HECT-type Ubiquitin Ligase ITCH Targets Lysosomal-associated Protein Multispanning Transmembrane 5 (LAPTM5) and Prevents LAPTM5-mediated Cell Death
HECT-type Ubiquitin Ligase ITCH Targets Lysosomal-associated Protein Multispanning Transmembrane 5 (LAPTM5) and Prevents LAPTM5-mediated Cell Death
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DOI：
10.1074/jbc.m111.251694
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发表时间：
2011-12-23
影响因子：
4.8
通讯作者：
Inazawa, Johji
中科院分区：
文献类型：
--
作者：
Ishihara, Takaya;Inoue, Jun;Inazawa, Johji
LAPTM5（溶酶体相关蛋白多跨膜5）是细胞内囊泡上的膜蛋白。我们之前已经证明laptm5阳性囊泡的积累与神经母细胞瘤自发消退过程中发生的程序性细胞死亡密切相关。虽然LAPTM5蛋白的积累可能发生在翻译后水平，但其分子机制尚不清楚。在这里，我们发现LAPTM5蛋白的水平受到E3泛素连接酶ITCH通过泛素化降解的负调控。ITCH通过其WW结构域直接结合LAPTM5的PPxY基序，并通过hect型连接酶结构域促进泛素化。ITCH过表达导致LAPTM5蛋白降解，相反，siRNA敲低ITCH导致LAPTM5蛋白稳定。此外，ITCH的抑制增强了神经母细胞瘤细胞中LAPTM5的积累导致的细胞死亡。这些发现表明，就泛素连接酶ITCH的降解而言，LAPTM5是一种新的底物，该系统可能通过阻止LAPTM5介导的细胞死亡，在神经母细胞瘤的自发消退中起负调节作用。
LAPTM5 (lysosomal-associated protein multispanning transmembrane 5) is a membrane protein on the intracellular vesicles. We have previously demonstrated that the accumulation of LAPTM5-positive vesicles was closely associated with the programmed cell death occurring during the spontaneous regression of neuroblastomas. Although the accumulation of LAPTM5 protein might occur at the post-translational level, the molecular mechanism has been unclear. Here, we found that the level of LAPTM5 protein is regulated negatively by the degradation through ubiquitination by ITCH, an E3 ubiquitin ligase. ITCH directly binds to the PPxY motif of LAPTM5 via its WW domains and promotes ubiquitination through a HECT-type ligase domain. Overexpression of ITCH led to the degradation of LAPTM5 protein, and conversely, knockdown of ITCH by siRNA resulted in the stabilization of LAPTM5 protein. In addition, the inhibition of ITCH enhanced the cell death occurred by accumulation of LAPTM5 in neuroblastoma cells. These findings suggest that LAPTM5 is a novel substrate in terms of degradation by the ubiquitin ligase ITCH, and this system might act as a negative regulator in the spontaneous regression of neuroblastomas by preventing LAPTM5-mediated cell death.