ERK2 but not ERK1 mediates HGF-induced motility in non-small cell lung carcinoma cell lines

A zebrafish embryo screen utilizing gastrulation identifies the HTR2C inhibitor pizotifen as a suppressor of EMT-mediated metastasis

Metastasis is responsible for approximately 90% of cancer-associated mortality but few models exist that allow for rapid and effective screening of anti-metastasis drugs. Current mouse models of metastasis are too expensive and time consuming to use for rapid and high-throughput screening. Therefore, we created a unique screening concept utilizing conserved mechanisms between zebrafish gastrulation and cancer metastasis for identification of potential anti-metastatic drugs. We hypothesized that small chemicals that interrupt zebrafish gastrulation might also suppress metastatic progression of cancer cells and developed a phenotype-based chemical screen to test the hypothesis. The screen used epiboly, the first morphogenetic movement in gastrulation, as a marker and enabled 100 chemicals to be tested in 5 hr. The screen tested 1280 FDA-approved drugs and identified pizotifen, an antagonist for serotonin receptor 2C (HTR2C) as an epiboly-interrupting drug. Pharmacological and genetic inhibition of HTR2C suppressed metastatic progression in a mouse model. Blocking HTR2C with pizotifen restored epithelial properties to metastatic cells through inhibition of Wnt signaling. In contrast, HTR2C induced epithelial-to-mesenchymal transition through activation of Wnt signaling and promoted metastatic dissemination of human cancer cells in a zebrafish xenotransplantation model. Taken together, our concept offers a novel platform for discovery of anti-metastasis drugs.

Mutations That Confer Drug-Resistance, Oncogenicity and Intrinsic Activity on the ERK MAP Kinases-Current State of the Art

Unique characteristics distinguish extracellular signal-regulated kinases (Erks) from other eukaryotic protein kinases (ePKs). Unlike most ePKs, Erks do not autoactivate and they manifest no basal activity; they become catalysts only when dually phosphorylated on neighboring Thr and Tyr residues and they possess unique structural motifs. Erks function as the sole targets of the receptor tyrosine kinases (RTKs)-Ras-Raf-MEK signaling cascade, which controls numerous physiological processes and is mutated in most cancers. Erks are therefore the executers of the pathway’s biology and pathology. As oncogenic mutations have not been identified in Erks themselves, combined with the tight regulation of their activity, Erks have been considered immune against mutations that would render them intrinsically active. Nevertheless, several such mutations have been generated on the basis of structure-function analysis, understanding of ePK evolution and, mostly, via genetic screens in lower eukaryotes. One of the mutations conferred oncogenic properties on Erk1. The number of interesting mutations in Erks has dramatically increased following the development of Erk-specific pharmacological inhibitors and identification of mutations that cause resistance to these compounds. Several mutations have been recently identified in cancer patients. Here we summarize the mutations identified in Erks so far, describe their properties and discuss their possible mechanism of action.

ERK1/ATF-2 signaling axis contributes to interleukin-1β-induced MMP-3 expression in dermal fibroblasts

Matrix metalloproteinases (MMPs) play a pivotal role in tissue remodeling by degrading the extracellular matrix (ECM) components. This mechanism is implicated in a variety of physiological and pathological cellular processes including wound healing. One of the key proteins involved in this process is the proinflammatory cytokine interleukin-1β (IL-1β, which induces the expression of MMP-3 mRNA and the secretion of MMP-3 protein by dermal fibroblasts. In this study, we first investigated the contribution of activating transcription factor 2 (ATF-2) to IL-1β-induced MMP-3 expression in dermal fibroblasts. Our results showed that in cells transfected with ATF-2 siRNA or treated with the ATF-2 inhibitor SBI-0087702, IL-1β-induced MMP-3 mRNA expression was reduced. We also demonstrated that IL-1β stimulates the phosphorylation of ATF-2. These observations suggest that ATF-2 plays an important role in IL-1β-induced MMP-3 expression. Next, we investigated the role of MAPK signaling in ATF-2 activation. In cells treated with the extracellular signal-regulated kinase (ERK) inhibitor FR180240, as well as in cells transfected with ERK1 and ERK2 siRNAs, IL-1β-induced MMP-3 mRNA expression was reduced. In addition, we showed that IL-1β induced the phosphorylation of ERK1/2. These observations suggest that ERK1 and ERK2 are involved in IL-1β-induced MMP-3 expression. However, ERK1 and ERK2 do seem to play different roles. While the ERK inhibitor FR180204 inhibited IL-1β-induced ATF-2 phosphorylation, only in cells transfected with ERK1 siRNA, but not ERK2 siRNA, IL-1β-induced ATF-2 phosphorylation was reduced. These findings suggest that the ERK1/ATF-2 signaling axis contributes to IL-1β-induced MMP-3 expression in dermal fibroblasts.

Rigidity controls human desmoplastic matrix anisotropy to enable pancreatic cancer cell spread via extracellular signal-regulated kinase 2

It is predicted that pancreatic ductal adenocarcinoma (PDAC) will become the second most lethal cancer in the US by 2030. PDAC includes a fibrous-like stroma, desmoplasia, encompassing most of the tumor mass, which is produced by cancer-associated fibroblasts (CAFs) and includes their cell-derived extracellular matrices (CDMs). Since elimination of desmoplasia has proven detrimental to patients, CDM reprogramming, as opposed to stromal ablation, is therapeutically desirable. Hence, efforts are being made to harness desmoplasia's anti-tumor functions. We conducted biomechanical manipulations, using variations of pathological and physiological substrates in vitro, to culture patient-harvested CAFs and generate CDMs that restrict PDAC growth and spread. We posited that extrinsic modulation of the environment, via substrate rigidity, influences CAF's cell-intrinsic forces affecting CDM production. Substrates used were polyacrylamide gels of physiological (~1.5 kPa) or pathological (~7 kPa) stiffnesses. Results showed that physiological substrates influenced CAFs to generate CDMs similar to normal/control fibroblasts. We found CDMs to be softer than the corresponding underlying substrates, and CDM fiber anisotropy (i.e., alignment) to be biphasic and informed via substrate-imparted morphological CAF aspect ratios. The biphasic nature of CDM fiber anisotropy was mathematically modeled and proposed a correlation between CAF aspect ratios and CDM alignment; regulated by extrinsic and intrinsic forces to conserve minimal free energy. Biomechanical manipulation of CDMs, generated on physiologically soft substrates, leads to reduction in nuclear translocation of pERK1/2 in KRAS mutated pancreatic cells. ERK2 was found essential for CDM-regulated tumor cell spread. In vitro findings correlated with in vivo observations; nuclear pERK1/2 is significantly high in human PDAC samples. The study suggests that altering underlying substrates enable CAFs to remodel CDMs and restrict pancreatic cancer cell spread in an ERK2 dependent manner.

Interleukin-1β promotes interleulin-6 expression via ERK1/2 signaling pathway in canine dermal fibroblasts

Interleukin-6 (IL-6) is a pleiotropic cytokine involved in the regulation of the immune response and inflammation. In this study, we investigated effect of the proinflammatory cytokine interleukin-1β (IL-1β) on IL-6 expression in canine dermal fibroblasts. IL-1β induced IL-6 mRNA expression and protein release in a time- and dose-dependent manner. When cells were treated with inhibitors of mitogen-activated protein kinases (MAPKs), the extracellular signal-regulated kinase (ERK) inhibitor FR180240 inhibited IL-1β-induced IL-6 mRNA expression, but not SP600125 or SKF86002, which are c-Jun N-terminal kinase (JNK) and p38 MAPK inhibitors, respectively. In cells treated with U0126, an inhibitor of MAPK/ERK kinase (MEK), which activates ERK, IL-1β-induced IL-6 mRNA expression was also inhibited. IL-1β stimulated ERK1/2 phosphorylation. In cells transfected with ERK1 and ERK2 isoform siRNAs, IL-1β-induced IL-6 mRNA expression was reduced. These observations suggest that IL-1β induces IL-6 expression via ERK1/2 signaling pathway in canine dermal fibroblasts.

ERK2 regulates epithelial-to-mesenchymal plasticity through DOCK10-dependent Rac1/FoxO1 activation

ERK is a key coordinator of the epithelial-to-mesenchymal transition (EMT) in that a variety of EMT-inducing factors activate signaling pathways that converge on ERK to regulate EMT transcription programs. However, the mechanisms by which ERK controls the EMT program are not well understood. Through an analysis of the global changes of gene expression mediated by ERK2, we identified the transcription factor FoxO1 as a potential mediator of ERK2-induced EMT, and thus we investigated the mechanism by which ERK2 regulates FoxO1. Additionally, our analysis revealed that ERK2 induced the expression of Dock10, a Rac1/Cdc42 GEF, during EMT. We demonstrate that the activation of the Rac1/JNK signaling axis downstream of Dock10 leads to an increase in FoxO1 expression and EMT. Taken together, our study uncovers mechanisms by which epithelial cells acquire less proliferative but more migratory mesenchymal properties and reveals potential therapeutic targets for cancers evolving into a metastatic disease state.

HGF regulate HTR-8/SVneo trophoblastic cells migration/invasion under hypoxic conditions through increased HIF-1α expression via MAPK and PI3K pathways

Hepatocyte growth factor (HGF) is reported to be down-regulated in pregnancy complications like intrauterine growth retardation and preeclampsia, which are associated with abnormal trophoblast migration/invasion. In this study, role of HGF and associated signaling pathways has been investigated in HTR-8/SVneo trophoblastic cells migration/invasion under normoxia (20% O₂) and hypoxia (2% O₂). HTR-8/SVneo cells exposed to hypoxia showed increase in migration and invasion as compared to cells incubated under normoxic conditions. The migration/invasion under both normoxic and hypoxic conditions was further enhanced after treatment with HGF. Subsequent to treatment with HGF, a significant increase in expression of MMP2 & MMP3 under normoxia and MMP1 & MMP9 under hypoxia was observed. Treatment of HTR-8/SVneo cells with HGF under hypoxia also led to decrease in TIMP1. Treatment of the cells with HGF led to activation of mitogen activated protein kinases (MAPK) and phosphatidylinositol 3-kinase (PI3K) signaling pathways. Inhibition of MAPK by U0126 and PI3K by LY294002 led to concomitant decrease in the HGF-mediated migration/invasion of HTR-8/SVneo cells. HGF treatment under hypoxia also led to a significant increase in hypoxia inducible factor (HIF-1α) expression. Additionally, inhibition of HIF-1α by siRNA led to decrease in HGF-mediated migration of HTR-8/SVneo cells under hypoxic conditions. Inhibition of HGF activated MAPK and PI3K signaling led to reduction in HIF-1α expression under hypoxia. In conclusion, HGF facilitates HTR-8/SVneo cell migration/invasion by activation of MAPK/PI3K signaling pathways and increased expression of MMPs. HIF-1α has a role in HGF-mediated increase in migration under hypoxic conditions.

Isoform-selective activity-based profiling of ERK signaling

Extracellular signal-regulated kinases (ERKs) mediate downstream signaling of RAS-RAF-MEK as key regulators of the mitogen-activated protein kinase (MAPK) pathway. Activation of ERK signaling is a hallmark of cancer and upstream MAPK proteins have been extensively pursued as drug targets for cancer therapies. However, the rapid rise of resistance to clinical RAF and MEK inhibitors has prompted interest in targeting ERK (ERK1 and ERK2 isoforms) directly for cancer therapy. Current methods for evaluating activity of inhibitors against ERK isoforms are based primarily on analysis of recombinant proteins. Strategies to directly and independently profile native ERK1 and ERK2 activity would greatly complement current cell biological tools used to probe and target ERK function. Here, we present a quantitative chemoproteomic strategy that utilizes active-site directed probes to directly quantify native ERK activity in an isoform-specific fashion. We exploit a single isoleucine/leucine difference in ERK substrate binding sites to enable activity-based profiling of ERK1 versus ERK2 across a variety of cell types, tissues, and species. We used our chemoproteomic strategy to determine potency and selectivity of academic (VX-11e) and clinical (Ulixertinib) ERK inhibitors. Correlation of potency estimates by chemoproteomics with anti-proliferative activity of VX-11e and Ulixertinib revealed that >90% inactivation of both native ERK1 and ERK2 is needed to mediate cellular activity of inhibitors. Our findings introduce one of the first assays capable of independent evaluation of native ERK1 and ERK2 activity to advance drug discovery of oncogenic MAPK pathways.

MiR-22 suppresses epithelial-mesenchymal transition in bladder cancer by inhibiting Snail and MAPK1/Slug/vimentin feedback loop

MicroRNAs (miRNAs) have been validated to play prominent roles in the occurrence and development of bladder cancer (BCa). MiR-22 was previously reported to act as a tumor suppressor or oncomiRNA in various types of cancer. However, its accurate expression, function, and mechanism in BCa remain unclear. Here, we find that miR-22 is frequently downregulated in BCa tissues compared with adjacent non-cancerous tissues. Overexpression of miR-22 significantly inhibits proliferation, migration, and invasion of BCa cells both in vitro and in vivo. Importantly, miR-22 is found to suppress cell proliferation/apoptosis by directly targeting MAPK1 (mitogen-activated protein kinase 1, ERK2) and inhibit cell motility by targeting both MAPK1 and Snail. Further statistical analysis shows that low-expression of MAPK1 or Snail is an independent prognostic factor for a better overall survival in patients with BCa (n = 401). Importantly, we describe an important regenerative feedback loop among vimentin, Slug and MAPK1 in BCa cells. MAPK1-induced Slug expression upregulates vimentin. Vimentin in turn activates MAPK1. By inhibiting Snail and MAPK1/Slug/vimentin feedback loop, miR-22 suppresses epithelial–mesenchymal transition (EMT) of BCa cells in vitro as well as in vivo. Taken together, this study reveals that miR-22 is critical to the proliferation, apoptosis and EMT progression in BCa cells. Targeting the pathway described here may be a novel approach for inhibiting proliferation and metastasis of BCa.

ERK1 is dispensable for mouse pancreatic beta cell function but is necessary for glucose-induced full activation of MSK1 and CREB

AIMS/HYPOTHESIS

Insufficient insulin secretion from pancreatic beta cells, which is associated with a decrease in beta cell mass, is a characteristic of type 2 diabetes. Extracellular signal-related kinase 1 and 2 (ERK1/2) inhibition in beta cells has been reported to affect insulin secretion, gene transcription and survival, although whether ERK1 and ERK2 play distinct roles is unknown. The aim of this study was to assess the individual roles of ERK1 and ERK2 in beta cells using ERK1 (also known as Mapk3)-knockout mice (Erk1 ^-/- mice) and pharmacological approaches.

METHODS

NAD(P)H, free cytosolic Ca²⁺ concentration and insulin secretion were determined in islets. ERK1 and ERK2 subplasmalemmal translocation and activity was monitored using total internal reflection fluorescence microscopy. ERK1/2, mitogen and stress-activated kinase1 (MSK1) and cAMP-responsive element-binding protein (CREB) activation were evaluated by western blot and/or immunocytochemistry. The islet mass was determined from pancreatic sections.

RESULTS

Glucose induced rapid subplasmalemmal recruitment of ERK1 and ERK2. When both ERK1 and ERK2 were inhibited simultaneously, the rapid transient peak of the first phase of glucose-induced insulin secretion was reduced by 40% (p < 0.01), although ERK1 did not appear to be involved in this process. By contrast, ERK1 was required for glucose-induced full activation of several targets involved in beta cell survival; MSK1 and CREB were less active in Erk1 ^-/- mouse beta cells (p < 0.01) compared with Erk1 ^+/+ mouse beta cells, and their phosphorylation could only be restored when ERK1 was re-expressed and not when ERK2 was overexpressed. Finally, the islet mass of Erk1 ^-/- mice was slightly increased in young animals (4-month-old mice) vs Erk1 ^+/+ mice (section occupied by islets [mean ± SEM]: 0.74% ± 0.03% vs 0.62% ± 0.04%; p < 0.05), while older mice (10 months old) were less prone to age-associated pancreatic peri-insulitis (infiltrated islets [mean ± SEM]: 7.51% ± 1.34% vs 2.03% ± 0.51%; p < 0.001).

CONCLUSIONS/INTERPRETATION

ERK1 and ERK2 play specific roles in beta cells. ERK2 cannot always compensate for the lack of ERK1 but the absence of a clear-cut phenotype in Erk1 ^-/- mice shows that ERK1 is dispensable in normal conditions.

ERK2 and JNK1 contribute to TNF-α-induced IL-8 expression in synovial fibroblasts

Tumor necrosis factor α (TNF-α) induces the expression and secretion of interleukin 8 (IL-8), which contributes to synovitis in rheumatoid arthritis (RA). To elucidate the mechanism of the onset of RA, we used synovial fibroblasts without autoimmune inflammatory diseases and investigated MAPK signaling pathways in TNF-α-induced IL-8 expression. Synovial fibroblasts isolated from healthy dogs were characterized by flow cytometry, which were positive for the fibroblast markers CD29, CD44, and CD90 but negative for the hematopoietic cell markers CD14, CD34, CD45, and HLA-DR. TNF-α stimulated the secretion and mRNA expression of IL-8 in a time- and dose-dependent manner. ERK and JNK inhibitors attenuated TNF-α-induced IL-8 expression and secretion. TNF-α induced the phosphorylation of ERK1/2 and JNK1/2. TNF-α-induced IL-8 expression was attenuated both in ERK2- and JNK1-knockdown cells. TNF-α-induced ERK1/2 or JNK1/2 was observed in ERK2- or JNK1-knockdown cells, respectively, showing that there is no crosstalk between ERK2 and JNK1 pathways. These observations indicate that the individual activation of ERK2 and JNK1 pathways contributes to TNF-α-induced IL-8 expression in synovial fibroblasts, which appears to be involved in the progress in RA.

Sesquiterpene binding Gly-Leu-Ser/Lys-"co-adaptation pocket" to inhibit lung cancer cell epithelial-mesenchymal transition

Sesquiterpene lactones (SL) have a wide range of applications in anti-tumor and anti-inflammatory therapy. However, the pharmacological mechanism of such substances is not clear. In this study, parthenolide (PTL) was used as an example to explore the anti-tumor effect of natural molecules and their common mechanism. We showed that PTL inhibited the proliferation and migration by reverse EMT via the ERK2/NF-κB/Snail pathway in vivo and in vitro. Interestingly, Multiple potential targets of PTL contain a Gly-Leu-Ser/Lys-“co-adaptation pocket”. This inspiring us analogies of PTL may also bind to these target proteins and play a similar function. Significantly, the Concept of co-adaptation pocket may help to increase the selectivity of drug research and development.

Membrane translocation of transient receptor potential ankyrin 1 induced by inflammatory cytokines in lung cancer cells

Transient receptor potential ankyrin 1 (TRPA1) is known as one of the nociceptors expressed in sensory neurons. It also plays a role in non-neural cells in inflammatory sites. However, the regulatory mechanisms for the reactivity of TRPA1 in these cells under inflammatory conditions are not clear. To clarify these mechanisms, we examined the effects of inflammatory cytokines (interleukin [IL]-1α, IL-1β and tumor necrosis factor α [TNFα]) on TRPA1 reactivity and expression in the endogenously TRPA1-expressing lung tumor cell line A549. Treatment with IL-1α, but not IL-1β or TNFα, increased the number of cells responding to allyl isothiocyanate, a TRPA1 agonist, in a dose- and time-dependent manner. The IL-1α-induced increase of TRPA1 responsiveness was inhibited by an extracellular-regulated kinase (Erk) inhibitor (PD98059) but not by inhibitors of c-Jun kinase, p38 mitogen-activated protein kinase or phosphatidylinositol-3 kinase. Phosphorylation of Erk gradually increased at 24 h after its transient induction in cells treated with IL-1α. IL-1α increased the TRPA1 levels on biotinylated cell surface proteins. These results suggest that IL-1α enhances the translocation of TRPA1 to the plasma membrane via the activation of Erk in A549. TRPA1 may have a pathophysiological role in non-neural lung cells under inflammatory conditions.

MET/ERK2 pathway regulates the motility of human alveolar rhabdomyosarcoma cells

In alveolar rhabdomyosarcoma (ARMS) that is a highly malignant pediatric soft tissue tumor, MET, a receptor of hepatocyte growth factor (HGF), was reported to be downstream of the PAX3-FOXO1 fusion gene specific to ARMS, and a key mediator of metastatic behavior in RMS. So far, no studies have investigated the downstream signaling pathways of MET in ARMS, even though HGF and MET have been suggested to be deeply involved in the invasiveness of ARMS. In this study, we demonstrated the functions of MET signaling in ARMS in vitro by using three human ARMS cell lines and three human embryonal rhabdomyosarcoma (ERMS) cell lines. MET mRNA levels and MET protein expression in ARMS cell lines was higher than those in ERMS cell lines as detected by real-time quantitative PCR and western blotting, respectively. Based on cell growth and cell cycle analyses it was found that HGF stimulation did not enhance the proliferation of ERMS or ARMS cell lines. HGF-stimulated cell motility of ARMS cell lines was inhibited by U0126 (ERK1/2 inhibitor) but was only partially inhibited by PD98059 (ERK1 inhibitor) or rapamycin (mTOR inhibitor) as observed in wound-healing and migration assays. Western blotting revealed that ERK1/2 was dephosphorylated by U0126 to a higher extent than by PD98059 in the ARMS cells. HGF-stimulated cell motility of Rh30 cell line was inhibited not by ERK1 siRNA, but by ERK2 siRNA. Our data thus suggest that HGF/MET signaling promotes motility of ARMS cells mainly through ERK2 signaling. A specific inhibitor of ERK2 phosphorylation could therefore be a specific anticancer agent against invasiveness and metastasis in ARMS.

Development of a 3D Tissue Culture-Based High-Content Screening Platform That Uses Phenotypic Profiling to Discriminate Selective Inhibitors of Receptor Tyrosine Kinases

3D tissue cultures provide a more physiologically relevant context for the screening of compounds, compared with 2D cell cultures. Cells cultured in 3D hydrogels also show complex phenotypes, increasing the scope for phenotypic profiling. Here we describe a high-content screening platform that uses invasive human prostate cancer cells cultured in 3D in standard 384-well assay plates to study the activity of potential therapeutic small molecules and antibody biologics. Image analysis tools were developed to process 3D image data to measure over 800 phenotypic parameters. Multiparametric analysis was used to evaluate the effect of compounds on tissue morphology. We applied this screening platform to measure the activity and selectivity of inhibitors of the c-Met and epidermal growth factor (EGF) receptor (EGFR) tyrosine kinases in 3D cultured prostate carcinoma cells. c-Met and EGFR activity was quantified based on the phenotypic profiles induced by their respective ligands, hepatocyte growth factor and EGF. The screening method was applied to a novel collection of 80 putative inhibitors of c-Met and EGFR. Compounds were identified that induced phenotypic profiles indicative of selective inhibition of c-Met, EGFR, or bispecific inhibition of both targets. In conclusion, we describe a fully scalable high-content screening platform that uses phenotypic profiling to discriminate selective and nonselective (off-target) inhibitors in a physiologically relevant 3D cell culture setting.

Redundancy in the World of MAP Kinases: All for One

The protein kinases ERK1 and ERK2 are the effector components of the prototypical ERK1/2 mitogen-activated protein (MAP) kinase pathway. This signaling pathway regulates cell proliferation, differentiation and survival, and is essential for embryonic development and cellular homeostasis. ERK1 and ERK2 homologs share similar biochemical properties but whether they exert specific physiological functions or act redundantly has been a matter of controversy. However, recent studies now provide compelling evidence in support of functionally redundant roles of ERK1 and ERK2 in embryonic development and physiology. In this review, we present a critical assessment of the evidence for the functional specificity or redundancy of MAP kinase isoforms. We focus on the ERK1/ERK2 pathway but also discuss the case of JNK and p38 isoforms.

Beta 1-integrin-c-Met cooperation reveals an inside-in survival signalling on autophagy-related endomembranes

Receptor tyrosine kinases (RTKs) and integrins cooperate to stimulate cell migration and tumour metastasis. Here we report that an integrin influences signalling of an RTK, c-Met, from inside the cell, to promote anchorage-independent cell survival. Thus, c-Met and β1-integrin co-internalize and become progressively recruited on LC3B-positive 'autophagy-related endomembranes' (ARE). In cells growing in suspension, β1-integrin promotes sustained c-Met-dependent ERK1/2 phosphorylation on ARE. This signalling is dependent on ATG5 and Beclin1 but not on ATG13, suggesting ARE belong to a non-canonical autophagy pathway. This β1-integrin-dependent c-Met-sustained signalling on ARE supports anchorage-independent cell survival and growth, tumorigenesis, invasion and lung colonization in vivo. RTK-integrin cooperation has been assumed to occur at the plasma membrane requiring integrin 'inside-out' or 'outside-in' signalling. Our results report a novel mode of integrin-RTK cooperation, which we term 'inside-in signalling'. Targeting integrin signalling in addition to adhesion may have relevance for cancer therapy.

ERK1 and ERK2 Map Kinases: Specific Roles or Functional Redundancy?

The MAP kinase signaling cascade Ras/Raf/MEK/ERK has been involved in a large variety of cellular and physiological processes that are crucial for life. Many pathological situations have been associated to this pathway. More than one isoform has been described at each level of the cascade. In this review we devoted our attention to ERK1 and ERK2, which are the effector kinases of the pathway. Whether ERK1 and ERK2 specify functional differences or are in contrast functionally redundant, constitutes an ongoing debate despite the huge amount of studies performed to date. In this review we compiled data on ERK1 vs. ERK2 gene structures, protein sequences, expression levels, structural and molecular mechanisms of activation and substrate recognition. We have also attempted to perform a rigorous analysis of studies regarding the individual roles of ERK1 and ERK2 by the means of morpholinos, siRNA, and shRNA silencing as well as gene disruption or gene replacement in mice. Finally, we comment on a recent study of gene and protein evolution of ERK isoforms as a distinct approach to address the same question. Our review permits the evaluation of the relevance of published studies in the field especially when measurements of global ERK activation are taken into account. Our analysis favors the hypothesis of ERK1 and ERK2 exhibiting functional redundancy and points to the concept of the global ERK quantity, and not isoform specificity, as being the essential determinant to achieve ERK function.

A natural small molecule, catechol, induces c-Myc degradation by directly targeting ERK2 in lung cancer

Various carcinogens induce EGFR/RAS/MAPK signaling, which is critical in the development of lung cancer. In particular, constitutive activation of extracellular signal-regulated kinase 2 (ERK2) is observed in many lung cancer patients, and therefore developing compounds capable of targeting ERK2 in lung carcinogenesis could be beneficial. We examined the therapeutic effect of catechol in lung cancer treatment. Catechol suppressed anchorage-independent growth of murine KP2 and human H460 lung cancer cell lines in a dose-dependent manner. Catechol inhibited ERK2 kinase activity in vitro, and its direct binding to the ERK2 active site was confirmed by X-ray crystallography. Phosphorylation of c-Myc, a substrate of ERK2, was decreased in catechol-treated lung cancer cells and resulted in reduced protein stability and subsequent down-regulation of total c-Myc. Treatment with catechol induced G1 phase arrest in lung cancer cells and decreased protein expression related to G1-S progression. In addition, we showed that catechol inhibited the growth of both allograft and xenograft lung cancer tumors in vivo. In summary, catechol exerted inhibitory effects on the ERK2/c-Myc signaling axis to reduce lung cancer tumor growth in vitro and in vivo, including a preclinical patient-derived xenograft (PDX) model. These findings suggest that catechol, a natural small molecule, possesses potential as a novel therapeutic agent against lung carcinogenesis in future clinical approaches.

Bisphenol A Induces Migration through a GPER-, FAK-, Src-, and ERK2-Dependent Pathway in MDA-MB-231 Breast Cancer Cells

Bisphenol A (BPA) is an industrial synthetic chemical utilized in the production of numerous products including food and beverage containers. Humans are exposed to BPA during ingestion of contaminated water and food because it can leach from polycarbonate containers, beverage cans, and epoxy resins. BPA has been related with the development of several diseases including breast cancer. However, the signal transduction pathways mediated by BPA and its role as a promoter of migration and invasion in breast cancer cells remain to be investigated. Here, we demonstrate that BPA promotes migration, invasion, and an increase in the number of focal contacts in MDA-MB-231 breast cancer cells. Moreover, MDA-MB-231 cells express GPER, and BPA promotes migration through a GPER-dependent pathway. BPA also induces activation of FAK, Src, and ERK2, whereas migration induced by BPA requires the activity of these kinases. In addition, BPA induces an increase on AP-1- and NFκB-DNA binding activity through an Src- and ERK2-dependent pathway. In conclusion, our findings demonstrate, that BPA induces the activation of signal transduction pathways, which mediate migration, AP-1/NFκB-DNA binding activity, and an invasion process in MDA-MB-231 breast cancer cells.

The RAF-MEK-ERK pathway: targeting ERK to overcome obstacles to effective cancer therapy

AIM

Currently, dozens of BRAF inhibitors and MEK inhibitors targeting RAF-MEK-ERK pathway have been introduced into clinical trials for cancer therapy. However, after 6-8 months of initial response, acquired drug resistance among the majority of those treated patients sharply diminished their clinical efficacy.

DISCUSSION

Important mechanisms responsible for acquired resistance of BRAF inhibitors and MEK inhibitors have been elucidated. Continually, ERK1/2 locates in the critical position and features unique characteristics, such as activating hundreds of substrates, participating in feedback regulation, being catalyzed by MEK specifically and no acquired resistant mutation.

CONCLUSION

Taking in account the inspiring outcomes of ERK inhibitors in preclinical research, ERK1/2 might be the optimal target to overcome acquired drug resistance in RAF-MEK-ERK pathway.

The HGF inhibitory peptide HGP-1 displays promising in vitro and in vivo efficacy for targeted cancer therapy

HGF/MET pathway mediates cancer initiation and development. Thus, inhibition on HGF-initiated MET signaling pathway would provide a new approach to cancer targeted therapeutics. In our study, we identified a targeting peptide candidate binding to HGF which was named HGF binding peptide-1 (HGP-1) via bacterial surface display methods coupled with fluorescence-activated cell sorting (FACS). HGP-1 showed the moderate affinity when determined with surface plasmon resonance (SPR) technique and high specificity in binding to HGF while assessed by fluorescence-based ELISA assay. The results from MTT and in vitro migration assay indicated that HGF-dependent cell proliferation and migration could be inhibited by HGP-1. In vivo administration of HGP-1 led to an effective inhibitory effect on tumor growth in A549 tumor xenograft models. Moreover, findings from Western Blots revealed that HGP-1 could down-regulated the phosphorylation levels of MET and ERK1/2 initiated by HGF, which suggested that HGP-1 could disrupt the activation of HGF/MET signaling to influence the cell activity. All the data highlighted the potential of HGP-1 to be a potent inhibitor for HGF/MET signaling.

ERK reinforces actin polymerization to power persistent edge protrusion during motility

Cells move through perpetual protrusion and retraction cycles at the leading edge. These cycles are coordinated with substrate adhesion and retraction of the cell rear. We tracked spatial and temporal fluctuations in the molecular activities of individual moving cells to elucidate how extracellular signal-regulated kinase (ERK) signaling controlled the dynamics of protrusion and retraction cycles. ERK is activated by many cell surface receptors, and we found that ERK signaling specifically reinforced cellular protrusions so that they translated into rapid, sustained forward motion of the leading edge. Using quantitative fluorescent speckle microscopy and cross-correlation analysis, we showed that ERK controlled the rate and timing of actin polymerization by promoting the recruitment of the actin nucleator Arp2/3 to the leading edge. These findings support a model in which surges in ERK activity induced by extracellular cues enhance Arp2/3-mediated actin polymerization to generate protrusion power phases with enough force to counteract increasing membrane tension and to promote sustained motility.

Preclinical trials for prevention of tumor progression of hepatocellular carcinoma by LZ-8 targeting c-Met dependent and independent pathways

Hepatocellular carcinoma (HCC) is among the most lethal cancers. Mounting studies highlighted the essential role of the HGF/c-MET axis in driving HCC tumor progression. Therefore, c-Met is a potential therapeutic target for HCC. However, several concerns remain unresolved in c-Met targeting. First, the status of active c-Met in HCC must be screened to determine patients suitable for therapy. Second, resistance and side effects have been observed frequently when using conventional c-Met inhibitors. Thus, a preclinical system for screening the status of c-Met signaling and identifying efficient and safe anti-HCC agents is urgently required. In this study, immunohistochemical staining of phosphorylated c-Met (Tyr1234) on tissue sections indicated that HCCs with positive c-Met signaling accounted for approximately 46% in 26 cases. Second, many patient-derived HCC cell lines were established and characterized according to motility and c-Met signaling status. Moreover, LZ8, a medicinal peptide purified from the herb Lingzhi, featuring immunomodulatory and anticancer properties, was capable of suppressing cell migration and slightly reducing the survival rate of both c-Met positive and negative HCCs, HCC372, and HCC329, respectively. LZ8 also suppressed the intrahepatic metastasis of HCC329 in SCID mice. On the molecular level, LZ8 suppressed the expression of c-Met and phosphorylation of c-Met, ERK and AKT in HCC372, and suppressed the phosphorylation of JNK, ERK, and AKT in HCC329. According to receptor array screening, the major receptor tyrosine kinase activated in HCC329 was found to be the epidermal growth factor receptor (EGFR). Moreover, tyrosine-phosphorylated EGFR (the active EGFR) was greatly suppressed in HCC329 by LZ8 treatment. In addition, LZ8 blocked HGF-induced cell migration and c-Met-dependent signaling in HepG2. In summary, we designed a preclinical trial using LZ8 to prevent the tumor progression of patient-derived HCCs with c-Met-positive or -negative signaling.

[Research progress of HGF/MET signaling pathway in EGFR-TKI resistance in non-small cell lung cancer]

肺癌是世界上最常见的恶性肿瘤之一，其中非小细胞肺癌约占80%。肝细胞生长因子（hepatocyte growth factor, HGF）/上皮间质转化因子（mesenchymal-epithelial transition factor, MET）信号通路在许多生物学进程中都发挥着多效性影响，然而，在多种类型的肿瘤中都观察到HGF/MET信号通路的异常激活，并且通过生长因子受体和其他致癌性基因受体通路促进细胞增殖和转移。近年来，HGF/MET信号通路的异常激活被认为是对表皮生长因子受体酪氨酸激酶抑制剂（epidermal growth factor receptor tyrosine kinase inhibitor, EGFR-TKI）产生耐药的一个重要原因。本文将重点阐述该通路异常激活与非小细胞肺癌患者EGFR-TKI耐药的联系。

Lung fibroblasts accelerate wound closure in human alveolar epithelial cells through hepatocyte growth factor/c-Met signaling

There are 190,600 cases of acute lung injury/acute respiratory distress syndrome (ALI/ARDS) each year in the United States, and the incidence and mortality of ALI/ARDS increase dramatically with age. Patients with ALI/ARDS have alveolar epithelial injury, which may be worsened by high-pressure mechanical ventilation. Alveolar type II (ATII) cells are the progenitor cells for the alveolar epithelium and are required to reestablish the alveolar epithelium during the recovery process from ALI/ARDS. Lung fibroblasts (FBs) migrate and proliferate early after lung injury and likely are an important source of growth factors for epithelial repair. However, how lung FBs affect epithelial wound healing in the human adult lung has not been investigated in detail. Hepatocyte growth factor (HGF) is known to be released mainly from FBs and to stimulate both migration and proliferation of primary rat ATII cells. HGF is also increased in lung tissue, bronchoalveolar lavage fluid, and serum in patients with ALI/ARDS. Therefore, we hypothesized that HGF secreted by FBs would enhance wound closure in alveolar epithelial cells (AECs). Wound closure was measured using a scratch wound-healing assay in primary human AEC monolayers and in a coculture system with FBs. We found that wound closure was accelerated by FBs mainly through HGF/c-Met signaling. HGF also restored impaired wound healing in AECs from the elderly subjects and after exposure to cyclic stretch. We conclude that HGF is the critical factor released from FBs to close wounds in human AEC monolayers and suggest that HGF is a potential strategy for hastening alveolar repair in patients with ALI/ARDS.

Growth arrest signaling of the Raf/MEK/ERK pathway in cancer

The Raf/MEK/extracellular signal-regulated kinase (ERK) pathway has a pivotal role in facilitating cell proliferation, and its deregulated activation is a central signature of many epithelial cancers. However paradoxically, sustained activity of Raf/MEK/ERK can also result in growth arrest in many different cell types. This anti-proliferative Raf/MEK/ERK signaling also has physiological significance, as exemplified by its potential as a tumor suppressive mechanism. Therefore, significant questions include in which cell types and by what mechanisms this pathway can mediate such an opposing context of signaling. Particularly, our understating of the role of ERK1 and ERK2, the focal points of pathway signaling, in growth arrest signaling is still limited. This review discusses these aspects of Raf/MEK/ERK-mediated growth arrest signaling.

Small G proteins Rac1 and Ras regulate serine/threonine protein phosphatase 5 (PP5)·extracellular signal-regulated kinase (ERK) complexes involved in the feedback regulation of Raf1

Serine/threonine protein phosphatase 5 (PP5, PPP5C) is known to interact with the chaperonin heat shock protein 90 (HSP90) and is involved in the regulation of multiple cellular signaling cascades that control diverse cellular processes, such as cell growth, differentiation, proliferation, motility, and apoptosis. Here, we identify PP5 in stable complexes with extracellular signal-regulated kinases (ERKs). Studies using mutant proteins reveal that the formation of PP5·ERK1 and PP5·ERK2 complexes partially depends on HSP90 binding to PP5 but does not require PP5 or ERK1/2 activity. However, PP5 and ERK activity regulates the phosphorylation state of Raf1 kinase, an upstream activator of ERK signaling. Whereas expression of constitutively active Rac1 promotes the assembly of PP5·ERK1/2 complexes, acute activation of ERK1/2 fails to influence the phosphatase-kinase interaction. Introduction of oncogenic HRas (HRas(V12)) has no effect on PP5-ERK1 binding but selectively decreases the interaction of PP5 with ERK2, in a manner that is independent of PP5 and MAPK/ERK kinase (MEK) activity, yet paradoxically requires ERK2 activity. Additional studies conducted with oncogenic variants of KRas4B reveal that KRas(L61), but not KRas(V12), also decreases the PP5-ERK2 interaction. The expression of wild type HRas or KRas proteins fails to reduce PP5-ERK2 binding, indicating that the effect is specific to HRas(V12) and KRas(L61) gain-of-function mutations. These findings reveal a novel, differential responsiveness of PP5-ERK1 and PP5-ERK2 interactions to select oncogenic Ras variants and also support a role for PP5·ERK complexes in regulating the feedback phosphorylation of PP5-associated Raf1.

Global characterization of signalling networks associated with tamoxifen resistance in breast cancer

Acquired resistance to the anti-estrogen tamoxifen remains a significant challenge in breast cancer management. In this study, we used an integrative approach to characterize global protein expression and tyrosine phosphorylation events in tamoxifen-resistant MCF7 breast cancer cells (TamR) compared with parental controls. Quantitative mass spectrometry and computational approaches were combined to identify perturbed signalling networks, and candidate regulatory proteins were functionally interrogated by siRNA-mediated knockdown. Network analysis revealed that cellular metabolism was perturbed in TamR cells, together with pathways enriched for proteins associated with growth factor, cell-cell and cell matrix-initiated signalling. Consistent with known roles for Ras/MAPK and PI3-kinase signalling in tamoxifen resistance, tyrosine-phosphorylated MAPK1, SHC1 and PIK3R2 were elevated in TamR cells. Phosphorylation of the tyrosine kinase Yes and expression of the actin-binding protein myristoylated alanine-rich C-kinase substrate (MARCKS) were increased two- and eightfold in TamR cells respectively, and these proteins were selected for further analysis. Knockdown of either protein in TamR cells had no effect on anti-estrogen sensitivity, but significantly decreased cell motility. MARCKS expression was significantly higher in breast cancer cell lines than normal mammary epithelial cells and in ER-negative versus ER-positive breast cancer cell lines. In primary breast cancers, cytoplasmic MARCKS staining was significantly higher in basal-like and HER2 cancers than in luminal cancers, and was independently predictive of poor survival in multivariate analyses of the whole cohort (P < 0.0001) and in ER-positive patients (P = 0.0005). These findings provide network-level insights into the molecular alterations associated with the tamoxifen-resistant phenotype, and identify MARCKS as a potential biomarker of therapeutic responsiveness that may assist in stratification of patients for optimal therapy.

ETS2 mediated tumor suppressive function and MET oncogene inhibition in human non-small cell lung cancer

PURPOSE

The ETS2 transcription factor is an evolutionarily conserved gene that is deregulated in cancer. We analyzed the transcriptome of lung adenocarcinomas and normal lung tissue by expression profiling and found that ETS2 was significantly downregulated in adenocarcinomas. In this study, we probed the yet unknown functional role of ETS2 in lung cancer pathogenesis.

EXPERIMENTAL DESIGN

Lung adenocarcinomas (n = 80) and normal lung tissues (n = 30) were profiled using the Affymetrix Human Gene 1.0 ST platform. Immunohistochemical (IHC) analysis was conducted to determine ETS2 protein expression in non-small cell lung cancer (NSCLC) histologic tissue specimens (n = 201). Patient clinical outcome, based on ETS2 IHC expression, was statistically assessed using the log-rank and Kaplan-Meier tests. RNA interference and overexpression strategies were used to assess the effects of ETS2 expression on the transcriptome and on various malignant phenotypes.

RESULTS

ETS2 expression was significantly reduced in lung adenocarcinomas compared with normal lung (P < 0.001). Low ETS2 IHC expression was a significant predictor of shorter time to recurrence in NSCLC (P = 0.009, HR = 1.89) and adenocarcinoma (P = 0.03, HR = 1.86). Moreover, ETS2 was found to significantly inhibit lung cancer cell growth, migration, and invasion (P < 0.05), and microarray and pathways analysis revealed significant (P < 0.001) activation of the HGF pathway following ETS2 knockdown. In addition, ETS2 was found to suppress MET phosphorylation and knockdown of MET expression significantly attenuated (P < 0.05) cell invasion mediated by ETS2-specific siRNA. Furthermore, knockdown of ETS2 augmented HGF-induced MET phosphorylation, cell migration, and invasion.

CONCLUSION(S)

Our findings point to a tumor suppressor role for ETS2 in human NSCLC pathogenesis through inhibition of the MET proto-oncogene.