Tibbles L A, Ing Y L, Kiefer F, Chan J, Iscove N, Woodgett J R, Lassam N J
Ontario Cancer Institute, Toronto, Canada.
EMBO J. 1996 Dec 16;15(24):7026-35.
Mixed lineage kinase-3 (MLK-3) is a 97 kDa serine/threonine kinase with multiple interaction domains, including a Cdc42 binding motif, but unknown function. Cdc42 and the related small GTP binding protein Rac1 can activate the SAPK/JNK and p38/RK stress-responsive kinase cascades, suggesting that MLK-3 may have a role in upstream regulation of these pathways. In support of this role, we demonstrate that MLK-3 can specifically activate the SAPK/JNK and p38/RK pathways, but has no effect on the activation of ERKs. Immunoprecipitated MLK-3 catalyzed the phosphorylation of SEK1 in vitro, and co-transfected MLK-3 induced phosphorylation of SEK1 and MKK3 at sites required for activation, suggesting direct regulation of these protein kinases. Furthermore, interactions between MLK-3 and SEK and MLK-3 and MKK6 were observed in co-precipitation experiments. Finally, kinase-dead mutants of MLK-3 blocked activation of the SAPK pathway by a newly identified mammalian analog of Ste20, germinal center kinase, but not by MEKK, suggesting that MLK-3 functions to activate the SAPK/JNK and p38/RK cascades in response to stimuli transduced by Ste20-like kinases.
混合谱系激酶-3（MLK-3）是一种97 kDa的丝氨酸/苏氨酸激酶，具有多个相互作用结构域，包括一个Cdc42结合基序，但功能未知。Cdc42和相关的小GTP结合蛋白Rac1可以激活SAPK/JNK和p38/RK应激反应激酶级联反应，这表明MLK-3可能在这些信号通路的上游调节中发挥作用。为支持这一作用，我们证明MLK-3可以特异性激活SAPK/JNK和p38/RK信号通路，但对ERK的激活没有影响。免疫沉淀的MLK-3在体外催化SEK1的磷酸化，共转染的MLK-3诱导SEK1和MKK3在激活所需位点的磷酸化，表明对这些蛋白激酶的直接调节。此外，在共沉淀实验中观察到MLK-3与SEK以及MLK-3与MKK6之间的相互作用。最后，MLK-3的激酶失活突变体阻断了由新鉴定的哺乳动物Ste20类似物生发中心激酶激活的SAPK信号通路，但不阻断由MEKK激活的SAPK信号通路，这表明MLK-3的功能是响应由Ste20样激酶转导的刺激来激活SAPK/JNK和p38/RK级联反应。
