An evolutionarily conserved Rit GTPase-p38 MAPK signaling pathway mediates oxidative stress resistance

Ras-related small GTP-binding proteins control a wide range of cellular processes by regulating a variety of effector pathways, including prominent roles in the control of mitogen-activated protein kinase (MAPK) cascades. Although the regulatory role(s) for many Ras family GTPases are well established, the physiological function for the Rit/Rin subfamily has been lacking. Here, using both knockout mice and Drosophila models, we demonstrate an evolutionarily conserved role for Rit subfamily GTPases (mammalian Rit and Rin, and the Drosophila RIC homologue) in governing survival in response to oxidative stress. Primary embryonic fibroblasts derived from Rit knockout mice display increased apoptosis and selective disruption of MAPK signaling following reactive oxygen species (ROS) exposure but not in response to endoplasmic reticulum stress or DNA damage. These deficits include a reduction in ROS-mediated stimulation of a p38-MK2-HSP27 signaling cascade that controls Akt activation, directing Bad phosphorylation to promote cell survival. Furthermore, D-RIC null flies display increased susceptibility to environmental stresses and reduced stress-dependent p38 signaling, extending the Rit-p38 survival pathway to Drosophila. Together, our studies establish the Rit GTPases as critical regulators of an evolutionarily conserved, p38 MAPK-dependent signaling cascade that functions as an important survival mechanism for cells in response to oxidative stress.     

MAPK mediates Hsp25 signaling in incisor development

Rodent incisors are continuously growing teeth that include all stages of amelogenesis. Understanding amelogenesis requires investigations of the genes and their gene products control the ameloblast phenotype. One of the mechanisms related to tooth differentiation is mitogen-activated protein kinase (MAPK) signaling. The extracellular-signal regulated kinase (ERK)/mitogen-activated protein kinase kinase (MEK) cascade is associated with mechanisms that control the cell cycle and cell survival. However, the roles of cascades in incisor development remain to be determined. In this study, we investigated incisor development and growth in the mouse based on MAPK signaling. Moreover, heat-shock protein (Hsp)-25 is well known to be a useful marker of odontoblast differentiation. We used anisomycin (a protein-synthesis inhibitor that activates MAPKs) and U0126 (a MAPK inhibitor that blocks ERK1/2 phosphorylation) to examine the role of MAPKs in Hsp25 signaling in the development of the mouse incisor. We performed immunohistochemistry and in vitro culture using incisor tooth germ, and found that phospho-ERK (pERK), pMEK, and Hsp25 localized in developing incisor ameloblasts and anisomycin failed to produce incisor development. In addition, Western blotting results showed that anisomycin stimulated the phosphorylation of ERK, MEK, and Hsp25, and that some of these proteins were blocked by the U0126. These findings suggest that MAPK signals play important roles in incisor formation, differentiation, and development by mediating Hsp25 signaling.     

The Caenorhabditis elegans MAPK phosphatase VHP-1 mediates a novel JNK-like signaling pathway in stress response

Mitogen-activated protein kinases (MAPKs) are integral to the mechanisms by which cells respond to physiological stimuli and to a wide variety of environmental stresses. MAPK cascades can be inactivated at the MAPK activation step by members of the MAPK phosphatase (MKP) family. However, the components that act in MKP-regulated pathways have not been well characterized in the context of whole organisms. Here we characterize the Caenorhabditis elegans vhp-1 gene, encoding an MKP that acts preferentially on the c-Jun N-terminal kinase (JNK) and p38 MAPKs. We found that animals defective in vhp-1 are arrested during larval development. This vhp-1 defect is suppressed by loss-of-function mutations in the kgb-1, mek-1, and mlk-1 genes encoding a JNK-like MAPK, an MKK7-type MAPKK, and an MLK-type MAPKKK, respectively. The genetic and biochemical data presented here demonstrate a critical role for VHP-1 in the KGB-1 pathway. Loss-of-function mutations in each component in the KGB-1 pathway result in hypersensitivity to heavy metals. These results suggest that VHP-1 plays a pivotal role in the integration and fine-tuning of the stress response regulated by the KGB-1 MAPK pathway.     

Role of lipids in the MAPK signaling pathway

The mitogen-activated protein kinase (MAPK) signaling pathway is activated in response to a variety of extracellular stimuli such as growth factor stimulation. The best-characterized MAPK pathway involves the sequential activation of Raf, MEK and ERK proteins, capable of regulating the gene expression required for cell proliferation. Binding to specific lipids can regulate both the subcellular localization of these MAPK signaling proteins as well as their kinase activities. More recently it has become increasingly clear that the majority of MAPK signaling takes place intracellularly on endosomes and that the perturbation of endocytic pathways has dramatic effects on the MAPK pathway. This review highlights the direct effects of lipids on the localization and regulation of MAPK pathway proteins. In addition, the indirect effects lipids have on MAPK signaling via their regulation of endocytosis and the biophysical properties of different membrane lipids as a result of growth factor stimulation are discussed. The ability of a protein to bind to both lipids and proteins at the same time may act like a "ZIP code" to target that protein to a highly specific microlocation and could also allow a protein to be "handed off" to maintain tight control over its binding partners and location.     

MAPK pathway mediates muscarinic receptor-induced human lung fibroblast proliferation

Airway remodelling is a pathological feature of chronic inflammatory and obstructive airway diseases like asthma and COPD wherein fibroblasts contribute to structural alteration processes. We recently reported expression of multiple muscarinic receptors in human lung fibroblasts and demonstrated muscarinic receptor-induced, G(i)-mediated proliferation in these cells. We now explore the underlying intracellular signalling pathways. As a measure of cell proliferation ((3)H)-thymidine incorporation in primary human lung fibroblasts and MRC-5 fibroblasts was increased by about 2 fold in presence of the muscarinic receptor agonist carbachol (10 microM) and this effect could be prevented by the MEK inhibitor PD 98059 (30 microM). Western blot analysis revealed a rapid (within 2 min) activation of p42/44 MAPK (ERK1, ERK2) following exposure to 10 microM carbachol or oxotremorine, effects blocked by tiotropium as well as atropine. In conclusion, the proliferative response of lung fibroblasts to muscarine receptor stimulation is mediated via activation of the classical MEK-ERK MAPK cascade. It is suggested that prevention of cholinergic driven fibroblast proliferation by prolonged blockade of airway muscarinic receptors may contribute to the reported long term beneficial effects of anticholinergics.     

白念珠菌MAPK信号通路研究进展

白念珠菌是人类最常见的条件致病菌。促分裂素原活化蛋白激酶（MAPK链）是真核生物信号传递网络中的重要途径之一,在基因表达调控和细胞质功能活动中发挥关键作用。在白念珠菌中主要有4条MAPK途径：Mkcl途径、Cekl途径、Cek2途径和HOG途径。其中HOG途径在白念珠菌MAPK信号通路起着重要的作用。对于白念珠菌MAPK信号通路的作用及相关调控机制的了解,可以为寻找新的药物作用靶点,治疗念珠菌病提供帮助。     

Genetic modulation of ethylene biosynthesis and signaling in plants

With the isolation and characterization of the key enzymes and proteins, and the corresponding genes, involved in ethylene biosynthesis and sensing it has become possible to manipulate plant ethylene levels and thereby alter a wide range of physiological processes. The phytohormone ethylene is an essential signaling molecule that affects a large number of physiological processes; plants deprived of ethylene do not grow and develop normally. In a search for flexible on-off ethylene control, scientists have used inducible organ- and tissue-specific promoters to drive expression of different transgenes. Here, the various strategies that have been used to genetically engineer plants with decreased ethylene biosynthesis and sensitivity are reviewed and discussed.     

Cross-talk between sulfur assimilation and ethylene signaling in plants

Sulfur (S) deficiency is prevailing all over the world and becoming an important issue for crop improvement through maximising its utilization efficiency by plants for sustainable agriculture. Its interaction with other regulatory molecules in plants is necessary to improve our understanding on its role under changing environment. Our knowledge on the influence of S on ethylene signaling is meagre although it is a constituent of cysteine (Cys) required for the synthesis of reduced glutathione (GSH) and S-adenosyl methionine (SAM), a precursor of ethylene biosynthesis. Thus, there may be an interaction between S assimilation, ethylene signaling and plant responses under optimal and stressful environmental conditions. The present review emphasizes that responses of plants to S involve ethylene action. This evaluation will provide an insight into the details of interactive role of S and ethylene signaling in regulating plant processes and prove profitable for developing sustainability under changing environmental conditions.     

Serum response factor controls CYLD expression via MAPK signaling pathway

Tumor suppressor gene CYLD is a deubiquitinating enzyme which negatively regulates various signaling pathways by removing the lysine 63-linked polyubiquitin chains from several specific substrates. Loss of CYLD in different types of tumors leads to either cell survival or proliferation. In this study we demonstrate that lack of CYLD expression in CYLD-/- MEFs increases proliferation rate of these cells compared to CYLD+/+ in a serum concentration dependent manner without affecting cell survival. The reduced proliferation rate in CYLD+/+ in the presence of serum was due to the binding of serum response factor (SRF) to the serum response element identified in the CYLD promoter for the up-regulation of CYLD levels. The serum regulated recruitment of SRF to the CYLD promoter was dependent on p38 mitogen-activated protein kinase (MAPK) activity. Elimination of SRF by siRNA or inhibition of p38 MAPK reduced the expression level of CYLD and increased cell proliferation. These results show that SRF acts as a positive regulator of CYLD expression, which in turn reduces the mitogenic activation of serum for aberrant proliferation of MEF cells.     

MAPK pathway mediates EGR-1-HSP70-dependent cigarette smoke-induced chemokine production

Cigarette smoking, a major risk factor for chronic obstructive pulmonary disease, can cause airway inflammation, airway narrowing, and loss of elasticity, leading to chronic airflow limitation. In this report, we sought to define the signaling pathways activated by smoke and to identify molecules responsible for cigarette smoke-induced inflammation. We applied cigarette smoke water extract (CSE) to primary human lung fibroblasts and found that CSE significantly increased CXC chemokine IL-8 production. Meanwhile, 70-kDa heat shock protein (HSP70) was also induced by CSE in a dose- and time-dependent manner. CSE treatment stimulated HSP70 secretion by primary fibroblasts, which augmented IL-8 production. This was further confirmed by exogenously added recombinant HSP70. Using HSP70 small interfering RNA, we confirmed that CSE-induced chemokine production was dependent on heat shock protein expression. Further investigation showed that CSE could also stimulate early growth response-1 (EGR-1) in an ERK-dependent manner and that the expression of HSP70 was EGR-1 dependent. In view of these findings, we hypothesize that the MAPK-EGR-1-HSP70 pathway regulates the cigarette smoke-induced inflammatory process.     

The p38 MAPK pathway mediates interleukin-1-induced Sertoli cell proliferation

We have reported earlier that interleukin-1 (IL-1) is a potent growth factor for immature Sertoli cells (somatic cells in the testis required for testicular development and later spermatogenesis) and that this effect is synergistic with the mitogenic effect of follicle-stimulating hormone (FSH). The aim of the present study was to determine whether MAPK pathways are involved in mediating the mitogenic effect of IL-1 on Sertoli cells. Western blotting revealed that IL-1alpha activated p38 MAPK and JNK/SAPK, but not ERK, in Sertoli cells from 8- or 9-day-old rat. The inhibitor of p38 MAPK SB203580 attenuated the IL-1alpha-induced proliferation of Sertoli cells, as assessed by (3)H-thymidine incorporation and supravital staining as well as by direct cell counting. We conclude that the p38 MAPK pathway mediates the proliferative effect of IL-1alpha on immature Sertoli cells in vitro. Since the mitogenic effect of FSH is mediated via ERK, the synergistic action of IL-1alpha and FSH may be explained by their different intracellular signalling pathways. Induction of IL-1 by inflammation, infection or other tissue injuries may result in testicular damage by interfering with normal Sertoli cell development and thus future spermatogenesis.     

S1P2 receptor mediates sphingosine-1-phosphate-induced fibronectin expression via MAPK signaling pathway in mesangial cells under high glucose condition

Accumulation of extracellular matrix including fibronectin in mesangium is one of the major pathologic characteristics in diabetic nephropathy. In the current study, we explored role of sphingosine-1-phosphate (S1P) receptor in fibronectin expression and underlying molecular mechanism. Among five S1P receptors the mRNA level of S1P2 receptor was the most abundant in kidney of diabetic rats and mesangial cells under high glucose condition. S1P augmentation of fibronectin was significantly inhibited by S1P2 receptor antagonist JTE-013 and S1P2-siRNA. S1P-stimulated fibronectin expression was remarkably blocked by ERK1/2 inhibitor PD98059 and p38MAPK inhibitor SB203580. Phospho-ERK1/2 and phospho-p38MAPK level induced by S1P were markedly abrogated by JTE-013 and S1P2-siRNA. In conclusion, S1P2 receptor was significantly up-regulated under diabetic condition. S1P2 receptor mediated fibronectin expression through the activation of S1P-S1P2-MAPK (ERK1/2 and p38MAPK) axis in mesangial cells under high glucose condition, suggesting that it might be a potential therapeutic target for diabetic nephropathy treatment.     

ERK MAPK activation mediates the antiapoptotic signaling of melatonin in UVB-stressed U937 cells

The pineal gland hormone melatonin has been recently described to downregulate the intrinsic (or damage-induced) pathway of apoptosis in human leukocytes. These properties appear to depend on a specific mitochondrial signaling of melatonin which is associated with a lower generation of reactive oxygen species and a better control of redox-sensitive components such as the antiapoptotic protein Bcl-2. Other elements upstream in this signaling are expected to contribute regulatory roles that remain unexplored. The aim of this study was to investigate whether the extracellular signal-regulated kinase (ERK), which controls the balance between survival and death-promoting genes throughout the MAPK pathway, is involved in the antiapoptotic signaling of melatonin. Human monocytic U937 cells irradiated with UVB light were used as a model of stress-induced apoptosis. In this model we found that pharmacological concentrations of melatonin (1 mM) were able to decrease superoxide anion production, mitochondrial damage, and caspase-dependent apoptosis by improved Bcl-2 levels and decreased Cyt c release in the cytoplasm. Moreover, melatonin increased the phosphorylative activation of ERK 1/2 independently from the presence of UVB stress, and decreased the UVB-mediated activation of the stress kinases p38 MAPK and JNK. The ERK 1/2 inhibitor PD98059, but not the p38 MAPK inhibitor SB203580, abolished to different extents the effects that melatonin had on the UVB-induced ROS generation, mitochondrial dysfunction, and apoptosis. Using these inhibitors, a cross-talk effect between stress and survival-promoting kinases was tentatively identified, and confirmed the hierarchical role of ERK MAPK phosphorylation in the signaling of melatonin. In conclusion, melatonin sustains the activation of the survival-promoting pathway ERK MAPK which is required to antagonize UVB-induced apoptosis of U937 cells. This kinase mediates also the antioxidant and mitochondrial protection effects of this hormonal substance that may find therapeutic applications in inflammatory and immune diseases associated with leukocyte oxidative stress and accelerated apoptosis.