Scaffold mediated regulation of MAPK signaling and cytoskeletal dynamics: a perspective

Compartmentalization proteomics revealed endolysosomal protein network changes in a goat model of atrial fibrillation

Endolysosomes (EL) are known for their role in regulating both intracellular trafficking and proteostasis. EL facilitate the elimination of damaged membranes, protein aggregates, membranous organelles and play an important role in calcium signaling. The specific role of EL in cardiac atrial fibrillation (AF) is not well understood. We isolated atrial EL organelles from AF goat biopsies and conducted a comprehensive integrated omics analysis to study the EL-specific proteins and pathways. We also performed electron tomography, protein and enzyme assays on these biopsies. Our results revealed the upregulation of the AMPK pathway and the expression of EL-specific proteins that were not found in whole tissue lysates, including GAA, DYNLRB1, CLTB, SIRT3, CCT2, and muscle-specific HSPB2. We also observed structural anomalies, such as autophagic-vacuole formation, irregularly shaped mitochondria, and glycogen deposition. Our results provide molecular information suggesting EL play a role in AF disease process over extended time frames.

Novel Kraft Softwood Lignin-Derived Carbon Quantum Dots: Synthesis, Characterization, and In Vitro Cytocompatibility

Carbon quantum dots (CQDs) have been investigated for biomedical applications in medical imaging due to their fluorescent properties, overall long-term stability, and excellent cytocompatibility and biocompatibility. Lignin is an organic polymer in the tissues of woody plants. It is also considered a byproduct of the wood and pulp industries. Hence, it presents as a renewable source of carbon nanoparticles. In this study, we report the synthesis and material and biological characterization of two colloidal suspensions of CQDs in water derived from lignin-based carbon. One was the native form of CQDs derived from lignin carbon, and the second was doped with nitrogen to evaluate material differences. Material characterization was carried out using various commonly used techniques, including Fourier transform infrared spectroscopy (FTIR), emission and absorbance spectra, zeta potential, transmission electron microscopy (TEM), and scanning electron microscopy (SEM). Thin films of CQDs were formed on glass and silicon substrates to assess the in vitro cytocompatibility with human mesenchymal stem cells (hMSCs). Observations suggest that the two forms of CQDs promote cell attachment within 24 h and sustain it for at least 7 days. The overall structure and shape of cells suggest a lack of any adverse or toxic effects of CQDs. The data lay down the novel foundation to support the use of lignin-derived CQDs in tissue engineering applications.

ERK hyperactivation in epidermal keratinocytes impairs intercellular adhesion and drives Grover disease pathology

Grover disease is an acquired dermatologic disorder characterized by pruritic vesicular and eroded skin lesions. While its pathologic features are well-defined, including impaired cohesion of epidermal keratinocytes, the etiology of Grover disease remains unclear and it lacks any FDA-approved therapy. Interestingly, drug-induced Grover disease occurs in patients treated with B-RAF inhibitors that can paradoxically activate C-RAF and the downstream kinase MEK. We recently identified hyperactivation of MEK and ERK as key drivers of Darier disease, which is histologically identical to Grover disease, supporting our hypothesis that they share a pathogenic mechanism. To model drug-induced Grover disease, we treated human keratinocytes with clinically utilized B-RAF inhibitors dabrafenib or vemurafenib and leveraged a fluorescent biosensor to confirm they activated ERK, which disrupted intercellular junctions and compromised keratinocyte sheet integrity. Consistent with clinical data showing concomitant MEK blockade prevents Grover disease in patients receiving B-RAF inhibitors, we found that MEK inhibition suppressed excess ERK activity to rescue cohesion of B-RAF-inhibited keratinocytes. Validating these results, we demonstrated ERK hyperactivation in skin biopsies of vemurafenib-induced Grover disease, but also in spontaneous Grover disease. In sum, our data define a pathogenic role for ERK hyperactivation in Grover disease and support MEK inhibition as a therapeutic strategy.

GRAPHICAL ABSTRACT

miR-4529-3p Promotes the Progression of Retinoblastoma by Inhibiting RB1 Expression and Activating the ERK Signaling Pathway

Retinoblastoma (RB) is a malignant ocular cancer that affects children. Several microRNAs (miRNAs) have been implicated in RB regulation. The present study aimed to investigate the role of miR-4529-3p in RB pathogenesis. Scratch, Transwell, and Cell Counting Kit (CCK)-8 assays were conducted to assess the migratory, invasive, and proliferative abilities of RB cells. The expression levels of miR-4529-3p, RB1, and ERK pathway-related proteins were analyzed using western blotting and real-time quantitative reverse transcription polymerase chain reaction (qRT-PCR). Target relationships were verified using dual-luciferase reporter experiments. A murine RB model was developed to analyze the effects of miR-4529-3p on RB tumor growth in vivo. Our experiments revealed high levels of miR-4529-3p and low levels of RB1 in RB tissues. Functional analyses revealed that the migratory, invasive, and proliferative abilities of RB cells were repressed by miR-4529-3p inhibition. Similarly, p-ERK 1/2 protein levels were suppressed by miR-4529-3p inhibition. Furthermore, downregulation of miR-4529-3p limited tumor growth in vivo. Mechanistically, miR-4259-3p targets RB1. Interestingly, RB1 silencing abrogated the alleviative effects of miR-4529-3p downregulation in RB cells. MiR-4529-3p promotes RB progression by inhibiting RB1 and activating the ERK pathway. This evidence suggests that the miR-4529-3p/RB1 regulatory axis may be a prospective target for RB treatment in clinical settings.

Characterization of Breast Cancer Aggressiveness by Cell Mechanics

In healthy tissues, cells are in mechanical homeostasis. During cancer progression, this equilibrium is disrupted. Cancer cells alter their mechanical phenotype to a softer and more fluid-like one than that of healthy cells. This is connected to cytoskeletal remodeling, changed adhesion properties, faster cell proliferation and increased cell motility. In this work, we investigated the mechanical properties of breast cancer cells representative of different breast cancer subtypes, using MCF-7, tamoxifen-resistant MCF-7, MCF10A and MDA-MB-231 cells. We derived viscoelastic properties from atomic force microscopy force spectroscopy measurements and showed that the mechanical properties of the cells are associated with cancer cell malignancy. MCF10A are the stiffest and least fluid-like cells, while tamoxifen-resistant MCF-7 cells are the softest ones. MCF-7 and MDA-MB-231 show an intermediate mechanical phenotype. Confocal fluorescence microscopy on cytoskeletal elements shows differences in actin network organization, as well as changes in focal adhesion localization. These findings provide further evidence of distinct changes in the mechanical properties of cancer cells compared to healthy cells and add to the present understanding of the complex alterations involved in tumorigenesis.

Hax1 regulate focal adhesion dynamics through IQGAP1

Cell migration is a highly orchestrated process requiring the coordination between the cytoskeleton, cell membrane and extracellular matrix adhesions. Our previous study demonstrated that Hax1 interacts with EB2, a microtubule end-binding protein, and this interaction regulate cell migration in keratinocytes. However, little is known about the underlying regulatory mechanism. Here, we show that Hax1 links dynamic focal adhesions to regulate cell migration via interacting with IQGAP1, a multidomain scaffolding protein, which was identified by affinity purification coupled with LC-MS/MS. Biochemical characterizations revealed that C-terminal region of Hax1 and RGCT domain of IQGAP1 are the most critical binding determinants for its interaction. IQGAP1/Hax1 interaction is essential for cell migration in MCF7 cells. Knockdown of HAX1 not only stabilizes focal adhesions, but also impairs the accumulation of IQGAP in focal adhesions. Further study indicates that this interaction is critical for maintaining efficient focal adhesion turnover. Perturbation of the IQGAP1/Hax1 interaction in vivo using a membrane-permeable TAT-RGCT peptide results in impaired focal adhesion turnover, thus leading to inhibition of directional cell migration. Together, our findings unravel a novel interaction between IQGAP1 and Hax1, suggesting that IQGAP1 association with Hax1 plays a significant role in focal adhesion turnover and directional cell migration. Video Abstract.

Crosstalk between phytochemicals and inflammatory signaling pathways

Novel bioactive constituents from natural sources are actively being investigated. The phytochemicals in these phenolic compounds are believed to have a variety of beneficial effects on human health. Several phenolic compounds have been found in plants. The antioxidant potential of phenols has been discussed in numerous studies along with their anti-inflammatory effects on pro-inflammatory cytokine, inducible cyclooxygenase-2, and nitric oxide synthase. Through current study, an attempt is made to outline and highlight a wide variety of inflammation-associated signaling pathways that have been modified by several natural compounds. These signaling pathways include nuclear factor-kappa B (NF-кB), activator protein (AP)-1, protein tyrosine kinases (PTKs), mitogen-activated protein kinases (MAPKs), nuclear factor erythroid 2-related factor 2 (Nrf2) transcription factors, tyrosine phosphatidylinositol 3-kinase (PI3K)/AKT, and the ubiquitin-proteasome system. In light of the influence of natural substances on signaling pathways, their impact on the production of inflammatory mediator is highlighted in this review.

The Therapeutic Potential of MAPK/ERK Inhibitors in the Treatment of Colorectal Cancer

The MAPK/ERK signaling pathway regulates cancer cell proliferation, apoptosis, inflammation, angiogenesis, metastasis and drug resistance. Mutations and up-regulation of components of the MAPK/ERK signaling pathway, as well as over-activation of this critical signaling pathway, are frequently observed in colorectal carcinomas. Targeting the MAPK/ERK signaling pathway, using specific pharmacological inhibitors, elicits potent anti-tumor effects, supporting the therapeutic potential of these inhibitors in the treatment of CRC. Several drugs have recently been developed for the inhibition of the MEK/ERK pathway in preclinical and clinical settings, such as MEK162 and MK-2206. MEK1/2 inhibitors demonstrate promising efficacy and anticancer activity for the treatment of this malignancy. This review summarizes the current knowledge on the role of the MAPK/ERK signaling pathway in the pathogenesis of CRC and the potential clinical value of synthetic inhibitors of this pathway in preventing CRC progression for a better understanding, and hence, better management of colorectal cancer.

Benzophenone-3 induced abnormal development of enteric nervous system in zebrafish through MAPK/ERK signaling pathway

Hirschsprung disease (HSCR) is a congenital disease characterized by the absence of enteric neurons, which is derived from the failure of the proliferation, differentiation or migration of the enteric neural crest cells (ENCCs). HSCR is associated with multiple risk factors, including polygenic inheritance factors and environmental factors. Genetic studies have been extensively performed, whereas studies related to environmental factors remain insufficient. Benzophenone-3 (BP-3), one important component of the ultraviolet (UV) filters, has been proved to have cytotoxicity and neurotoxicity which might be associated with HSCR. In this study, we used zebrafish as a model to investigate the relationship between BP-3 exposure and the development of the enteric nervous system (ENS) in vivo. Embryos exposed to BP-3 showed an average of 46% reduction of the number of the enteric neurons number. Besides, the ENCCs specific markers (ret and hand2) were downregulated upon BP-3 exposure. Moreover, we identified potential targets of BP-3 through Network Pharmacology Analysis and Autodock and demonstrated that the attenuation of the MAPK/ERK signaling might be the potential mechanism underlying the inhibition of the ENS development by BP-3. Importantly, MAPK/ERK signaling agonist could be used to rescue the ENS defects of zebrafish induced by BP-3. Overall, we characterized the influence of BP-3 on ENS development in vivo and explored possible molecular mechanisms.

Negative control of cytokinesis by stress-activated MAPK signaling

Mitogen-activated protein kinase (MAPK) signalling pathways regulate multiple cellular functions in eukaryotic organisms in response to environmental cues, including the dynamic remodeling of the actin cytoskeleton. The fission yeast S. pombe is an optimal model to investigate the conserved regulatory mechanisms of cytokinesis, which relies in an actomyosin-based contractile ring (CAR) that prompts the physical separation of daughter cells during cellular division. Our group has recently shown that p38 MAPK ortholog Sty1, the core component of the stress-activated pathway (SAPK), negatively modulates CAR assembly and integrity in S. pombe during actin cytoskeletal damage induced with Latrunculin A and in response to environmental stress. This response involves downregulation of protein levels of the formin For3, which assembles actin filaments for cables and the CAR, likely through an ubiquitin-mediated degradation mechanism. Contrariwise, Sty1 function positively reinforces CAR assembly during stress in the close relative dimorphic fission yeast S. japonicus. The opposite effect of SAPK signaling on CAR integrity may represent an evolutionary refined adaptation to cope with the marked differences in cytokinesis onset in both fission yeast species.

Stress-activated MAPK signaling controls fission yeast actomyosin ring integrity by modulating formin For3 levels

Cytokinesis, which enables the physical separation of daughter cells once mitosis has been completed, is executed in fungal and animal cells by a contractile actin- and myosin-based ring (CAR). In the fission yeast Schizosaccharomyces pombe, the formin For3 nucleates actin cables and also co-operates for CAR assembly during cytokinesis. Mitogen-activated protein kinases (MAPKs) regulate essential adaptive responses in eukaryotic organisms to environmental changes. We show that the stress-activated protein kinase pathway (SAPK) and its effector, MAPK Sty1, downregulates CAR assembly in S. pombe when its integrity becomes compromised during cytoskeletal damage and stress by reducing For3 levels. Accurate control of For3 levels by the SAPK pathway may thus represent a novel regulatory mechanism of cytokinesis outcome in response to environmental cues. Conversely, SAPK signaling favors CAR assembly and integrity in its close relative Schizosaccharomyces japonicus, revealing a remarkable evolutionary divergence of this response within the fission yeast clade.

MAP Kinase driven actomyosin rearrangement is a crucial regulator of monocyte to macrophage differentiation

Rearrangement of actin cytoskeleton correlates significantly with the immune responses as the perturbation of cytoskeletal dynamics leads to many immune deficiencies. Mechanistic insights into this correlation remain unknown. Cellular spreading, the most characteristic phenotype associated with monocyte to macrophage differentiation, led us to investigate the contribution of actomyosin dynamics in monocyte differentiation. Our observation revealed that actomyosin reorganization intrinsically governs the process of monocyte to macrophage differentiation. Further, we established that the MAPK-driven signaling pathways regulate the cellular actomyosin dynamics that direct monocyte to macrophage differentiation. We also identified P42/44 Mitogen-Activated Protein Kinase (P42/44 MAPK), P38 Mitogen-Activated Protein Kinase (P38 MAPK), MAP Kinase Activated Protein Kinase 2 (MK-2), Heat Shock Protein 27 (Hsp-27), Lim Kinase (Lim K), non-muscle cofilin (n-cofilin), Myosin Light Chain Kinase (MLCK) and Myosin Light Chain (MLC) as critical components of the signaling network. Moreover, we have shown the involvement of the same signaling cascade in 3D gel-like microenvironment induced spontaneous monocyte to macrophage differentiation and in human blood-derived PBMC differentiation. Our study reveals new mechanistic insights into the process of monocyte to macrophage differentiation.

Dopamine Receptor Dop1R2 Stabilizes Appetitive Olfactory Memory through the Raf/MAPK Pathway in Drosophila

In Drosophila, dopamine signaling to the mushroom body intrinsic neurons, Kenyon cells (KCs), is critical to stabilize olfactory memory. Little is known about the downstream intracellular molecular signaling underlying memory stabilization. Here we address this question in the context of sugar-rewarded olfactory long-term memory (LTM). We show that associative training increases the phosphorylation of MAPK in KCs, via Dop1R2 signaling. Consistently, the attenuation of Dop1R2, Raf, or MAPK expression in KCs selectively impairs LTM, but not short-term memory. Moreover, we show that the LTM deficit caused by the knockdown of Dop1R2 can be rescued by expressing active Raf in KCs. Thus, the Dop1R2/Raf/MAPK pathway is a pivotal downstream effector of dopamine signaling for stabilizing appetitive olfactory memory.SIGNIFICANCE STATEMENT Dopaminergic input to the Kenyon cells (KCs) is pivotal to stabilize memory in Drosophila This process is mediated by dopamine receptors like Dop1R2. Nevertheless, little is known for its underlying molecular mechanism. Here we show that the Raf/MAPK pathway is specifically engaged in appetitive long-term memory in KCs. With combined biochemical and behavioral experiments, we reveal that activation of the Raf/MAPK pathway is regulated through Dop1R2, shedding light on how dopamine modulates intracellular signaling for memory stabilization.

Internal Clocks, mGluR7 and Microtubules: A Primer for the Molecular Encoding of Target Durations in Cerebellar Purkinje Cells and Striatal Medium Spiny Neurons

The majority of studies in the field of timing and time perception have generally focused on sub- and supra-second time scales, specific behavioral processes, and/or discrete neuronal circuits. In an attempt to find common elements of interval timing from a broader perspective, we review the literature and highlight the need for cell and molecular studies that can delineate the neural mechanisms underlying temporal processing. Moreover, given the recent attention to the function of microtubule proteins and their potential contributions to learning and memory consolidation/re-consolidation, we propose that these proteins play key roles in coding temporal information in cerebellar Purkinje cells (PCs) and striatal medium spiny neurons (MSNs). The presence of microtubules at relevant neuronal sites, as well as their adaptability, dynamic structure, and longevity, makes them a suitable candidate for neural plasticity at both intra- and inter-cellular levels. As a consequence, microtubules appear capable of maintaining a temporal code or engram and thereby regulate the firing patterns of PCs and MSNs known to be involved in interval timing. This proposed mechanism would control the storage of temporal information triggered by postsynaptic activation of mGluR7. This, in turn, leads to alterations in microtubule dynamics through a "read-write" memory process involving alterations in microtubule dynamics and their hexagonal lattice structures involved in the molecular basis of temporal memory.

Ginsenoside Rg3 promotes Fc gamma receptor-mediated phagocytosis of bacteria by macrophages via an extracellular signal-regulated kinase 1/2 and p38 mitogen-activated protein kinase-dependent mechanism

Ginsenoside Rg3 is a steroidal saponin abundant in Korean red ginseng that has high anti-inflammatory activity. Rg3 exerts an immunomodulatory effect in acute inflammatory conditions such as bacterial infections. In this study, we determined the effect of Rg3 on bacterial uptake by macrophages and the related intracellular signaling pathways. Rg3 increased macrophage phagocytosis of IgG-opsonized Escherichia coli and IgG-opsonized beads (IgGbeads), but not of non-opsonized beads. Rg3 also enhanced the phosphorylation of extracellular signal-regulated kinase (ERK) 1/2 and p38 mitogen-activated protein kinase (p38 MAPK), but not that of Akt. The inclusion of IgGbeads in macrophage cultures also increased the phosphorylation of ERK1/2 and p38, but co-culture of macrophages with non-opsonized beads did not affect the phosphorylation of ERK1/2 and p38. The Rg3-induced promotion of phagocytosis was inhibited by PD98059, an ERK1/2 inhibitor, and SB203580, a p38 inhibitor. PD98059 inhibited Rg3-induced p38 MAPK phosphorylation, but SB203580 did not suppress ERK1/2 phosphorylation. Culture of macrophages with Rg3 increased actin polymerization, and this effect was inhibited by SB203580 and PD98059. The Rg3-induced increase in phagocytosis was also inhibited by NSC23766, a Rac1 inhibitor and CASIN, a Cdc42 inhibitor. Intraperitoneal injection of Rg3 increased the phosphorylation of ERK1/2 and p38 as well as the phagocytosis of bacteria by lung cells. These results demonstrate that ginsenoside Rg3 enhances macrophage phagocytosis of bacteria by activating the ERK1/2 and p38 MAPK pathways.

Targeting the "undruggable" RAS - new strategies - new hope?

K-RAS is the most frequently mutated oncogene in solid tumors, such as pancreatic, colon or lung cancer. The GTPase K-RAS can either be in an active (GTP-loaded) or inactive (GDP-loaded) form. In its active form K-RAS forwards signals from growth factors, cytokines or hormones to the nucleus, regulating essential pathways, such as cell proliferation and differentiation. In turn, activating somatic mutations of this proto-oncogene deregulate the complex interplay between GAP (GTPase-activating) - and GEF (Guanine nucleotide exchange factor) - proteins, driving neoplastic transformation. Due to a rather shallow surface, K-RAS lacks proper binding pockets for small molecules, hindering drug development over the past thirty years. This review summarizes recent progress in the development of low molecular antagonists and further shows insights of a newly described interaction between mutant K-RAS signaling and PD-L1 induced immunosuppression, giving new hope for future treatments of K-RAS mutated cancer.

Triptolide prevents proliferation and migration of Esophageal Squamous Cell Cancer via MAPK/ERK signaling pathway

Triptolide, the component of traditional Chinese herb, has been used as an inflammatory medicine and reported to be anti-tumor for various cancers recently. However, the effect of triptolide on Esophageal Squamous Cell Cancer (ESCC) has not yet been elucidated. In the study, we found that triptolide significantly inhibited cell proliferation, invasion, migration and survivability of ESCC cells. Moreover, we observed that triptolide induced ESCC cell cycle arrest at the G1/S phase and apoptosis through cyclin D1-CDK4/6 regulation and caspases activation. In addition, we revealed that triptolide regulates cell apoptosis and metastasis by p53 and mitogen-activated protein kinases/extracellular signal-regulated kinase (MAPK/ERK) signaling pathway, respectively. Meanwhile, the inhibitory effect of triptolide on ESCC was validated in mouse xenograft model. So, we propose that triptolide may be a candidate drug for ESCC.

The Mechanobiology of the Actin Cytoskeleton in Stem Cells during Differentiation and Interaction with Biomaterials

An understanding of the cytoskeleton's importance in stem cells is essential for their manipulation and further clinical application. The cytoskeleton is crucial in stem cell biology and depends on physical and chemicals signals to define its structure. Additionally, cell culture conditions will be important in the proper maintenance of stemness, lineage commitment, and differentiation. This review focuses on the following areas: the role of the actin cytoskeleton of stem cells during differentiation, the significance of cellular morphology, signaling pathways involved in cytoskeletal rearrangement in stem cells, and the mechanobiology and mechanotransduction processes implicated in the interactions of stem cells with different surfaces of biomaterials, such as nanotopography, which is a physical cue influencing the differentiation of stem cells. Also, cancer stem cells are included since it is necessary to understand the role of their mechanical properties to develop new strategies to treat cancer. In this context, to study the stem cells requires integrated disciplines, including molecular and cellular biology, chemistry, physics, and immunology, as well as mechanobiology. Finally, since one of the purposes of studying stem cells is for their application in regenerative medicine, the deepest understanding is necessary in order to establish safety protocols and effective cell-based therapies.

Exploring major signaling cascades in melanomagenesis: a rationale route for targetted skin cancer therapy

Although most melanoma cases may be treated by surgical intervention upon early diagnosis, a significant portion of patients can still be refractory, presenting low survival rates within 5 years after the discovery of the illness. As a hallmark, melanomas are highly prone to evolve into metastatic sites. Moreover, melanoma tumors are highly resistant to most available drug therapies and their incidence have increased over the years, therefore leading to public health concerns about the development of novel therapies. Therefore, researches are getting deeper in unveiling the mechanisms by which melanoma initiation can be triggered and sustained. In this context, important progress has been achieved regarding the roles and the impact of cellular signaling pathways in melanoma. This knowledge has provided tools for the development of therapies based on the intervention of signal(s) promoted by these cascades. In this review, we summarize the importance of major signaling pathways (mitogen-activated protein kinase (MAPK), phosphoinositide 3-kinase (PI3K)-Akt, Wnt, nuclear factor κ-light-chain-enhancer of activated B cell (NF-κB), Janus kinase (JAK)-signal transducer and activator of transcription (STAT), transforming growth factor β (TGF-β) and Notch) in skin homeostasis and melanoma progression. Available and developing melanoma therapies interfering with these signaling cascades are further discussed.

Parthenolide suppresses non-small cell lung cancer GLC-82 cells growth via B-Raf/MAPK/Erk pathway

Non-small cell lung cancer (NSCLC), one type of lung cancer, owns high rates of morbidity and mortality. B-Raf is one of the promising oncogenic drivers of NSCLC. Parthenolide, a natural product, is mainly extracted from the herbal plant Tanacetum parthenium. The effect of parthenolide on NSCLC cells and its potential as B-Raf inhibitor were studied in this study. It's shown that parthenolide exhibited the strong cytotoxicity against NSCLC cells with IC50 ranging from 6.07 ± 0.45 to 15.38 ± 1.13 μM. Parthenolide was also able to induce apoptosis, suppress proliferation and invasion in NSCLC cells. In terms of the involved mechanism, parthenolide suppressed GLC-82 cell response via targeting on B-Raf and inhibiting MAPK/Erk pathway signaling. The effect of parthenolide on B-Raf and MAPK/Erk pathway was further confirmed by RNA interference of B-Raf. Decreased expression of c-Myc in protein and mRNA level was also discovered, which is considered as the further downstream of the MAPK/Erk pathway. In addition, STAT3 activity inhibition by parthenolide contributed to its effect on GLC-82 cells, which is independent of PI3K pathway signaling and GSK3. All above provide an insight to understand the action of parthenolide as a potential B-Raf inhibitor in treatment of NSCLC.

Matrix-Embedded Endothelial Cells Attain a Progenitor-Like Phenotype

Culture of endothelial cells (ECs) embedded in 3D scaffolds of denatured collagen has shown tremendous therapeutic potential in clinical trials of tissue repair. It is postulated that these matrix-embedded ECs (MEECs) attain a differential phenotype similar to early progenitor forms, which cannot be attained in 2D culture. MEECs are compared to 2D-ECs and endothelial progenitor cells (EPCs) by secretome, phenotype, and genetic fingerprint, and are found to be altered from 2D-ECs on all levels, adopting an EPC-like phenotype. This manifests in elevation of CD34 expression-a progenitor cell marker-and protein secretion and gene expression pro-files that are similar to EPCs. Even more striking is that EPCs in 2D lose their phenotype, evident by the loss of CD34 expression, but are able to regain expression over time when embedded in the same 3D matrices, suggesting that future in vitro EPC work should use ME-EPCs to recapitulate in vivo phenotype. These findings elucidate the relationship between EPCs and the substratum-dependent regulation imparted by ECs which is critical to understand in order to optimize MEEC therapy and propel it into the clinic.

Alendronate Attenuates Spinal Microglial Activation and Neuropathic Pain

Many derivatives of bisphosphonates, which are inhibitors of bone resorption, have been developed as promising agents for painful pathologies in patients with bone resorption-related diseases. The mechanism for pain relief by bisphosphonates remains uncertain. Studies have reported that bisphosphonates could reduce central neurochemical changes involved in the generation and maintenance of bone cancer pain. In this study, we hypothesized that bisphosphonates would inhibit spinal microglial activation and prevent the development of hyperalgesia caused by peripheral tissue injury. We investigated the effects of alendronate (a nitrogen-containing bisphosphonate) on the development of neuropathic pain and its role in modulating microglial activation in vivo and in vitro. Intrathecal and intraperitoneal administration of alendronate relieved neuropathic pain behaviors induced by chronic constriction sciatic nerve injury. Alendronate also significantly attenuated spinal microglial activation and p38 mitogen-activated protein kinase (MAPK) phosphorylation without affecting astrocytes. In vitro, alendronate downregulated phosphorylated p38 and phosphorylated extracellular signal regulated kinase expression in lipopolysaccharide-stimulated primary microglia within 1 hour, and pretreatment with alendronate for 12 and 24 hours decreased the expression of inflammatory cytokines (tumor necrosis factor α, and interleukins 1β and 6). These findings indicate that alendronate could effectively relieve chronic constriction sciatic nerve injury-induced neuropathic pain by at least partially inhibiting the activation of spinal microglia and the p38 MAPK signaling pathway.

PERSPECTIVE

Alendronate could relieve neuropathic pain behaviors in animals by inhibiting the activation of spinal cord microglia and the p38 MAPK cell signaling pathway. Therapeutic applications of alendronate may be extended beyond bone metabolism-related disease.

Shoc2-tranduced ERK1/2 motility signals--Novel insights from functional genomics

The extracellular signal-regulated kinase 1 and 2 (ERK1/2) pathway plays a central role in defining various cellular fates. Scaffold proteins modulating ERK1/2 activity control growth factor signals transduced by the pathway. Here, we analyzed signals transduced by Shoc2, a critical positive modulator of ERK1/2 activity. We found that loss of Shoc2 results in impaired cell motility and delays cell attachment. As ERKs control cellular fates by stimulating transcriptional response, we hypothesized that the mechanisms underlying changes in cell adhesion could be revealed by assessing the changes in transcription of Shoc2-depleted cells. Using quantitative RNA-seq analysis, we identified 853 differentially expressed transcripts. Characterization of the differentially expressed genes showed that Shoc2 regulates the pathway at several levels, including expression of genes controlling cell motility, adhesion, crosstalk with the transforming growth factor beta (TGFβ) pathway, and expression of transcription factors. To understand the mechanisms underlying delayed attachment of cells depleted of Shoc2, changes in expression of the protein of extracellular matrix (lectin galactoside-binding soluble 3-binding protein; LGALS3BP) were functionally analyzed. We demonstrated that delayed adhesion of the Shoc2-depleted cells is a result of attenuated expression and secretion of LGALS3BP. Together our results suggest that Shoc2 regulates cell motility by modulating ERK1/2 signals to cell adhesion.

Spatial control of Shoc2-scaffold-mediated ERK1/2 signaling requires remodeling activity of the ATPase PSMC5

The scaffold protein Shoc2 accelerates activity of the ERK1 and ERK2 (ERK1/2, also known as MAPK3 and MAPK1) pathway. Mutations in Shoc2 result in Noonan-like RASopathy, a developmental disorder with a wide spectrum of symptoms. The amplitude of the ERK1/2 signals transduced through the complex is fine-tuned by the HUWE1-mediated ubiquitylation of Shoc2 and its signaling partner RAF-1. Here, we provide a mechanistic basis of how ubiquitylation of Shoc2 and RAF-1 is controlled. We demonstrate that the newly identified binding partner of Shoc2, the (AAA+) ATPase PSMC5, triggers translocation of Shoc2 to endosomes. At the endosomes, PSMC5 displaces the E3 ligase HUWE1 from the scaffolding complex to attenuate ubiquitylation of Shoc2 and RAF-1. We show that a RASopathy mutation that changes the subcellular distribution of Shoc2 leads to alterations in Shoc2 ubiquitylation due to the loss of accessibility to PSMC5. In summary, our results demonstrate that PSMC5 is a new and important player involved in regulating ERK1/2 signal transmission through the remodeling of Shoc2 scaffold complex in a spatially-defined manner.

Lipocalin 2 promotes the migration and invasion of esophageal squamous cell carcinoma cells through a novel positive feedback loop

Lipocalin 2 (LCN2) is a poor prognostic factor in esophageal squamous cell carcinoma (ESCC), however its functional roles and molecular mechanisms of action remain to be clarified. Here, we described the functions and signaling pathways for LCN2 in ESCC. Overexpression of LCN2 in ESCC cells accelerated cell migration and invasion in vitro, and promoted lung metastasis in vivo. Blocking LCN2 expression inhibited its pro-oncogenic effect. Either overexpression of LCN2 or treatment with recombinant human LCN2 protein enhanced the activation of MEK/ERK pathway, which in turn increases endogenous LCN2 to increase MMP-9 activity. The decreased p-cofilin and increased p-ERM induced by pERK1/2 cause the cytoskeleton F-actin rearrangement and alter the behavior of ESCC cells mediated by LCN2. As a consequence, activation of MMP-9 and the rearrangement of F-actin throw light on the mechanisms for LCN2 in ESCC. These results imply that LCN2 promotes the migration and invasion of ESCC cells through a novel positive feedback loop.

The NF-κB essential modulator (NEMO) controls podocyte cytoskeletal dynamics independently of NF-κB

Maintenance of the glomerular filtration barrier with its fenestrated endothelium, the glomerular basement membrane, and the podocytes as the outer layer, is a major prerequisite for proper renal function. Tight regulation of the balance between plasticity and rigidity of the podocytes' architecture is required to prevent the onset of glomerular disease, mainly proteinuria. The underlying cellular signaling pathways that regulate the organization of the podocytes' cytoskeleton are still a matter of controversial debate. In this study, we investigated the role of the NF-κB signaling pathway in podocyte cytoskeletal dynamics. As previously published, genetic inhibition of the NF-κB essential modulator (NEMO) in podocytes does not affect glomerular function under physiological, nonstressed conditions nor does it alter the initial podocyte response in an experimental glomerulonephritis (NTN) model (Brähler S, Ising C, Hagmann H, Rasmus M, Hoehne M, Kurschat C, Kisner T, Goebel H, Shankland SJ, Addicks K, Thaiss F, Schermer B, Pasparakis M, Benzing T, Brinkkoetter PT. Am J Physiol Renal Physiol 303: F1473-F1475, 2012). Quite the contrary, podocyte-specific NEMO null mice recovered significantly faster and did not develop glomerulosclerosis and end-stage renal failure over time. Here, we show that cytoskeletal rearrangements and increased podocyte motility following stimulation with IL-1, TNF-α, or LPS depend on NEMO. NEMO also regulates the phosphorylation of the MAP kinase ERK1/2 and suppresses the activation of RhoA following stimulation with IL-1. The migratory response and altered ERK1/2 phosphorylation is independent of NF-κB signaling as demonstrated by expression of a mutant IκB resistant to phosphorylation and degradation. In conclusion, signaling through NEMO might not only be involved in the production of NF-κB proinflammatory chemokines but also regulates podocyte dynamics independently of NF-κB, most likely through small GTPases and MAP kinases.

In vivo profiling reveals immunomodulatory effects of sorafenib and dacarbazine on melanoma

Sorafenib is a multi-kinase inhibitor used alone or in combination with dacarbazine to treat metastasized melanoma. Our study investigated the relationship between metabolic response assessed by PET-CT and global transcriptome changes during sorafenib and dacarbazine therapy in patients with advanced melanoma. We conducted an open-label, investigator-initiated study that enrolled 13 sorafenib-naïve Stage IV melanoma patients, whose metastases were accessible for repeated biopsies. Treatment regimen included orally administered sorafenib and intravenous dacarbazine. Biopsies of skin or superficial lymph node metastases were taken before treatment (baseline), during sorafenib and after dacarbazine therapy and used for transcriptional profiling and validation experiments. Serum samples were evaluated for cytokine production. Metabolic response to therapy was observed in 45.5% of patients. The study drugs were well tolerated. We observed a clear upregulation of interferon (IFN)-stimulated immune response genes in profiled metastases. The IFNγ-induced gene signature seemed to be enhanced after addition of dacarbazine to sorafenib. Serum IFNγ also increased during therapy, particularly after addition of dacarbazine. Induction of IFNγ stimulated genes correlating with increased serum IFNγ was predictive of better clinical outcome and responders who had significantly higher serum IFNγ levels lived longer. Our data reveal in situ changes in melanoma metastases during treatment with sorafenib and dacarbazine and suggest an additional mechanism of action through immunomodulation.

HUWE1 is a molecular link controlling RAF-1 activity supported by the Shoc2 scaffold

Scaffold proteins play a critical role in controlling the activity of the extracellular signal-regulated kinase 1/2 (ERK1/2) pathway. Shoc2 is a leucine-rich repeat scaffold protein that acts as a positive modulator of ERK1/2 signaling. However, the precise mechanism by which Shoc2 modulates the activity of the ERK1/2 pathway is unclear. Here we report the identification of the E3 ubiquitin ligase HUWE1 as a binding partner and regulator of Shoc2 function. HUWE1 mediates ubiquitination and, consequently, the levels of Shoc2. Additionally, we show that both Shoc2 and HUWE1 are necessary to control the levels and ubiquitination of the Shoc2 signaling partner, RAF-1. Depletion of HUWE1 abolishes RAF-1 ubiquitination, with corresponding changes in ERK1/2 pathway activity occurring. Our results indicate that the HUWE1-mediated ubiquitination of Shoc2 is the switch that regulates the transition from an active to an inactive state of the RAF-1 kinase. Taken together, our results demonstrate that HUWE1 is a novel player involved in regulating ERK1/2 signal transmission through the Shoc2 scaffold complex.

The MAPK pathway across different malignancies: a new perspective

The mitogen-activated protein kinase/extracellular signal-regulated (MAPK/ERK) pathway is activated by upstream genomic events and/or activation of multiple signaling events in which information coalesces at this important nodal pathway point. This pathway is tightly regulated under normal conditions by phosphatases and bidirectional communication with other pathways, like the protein kinase B/mammalian target of rapamycin (AKT/m-TOR) pathway. Recent evidence indicates that the MAPK/ERK signaling node can function as a tumor suppressor as well as the more common pro-oncogenic signal. The effect that predominates depends on the intensity of the signal and the context or tissue in which the signal is aberrantly activated. Genomic profiling of tumors has revealed common mutations in MAPK/ERK pathway components, such as v-raf murine sarcoma viral oncogene homolog B1 (BRAF). Currently approved for the treatment of melanoma, inhibitors of BRAF kinase are being studied alone and in combination with inhibitors of the MAPK and other pathways to optimize the treatment of many tumor types. Therapies targeted toward MAPK/ERK components have various response rates when used in different solid tumors, such as colorectal cancer and ovarian cancer. Understanding the differential nature of activation of the MAPK/ERK pathway in each tumor type is critical in developing single and combination regimens, because different tumors have unique mechanisms of primary and secondary signaling and subsequent sensitivity to drugs.

The late endosomal p14-MP1 (LAMTOR2/3) complex regulates focal adhesion dynamics during cell migration

Late endosomes locally regulate cell migration by transporting the p14–MP1 scaffold complex to the vicinity of focal adhesions.

Cell migration is mediated by the dynamic remodeling of focal adhesions (FAs). Recently, an important role of endosomal signaling in regulation of cell migration was recognized. Here, we show an essential function for late endosomes carrying the p14–MP1 (LAMTOR2/3) complex in FA dynamics. p14–MP1-positive endosomes move to the cell periphery along microtubules (MTs) in a kinesin1- and Arl8b-dependent manner. There they specifically target FAs to regulate FA turnover, which is required for cell migration. Using genetically modified fibroblasts from p14-deficient mice and Arl8b-depleted cells, we demonstrate that MT plus end–directed traffic of p14–MP1-positive endosomes triggered IQGAP1 disassociation from FAs. The release of IQGAP was required for FA dynamics. Taken together, our results suggest that late endosomes contribute to the regulation of cell migration by transporting the p14–MP1 scaffold complex to the vicinity of FAs.

Subependymal giant cell astrocytoma: current concepts, management, and future directions

BACKGROUND

Subependymal giant cell astrocytoma (SEGA) is the most common central nervous system tumor in patients with tuberous sclerosis complex (TSC). SEGAs are generally benign, non-infiltrative lesions, but they can lead to intracranial hypertension, obstructive hydrocephalus, focal neurologic deficits, and even sudden death.

DISCUSSION

Surgical resection has been the standard treatment for SEGAs, and it is generally curative with complete resection. However, not all SEGAs are amenable to safe and complete resection. Gamma Knife stereotactic radiosurgery provides another treatment option as a primary or adjuvant treatment for SEGAs, but it has highly variable response effects with sporadic cases demonstrating its efficacy. Recently, biologically targeted pharmacotherapy with mammalian target of rapamycin (mTOR) inhibitors such as sirolimus and everolimus has provided a safe and efficacious treatment option for patients with SEGAs. However, SEGAs can recur few months after drug discontinuation, indicating that mTOR inhibitors may need to be continued to avoid recurrence. Further studies are needed to evaluate the advantages and adverse effects of long-term treatment with mTOR inhibitors. This review presents an overview of the current knowledge and particularly highlights the surgical and medical options of SEGAs in patients with TSC.

Optimization of ERK activity biosensors for both ratiometric and lifetime FRET measurements

Among biosensors, genetically-encoded FRET-based biosensors are widely used to localize and measure enzymatic activities. Kinases activities are of particular interest as their spatiotemporal regulation has become crucial for the deep understanding of cell fate decisions. This is especially the case for ERK, whose activity is a key node in signal transduction pathways and can direct the cell into various processes. There is a constant need for better tools to analyze kinases in vivo, and to detect even the slightest variations of their activities. Here we report the optimization of the previous ERK activity reporters, EKAR and EKAREV. Those tools are constituted by two fluorophores adapted for FRET experiments, which are flanking a specific substrate of ERK, and a domain able to recognize and bind this substrate when phosphorylated. The latter phosphorylation allows a conformational change of the biosensor and thus a FRET signal. We improved those biosensors with modifications of: (i) fluorophores and (ii) linkers between substrate and binding domain, resulting in new versions that exhibit broader dynamic ranges upon EGF stimulation when FRET experiments are carried out by fluorescence lifetime and ratiometric measurements. Herein, we characterize those new biosensors and discuss their observed differences that depend on their fluorescence properties.

Immunofluorescent localization of MAPKs and colocalization with microtubules in Arabidopsis seedling whole-mount probes

In all eukaryotes, signaling by mitogen-activated protein kinase (MAPK) pathways plays a crucial role in signal transduction during regulation of cell growth, differentiation, proliferation as well as death and stress responses. In this chapter we describe a reliable method to immunolocalize MAPKs in roots of Arabidopsis thaliana by using whole-mount seedling probes. This method relies on quick and efficient chemical fixation, partial cell wall digestion, plasma membrane permeabilization, subsequent antibody incubation, and visualization by high-end confocal laser scanning microscopy (CLSM) performed on whole Arabidopsis seedlings. Protocols are provided for immunofluorescent localization of MPK3, MPK4, and MPK6, representing three major developmentally and stress-regulated MAPKs of Arabidopsis. In addition, protocols for colocalization of these MAPKs with microtubules are also provided.

p38 mitogen-activated protein kinase interacts with vinculin at focal adhesions during fatty acid-stimulated cell adhesion

Arachidonic acid stimulates cell adhesion by activating α2β1 integrins in a process that depends on protein kinases, including p38 mitogen activated protein kinase. Here, we describe the interaction of cytoskeletal components with key signaling molecules that contribute to the spreading of, and morphological changes in, arachidonic acid-treated MDA-MB-435 human breast carcinoma cells. Arachidonic acid-treated cells showed increased attachment and spreading on collagen type IV, as measured by electric cell-substrate impedance sensing. Fatty acid-treated cells displayed short cortical actin filaments associated with an increased number of β1 integrin-containing pseudopodia, whereas untreated cells displayed elongated stress fibers and fewer clusters of β1 integrins. Confocal microscopy of arachidonic acid-treated cells showed that vinculin and phospho-p38 both appeared enriched in pseudopodia and at the tips of actin filaments, and fluorescence ratio imaging indicated the increase was specific for the phospho-(active) form of p38. Immunoprecipitates of phospho-p38 from extracts of arachidonic acid-treated cells contained vinculin, and GST-vinculin fusion proteins carrying the central region of vinculin bound phospho-p38, whereas fusion proteins expressing the terminal portions of vinculin did not. These data suggest that phospho-p38 associates with particular domains on critical focal adhesion proteins that are involved in tumor cell adhesion and spreading, and that this association can be regulated by factors in the tumor microenvironment.

Kisspeptin/KISS1R signaling potentiates extravillous trophoblast adhesion to type-I collagen in a PKC- and ERK1/2-dependent manner

During the first trimester of human pregnancy, cytotrophoblasts proliferate within the tips of the chorionic villi to form cell columns that anchor the placenta to the uterus. This migration coincides with a widespread change in the adhesion molecule repertoire of these trophoblasts. Kisspeptin and its receptor, KISS1R, are best known as potent triggers of gonadotropin-releasing hormone secretion. The kisspeptin/KISS1R signaling system is also highly expressed in the human placenta, where it was demonstrated to inhibit extra-villous trophoblast (EVT) migration and invasion in vitro. Here we show that kisspeptin, in a dose- and time-dependent manner, induces increased adhesion of human EVTs to type-I collagen, a major component of the human placenta. This increased adhesion was both rapid and transient, suggesting that it likely occurred through the activation of KISS1R secondary effectors such as PKC and ERK, which underwent rapid and transient kisspeptin-dependent activation in EVTs. We then showed that inhibition of both PKC and ERK1/2 attenuated the kisspeptin-dependent increase in EVT adhesion, suggesting that these molecules are key positive regulators of trophoblast adhesion. We therefore propose that kisspeptin/KISS1R signaling potentiates EVT adhesion to type-I collagen via "inside-out signaling." Furthermore, kisspeptin treatment increased mouse blastocyst adhesion to collagen I, suggesting that kisspeptin signaling is a key regulator of trophoblast function during implantation as well as early placentation.

Antibody-induced acetylcholine receptor clusters inhabit liquid-ordered and liquid-disordered domains

The distribution of nicotinic acetylcholine receptor (AChR) clusters at the cell membrane was studied in CHO-K1/A5 cells using fluorescence microscopy. Di-4-ANEPPDHQ, a fluorescent probe that differentiates between liquid-ordered (Lo) and liquid-disordered (Ld) phases in model membranes, was used in combination with monoclonal anti-AChR antibody labeling of live cells, which induces AChR clustering. The so-called generalized polarization (GP) of di-4-ANEPPDHQ was measured in regions of the cell-surface membrane associated with or devoid of antibody-induced AChR clusters, respectively. AChR clusters were almost equally distributed between Lo and Ld domains, independently of receptor surface levels and agonist (carbamoylcholine and nicotine) or antagonist (α-bungarotoxin) binding. Cholesterol depletion diminished the cell membrane mean di-4-ANEPPDHQ GP and the number of AChR clusters associated with Ld membrane domains increased concomitantly. Depolymerization of the filamentous actin cytoskeleton by Latrunculin A had the opposite effect, with more AChR clusters associated with Lo domains. AChR internalized via small vesicles having lower GP and lower cholesterol content than the surface membrane. Upon cholesterol depletion, only 12% of the AChR-containing vesicles costained with the fluorescent cholesterol analog fPEG-cholesterol, i.e., AChR endocytosis was essentially dissociated from that of cholesterol. In conclusion, the distribution of AChR submicron-sized clusters at the cell membrane appears to be regulated by cholesterol content and cytoskeleton integrity.

Phosphorylation of human cytochrome P450c17 by p38α selectively increases 17,20 lyase activity and androgen biosynthesis

Cytochrome P450c17, a steroidogenic enzyme encoded by the CYP17A1 gene, catalyzes the steroid 17α-hydroxylation needed for glucocorticoid synthesis, which may or may not be followed by 17,20 lyase activity needed for sex steroid synthesis. Whether or not P450c17 catalyzes 17,20 lyase activity is determined by three post-translational mechanisms influencing availability of reducing equivalents donated by P450 oxidoreductase (POR). These are increased amounts of POR, the allosteric action of cytochrome b5 to promote POR-P450c17 interaction, and Ser/Thr phosphorylation of P450c17, which also appears to promote POR-P450c17 interaction. The kinase(s) that phosphorylates P450c17 is unknown. In a series of kinase inhibition experiments, the pyridinyl imidazole drugs SB202190 and SB203580 inhibited 17,20 lyase but not 17α-hydroxylase activity in human adrenocortical HCI-H295A cells, suggesting an action on p38α or p38β. Co-transfection of non-steroidogenic COS-1 cells with P450c17 and p38 expression vectors showed that p38α, but not p38β, conferred 17,20 lyase activity on P450c17. Antiserum to P450c17 co-immunoprecipitated P450c17 and both p38 isoforms; however, knockdown of p38α, but not knockdown of p38β, inhibited 17,20 lyase activity in NCI-H295A cells. Bacterially expressed human P450c17 was phosphorylated by p38α in vitro at a non-canonical site, conferring increased 17,20 lyase activity. This phosphorylation increased the maximum velocity, but not the Michaelis constant, of the 17,20 lyase reaction. p38α phosphorylates P450c17 in a fashion that confers increased 17,20 lyase activity, implying that the production of adrenal androgens (adrenarche) is a regulated event.

Functional Integration of the Conserved Domains of Shoc2 Scaffold

Shoc2 is a positive regulator of signaling to extracellular signal-regulated protein kinases 1 and 2 (ERK1/2). Shoc2 is also proposed to interact with RAS and Raf-1 in order to accelerate ERK1/2 activity. To understand the mechanisms by which Shoc2 regulates ERK1/2 activation by the epidermal growth factor receptor (EGFR), we dissected the role of Shoc2 structural domains in binding to its signaling partners and its role in regulating ERK1/2 activity. Shoc2 is comprised of two main domains: the 21 leucine rich repeats (LRRs) core and the N-terminal non-LRR domain. We demonstrated that the N-terminal domain mediates Shoc2 binding to both M-Ras and Raf-1, while the C-terminal part of Shoc2 contains a late endosomal targeting motif. We found that M-Ras binding to Shoc2 is independent of its GTPase activity. While overexpression of Shoc2 did not change kinetics of ERK1/2 activity, both the N-terminal and the LRR-core domain were able to rescue ERK1/2 activity in cells depleted of Shoc2, suggesting that these Shoc2 domains are involved in modulating ERK1/2 activity.

Decreased tumor progression and invasion by a novel anti-cell motility target for human colorectal carcinoma cells

We have previously described a novel modulator of the actin cytoskeleton that also regulates Ras and mitogen-activated protein kinase activities in TGFβ-sensitive epithelial cells. Here we examined the functional role of this signaling regulatory protein (km23-1) in mediating the migration, invasion, and tumor growth of human colorectal carcinoma (CRC) cells. We show that small interfering RNA (siRNA) depletion of km23-1 in human CRC cells inhibited constitutive extracellular signal-regulated kinase (ERK) activation, as well as pro-invasive ERK effector functions that include phosphorylation of Elk-1, constitutive regulation of c-Fos-DNA binding, TGFβ1 promoter transactivation, and TGFβ1 secretion. In addition, knockdown of km23-1 reduced the paracrine effects of CRC cell-secreted factors in conditioned medium and in fibroblast co-cultures. Moreover, km23-1 depletion in human CRC cells reduced cell migration and invasion, as well as expression of the ERK-regulated, metastasis-associated scaffold protein Ezrin. Finally, km23-1 inhibition significantly suppressed tumor formation in vivo. Thus, our results implicate km23-1 as a novel anti-metastasis target for human colon carcinoma cells, capable of decreasing tumor growth and invasion via a mechanism involving suppression of various pro-migratory features of CRC. These include a reduction in ERK signaling, diminished TGFβ1 production, decreased expression of the plasma membrane-cytoskeletal linker Ezrin, as well as attenuation of the paracrine effects of colon carcinoma-secreted factors on fibroblast migration and mitogenesis. As such, km23-1 inhibitors may represent a viable therapeutic strategy for interfering with colon cancer progression and invasion.

The role of mechanical force and ROS in integrin-dependent signals

Cells are exposed to several types of integrin stimuli, which generate responses generally referred to as “integrin signals”, but the specific responses to different integrin stimuli are poorly defined. In this study, signals induced by integrin ligation during cell attachment, mechanical force from intracellular contraction, or cell stretching by external force were compared. The elevated phosphorylation levels of several proteins during the early phase of cell attachment and spreading of fibroblast cell lines were not affected by inhibition of ROCK and myosin II activity, i.e. the reactions occurred independently of intracellular contractile force acting on the adhesion sites. The contraction-independent phosphorylation sites included ERK1/2 T202/Y204, AKT S473, p130CAS Y410, and cofilin S3. In contrast to cell attachment, cyclic stretching of the adherent cells induced a robust phosphorylation only of ERK1/2 and the phosphorylation levels of the other investigated proteins were not or only moderately affected by stretching. No major differences between signaling via α5β1 or αvβ3 integrins were detected. The importance of mitochondrial ROS for the integrin-induced signaling pathways was investigated using rotenone, a specific inhibitor of complex I in the respiratory chain. While rotenone only moderately reduced ATP levels and hardly affected the signals induced by cyclic cell stretching, it abolished the activation of AKT and reduced the actin polymerization rate in response to attachment in both cell lines. In contrast, scavenging of extracellular ROS with catalase or the vitamin C analog Asc-2P did not significantly influence the attachment-derived signaling, but caused a selective and pronounced enhancement of ERK1/2 phosphorylation in response to stretching. In conclusion, the results showed that “integrin signals” are composed of separate sets of reactions triggered by different types of integrin stimulation. Mitochondrial ROS and extracellular ROS had specific and distinct effects on the integrin signals induced by cell attachment and mechanical stretching.

Heat shock protein 90 is an essential molecular chaperone for CB2 cannabinoid receptor-mediated signaling in trabecular meshwork cells

PURPOSE

To examine the interaction of heat shock protein 90 (Hsp90) with the CB2 cannabinoid receptor in trabecular meshwork (TM) cells and to investigate the roles of Hsp90 in CB2 receptor-mediated cell signaling and actin cytoskeleton remodeling.

METHODS

Coimmunoprecipitation experiments and western blot analyses, using specific anti-CB2 and anti-Hsp90 antibodies, were performed to study the interaction of Hsp90 with the CB2 receptor in TM cells. An antiphospho-extracellular-signal-regulated kinases 1/2 (ERK1/2) antibody was used to detect the CB2 receptor-mediated phosphrylation of ERK1/2. In cytoskeleton studies, Alexa Fluor 488-labeled phalloidin staining was used to examine actin filaments of TM cells. PD98059, a specific inhibitor of the ERK1/2 pathway, was used to evaluate the role ERK1/2 pathway in CB2 receptor-mediated actin cytoskeleton changes. Geldanamycin, an inhibitor of Hsp90, was used to investigate the roles of Hsp90 in CB2 receptor-mediated ERK1/2 phosphorylation and actin cytoskeleton remodeling.

RESULTS

The interaction of Hsp90 with the CB2 receptor was established in TM cells with coimmunoprecipitation experiments and western blot analyses. Treatment of TM cells with geldanamycin significantly inhibited the interaction of Hsp90 with the CB2 receptor. Disruption of the CB2/Hsp90 interaction by treating TM cells with geldanamycin inhibited CB2 receptor-mediated ERK1/2 phosphorylation, as well as actin cytoskeleton remodeling. Furthermore, treatment of TM cells with PD98059 profoundly attenuated CB2 receptor-mediated actin cytoskeleton changes.

CONCLUSIONS

The data from this study establish a specific interaction between Hsp90 and the CB2 receptor in TM cells. In addition, the current study demonstrates that by interacting with the CB2 receptor, Hsp90 plays an important role as a molecular chaperone in CB2 receptor-mediated cell signaling and actin cytoskeleton rearrangement in TM cells.

Gravity-sensitive signaling drives 3-dimensional formation of multicellular thyroid cancer spheroids

This study focused on the effects induced by a random positioning machine (RPM) on FTC-133 thyroid cancer cells and evaluated signaling elements involved in 3-dimensional multicellular tumor spheroid (MCTS) formation. The cells were cultured on the RPM, a device developed to simulate microgravity, and under static 1-g conditions. After 24 h on the RPM, MCTSs swimming in culture supernatants were found, in addition to growth of adherent (AD) cells. Cells grown on the RPM showed higher levels of NF-κB p65 protein and apoptosis than 1-g controls, a result also found earlier in endothelial cells. Employing microarray analysis, we found 487 significantly regulated transcripts belonging not only to the apoptosis pathway but also to other biological processes. Selected transcripts were analyzed with quantitative real-time PCR using the same samples. Compared with 1-g IL-6, IL-8, CD44, and OPN were significantly up-regulated in AD cells but not in MCTSs, while ERK1/2, CAV2, TLN1, and CTGF were significantly down-regulated in AD cells. Simultaneously, the expression of ERK2, IL-6, CAV2, TLN1, and CTGF was reduced in MCTSs. IL-6 protein expression and secretion mirrored its gene expression. Thus, we concluded that the signaling elements IL-6, IL-8, OPN, TLN1, and CTGF are involved with NF-κB p65 in RPM-dependent thyroid carcinoma cell spheroid formation.

ERK1/2 regulate exocytosis through direct phosphorylation of the exocyst component Exo70

The exocyst is a multiprotein complex essential for exocytosis and plasma membrane remodeling. The assembly of the exocyst complex mediates the tethering of post-Golgi secretory vesicles to the plasma membrane prior to fusion. Elucidating the mechanisms regulating exocyst assembly is important for the understanding of exocytosis. Here we show that the exocyst component Exo70 is a direct substrate of the extracellular signal-regulated kinases 1/2 (ERK1/2). ERK1/2 phosphorylation enhances the binding of Exo70 to other exocyst components and promotes the assembly of the exocyst complex in response to epidermal growth factor (EGF) signaling. We further demonstrate that ERK1/2 regulates exocytosis, because blocking ERK1/2 signaling by a chemical inhibitor or the expression of an Exo70 mutant defective in ERK1/2 phosphorylation inhibited exocytosis. In tumor cells, blocking Exo70 phosphorylation inhibits matrix metalloproteinase secretion and invadopodia formation. ERK1/2 phosphorylation of Exo70 may thus coordinate exocytosis with other cellular events in response to growth factor signaling.