Gao Y, Pimplikar S W
Institute of Pathology, Case Western Reserve University, Cleveland, OH 44106, USA.
Proc Natl Acad Sci U S A. 2001 Dec 18;98(26):14979-84. doi: 10.1073/pnas.261463298. Epub 2001 Dec 11.
Sequential processing of the amyloid precursor protein (APP) by beta- and gamma-secretases generates the Abeta peptide, a major constituent of the senile plaques observed in Alzheimer's disease. The cleavage by gamma-secretase also results in the cytoplasmic release of a 59- or 57-residue-long C-terminal fragment (Cgamma). This processing resembles regulated intramembrane proteolysis of transmembrane proteins such as Notch, where the released cytoplasmic fragments enter the nucleus and modulate gene expression. Here, we examined whether the analogous Cgamma fragments of APP also exert effects in the nucleus. We find that ectopically expressed Cgamma is present both in the cytoplasm and in the nucleus. Interestingly, expression of Cgamma59 causes disappearance of PAT1, a protein that interacts with the APP cytoplasmic domain, from the nucleus and induces its proteosomal degradation. Treatment of cells with lactacystin prevents PAT1 degradation and retains its nuclear localization. By contrast, Cgamma57, a minor product of gamma-cleavage, is only marginally effective in PAT1 degradation. Furthermore, Cgamma59 but not Cgamma57 potently represses retinoic acid-responsive gene expression. Thus, our studies provide the evidence that, as predicted by the regulated intramembrane proteolysis mechanism, Cgamma seems to function in the nucleus.
β-分泌酶和γ-分泌酶对淀粉样前体蛋白（APP）的顺序加工产生了Aβ肽，这是在阿尔茨海默病中观察到的老年斑的主要成分。γ-分泌酶的切割还导致一个59或57个残基长的C末端片段（Cγ）在细胞质中释放。这种加工类似于跨膜蛋白如Notch的调节性膜内蛋白水解，其中释放的细胞质片段进入细胞核并调节基因表达。在这里，我们研究了APP类似的Cγ片段是否也在细胞核中发挥作用。我们发现异位表达的Cγ存在于细胞质和细胞核中。有趣的是，Cγ59的表达导致PAT1（一种与APP细胞质结构域相互作用的蛋白质）从细胞核中消失，并诱导其蛋白酶体降解。用乳胞素处理细胞可防止PAT1降解并保留其核定位。相比之下，γ-切割的次要产物Cγ57在PAT1降解中仅具有微弱的作用。此外，Cγ59而非Cγ57强烈抑制视黄酸反应性基因的表达。因此，我们的研究提供了证据，正如调节性膜内蛋白水解机制所预测的那样，Cγ似乎在细胞核中发挥作用。
