探討伴侶蛋白在神經性退化性疾病中的調控

Abstract

神經性退化性疾病例如阿茲海默症、帕金森氏症以及亨丁頓舞蹈症的共同特徵為大腦中不正常的蛋白堆積。近期有越來越多研究指出老化在神經性退化疾病中扮演著至關重要的角色。另外，先前已被報導過會造成老化的許多壓力也會同時引起DNA受損。當DNA受損時，ATM與ATR這兩個關鍵的激酶會被活化並磷酸化下游傳遞蛋白以促進DNA修復路徑。而根據先前實驗室的研究發現伴侶蛋白 (chaperone/co-chaperone)的磷酸化會影響彼此之間的結合，進而導致蛋白堆疊。因此，我們推測受到壓力活化的ATM/ATR會磷酸化下游的伴侶蛋白並且導致神經性退化性疾病的發生。為了找出ATM/ATR的受質，我們參考先前的蛋白質體分析並選出11個伴侶蛋白受質，並發現HSPA4以及HSPA8的磷酸化可能參與調控蛋白質堆疊。HSPA8可以幫助穩定細胞週期蛋白D1，並減少病理蛋白-syn的堆積。HSPA8 S153A及S329D突變大幅降低細胞週期蛋白D1的穩定性。除此之外，HSPA4同HSPA8可以幫助細胞週期蛋白D1的穩定，S552D突變則會降低此效果。過表現HSPA4一樣可以減少-syn的聚集，而S552A突變更進一步降低了-syn堆疊程度。

Neurodegenerative diseases, such as Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's disease (HD), are characterized by distinct protein aggregates in the brain. Recently, increasing researches had pointed out that aging plays a vital role in neurodegenerative diseases. Additionally, numerous stresses which were previously identified to precipitate aging would also lead to DNA damage. In response to DNA damage, ATM and ATR, two crucial kinases would be activated and phosphorylate downstream transducer proteins to mediate DNA damage response. Based on our previous study, we found that the phosphorylation of a co-chaperone would impede its association with a chaperone, thus leads to protein aggregation. As a result, we speculated that the phosphorylation of chaperones/co-chaperones by ATM/ATR under stress may contribute to neurodegenerative diseases. Thus, to find out ATM/ATR substrates, we screened a proteomic analysis and selected 11 chaperones/co-chaperones for further evaluation. In my screen, I found that the phosphorylation of HSPA4 and HSPA8 might participate in the regulation of protein aggregation. HSPA8 enhances the stability of cyclin D1 and downregulates the aggregation of the pathological protein, -syn. HSPA8 S153A and S329D mutations greatly reduce the stability of cyclin D1. As for HSPA4, it also promotes the stability of cyclin D1, yet S552D mutation fails to promote cyclin D1’s stability. Overexpression of HSPA4 reduces the aggregation of -syn, and S552A further lowers the levels of aggregates. Together, my study reveals that double-strand break may boost protein folding through phosphorylations of the ATM and ATR substrates in the protein folding system.