A divergence in the MAP kinase regulatory network defined by MEK kinase and Raf

Modulators of MAPK pathway activity during filamentous growth in Saccharomyces cerevisiae

Mitogen-activated protein kinase (MAPK) pathways control the response to intrinsic and extrinsic stimuli. In the budding yeast Saccharomyces cerevisiae, cells undergo filamentous growth, which is regulated by the fMAPK pathway. To better understand the regulation of the fMAPK pathway, a genetic screen was performed to identify spontaneous mutants with elevated activity of an fMAPK pathway-dependent growth reporter (ste4  FUS1-HIS3). In total, 159 mutants were isolated and analyzed by secondary screens for invasive growth by the plate-washing assay and filament formation by microscopy. Thirty-two mutants were selected for whole-genome sequencing, which identified new alleles in genes encoding known regulators of the fMAPK pathway. These included gain-of-function alleles in STE11, which encodes the MAPKKK, as well as loss-of-function alleles in KSS1, which encodes the MAP kinase, and loss-of-function alleles in RGA1, which encodes a GTPase-activating protein (GAP) for CDC42. New alleles in previously identified pathway modulators were also uncovered in ALY1, AIM44, RCK2, IRA2, REG1, and in genes that regulate protein folding (KAR2), glycosylation (MNN4), and turnover (BLM10). Mutations leading to C-terminal truncations in the transcription factor Ste12p were also uncovered that resulted in elevated reporter activity, identifying an inhibitory domain of the protein from residues 491 to 688. We also find that a diversity of filamentous growth phenotypes can result from combinatorial effects of multiple mutations and by loss of different regulators of the response. The alleles identified here expand the connections surrounding MAPK pathway regulation and reveal new features of proteins that function in the signaling cascade.

Growing and dividing: how O-GlcNAcylation leads the way

Cell cycle errors can lead to mutations, chromosomal instability, or death; thus, the precise control of cell cycle progression is essential for viability. The nutrient-sensing posttranslational modification, O-GlcNAc, regulates the cell cycle allowing one central control point directing progression of the cell cycle. O-GlcNAc is a single N-acetylglucosamine sugar modification to intracellular proteins that is dynamically added and removed by O-GlcNAc transferase (OGT) and O-GlcNAcase (OGA), respectively. These enzymes act as a rheostat to fine-tune protein function in response to a plethora of stimuli from nutrients to hormones. O-GlcNAc modulates mitogenic growth signaling, senses nutrient flux through the hexosamine biosynthetic pathway, and coordinates with other nutrient-sensing enzymes to progress cells through Gap phase 1 (G1). At the G1/S transition, O-GlcNAc modulates checkpoint control, while in S Phase, O-GlcNAcylation coordinates the replication fork. DNA replication errors activate O-GlcNAcylation to control the function of the tumor-suppressor p53 at Gap Phase 2 (G2). Finally, in mitosis (M phase), O-GlcNAc controls M phase progression and the organization of the mitotic spindle and midbody. Critical for M phase control is the interplay between OGT and OGA with mitotic kinases. Importantly, disruptions in OGT and OGA activity induce M phase defects and aneuploidy. These data point to an essential role for the O-GlcNAc rheostat in regulating cell division. In this review, we highlight O-GlcNAc nutrient sensing regulating G1, O-GlcNAc control of DNA replication and repair, and finally, O-GlcNAc organization of mitotic progression and spindle dynamics.

Ecological inducers of the yeast filamentous growth pathway reveal environment-dependent roles for pathway components

Signaling modules, such as mitogen-activated protein kinase (MAPK) pathways, are evolutionarily conserved drivers of cell differentiation and stress responses. In many fungal species including pathogens, MAPK pathways control filamentous growth, where cells differentiate into an elongated cell type. The convenient model budding yeast Saccharomyces cerevisiae undergoes filamentous growth by the filamentous growth (fMAPK) pathway; however, the inducers of the pathway remain unclear, perhaps because pathway activity has been mainly studied in laboratory conditions. To address this knowledge gap, an ecological framework was used, which uncovered new fMAPK pathway inducers, including pectin, a material found in plants, and the metabolic byproduct ethanol. We also show that induction by a known inducer of the pathway, the non-preferred carbon source galactose, required galactose metabolism and induced the pathway differently than glucose limitation or other non-preferred carbon sources. By exploring fMAPK pathway function in fruit, we found that induction of the pathway led to visible digestion of fruit rind through a known target, PGU1, which encodes a pectolytic enzyme. Combinations of inducers (galactose and ethanol) stimulated the pathway to near-maximal levels, which showed dispensability of several fMAPK pathway components (e.g., mucin sensor, p21-activated kinase), but not others (e.g., adaptor, MAPKKK) and required the Ras2-protein kinase A pathway. This included a difference between the transcription factor binding partners for the pathway, as Tec1p, but not Ste12p, was partly dispensable for fMAPK pathway activity. Thus, by exploring ecologically relevant stimuli, new modes of MAPK pathway signaling were uncovered, perhaps revealing how a pathway can respond differently to specific environments. IMPORTANCE Filamentous growth is a cell differentiation response and important aspect of fungal biology. In plant and animal fungal pathogens, filamentous growth contributes to virulence. One signaling pathway that regulates filamentous growth is an evolutionarily conserved MAPK pathway. The yeast Saccharomyces cerevisiae is a convenient model to study MAPK-dependent regulation of filamentous growth, although the inducers of the pathway are not clear. Here, we exposed yeast cells to ecologically relevant compounds (e.g., plant compounds), which identified new inducers of the MAPK pathway. In combination, the inducers activated the pathway to near-maximal levels but did not cause detrimental phenotypes associated with previously identified hyperactive alleles. This context allowed us to identify conditional bypass for multiple pathway components. Thus, near-maximal induction of a MAPK pathway by ecologically relevant inducers provides a powerful tool to assess cellular signaling during a fungal differentiation response.

Mitogen-activated protein kinase (MAPK) cascades-A yeast perspective

Discovery of the class of protein kinase now dubbed a mitogen (or messenger)-activated protein kinase (MAPK) is an illustrative example of how disparate lines of investigation can converge and reveal an enzyme family universally conserved among eukaryotes, from single-celled microbes to humans. Moreover, elucidation of the circuitry controlling MAPK function defined a now overarching principle in enzyme regulation-the concept of an activation cascade mediated by sequential phosphorylation events. Particularly ground-breaking for this field of exploration were the contributions of genetic approaches conducted using several model organisms, but especially the budding yeast Saccharomyces cerevisiae. Notably, examination of how haploid yeast cells respond to their secreted peptide mating pheromones was crucial in pinpointing genes encoding MAPKs and their upstream activators. Fully contemporaneous biochemical analysis of the activities elicited upon stimulation of mammalian cells by insulin and other growth- and differentiation-inducing factors lead eventually to the demonstration that components homologous to those in yeast were involved. Continued studies of these pathways in yeast were integral to other foundational discoveries in MAPK signaling, including the roles of tethering, scaffolding and docking interactions.

Regulators involved in trophoblast syncytialization in the placenta of intrauterine growth restriction

Placental dysfunction refers to the insufficiency of placental perfusion and chronic hypoxia during early pregnancy, which impairs placental function and causes inadequate supply of oxygen and nutrients to the fetus, affecting fetal development and health. Fetal intrauterine growth restriction, one of the most common outcomes of pregnancy-induced hypertensions, can be caused by placental dysfunction, resulting from deficient trophoblast syncytialization, inadequate trophoblast invasion and impaired vascular remodeling. During placental development, cytotrophoblasts fuse to form a multinucleated syncytia barrier, which supplies oxygen and nutrients to meet the metabolic demands for fetal growth. A reduction in the cell fusion index and the number of nuclei in the syncytiotrophoblast are found in the placentas of pregnancies complicated by IUGR, suggesting that the occurrence of IUGR may be related to inadequate trophoblast syncytialization. During the multiple processes of trophoblasts syncytialization, specific proteins and several signaling pathways are involved in coordinating these events and regulating placental function. In addition, epigenetic modifications, cell metabolism, senescence, and autophagy are also involved. Study findings have indicated several abnormally expressed syncytialization-related proteins and signaling pathways in the placentas of pregnancies complicated by IUGR, suggesting that these elements may play a crucial role in the occurrence of IUGR. In this review, we discuss the regulators of trophoblast syncytialization and their abnormal expression in the placentas of pregnancies complicated by IUGR.

miR-375 Induced the Formation and Transgenerational Inheritance of Fatty Liver in Poultry by Targeting MAP3K1

The liver of poultry is the primary site of lipid synthesis. The excessive production of lipids accumulates in liver tissues causing lipid metabolism disorders, which result in fatty liver disease and have a transgenerational effect of acquired phenotypes. However, its specific mechanisms have not yet been fully understood. In this study, the differentially expressed miR-375 as well as its target gene MAP3K1 (mitogen-activated protein kinase kinase kinase 1) were screened out by interaction network analysis of microRNA sequencing results and transcriptome profiling in the fatty liver group of the F0-F3 generation (p < 0.05 or p < 0.01). Furthermore, the results showed that the number of lipid droplets and triglyceride content were significantly decreased after upregulation of miR-375 in primary hepatocyte culture in vitro (p < 0.05 or p < 0.01). The MAP3K1 knockdown group exhibited the opposite trends (p < 0.05 or p < 0.01). P53, Bcl-x, PMP22, and CDKN2C related to cell proliferation were significantly upregulated or downregulated after knocking down MAP3K1 (p < 0.05). This research uniquely revealed that silencing miR-375 inhibits lipid biosynthesis and promotes cell proliferation, which may be due to the partial regulation of the expression level of MAP3K1, thereby further participating in the transgenerational inheritance process of regulating liver lipid metabolism. These results reveal the pathogenesis of fatty liver in noncoding RNA and provide good candidate genes for breeding progress of disease resistance in chickens.

Swine acute diarrhea syndrome coronavirus replication is reduced by inhibition of the extracellular signal-regulated kinase (ERK) signaling pathway

Swine acute diarrhea syndrome coronavirus (SADS-CoV) is a newly discovered enteric coronavirus. We have previously shown that the caspase-dependent FASL-mediated and mitochondrion-mediated apoptotic pathways play a central role in SADS-CoV-induced apoptosis, which facilitates viral replication. However, the roles of intracellular signaling pathways in SADS-CoV-mediated cell apoptosis and the relative advantages that such pathways confer on the host or virus remain largely unknown. In this study, we show that SADS-CoV induces the activation of ERK during infection, irrespective of viral biosynthesis. The knockdown or chemical inhibition of ERK1/2 significantly suppressed viral protein expression and viral progeny production. The inhibition of ERK activation also circumvented SADS-CoV-induced apoptosis. Taken together, these data suggest that ERK activation is important for SADS-CoV replication, and contributes to the virus-mediated changes in host cells. Our findings demonstrate the takeover of a particular host signaling mechanism by SADS-CoV and identify a potential approach to inhibiting viral spread.

A review of the biological and clinical implications of RAS-MAPK pathway alterations in neuroblastoma

Neuroblastoma is the most common extra-cranial solid tumor in children, representing approximately 8% of all malignant childhood tumors and 15% of pediatric cancer-related deaths. Recent sequencing and transcriptomics studies have demonstrated the RAS-MAPK pathway’s contribution to the development and progression of neuroblastoma. This review compiles up-to-date evidence of this pathway’s involvement in neuroblastoma. We discuss the RAS-MAPK pathway’s general functioning, the clinical implications of its deregulation in neuroblastoma, and current promising therapeutics targeting proteins involved in signaling.

Lipopolysaccharides induce a RAGE-mediated sensitization of sensory neurons and fluid hypersecretion in the upper airways

Thoracic dorsal root ganglia (tDRG) contribute to fluid secretion in the upper airways. Inflammation potentiates DRG responses, but the mechanisms remain under investigation. The receptor for advanced glycation end-products (RAGE) underlies potentiation of DRG responses in pain pathologies; however, its role in other sensory modalities is less understood. We hypothesize that RAGE contributes to electrophysiological and biochemical changes in tDRGs during inflammation. We used tDRGs and tracheas from wild types (WT), RAGE knock-out (RAGE-KO), and with the RAGE antagonist FPS-ZM1, and exposed them to lipopolysaccharides (LPS). We studied: capsaicin (CAP)-evoked currents and action potentials (AP), tracheal submucosal gland secretion, RAGE expression and downstream pathways. In WT neurons, LPS increased CAP-evoked currents and AP generation, and it caused submucosal gland hypersecretion in tracheas from WT mice exposed to LPS. In contrast, LPS had no effect on tDRG excitability or gland secretion in RAGE-KO mice or mice treated with FPS-ZM1. LPS upregulated full-length RAGE (encoded by Tv1-RAGE) and downregulated a soluble (sRAGE) splice variant (encoded by MmusRAGEv4) in tDRG neurons. These data suggest that sensitization of tDRG neurons contributes to hypersecretion in the upper airways during inflammation. And at least two RAGE variants may be involved in these effects of LPS.

Silencing MAP3K1 expression inhibits the proliferation of goat hair follicle stem cells

The Yangtze River Delta White Goat is the only goat breed in the world that can produce superior-quality brush hair. Previous studies have shown that some genes are expressed differentially in the skin tissues between the goats produced superior-quality and normal-quality brush hair. Studies also have shown that different gene play varied roles in regulating the proliferation and apoptosis of hair follicle stem cells. However, the biological function of MAP3K1 (mitogen-activated protein kinase kinase kinase 1) gene in hair follicle stem cells is not fully understood. This study aims to investigate the role of MAP3K1 knockdown during the proliferation and apoptosis of hair follicle stem cells. RT-qPCR and Western blot were used to detect mRNA gene and protein expression level, CCK-8 and EdU assays were used to detect cell proliferation, and cell cycle and apoptosis were detected by flow cytometry. The results showed that the MAP3K1 expression level was significantly higher in the skin tissue of produced superior-quality brush hair than that in produced normal-quality brush hair. Moreover, functional studies indicated that si-MAP3K1 significantly inhibits the proliferation of hair follicle stem cells that came from a superior goat and promotes its apoptosis. Based on aforementioned assays, we speculated that MAP3K1 might play a regulatory effect in superior-quality brush hair traits.

Integrated Transcriptomic and Epigenetic Study of PCOS: Impact of Map3k1 and Map1lc3a Promoter Methylation on Autophagy

Polycystic ovary syndrome (PCOS) is a prevalent heterogeneous endocrine and metabolic disorder in women of reproductive age. Epigenetic mechanisms contribute to the development of PCOS. Nevertheless, the role of DNA methylation in the development of PCOS remains unclear. To investigate the molecular mechanisms underlying the hyperandrogenic phenotype of PCOS, dihydrotestosterone (DHT)-induced prenatally androgenized (PNA) mice were used to mimic this phenotype. Ovarian samples from PNA and control mice were subjected to methyl-CpG-binding domain (MBD)-seq and RNA-seq, and validation was conducted using methylation-specific polymerase chain reaction (MSP) and quantitative real-time PCR (RT-qPCR). Immunohistochemical analysis (using anti-LC3II antibody) and transmission electron microscopy were conducted using ovarian tissue sections (which included granulosa cells) from PNA and control mice. There were 857 genes with differentially methylated promoter regions and 3,317 differentially expressed genes (DEGs) in the PNA mice compared to the control mice. Downregulation of Dnmt1 (which encodes DNA methyltransferase 1), accompanied by global hypomethylation, was observed in the PNA mice compared to the control mice. The promoter regions of Map3k1 (which encodes MEKK1) and Map1lc3a (which encodes LC3II) were hypomethylated, accompanied by upregulation of Map3k1 and Map1lc3a mRNA expression. The autophagy profiling results showed that LC3II protein expression and autophagosomes were significantly increased in the granulosa cells of PNA mice. Additionally, the mRNA expression of genes related to the mitogen-activated protein kinase (MAPK)/p53 pathway (Mapk14, Mapkapk3, and Trp53) and the autophagy-related gene Becn1 were significantly increased. DHT could change the DNA methylation and transcription level of Map3k1 and lead to an activation of autophagy in granulosa cells. These observations indicated that the change in autophagy may be driven by MAPK/p53 pathway activation, which may have been caused by DHT-induced transcriptional, and the methylation level changed of the key upstream gene Map3k1. Our study provides a novel genetic basis and new insights regarding the pathogenesis of PCOS.

MicroRNAs as regulators of ERK/MAPK pathway: A comprehensive review

The ERK/MAPK cascade is one the four distinctive MAPK cascades which transmit extracellular signals to intracellular targets. This cascade has an important role in the regulation of several fundamental processes such as proliferation, differentiation and cell response to diverse extrinsic stresses. Moreover, several studies have shown participation of this cascade in the pathogenesis of cancer. Recent investigations have unraveled interaction between microRNAs (miRNAs) and ERK/MAPK cascade. These transcripts reside in both upstream and downstream of this cascade, regulating or being regulated by ERK/MAPK proteins. In the current review, we summarize the role of miRNAs in the regulation of ERK/MAPK and their contribution in the pathogenesis of human disorders with particular focus on cancers.

Long noncoding RNA FOXD2-AS1 aggravates hepatocellular carcinoma tumorigenesis by regulating the miR-206/MAP3K1 axis

LncRNAs play crucial roles in the development of various cancers including hepatocellular carcinoma (HCC). Nevertheless, the function of the long noncoding RNA (lncRNA) FOXD2‐AS1 in HCC is still poorly understood. In this study, we focused on the role of FOXD2‐AS1 in HCC. We found that FOXD2‐AS1 was significantly upregulated in HCC cells in comparison to normal human liver cells, LO2. In this study, we also demonstrated that miR‐206 expression was greatly reduced in HCC cells. Furthermore, the inhibition of FOXD2‐AS1 repressed HCC cell proliferation, enhanced cell apoptosis, and restrained cell invasion and migration. The knockdown of FOXD2‐AS1 elevated miR‐206 expression, and we validated an interaction between these RNAs. Additionally, miR‐206 mimics inhibited HCC development while miR‐206 mimics had the opposite effect. MAP kinase 1 (MAP3K1) was predicted to be a target of miR‐206. We discovered that FOXD2‐AS1 modulated MAP3K1 expression by sponging miR‐206 in MHCC‐97L and HepG2 cells. Finally, our in vivo experiments validated that the knockdown of FOXD2‐AS1 inhibited HCC progression by modulating the miR‐206/MAP3K1 axis. In conclusion, this work implies FOXD2‐AS1 accelerates HCC progression through sponging miR‐206 and regulating MAP3K1 expression.

miR-203 affects esophageal cancer cell proliferation, apoptosis and invasion by targeting MAP3K1

miR-203 has been indicated to be a tumor suppressor in esophageal cancer, however, the underlying molecular mechanisms by which it functions are not fully understood. The present study aimed to investigate the molecular mechanisms underlying the regulatory activities of microRNA (miR)-203 in esophageal cancer. The miR-203 mimic/inhibitor, Mitogen-Activated Protein Kinase Kinase Kinase 1 (MAP3K1) overexpression plasmid and MAP3K1 small interfering (si)RNA were transfected into TE-1 cells. miR-203 and MAP3K1 mRNA expression were detected via reverse transcription-quantitative PCR analysis, while MAP3K1 protein expression was detected via western blot analysis. Dual-luciferase reporter assay was used to determine whether MAP3K1 was a direct target of miR-203. Cell proliferation and invasion abilities were assessed via MTT and Matrigel assays, respectively. Cell apoptosis was analyzed via flow cytometry, Caspase 8/3 Assay kits and western blot analysis. The results demonstrated that MAP3K1 was a direct target of miR-203. Overexpression of MAP3K1 reversed the suppressed cell proliferation and invasion abilities induced by miR-203 mimic, as well as the inhibitory effect of miR-203 mimic on cell apoptosis. Furthermore, MAP3K1 siRNA weakened the effect of miR-203 inhibitor on cell proliferation, apoptosis and invasion.

TAOK1 positively regulates TLR4-induced inflammatory responses by promoting ERK1/2 activation in macrophages

Thousand and one amino acid kinase 1 (TAOK1) is a member of Ste20-like kinases, but its function in regulating inflammatory responses remains largely unknown. In this study, we identify TAOK1 as a positive regulator of TLR4-triggered inflammatory responses in macrophages. TAOK1 increases LPS-induced production of pro-inflammatory cytokine such as IL-6, TNF-α and IL12p40 in macrophages. TAOK1 deficient mice showed decreased susceptibility to endotoxin shock, with less pro-inflammatory cytokine production than control mice. TAOK1 promotes LPS-induced activation of ERK1/2 by constitutively interacting with TRAF6 and TPL2. These finding unravel the important role of TAOK1 as a positive regulator of TLR4-induced inflammatory responses.

Prevention of calpain-dependent degradation of STK38 by MEKK2-mediated phosphorylation

Serine-threonine kinase 38 (STK38) is a member of the protein kinase A (PKA)/PKG/PKC-family implicated in the regulation of cell division and morphogenesis. However, the molecular mechanisms underlying STK38 stability remain largely unknown. Here, we show that treatment of cells with either heat or the calcium ionophore A23187 induced STK38 degradation. The calpain inhibitor calpeptin suppressed hyperthermia-induced degradation or the appearance of A23187-induced cleaved form of STK38. An in vitro cleavage assay was then used to demonstrate that calpain I directly cleaves STK38 at the proximal N-terminal region. Deletion of the N-terminal region of STK38 increased its stability against hyperthermia. We further demonstrated that the MAPKK kinase (MAP3K) MEKK2 prevented both heat- and calpain-induced cleavage of STK38. MEKK2 knockdown enhanced hyperthermia-induced degradation of STK38. We performed an in vitro MEKK2 assay and identified the key regulatory site in STK38 phosphorylated by MEKK2. Experiments with a phosphorylation-defective mutant demonstrated that phosphorylation of Ser 91 is important for STK38 stability, as the enzyme is susceptible to degradation by the calpain pathway unless this residue is phosphorylated. In summary, we demonstrated that STK38 is a calpain substrate and revealed a novel role of MEKK2 in the process of STK38 degradation by calpain.

The Role of PI3K/Akt and ERK in Neurodegenerative Disorders

Disruption of Akt and Erk-mediated signal transduction significantly contributes in the pathogenesis of various neurodegenerative diseases (NDs), such as Parkinson's disease, Alzheimer's diseases, Huntington's disease, and many others. These regulatory proteins serve as the regulator of cell survival, motility, transcription, metabolism, and progression of the cell cycle. Therefore, targeting Akt and Erk pathway has been proposed as a reasonable approach to suppress ND progression. This review has emphasized on involvement of Akt/Erk cascade in the neurodegeneration. Akt has been reported to regulate neuronal toxicity through its various substrates like FOXos, GSK3β, and caspase-9 etc. Akt is also involved with PI3K in signaling pathway to mediate neuronal survival. ERK is another kinase which also regulates proliferation, differentiation, and survival of the neural cell. There has also been much progress in developing a therapeutic molecule targeting Akt and Erk signaling. Therefore, improved understanding of the molecular mechanism behind the regulatory aspect of Akt and Erk networks can make strong impact on exploration of the neurodegenerative disease pathogenesis.

ERK/MAPK signaling and autism spectrum disorders

The MAPK pathway is a prominent intracellular signaling pathway regulating various intracellular functions. Components of this pathway are mutated in a related collection of congenital syndromes collectively referred to as neuro-cardio-facio-cutaneous syndromes (NCFC) or Rasopathies. Recently, it has been appreciated that these disorders are associated with autism spectrum disorders (ASD). In addition, idiopathic ASD has also implicated the MAPK signaling cascade as a common pathway that is affected by many of the genetic variants that have been found to be linked to ASDs. This chapter describes the components of the MAPK pathway and how it is regulated. Furthermore, this chapter will highlight the various functions of the MAPK pathway during both embryonic development of the central nervous system (CNS) and its roles in neuronal physiology and ultimately, behavior. Finally, we will summarize the perturbations to MAPK signaling in various models of autism spectrum disorders and Rasopathies to highlight how dysregulation of this pivotal pathway may contribute to the pathogenesis of autism.

Role of MEKK1 in the anterior-posterior patterning during planarian regeneration

Planarians have established a unique body pattern along the anterior-posterior (AP) axis, which consists of at least four distinct body regions arranged in an anterior to posterior sequence: head, prepharyngeal, pharyngeal (containing a pharynx), and tail regions, and possess high regenerative ability. How they reconstruct the regional continuity in a head-to-tail sequence after amputation still remains unknown. We use as a model planarian Dugesia japonica head regeneration from tail fragments, which involves dynamic rearrangement of the body regionality of preexisting tail tissues along the AP axis, and show here that RNA interference of the gene D. japonica mek kinase 1 (Djmekk1) caused a significant anterior shift in the position of pharynx regeneration at the expense of the prepharyngeal region, while keeping the head region relatively constant in size, and accordingly led to development of a relatively longer tail region. Our data suggest that DjMEKK1 regulates anterior extracellular signal-regulated kinase (ERK) and posterior β-catenin signaling pathways in a positive and negative manner, respectively, to establish a proper balance resulting in the regeneration of planarian's scale-invariant trunk-to-tail patterns across individuals. Furthermore, we demonstrated that DjMEKK1 negatively modulates planarian β-catenin activity via its serine/threonine kinase domain, but not its PHD/RING finger domain, by testing secondary axis formation in Xenopus embryos. The data suggest that Djmekk1 plays an instructive role in the coordination between the establishment of the prepharyngeal region and posteriorizing of pharynx formation by balancing the two opposing morphogenetic signals along the AP axis during planarian regeneration.

Functional significance of co-occurring mutations in PIK3CA and MAP3K1 in breast cancer

The PI3Kα signaling pathway is frequently hyper-activated in breast cancer (BrCa), as a result of mutations/amplifications in oncogenes (e.g. HER2), decreased function in tumor suppressors (e.g. PTEN) or activating mutations in key components of the pathway. In particular, activating mutations of PIK3CA (~45%) are frequently found in luminal A BrCa samples. Genomic studies have uncovered inactivating mutations in MAP3K1 (13-20%) and MAP2K4 (~8%), two upstream kinases of the JNK apoptotic pathway in luminal A BrCa samples. Further, simultaneous mutation of PIK3CA and MAP3K1 are found in ~11% of mutant PIK3CA tumors. How these two alterations may cooperate to elicit tumorigenesis and impact the sensitivity to PI3K and AKT inhibitors is currently unknown. Using CRISPR gene editing we have genetically disrupted MAP3K1 expression in mutant PIK3CA cell lines to specifically create in vitro models reflecting the mutational status of PIK3CA and MAP3K1 in BrCa patients. MAP3K1 deficient cell lines exhibited ~2.4-fold increased proliferation rate and decreased sensitivity to PI3Kα/δ(AZD8835) and AKT (AZD5363) inhibitors (~2.61 and ~5.23-fold IC₅₀ increases, respectively) compared with parental control cell lines. In addition, mechanistic analysis revealed that MAP3K1 disruption enhances AKT phosphorylation and downstream signaling and reduces sensitivity to AZD5363-mediated pathway inhibition. This appears to be a consequence of deficient MAP3K1-JNK signaling increasing IRS1 stability and therefore promoting IRS1 binding to p85, resulting in enhanced PI3Kα activity. Using 3D-MCF10A-PI3Kα^H1047R models, we found that MAP3K1 depletion increased overall acinar volume and counteracted AZD5363-mediated reduction of acinar growth due to enhanced proliferation and reduced apoptosis. Furthermore, in vivo efficacy studies revealed that MAP3K1-deficient MCF7 tumors were less sensitive to AKT inhibitor treatment, compared with parental MCF7 tumors. Our study provides mechanistic and in vivo evidence indicating a role for MAP3K1 as a tumor suppressor gene at least in the context of PIK3CA-mutant backgrounds. Further, our work predicts that MAP3K1 mutational status may be considered as a predictive biomarker for efficacy in PI3K pathway inhibitor trials.

MEKK1, JNK, and SMAD3 mediate CXCL12-stimulated connective tissue growth factor expression in human lung fibroblasts

Background

In idiopathic pulmonary fibrosis, the interaction of CXCL12 and CXC receptor 4 (CXCR4) plays a critical role in lung fibrosis. Connective tissue growth factor (CTGF) overexpression underlies the development of pulmonary fibrosis. Our previous report showed that the Rac1-dependent extracellular signal-regulated kinase (ERK), c-Jun N-terminal kinase (JNK), and activator protein (AP)-1 pathways are involved in CXCL12-generated CTGF expression in human lung fibroblasts (WI-38). In present study, we additionally inspected the involvement of mitogen-activated protein kinase kinase kinase 1 (MEKK1)/JNK-dependent SMAD3 in CXCL12-triggered CTGF expression in WI-38 cells.

Methods

WI-38 cells were stimulated with CXCL12 in the absence or presence of specific inhibitors or small interfering RNAs (siRNAs). CTGF expression and signaling transduction molecules were assessed by Western blot, luciferase activity assay, or ChIP assay.

Results

CXCL-12-induced CTGF expression was attenuated by SIS3 (a SMAD3 inhibitor) and SMAD3 siRNA, but not by SB431542 (an activin receptor-like kinase 5, ALK5, inhibitor). CXCL12-stimulated CTGF expression was also attenuated by MEKK1 siRNA. Treatment of cells with CXCL12 caused an increase in SMAD3 phosphorylation at Ser208, translocation to nuclei, SMAD3-luciferase activity, and recruitment of SMAD3 to the CTGF promoter. Stimulation of cells with CXCL12 resulted in increase in JNK phosphorylation at Thr183/Tyr185 and MEKK1 phosphorylation at Thr261. Moreover, CXCL12-mediated SMAD3 phosphorylation or SMAD3-luciferase activity was inhibited by MEKK1 siRNA or SP600125. Finally, CXCL12-mediated JNK phosphorylation was attenuated by MEKK1 siRNA.

Conclusion

In conclusion, results of this study suggest that CXCL12 activates the MEKK1/JNK signaling pathway, which in turn initiates SMAD3 phosphorylation, its translocation to nuclei, and recruitment of SMAD3 to the CTGF promoter, which ultimately induces CTGF expression in human lung fibroblasts.

Involvement of leptin in the molecular physiology of the placenta

Leptin is a homeostatic regulator in the placenta where it promotes proliferation, protein synthesis and the expression of tolerogenic maternal response molecules such as HLA-G. Leptin also exerts an anti-apoptotic action in placenta controlling the expression of p53 master cell cycle regulator under different stress conditions. On the other hand, leptin is an integrative target of different placental stimuli. The expression of leptin in placenta is regulated by hCG, insulin, steroids, hypoxia and many other growth hormones, suggesting that it might have an important endocrine function in the trophoblastic cells. The leptin expression is induced involving the cAMP/PKA or cAMP/Epac pathways which have profound actions upon human trophoblast function. The activation of PI3K and MAPK pathways also participates in the leptin expression. Estrogens play a central role during pregnancy, particularly 17β-estradiol upregulates the leptin expression in placental cells through genomic and non-genomic actions. The leptin promoter analysis reveals specific elements that are active in placental cells. The transcription factors CREB, AP1, Sp1, NFκB and the coactivator CBP are involved in the placental leptin expression. Moreover, placental leptin promoter is a target of epigenetic marks such as DNA methylation and histone acetylation that regulates not only the leptin expression in placenta during pregnancy but also determines the predisposition of acquiring adult metabolism diseases. Taken together, all these results allow a better understanding of leptin function and regulatory mechanisms of leptin expression in human placental trophoblasts, and support the importance of leptin during pregnancy and in programming adult health.

Development of a Nonradioactive, Time-Resolved Fluorescence Assay for the Measurement of Jun N-Terminal Kinase Activity

Activated transcription factor AP-1 is composed of c-Jun homodimers or c-Jun/c-Fos heterodimers and mediates expression of several gene products that have been implicated in disease pathogenesis. Activation of AP-1 is dependent on phosphorylation of c-Jun by Jun N-terminal kinase (JNK). Therefore, identification of inhibitors of JNK-mediated phosphorylation of c-Jun may lead to a novel class of therapeutics. A nonradioactive, high-through-put, time-resolved fluorescence assay was developed to measure and identify inhibitors of JNK activity. This assay utilized a lanthanide (europium)-labeled antibody that was specific for N-terminally phosphorylated c-Jun. The optimized europium-based assay was approximately 15-fold more sensitive compared to a similar 32P-based JNK assay. Compounds that were identified as inhibitors of JNK using the europium-based assay also inhibited JNK activity in the 32P-based assay with similar IC50 values. The europium-based JNK assay eliminates the contamination problems associated with the use of radioactivity. The sensitivity and safety of the europium-based assay make it amenable to robotics that will significantly increase screening throughput.

Genomic Alterations in Langerhans Cell Histiocytosis

The discovery of recurrent somatic genomic alterations in Langerhans cell histiocytosis (LCH) has led to a new understanding of LCH as a clonal neoplastic disorder. Most of the abnormalities described to date affect the RAS/RAF/MEK/extracellular-signal-regulated kinase (ERK) pathway: more than 50% of LCH cases carry activating mutations in BRAF, whereas another 10% to 28% carry activating mutations of MAP2K1, which encodes MEK1. The pathogenetic importance of these mutations has been confirmed by reports of significant clinical responses to RAF inhibitors.

Effects of sodium selenite on c-Jun N-terminal kinase signalling pathway induced by oxidative stress in human chondrocytes and c-Jun N-terminal kinase expression in patients with Kashin-Beck disease, an endemic osteoarthritis

The c-Jun N-terminal kinases (JNK) are members of the mitogen-activated protein kinase family and are activated by environmental stress. Se plays an important role in the biological pathways by forming selenoprotein. Selenoproteins have been shown to exhibit a variety of biological functions including antioxidant functions and maintaining cellular redox balance, and compromise of such important proteins would lead to oxidative stress and apoptosis. We examined the expression levels of JNK in Kashin-Beck disease (KBD) patients, tested the potential protective effects of sodium selenite on tert-butyl hydroperoxide (tBHP)-induced oxidative injury and apoptosis in human chondrocytes as well as its underlying mechanism in this study. We produced an oxidative damage model induced by tBHP in C28/I2 human chondrocytes to test the essential anti-apoptosis effects of Se in vitro. The results indicated that the expression level of phosphorylated JNK was significantly increased in KBD patients. Cell apoptosis was increased and molecule expressions of the JNK signalling pathway were activated in the tBHP-injured chondrocytes. Na2SeO3 protected against tBHP-induced oxidative stress and apoptosis in cells by increasing cell viability, reducing reactive oxygen species generation, increasing Glutathione peroxidase (GPx) activity and down-regulating the JNK pathway. These results demonstrate that apoptosis induced by tBHP in chondrocytes might be mediated via up-regulation of the JNK pathway; Na2SeO3 has an effect of anti-apoptosis by down-regulating the JNK signalling pathway.

Biophysical Characterization of Essential Phosphorylation at the Flexible C-Terminal Region of C-Raf with 14-3-3ζ Protein

Phosphorylation at the C-terminal flexible region of the C-Raf protein plays an important role in regulating its biological activity. Auto-phosphorylation at serine 621 (S621) in this region maintains C-Raf stability and activity. This phosphorylation mediates the interaction between C-Raf and scaffold protein 14-3-3ζ to activate the downstream MEK kinase pathway. In this study, we have defined the interaction of C-terminal peptide sequence of C-Raf with 14-3-3ζ protein and determined the possible structural adaptation of this region. Biophysical elucidation of the interaction was carried out using phosphopeptide (residue number 615–630) in the presence of 14-3-3ζ protein. Using isothermal titration calorimetry (ITC), a high binding affinity with micro-molar range was found to exist between the peptide and 14-3-3ζ protein, whereas the non-phosphorylated peptide did not show any appreciable binding affinity. Further interaction details were investigated using several biophysical techniques such as circular dichroism (CD), fluorescence, and nuclear magnetic resonance (NMR) spectroscopy, in addition to molecular modeling. This study provides the molecular basis for C-Raf C-terminal-derived phosphopeptide interaction with 14-3-3ζ protein as well as structural insights responsible for phosphorylated S621-mediated 14-3-3ζ binding at an atomic resolution.

MiR-451 inhibits proliferation of esophageal carcinoma cell line EC9706 by targeting CDKN2D and MAP3K1

AIM: To investigate the underlying molecular mechanisms of miR-451 to inhibit proliferation of esophageal carcinoma cell line EC9706.

METHODS: Assays for cell growth, apoptosis and invasion were used to evaluate the effects of miR-451 expression on EC cells. Luciferase reporter and Western blot assays were used to test whether cyclin-dependent kinase inhibitor 2D (CDKN2D) and MAP3K1 act as major targets of miR-451.

RESULTS: The results showed that CDKN2D and MAP3K1 are direct targets of miR-451. CDKN2D and MAP3K1 overexpression reversed the effect of miR-451. MiR-451 inhibited the proliferation of EC9706 by targeting CDKN2D and MAP3K1.

CONCLUSION: These findings suggest that miR-451 might be a novel prognostic biomarker and a potential target for the treatment of esophageal squamous cell carcinoma in the future.

MAP2K1 and MAP3K1 mutations in Langerhans cell histiocytosis

Langerhans cell histiocytosis (LCH) is now understood to be a neoplastic disease in which over 50% of cases have somatic activating mutations of BRAF. However, the extracellular signal-related (ERK) pathway is activated in all cases including those with wild type BRAF alleles. Here, we applied a targeted massively parallel sequencing panel to 30 LCH samples to test for the presence of additional genetic alterations that might cause ERK pathway activation. In 20 BRAF wild type samples, we found 3 somatic mutations in MAP2K1 (MEK1) including C121S and C121S/G128D in the kinase domain, and 56_61QKQKVG>R, an in-frame deletion in the N-terminal regulatory domain. All three variant proteins constitutively phosphorylated ERK in in vitro kinase assays. The C121S/G128D and 56_61QKQKVG>R variants were resistant to the mitogen-activated protein kinase kinase (MEK) inhibitor trametinib in vitro. Within the entire sample set, we found 3 specimens with mutations in MAP3K1 (MEKK1), including two truncation mutants, T779fs and T1481fs; T1481fs encoded an unstable and nonfunctional protein when expressed in vitro. T779fs was present in a specimen carrying BRAF V600E. The third variant was a single nucleotide substitution, E1286V, which was fully functional and is likely a germline polymorphism. These results indicate that LCH cells can harbor additional genetic alterations in the RAS-RAF-MEK pathway which, in the case of MAP2K1, may be responsible for ERK activation in a wild type BRAF setting. The resistance of some of these variants to trametinib may also have clinical implications for the combined use of RAF and MEK inhibitors in LCH.

A RING to rule them all? Insights into the Map3k1 PHD motif provide a new mechanistic understanding into the diverse roles of Map3k1

Despite the sizable number of components that comprise Mapk cascades, Map3k1 is the only element that contains both a kinase domain and a plant homeodomain (PHD) motif, allowing Map3k1 to regulate the protein phosphorylation and ubiquitin proteasome systems. As such, Map3k1 has complex roles in the regulation of cell death, survival, migration and differentiation. Numerous mouse and human genetic analyses have demonstrated that Map3k1 is of critical importance for the immune system, cardiac tissue, testis, wound healing, tumorigenesis and cancer. Recent gene knockin of Map3k1 to mutate the E2 binding site within the Map3k1 PHD motif and high throughput ubiquitin protein array screening for Map3k1 PHD motif substrates provide critical novel insights into Map3k1 PHD motif signal transduction and bring a brand-new understanding to Map3k1 signaling in mammalian biology.

Retardation of C2C12 myoblast cell proliferation by exposure to low-temperature atmospheric plasma

As the first step in evaluating the possibility of low-temperature atmospheric plasma for clinical applications in the treatment of rhabdomyosarcoma (RMS), we determined the effects of plasma exposure on C2C12 myoblasts. The low-temperature atmospheric plasma was generated through an electrical discharge in argon gas. One minute of plasma exposure every 24 h inhibited the cell proliferation, whereas myoblast differentiation was not affected. Plasma exposure increased the phosphorylation of ERK and JNK at 30 min after the exposure, but the phosphorylation of both was decreased to less than control levels at 1 and 4 h after the exposure. Plasma exposure increased the percentage of cells in the G2/M phase at 8 h after the exposure. In conclusion, plasma exposure retarded the proliferation of C2C12 myoblasts by G2/M arrest. Therefore, plasma exposure can be a possible treatment for the anti-proliferative effects of malignant tumors, such as RMS, without affecting differentiated skeletal muscle cells.

The water-soluble triptolide derivative PG490-88 protects against cisplatin-induced acute kidney injury

Triptolide, a traditional Chinese medicine, has anti-inflammatory, antiproliferative, and proapoptotic properties. As interstitial inflammation and tubular apoptosis are features of cisplatin-induced acute kidney injury (AKI), we determined the effect of the water-soluble triptolide derivative 14-succinyl triptolide sodium salt (PG490-88) in a mouse model of cisplatin-induced AKI. PG490-88 resulted in a significant decrease in blood urea nitrogen (BUN), serum creatinine, and acute tubular necrosis (ATN) score, and a nonsignificant increase in tubular apoptosis score in AKI. The mitogen-activated protein kinase (MAPK) pathway is activated in AKI. On immunoblot analysis, phosphoextracellular signal-regulated kinase (p-ERK) was increased 3.6-fold in AKI and 2.0-fold inhibited by PG490-88. Phospho-c-Jun N-terminal kinase (p-JNK) was increased in AKI. PG490-88 resulted in a nonsignificant decrease in p-JNK. Phospho-p38 was not affected by cisplatin or PG490-88. MAPK phosphatase-1 (MKP-1) that negatively regulates MAPK signaling has not previously been studied in AKI. MKP-1 activity was not affected by cisplatin or PG490-88. Changes in p-ERK, p-JNK, and MKP-1 were confirmed on reverse protein phase analysis. The ERK inhibitor U0126 resulted in lower BUN and serum creatinine, suggesting a mechanistic role of ERK in AKI. The increase in interleukin-1α (IL-1α), IL-1β, IL-6, CXCL1, and IL-33 in the kidney in AKI was unaffected by PG490-88. In summary, PG490-88 protects against AKI and ATN despite no decrease in tubular apoptosis. The protection of PG490-88 against AKI was associated with a decrease in p-ERK and was independent of MKP-1 and proinflammatory cytokines. In conclusion, PG490-88 protects against cisplatin-induced AKI possibly by decreasing p-ERK.

MAP3K1: Genomic Alterations in Cancer and Function in Promoting Cell Survival or Apoptosis

MAP3K1 is a member of the mitogen-activated protein kinase kinase kinase (MAP3K) family of serine/threonine kinases. MAP3K1 regulates JNK activation and is unique among human kinases in that it also encodes an E3 ligase domain that ubiquitylates c-Jun and ERK1/2. Full length MAP3K1 regulates cell migration and contributes to pro-survival signaling while its caspase 3-mediated cleavage generates a C-terminal kinase domain that promotes apoptosis. The critical function of MAP3K1 in cell fate decisions suggests that it may be a target for deregulation in cancer. Recent large-scale genomic studies have revealed that MAP3K1 copy number loss and somatic missense or nonsense mutations are observed in a significant number of different cancers, being most prominent in luminal breast cancer. The alteration of MAP3K1 in diverse cancer types demonstrates the importance of defining phenotypes for possible therapeutic targeting of tumor cell vulnerabilities created when MAP3K1 function is lost or gained.

Impaired insulin signaling and mechanisms of memory loss

Insulin is secreted from the β-cells of the pancreas and helps maintain glucose homeostasis. Although secreted peripherally, insulin also plays a profound role in cognitive function. Increasing evidence suggests that insulin signaling in the brain is necessary to maintain health of neuronal cells, promote learning and memory, decrease oxidative stress, and ultimately increase neuronal survival. This chapter summarizes the different facets of insulin signaling necessary for learning and memory and additionally explores the association between cognitive impairment and central insulin resistance. The role of impaired insulin signaling in the advancement of cognitive dysfunction is relevant to the current debate of whether the shared pathophysiological mechanisms between diabetes and cognitive impairment implicate a direct relationship. Here, we summarize a vast amount of literature that suggests a strong association between impaired brain insulin signaling and cognitive impairment.

ERK phosphorylation of MED14 in promoter complexes during mitogen-induced gene activation by Elk-1

The ETS domain transcription factor Elk-1 stimulates expression of immediate early genes (IEGs) in response to mitogens. These events require phosphorylation of Elk-1 by extracellular signal-regulated kinase (ERK) and phosphorylation-dependent interaction of Elk-1 with co-activators, including histone acetyltransferases and the Mediator complex. Elk-1 also recruits ERK to the promoters of its target genes, suggesting that ERK phosphorylates additional substrates in transcription complexes at mitogen-responsive promoters. Here we report that MED14, a core subunit of the Mediator, is a bona fide ERK substrate and identify serine 986 (S986) within a serine-proline rich region of MED14 as the major ERK phosphorylation site. Mitogens induced phosphorylation of MED14 on S986 at IEG promoters; RNAi knockdown of MED14 reduced CDK8 and RNA polymerase II (RNAPII) recruitment, RNAPII C-terminal domain phosphorylation and impaired activation of IEG transcription. A single alanine substitution at S986 reduced activation of an E26 (ETS)-responsive reporter by oncogenic Ras and mitogen-induced, Elk-1-dependent transcription, whereas activities of other transcriptional activators were unaffected. We also demonstrate that Elk-1 can associate with MED14 independently of MED23, which may facilitate phosphorylation of MED14 by ERK to impart a positive and selective impact on mitogen-responsive gene expression.

HER2/HER3 regulates extracellular acidification and cell migration through MTK1 (MEKK4)

Human MAP3K4 (MTK1) functions upstream of mitogen activated protein kinases (MAPKs). In this study we show MTK1 is required for human epidermal growth factor receptor 2/3 (HER2/HER3)-heregulin beta1 (HRG) induced cell migration in MCF-7 breast cancer cells. We demonstrate that HRG stimulation leads to association of MTK1 with activated HER3 in MCF-7 and T-47D breast cancer cells. Activated HER3 association with MTK1 is dependent on HER2 activation and is decreased by pre-treatment with the HER2 inhibitor, lapatinib. Moreover, we also identify the actin interacting region (AIR) on MTK1. Disruption of actin cytoskeletal polymerization with cytochalasin D inhibited HRG induced MTK1/HER3 association. Additionally, HRG stimulation leads to extracellular acidification that is independent of cellular proliferation. HRG induced extracellular acidification is significantly inhibited when MTK1 is knocked down in MCF-7 cells. Similarly, pre-treatment with lapatinib significantly decreased HRG induced extracellular acidification. Extracellular acidification is linked with cancer cell migration. We performed scratch assays that show HRG induced cell migration in MCF-7 cells. Knockdown of MTK1 significantly inhibited HRG induced cell migration. Furthermore, pre-treatment with lapatinib also significantly decreased cell migration. Cell migration is required for cancer cell metastasis, which is the major cause of cancer patient mortality. We identify MTK1 in the HER2/HER3-HRG mediated extracellular acidification and cell migration pathway in breast cancer cells.

Branched motifs enable long-range interactions in signaling networks through retrograde propagation

Branched structures arise in the intra-cellular signaling network when a molecule is involved in multiple enzyme-substrate reaction cascades. Such branched motifs are involved in key biological processes, e.g., immune response activated by T-cell and B-cell receptors. In this paper, we demonstrate long-range communication through retrograde propagation between branches of signaling pathways whose molecules do not directly interact. Our numerical simulations and experiments on a system comprising branches with JNK and p38MAPK as terminal molecules respectively that share a common MAP3K enzyme MEKK3/4 show that perturbing an enzyme in one branch can result in a series of changes in the activity levels of molecules “upstream” to the enzyme that eventually reaches the branch-point and affects other branches. In the absence of any evidence for explicit feedback regulation between the functionally distinct JNK and p38MAPK pathways, the experimentally observed modulation of phosphorylation amplitudes in the two pathways when a terminal kinase is inhibited implies the existence of long-range coordination through retrograde information propagation previously demonstrated in single linear reaction pathways. An important aspect of retrograde propagation in branched pathways that is distinct from previous work on retroactivity focusing exclusively on single chains is that varying the type of perturbation, e.g., between pharmaceutical agent mediated inhibition of phosphorylation or suppression of protein expression, can result in opposing responses in the other branches. This can have potential significance in designing drugs targeting key molecules which regulate multiple pathways implicated in systems-level diseases such as cancer and diabetes.

Oxidized DJ-1 inhibits p53 by sequestering p53 from promoters in a DNA-binding affinity-dependent manner

DJ-1 is an oncogene and the causative gene for familial Parkinson's disease. Although the oxidative status of DJ-1 at cysteine 106 (C106) is thought to affect all of the activities of DJ-1 and excess oxidation leads to the onset of various diseases, the precise molecular mechanisms underlying the effects of oxidation of DJ-1 on protein-protein interactions of DJ-1 remain unclear. In this study, we found that DJ-1 bound to the DNA-binding region of p53 in a manner dependent on the oxidation of C106. Of the p53 target genes, the expression level and promoter activity of the DUSP1 gene, but not those of the p21 gene, were increased in H(2)O(2)-treated DJ-1(-/-) cells and were decreased in wild-type DJ-1- but not C106S DJ-1-transfected H1299 cells through sequestration of p53 from the DUSP1 promoter by DJ-1. DUSP1 downregulated by oxidized DJ-1 activated extracellular signal-regulated kinase (ERK) and decreased apoptosis. The DUSP1 and p21 promoters harbor nonconsensus and consensus p53 recognition sequences, respectively, which have low affinity and high affinity for p53. However, DJ-1 inhibited p21 promoter activity exhibited by p53 mutants harboring low DNA-binding affinity but not by wild-type p53. These results indicate that DJ-1 inhibits the expression of p53 target genes and depend on p53 DNA-binding affinity and oxidation of DJ-1 C106.

Anthrax lethal toxin and the induction of CD4 T cell immunity

Bacillus anthracis secretes exotoxins which act through several mechanisms including those that can subvert adaptive immunity with respect both to antigen presenting cell and T cell function. The combination of Protective Antigen (PA) and Lethal Factor (LF) forming Lethal Toxin (LT), acts within host cells to down-regulate the mitogen activated protein kinase (MAPK) signaling cascade. Until recently the MAPK kinases were the only known substrate for LT; over the past few years it has become evident that LT also cleaves Nlrp1, leading to inflammasome activation and macrophage death. The predicted downstream consequences of subverting these important cellular pathways are impaired antigen presentation and adaptive immunity. In contrast to this, recent work has indicated that robust memory T cell responses to B. anthracis antigens can be identified following natural anthrax infection. We discuss how LT affects the adaptive immune response and specifically the identification of B. anthracis epitopes that are both immunogenic and protective with the potential for inclusion in protein sub-unit based vaccines.

The alternative Epac/cAMP pathway and the MAPK pathway mediate hCG induction of leptin in placental cells

Pleiotropic effects of leptin have been identified in reproduction and pregnancy, particularly in the placenta, where it works as an autocrine hormone. In this work, we demonstrated that human chorionic gonadotropin (hCG) added to JEG-3 cell line or to placental explants induces endogenous leptin expression. We also found that hCG increased cAMP intracellular levels in BeWo cells in a dose-dependent manner, stimulated cAMP response element (CRE) activity and the cotransfection with an expression plasmid of a dominant negative mutant of CREB caused a significant inhibition of hCG stimulation of leptin promoter activity. These results demonstrate that hCG indeed activates cAMP/PKA pathway, and that this pathway is involved in leptin expression. Nevertheless, we found leptin induction by hCG is dependent on cAMP levels. Treatment with (Bu)₂cAMP in combination with low and non stimulatory hCG concentrations led to an increase in leptin expression, whereas stimulatory concentrations showed the opposite effect. We found that specific PKA inhibition by H89 caused a significant increase of hCG leptin induction, suggesting that probably high cAMP levels might inhibit hCG effect. It was found that hCG enhancement of leptin mRNA expression involved the MAPK pathway. In this work, we demonstrated that hCG leptin induction through the MAPK signaling pathway is inhibited by PKA. We observed that ERK1/2 phosphorylation increased when hCG treatment was combined with H89. In view of these results, the involvement of the alternative cAMP/Epac signaling pathway was studied. We observed that a cAMP analogue that specifically activates Epac (CPT-OMe) stimulated leptin expression by hCG. In addition, the overexpression of Epac and Rap1 proteins increased leptin promoter activity and enhanced hCG. In conclusion, we provide evidence suggesting that hCG induction of leptin gene expression in placenta is mediated not only by activation of the MAPK signaling pathway but also by the alternative cAMP/Epac signaling pathway.

Molecular atherectomy for restenosis

Receptors for basic (b) and acidic (a) fibroblast growth factor (FGF) are upregulated in activated smooth muscle cells. These cells, which proliferate in response to bFGF, can thus be killed by a conjugate of bFGF and the ribosome-inactivating enzyme, saporin (which, by itself, does not enter the cells). Quiescent smooth muscle cells and other cells that have few FGF receptors are not killed. In vivo, bFGF-saporin transiently inhibits smooth muscle cell proliferation and neointimal accumulation after balloon injury to the rat carotid artery. Delivery of saporin, diagnostic imaging agents, or antisense oligodeoxynucleotides might be made even more selective by linking these substances to antibodies against the extracellular domains of the putative FGF receptor isoform specific for activated smooth muscle cells.

Mammalian MAPK signal transduction pathways activated by stress and inflammation: a 10-year update

The mammalian stress-activated families of mitogen-activated protein kinases (MAPKs) were first elucidated in 1994, and by 2001, substantial progress had been made in identifying the architecture of the pathways upstream of these kinases as well as in cataloguing candidate substrates. This information remains largely sound. Nevertheless, an informed understanding of the physiological and pathophysiological roles of these kinases remained to be accomplished. In the past decade, there has been an explosion of new work using RNAi in cells, as well as transgenic, knockout and conditional knockout technology in mice that has provided valuable insight into the functions of stress-activated MAPK pathways. These findings have important implications in our understanding of organ development, innate and acquired immunity, and diseases such as atherosclerosis, tumorigenesis, and type 2 diabetes. These new developments bring us within striking distance of the development and validation of novel treatment strategies. Herein we first summarize the molecular components of the mammalian stress-regulated MAPK pathways and their regulation as described thus far. We then review some of the in vivo functions of these pathways.

Pathophysiology of astroglial purinergic signalling

Astrocytes are fundamental for central nervous system (CNS) physiology and are the fulcrum of neurological diseases. Astroglial cells control development of the nervous system, regulate synaptogenesis, maturation, maintenance and plasticity of synapses and are central for nervous system homeostasis. Astroglial reactions determine progression and outcome of many neuropathologies and are critical for regeneration and remodelling of neural circuits following trauma, stroke, ischaemia or neurodegenerative disorders. They secrete multiple neurotransmitters and neurohormones to communicate with neurones, microglia and the vascular walls of capillaries. Signalling through release of ATP is the most widespread mean of communication between astrocytes and other types of neural cells. ATP serves as a fast excitatory neurotransmitter and has pronounced long-term (trophic) roles in cell proliferation, growth, and development. During pathology, ATP is released from damaged cells and acts both as a cytotoxic factor and a proinflammatory mediator, being a universal "danger" signal. In this review, we summarise contemporary knowledge on the role of purinergic receptors (P2Rs) in a variety of diseases in relation to changes of astrocytic functions and nucleotide signalling. We have focussed on the role of the ionotropic P2X and metabotropic P2YRs working alone or in concert to modify the release of neurotransmitters, to activate signalling cascades and to change the expression levels of ion channels and protein kinases. All these effects are of great importance for the initiation, progression and maintenance of astrogliosis-the conserved and ubiquitous glial defensive reaction to CNS pathologies. We highlighted specific aspects of reactive astrogliosis, especially with respect to the involvement of the P2X(7) and P2Y(1)R subtypes. Reactive astrogliosis exerts both beneficial and detrimental effects in a context-specific manner determined by distinct molecular signalling cascades. Understanding the role of purinergic signalling in astrocytes is critical to identifying new therapeutic principles to treat acute and chronic neurological diseases.

c-Jun, at the crossroad of the signaling network

c-Jun, the most extensively studied protein of the activator protein-1 (AP-1) complex, is involved in numerous cell activities, such as proliferation, apoptosis, survival, tumorigenesis and tissue morphogenesis. Earlier studies focused on the structure and function have led to the identification of c-Jun as a basic leucine zipper (bZIP) transcription factor that acts as homo- or heterodimer, binding to DNA and regulating gene transcription. Later on, it was shown that extracellular signals can induce post-translational modifications of c-Jun, resulting in altered transcriptional activity and target gene expression. More recent work has uncovered multiple layers of a complex regulatory scheme in which c-Jun is able to crosstalk, amplify and integrate different signals for tissue development and disease. One example of such scheme is the autocrine amplification loop, in which signal-induced AP-1 activates the c-Jun gene promoter, while increased c-Jun expression feedbacks to potentiate AP-1 activity. Another example of such scheme, based on recent characterization of gene knockout mice, is that c-Jun integrates signals of several developmental pathways, including EGFR-ERK, EGFR-RhoA-ROCK, and activin B-MAP3K1-JNK for embryonic eyelid closure. After more than two decades of extensive research, c-Jun remains at the center stage of a molecular network with mysterious functional properties, some of which are yet to be discovered. In this article, we will provide a brief historical overview of studies on c-Jun regulation and function, and use eyelid development as an example to illustrate the complexity of c-Jun crosstalking with signaling pathways.

Ste11p MEKK signals through HOG, mating, calcineurin and PKC pathways to regulate the FKS2 gene

Background

The S. cerevisiae MAPKKK Ste11p, a homologue of mammalian MEKK1, regulates three MAPK cascades for mating, invasive growth and osmotic stress and provides functions that are additive with the cell wall integrity pathway. Cell wall integrity requires the FKS2 gene that encodes a stress-induced alternative subunit of beta-1, 3 glucan synthase that is the target of echinocandin 1,3- beta glucan synthase inhibitors. The major signal transduction pathways that activate transcription of the FKS2 gene include the cell wall integrity and calcineurin pathways, and the Ste11p pathway.

Results

Here it is shown that catalytically active Ste11p regulates FKS2-lacZ reporter genes through Ste12, calcineurin/Crz1p- and PKC pathways and the high osmolarity pathway. Ste11p stimulated the cell wall integrity MAPK Mpk1p (Erk5 homologue) and FKS2 independently of the mating pathway. Ste11p regulated FKS2 through all known and putative substrates: Pbs2p MAPKK, Ste7 MAPKK, Cmk2p calmodulin dependent kinase and Ptk2p kinase. Ste11p increased the expression level of Cmk2p through transcription-dependent and -independent mechanisms.

Conclusions

The data suggest Ste11p regulates the FKS2 gene through all its known and putative downstream kinase substrates (Pbs2p, Ste7p, Cmk2p, and Ptk2p) and separately through Mpk1p MAPK. The patterns of control by Ste11p targets revealed novel functional linkages, cross-regulation, redundancy and compensation.

The ERK Cascade: Distinct Functions within Various Subcellular Organelles

The extracellular signal-regulated kinase 1/2 (ERK1/2) cascade is a central signaling pathway that regulates a wide variety of stimulated cellular processes, including mainly proliferation, differentiation, and survival, but apoptosis and stress response as well. The ability of this linear cascade to induce so many distinct and even opposing effects after various stimulations raises the question as to how the signaling specificity of the cascade is regulated. Over the past years, several specificity-mediating mechanisms have been elucidated, including temporal regulation, scaffolding interactions, crosstalks with other signaling components, substrate competition, and multiple components in each tier of the cascade. In addition, spatial regulation of various components of the cascade is probably one of the main ways by which signals can be directed to some downstream targets and not to others. In this review, we describe first the components of the ERK1/2 cascade and their mode of regulation by kinases, phosphatases, and scaffold proteins. In the second part, we focus on the role of MEK1/2 and ERK1/2 compartmentalization in the nucleus, mitochondria, endosomes, plasma membrane, cytoskeleton, and Golgi apparatus. We explain that this spatial distribution may direct ERK1/2 signals to regulate the organelles' activities. However, it can also direct the activity of the cascade's components to the outer surface of the organelles in order to bring them to close proximity to specific cytoplasmic targets. We conclude that the dynamic localization of the ERK1/2 cascade components is an important regulatory mechanism in determining the signaling specificity of the cascade, and its understanding should shed a new light on the understanding of many stimulus-dependent processes.

Advances in the understanding of the structure and function of ER-α36,a novel variant of human estrogen receptor-alpha

Estrogen receptors (ERs) belong to the nuclear receptor superfamily, whose members include ER-α66, ER-α36, ER-α46 and ER-β. Each receptor performs specific functions through binding with a specific ligand, such as estrogen. Recently, ER-α36, a novel variant of human estrogen receptor-alpha (ER-α), was identified and cloned. ER-α36 inhibits, in a dominant-negative manner, the transactivation of both the wild-type ER-α (ER-α66) and ER-β. As a predominantly membrane-based ER, ER-α36 mediates nongenomic estrogen signaling and is involved in the resistance of breast cancer to endocrine therapy, i.e., tamoxifen. This review summarizes recent studies on the structure and function of ER-α36 and the relationship of ER-α36 with cancer, with special emphasis on its function in the resistance of breast cancer to endocrine therapy.