Maturity-onset diabetes of the young type 1 (MODY1)-associated mutations R154X and E276Q in hepatocyte nuclear factor 4 alpha (HNF4 alpha) gene impair recruitment of p300, a key transcriptional coactivator

Hepatocyte nuclear factor 4 alpha (HNF4 alpha) is a nuclear receptor involv ed in glucose homeostasis and is required for normal p-cell function. Mutat ions in the HNF4 alpha gene are associated with maturity-onset diabetes of the young type 1. E276Q and R154X mutations were previously shown to impair intrinsic transcriptional activity (without exogenously supplied coactivat ors) of HNF4 alpha. Given that transcriptional partners of HNF4 alpha modul ate its intrinsic transcriptional activity and play crucial roles in HNF al pha function, we investigated the effects of these mutations on potentiatio n of HNF4 alpha activity by p300, a key coactivator for HNF4 alpha. We show here that loss of HNF4 alpha function by both mutations is increased throu gh impaired physical interaction and functional cooperation between HNF4 al pha and p300. Impairment of p300-mediated potentiation of HNF4 alpha transc riptional activity is of particular importance for the E276Q mutant since i ts intrinsic transcriptional activity is moderately affected. Together with previous results obtained with chicken ovalbumin upstream promoter-transcr iption factor II, our results highlight that impairment of recruitment of t ranscriptional partners represents an important mechanism leading to abnorm al HNF4 alpha function resulting from the MODY1 E276Q mutation. The impaire d potentiations of HNF4 alpha activity were observed on the promoter of HNF 1 alpha, a transcription factor involved in a transcriptional network and r equired for beta -cell function. Given its involvement in a regulatory sign aling cascade, loss of HNF4 alpha function may cause reduced beta -cell Fun ction secondary to defective HNF1 alpha expression, Our results also shed l ight on a better structure-function relationship of HNF4 alpha and on p300 sequences involved in the interaction with HNF4 alpha.