Gowrishankar Kavitha, Zeidler Michael G, Vincenz Claudius
Department of Pathology, University of Michigan Medical School, 1150 West Medical Center Drive, Ann Arbor, MI 48109, USA.
J Cell Sci. 2004 Aug 15;117(Pt 18):4099-111. doi: 10.1242/jcs.01263. Epub 2004 Jul 27.
Neurotrophin receptor alike death domain protein (NRADD) is a death-receptor-like protein with a unique ectodomain and an intracellular domain homologous to p75(NTR). Expression of NRADD results in apoptosis, but only in certain cell types. This paper characterizes the expression and proteolytic processing of the mature 55 kDa glycoprotein. N-terminally truncated NRADD is processed by a gamma-secretase activity that requires presenilins and has the same susceptibility to gamma-secretase inhibitors as the secretion of amyloid beta (A beta). The ectodomain of endogenous NRADD is shed by activation of metalloproteinases. Inhibitor studies provide evidence that NRADD is cleaved in two steps typical of regulated intramembrane proteolysis (RIP). Inhibition of gamma-secretase abrogates both the production of the soluble intracellular domain of NRADD and the appearance of NRADD in subnuclear structures. Thus, solubilized death domains with close homology to p75(NTR) might have a nuclear function. Furthermore, presenilin deficiency leads to abnormally glycosylated NRADD and overexpression of presenilin 2 inhibits NRADD maturation, which is dependent on the putative active site residue D366 but not on gamma-secretase activity. Our results demonstrate that NRADD is an additional gamma-secretase substrate and suggest that drugs against Alzheimer's disease will need to target gamma-secretase in a substrate-specific manner.
神经营养因子受体样死亡结构域蛋白（NRADD）是一种具有独特胞外结构域和与p75（NTR）同源的胞内结构域的死亡受体样蛋白。NRADD的表达会导致细胞凋亡，但仅在某些细胞类型中发生。本文对成熟的55 kDa糖蛋白的表达和蛋白水解加工进行了表征。N端截短的NRADD由一种需要早老素的γ-分泌酶活性进行加工，并且对γ-分泌酶抑制剂的敏感性与淀粉样β蛋白（Aβ）的分泌相同。内源性NRADD的胞外结构域通过金属蛋白酶的激活而脱落。抑制剂研究提供了证据，表明NRADD以典型的调节性膜内蛋白水解（RIP）的两个步骤进行切割。γ-分泌酶的抑制消除了NRADD可溶性胞内结构域的产生以及NRADD在亚核结构中的出现。因此，与p75（NTR）具有密切同源性的可溶性死亡结构域可能具有核功能。此外，早老素缺陷导致NRADD异常糖基化，早老素2的过表达抑制NRADD成熟，这取决于推定的活性位点残基D366，而不取决于γ-分泌酶活性。我们的结果表明NRADD是另一种γ-分泌酶底物，并表明抗阿尔茨海默病药物将需要以底物特异性方式靶向γ-分泌酶。
