Wileman T, Carson G R, Shih F F, Concino M F, Terhorst C
Laboratory of Molecular Immunology, Dana Farber Cancer Institute, Boston, Massachusetts 02115, USA.
Cell Regul. 1990 Nov;1(12):907-19. doi: 10.1091/mbc.1.12.907.
Studies with the T-cell antigen receptor (TCR) have shown that the endoplasmic reticulum, or an organelle closely associated with it, can retain and degrade membrane proteins selectively. The observation that only three (alpha, beta, and delta) of the six (alpha beta gamma delta epsilon zeta) subunits of the TCR are susceptible to proteolysis implies that structural features within the labile proteins mark them for degradation. The TCR beta chain is degraded in the endoplasmic reticulum, and, in this study, we have started to define the domains of the protein that make it susceptible to proteolysis. The experiments show that the transmembrane anchor and short five-amino-acid cytoplasmic tail of the protein contain a dominant determinant of proteolysis. When these residues were removed from the beta chain, the protein became resistant to proteolysis. Even though the resulting ectodomain of the beta chain lacked a transmembrane anchor, it was not secreted by cells and was retained in the endoplasmic reticulum. We conclude that retention in the endoplasmic reticulum alone does not lead to degradation. The results suggest that structural features within the membrane anchor of the protein predispose the beta chain to proteolysis. This was confirmed by replacing the membrane anchor of the interleukin 2 (IL2) receptor, a protein that was stable within the secretory pathway, with that of the TCR beta chain. The unmodified IL2 receptor was transported efficiently to the surface of cells, and an "anchor minus" construct was secreted quantitatively into the culture media. When the membrane anchor of the IL2 receptor was replaced with that of the TCR beta chain, the chimera was unable to reach the Golgi apparatus and was degraded rapidly.
对T细胞抗原受体（TCR）的研究表明，内质网或与其紧密相关的细胞器能够选择性地保留和降解膜蛋白。TCR的六个亚基（αβγδεζ）中只有三个（α、β和δ）易受蛋白水解作用影响，这一观察结果表明不稳定蛋白中的结构特征使其成为降解的目标。TCRβ链在内质网中被降解，在本研究中，我们已开始确定该蛋白中使其易受蛋白水解作用影响的结构域。实验表明，该蛋白的跨膜锚定区和短的五氨基酸胞质尾含有蛋白水解作用的主要决定因素。当从β链中去除这些残基时，该蛋白变得对蛋白水解作用具有抗性。尽管由此产生的β链胞外结构域缺乏跨膜锚定区，但它并未被细胞分泌，而是保留在内质网中。我们得出结论，仅在内质网中的保留不会导致降解。结果表明，该蛋白膜锚定区内的结构特征使β链易于发生蛋白水解作用。通过用TCRβ链的膜锚定区替换白细胞介素2（IL-2）受体（一种在分泌途径中稳定的蛋白）的膜锚定区，这一点得到了证实。未修饰的IL-2受体有效地转运到细胞表面，而“无锚定区”构建体则被定量分泌到培养基中。当用TCRβ链的膜锚定区替换IL-2受体的膜锚定区时，嵌合体无法到达高尔基体并迅速降解。
