Tekirian T L, Merriam D E, Marshansky V, Miller J, Crowley A C, Chan H, Ausiello D, Brown D, Buxbaum J D, Xia W, Wasco W
Genetics and Aging Unit, Department of Neurology, Massachusetts General Hospital, Harvard Medical School, Charlestown, MA 02129, USA.
Brain Res Mol Brain Res. 2001 Nov 30;96(1-2):14-20. doi: 10.1016/s0169-328x(01)00250-9.
Mutations in the genes that encode the presenilin 1 and 2 (PS1 and PS2) proteins cause the majority of familial Alzheimer's disease (FAD). Differential cleavage of the presenilins results in a generation of at least two C-terminal fragments (CTFs). An increase in the smaller of these two CTFs is one of the few changes in presenilin processing associated with FAD mutations in both PS1 and PS2. Interestingly, the phosphorylation of PS2 modulates the production of the smaller, caspase-derived PS2 CTF, which indicates that the generation of this fragment is a regulated, physiologic event. To date, there is no data concerning the subcellular distribution of the caspase-derived PS2 CTF. Because this fragment is normally present at levels that are difficult to detect, we have used cell lines in which the production of wild-type or N141I mutant PS2 is controlled by a tetracycline-regulated promoter in order to assess the subcellular localization of the caspase CTF in relation to the larger, constitutive PS2 CTF and to PS2 holoprotein. We have found that when levels of PS2 are low, the constitutive CTF colocalizes with markers consistent with localization in the early Golgi-ER-Golgi intermediate compartment (ERGIC) while the caspase CTF colocalizes with markers for the endoplasmic reticulum (ER). Following induction of wild-type or mutant PS2, when the levels of PS2 are high, the primary localization of the constitutive CTF appears to shift from the early Golgi-ERGIC in addition to the ER. Interestingly, while the induction of wild-type PS2 resulted in the localization of the caspase CTF primarily in the ER, the induction of mutant PS2 resulted in the localization of the caspase CTF to both the ER and the early Golgi-ERGIC. In summary, these data suggest that the two presenilin 2 CTFs have different patterns of subcellular localization and that the N141I PS2 mutation alters the localization pattern of the PS2 caspase fragment.
编码早老素1和2（PS1和PS2）蛋白的基因突变会导致大多数家族性阿尔茨海默病（FAD）。早老素的差异性切割会产生至少两个C末端片段（CTF）。这两个CTF中较小的那个片段增加是与PS1和PS2中FAD突变相关的早老素加工过程中为数不多的变化之一。有趣的是，PS2的磷酸化调节了较小的、由半胱天冬酶衍生的PS2 CTF的产生，这表明该片段的产生是一个受调控的生理事件。迄今为止，尚无关于由半胱天冬酶衍生的PS2 CTF亚细胞分布的数据。由于该片段通常以难以检测到的水平存在，我们使用了细胞系，其中野生型或N141I突变型PS2的产生由四环素调控启动子控制，以便评估半胱天冬酶CTF相对于较大的、组成型PS2 CTF和PS2全蛋白的亚细胞定位。我们发现，当PS2水平较低时，组成型CTF与与早期高尔基体-内质网-高尔基体中间区室（ERGIC）定位一致的标记物共定位，而半胱天冬酶CTF与内质网（ER）的标记物共定位。在诱导野生型或突变型PS2后，当PS2水平较高时，组成型CTF的主要定位似乎从早期高尔基体-ERGIC转移到了ER。有趣的是，虽然诱导野生型PS2导致半胱天冬酶CTF主要定位于ER，但诱导突变型PS2导致半胱天冬酶CTF定位于ER和早期高尔基体-ERGIC。总之，这些数据表明两个早老素2 CTF具有不同的亚细胞定位模式，并且N141I PS2突变改变了PS2半胱天冬酶片段的定位模式。
