Mechanisms of mutual functional interactions between HNF-4alpha and HNF-1alpha revealed by mutations that cause maturity onset diabetes of the young.
Hepatic nuclear factor (HNF)-4alpha and HNF-1alpha are key endodermal transcriptional regulators that physically and functionally interact. HNF-4alpha and HNF-1alpha cooperatively activate genes with binding sites for both factors, whereas suppressive interactions occur at regulatory sequences with a binding site for only one factor. The liver fatty acid binding protein gene (Fabp1) has binding sites for both factors, and chromatin precipitation assays were utilized to demonstrate that HNF-4alpha increased HNF-1alpha Fabp1 promoter occupancy during cooperative transcriptional activation. The HNF4 P2 promoter contains a HNF-1 but not HNF-4 binding site, and HNF-4alpha suppressed HNF-1alpha HNF4 P2 activation and decreased promoter HNF-1alpha occupancy. The apolipoprotein C III (APOC3) promoter contains a HNF-4 but not HNF-1 binding site, and HNF-1alpha suppressed HNF-4alpha APOC3 activation and decreased HNF-4alpha promoter occupancy. Maturity onset diabetes of the young (MODY) as well as defects in hepatic lipid metabolism result from mutations in either HNF-4alpha or HNF-1alpha. We found that MODY missense mutant R127W HNF-4alpha retained wild-type individual Fabp1 activation and bound to HNF-1alpha better than wild-type HNF-4alpha, yet did not cooperate with HNF-1alpha or increase HNF-1alpha Fabp1 promoter occupancy. The R127W mutant was also defective in both suppressing HNF-1alpha activation of HNF4 P2 and decreasing HNF-1alpha promoter occupancy. The HNF-1alpha R131Q MODY mutant also retained wild-type Fabp1 activation and bound to HNF-4alpha as well as the wild type but was defective in both suppressing HNF-4alpha APOC3 activation and decreasing HNF-4alpha promoter occupancy. These results suggest HNF-1alpha-HNF-4alpha functional interactions are accomplished by regulating factor promoter occupancy and that defective factor-factor interactions may contribute to the MODY phenotype.
Rowley
Christopher W
CW
Department of Pediatrics, Washington University School of Medicine, Campus Box 8208, St. Louis, MO 63110, USA.
Staloch
Lora J
LJ
Divine
Joyce K
JK
McCaul
Sean P
SP
Simon
Theodore C
TC
D018938:Caco-2 Cells; D003924:Diabetes Mellitus, Type 2 / Q000235:genetics* / Q000503:physiopathology; D050556:Fatty Acid-Binding Proteins / Q000235:genetics; D006367:HeLa Cells; D051538:Hepatocyte Nuclear Factor 1-alpha / Q000235:genetics* / Q000502:physiology*; D051557:Hepatocyte Nuclear Factor 4 / Q000235:genetics* / Q000502:physiology*; D006801:Humans; D020125:Mutation, Missense; D011401:Promoter Regions, Genetic; D019076:Transgenes / Q000502:physiology
C493319:FABP1 protein, human; D050556:Fatty Acid-Binding Proteins; C496592:HNF4A protein, human; D051538:Hepatocyte Nuclear Factor 1-alpha; D051557:Hepatocyte Nuclear Factor 4