癌癥治療目前最大的挑戰(zhàn)之一是腫瘤細(xì)胞具有原發(fā)的耐藥性以及治療后逐漸產(chǎn)生抗藥性,。順鉑是目前廣泛用于臨床治療乳腺癌,、卵巢癌、前列腺癌等實(shí)體瘤的化療藥物,，它通過造成DNA損傷誘導(dǎo)細(xì)胞凋亡殺死癌細(xì)胞,。但是癌細(xì)胞抗藥的分子機(jī)制還不是很清楚。
泛素化是一種蛋白質(zhì)的翻譯后修飾,，參與調(diào)控多種生物學(xué)過程,，其系統(tǒng)功能紊亂與癌細(xì)胞凋亡以及癌癥發(fā)展進(jìn)程中起到了關(guān)鍵作用。蛋白泛素化過程由三種酶依次催化完成,，包括泛素激活酶（E1）,、泛素連接酶（E2）和泛素連接酶（E3）。其中,，E3泛素連接酶決定修飾底物的特異性。HECTD3 (Homologous to the E6-associated protein carboxyl terminus domain containing 3) 是一個(gè)功能未知的新的E3泛素連接酶,。
2013年1月的癌癥領(lǐng)域主流雜志NEOPLASIA發(fā)表了中國科學(xué)院昆明動物研究所陳策實(shí)研究員課題組的工作The HECTD3 E3 Ubiquitin Ligase Suppresses Cisplatin-induced Apoptosis via Stabilizing MALT1,。該研究首次發(fā)現(xiàn)：在乳腺癌和宮頸癌細(xì)胞抑制E3泛素連接酶HECTD3表達(dá)后能讓癌細(xì)胞對順鉑更加敏感，小鼠實(shí)驗(yàn)也充分證明了這一點(diǎn),。進(jìn)一步研究發(fā)現(xiàn),，敲低HECTD3表達(dá)使癌細(xì)胞對紫杉醇以及放射治療也更加敏感。
為了探索其分子機(jī)制,，課題組利用酵母雙雜交和免疫共沉淀實(shí)驗(yàn)發(fā)現(xiàn),，MALT1（mucosa-associated lymphoid tissue 1）是HECTD3的底物蛋白。HECTD3通過其N端DOC結(jié)構(gòu)域與MALT1的DD結(jié)構(gòu)域直接作用,，然后促進(jìn)MALT1泛素化修飾,。有趣的是，這種泛素化修飾不像大多數(shù)情況下導(dǎo)致底物蛋白降解,，相反地,，使MALT1蛋白在順鉑存在的情況下更加穩(wěn)定。這是因?yàn)镠ECTD3介導(dǎo)的MLAT1多聚泛素化鏈結(jié)構(gòu)不是通過泛素分子傳統(tǒng)的賴氨酸48位延伸,，而是通過泛素分子其它賴氨酸殘基延伸,。
MALT1已知在淋巴細(xì)胞的NF-kB信號通路活化中扮演重要角色，但是在實(shí)體瘤中的角色還沒有任何研究。該研究首次發(fā)現(xiàn)在實(shí)體癌細(xì)胞中敲低MALT1表達(dá)能夠增強(qiáng)順鉑誘導(dǎo)的細(xì)胞凋亡,。這個(gè)功能雖然比敲低HECTD3微弱一些,，但是足以說明MALT1和HECTD3的抑制細(xì)胞凋亡功能基本一致。相反,，過表達(dá)MALT1則能抑制細(xì)胞凋亡并挽救敲低HECTD3引起的順鉑敏感性增加,。
此項(xiàng)研究表明，HECTD3至少部分通過穩(wěn)定MALT1來促進(jìn)癌細(xì)胞存活,。這些結(jié)果為克服癌癥治療抗性提供了新的治療策略,。
該研究項(xiàng)目得到了國家自然科學(xué)基金，科技部蛋白質(zhì)重大研究計(jì)劃以及云南省高端科技人才項(xiàng)目的資助,。(生物谷Bioon.com)
DOI 10.1593/neo.121362
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PMID:
The HECTD3 E3 Ubiquitin Ligase Suppresses Cisplatin-induced Apoptosis via Stabilizing MALT1
Yi Li*,†,3, Xi Chen*,‡,3, Zehua Wang*, Dong Zhao§, Hui Chen¶, Wenlin Chen#, Zhongmei Zhou*, Junran Zhang**, Jing Zhang¶, Hongmin Li¶,†† and Ceshi Chen*
Homologous to the E6-associated protein carboxyl terminus domain containing 3 (HECTD3) is an E3 ubiquitin ligase with unknown functions. Here, we show that HECTD3 confers cancer cell resistance to cisplatin. To understand the molecular mechanisms, we performed a yeast two-hybrid analysis and identified mucosa-associated lymphoid tissue 1 (MALT1) as an HECTD3-interacting protein. HECTD3 promotes MALT1 ubiquitination with nondegradative polyubiquitin chains by direct interacting with the MALT1 through its N-terminal destruction of cyclin domain. HECTD3 does not target MALT1 for degradation but stabilize it. HECTD3 depletion dramatically decreases the levels of MALT1 in MCF7 and HeLa cells treated with cisplatin, which is correlated to an increase in apoptosis. Knockdown of MALT1 likewise increases cisplatin-induced apoptosis in these cancer cells. However, HECTD3 overexpression leads to a decreased cisplatin-induced apoptosis, whereas overexpression of MALT1 partially rescues HECTD3 depletion–induced apoptosis. These findings suggest that HECTD3 promotes cell survival through stabilizing MALT1. Our data have important implications in cancer therapy by providing novel molecular targets.
