A.N. Bach Institute of Biochemistry, Federal Research Center "Fundamentals of Biotechnology" of the Russian Academy of Sciences, 119071 Moscow, Russia.
Int J Mol Sci. 2021 Feb 3;22(4):1542. doi: 10.3390/ijms22041542.
Amyloid formation is associated with many incurable diseases. For some of these, sporadic cases are much more common than familial ones. Some reports point to the role of somatic cell mosaicism in these cases via origination of amyloids in a limited number of cells, which can then spread through tissues. However, specific types of sporadic mutations responsible for such effects are unknown. In order to identify mutations capable of increasing the de novo appearance of amyloids, we searched for such mutants in the yeast prionogenic protein Sup35. We introduced to yeast cells an additional copy of the gene with mutated amyloidogenic domain and observed that some nonsense mutations increased the incidence of prions by several orders of magnitude. This effect was related to exposure at the C-terminus of an internal amyloidogenic region of Sup35. We also discovered that mRNA could undergo splicing, although inefficiently, causing appearance of a shortened Sup35 isoform lacking its functional domain, which was also highly prionogenic. Our data suggest that truncated forms of amyloidogenic proteins, resulting from nonsense mutations or alternative splicing in rare somatic cells, might initiate spontaneous localized formation of amyloids, which can then spread, resulting in sporadic amyloid disease.
淀粉样蛋白的形成与许多无法治愈的疾病有关。对于其中一些疾病，散发性病例比家族性病例更为常见。一些报告指出，体细胞镶嵌现象在这些病例中起作用，通过少数细胞中的淀粉样蛋白起源，然后扩散到组织中。然而，导致这种影响的特定类型的散发性突变尚不清楚。为了确定能够增加淀粉样蛋白从头出现的突变，我们在酵母朊病毒蛋白 Sup35 中寻找这种突变体。我们向酵母细胞中引入了一个带有突变淀粉样结构域的额外的基因拷贝，并且发现一些无义突变使朊病毒的发生率增加了几个数量级。这种效应与 Sup35 的内部淀粉样结构域的 C 末端暴露有关。我们还发现，虽然效率不高，但 mRNA 可以进行剪接，导致缺乏功能域的缩短 Sup35 同工型的出现，其也具有高度朊病毒原性。我们的数据表明，来自罕见体细胞中的无义突变或选择性剪接的淀粉样蛋白原性蛋白的截断形式，可能引发淀粉样蛋白的自发局部形成，然后扩散，导致散发性淀粉样疾病。
