Specific phosphorylation and activation of ERK1c by MEK1b: a unique route in the ERK cascade

Extracellular signal-regulated kinases (ERKs) are key signaling molecules that regulate a large number of cellular processes, including mitosis. We showed previously that ERK1c, an alternatively spliced form of ERK1, facilitates mitotic Golgi fragmentation without the involvement of ERK1 and ERK2. Here we demonstrate that activation of ERK1c is mainly mediated by mitogen-activated protein kinase (MAPK)/ERK kinase 1b (MEK1b), which is an alternatively spliced form of MEK1 that was previously considered an inactive kinase. MEK1b phosphorylation and activity are preferentially stimulated by nocodazole, to induce its specific activity toward ERK1c. MEK1/2, on the other hand, preferentially target ERK1/2 in response to growth factors, such as EGF. As previously demonstrated for ERK1c, also MEK1b expression and activity are elevated during mitosis, and thereby enhance Golgi fragmentation and mitotic rate. MEK1 activity is also increased during mitosis, but this isoform facilitates mitotic progression without affecting the Golgi architecture. These results illustrate that the ERK cascade is divided into two routes: the classic MEK1/2–ERK1/2 and the splice-variant MEK1b–ERK1c, each of which regulates distinct cellular processes and thus extends the cascade specificity.     

猫视皮层ERK mRNA表达的研究

丝裂原激活的蛋白激酶又称细胞外信号调节激酶,具有神经元信号传导功能,参与多种发育过程。它由细胞外特殊信号激活,将酪氨酸磷酸化过程转化为丝氨酸／苏氨酸磷酸化过程,后者进一步调节下游的蛋白激酶。因此,细胞外信号调节激酶在磷酸化的连锁反应过程中起着枢纽作用。本文应用地高辛标记寡核苷酸探针的原位杂交技术,研究了细胞外信号调节激酶的２ 种亚型 ＥＲＫ１ 和ＥＲＫ２ ｍ ＲＮＡ 在生后４ 周龄的幼猫视皮层各层的分布。结果表明,ＥＲＫ１ ｍ ＲＮＡ 在视皮层的表达层次明确,以第Ⅴ层和第Ⅲ层的表达为最强,Ⅱ层呈中等表达,Ⅳ层较弱,Ⅵ层最弱,即在视皮层的表达强度为Ⅴ、Ⅲ＞ Ⅱ＞ Ⅳ＞ Ⅵ。与ＥＲＫ１相比,ＥＲＫ２ 的表达普遍较强,但层次欠清晰,其表达强度为Ⅴ、Ⅱ＞ Ⅲ、Ⅳ＞ Ⅵ。ＥＲＫ 的２ 种亚型在视皮层的Ⅰ层即分子层均不表达。ＥＲＫ１ 和ＥＲＫ２ ｍ ＲＮＡ 在视皮层的这种特征性分布提示,在幼猫的视皮层发育过程中,ＥＲＫ 可能具有独特的信号传递作用。     

Conformational snapshots of Tec kinases during signaling

Summary:  The control of cellular signaling cascades is of utmost importance in regulating the immune response. Exquisitely precise protein–protein interactions and chemical modification of substrates by enzymatic catalysis are the fundamental components of the signals that alert immune cells to the presence of a foreign antigen. In particular, the phosphorylation events induced by protein kinase activity must be spatially and temporally regulated by specific interactions to maintain a normal and effective immune response. High resolution structures of many protein kinases along with supporting biochemical data are providing significant insight into the intricate regulatory mechanisms responsible for controlling cellular signaling. The Tec family kinases are immunologically important kinases for which regulatory details are beginning to emerge. This review focuses on bringing together structural insights gained over the years to develop an understanding of how domain interactions both within the Tec kinases and between the Tec kinases and other signaling molecules control immune cell function.     

Japanese encephalitis virus infection stimulates Src tyrosine kinase in neuron/glia

Japanese encephalitis virus (JEV) is a neurotropic virus. The clinically manifestation of JEV-induced encephalitis is characterized by the brain inflammation and neuronal dysfunction and/or destruction. Currently, the cellular signaling molecules that underlie JEV-induced cerebral inflammation and cellular alterations are not well understood. Protein tyrosine phosphorylation events are key regulators of cellular signaling processes, including inflammation. We investigated whether Src protein tyrosine kinase (PTK) function in JEV-induced cellular changes in neuron/glia cultures. JEV infection modulated tyrosine phosphorylation events. Src PTK was hyperphosphorylated at the early stage of infection. Biochemical studies demonstrated that both inhibitors of the Src family PTK and Ras attenuated JEV-induced extracellular signal-regulated kinase (ERK) activation. Our results further revealed that PTK, Ras, and ERK inhibitors effectively suppressed JEV-induced pro-inflammatory cytokine expression and neurotoxicity. Pharmacological studies suggested that microglia secreted pro-inflammatory cytokine via Src/Ras/ERK pathway in responding to JEV infection. Another interesting observation was that nonstructural protein 3 (NS3) was able to interact with Src and showed tyrosine phosphorylation. However, the biological consequences of their interaction and exact control of NS3 tyrosine phosphorylation required further investigation. Our results suggest that the Src/Ras/ERK signaling cascade is involved in JEV-induced pro-inflammatory cytokine expression and neurotoxicity.     

Progesterone stimulates p42 extracellular signal-regulated kinase (p42erk) in human spermatozoa

Mitogen-activated protein kinases (MAPK), also known as extracellular signal-regulated kinases (ERKs) are cytoplasmic and nuclear serine/threonine kinases involved in signal transduction of several extracellular effectors. Recently, we have demonstrated that ERKs are present in spermatozoa and are involved in the regulation of the process of capacitation. We report here the effect of progesterone, a well-known inducer of the acrosome reaction in mammalian spermatozoa, on the immunolocalization, phosphorylation and activity of ERKs in capacitated human spermatozoa. We demonstrated that short-term incubation of spermatozoa with progesterone induces phosphorylation and activation of ERKs, resulting in redistribution of the proteins from the post-acrosomal region to the equatorial segment within the sperm head. To investigate the role of ERKs on the biological effects of progesterone, we used the MAPK cascade inhibitor PD098059, which strongly inhibited progesterone-induced activation of ERK-2. This compound did not inhibit progesterone-induced acrosome reaction, although it prevented redistribution of the enzyme to the equatorial region of the sperm head. These results suggest that the two processes, although temporally related, are independent. In conclusion, we provide new insight into the signal transduction pathways involved in the non- genomic action of progesterone in spermatozoa and suggest a possible involvement of ERKs in the process of fertilization.      

ERK信号通路的信号转导调控机制

胞外信号调控激酶（ERK）是发现的第1个丝裂原活化蛋白激酶（MAPK）,它调控多种重要的细胞生物学过程,包括细胞增殖、分化和凋亡等。ERK信号级联反应能够特异地介导广泛的生物学过程,其机制主要是通过信号的反馈调控,与支架蛋白的相互作用,亚细胞定位的改变,在级联反应的每一个环节存在不同功能的多种组分,细胞内非磷酸酶抑制物和G蛋白等的调控实现的。     

Activation of mitogen-activated protein kinases via CD40 is distinct from that stimulated by surface IgM on B cells

CD40 plays critical roles in B cell proliferation and differentiation in response to T cell-dependent antigenic stimulation. It has been suggested that CD40-mediated biological activities are transduced by a CD40 receptor-associated factor, CRAF1 and probably by protein tyrosine kinase Lyn and its substrates, phospholipase Cγ (PLCγ) and phosphatidylinositol-3 kinase (PI-3 kinase). Here, we describe the novel finding that a mitogen-activated protein kinase (MAPK)/extracellular signal-regulated protein kinase (ERK) cascade is involved in CD40 signaling in mouse B cells. Analysis of ERK activities in the B cell lymphoma cell line WEHI 231, which shows an increase in DNA synthesis or arrest of the cell cycle by cross-linking of CD40 or surface IgM (sIgM) cross-linking, respectively, indicated that one of the ERK isoforms, ERK2, was preferentially and rapidly activated after CD40 cross-linking. The CD40-mediated ERK2 activation was comparable to that after sIgM stimulation, although the activity was reduced toward the basal level within several minutes after stimulation. In contrast, ERK1 and ERK2 were activated to a similar extent by sIgM cross-linking, and the activities remained stable for at least 10 min. Furthermore, similar features of differential activation of ERK isoforms were observed in normal resting B cells in CD40 and sIgM signaling. These results suggest divergent regulatory pathways for ERK1 and ERK2 activation, and they support the notion that CD40 signaling may utilize a limited set of elements in the ERK cascade. Co-stimulation of WEHI 231 cells with anti-CD40 mAb rescues the cells from anti-IgM-mediated apoptosis, whereas this co-stimulation resulted in activation of ERK isoforms comparable to that in sIgM stimulation, without a synergistic effect. This result indicates the dominance of ERK activation in sIgM signaling over that of CD40, and it suggests that ERK activation may not be linked to the biological effect that CD40 stimulation in this cell line.     

Sustained activation of Src-family tyrosine kinases by ischemia: a potential mechanism mediating extracellular signal-regulated kinase cascades in hippocampal dentate gyrus

In the present report, we investigated the association between the sustained activation of Src family tyrosine kinases (primarily Src kinase) with the biphasic phosphorylation of extracellular signal-regulated kinase (ERK) induced by ischemia in the rat hippocampal CA3/dentate gyrus subfield. Post-ischemia reperfusion resulted in the phosphorylation of ERK in a Ras-dependent manner; down-regulation of NMDA receptors or Src family protein kinases by ketamine or 4-amino-5-(4-chlorophenyl)-7-(t-butyl) pyrazolo[3,4-d] pyrimidine (PP2) potently antagonized the activation of ERK, indicating that NMDA receptors and Src family tyrosine kinases are essential for the up-regulation of ERK activity following ischemic stimuli. Additionally, an ischemia-induced association between RKIP and Raf-1 resulted in the inhibition of the ERK signaling cascade through an inhibition of Src-mediated Raf-1 phosphorylation at Tyr340/341 residues. This ischemia-induced inhibition of ERK was not associated with other downstream pathways involving Raf-1 phosphorylation at Ser 259 elicited by protein kinase B (Akt). Dissociation of Raf-1 from RKIP by 24 h reperfusion or (4S)-3-[(E)-but-2-enoyl]-4-benzyl-2-oxazolidinone (locostatin) influenced the second phase of ERK activation elicited by the Src-Raf cassette. We propose that, following ischemia, the Src family tyrosine kinases are critical for modulation of the Ras/Raf/MEK/ERK cascade, in which RKIP is involved in biphasic phosphorylation of ERK via a blockade of Src-Raf cascades.     

MAPK/ERK1与STAT3在脂多糖诱导的腺性膀胱炎动物模型中的表达 

目的 研究丝裂原激活蛋白激酶(MAPK)成员之一ERK1与信号转导子与转录激活子3（STAT3）在内毒素脂多糖(LPS)诱导的大鼠腺性膀胱炎动物模型中的表达。方法 成年雌性SD大鼠24只,建立腺性膀胱炎动物模型,免疫组织化学染色检测上皮组织中ERK1及STAT3的表达,用RT-PCR技术及Western blotting检测ERK1及STAT3基因及蛋白表达量的变化     

细胞凋亡相关的信号通路

目前研究较多的细胞凋亡信号通路有wnt及JNK两条。Wnt信号通路有经典wnt通路,wnt/PCP通路和wnt/钙离子通路三个分支,引起细胞凋亡的机制主要有β-连环蛋白/tcf的转录调节途径,APC激活途径两种。JNK信号通路通过MKKKs-MKKs-MAPK转导。激活的JNK信号通路通过磷酸化转录因子、细胞骨架相关蛋白、酶等多种底物来调节细胞的生理过程,最终导致细胞凋亡。     

缺血/再灌注损伤时丝裂原活化蛋白激酶信号转导通路的变化

丝裂原活化蛋白激酶 (ｍｉｔｏｇｅｎ -ａｃｔｉｖａｔｅｄｐｒｏｔｅｉｎｋｉｎａｓｅｓ,ＭＡＰＫｓ)是一类丝 /苏氨酸蛋白激酶 ,是公认与细胞增殖、分化或凋亡调控密切相关的细胞内信号转导酶类 ,到目前为止 ,在哺乳类动物细胞中 ,已经发现ＭＡＰＫｓ家族具有ＥＲＫｓ(ｅｘｔｒａｃｅｌｌｕｌａｒｓｉｇｎａｌ-ｒｅｇｕｌａｔｅｄｋｉｎａｓｅｓ)、ＪＮＫｓ/ＳＡＰＫｓ(ｃ -ＪｕｎＮＨ2 -ｔｅｒ ｍｉｎａｌｋｉｎａｓｅｓ/ｓｔｒｅｓｓ -ａｃｔｉｖａｔｅｄｐｒｏｔｅｉｎｋｉｎａｓｅｓ)、ｐ38ＭＡＰＫ等不同亚类 ,其信号途径上游的信号…     

Cocaine- and amphetamine-regulated transcript (CART) peptide activates the extracellular signal-regulated kinase (ERK) pathway in AtT20 cells via putative G-protein coupled receptors

CART peptides are important neurotransmitters, but little is known about their receptors or signaling pathways in cells. In this study we describe the effects of CART 55-102 on the stimulation of extracellular signal-related kinase (ERK) in a pituitary-derived cell line. CART 55-102 treatment resulted in markedly enhanced ERK phosphorylation in AtT20 and GH3 cells, but had no significant effect on ERK phosphorylation levels in a variety of other cell types that were examined. The peptide activated ERK1 and 2 in AtT20 cells in a dose- and time-dependent manner, but an inactive peptide, CART 1-27, had no effect. U0126, an inhibitor of the MEK kinases, blocked the CART-stimulated activation of ERKs. ERK activation was also attenuated by pertussis toxin pre-treatment, but not by genistein, suggesting a Gi/o-dependent mechanism. Overall, these data strongly support the existence of a specific receptor for CART peptide that is a G-protein coupled receptor utilizing a Gi/o mechanism involving MEK1 and 2.