Synergistic Interaction of MEK Kinase 2, c-Jun N-Terminal Kinase (JNK) Kinase 2, and JNK1 Results in Efficient and Specific JNK1 Activation

Mitogen-activated protein kinases (MAPKs) are activated through cascades or modules consisting of a MAPK, a MAPK kinase (MAPKK), and a MAPKK kinase (MAPKKK). Investigating the molecular basis of activation of the c-Jun N-terminal kinase (JNK) subgroup of MAPK by the MAPKKK MEKK2, we found that strong and specific JNK1 activation by MEKK2 was mediated by the MAPKK JNK kinase 2 (JNKK2) rather than by JNKK1 through formation of a tripartite complex consisting of MEKK2, JNKK2, and JNK1. No scaffold protein was required for the MEKK2-JNKK2-JNK1 tripartite-complex formation. Expression of JNK1, JNKK2, and MEKK2 significantly augmented the coprecipitation of, respectively, MEKK2-JNKK2, MEKK2-JNK1, and JNKK2-JNK1, indicating that the interaction of MEKK2, JNKK2, and JNK1 is synergistic. Finally, the JNK1 was activated more efficiently in the MEKK2-JNKK2-JNK1 complex than was the JNK1 excluded from the complex. Thus, formation of a signaling complex through synergistic interaction of a MAPKKK, a MAPKK, and a MAPK molecule like MEKK2-JNKK2-JNK1 is likely to be responsible for the efficient, specific flow of information via MAPK cascades.

丝裂原活化蛋白激酶（Mitogen-activated protein kinases, MAPKs）通过由1个MAPK、1个MAPK激酶（MAPK kinase, MAPKK）以及1个MAPK激酶激酶（MAPKK kinase, MAPKKK）组成的信号级联或模块被激活。本研究针对MAPK家族的c-Jun氨基末端激酶（c-Jun N-terminal kinase, JNK）亚型被MAPKKK MEKK2激活的分子机制展开探究，结果发现MEKK2对JNK1的强效特异性激活并非通过JNKK1介导，而是经由MAPKK JNK激酶2（JNKK2），并形成由MEKK2、JNKK2与JNK1组成的三元复合物（tripartite complex）实现。MEKK2-JNKK2-JNK1三元复合物的组装无需支架蛋白参与。分别过表达JNK1、JNKK2与MEKK2可显著增强MEKK2-JNKK2、MEKK2-JNK1以及JNKK2-JNK1的共沉淀水平，这表明MEKK2、JNKK2与JNK1三者间的相互作用具有协同效应。最后，相较于未结合入该复合物的JNK1，整合于MEKK2-JNKK2-JNK1复合物中的JNK1激活效率更高。因此，由MAPKKK、MAPKK与MAPK分子（如MEKK2-JNKK2-JNK1）通过协同相互作用形成的信号复合物，极有可能是介导MAPK级联通路实现高效且特异性信息传递的关键机制。