EMP2 (Epithelial membrane protein-2)，為GAS3/PMP22 family的成員，以tetraspan形式表現在細胞膜上之蛋白質。已知可抑制細胞分化、生長以及影響細胞凋亡。Dr. N. H. Chow以大豆萃取物Isoflavones處理膀胱癌細胞，EMP2基因有過量表現之情形，進一步研究發現EMP2可抑制膀胱癌細胞生長。此外，microarray結果顯示EMP2的過量表現可抑制Ras相關基因的表現例如: Ras homolog gene family, member Q (RHOQ)、member of Ras oncogene family-like 4 (RABL4)、Ras and Rab interactor 3 (RIN3)。已知人類約有30%的腫瘤具有Ras突變，膀胱癌為Ras 突變的好發腫瘤之一。但目前對EMP2如何抑制腫瘤形成的機制並不清楚。本研究主要探討EMP2是否可抑制Ras活化所誘發之腫瘤以及影響哪些生物特性。首先將EMP2綠色螢光蛋白質體pEMP2-GFP送入一個具有Ras 可調控系統的細胞株 (7-4)，建立永久之細胞株。結果發現EMP2可抑制Ras之表現量以及活性，此抑制是在後轉錄之階段，然而究竟是Ras合成減少或是Ras 蛋白的分解加速有待進一步之釐清。活體外試驗中(in vitro)也證實過量表現EMP2的細胞生長速率降低，但細胞的移動性並沒有明顯的被抑制。而EMP2過量表達可抑制Ras活化誘發之群落形成能力。此外，EMP2過量表達亦會引起細胞之凋亡並且影響細胞週期。將同時表現EMP2以及Ras之細胞株利用皮下方式分別注入免疫正常(ICR)以及免疫缺失(SCID)之老鼠，均可抑制Ras誘發的腫瘤。在ICR老鼠實驗中腫瘤大小約減少6-27倍，而在免疫缺失的SCID老鼠中腫瘤只減少3倍，此結果顯示EMP2的確可抑制Ras活化導致的腫瘤形成，此外宿主免疫力亦扮演一定之角色。進一步分析老鼠的腫瘤，表現EMP2之腫瘤血管的數量也比較少。綜合以上所述，本研究發現EMP2可透過抑制Ras活性影響細胞的生長，誘發細胞凋亡以及抑制血管新生達到抑制腫瘤形成。本研究證實EMP2具有Ras所誘發之腫瘤，對抑制Ras相關腫瘤之治療提供莫大的幫助。

Epithelial membrane protein-2 (EMP2), a member of GAS3/PMP22 family, is a tetraspan protein and has been implicated in the control of cell growth, proliferation and cell apoptosis. Dr. N. H. Chow’s study revealed that soy isoflavones could enhance the expression level of EMP2 and inhibited the growth of bladder cancer cells. Besides, in microarray data EMP2 overexpression inhibited Ras related genes, such as Ras homolog gene family, member Q (RHOQ)、member of Ras oncogene family-like 4 (RABL4)、Ras and Rab interactor 3 (RIN3)。Ha-ras mutations are common in bladder carcinomas. It is interesting to reveal whether EMP2 overexpression can inhibit Ras related tumor formation. pEMP2-GFP fusion plasmid was transfected into Ras inducible cell line (7-4) to establish the stable cell lines. The results of the stable cell lines overexpressing EMP2 demonstrated that EMP2 can inhibit Ras activity as well as Ras protein expression and the regulation is at post-transcription level. EMP2 overexpression suppressed Ras induced cell proliferation but not cell migration. Further analysis showed that EMP2 overexpresion can induce cell apoptosis through disruption of the cell cycle progression. EMP overexpression could also suppress Ras induced colony formation. The EMP2 overexpression cells and 7-4 cells were subcutaneously injected into ICR and SCID mice, which are immune competent and immune deficient, respectively. For tumor formation, the tumor size in ICR and SCID mice was 6~27 fold and 3 fold smaller than the control Ras alone induced tumor. These results suggest that EMP2 can inhibit Ras induced tumor formation in mice and host immunity is also involved. Moreover, EMP2 overexpression can inhibit blood vessel formation. All toghther, we reveal that EMP2 overexpression inhibits Ras-related tumorigenesis, possibly through suppressing Ras activity, inducing cell apoptosis and decreasing blood vessels. In conclusion, EMP2 possesses features of tumor suppresser and has the potential to be used to against Ras-related cancers.

孫瑩. (2004) 探索大豆異黃酮類抗癌的機轉: EMP2和ITM1基因之研究. 國立成功大學碩士論文
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