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  4. The role of endocytosis in Notch signal in T cell
 
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The role of endocytosis in Notch signal in T cell

Date Issued
2006
Date
2006
Author(s)
Hsu, Ta-Chou
DOI
zh-TW
URI
http://ntur.lib.ntu.edu.tw//handle/246246/63313
Abstract
Notch signals play critical roles in immune system. Notch signal determine the development of T cell lineage and the differentiation of mature T cell. Recent studies in Drosophila and mammalian suggest that endocytosis is required for the generation of Notch intracellular domain (NICD) and initiation of Notch signal. Whether endocytosis is required for Notch signal in T cell remains unclear. Monoubquitination of target protein provides the internalization signal during endocytosis. Deltex is a Notch-binding E3 ligase containing RING finger. In this study, we investigated the role of endocytosis in the generation of Notch signal in T cell, and examine the possibility whether deltex is the E3 ligase for Notch receptor monoubquitination. We found that overexpression of deltex in DO11.10 T cell led to reduced NICD generation after delta-like-1 (Dl-1) stimulation compared to YFP control. Dl-1 induced HES-1 expression was also decreased in deltex-overexpressiing DO11.10 than YFP control. In contrast, knock-down of deltex slightly increased Dl-1-induced HES-1 expression in DO11.10 T cell related to pLL3.7 control. Our results indicate that deltex may play negative role in regulating Notch signal, and that deltex is likely not the E3 ligase required for Notch signal activation. To investigate the role of endocytosis in NICD generation, we first used dominant negative Dynamin2 (Dynamin2 K44A) to block endocytosis in T cells. The inducible expression of Dyn2 K44A in Jurkat cells led to apoptosis. We therefore switched to dominant negative Eps15 (Eps15 DIII) to study the effect of endocytosis blockage on NICD generation. To our surprise, we found that Eps15 DIII profoundly enhanced NICD generation after Dl-1 stimulation in DO11.10 cells. The cell surface staining of Notch indicates that Eps15 DIII expression did not lead to elevated Notch receptor accumulation on cell membrane for the observed NICD generation. However, the expression of NICD transcription target HES-1 was not significantly increased in Eps15 DII-expressing DO11.10 cells, suggesting there is difference between the generation of NICD and the activation of NICD transcription. Our results indicate that endocytosis is participated in the process of NICD generation after Dl-1 ligand stimulation, yet deltex may not be the E3 ligase that monoubquitinates Notch receptor after Dl-1 ligad stimulation. Further studies are required to reveal the detailed mechanism on how endocytosis is involved in NICD generation and on how NICD transcription activity is activated.
Subjects
T 細胞
內噬作用
Notch
Endocytosis
Eps15
dynamin2
Type
other
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