2017年7月28日，国际微生物学知名期刊《PLOS Pathogens》在线发表了中国科学院生物化学与细胞生物学研究所胡荣贵研究组的论文“Bacterial effector NleL promotes enterohemorrhagic E. coli-induced attaching and effacing lesions by ubiquitylating and inactivating JNK”。该研究阐释了肠出血性大肠杆菌EHEC O157:H7的毒力蛋白NleL通过泛素化宿主JNK蛋白从而促进细菌感染的新分子机制。盛相鹏和尤青为论文第一作者，胡荣贵研究员为论文通讯作者。

肠出血性大肠杆菌(EHEC)是一类可引起严重食源性疾病的致病菌，其中最重要的是血清型为O157:H7的菌株。EHEC O157:H7是导致人和牲畜发生腹泻和出血性肠炎的主要原因之一，其引起的爆发感染逐年增加。EHEC O157:H7感染时会在宿主细胞上引起特征性的A/E损伤，形成独特的肌动蛋白聚集结构actin pedestals;A/E损伤的出现是EHEC成功感染宿主的标志之一。一种来源于EHEC O157:H7的细菌效应蛋白NleL曾被证实在体外具有类真核生物泛素连接酶的活性，但是其在EHEC感染过程中的生物学特性及作用机理尚未清楚。

EHEC在感染过程中可以将NleL蛋白传递到宿主细胞内。本研究发现，细菌蛋白NleL能够结合宿主JNK蛋白并对其特定位点进行单泛素化修饰和多泛素修饰。更为重要的是，NleL还可以有效地抑制JNK的磷酸化激活。NleL对JNK特定位点(K68)的单泛素化修饰干扰了JNK与上游磷酸激酶MKK7的结合，从而抑制了JNK磷酸化激活，进而抑制了下游c-Jun的磷酸化及转录因子AP-1的活性。AP-1还被发现可以参与调节actin pedestals(A/E损伤)的形成;而且NleL最终被证实可以通过抑制宿主JNK/AP-1通路来促进EHEC粘附宿主并形成A/E损伤。通过选用在结构和功能上类似于结肠上皮的人源Caco-2单层细胞模型进行体外细菌感染实验，发现EHEC可以在Caco-2单层上形成明显的A/E损伤，可用来替代体内感染实验，弥补EHEC不能以普通小鼠作为实验动物的缺陷。该项研究首次发现了NleL的作用底物并明确了NleL在EHEC感染过程中的生物学意义。这也是JNK蛋白首次被报道可以被进行泛素化修饰且泛素化修饰负调控磷酸化激活。

原文链接：

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.