HNF1beta/TCF2 mutations impair transactivation potential through altered co-regulator recruitment.

Abstract

Mutations in the HNF1beta gene, encoding the dimeric POU-homeodomain transcription factor HNF1beta (TCF2 or vHNF1), cause various phenotypes including maturity onset diabetes of the young 5 (MODY5), and abnormalities in kidney, pancreas and genital tract development. To gain insight into the molecular mechanisms underlying these phenotypes and into the structure of HNF1beta, we functionally characterized eight disease-causing mutations predicted to produce protein truncations, amino acids substitutions or frameshift deletions in different domains of the protein. Truncated mutations, retaining the dimerization domain, displayed defective nuclear localization and weak dominant-negative activity when co-expressed with the wild-type protein. A frameshift mutation located within the C-terminal QSP-rich domain partially reduced transcriptional activity, whereas selective deletion of this domain abolished transactivation. All five missense mutations, which concern POU-specific and homeodomain residues, were correctly expressed and localized to the nucleus. Although having different effects on DNA-binding capacity, which ranged from complete loss to a mild reduction, these mutations exhibited a severe reduction in their transactivation capacity. The transcriptional impairment of those mutants, whose DNA-binding activity was weakly or not affected, correlated with the loss of association with one of the histone-acetyltransferases CBP or PCAF. In contrast to wild-type HNF1beta, whose transactivation potential depends on the synergistic action of CBP and PCAF, the activity of these mutants was not increased by the synergistic action of these two coactivators or by treatment with the specific histone-deacetylase inhibitor TSA. Our findings suggest that the complex syndrome associated with HNF1beta-MODY5 mutations arise from either defective DNA-binding or transactivation function through impaired coactivator recruitment.

• Authors: Elena Barbacci, Angeliki Chalkiadaki, Christelle Masdeu, Cécile Haumaitre, Ludmilla Lokmane, Chantal Loirat, Sylvie Cloarec, Iannis Talianidis, Christine Bellanne-Chantelot, Silvia Cereghini
• Journal: Human molecular genetics (Hum Mol Genet) Vol. 13 Issue 24 Pg. 3139-49 (Dec 15 2004) ISSN: 0964-6906 [Print] England
• PMID: 15509593 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)

Chemical References

• DNA-Binding Proteins
• Genetic Markers
• HNF1B protein, human
• Transcription Factors
• Hepatocyte Nuclear Factor 1-beta
• DNA

Topics

• DNA (metabolism)
• DNA-Binding Proteins (genetics, metabolism)
• Dimerization
• Female
• Gene Expression Regulation (physiology)
• Genetic Markers
• Hepatocyte Nuclear Factor 1-beta
• Humans
• Male
• Mutation
• Pedigree
• Transcription Factors (genetics, metabolism)
• Transcriptional Activation