Zhang J, Kang D E, Xia W, Okochi M, Mori H, Selkoe D J, Koo E H
Department of Neurology, Harvard Medical School and Center for Neurologic Diseases, Brigham and Women's Hospital, Boston, Massachusetts 02115, USA.
J Biol Chem. 1998 May 15;273(20):12436-42. doi: 10.1074/jbc.273.20.12436.
The mechanisms by which mutations in presenilin-1 (PS1) and presenilin-2 (PS2) result in the Alzheimer's disease phenotype are unclear. Full-length PS1 and PS2 are each processed into stable proteolytic fragments after their biosynthesis in transfected cells. PS1 and PS2 have been localized by immunocytochemistry to the endoplasmic reticulum (ER) and Golgi compartments, but previous studies could not differentiate between the full-length presenilin proteins and their fragments. We carried out subcellular fractionation of cells stably transfected with PS1 or PS2 to determine the localization of full-length presenilins and their fragments. Full-length PS1 and PS2 were principally distributed in ER fractions, whereas the N- and C-terminal fragments were localized predominantly to the Golgi fractions. In cells expressing the PS1 mutant lacking exon 9 (DeltaE9), we observed only full-length molecules that were present in the ER and Golgi fractions. The turnover rate was considerably slower for the DeltaE9 holoprotein, apparently due to decreased degradation within the ER. Our results suggest that that full-length presenilin proteins are primarily ER resident molecules and undergo endoproteolysis within the ER. The fragments are subsequently transported to the Golgi compartment, where their turnover rate is much slower than that of the full-length presenilin in the ER.
早老素-1（PS1）和早老素-2（PS2）中的突变导致阿尔茨海默病表型的机制尚不清楚。全长PS1和PS2在转染细胞中生物合成后均被加工成稳定的蛋白水解片段。通过免疫细胞化学已将PS1和PS2定位于内质网（ER）和高尔基体区室，但先前的研究无法区分全长早老素蛋白及其片段。我们对稳定转染了PS1或PS2的细胞进行了亚细胞分级分离，以确定全长早老素及其片段的定位。全长PS1和PS2主要分布在内质网部分，而N端和C端片段主要定位于高尔基体部分。在表达缺失外显子9（DeltaE9）的PS1突变体的细胞中，我们仅观察到存在于内质网和高尔基体部分的全长分子。DeltaE9全蛋白的周转速度明显较慢，显然是由于内质网内降解减少所致。我们的结果表明，全长早老素蛋白主要是内质网驻留分子，并在内质网内进行内蛋白水解。这些片段随后被转运至高尔基体区室，在那里它们的周转速度比内质网中全长早老素的周转速度慢得多。
