Huppa J B, Ploegh H L
Center for Cancer Research, Massachusetts Institute of Technology, Cambridge 02139, USA.
Immunity. 1997 Jul;7(1):113-22. doi: 10.1016/s1074-7613(00)80514-2.
To reach the cell surface, the T cell receptor for antigen (TCR)-CD3 complex must assemble in the endoplasmic reticulum (ER), where single subunits are retained and degraded. However, the exact location of breakdown and the mechanism and proteases involved in destruction of free subunits have remained elusive. We show that degradation of the TCR alpha chain is impaired in the presence of lactacystin and carboxybenzyl-leucyl-leucyl-leucinal, two inhibitors for proteasomal proteolysis. We identified breakdown intermediates that were either soluble, cytosolic, and devoid of N-linked glycans, or membrane-associated and partially deglycosylated by cytosolic N-glycanase. Protease protection experiments showed a cytosolic disposition of these membrane-associated intermediates. Combined, these results argue for a cytosolic degradation route of the TCR alpha chain involving dislocation from the ER, followed by cytosolic deglycosylation and proteolysis by the proteasome.
为了到达细胞表面，抗原T细胞受体（TCR）-CD3复合物必须在内质网（ER）中组装，单个亚基会在内质网中被滞留并降解。然而，自由亚基分解的确切位置以及参与其破坏的机制和蛋白酶一直难以捉摸。我们发现，在乳胞素和羧苄基-亮氨酰-亮氨酰-亮氨酸（两种蛋白酶体蛋白水解抑制剂）存在的情况下，TCRα链的降解受到损害。我们鉴定出了分解中间体，它们要么是可溶的、存在于胞质溶胶中且没有N-连接聚糖，要么是与膜相关的并且被胞质N-聚糖酶部分去糖基化。蛋白酶保护实验表明这些与膜相关的中间体存在于胞质溶胶中。综合来看，这些结果表明TCRα链存在一条胞质溶胶降解途径，该途径涉及从内质网中错位，随后进行胞质溶胶去糖基化和蛋白酶体介导的蛋白水解。
