Levin-Salomon Vered, Maayan Inbal, Avrahami-Moyal Liat, Marbach Irit, Livnah Oded, Engelberg David
Department of Biological Chemistry, The Alexander Silberman Institute of Life Sciences, The Hebrew University of Jerusalem, Jerusalem 91904, Israel.
Biochem J. 2009 Jan 1;417(1):331-40. doi: 10.1042/BJ20081335.
MAPKs (mitogen-activated protein kinases) are key components in cell signalling pathways. Under optimal growth conditions, their activity is kept off, but in response to stimulation it is dramatically evoked. Because of the high degree of evolutionary conservation at the levels of sequence and mode of activation, MAPKs are believed to share similar regulatory mechanisms in all eukaryotes and to be functionally substitutable between them. To assess the reliability of this notion, we systematically analysed the activity, regulation and phenotypic effects of mammalian MAPKs in yeast. Unexpectedly, all mammalian MAPKs tested were spontaneously phosphorylated in yeast. JNKs (c-Jun N-terminal kinases) lost their phosphorylation in pbs2Delta cells, but p38s and ERKs (extracellular-signal-regulated kinases) maintained their spontaneous phosphorylation even in pbs2Deltaste7Deltamkk1Deltamkk2Delta cells. Kinase-dead variants of ERKs and p38s were phosphorylated in strains lacking a single MEK (MAPK/ERK kinase), but not in pbs2Deltaste7Deltamkk1Deltamkk2Delta cells. Thus, in yeast, p38 and ERKs are phosphorylated via a combined mechanism of autophosphorylation and MEK-mediated phosphorylation (any MEK). We further addressed the mechanism allowing mammalian MAPKs to exploit yeast MEKs in the absence of any activating signal. We suggest that mammalian MAPKs lost during evolution a C-terminal region that exists in some yeast MAPKs. Indeed, removal of this region from Hog1 and Mpk1 rendered them spontaneously and highly phosphorylated. It implies that MAPKs possess an efficient inherent autoposphorylation capability that is suppressed in yeast MAPKs via a C-terminal domain and in mammalian MAPKs via as yet unknown means.
丝裂原活化蛋白激酶（MAPKs）是细胞信号通路中的关键组成部分。在最佳生长条件下，它们的活性处于关闭状态，但在受到刺激时会被显著激活。由于在序列和激活模式水平上具有高度的进化保守性，MAPKs被认为在所有真核生物中共享相似的调节机制，并且在它们之间具有功能可替代性。为了评估这一观点的可靠性，我们系统地分析了哺乳动物MAPKs在酵母中的活性、调节和表型效应。出乎意料的是，所有测试的哺乳动物MAPKs在酵母中都会自发磷酸化。JNKs（c-Jun氨基末端激酶）在pbs2Delta细胞中失去磷酸化，但p38s和细胞外信号调节激酶（ERKs）即使在pbs2Delta ste7Delta mkk1Delta mkk2Delta细胞中仍保持自发磷酸化。ERK和p38的激酶失活变体在缺乏单个MEK（MAPK/ERK激酶）的菌株中被磷酸化，但在pbs2Delta ste7Delta mkk1Delta mkk2Delta细胞中则不会。因此，在酵母中，p38和ERK通过自磷酸化和MEK介导的磷酸化（任何MEK）的联合机制被磷酸化。我们进一步探讨了哺乳动物MAPKs在没有任何激活信号的情况下利用酵母MEKs的机制。我们认为哺乳动物MAPKs在进化过程中失去了一些酵母MAPKs中存在的C末端区域。事实上，从Hog1和Mpk1中去除该区域会使它们自发且高度磷酸化。这意味着MAPKs具有一种有效的固有自磷酸化能力，这种能力在酵母MAPKs中通过C末端结构域被抑制，而在哺乳动物MAPKs中则通过尚未知的方式被抑制。
