Riboni L, Caminiti A, Bassi R, Tettamanti G
Department of Medical Chemistry and Biochemistry, Medical School, University of Milan, Italy.
J Neurochem. 1995 Jan;64(1):451-4. doi: 10.1046/j.1471-4159.1995.64010451.x.
Gangliosides GM1 [3H-labeled at the sphingosine (Sph) moiety] and GM2 [3H-labeled at the Sph or N-acetylgalactosamine (GalNAc) moiety] were administered to cultured Neuro2a cells for varying pulse (1-4 h) and chase (up to 4 h) periods, and their metabolic processing was followed. The main and earliest formed 3H-metabolites of [Sph-3H]GM1 were GM2, asialo-GM1 asialo-GM2, and lactose-ceramide, and those of [Sph-3H]GM2 were asialo-GM2 and lactose-ceramide. The asialo-GM1 and asialo-GM2 formed were isolated and chemically characterized. [3H]Asialo-GM2 was produced in identical amounts after treatment with equimolar [Sph-3H]GM2 and [GalNAc-3H]GM2. At low temperature or in the presence of chloroquine, the formation of all 3H-metabolites, including asialo-GM2 and asialo-GM1, was undetectable, indicating that ganglioside metabolic processing was an endocytosis- and lysosome-dependent process. These results demonstrate that in Neuro2a cells exogenous GM1 (and GM2) is mainly degraded through the pathway GM1-->GM2-->asialo-GM2-->-->Sph, with a minor fraction of GM1 undergoing degradation with the sequence GM1-->asialo-GM-1-->asialo-GM2-->-->Sph. These findings are consistent with the hypothesis that Neuro2a cells contain a sialidase (likely of lysosomal nature) affecting ganglioside GM1 and GM2. The sialidase-mediated degradative pathway of GM1 and GM2 in Neuro2a cells might be related to the tumoral nature of these cells.
将[鞘氨醇（Sph）部分用³H标记的]神经节苷脂GM1和[鞘氨醇或N - 乙酰半乳糖胺（GalNAc）部分用³H标记的]GM2给予培养的Neuro2a细胞，进行不同时长的脉冲（1 - 4小时）和追踪（最长4小时），并追踪它们的代谢过程。[Sph - ³H]GM1的主要且最早形成的³H代谢产物是GM2、脱唾液酸GM1、脱唾液酸GM2和乳糖神经酰胺，[Sph - ³H]GM2的主要³H代谢产物是脱唾液酸GM2和乳糖神经酰胺。分离并化学鉴定了所形成的脱唾液酸GM1和脱唾液酸GM2。用等摩尔的[Sph - ³H]GM2和[GalNAc - ³H]GM2处理后，产生的[³H]脱唾液酸GM2量相同。在低温或存在氯喹的情况下，所有³H代谢产物，包括脱唾液酸GM2和脱唾液酸GM1的形成均无法检测到，这表明神经节苷脂的代谢过程是一个依赖内吞作用和溶酶体的过程。这些结果表明，在Neuro2a细胞中，外源性GM1（和GM2）主要通过GM1→GM2→脱唾液酸GM2→→Sph途径降解，一小部分GM1通过GM1→脱唾液酸GM - 1→脱唾液酸GM2→→Sph序列进行降解。这些发现与Neuro2a细胞含有影响神经节苷脂GM1和GM2的唾液酸酶（可能具有溶酶体性质）这一假设一致。Neuro2a细胞中GM1和GM2的唾液酸酶介导的降解途径可能与这些细胞的肿瘤性质有关。
