Regulation Of Tyrosine Hydroxylase And P53 Transcriptional Activity By Nurr1, A Parkinson's Disease Related Protein

Parkinson's disease(PD),the second common neurodegenerative diseases following Alzheimer's disease in the world,affects 1%people over sixty years old. PD is a progressive movement disorder that results primarily from the death of dopaminergic neurons in the substantia nigra and the presence of some kind of protein aggregates termed Lewy Body,a hallmark of PD,in surviving neurons.The loss of dopamine production in the brain causes the primary symptoms of Parkinson disease including tremor,slowness of movement,rigidity and difficulty with balance.Up to now,the etiology of PD has still been unclear.Nurr1 is an orphan nuclear receptor essential for the development and survival of dopaminergic neurons.Mutations in Nurr1(-291Tdel and -254T→G) are associated with Parkinson's disease(PD) and the two mutations decrease TH expression.There is a correlation between Nurr1 and TH expressions in PD brain.It was reported that post-translational modifications of nuclear factors will change their transcriptional activity.Recently,Nurr1 was reported to have effects on anti-apoptosis,but the mechanism is still unknown.In this thesis,we mainly focus on phosphorylation of Nurr1 by ERK2 and the protective function of Nurr1 by repressing p53 transcriptional activity.The main results are below:1.We show that ERK2 is a kinase to phosphorylate Nurr1 on multiple sites.S126 and T132,which are located near AF1 core of Nurr1,are dominant sites phosphorylated by ERK2.Moreover,we identified that both the N-terminus of Nurr1 containing three ERK docking domains and another ERK docking domain in Nurr1 DNA binding domain are able to bind to ERK2.Furthermore, overexpression of a constitutively active form of MEK1,together with Nurr1 and mouse ERK2,greatly increases the tyrosine hydroxylase expression in SH-SY5Y cells,suggesting that Nurr1 phosphorylation by ERK2 may regulate its transcriptional activity on TH promoter.Thus,our results indicate that Nurr1 phosphorylation by ERK2 plays an important role in regulating the TH expression.2.We show that overexpression of Nurr1 decreases Bax expression,whereas, knockdown of Nurr1 increases Bax expression.Nurr1 interacts with p53 and represses its assembly.Furthermore,Nurr1 represses p53 transcriptional activity in interaction-dependent and dose-dependent manners.Moreover,Nurr1 protects cells from apoptosis under stimulation of doxorubicin.These findings provide evidence that Nurr1 survives cells through interacting with and repressing p53, thus implicating that Nurr1 may play an important role in carcinogenesis and other diseases.Taken together,our findings suggest that phosphoryaltion of Nurr1 by ERK2 regulates its transcriptional activity,increasing the expression of TH and Nurr1 protects cells from death by interacting with p53 and repressing its transcriptional activity.These results may play a role in the pathogenesis of neurodegenerative diseases or carcinogenesis.