Maturity-onset diabetes of the young (MODY): Mutations in five different transcription factors, including HNF-1a, NeuroD1, and Pdx1 can cause MODY, a familial, monogenic disorder. Over 50 point mutations in the hnf-1a gene have been identified throughout the sequence, suggesting HNF-1a is particularly susceptible to disruption. We are investigating how HNF-1a activity is regulated, and how MODY mutations disrupt its activity.

1) The role of dimerization in dominant inheritance: MODY is an autosomal dominant disorder, meaning a mutation in a single allele of HNF-1a is sufficient to cause diabetes. Because HNF-1a is an obligate dimer, it has been proposed that dimerization between a wild type and mutant allele partially explains the vulnerability of HNF-1a to disruption. In order to test this assumption, we developed an assay in a mouse b cell line to measure the effect of HNF-1a mutations. Our data demonstrate that dimerization is not required to observe a dominant negative phenotype in cell culture. Surprisingly, the transfected HNF-1a does not dimerize with the endogenous protein, presumably due to the role of DCoH. This suggests that the mutant and wild type alleles do not form mixed dimers in MODY patients. Instead, we propose that mutated HNF-1a dimers directly compete with the wild type allele (paper in progress).

2) Regulation of HNF-1a by the kinase Dyrk1B: The kinase Dryk1B phosphorylates HNF-1a and stimulates its transcriptional activity. We have purified a soluble, active domain of Dyrk1B, which we are using for crystallization trials and to determine the substrate specificity and kinetic constants of Dyrk1B.