2017年7月28日，國際微生物學知名期刊《PLOS Pathogens》在線發(fā)表了中國科學院生物化學與細胞生物學研究所胡榮貴研究組的論文“Bacterial effector NleL promotes enterohemorrhagic E. coli-induced attaching and effacing lesions by ubiquitylating and inactivating JNK”。該研究闡釋了腸出血性大腸桿菌EHEC O157:H7的毒力蛋白NleL通過泛素化宿主JNK蛋白從而促進細菌感染的新分子機制。盛相鵬和尤青為論文第一作者，胡榮貴研究員為論文通訊作者。

腸出血性大腸桿菌(EHEC)是一類可引起嚴重食源性疾病的致病菌，其中最重要的是血清型為O157:H7的菌株。EHEC O157:H7是導致人和牲畜發(fā)生腹瀉和出血性腸炎的主要原因之一，其引起的爆發(fā)感染逐年增加。EHEC O157:H7感染時會在宿主細胞上引起特征性的A/E損傷，形成獨特的肌動蛋白聚集結(jié)構(gòu)actin pedestals;A/E損傷的出現(xiàn)是EHEC成功感染宿主的標志之一。一種來源于EHEC O157:H7的細菌效應蛋白NleL曾被證實在體外具有類真核生物泛素連接酶的活性，但是其在EHEC感染過程中的生物學特性及作用機理尚未清楚。

EHEC在感染過程中可以將NleL蛋白傳遞到宿主細胞內(nèi)。本研究發(fā)現(xiàn)，細菌蛋白NleL能夠結(jié)合宿主JNK蛋白并對其特定位點進行單泛素化修飾和多泛素修飾。更為重要的是，NleL還可以有效地抑制JNK的磷酸化激活。NleL對JNK特定位點(K68)的單泛素化修飾干擾了JNK與上游磷酸激酶MKK7的結(jié)合，從而抑制了JNK磷酸化激活，進而抑制了下游c-Jun的磷酸化及轉(zhuǎn)錄因子AP-1的活性。AP-1還被發(fā)現(xiàn)可以參與調(diào)節(jié)actin pedestals(A/E損傷)的形成;而且NleL最終被證實可以通過抑制宿主JNK/AP-1通路來促進EHEC粘附宿主并形成A/E損傷。通過選用在結(jié)構(gòu)和功能上類似于結(jié)腸上皮的人源Caco-2單層細胞模型進行體外細菌感染實驗，發(fā)現(xiàn)EHEC可以在Caco-2單層上形成明顯的A/E損傷，可用來替代體內(nèi)感染實驗，彌補EHEC不能以普通小鼠作為實驗動物的缺陷。該項研究首次發(fā)現(xiàn)了NleL的作用底物并明確了NleL在EHEC感染過程中的生物學意義。這也是JNK蛋白首次被報道可以被進行泛素化修飾且泛素化修飾負調(diào)控磷酸化激活。

原文鏈接：

Bacterial effector NleL promotes enterohemorrhagic E. coli-induced attaching and effacing lesions by ubiquitylating and inactivating jnk

原文摘要：

As a major diarrheagenic human pathogen, enterohemorrhagic Escherichia coli (EHEC) produce attaching and effacing (A/E) lesions, characterized by the formation of actin pedestals, on mammalian cells. A bacterial T3SS effector NleL from EHEC O157:H7 was recently shown to be a HECT-like E3 ligase in vitro, but its biologicalfunctions and host targets remain elusive. Here, we report that NleL is required to effectively promote EHEC-induced A/E lesions and bacterial infection. Furthermore, human c-Jun NH2-terminal kinases (JNKs) were identified as primary substrates of NleL. NleL-induced JNK ubiquitylation, particularly mono-ubiquitylation at the Lys 68 residue of JNK, impairs JNK’s interaction with an upstream kinase MKK7, thus disrupting JNK phosphorylation and activation. This subsequently suppresses the transcriptional activity of activator protein-1 (AP-1), which modulates the formation of the EHEC-induced actin pedestals. Moreover, JNK knockdown or inhibition in host cells complements NleL deficiency in EHEC infection. Thus, we demonstrate that the effector protein NleL enhances the ability of EHEC to infect host cells by targeting host JNK, and elucidate an inhibitory role of ubiquitylation in regulating JNK phosphorylation.