Human mutations affect the epigenetic/bookmarking function of HNF1B

International audienceBookmarking factors are transcriptional regulators involved in the mitotic transmission of epigenetic information via their ability to remain associated with mitotic chromatin. The mechanisms through which bookmarking factors bind to mitotic chromatin remain poorly understood. HNF1␤ is a bookmarking transcription factor that is frequently mutated in patients suffering from renal multicystic dysplasia and diabetes. Here, we show that HNF1␤ bookmark-ing activity is impaired by naturally occurring mutations found in patients. Interestingly, this defect in HNF1␤ mitotic chromatin association is rescued by an abrupt decrease in temperature. The rapid re-localization to mitotic chromatin is reversible and driven by a specific switch in DNA-binding ability of HNF1␤ mutants. Furthermore, we demonstrate that importin-␤ is involved in the maintenance of the mi-totic retention of HNF1␤, suggesting a functional link between the nuclear import system and the mi-totic localization/translocation of bookmarking factors. Altogether, our studies have disclosed novel aspects on the mechanisms and the genetic programs that account for the mitotic association of HNF1␤, a bookmarking factor that plays crucial roles in the epigenetic transmission of information through the cell cycle

Low-dose aspirin protective effects are correlated with deregulation of HNF factor expression in the preeclamptic placentas from mice and humans

Aspirin (acetyl-salicylic acid) is one of the most ancient drugs of the human pharmacopeia. Nonetheless, its action atlow doses is not well understood at the molecular level. One of the applications of low-dose aspirin treatment is theprevention of preeclampsia (PE) in patients at risk. Foeto-placental overexpression of the STOX1A transcription factor inmice triggers PE symptoms. Transcriptomic analysis of the placentas, showed that aspirin massively down-regulatesgenes of the coagulation and complement cascade, as well as genes involved in lipid transport. The genes modifiedby aspirin treatment are not the ones that are modified by STOX1 overexpression, suggesting that aspirin could actdownstream, symptomatically on the preeclamptic disease. Bioinformatics analysis of the promoters of thederegulated genes showed that they are strongly enriched in HNF transcription factors-binding sites, in accordancewith existing literature showing their roles as regulators of coagulation. Two of these transcription factors,Hnf1βandHnf4αare found down-regulated by aspirin treatment. In parallel, we show that in human patient placentas, aspirin-induced deregulations of genes of the coagulation cascade are also observed. Finally, the expression of Hnf1βtargetsequences (Kif12,F2,Hnf4αpromoters and a synthetic concatemer of the Hnf1β-binding site) were investigated bytransfection in trophoblast cell models, with or without aspirin treatment and with or without STOX1A overexpression.In this model we observed that STOX1A and aspirin tended to synergize in the down-regulation of Hnf1βtarget genesin trophoblasts

A suppressor locus for MODY3-diabetes

International audienceMaturity Onset Diabetes of the Young type 3 (MODY3), linked to mutations in the transcription factor HNF1A, is the most prevalent form of monogenic diabetes mellitus. HNF1alpha-deficiency leads to defective insulin secretion via a molecular mechanism that is still not completely understood. Moreover, in MODY3 patients the severity of insulin secretion can be extremely variable even in the same kindred, indicating that modifier genes may control the onset of the disease. With the use of a mouse model for HNF1alpha-deficiency, we show here that specific genetic backgrounds (C3H and CBA) carry a powerful genetic suppressor of diabetes. A genome scan analysis led to the identification of a major suppressor locus on chromosome 3 (Moda1). Moda1 locus contains 11 genes with non-synonymous SNPs that significantly interacts with other loci on chromosomes 4, 11 and 18. Mechanistically, the absence of HNF1alpha in diabetic-prone (sensitive) strains leads to postnatal defective islets growth that is remarkably restored in resistant strains. Our findings are relevant to human genetics since Moda1 is syntenic with a human locus identified by genome wide association studies of fasting glycemia in patients. Most importantly, our results show that a single genetic locus can completely suppress diabetes in Hnf1a-deficiency. Hepatocyte Nuclear Factor 1 alpha (HNF1A) encodes for a transcription factor expressed in liver, kidney, intestine and pancreas. Mutations in this gene lead to Maturity Onset Diabetes of the Young type 3 (MODY3) 1. This genetic defect represents the most prevalent form of monogenic diabetes 2. HNF1alpha-deficiency leads to an insulin secretion defect that is characterized by a significant phenotypic variability 3. Indeed, even in the same kindred, patients carrying the very same mutation may develop diabetes during childhood whereas other members of the family may develop hyperglycemia only after 50 years of age 3. It has been postulated that this variability may be ascribed to the effect of modifier genes. In support of this hypothesis, a genome scan on different MODY3 families has demonstrated the existence of loci in linkage with the age of onset of the disease 4. One of the limitations of human genetics approach is represented by the complexity of the interaction between the nature of the mutation and the phenotype 5. These limitations prevented the identification of the genetic variations responsible for these effects. To circumvent this problem we took advantage of mouse genetics and in particular of a mouse model that recapitulates the main phenotypic traits of MODY3. It has been previously shown that Hnf1a −/− mice tend to have smaller Langerhans islets and exhibit a profound defect in glucose-dependent insulin secretion that is comparable to that presented by MODY3 patients 6,7. In the kidney, a specific set of sodium dependent co-transporters including Slc5a2 is defectively expressed leading to renal Fanconi syndrome characterized by massive glucose, phosphate and amino acid urinary wasting 8. In a similar way, MODY3 patients suffer from a reduced maximal renal reabsorption capacity for glucose 8. It has been shown that Hnf1a-deficiency leads to a reduced nutrient secretagogue-induced insulin release that is linked to impaired glycolysis 9 and uncou-pling of mitochondrial oxidative phosphorylation 10 in beta islets. Hnf1a-deficiency leads to the significant los

Juvenile sudden death in a family with polymorphic ventricular arrhythmias caused by a novel RyR2 gene mutation: evidence of specific morphological substrates

We report on a family with a history of sudden death and effort-induced polymorphic ventricular arrhythmias. The index case was a 17-year-old boy who died suddenly and at postmortem had evidence of fibrofatty replacement in the right ventricular free wall, consistent with arrhythmogenic right ventricular cardiomyopathy, as well as calcium phosphate deposits within the myocytes. A molecular genetics investigation carried out in the paraffin-embedded myocardium of the subject and in blood samples of family members disclosed a missense mutation in exon 3 (230C-->T; A77V) of the cardiac ryanodine receptor type 2 gene. The carriers showed effort-induced polymorphic ventricular tachycardia in the setting of normal resting electrocardiogram and trivial echocardiographic abnormalities, consistent with catecholaminergic polymorphic ventricular tachycardia. The observation of both arrhythmogenic right ventricular cardiomyopathy type 2 and catecholaminergic polymorphic ventricular tachycardia in the same family suggests that the two entities might correspond to different degrees of phenotypic expression of the same disease. This experience underscores the importance of a precise autopsy diagnosis in the case of sudden cardiac death, including molecular genetics, and the mission of pathologists to guide further clinical investigation of family members

Serum- and Glucocorticoid-Inducible Kinase 1 (SGK1) Regulates Adipocyte Differentiation via Forkhead Box O1

The serum and glucocorticoid-inducible kinase 1 (SGK1) is an inducible kinase the physiological function of which has been characterized primarily in the kidney. Here we show that SGK1 is expressed in white adipose tissue and that its levels are induced in the conversion of preadipocytes into fat cells. Adipocyte differentiation is significantly diminished via small interfering RNA inhibition of endogenous SGK1 expression, whereas ectopic expression of SGK1 in mesenchymal precursor cells promotes adipogenesis. The SGK1-mediated phenotypic effects on differentiation parallel changes in the mRNA levels for critical regulators and markers of adipogenesis, such as peroxisome proliferator-activated receptor γ, CCAAT enhancer binding protein α, and fatty acid binding protein aP2. We demonstrate that SGK1 affects differentiation by direct phosphorylation of Foxo1, thereby changing its cellular localization from the nucleus to the cytosol. In addition we show that SGK1−/− cells are unable to relocalize Foxo1 to the cytosol in response to dexamethasone. Together these results show that SGK1 influences adipocyte differentiation by regulating Foxo1 phosphorylation and reveal a potentially important function for this kinase in the control of fat mass and function