Mechanism of gene regulation of HNF4α

Abstract

Hepatocyte Nuclear Factor 4 alpha(HNF4α)is a masterregulatorthat modulatesthe liver development andfunction. The dysfunction of HNF4αcauses multiplehumandiseases, such as hepatocellular carcinoma(HCC) and maturity onset diabetes of the young1 (MODY1). Incontrast,the restoration of HNF4α can inhibit the development of liver cancer and improve the liver function simultaneously.However, HNF4αis anorphan nuclear receptor whose activating ligand remains elusive. Therefore, an alternative approach to enhance the HNF4αactivity is to up-regulate the proteinexpression.While a great progress has been made on the functional study of HNF4α,the mechanistic details regarding the gene regulationofHNF4αare still a vast knowledge gap. The present study was aimed to investigatethe mechanism of gene regulation ofHNF4αsystematically. In chapter 2 and chapter 3, we reported the strong translational inhibition of both humanand mouse HNF4αinduced by the nucleicacid secondary structuretermed “G-quadruplex”(G4)within the 5` untranslated region(UTR).By performing the deletion/mutation studies, we determined the compositionof the G4in HNF4A 5`UTR. We further speculated thatthis G4 required the adjacent cis-elements, such as the RNA-binding proteins and other secondary structures, to form a conjunction for the strong translational inhibition. We for the first time reported the RNA-G4 induced translational repression within the 5`UTR of a tumor suppressor and highlighted the significanceof the “biostability”of G4s in exerting their biological functions. In chapter 4, we conductedacomprehensivestudy that coveredthe auto-regulation, transcriptionalregulation and transactivation activity of HNF4α. By creatingvariousreporter constructs, we were able to validate the self-stimulation of HNF4αand discovered the strong correlation between HNF4αand its corresponding anti-sense RNA, HNF4A-AS1. Additionally, we identified novel HNF4αmutations such as Q277X that may affect the crosstalk of HNF4αwith other transcriptionfactors.Overall, the novel findings from our study shedlight on the gene regulation of HNF4αand providefurther insights into ourultimate goal that is to up-regulate HNF4αprotein expression/activity to treat human diseases.