Merlos-Suárez A, Fernández-Larrea J, Reddy P, Baselga J, Arribas J
Laboratori de Recerca Oncològica, Servei d'Oncologia Mèdica, Hospital General Universitari Vall d'Hebron, Psg. Vall d'Hebron 119-129, Barcelona 08035, Spain.
J Biol Chem. 1998 Sep 18;273(38):24955-62. doi: 10.1074/jbc.273.38.24955.
The extracellular domain of a heterogeneous group of transmembrane proteins can be proteolytically released from the cell surface, a process known as protein ectodomain shedding. Despite the biomedical importance of several substrates of the shedding system, such as the beta-amyloid precursor protein (betaAPP), little is known about the regulation of protein ectodomain shedding, and the only protease known to be involved is the metalloprotease disintegrin, tumor necrosis factor-alpha converting enzyme (TACE). Here, we show that previously described pro-transforming growth factor-alpha shedding-defective cell mutants (M2 cells), known to be defective in ectodomain shedding of several molecules, that include betaAPP, fail to shed the ectodomain of pro-TNF-alpha. The target of the mutation is a component required for TACE activity, since transfection of TACE into M2 cells has no effect on the shedding of pro-TNF-alpha and somatic cell fusions between M2 cells and TACE null cells recover the ability to shed pro-TNF-alpha, pro-transforming growth factor-alpha, and betaAPP. Furthermore, we show that TACE is also necessary for the shedding of betaAPP since TACE null cells show defective betaAPP shedding. Biochemical evidence shows that the component that controls TACE is different from protein kinase C, the only known activator of protein ectodomain shedding, and that this component does not affect biosynthesis or processing of TACE or other metalloprotease disintegrins. The component mutated in M2 cells is likely to control only a subset of metalloprotease disintegrins involved in regulated ectodomain shedding, since Notch processing, a process known to be dependent on the activity of another metalloprotease disintegrin, Kuzbanian, is normal in M2 cells.
一组异质性跨膜蛋白的细胞外结构域可从细胞表面通过蛋白水解作用释放出来，这一过程称为蛋白质胞外域脱落。尽管脱落系统的几种底物（如β-淀粉样前体蛋白（βAPP））具有重要的生物医学意义，但人们对蛋白质胞外域脱落的调控知之甚少，已知参与其中的唯一蛋白酶是金属蛋白酶解整合素——肿瘤坏死因子-α转换酶（TACE）。在此，我们表明，先前描述的促转化生长因子-α脱落缺陷型细胞突变体（M2细胞），已知在包括βAPP在内的几种分子的胞外域脱落方面存在缺陷，也无法脱落前肿瘤坏死因子-α的胞外域。突变的靶点是TACE活性所需的一种成分，因为将TACE转染到M2细胞中对前肿瘤坏死因子-α的脱落没有影响，并且M2细胞与TACE之间的体细胞融合恢复了脱落前肿瘤坏死因子-α、促转化生长因子-α和βAPP的能力。此外，我们表明TACE对于βAPP的脱落也是必需的，因为TACE缺陷型细胞显示出βAPP脱落缺陷。生化证据表明，控制TACE的成分不同于蛋白激酶C（已知的唯一蛋白质胞外域脱落激活剂），并且该成分不影响TACE或其他金属蛋白酶解整合素的生物合成或加工。M2细胞中发生突变的成分可能仅控制参与调控胞外域脱落的一部分金属蛋白酶解整合素，因为Notch加工（已知依赖于另一种金属蛋白酶解整合素库兹班尼亚的活性）在M2细胞中是正常的。
