PDF(Sci-hub)
Abstract：
Xenopus ERK2, also known as Xp42 MAPK, is activated by progesterone and regulates meiotic progression in the oocytes through activation of the phosphatase Cdc25C and inhibition of the protein kinase Myt1, thus promoting dephosphorylation and activation of cyclinB/Cdc2 (MPF). Indeed, it has been reported that stress protein kinases p38 and JNK are activated during meiotic progression and, more specifically, that p38γ regulates meiosis through activation of Cdc25C. However, the role of JNK in meiotic progression is not so clear, and despite a 42kDa protein is detected with pJNK antibodies (XpJNK-p42), the specific isoform activated by progesterone has not been characterized in detail. The serine/threonine kinase MEKK1, an upstream activator of JNK and p38, is activated during stress conditions and regulates apoptosis in different cell types. Here we show that ectopic expression of a constitutively active MEKK1 in Xenopus oocytes induces phosphorylation of p38, JNK and ERK and accelerates meiotic progression induced by progesterone. Inhibition of each individual pathway reduces the acceleration of meiosis induced by MEKK1. However, constitutively active MEKK1 induces phosphorylation of two JNK isoforms (p40 and p49, corresponding to JNK1-1 and JNK1-2 respectively) distinct to the p42 protein detected with pJNK antibodies during meiotic progression (XpJNK-p42). Moreover, a constitutively active MKK7, which specifically activates the JNK signaling pathway and induces phosphorylation of the p40 and p49 isoforms, does not accelerate meiotic progression. Immunoprecipitation of the p42 protein with pJNK antibodies and subsequent analysis by mass spectrometry shows that XpJNK-p42 is, in fact, pERK2. Ectopic expression of ERK2 in oocytes treated with progesterone or hyperosmotic shock indicates that ERK2 is phosphorylated in both conditions but is only detected with pJNK antibodies in progesterone-treated oocytes. In addition, mature oocytes only present a moderate increase of Jun kinase activity, which is not inhibited by SP600125. In conclusion, JNKs are not activated during meiotic progression and XpJNK-p42 is a post-translational modification of pERK induced by progesterone.
摘要：
非洲爪狼ERK2，也被称为Xp42MAPK，被孕酮激活，并通过激活磷酸酶Cdc25C和抑制蛋白激酶Myt1来调节卵母细胞的减数分裂进程，从而促进去磷酸化和cyclinB/Cdc2（MPF）的激活。的确,据报道，应激蛋白激酶p38和JNK在减数分裂过程中被激活，更具体地说,p38γ通过激活Cdc25C调节减数分裂。然而,JNK在减数分裂进程中的作用尚不清楚，尽管用pJNK抗体（XpJNK-p42）检测到42kDa蛋白，孕酮激活的特定同工型尚未详细表征。丝氨酸/苏氨酸激酶MEKK1是JNK和p38的上游激活剂，在应激条件下被激活并调节不同细胞类型的细胞凋亡。在这里，我们表明，在非洲爪的卵母细胞中组成型活性MEKK1的异位表达诱导p38，JNK和ERK的磷酸化，并加速孕酮诱导的减数分裂进程。每个单独途径的抑制降低了MEKK1诱导的减数分裂的加速。然而,组成型活性MEKK1诱导两种JNK同工型（p40和p49，分别对应于JNK1-1和JNK1-2）的磷酸化，这与减数分裂过程中用pJNK抗体检测到的p42蛋白不同（XpJNK-p42）。此外，组成型活性MKK7，其特异性激活JNK信号通路并诱导p40和p49亚型的磷酸化，不会加速减数分裂的进展。p42蛋白与pJNK抗体的免疫沉淀和随后的质谱分析表明，XpJNK-p42是，事实上,pERK2。用孕酮或高渗休克处理的卵母细胞中ERK2的异位表达表明ERK2在两种情况下都被磷酸化，但仅在孕酮处理的卵母细胞中用pJNK抗体检测到。此外,成熟卵母细胞仅呈现Jun激酶活性的适度增加，SP600125不抑制。总之,JNK在减数分裂过程中不被激活,并且XpJNK-p42是由孕酮诱导的pERK的翻译后修饰。
