BACE1 Protein Endocytosis and Trafficking Are Differentially Regulated by Ubiquitination at Lysine 501 and the Di-leucine Motif in the Carboxyl Terminus
BACE1 Protein Endocytosis and Trafficking Are Differentially Regulated by Ubiquitination at Lysine 501 and the Di-leucine Motif in the Carboxyl Terminus
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DOI：
10.1074/jbc.m112.407072
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发表时间：
2012-12-14
影响因子：
4.8
通讯作者：
Tesco, Giuseppina
中科院分区：
文献类型：
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作者：
Kang, Eugene L.;Biscaro, Barbara;Tesco, Giuseppina
β位点淀粉样蛋白前体蛋白切割酶（BACE1）是天冬氨酸蛋白酶的一个膜系成员，已被确定为β分泌酶。BACE1通过分泌途径靶向到质膜，然后内化到核内体。膜蛋白向核内体和溶酶体的分选是由它们的羧基末端片段中存在的信号与特定运输分子的相互作用调节的。BACE1羧基末端片段包含二亮氨酸分选信号（(DDISLL500)-D-495）和一个泛素化位点Lys-501。在这里，我们报道了lys501 （BACE1K501R）泛素化的缺乏不影响内噬作用的速率，但在早期和晚期的内体/溶酶体以及细胞膜中产生BACE1的稳定和积累。相反，二亮氨酸基序（BACE1LLAA）的破坏极大地损害了BACE1的内吞作用，并产生BACE1向反式高尔基网络（TGN）的延迟逆行转运和BACE1向溶酶体的延迟递送，从而降低了其降解。此外，Lys-501泛素化缺失和二亮氨酸基序（BACE1LLAA/KR）的破坏共同导致BACE1稳定化和内化缺陷的叠加效应。最后，BACE1LLAA/KR在TGN中积累，而在eea1阳性区室中其水平降低，这表明lys501和二亮氨酸基元的泛素化对于BACE1从TGN转运到早期核内体是必要的。我们的研究已经阐明了二亮氨酸基序和Lys-501泛素化在BACE1内吞、运输和降解中的不同作用，并表明多个接头分子参与其中。
beta-Site amyloid precursor protein-cleaving enzyme (BACE1) is a membrane-tethered member of the aspartyl proteases that has been identified as beta-secretase. BACE1 is targeted through the secretory pathway to the plasma membrane and then is internalized to endosomes. Sorting of membrane proteins to the endosomes and lysosomes is regulated by the interaction of signals present in their carboxyl-terminal fragment with specific trafficking molecules. The BACE1 carboxyl-terminal fragment contains a di-leucine sorting signal ((DDISLL500)-D-495) and a ubiquitination site at Lys-501. Here, we report that lack of ubiquitination at Lys-501 (BACE1K501R) does not affect the rate of endocytosis but produces BACE1 stabilization and accumulation of BACE1 in early and late endosomes/lysosomes as well as at the cell membrane. In contrast, the disruption of the di-leucine motif (BACE1LLAA) greatly impairs BACE1 endocytosis and produces a delayed retrograde transport of BACE1 to the trans-Golgi network (TGN) and a delayed delivery of BACE1 to the lysosomes, thus decreasing its degradation. Moreover, the combination of the lack of ubiquitination at Lys-501 and the disruption of the di-leucine motif (BACE1LLAA/KR) produces additive effects on BACE1 stabilization and defective internalization. Finally, BACE1LLAA/KR accumulates in the TGN, while its levels are decreased in EEA1-positive compartments indicating that both ubiquitination at Lys-501 and the di-leucine motif are necessary for the trafficking of BACE1 from the TGN to early endosomes. Our studies have elucidated a differential role for the di-leucine motif and ubiquitination at Lys-501 in BACE1 endocytosis, trafficking, and degradation and suggest the involvement of multiple adaptor molecules.