THE ROLE OF PIAS PROTEINS IN THE SUMOYLATION OF 5-HT1A RECEPTORS

Abstract

Serotonin 1A receptors (5-HT1A Rs) are implicated in the control of mood, cognition and memory. Dysfunction of 5-HT1A R signaling results in various neuropsychiatric disorders such as depression, anxiety and schizophrenia. Thus, 5-HT1A Rs are a good target for the treatment of the neuropsychiatric diseases. Previous studies have shown that 5-HT1A Rs can be SUMOylated by SUMO1 in rat brain areas such as cortex, hypothalamus and hippocampus. Studies have also shown that SUMOylated 5-HT1A Rs cannot bind to agonist. In addition, it was reported that SUMOylation of 5-HT1A Rs in the hypothalamic membrane increased by treatment with the 5-HT1A R agonist (+)-8-Hydroxy-2-dipropylaminotetralin ((+)8-OH-DPAT) and was further enhanced by combination of treatment of 17β-estradiol-3-benzoate (EB) and 8-OH-DPAT. Identifying the mechanism involved in SUMOylation of 5-HT1A Rs will be important for understanding the regulation of 5-HT1A Rs, which will inform the development of novel therapeutic approaches to the neuropsychiatric diseases. Therefore, the purpose of this thesis is to investigate the mechanisms involved in SUMOylation of 5-HT1A Rs, specifically to determine whether PIAS proteins play a role in the SUMOylation of 5-HT1A Rs. I hypothesize that selective PIAS proteins increase SUMOylation of 5-HT1A Rs. In the first study, I developed a cell culture model to examine the SUMOylation of 5-HT1A Rs. I found that mouse Neuroblastoma 2a (N2a) cells express endogenous 5-HT1A Rs and PIAS proteins. In addition, N2a cells can overexpress PIAS proteins and SENPs. The SUMOylation of 5-HT1A Rs was detected around 55 kDa in N2a cells similar to that reported in rat brain tissue. Transfected PIAS constructs expressed in the membrane and cytosol fractions of N2a cells and various PIAS constructs showed different expression levels. PIASxα significantly increased the SUMOylated 5-HT1A Rs compared to other PIAS proteins. In the second study, I tested the hypothesis that the treatment of rats with 8-OH-DPAT and/or EB increased expression of PIASxα resulting in an increased level of SUMO 1-5-HT1A Rs. The results show an increase in the expression level of PIASxα in rats co-treated with EB and 8-OH-DPAT compared to the expression level of PIASxα in either the EB treated or vehicle treated groups. Interestingly, the expression level of PIASy was increased in the rats treated with EB alone compared to vehicle treated rats. Together, these data suggest that PIASxα plays a role in increasing SUMOylation of 5-HT1A Rs. Targeting PIASxα in the SUMOylation of 5-HT1A Rs could have important clinical relevance for the therapy towards the neuropsychiatric disorders such as depression, anxiety and schizophrenia.