The relationship between the intracellular stability of tyrosine hydroxylase and the neurodegeneration regulated by α-synuclein

在一系列早期的实验中，我们研究了突变形式的人酪氨酸羟化酶1型（hTH 1），这是比野生型hTH 1更稳定，因为他们应该是有前途的工具，帕金森氏病（PD）的基因治疗。我们最近报道了以下观察结果：1）在哺乳动物细胞中，其N-末端缺失至Ala^的突变型hTH <52>1比野生型hTH 1稳定得多; 2）预测N-末端区域存在PEST基序（脯氨酸、谷氨酸/天冬氨酸、丝氨酸和苏氨酸基序），其赋予许多短寿命调节蛋白的快速更新。在该研究中，我们提出N-末端缺失的hTH 1比野生型hTH 1更稳定的现象可能是PEST基序（PEST-1，Met ^1-Lys^）缺失的直接结果<12>。因此，本研究的主要目的之一是阐明PEST-1模体是否参与了hTH 1蛋白降解速率的决定，本研究阐明了14-3-3η蛋白是神经细胞中hTH 1蛋白量的可能调节因子，并且该酶的N端至Asp^<22>是14-3-3η蛋白发挥这种作用的重要序列。然而，14-3-34蛋白对hTH 1分子发挥作用的确切机制仍有待解决。值得注意的是，α-突触核蛋白是另一种普遍存在的细胞质伴侣，是Lewy小体的主要成分之一，与14-3-3蛋白具有物理和功能同源性（共享超过40%的同源性）。此外，α-突触核蛋白与14-3-3蛋白结合。因此，我们认为，阐明胞质伴侣蛋白如14-3-3和α-synuclein在蛋白水解系统中的作用，将为深入了解hTH 1分子在神经变性过程中的细胞内稳定性提供新的研究热点。

In a series of earlier experiments we examined mutated forms of human tyrosine hydroxylase type 1 (hTH1), which are more stable than wild-type hTH1, because they should be promising tools for the gene therapy of Parkinson's disease (PD). We recently reported the following observations: 1) a mutant hTH1 with a deletion of its N-terminus up to Ala^<52> was much more stable than wild-type hTH1 in mammalian cells; 2) the presence of a PEST motif (a proline, glutamate/aspartate, serine, and threonine motif), which confers rapid turnover of many short-lived regulatory proteins, was predicted for the N-terminus region. In that research, we proposed that the phenomenon that N-terminus-deleted hTH1 was more stable than wild-type hTH1 might be a straightforward result of the loss of the PEST motif (PEST-1, Met^1-Lys^<12>). Therefore, one of the main aims of this study was to clarify whether the PEST-1 motif was involved in determining the degradation rate of the hTH1 protein.In this research, we clarified that 14-3-3η protein is a poisible regulator of the quantity of hTH1 protein in neuronal cells and that the N-terminus of the enzyme up to Asp^<22> is an important sequence in order for 14-3-3η protein to play such a role. However, the precise mechanism by which the 14-3-34 protein exerts its effect on the hTH1 molecule still remains to be solved. It is noteworthy that α-synuclein, which is another ubiquitous cytoplasmic chaperone and one of the main components of Lewy bodies, shares physical and functional homology with 14-3-3 proteins (sharing over 40% homology). In addition, α-synuclein binds to 14-3-3 proteins. Therefore, we believe that the research to clarify the roles of ubiquitous cytoplasmic chaperones such as 14-3-3 and α-synuclein in the proteolytic system will provide a new focus to afford a better understanding of the intracellular stability of the hTH1 molecule concerning the neurodegenaration.