Extracellular-Regulated Kinases: Signaling From Ras to ERK Substrates to Control Biological Outcomes

Inhibition of Nrf2 might enhance the anti-tumor effect of temozolomide in glioma cells via inhibition of Ras/Raf/MEK signaling pathway

BACKGROUND

Glioblastoma (GBM) is the most common aggressive primary cancer occurring in the brain tissue. GBM accounts 16% of primary brain tumors and half of gliomas. Additionally, the incidence of GBM is increases with aging, and reaches the peak at the age of 75 to 84 years. The survival of patients with GBM remains at a low level, only less than 5% patients diagnosed with GBM survive for 5 years. Temozolomide (TMZ) is a DNA alkylating agent and is currently a first line chemotherapeutic treatment for GBM. TMZ combined with radiation therapy has been shown to prolong the overall survival (OS) to 14.6 months compared with 12.1 months for radiation therapy alone. NF-E2-related factor 2 (Nrf2) is a transcription factor that contains seven functional domains. The binding of Keap1 to Nrf2 is a central regulator of the cellular defense mechanism against environmental stresses.

METHODS

First, Nrf2 overexpression and inhibition models were constructed in U251 cells using transfection. The percentage of viable cells was detected using the MTT assay. Then, the expression of the HO-1 regulator was detected using qPCR, and the concentrations of oxidative stress related factors were detected using ELISAs. The levels of proteins related to oxidative stress and the Ras/Raf/MEK signaling pathway was detected using western blotting analysis.

RESULTS

We initially established Nrf2 inhibition and activation cell models in U251 cells and found that the inhibition of Nrf2 expression decreased the mRNA and protein levels of the anti-oxidative enzymes, as well as the secretion of these enzymes into the cellular microenvironment. These effects might be mediated by the inhibition of Ras/Raf/MEK signaling pathway, leading to the inhibition of cellular proliferation.

CONCLUSIONS

Inhibition of Nrf2 expression might enhance the effect of TMZ on the treatment of GBM and might be a new therapeutic strategy.

The unicellular eukaryotic parasite Toxoplasma gondii hijacks the migration machinery of mononuclear phagocytes to promote its dissemination

Toxoplasma gondii is an obligate intracellular protozoan with the ability to infect virtually any type of nucleated cell in warm-blooded vertebrates including humans. Toxoplasma gondii invades immune cells, which the parasite employs as shuttles for dissemination by a Trojan horse mechanism. Recent findings are starting to unveil how this parasite orchestrates the subversion of the migratory functions of parasitised mononuclear phagocytes, especially dendritic cells (DCs) and monocytes. Here, we focus on how T. gondii impacts host cell signalling that regulates leukocyte motility and systemic migration in tissues. Shortly after active parasite invasion, DCs undergo mesenchymal-to-amoeboid transition and adopt a high-speed amoeboid mode of motility. To trigger migratory activation - termed hypermigratory phenotype - T. gondii induces GABAergic signalling, which results in calcium fluxes mediated by voltage-gated calcium channels in parasitised DCs and brain microglia. Additionally, a TIMP-1-CD63-ITGB1-FAK signalling axis and signalling via the receptor tyrosine kinase MET promotes sustained hypermigration of parasitised DCs. Recent reports show that the activated signalling pathways converge on the small GTPase Ras to activate the MAPK Erk signalling cascade, a central regulator of cell motility. To date, three T. gondii-derived putative effector molecules have been linked to hypermigration: Tg14-3-3, TgWIP and ROP17. Here, we discuss their impact on the hypermigratory phenotype of phagocytes. Altogether, the emerging concept suggests that T. gondii induces metastasis-like migratory properties in parasitised mononuclear phagocytes to promote infection-related dissemination.

Controlling Phosphate Removal with Light: The Development of Optochemical Tools to Probe Protein Phosphatase Function

Protein phosphatases play an essential role in cell signaling; however, they remain understudied compared with protein kinases, in part due to a lack of appropriate tools. In order to provide conditional control over phosphatase function, we developed two different approaches for rendering MKP3 (a dual-specific phosphatase, also termed DUSP6) activatable by light. Specifically, we expressed the protein with strategically placed light-removable protecting groups in cells with an expanded genetic code. This allowed for the acute perturbation of the Ras/MAPK signaling pathway upon photoactivation in live cells. In doing so, we confirmed that MKP3 does not act as a thresholding gate for growth factor stimulation of the extracellular signal-regulated kinase (ESRK) pathway.

Perspectives for repurposing drugs for the coronavirus disease 2019

The newly emerged 2019 novel coronavirus (CoV), named as severe acute respiratory syndrome CoV-2 (SARS-CoV-2), like SARS-CoV (now, SARS-CoV-1) and Middle East respiratory syndrome CoV (MERS-CoV), has been associated with high infection rates with over 36,405 deaths. In the absence of approved marketed drugs against coronaviruses, the treatment and management of this novel CoV disease (COVID-19) worldwide is a challenge. Drug repurposing that has emerged as an effective drug discovery approach from earlier approved drugs could reduce the time and cost compared to de novo drug discovery. Direct virus-targeted antiviral agents target specific nucleic acid or proteins of the virus while host-based antivirals target either the host innate immune responses or the cellular machineries that are crucial for viral infection. Both the approaches necessarily interfere with viral pathogenesis. Here we summarize the present status of both virus-based and host-based drug repurposing perspectives for coronaviruses in general and the SARS-CoV-2 in particular.

Protein synthesis inhibition promotes nitric oxide generation and activation of CGKII-dependent downstream signaling pathways in the retina

Nitric oxide is an important neuromodulator in the CNS, and its production within neurons is modulated by NMDA receptors and requires a fine-tuned availability of L-arginine. We have previously shown that globally inhibiting protein synthesis mobilizes intracellular L-arginine "pools" in retinal neurons, which concomitantly enhances neuronal nitric oxide synthase-mediated nitric oxide production. Activation of NMDA receptors also induces local inhibition of protein synthesis and L-arginine intracellular accumulation through calcium influx and stimulation of eucariotic elongation factor type 2 kinase. We hypothesized that protein synthesis inhibition might also increase intracellular L-arginine availability to induce nitric oxide-dependent activation of downstream signaling pathways. Here we show that nitric oxide produced by inhibiting protein synthesis (using cycloheximide or anisomycin) is readily coupled to AKT activation in a soluble guanylyl cyclase and cGKII-dependent manner. Knockdown of cGKII prevents cycloheximide or anisomycin-induced AKT activation and its nuclear accumulation. Moreover, in retinas from cGKII knockout mice, cycloheximide was unable to enhance AKT phosphorylation. Indeed, cycloheximide also produces an increase of ERK phosphorylation which is abrogated by a nitric oxide synthase inhibitor. In summary, we show that inhibition of protein synthesis is a previously unanticipated driving force for nitric oxide generation and activation of downstream signaling pathways including AKT and ERK in cultured retinal cells. These results may be important for the regulation of synaptic signaling and neuronal development by NMDA receptors as well as for solving conflicting data observed when using protein synthesis inhibitors for studying neuronal survival during development as well in behavior and memory studies.

Exposure to mold proteases stimulates mucin production in airway epithelial cells through Ras/Raf1/ERK signal pathway

Environmental mold (fungus) exposure poses a significant threat to public health by causing illnesses ranging from invasive fungal diseases in immune compromised individuals to allergic hypertensive diseases such as asthma and asthma exacerbation in otherwise healthy people. However, the molecular pathogenesis has not been completely understood, and treatment options are limited. Due to its thermo-tolerance to the normal human body temperature, Aspergillus. fumigatus (A.fumigatus) is one of the most important human pathogens to cause different lung fungal diseases including fungal asthma. Airway obstruction and hyperresponsiveness caused by mucus overproduction are the hallmarks of many A.fumigatus induced lung diseases. To understand the underlying molecular mechanism, we have utilized a well-established A.fumigatus extracts (AFE) model to elucidate downstream signal pathways that mediate A.fumigatus induced mucin production in airway epithelial cells. AFE was found to stimulate time- and dose-dependent increase of major airway mucin gene expression (MUC5AC and MUC5B) partly via the elevation of their promoter activities. We also demonstrated that EGFR was required but not sufficient for AFE-induced mucin expression, filling the paradoxical gap from a previous study using the same model. Furthermore, we showed that fungal proteases in AFE were responsible for mucin induction by activating a Ras/Raf1/ERK signaling pathway. Ca2+ signaling, but ROS, both of which were stimulated by fungal proteases, was an indispensable determinant for ERK activation and mucin induction. The discovery of this novel pathway likely contributes to our understanding of the pathogenesis of fungal sensitization in allergic diseases such as fungal asthma.

Convergent Met and voltage-gated Ca2+ channel signaling drives hypermigration of Toxoplasma-infected dendritic cells

Ras-Erk MAPK signaling controls many of the principal pathways involved in metazoan cell motility, drives metastasis of multiple cancer types and is targeted in chemotherapy. However, its putative roles in immune cell functions or in infections have remained elusive. Here, using primary dendritic cells (DCs) in an infection model with the protozoan Toxoplasma gondii, we show that two pathways activated by infection converge on Ras-Erk MAPK signaling to promote migration of parasitized DCs. We report that signaling through the receptor tyrosine kinase Met (also known as HGF receptor) contributes to T. gondii-induced DC hypermotility. Furthermore, voltage-gated Ca2+ channel (VGCC, subtype CaV1.3) signaling impacted the migratory activation of DCs via calmodulin-calmodulin kinase II. We show that convergent VGCC signaling and Met signaling activate the GTPase Ras to drive Erk1 and Erk2 (also known as MAPK3 and MAPK1, respectively) phosphorylation and hypermotility of T. gondii-infected DCs. The data provide a molecular basis for the hypermigratory mesenchymal-to-amoeboid transition (MAT) of parasitized DCs. This emerging concept suggests that parasitized DCs acquire metastasis-like migratory properties that promote infection-related dissemination.

Cannabidiol exerts protective effects in an in vitro model of Parkinson's disease activating AKT/mTOR pathway

Parkinson's disease (PD) is a neurodegenerative disorder characterized by the degeneration of the nigrostriatal dopaminergic pathway with loss of substantia nigra pars compacta neurons and dopamine depletion. Various natural compounds showed protective actions against PD. In this work, the protective effects of cannabidiol (CBD), obtained from Cannabis sativa, were evaluated in retinoic acid differentiated SH-SY5Y cells exposed to 1-methyl-4-phenylpyridinium (MPP⁺), an in vitro PD model. In order to evaluate which receptor is involved in CBD actions CB1, CB2 and TRPV1 receptor antagonists were used. CBD counteracted the loss of cell viability caused by MPP⁺, reducing apoptosis as demonstrated by the reduction of Bax and caspase 3. Moreover, CBD reduced the nuclear levels of PARP-1. The protective effects of CBD seem to be mediated by the activation of ERK and AKT/mTOR pathways. The treatment with AKT1/2 inhibitor and the mTOR inhibitor rapamycin abolished CBD protective effects. The CBD-induced ERK activation may be mediated by CBD interaction with CB2 and TRPV1. We also investigated the protein levels of the autophagic proteins LC3 and beclin 1. CBD reduced the MPP⁺-induced increase of LC3 by CB2 and TRPV1 receptors. These data suggested the involvement of ERK in the modulation of autophagy. However, beclin 1 levels were not modified neither by MPP⁺ nor by CBD. These results indicated that CBD may exert preventive and protective actions in PD.

IODVA1, a guanidinobenzimidazole derivative, targets Rac activity and Ras-driven cancer models

We report the synthesis and preliminary characterization of IODVA1, a potent small molecule that is active in xenograft mouse models of Ras-driven lung and breast cancers. In an effort to inhibit oncogenic Ras signaling, we combined in silico screening with inhibition of proliferation and colony formation of Ras-driven cells. NSC124205 fulfilled all criteria. HPLC analysis revealed that NSC124205 was a mixture of at least three compounds, from which IODVA1 was determined to be the active component. IODVA1 decreased 2D and 3D cell proliferation, cell spreading and ruffle and lamellipodia formation through downregulation of Rac activity. IODVA1 significantly impaired xenograft tumor growth of Ras-driven cancer cells with no observable toxicity. Immuno-histochemistry analysis of tumor sections suggests that cell death occurs by increased apoptosis. Our data suggest that IODVA1 targets Rac signaling to induce death of Ras-transformed cells. Therefore, IODVA1 holds promise as an anti-tumor therapeutic agent.

Simulated Microgravity Influences VEGF, MAPK, and PAM Signaling in Prostate Cancer Cells

Prostate cancer is one of the leading causes of cancer mortality in men worldwide. An unusual but unique environment for studying tumor cell processes is provided by microgravity, either in space or simulated by ground-based devices like a random positioning machine (RPM). In this study, prostate adenocarcinoma-derived PC-3 cells were cultivated on an RPM for time periods of 3 and 5 days. We investigated the genes associated with the cytoskeleton, focal adhesions, extracellular matrix, growth, survival, angiogenesis, and metastasis. The gene expression of signaling factors of the vascular endothelial growth factor (VEGF), mitogen-activated protein kinase (MAPK), and PI3K/AKT/mTOR (PAM) pathways was investigated using qPCR. We performed immunofluorescence to study the cytoskeleton, histological staining to examine the morphology, and a time-resolved immunofluorometric assay to analyze the cell culture supernatants. When PC-3 cells were exposed to simulated microgravity (s-µg), some cells remained growing as adherent cells (AD), while most cells detached from the cell culture flask bottom and formed multicellular spheroids (MCS). After 3-day RPM exposure, PC-3 cells revealed significant downregulation of the VEGF, SRC1, AKT, MTOR, and COL1A1 gene expression in MCS, whereas FLT1, RAF1, MEK1, ERK1, FAK1, RICTOR, ACTB, TUBB, and TLN1 mRNAs were not significantly changed. ERK2 and TLN1 were elevated in AD, and FLK1, LAMA3, COL4A5, FN1, VCL, CDH1, and NGAL mRNAs were significantly upregulated in AD and MCS after 3 days. After a 5-day culture in s-µg, the PC-3 cells showed significant downregulations of VEGF mRNA in AD and MCS, and FN1, CDH1, and LAMA3 in AD and SCR1 in MCS. In addition, we measured significant upregulations in FLT1, AKT, ERK1, ERK2, LCN2, COL1A1, TUBB, and VCL mRNAs in AD and MCS, and increases in FLK1, FN1, and COL4A5 in MCS as well as LAMB2, CDH1, RAF1, MEK1, SRC1, and MTOR mRNAs in AD. FAK1 and RICTOR were not altered by s-µg. In parallel, the secretion rate of VEGFA and NGAL proteins decreased. Cytoskeletal alterations (F-actin) were visible, as well as a deposition of collagen in the MCS. In conclusion, RPM-exposure of PC-3 cells induced changes in their morphology, cytoskeleton, and extracellular matrix protein synthesis, as well as in their focal adhesion complex and growth behavior. The significant upregulation of genes belonging to the PAM pathway indicated their involvement in the cellular changes occurring in microgravity.

ERK/MAPK signalling pathway and tumorigenesis

Mitogen-activated protein kinase (MAPK) cascades are key signalling pathways that regulate a wide variety of cellular processes, including proliferation, differentiation, apoptosis and stress responses. The MAPK pathway includes three main kinases, MAPK kinase kinase, MAPK kinase and MAPK, which activate and phosphorylate downstream proteins. The extracellular signal-regulated kinases ERK1 and ERK2 are evolutionarily conserved, ubiquitous serine-threonine kinases that regulate cellular signalling under both normal and pathological conditions. ERK expression is critical for development and their hyperactivation plays a major role in cancer development and progression. The Ras/Raf/MAPK (MEK)/ERK pathway is the most important signalling cascade among all MAPK signal transduction pathways, and plays a crucial role in the survival and development of tumour cells. The present review discusses recent studies on Ras and ERK pathway members. With respect to processes downstream of ERK activation, the role of ERK in tumour proliferation, invasion and metastasis is highlighted, and the role of the ERK/MAPK signalling pathway in tumour extracellular matrix degradation and tumour angiogenesis is emphasised.

Characterization of Melanoma Cell Lines Resistant to Vemurafenib and Evaluation of Their Responsiveness to EGFR- and MET-Inhibitor Treatment

Constitutively active mutated BRAF kinase occurs in more than 40% of patients suffering from melanoma. To block its activity, a specific inhibitor, vemurafenib, is applied as a therapy. Unfortunately, patients develop resistance to this drug rather quickly. Previously, we demonstrated that pairs of inhibitors directed against EGFR (epidermal growth factor receptor) and MET (hepatocyte growth factor receptor) trigger a synergistic cytotoxic effect in human melanoma cells, and decrease their invasive abilities. In this study, we aimed to generate and characterize melanoma cells resistant to vemurafenib treatment, and then to evaluate the effectiveness of a previously developed therapy in this model. We showed that melanoma cells resistant to the BRAF inhibitor are characterized by a lower proliferation rate and they acquire a spindle-like shape. Using Western Blot, we also noticed increased levels of EGFR, MET, and selected markers of cancer stem cells in generated cell lines. Resistant cells also exhibited increased invasive abilities and elevated proteolytic activity, observed using scratch wound assays and gelatin zymography. Moreover, combination therapy reduced their viability, as measured with a colorimetric cytotoxicity test, and decreased invasiveness. The obtained results validate the application of combination therapy directed against EGFR and MET in melanoma cells resistant to treatment with inhibitors of mutated BRAF.

Short-Term Microgravity Influences Cell Adhesion in Human Breast Cancer Cells

With the commercialization of spaceflight and the exploration of space, it is important to understand the changes occurring in human cells exposed to real microgravity (r-µg) conditions. We examined the influence of r-µg, simulated microgravity (s-µg, incubator random positioning machine (iRPM)), hypergravity (hyper-g), and vibration (VIB) on triple-negative breast cancer (TNBC) cells (MDA-MB-231 cell line) with the aim to study early changes in the gene expression of factors associated with cell adhesion, apoptosis, nuclear factor "kappa-light-chain-enhancer" of activated B-cells (NF-κB) and mitogen-activated protein kinase (MAPK) signaling. We had the opportunity to attend a parabolic flight (PF) mission and to study changes in RNA transcription in the MDA-MB cells exposed to PF maneuvers (29th Deutsches Zentrum für Luft- und Raumfahrt (DLR) PF campaign). PF maneuvers induced an early up-regulation of ICAM1, CD44 and ERK1 mRNAs after the first parabola (P1) and a delayed upregulation of NFKB1, NFKBIA, NFKBIB, and FAK1 after the last parabola (P31). ICAM-1, VCAM-1 and CD44 protein levels were elevated, whereas the NF-κB subunit p-65 and annexin-A2 protein levels were reduced after the 31st parabola (P31). The PRKCA, RAF1, BAX mRNA were not changed and cleaved caspase-3 was not detectable in MDA-MB-231 cells exposed to PF maneuvers. Hyper-g-exposure of the cells elevated the expression of CD44 and NFKBIA mRNAs, iRPM-exposure downregulated ANXA2 and BAX, whereas VIB did not affect the TNBC cells. The early changes in ICAM-1 and VCAM-1 and the rapid decrease in the NF-κB subunit p-65 might be considered as fast-reacting, gravity-regulated and cell-protective mechanisms of TNBC cells exposed to altered gravity conditions. This data suggest a key role for the detected gravity-signaling elements in three-dimensional growth and metastasis.

Molecular regulation of human skeletal muscle protein synthesis in response to exercise and nutrients: a compass for overcoming age-related anabolic resistance

Skeletal muscle mass, a strong predictor of longevity and health in humans, is determined by the balance of two cellular processes, muscle protein synthesis (MPS) and muscle protein breakdown. MPS seems to be particularly sensitive to changes in mechanical load and/or nutritional status; therefore, much research has focused on understanding the molecular mechanisms that underpin this cellular process. Furthermore, older individuals display an attenuated MPS response to anabolic stimuli, termed anabolic resistance, which has a negative impact on muscle mass and function, as well as quality of life. Therefore, an understanding of which, if any, molecular mechanisms contribute to anabolic resistance of MPS is of vital importance in formulation of therapeutic interventions for such populations. This review summarizes the current knowledge of the mechanisms that underpin MPS, which are broadly divided into mechanistic target of rapamycin complex 1 (mTORC1)-dependent, mTORC1-independent, and ribosomal biogenesis-related, and describes the evidence that shows how they are regulated by anabolic stimuli (exercise and/or nutrition) in healthy human skeletal muscle. This review also summarizes evidence regarding which of these mechanisms may be implicated in age-related skeletal muscle anabolic resistance and provides recommendations for future avenues of research that can expand our knowledge of this area.

SerpinB2 inhibits migration and promotes a resolution phase signature in large peritoneal macrophages

SerpinB2 (plasminogen activator inhibitor type 2) has been called the "undecided serpin" with no clear consensus on its physiological role, although it is well described as an inhibitor of urokinase plasminogen activator (uPA). In macrophages, pro-inflammatory stimuli usually induce SerpinB2; however, expression is constitutive in Gata6+ large peritoneal macrophages (LPM). Interrogation of expression data from human macrophages treated with a range of stimuli using a new bioinformatics tool, CEMiTool, suggested that SerpinB2 is most tightly co- and counter-regulated with genes associated with cell movement. Using LPM from SerpinB2-/- and SerpinB2R380A (active site mutant) mice, we show that migration on Matrigel was faster than for their wild-type controls. Confocal microscopy illustrated that SerpinB2 and F-actin staining overlapped in focal adhesions and lamellipodia. Genes associated with migration and extracellular matrix interactions were also identified by RNA-Seq analysis of migrating RPM from wild-type and SerpinB2R380A mice. Subsequent gene set enrichment analyses (GSEA) suggested SerpinB2 counter-regulates many Gata6-regulated genes associated with migration. These data argue that the role of SerpinB2 in macrophages is inhibition of uPA-mediated plasmin generation during cell migration. GSEA also suggested that SerpinB2 expression (likely via ensuing modulation of uPA-receptor/integrin signaling) promotes the adoption of a resolution phase signature.

Cadmium induces A549 cell migration and invasion by activating ERK

Cadmium (Cd) is an established carcinogen that is involved in the progression of lung cancer. However, the mechanisms underlying this Cd-induced process have yet to be fully elucidated. The present study explored the potential roles of phosphorylated (p)-ERK in the Cd-induced migration and invasion of lung cancer cells. An MTT assay was performed to evaluate cell viability whilst western blot analysis and reverse transcription-quantitative PCR were used to detect the expression of protein and mRNA, respectively. Migration and invasion assays were performed to assess cell migratory and invasive abilities. The results demonstrated that exposure to Cd increased the expression of p-ERK in A549 cells. Cd also enhanced the migration and invasion of A549 cells, which could be blocked via U0126 treatment (an inhibitor of mitogen activated protein kinase). In addition, it was identified that Cd-induced expression of matrix metalloproteinases 2 mRNA was mediated by p-ERK. In conclusion, the present findings indicated that Cd induced A549 cell migration and invasion by activating ERK, and it was hypothesized that p-ERK could serve as a target in the clinical treatment of Cd-induced lung cancer.

A Novel Class of Common Docking Domain Inhibitors That Prevent ERK2 Activation and Substrate Phosphorylation

Extracellular signal-regulated kinases (ERK1/2) are mitogen-activated protein kinases (MAPKs) that play a pro-tumorigenic role in numerous cancers. ERK1/2 possess two protein-docking sites that are distinct from the active site: the D-recruitment site (DRS) and the F-recruitment site. These docking sites facilitate substrate recognition, intracellular localization, signaling specificity, and protein complex assembly. Targeting these sites on ERK in a therapeutic context may overcome many problems associated with traditional ATP-competitive inhibitors. Here, we identified a new class of inhibitors that target the ERK DRS by screening a synthetic combinatorial library of more than 30 million compounds. The screen detects the competitive displacement of a fluorescent peptide from the DRS of ERK2. The top molecular scaffold from the screen was optimized for structure-activity relationship by positional scanning of different functional groups. This resulted in 10 compounds with similar binding affinities and a shared core structure consisting of a tertiary amine hub with three functionalized cyclic guanidino branches. Compound 2507-1 inhibited ERK2 from phosphorylating a DRS-targeting substrate and prevented the phosphorylation of ERK2 by a constitutively active MEK1 (MAPK/ERK kinase 1) mutant. Interaction between an analogue, 2507-8, and the ERK2 DRS was confirmed by nuclear magnetic resonance and X-ray crystallography. 2507-8 forms critical interactions at the common docking domain residue Asp319 via an arginine-like moiety that is shared by all 10 hits, suggesting a common binding mode. The structural and biochemical insights reported here provide the basis for developing new ERK inhibitors that are not ATP-competitive but instead function by disrupting critical protein-protein interactions.

Targeting ERK beyond the boundaries of the kinase active site in melanoma

Extracellular signal-regulated kinase 1/2 (ERK1/2) constitute a point of convergence for complex signaling events that regulate essential cellular processes, including proliferation and survival. As such, dysregulation of the ERK signaling pathway is prevalent in many cancers. In the case of BRAF-V600E mutant melanoma, ERK inhibition has emerged as a viable clinical approach to abrogate signaling through the ERK pathway, even in cases where MEK and Raf inhibitor treatments fail to induce tumor regression due to resistance mechanisms. Several ERK inhibitors that target the active site of ERK have reached clinical trials, however, many critical ERK interactions occur at other potentially druggable sites on the protein. Here we discuss the role of ERK signaling in cell fate, in driving melanoma, and in resistance mechanisms to current BRAF-V600E melanoma treatments. We explore targeting ERK via a distinct site of protein-protein interaction, known as the D-recruitment site (DRS), as an alternative or supplementary mode of ERK pathway inhibition in BRAF-V600E melanoma. Targeting the DRS with inhibitors in melanoma has the potential to not only disrupt the catalytic apparatus of ERK but also its noncatalytic functions, which have significant impacts on spatiotemporal signaling dynamics and cell fate.

Biological Rationale for Targeting MEK/ERK Pathways in Anti-Cancer Therapy and to Potentiate Tumour Responses to Radiation

ERK1 and ERK2 (ERKs), two extracellular regulated kinases (ERK1/2), are evolutionary-conserved and ubiquitous serine-threonine kinases involved in regulating cell signalling in normal and pathological tissues. The expression levels of these kinases are almost always different, with ERK2 being the more prominent. ERK1/2 activation is fundamental for the development and progression of cancer. Since their discovery, much research has been dedicated to their role in mitogen-activated protein kinases (MAPK) pathway signalling and in their activation by mitogens and mutated RAF or RAS in cancer cells. In order to gain a better understanding of the role of ERK1/2 in MAPK pathway signalling, many studies have been aimed at characterizing ERK1/2 splicing isoforms, mutants, substrates and partners. In this review, we highlight the differences between ERK1 and ERK2 without completely discarding the hypothesis that ERK1 and ERK2 exhibit functional redundancy. The main goal of this review is to shed light on the role of ERK1/2 in targeted therapy and radiotherapy and highlight the importance of identifying ERK inhibitors that may overcome acquired resistance. This is a highly relevant therapeutic issue that needs to be addressed to combat tumours that rely on constitutively active RAF and RAS mutants and the MAPK pathway.

Mitochondrial stress triggers a pro-survival response through epigenetic modifications of nuclear DNA

Mitochondrial dysfunction represents an important cellular stressor and when intense and persistent cells must unleash an adaptive response to prevent their extinction. Furthermore, mitochondria can induce nuclear transcriptional changes and DNA methylation can modulate cellular responses to stress. We hypothesized that mitochondrial dysfunction could trigger an epigenetically mediated adaptive response through a distinct DNA methylation patterning. We studied cellular stress responses (i.e., apoptosis and autophagy) in mitochondrial dysfunction models. In addition, we explored nuclear DNA methylation in response to this stressor and its relevance in cell survival. Experiments in cultured human myoblasts revealed that intense mitochondrial dysfunction triggered a methylation-dependent pro-survival response. Assays done on mitochondrial disease patient tissues showed increased autophagy and enhanced DNA methylation of tumor suppressor genes and pathways involved in cell survival regulation. In conclusion, mitochondrial dysfunction leads to a "pro-survival" adaptive state that seems to be triggered by the differential methylation of nuclear genes.

Heterogeneous pathway activation and drug response modelled in colorectal-tumor-derived 3D cultures

Organoid cultures derived from colorectal cancer (CRC) samples are increasingly used as preclinical models for studying tumor biology and the effects of targeted therapies under conditions capturing in vitro the genetic make-up of heterogeneous and even individual neoplasms. While 3D cultures are initiated from surgical specimens comprising multiple cell populations, the impact of tumor heterogeneity on drug effects in organoid cultures has not been addressed systematically. Here we have used a cohort of well-characterized CRC organoids to study the influence of tumor heterogeneity on the activity of the KRAS/MAPK-signaling pathway and the consequences of treatment by inhibitors targeting EGFR and downstream effectors. MAPK signaling, analyzed by targeted proteomics, shows unexpected heterogeneity irrespective of RAS mutations and is associated with variable responses to EGFR inhibition. In addition, we obtained evidence for intratumoral heterogeneity in drug response among parallel “sibling” 3D cultures established from a single KRAS-mutant CRC. Our results imply that separate testing of drug effects in multiple subpopulations may help to elucidate molecular correlates of tumor heterogeneity and to improve therapy response prediction in patients.

Commonly occurring genetic alterations and patient-specific genetic features are increasingly used to predict the possible action of targeted cancer therapies. Although several lines of evidence have suggested that preclinical and clinical responses concur, the heterogeneity of tumors remains a severe obstacle in routinely translating preclinical data to patient treatments. Here we present a rapid work flow that integrates drug testing of three-dimensional patient tumor-derived (organoid) cultures and assessment of their genetic make-up as well as that of their donor tumors by amplicon sequencing and targeted proteomics. While the organoid cultures largely recapitulated the genomic profiles of donor tumors, the overall treatment responses and inhibitor effects on the intracellular signaling system were quite variable. Notably, organoid cultures obtained by synchronous multi-regional sampling of the same colorectal tumor showed an up to 30-fold difference in drug response. A combinatorial drug treatment improved the response. These data were confirmed in matched mouse xenograft models from the same tumor. Our findings may help to refine preclinical testing of individual tumors by modelling heterogeneity in cultures, to better understand therapeutic failure in clinical settings and to find ways to overcome treatment resistance.

Nuclear ERK: Mechanism of Translocation, Substrates, and Role in Cancer

The extracellular signal-regulated kinases 1/2 (ERK) are central signaling components that regulate stimulated cellular processes such as proliferation and differentiation. When dysregulated, these kinases participate in the induction and maintenance of various pathologies, primarily cancer. While ERK is localized in the cytoplasm of resting cells, many of its substrates are nuclear, and indeed, extracellular stimulation induces a rapid and robust nuclear translocation of ERK. Similarly to other signaling components that shuttle to the nucleus upon stimulation, ERK does not use the canonical importinα/β mechanism of nuclear translocation. Rather, it has its own unique nuclear translocation signal (NTS) that interacts with importin7 to allow stimulated shuttling via the nuclear pores. Prevention of the nuclear translocation inhibits proliferation of B-Raf- and N/K-Ras-transformed cancers. This effect is distinct from the one achieved by catalytic Raf and MEK inhibitors used clinically, as cells treated with the translocation inhibitors develop resistance much more slowly. In this review, we describe the mechanism of ERK translocation, present all its nuclear substrates, discuss its role in cancer and compare its translocation to the translocation of other signaling components. We also present proof of principle data for the use of nuclear ERK translocation as an anti-cancer target. It is likely that the prevention of nuclear ERK translocation will eventually serve as a way to combat Ras and Raf transformed cancers with less side-effects than the currently used drugs.

Metformin triggers the intrinsic apoptotic response in human AGS gastric adenocarcinoma cells by activating AMPK and suppressing mTOR/AKT signaling

Metformin is commonly used to treat patients with type 2 diabetes and is associated with a decreased risk of cancer. Previous studies have demonstrated that metformin can act alone or in synergy with certain anticancer agents to achieve anti-neoplastic effects on various types of tumors via adenosine monophosphate-activated protein kinase (AMPK) signaling. However, the role of metformin in AMPK-mediated apoptosis of human gastric cancer cells is poorly understood. In the current study, metformin exhibited a potent anti-proliferative effect and induced apoptotic characteristics in human AGS gastric adenocarcinoma cells, as demonstrated by MTT assay, morphological observation method, terminal deoxynucleotidyl transferase dUTP nick end labeling and caspase-3/7 assay kits. Western blot analysis demonstrated that treatment with metformin increased the phosphorylation of AMPK, and decreased the phosphorylation of AKT, mTOR and p70S6k. Compound C (an AMPK inhibitor) suppressed AMPK phosphorylation and significantly abrogated the effects of metformin on AGS cell viability. Metformin also reduced the phosphorylation of mitogen-activated protein kinases (ERK, JNK and p38). Additionally, metformin significantly increased the cellular ROS level and included loss of mitochondrial membrane potential (ΔΨm). Metformin altered apoptosis-associated signaling to downregulate the BAD phosphorylation and Bcl-2, pro-caspase-9, pro-caspase-3 and pro-caspase-7 expression, and to upregulate BAD, cytochrome c, and Apaf-1 proteins levels in AGS cells. Furthermore, z-VAD-fmk (a pan-caspase inhibitor) was used to assess mitochondria-mediated caspase-dependent apoptosis in metformin-treated AGS cells. The findings demonstrated that metformin induced AMPK-mediated apoptosis, making it appealing for development as a novel anticancer drug for the treating gastric cancer.

The Nuclear Translocation of Mitogen-Activated Protein Kinases: Molecular Mechanisms and Use as Novel Therapeutic Target

The mitogen-activated protein kinase (MAPK) cascades are central signaling pathways that play a central role in the regulation of most stimulated cellular processes including proliferation, differentiation, stress response and apoptosis. Currently 4 such cascades are known, each termed by its downstream MAPK components: the extracellular signal-regulated kinase 1/2 (ERK1/2), cJun-N-terminal kinase (JNK), p38 and ERK5. One of the hallmarks of these cascades is the stimulated nuclear translocation of their MAPK components using distinct mechanisms. ERK1/2 are shuttled into the nucleus by importin7, JNK and p38 by a dimer of importin3 with either importin9 or importin7, and ERK5 by importin-α/β. Dysregulation of these cascades often results in diseases, including cancer and inflammation, as well as developmental and neurological disorders. Much effort has been invested over the years in developing inhibitors to the MAPK cascades to combat these diseases. Although some inhibitors are already in clinical use or clinical trials, their effects are hampered by development of resistance or adverse side-effects. Recently, our group developed 2 myristoylated peptides: EPE peptide, which inhibits the interaction of ERK1/2 with importin7, and PERY peptide, which prevents JNK/p38 interaction with either importin7 or importin9. These peptides block the nuclear translocation of their corresponding kinases, resulting in prevention of several cancers, while the PERY peptide also inhibits inflammation-induced diseases. These peptides provide a proof of concept for the use of the nuclear translocation of MAPKs as therapeutic targets for cancer and/or inflammation.

Differential Apoptotic and Mitogenic Effects of Lectins in Zebrafish

Plant lectins represent a major group of anti-nutritional factors that can be toxic to human and animals. However, the mechanisms by which lectins regulate cell fates are not well-understood. In the present study, the cellular and molecular impacts of three common lectins, agglutinins from wheat germ [wheat germ agglutinin (WGA)], soybean [soybean agglutinin (SBA)], and peanut [peanut agglutinin (PNA)] were examined in zebrafish embryo and liver cells. WGA and SBA were found to induce cell apoptosis both in vitro and in vivo, while PNA stimulated cell proliferation. WGA and SBA reduced levels of B cell lymphoma-2 (Bcl-2), phosphorylation of Bcl-2-associated death promoter (Bad), cyclin-dependent kinase 4 (Cdk4), and phosphorylation of the retinoblastoma (Rb). WGA and SBA also inhibited the activities of cell survival pathways including protein kinase B (Akt), extracellular signal-regulated protein kinases 1 and 2 (Erk1/2), and target of rapamycin (Tor). Furthermore, WGA and SBA shifted the cellular metabolism characterized by reduced expression of glucose-6-phosphate dehydrogenase (g6pd) and increased expression of glutamine synthetase (glul) and glutamate dehydrogenase (glud). However, PNA showed the opposite effects toward these molecular markers compared to those of WGA and SBA. Therefore, our results revealed some plant lectins (WGA and SBA) were toxic while the other (PNA) was mitogenic. Further characterization of the distinct functions of individual lectins should be valuable for both nutrition and other potential applications.

Polymorphisms in RAS/RAF/MEK/ERK Pathway Are Associated with Gastric Cancer

The RAS/RAF/MEK/ERK pathway regulates certain cellular functions, including cell proliferation, differentiation, survival, and apoptosis. Dysregulation of this pathway leads to the occurrence and progression of cancers mainly by somatic mutations. This study aimed to assess if polymorphisms of the RAS/RAF/MEK/ERK pathway are associated with gastric cancer. A case-control study of 242 gastric cancer patients and 242 controls was performed to assess the association of 27 single nucleotide polymorphisms (SNPs) in the RAS/RAF/MEK/ERK pathway genes with gastric cancer. Analyses performed under the additive model (allele) showed four significantly associated SNPs: RAF1 rs3729931 (Odds ratio (OR) = 1.54, 95%, confidence interval (CI): 1.20–1.98, p-value = 7.95 × 10⁻⁴), HRAS rs45604736 (OR = 1.60, 95% CI: 1.16–2.22, p-value = 4.68 × 10⁻³), MAPK1 rs2283792 (OR = 1.45, 95% CI: 1.12–1.87, p-value = 4.91 × 10⁻³), and MAPK1 rs9610417 (OR = 0.60, 95% CI: 0.42–0.87, p-value = 6.64 × 10⁻³). Functional annotation suggested that those variants or their proxy variants may have a functional effect. In conclusion, this study suggests that RAF1 rs3729931, HRAS rs45604736, MAPK1 rs2283792, and MAPK1 rs9610417 are associated with gastric cancer.

Reconstruction of global regulatory network from signaling to cellular functions using phosphoproteomic data

Cellular signaling regulates various cellular functions via protein phosphorylation. Phosphoproteomic data potentially include information for a global regulatory network from signaling to cellular functions, but a procedure to reconstruct this network using such data has yet to be established. In this paper, we provide a procedure to reconstruct a global regulatory network from signaling to cellular functions from phosphoproteomic data by integrating prior knowledge of cellular functions and inference of the kinase-substrate relationships (KSRs). We used phosphoproteomic data from insulin-stimulated Fao hepatoma cells and identified protein phosphorylation regulated by insulin specifically over-represented in cellular functions in the KEGG database. We inferred kinases for protein phosphorylation by KSRs, and connected the kinases in the insulin signaling layer to the phosphorylated proteins in the cellular functions, revealing that the insulin signal is selectively transmitted via the Pi3k-Akt and Erk signaling pathways to cellular adhesions and RNA maturation, respectively. Thus, we provide a method to reconstruct global regulatory network from signaling to cellular functions based on phosphoproteomic data.