in the HNF1A gene is presumed to be disease-causing and the GCK promoter variant set could be a phenotype modifier.

The N-Terminus of the Floral Arabidopsis TGA Transcription Factor PERIANTHIA Mediates Redox-Sensitive DNA-Binding

The Arabidopsis TGA transcription factor (TF) PERIANTHIA (PAN) regulates the formation of the floral organ primordia as revealed by the pan mutant forming an abnormal pentamerous arrangement of the outer three floral whorls. The Arabidopsis TGA bZIP TF family comprises 10 members, of which PAN and TGA9/10 control flower developmental processes and TGA1/2/5/6 participate in stress-responses. For the TGA1 protein it was shown that several cysteines can be redox-dependently modified. TGA proteins interact in the nucleus with land plant-specific glutaredoxins, which may alter their activities posttranslationally. Here, we investigated the DNA-binding of PAN to the AAGAAT motif under different redox-conditions. The AAGAAT motif is localized in the second intron of the floral homeotic regulator AGAMOUS (AG), which controls stamen and carpel development as well as floral determinacy. Whereas PAN protein binds to this regulatory cis-element under reducing conditions, the interaction is strongly reduced under oxidizing conditions in EMSA studies. The redox-sensitive DNA-binding is mediated via a special PAN N-terminus, which is not present in other Arabidopsis TGA TFs and comprises five cysteines. Two N-terminal PAN cysteines, Cys68 and Cys87, were shown to form a disulfide bridge and Cys340, localized in a C-terminal putative transactivation domain, can be S-glutathionylated. Comparative land plant analyses revealed that the AAGAAT motif exists in asterid and rosid plant species. TGA TFs with N-terminal extensions of variable length were identified in all analyzed seed plants. However, a PAN-like N-terminus exists only in the rosids and exclusively Brassicaceae homologs comprise four to five of the PAN N-terminal cysteines. Redox-dependent modifications of TGA cysteines are known to regulate the activity of stress-related TGA TFs. Here, we show that the N-terminal PAN cysteines participate in a redox-dependent control of the PAN interaction with a highly conserved regulatory AG cis-element, emphasizing the importance of redox-modifications in the regulation of flower developmental processes.