Subcellular Localization Determines the Protective Effects of Activated ERK2 against Distinct Apoptogenic Stimuli in Myeloid Leukemia Cells

Nuclear translocation of the tagged endogenous MAPK MPK-1 denotes a subset of activation events in C. elegans development

The extracellular signal-regulated kinases (ERKs) are mitogen-activated protein kinases (MAPKs) that are utilized downstream of Ras to Raf to MEK signaling to control activation of a wide array of targets. Activation of ERKs is elevated in Ras-driven tumors and RASopathies, and thus is a target for pharmacological inhibition. Regulatory mechanisms of ERK activation have been studied extensively in vitro and in cultured cells, but little in living animals. In this study, we tagged the Caenorhabditis elegans ERK-encoding gene, mpk-1. MPK-1 is ubiquitously expressed with elevated expression in certain contexts. We detected cytosol-to-nuclear translocation of MPK-1 in maturing oocytes and hence validated nuclear translocation as a reporter of some activation events. During patterning of vulval precursor cells (VPCs), MPK-1 is necessary and sufficient for the central cell, P6.p, to assume the primary fate. Yet MPK-1 translocates to the nuclei of all six VPCs in a temporal and concentration gradient centered on P6.p. This observation contrasts with previous results using the ERK nuclear kinase translocation reporter of substrate activation, raising questions about mechanisms and indicators of MPK-1 activation. This system and reagent promise to provide critical insights into the regulation of MPK-1 activation within a complex intercellular signaling network.

Summary: Tagged endogenous C. elegans MPK-1 shows activation-dependent cytosol-to-nuclear translocation. This tool provides novel insights into MPK-1 localization compared with other markers of in vivo ERK activation.

Ginsenoside Rb3 Alleviates CSE-induced TROP2 Upregulation through p38 MAPK and NF-κB Pathways in Basal Cells

Smoking-mediated reprogramming of the phenotype and function of airway basal cells (BCs) disrupts airway homeostasis and is an early event in chronic obstructive pulmonary disease (COPD)-associated airway remodeling. Here, we examined the expression and regulation of the transmembrane glycoprotein TROP2 (trophoblast antigen 2), a putative stem cell marker in airway BCs, in lung tissue samples from healthy smokers and healthy nonsmokers and in models in culture to identify therapeutic targets. TROP2 expression was upregulated in the airway epithelia of smokers and positively correlated with the smoking index. In vitro, cigarette smoke extract (CSE) induced TROP2 expression in airway BCs in a time- and dose-dependent manner. The p38 MAPK and NF-κB pathways were also activated by CSE, and their specific antagonists inhibited CSE-induced TROP2 expression. A therapeutic component derived from traditional Chinese medicine, ginsenoside Rb3, inhibited CSE-induced TROP2 expression as well as activation of the p38 MAPK and NF-κB pathways in BCs in monolayer culture. Furthermore, ginsenoside Rb3 prevented the increase in TROP2 expression and antagonized CSE-induced BC hyperplasia and expression of inflammatory factors and epithelial-mesenchymal transition changes in an air-liquid culture model. Thus, CSE-induced TROP2 is a possible biomarker for early changes in the epithelium of smokers, and ginsenoside Rb3 may serve as a therapeutic molecule, preventing the disruption of epithelial homeostasis in COPD.

Dual effects of active ERK in cancer: A potential target for enhancing radiosensitivity

Ionizing radiation (IR) is an important cancer treatment approach. However, radioresistance eventually occurs, resulting in poor outcomes in patients with cancer. Radioresistance is associated with multiple signaling pathways, particularly pro-survival signaling pathways. The extracellular signal-regulated kinase 1/2 (ERK1/2) cascade is an important signaling pathway that initiates several cellular processes and is regulated by various stimuli, including IR. Although numerous studies have demonstrated the pro-survival effects of active ERK, activation of ERK has also been associated with cell death, indicating that radiosensitization may occur by ERK stimulation. In this context, the present review describes the associations between ERK signaling, cancer and IR, and discusses the association between ERK and its pro-survival function in cancer cells, including stimuli, molecular mechanisms, clinical use of inhibitors and underlying limitations. Additionally, the present review introduces the view that active ERK may induce cell death, and describes the potential factors associated with this process. This review describes the various outcomes induced by active ERK to prompt future studies to aim to enhance radiosensitivity in the treatment of cancer.

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

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

Analysis of Ras/ERK Compartmentalization by Subcellular Fractionation

A vast number of stimuli use the Ras/Raf/MEK/ERK signaling cascade to transmit signals from their cognate receptors, in order to regulate multiple cellular functions, including key processes such as proliferation, cell cycle progression, differentiation, and survival. The duration, intensity and specificity of the responses are, in part, controlled by the compartmentalization/subcellular localization of the signaling intermediaries. Ras proteins are found in different plasma membrane microdomains and endomembranes. At these localizations, Ras is subject to site-specific regulatory mechanisms, distinctively engaging effector pathways and switching-on diverse genetic programs to generate a multitude of biological responses. The Ras effector pathway leading to ERKs activation is also subject to space-related regulatory processes. About half of ERK1/2 substrates are found in the nucleus and function mainly as transcription factors. The other half resides in the cytosol and other cellular organelles. Such subcellular distribution enhances the complexity of the Ras/ERK cascade and constitutes an essential mechanism to endow variability to its signals, which enables their participation in the regulation of a broad variety of functions. Thus, analyzing the subcellular compartmentalization of the members of the Ras/ERK cascade constitutes an important factor to be taken into account when studying specific biological responses evoked by Ras/ERK signals. Herein, we describe methods for such purpose.

The D Domain of LRRC4 anchors ERK1/2 in the cytoplasm and competitively inhibits MEK/ERK activation in glioma cells

Background

As a well-characterized key player in various signal transduction networks, extracellular-signal-regulated kinase (ERK1/2) has been widely implicated in the development of many malignancies. We previously found that Leucine-rich repeat containing 4 (LRRC4) was a tumor suppressor and a negative regulator of the ERK/MAPK pathway in glioma tumorigenesis. However, the precise molecular role of LRRC4 in ERK signal transmission is unclear.

Methods

The interaction between LRRC4 and ERK1/2 was assessed by co-immunoprecipitation and GST pull-down assays in vivo and in vitro. We also investigated the interaction of LRRC4 and ERK1/2 and the role of the D domain in ERK activation in glioma cells.

Results

Here, we showed that LRRC4 and ERK1/2 interact via the D domain and CD domain, respectively. Following EGF stimuli, the D domain of LRRC4 anchors ERK1/2 in the cytoplasm and abrogates ERK1/2 activation and nuclear translocation. In glioblastoma cells, ectopic LRRC4 expression competitively inhibited the interaction of endogenous mitogen-activated protein kinase (MEK) and ERK1/2. Mutation of the D domain decreased the LRRC4-mediated inhibition of MAPK signaling and its anti-proliferation and anti-invasion roles.

Conclusions

Our results demonstrated that the D domain of LRRC4 anchors ERK1/2 in the cytoplasm and competitively inhibits MEK/ERK activation in glioma cells. These findings identify a new mechanism underlying glioblastoma progression and suggest a novel therapeutic strategy by restoring the activity of LRRC4 to decrease MAPK cascade activation.

Electronic supplementary material

The online version of this article (doi:10.1186/s13045-016-0355-1) contains supplementary material, which is available to authorized users.

Cell Cycle Arrest and Apoptosis Induction via Modulation of Mitochondrial Integrity by Bcl-2 Family Members and Caspase Dependence in Dracaena cinnabari-Treated H400 Human Oral Squamous Cell Carcinoma

Dracaena cinnabari Balf.f. is a red resin endemic to Socotra Island, Yemen. Although there have been several reports on its therapeutic properties, information on its cytotoxicity and anticancer effects is very limited. This study utilized a bioassay-guided fractionation approach to determine the cytotoxic and apoptosis-inducing effects of D. cinnabari on human oral squamous cell carcinoma (OSCC). The cytotoxic effects of D. cinnabari crude extract were observed in a panel of OSCC cell lines and were most pronounced in H400. Only fractions DCc and DCd were active on H400 cells; subfractions DCc15 and DCd16 exhibited the greatest cytotoxicity against H400 cells and D. cinnabari inhibited cells proliferation in a time-dependent manner. This was achieved primarily via apoptosis where externalization of phospholipid phosphatidylserine was observed using DAPI/Annexin V fluorescence double staining mechanism studied through mitochondrial membrane potential assay cytochrome c enzyme-linked immunosorbent and caspases activities revealed depolarization of mitochondrial membrane potential (MMP) and significant activation of caspases 9 and 3/7, concomitant with S phase arrest. Apoptotic proteins array suggested that MMP was regulated by Bcl-2 proteins family as results demonstrated an upregulation of Bax, Bad, and Bid as well as downregulation of Bcl-2. Hence, D. cinnabari has the potential to be developed as an anticancer agent.

Goniothalamin induces cell cycle arrest and apoptosis in H400 human oral squamous cell carcinoma: A caspase-dependent mitochondrial-mediated pathway with downregulation of NF-κβ

Goniothalamin is a natural occurring styryl-lactone compound isolated from Goniothalamus macrophyllus. It had been demonstrated to process promising anticancer activity on various cancer cell lines. However, little study has been carried out on oral cancer. The aim of this study was to determine the cytotoxic effects of goniothalamin against H400 oral cancer cells and its underlying molecular pathways. Results from MTT assay demonstrated that goniothalamin exhibited selective cytotoxicity as well as inhibited cells growth of H400 in dose and time-dependent manner. This was achieved primarily via apoptosis where apoptotic bodies and membrane blebbing were observed using AO/PI and DAPI/Annexin V-FITC fluorescence double staining. In order to understand the apoptosis mechanisms induced by goniothalamin, apoptosis assessment based on mitochondrial membrane potential assay and cytochrome c enzyme-linked immunosorbent assay were carried out. Results demonstrated that the depolarization of mitochondrial transmembrane potential facilitated the release of mitochondrial cytochrome c into cytosol. Caspases assays revealed the activation of initiator caspase-9 and executioner caspase-3/7 in dose-dependent manners. This form of apoptosis was closely associated with the regulation on Bcl-2 family proteins, cell cycle arrest at S phase and inhibition of NF-κβ translocation from cytoplasm to nucleus. Conclusion, goniothalamin has the potential to act as an anticancer agent against human oral squamous cell carcinoma (H400 cells).

LPS-Induced G-CSF Expression in Macrophages Is Mediated by ERK2, but Not ERK1

Granulocyte colony-stimulating factor (G-CSF) selectively stimulates proliferation and differentiation of neutrophil progenitors which play important roles in host defense against infectious agents. However, persistent G-CSF production often leads to neutrophilia and excessive inflammatory reactions. There is therefore a need to understand the mechanism regulating G-CSF expression. In this study, we showed that U0126, a MEK1/2 inhibitor, decreases lipopolysaccharide (LPS)-stimulated G-CSF promoter activity, mRNA expression and protein secretion. Using short hairpin RNA knockdown, we demonstrated that ERK2, and not ERK1, involves in LPS-induced G-CSF expression, but not LPS-regulated expression of TNF-α. Reporter assays showed that ERK2 and C/EBPβ synergistically activate G-CSF promoter activity. Further chromatin immunoprecipitation (ChIP) assays revealed that U0126 inhibits LPS-induced binding of NF-κB (p50/p65) and C/EBPβ to the G-CSF promoter, but not their nuclear protein levels. Knockdown of ERK2 inhibits LPS-induced accessibility of the G-CSF promoter region to DNase I, suggesting that chromatin remodeling may occur. These findings clarify that ERK2, rather than ERK1, mediates LPS-induced G-CSF expression in macrophages by remodeling chromatin, and stimulates C/EBPβ-dependent activation of the G-CSF promoter. This study provides a potential target for regulating G-CSF expression.

Koenimbin, a natural dietary compound of Murraya koenigii (L) Spreng: inhibition of MCF7 breast cancer cells and targeting of derived MCF7 breast cancer stem cells (CD44(+)/CD24(-/low)): an in vitro study

BACKGROUND

Inhibition of breast cancer stem cells has been shown to be an effective therapeutic strategy for cancer prevention. The aims of this work were to evaluate the efficacy of koenimbin, isolated from Murraya koenigii (L) Spreng, in the inhibition of MCF7 breast cancer cells and to target MCF7 breast cancer stem cells through apoptosis in vitro.

METHODS

Koenimbin-induced cell viability was evaluated using the MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay. Nuclear condensation, cell permeability, mitochondrial membrane potential, and cytochrome c release were observed using high-content screening. Cell cycle arrest was examined using flow cytometry, while human apoptosis proteome profiler assays were used to investigate the mechanism of apoptosis. Protein expression levels of Bax, Bcl2, and heat shock protein 70 were confirmed using Western blotting. Caspase-7, caspase-8, and caspase-9 levels were measured, and nuclear factor kappa B (NF-κB) activity was assessed using a high-content screening assay. Aldefluor™ and mammosphere formation assays were used to evaluate the effect of koenimbin on MCF7 breast cancer stem cells in vitro. The Wnt/β-catenin signaling pathway was investigated using Western blotting.

RESULTS

Koenimbin-induced apoptosis in MCF7 cells was mediated by cell death-transducing signals regulating the mitochondrial membrane potential by downregulating Bcl2 and upregulating Bax, due to cytochrome c release from the mitochondria to the cytosol. Koenimbin induced significant (P<0.05) sub-G0 phase arrest in breast cancer cells. Cytochrome c release triggered caspase-9 activation, which then activated caspase-7, leading to apoptotic changes. This form of apoptosis is closely associated with the intrinsic pathway and inhibition of NF-κB translocation from the cytoplasm to the nucleus. Koenimbin significantly (P<0.05) decreased the aldehyde dehydrogenase-positive cell population in MCF7 cancer stem cells and significantly (P<0.01) decreased the size and number of MCF7 cancer stem cells in primary, secondary, and tertiary mammospheres in vitro. Koenimbin also significantly (P<0.05) downregulated the Wnt/β-catenin self-renewal pathway.

CONCLUSION

Koenimbin has potential for future chemoprevention studies, and may lead to the discovery of further cancer management strategies by reducing cancer resistance and recurrence and improving patient survival.

Berberine-induced apoptosis in human breast cancer cells is mediated by reactive oxygen species generation and mitochondrial-related apoptotic pathway

Berberine has drawn extensive attention toward their wide range of biochemical and pharmacological effects, including antineoplastic effect in recent years, but the precise mechanisms remain unclear. Treatment of human breast cancer cells (MCF-7 and MDA-MB-231 cells) with berberine induced inhibition of cell viability in concentration- and time-dependent manner irrespective of their estrogen receptor (ER) expression. Hoechst33342 staining confirmed berberine induced breast cancer cell apoptosis in time-dependent manner. Because apoptosis induction is considered to be a crucial strategy for cancer prevention and therapy, berberine may be an effective chemotherapeutic agent against breast cancer. To explore the precise mechanism, berberine-induced oxidative stress and mitochondrial-related apoptotic pathway in human breast cancer cells were investigated in this study. In both MCF-7 and MDA-MB-231 cells, berberine increased the production of reactive oxygen species (ROS), which activated the pro-apoptotic JNK signaling. Phosphorylated JNK triggered mitochondria membrane potential (ΔΨm) depolarization and downregulation expression of anti-apoptotic protein Bcl-2 concomitant with the upregulation expression of pro-apoptotic protein Bax. Downregulation of anti-apoptotic Bcl-2 family protein in parallel with loss of ΔΨm, leading to increased the release of cytochrome c and apoptosis-inducing factor (AIF) from mitochondria, and eventually triggered the caspase-dependent and caspase-independent apoptosis. Taken together, our study reveled that berberine exerted an antitumor activity in breast cancer cells by reactive oxygen species generation and mitochondrial-related apoptotic pathway. These finding provide an insight into the potential of berberine for breast cancer therapy.

Alpha2beta1 integrin promotes T cell survival and migration through the concomitant activation of ERK/Mcl-1 and p38 MAPK pathways

Integrin-mediated attachment to extracellular matrix (ECM) is crucial for cancer progression. Malignant T cells such as acute lymphoblastic leukemia (T-ALL) express β1 integrins, which mediate their interactions with ECM. However, the role of these interactions in T-ALL malignancy is still poorly explored. In the present study, we investigated the effect of collagen; an abundant ECM, on T-ALL survival and migration. We found that collagen through α2β1 integrin promotes the survival of T-ALL cell lines in the absence of growth factors. T-ALL cell survival by collagen is associated with reduced caspase activation and maintenance of Mcl-1 levels. Collagen activated both ERK and p38 MAPKs but only MAPK/ERK was required for collagen-induced T-ALL survival. However, we found that α2β1 integrin promoted T-ALL migration via both ERK and p38. Together these data indicate that α2β1 integrin signaling can represent an important signaling pathway in T-ALL pathogenesis and suggest that its blockade could be beneficial in T-ALL treatment.

Apoptosis Effect of Girinimbine Isolated from Murraya koenigii on Lung Cancer Cells In Vitro

Murraya koenigii Spreng has been traditionally claimed as a remedy for cancer. The current study investigated the anticancer effects of girinimbine, a carbazole alkaloid isolated from Murraya koenigii Spreng, on A549 lung cancer cells in relation to apoptotic mechanistic pathway. Girinimbine was isolated from Murraya koenigii Spreng. The antiproliferative activity was assayed using MTT and the apoptosis detection was done by annexin V and lysosomal stability assays. Multiparameter cytotoxicity assays were performed to investigate the change in mitochondrial membrane potential and cytochrome c translocation. ROS, caspase, and human apoptosis proteome profiler assays were done to investigate the apoptotic mechanism of cell death. The MTT assay revealed that the girinimbine induces cell death with an IC₅₀ of 19.01 μM. A significant induction of early phase of apoptosis was shown by annexin V and lysosomal stability assays. After 24 h treatment with 19.01 μM of girinimbine, decrease in the nuclear area and increase in mitochondrial membrane potential and plasma membrane permeability were readily visible. Moreover the translocation of cytochrome c also was observed. Girinimbine mediates its antiproliferative and apoptotic effects through up- and downregulation of apoptotic and antiapoptotic proteins. There was a significant involvement of both intrinsic and extrinsic pathways. Moreover, the upregulation of p53 as well as the cell proliferation repressor proteins, p27 and p21, and the significant role of insulin/IGF-1 signaling were also identified. Moreover the caspases 3 and 8 were found to be significantly activated. Our results taken together indicated that girinimbine may be a potential agent for anticancer drug development.

Inhibition of CRM1-mediated nucleocytoplasmic transport: triggering human melanoma cell apoptosis by perturbing multiple cellular pathways

Development of multiple drug resistance mechanisms in melanomas necessitates the identification of new drug targets, which when inhibited could impact multiple cellular pathways, thus circumventing potential resistance. By performing complementary DNA microarray analysis, we identified four key components of the nucleocytoplasmic transport machinery-CRM1, RAN (RAN-GTPase), RANGAP1, and RANBP1-to be overexpressed in human melanoma metastases. Chromosome region maintenance 1 (CRM1) inhibition induced a marked depletion of prosurvival/cytoplasmic extracellular signal-regulated kinase 1/2 (Erk1/2) and p90 ribosomal S6 kinase1 and elicited persistent Erk-signaling hyperactivation. Consistently, CRM1 inhibition inflicted extensive apoptosis in melanoma cells while sparing nontransformed melanocytes and primary lung fibroblasts. Apoptosis required both the intrinsic and extrinsic apoptotic pathways and was associated with a nuclear entrapment and downregulation of the antiapoptotic CRM1 target protein, Survivin. Apoptosis was preceded by a G1 cell-cycle arrest, and even though CRM1 inhibition mediated marked p53 and p21 induction in wild-type p53 melanoma cells, the latter's silencing or inactivation failed to alleviate apoptosis. Notably, CRM1 inhibition induced cell line-specific, G1 to S progression-retarding changes in the expression of multiple cell-cycle regulatory proteins, thus potentially explaining p53 dispensability. We propose CRM1 as a potential therapeutic target in human melanoma, whose inhibition induces loss of prosurvival/cytoplasmic Erk1/2, mediates persistent Erk hyperactivation, and initiates a multitude of cell context-dependent molecular events to trigger G1 arrest followed by massive apoptosis.

Involvement of NF-κB and Bcl2/Bax signaling pathways in the apoptosis of MCF7 cells induced by a xanthone compound Pyranocycloartobiloxanthone A

The plant Artocarpus obtusus is a tropical plant that belongs to the family Moraceae. In the present study a xanthone compound Pyranocycloartobiloxanthone A (PA) was isolated from this plant and the apoptosis mechanism was investigated. PA induced cytotoxicity was observed using MTT assay. High content screening (HCS) was used to observe the nuclear condensation, cell permeability, mitochondrial membrane potential (MMP) and cytochrome c release. Reactive oxygen species formation was investigated on treated cells by using fluorescent analysis. Human apoptosis proteome profiler assays were performed to investigate the mechanism of cell death. In addition mRNA levels of Bax and Bcl2 were also checked using RT-PCR. Caspase 3/7, 8 and 9 were measured for their induction while treatment. The involvement of NF-κB was analyzed using HCS assay. The results showed that PA possesses the characteristics of selectively inducing cell death of tumor cells as no inhibition was observed in non-tumorigenic cells even at 30 μg/ml. Treatment of MCF7 cells with PA induced apoptosis with cell death-transducing signals, that regulate the MMP by down-regulation of Bcl2 and up-regulation of Bax, triggering the cytochrome c release from mitochondria to cytosol. The release of cytochrome c triggered the activation of caspases-9, then activates downstream executioner caspase-3/7 and consequently cleaved specific substrates leading to apoptotic changes. This form of apoptosis was found closely associated with the extrinsic pathway caspase (caspase-8) and inhibition of translocation of NF-κB from cytoplasm to nucleus. The results demonstrated that PA induced apoptosis of MCF7 cells through NF-κB and Bcl2/Bax signaling pathways with the involvement of caspases.

Mxi2 sustains ERK1/2 phosphorylation in the nucleus by preventing ERK1/2 binding to phosphatases

ERK1/2 (extracellular-signal-regulated kinase 1/2) MAPKs (mitogen-activated protein kinases) are tightly regulated by the cellular microenvironment in which they operate. Mxi2 is a p38α splice isoform capable of binding to ERK1/2 and ensuring their translocation to the nucleus. Therein Mxi2 sustains ERK1/2 phosphorylation levels and, as a consequence, ERK1/2 nuclear signals are enhanced. However, the molecular mechanisms underlying this process are still unclear. In the present study, we show that Mxi2 prevents nuclear but not cytoplasmic phosphatases from binding to and dephosphorylating ERK1/2, disclosing an unprecedented mechanism for the spatial regulation of ERK1/2 activation. We also demonstrate that the kinetics of ERK1/2 extranuclear signals can be significantly altered by artificially tethering Mxi2 to the cytoplasm. In this case, Mxi2 abolishes ERK1/2 inactivation by cytoplasmic phosphatases and potentiates ERK1/2 functions at this compartment. These results highlight Mxi2 as a key spatial regulator of ERK1/2 functions, playing a pivotal role in the balance between ERK1/2 nuclear and cytoplasmic signals.

SPARCL1, Shp2, MSH2, E-cadherin, p53, ADCY-2 and MAPK are prognosis-related in colorectal cancer

AIM: To investigate the expression of markers that are correlated with the prognosis of colorectal cancer (CRC) patients.

METHODS: One hundred and fifty-six CRC patients were followed up for more than 3 years after radical surgery. Immunohistochemical (IHC) analysis was performed to detect the expression of 14 pathway-related markers (p53, APC, p21ras, E-cadherin, endothelin-B receptor, Shp2, ADCY-2, SPARCL1, neuroligin1, hsp27, mmp-9, MAPK, MSH2 and rho) in specimens from these patients. Bioinformatics analysis involving a Support Vector Machine (SVM) was used to determine the best prognostic model from combinations of these markers.

RESULTS: Seven markers (SPARCL1, Shp2, MSH2, E-cadherin, p53, ADCY-2 and MAPK) were significantly related to the prognosis and clinical pathological features of the CRC patients (P < 0.05). Prognostic models were established through SVM from combinations of these 7 markers and proved able to differentiate patients with dissimilar survival, especially in stage II/III patients. According to the best prognostic model, the p53/SPARCL1 model, patients having high p53 and low SPARCL1 expression had about 50% lower 3-year survival than others (P < 0.001).

CONCLUSION: SPARCL1, Shp2, MSH2, E-cadherin, p53, ADCY-2 and MAPK are potential prognostic markers in CRC. A p53/SPARCL1 bioinformatics model may be used as a supplement to tumor-nodes-metastasis staging.

The Ras-ERK pathway: understanding site-specific signaling provides hope of new anti-tumor therapies

Recent discoveries have suggested the concept that intracellular signals are the sum of multiple, site-specified subsignals, rather than single, homogeneous entities. In the context of cancer, searching for compounds that selectively block subsignals essential for tumor progression, but not those regulating "house-keeping" functions, could help in producing drugs with reduced side effects compared to compounds that block signaling completely. The Ras-ERK pathway has become a paradigm of how space can differentially shape signaling. Today, we know that Ras proteins are found in different plasma membrane microdomains and endomembranes. At these localizations, Ras is subject to site-specific regulatory mechanisms, distinctively engaging effector pathways and switching-on diverse genetic programs to generate different biological responses. The Ras effector pathway leading to ERKs activation is also under strict, space-related regulatory processes. These findings may open a gate for aiming at the Ras-ERK pathway in a spatially restricted fashion, in our quest for new anti-tumor therapies.

p21(Cip1) confers resistance to imatinib in human chronic myeloid leukemia cells

Imatinib is a Bcr-Abl inhibitor used as first-line therapy of chronic myeloid leukemia (CML). p21(Cip1), initially described as a cell cycle inhibitor, also protects from apoptosis in some models. We describe that imatinib down-regulates p21(Cip1) expression in CML cells. Using K562 cells with inducible p21 expression and transient transfections we found that p21 confers partial resistance to imatinib-induced apoptosis. This protection is not related to the G2-arrest provoked by p21, a decrease in the imatinib activity against Bcr-Abl or a cytoplasmic localization of p21. The results suggest an involvement of p21(Cip1) in the response to imatinib in CML.

The ERK signaling cascade--views from different subcellular compartments

The extracellular signal-regulated kinase cascade is a central signaling pathway that is stimulated by various extracellular stimuli. The signals of these stimuli are then transferred by the cascade's components to a large number of targets at distinct subcellular compartments, which in turn induce and regulate a large number of cellular processes. To achieve these functions, the cascade exhibits versatile and dynamic subcellular distribution that allows proper temporal and spatial modulation of the appropriate processes. In this review, we discuss the intracellular localizations of different components of the ERK cascade, and the impact of these localizations on their activation and specificity.

The constitutive activity of the ghrelin receptor attenuates apoptosis via a protein kinase C-dependent pathway

The ghrelin receptor (GHS-R1a) displays a high level of constitutive signaling through a phospholipase C/protein kinase C-dependent pathway. Therefore, we have investigated the role of agonist-dependent and agonist-independent signaling of GHS-R1a in apoptosis using the seabream GHS-R1a stably expressed in human embryonic kidney 293 cells (HEK-sbGHS-R1a cells). Cadmium-induced activation of caspase-3 was significantly attenuated in HEK-sbGHS-R1a cells compared to wild-type HEK293 cells, while the apoptotic responses to the protein kinase C inhibitor staurosporine were similar. GHS-R1a ligands had no effect on caspase-3 activation or on cell proliferation. Concentrations of the inverse agonist [d-Arg(1),d-Phe(5),d-Trp(7,9),Leu(11)]-substance P sufficient to inhibit constitutive inositol phosphate generation did not enhance caspase-3 activity, suggesting a possible role of phosphatidylcholine-specific phospholipase C in the anti-apoptotic activity of GHS-R1a. In conclusion, our data suggests that the constitutive activity of sbGHS-R1a may be sufficient alone to attenuate apoptosis via a protein kinase C-dependent pathway.

Ras subcellular localization defines extracellular signal-regulated kinase 1 and 2 substrate specificity through distinct utilization of scaffold proteins

Subcellular localization influences the nature of Ras/extracellular signal-regulated kinase (ERK) signals by unknown mechanisms. Herein, we demonstrate that the microenvironment from which Ras signals emanate determines which substrates will be preferentially phosphorylated by the activated ERK1/2. We show that the phosphorylation of epidermal growth factor receptor (EGFr) and cytosolic phospholipase A(2) (cPLA(2)) is most prominent when ERK1/2 are activated from lipid rafts, whereas RSK1 is mainly activated by Ras signals from the disordered membrane. We present evidence indicating that the underlying mechanism of this substrate selectivity is governed by the participation of different scaffold proteins that distinctively couple ERK1/2, activated at defined microlocalizations, to specific substrates. As such, we show that for cPLA(2) activation, ERK1/2 activated at lipid rafts interact with KSR1, whereas ERK1/2 activated at the endoplasmic reticulum utilize Sef-1. To phosphorylate the EGFr, ERK1/2 activated at lipid rafts require the participation of IQGAP1. Furthermore, we demonstrate that scaffold usage markedly influences the biological outcome of Ras site-specific signals. These results disclose an unprecedented spatial regulation of ERK1/2 substrate specificity, dictated by the microlocalization from which Ras signals originate and by the selection of specific scaffold proteins.

Essential role of ERK dimers in the activation of cytoplasmic but not nuclear substrates by ERK-scaffold complexes

Signals transmitted by ERK MAP kinases regulate the functions of multiple substrates present in the nucleus and in the cytoplasm. ERK signals are optimized by scaffold proteins that modulate their intensity and spatial fidelity. Once phosphorylated, ERKs dimerize, but how dimerization impacts on the activation of the different pools of substrates and whether it affects scaffolds functions as spatial regulators are unknown aspects of ERK signaling. Here we demonstrate that scaffolds and ERK dimers are essential for the activation of cytoplasmic but not nuclear substrates. Dimerization is critical for connecting the scaffolded ERK complex to cognate cytoplasmic substrates. Contrarily, nuclear substrates associate to ERK monomers. Furthermore, we show that preventing ERK dimerization is sufficient for attenuating cellular proliferation, transformation, and tumor development. Our results disclose a functional relationship between scaffold proteins and ERK dimers and identify dimerization as a key determinant of the spatial specificity of ERK signals.

Phosphorylation of protein kinase Cdelta on distinct tyrosine residues induces sustained activation of Erk1/2 via down-regulation of MKP-1: role in the apoptotic effect of etoposide

The mechanism underlying the important role of protein kinase Cdelta (PKCdelta) in the apoptotic effect of etoposide in glioma cells is incompletely understood. Here, we examined the role of PKCdelta in the activation of Erk1/2 by etoposide. We found that etoposide induced persistent activation of Erk1/2 and nuclear translocation of phospho-Erk1/2. MEK1 inhibitors decreased the apoptotic effect of etoposide, whereas inhibitors of p38 and JNK did not. The activation of Erk1/2 by etoposide was downstream of PKCdelta since the phosphorylation of Erk1/2 was inhibited by a PKCdelta-KD mutant and PKCdelta small interfering RNA. We recently reported that phosphorylation of PKCdelta on tyrosines 64 and 187 was essential for the apoptotic effect of etoposide. Using PKCdeltatyrosine mutants, we found that the phosphorylation of PKCdeltaon these tyrosine residues, but not on tyrosine 155, was also essential for the activation of Erk1/2 by etoposide. In contrast, nuclear translocation of PKCdelta was independent of its tyrosine phosphorylation and not necessary for the phosphorylation of Erk1/2. Etoposide induced down-regulation of kinase phosphatase-1 (MKP-1), which correlated with persistent phosphorylation of Erk1/2 and was dependent on the tyrosine phosphorylation of PKCdelta. Moreover, silencing of MKP-1 increased the phosphorylation of Erk1/2 and the apoptotic effect of etoposide. Etoposide induced polyubiquitylation and degradation of MKP-1 that was dependent on PKCdelta and on its tyrosine phosphorylation. These results indicate that distinct phosphorylation of PKCdeltaon tyrosines 64 and 187 specifically activates the Erk1/2 pathway by the down-regulation of MKP-1, resulting in the persistent phosphorylation of Erk1/2 and cell apoptosis.

The pheromone-induced nuclear accumulation of the Fus3 MAPK in yeast depends on its phosphorylation state and on Dig1 and Dig2

BACKGROUND

Like mammalian MAP kinases, the mating-specific Fus3 MAPK of yeast accumulates in the nuclei of stimulated cells. Because Fus3 does not appear to be subjected to active nucleo-cytoplasmic transport, it is not clear how its activation by mating pheromone effects the observed change in its localization. One possibility is that the activation of Fus3 changes its affinity for nuclear and cytoplasmic tethers.

RESULTS

Dig1, Dig2, and Ste12 are nuclear proteins that interact with Fus3. We found that the pheromone-induced nuclear accumulation of a Fus3-GFP reporter is reduced in cells lacking Dig1 or Dig2, whereas Fus3T180AY182A-GFP localization was unaffected by the absence of these proteins. This suggests that Dig1 and Dig2 contribute to the retention of phosphorylated Fus3 in the nucleus. Moreover, overexpression of Ste12 caused the hyper-accumulation of Fus3-GFP (but not Fus3T180AY182A-GFP) in the nuclei of pheromone-treated cells, suggesting that Ste12 also plays a role in the nuclear retention of phosphorylated Fus3, either by directly interacting with it or by transcribing genes whose protein products are Fus3 tethers. We have previously reported that overexpression of the Msg5 phosphatase inhibits the nuclear localization of Fus3. Here we show that this effect depends on the phosphatase activity of Msg5, and provide evidence that both nuclear and cytoplasmic Msg5 can affect the localization of Fus3.

CONCLUSION

Our data are consistent with a model in which the pheromone-induced phosphorylation of Fus3 increases its affinity for nuclear tethers, which contributes to its nuclear accumulation and is antagonized by Msg5.

The Localization of Protein Kinase Cδ in Different Subcellular Sites Affects Its Proapoptotic and Antiapoptotic Functions and the Activation of Distinct Downstream Signaling Pathways

Protein kinase Cdelta (PKCdelta) regulates cell apoptosis and survival in diverse cellular systems. PKCdelta translocates to different subcellular sites in response to apoptotic stimuli; however, the role of its subcellular localization in its proapoptotic and antiapoptotic functions is just beginning to be understood. Here, we used a PKCdelta constitutively active mutant targeted to the cytosol, nucleus, mitochondria, and endoplasmic reticulum (ER) and examined whether the subcellular localization of PKCdelta affects its apoptotic and survival functions. PKCdelta-Cyto, PKCdelta-Mito, and PKCdelta-Nuc induced cell apoptosis, whereas no apoptosis was observed with the PKCdelta-ER. PKCdelta-Cyto and PKCdelta-Mito underwent cleavage, whereas no cleavage was observed in the PKCdelta-Nuc and PKCdelta-ER. Similarly, caspase-3 activity was increased in cells overexpressing PKCdelta-Cyto and PKCdelta-Mito. In contrast to the apoptotic effects of the PKCdelta-Cyto, PKCdelta-Mito, and PKCdelta-Nuc, the PKCdelta-ER protected the cells from tumor necrosis factor-related apoptosis-inducing ligand-induced and etoposide-induced apoptosis. Moreover, overexpression of a PKCdelta kinase-dead mutant targeted to the ER abrogated the protective effect of the endogenous PKCdelta and increased tumor necrosis factor-related apoptosis-inducing ligand-induced apoptosis. The localization of PKCdelta differentially affected the activation of downstream signaling pathways. PKCdelta-Cyto increased the phosphorylation of p38 and decreased the phosphorylation of AKT and the expression of X-linked inhibitor of apoptosis protein, whereas PKCdelta-Nuc increased c-Jun NH(2)-terminal kinase phosphorylation. Moreover, p38 phosphorylation and the decrease in X-linked inhibitor of apoptosis protein expression played a role in the apoptotic effect of PKCdelta-Cyto, whereas c-Jun NH(2)-terminal kinase activation mediated the apoptotic effect of PKCdelta-Nuc. Our results indicate that the subcellular localization of PKCdelta plays important roles in its proapoptotic and antiapoptotic functions and in the activation of downstream signaling pathways.

Simvastatin reduces insulin-like growth factor-1 signaling in differentiating C2C12 mouse myoblast cells in an HMG-CoA reductase inhibition-independent manner

Inhibitors of 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase occasionally cause myopathy characterized by weakness, pain, and elevated serum creatine phosphokinase (CK). In this study, we investigated the effects of simvastatin, an HMG-CoA reductase inhibitor, on the viability and insulin-like growth factor-1 (IGF-1) signaling in differentiating C2C12 mouse myoblast cells. Simvastatin decreased cell viability and CK activity, a marker of myogenesis, in differentiating cells in a dose-dependent manner. Although the simvastatin-induced decrease in viability in proliferating and differentiated cells was completely abolished by mevalonate or geranylgeranyl-pyrophosphate, the inhibitory effects of simvastatin in differentiating cells were not abolished by mevalonate or isoprenoid derivatives of mevalonate. Moreover, the sensitivity of differentiating cells to simvastatin regarding cell viability was about 7 times higher than that of proliferating cells. After induction of differentiation in the presence of 1 microM simvastatin for 2 days, IGF-1-induced activation of ERK1/2 and Akt was significantly decreased. Although mRNA expression of the IGF-1 receptor beta-chain (IGF-1R beta) did not change, protein level of the 200 kDa IGF-1Rbeta precursor was significantly increased by simvastatin in a dose-dependent manner. Mevalonate did not abolish the effect of simvastatin on IGF-1Rbeta expression. These results suggest that simvastatin decreases IGF-1 signaling via a regulation of the post-translational modification of IGF-1Rbeta in an HMG-CoA reductase inhibition-independent manner.

Mxi2 promotes stimulus-independent ERK nuclear translocation

Spatial regulation of ERK1/2 MAP kinases is an essential yet largely unveiled mechanism for ensuring the fidelity and specificity of their signals. Mxi2 is a p38alpha isoform with the ability to bind ERK1/2. Herein we show that Mxi2 has profound effects on ERK1/2 nucleocytoplasmic distribution, promoting their accumulation in the nucleus. Downregulation of endogenous Mxi2 by RNAi causes a marked reduction of ERK1/2 in the nucleus, accompanied by a pronounced decline in cellular proliferation. We demonstrate that Mxi2 functions in nuclear shuttling of ERK1/2 by enhancing the nuclear accumulation of both phosphorylated and unphosphorylated forms in the absence of stimulation. This process requires the direct interaction of both proteins and a high-affinity binding of Mxi2 to ERK-binding sites in nucleoporins, In this respect, Mxi2 acts antagonistically to PEA15, displacing it from ERK1/2 complexes. These results point to Mxi2 as a key spatial regulator for ERK1/2 and disclose an unprecedented stimulus-independent mechanism for ERK nuclear import.

Nuclear factor-kappaB p65 inhibits mitogen-activated protein kinase signaling pathway in radioresistant breast cancer cells

The molecular mechanism by which tumor cells increase their resistance to therapeutic radiation remains to be elucidated. We have previously reported that activation of nuclear factor-kappaB (NF-kappaB) is causally associated with the enhanced cell survival of MCF+FIR cells derived from breast cancer MCF-7 cells after chronic exposure to fractionated ionizing radiation. The aim of the present study was to reveal the context of NF-kappaB pathways in the adaptive radioresistance. Using cell lines isolated from MCF+FIR populations, we found that the elevated NF-kappaB activity was correlated with enhanced clonogenic survival, and increased NF-kappaB subunit p65 levels were associated with a decrease in phosphorylation of mitogen-activated protein kinase/extracellular signal-regulated kinase (ERK) kinase (MEK)/ERK in all radioresistant MCF+FIR cell lines. Further irradiation with 30 fractions of radiation also inhibited MEK/ERK phosphorylation in paired cell lines of MCF+FIR and parental MCF-7 cells. Activation of ataxia-telangiectasia mutated (ATM) protein, a sensor to radiation-induced DNA damage, was elevated with increased interaction with NF-kappaB subunits p65 and p50. The interaction between p65 and MEK was also enhanced in the presence of activated ATM. In contrast, both interaction and nuclear translocation of p65/ERK were reduced. Inhibition of NF-kappaB by overexpression of mutant IkappaB increased ERK phosphorylation. In addition, MEK/ERK inhibitor (PD98059) reduced the interaction between p65 and ERK. Taken together, these results suggest that NF-kappaB inhibits ERK activation to enhance cell survival during the development of tumor adaptive radioresistance.

Diverse pathways for nuclear signaling by G protein‐coupled receptors and their ligands

Recent realization that plasma membrane G protein-coupled receptors (GPCRs) may translocate and establish ligand-responsive signaling complexes in other cellular structures has motivated studies of site-specific differences in transductional pathways. GPCRs and their ligands may signal transcription and other nuclear events by two basic mechanisms. The first consists of GPCR-complex activation of messengers that enter the nucleus and there initiate cell-modifying processes without the GPCR leaving the plasma membrane. The second encompasses entry into the nuclear membranes or matrix of either GPCR ligands, which bind to non-GPCR nuclear signaling proteins, proteolytic fragments of GPCRs capable of ligand-independent signaling, or intact GPCRs with transduction-competent factors that directly initiate or regulate transcriptional events. With the second mechanism, often concurrent down-regulation of plasma membrane GPCRs terminates signaling from the cell-surface and moves it into the nuclear domain. Site-dependent differences in signals from the same GPCR provide potentials for unique cellular abnormalities attributable to defective intracellular movement and distribution of a GPCR, site-specific alterations in ligand concentration, and limited intracellular bioavailability of pharmacological agents that can interact specifically with both nuclear and plasma membrane forms of a GPCR.

Focal adhesion kinase mediates cell survival via NF-kappaB and ERK signaling pathways

Focal adhesion kinase (FAK) is important to cellular functions such as proliferation, migration, and survival of anchorage-dependent cells. We investigated the role of FAK in modulating normal cellular responses, specifically cell survival in response to inflammatory stimuli and serum withdrawal, using FAK-knockout (FAK(-/-)) embryonic fibroblasts. FAK(-/-) fibroblasts were more vulnerable to TNF-alpha-induced apoptosis, as measured by terminal deoxynucleotidyl transferase positivity. FAK(-/-) fibroblasts also demonstrated increased procaspase-3 cleavage to p17 subunit, whereas this was undetectable in FAK(+/+) fibroblasts. Insulin receptor substrate-1 expression was completely abolished and NF-kappaB activity was reduced, with a concomitant decrease in abundance of the anti-apoptotic protein Bcl-x(L) in FAK(-/-) cells. Upon serum withdrawal, FAK(+/+) cells exhibited marked attenuation of basal ERK phosphorylation, while FAK(-/-) cells, in contrast, maintained high basal ERK phosphorylation. Moreover, inhibition of ERK phosphorylation potentiated serum withdrawal-induced caspase-3 activity. This was paralleled by increased insulin receptor substrate (IRS)-2 expression in FAK(-/-) cells, although both insulin- and IGF-1-mediated phosphorylation of Akt/PKB and GSK-3 were impaired. This suggests that IRS-2 protects against apoptosis upon serum withdrawal via the ERK signaling pathway. The specific role of FAK to protect cells from apoptosis is regulated by activation and phosphorylation of NF-kappaB and interaction between activated growth factor anti-apoptotic signaling pathways involving both phosphatidylinositol 3-kinase/Akt and MAPK/ERK1/2. We demonstrate that FAK is necessary for upregulation of the anti-apoptotic NF-kappaB response, as well as for normal expression of growth factor signaling proteins. Thus we propose a novel role for FAK in protection from cytokine-mediated apoptosis.

The MEK/ERK cascade: from signaling specificity to diverse functions

The ERK signaling cascade is a central MAPK pathway that plays a role in the regulation of various cellular processes such as proliferation, differentiation, development, learning, survival and, under some conditions, also apoptosis. The ability of this cascade to regulate so many distinct, and even opposing, cellular processes, raises the question of signaling specificity determination by this cascade. Here we describe mechanisms that cooperate to direct MEK-ERK signals to their appropriate downstream destinations. These include duration and strength of the signals, interaction with specific scaffolds, changes in subcellular localization, crosstalk with other signaling pathways, and presence of multiple components with distinct functions in each tier of the cascade. Since many of the mechanisms do not function properly in cancer cells, understanding them may shed light not only on the regulation of normal cell proliferation, but also on mechanisms of oncogenic transformation.

A high nuclear basal level of ERK2 phosphorylation contributes to the resistance of cisplatin-resistant human ovarian cancer cells

OBJECTIVE

The aim of this study was to elucidate the role of ERK1/2 on cisplatin resistance in human ovarian cancer cells.

METHODS

The relationship between nuclear levels of ERK2 and cisplatin-induced apoptosis in human ovarian carcinoma cell line, OVCAR-3, and in cells of the cisplatin-resistant subclone, OVCAR-3/CDDP, was examined using immunoblotting and immunocytochemistry.

RESULTS

Cisplatin treatment resulted in the activation of ERK2, both in OVCAR-3 and OVCAR-3/CDDP cells. However, considerable levels of activated ERK2 existed in the nuclei of OVCAR-3/CDDP cells during serum starvation and in the early period (1-3 h) after cisplatin treatment. Conversely, phospho-ERK2 was marginally detected in the nuclei of OVCAR-3 cells prior to cisplatin treatment. These phenomena were confirmed by immunofluorescence staining of the phosphorylated ERK2 in the nuclei of both cells. High basal phospho-ERK2 in the nuclei of OVCAR-3/CDDP cells contributed to cisplatin resistance, and was supported by several observations; (1) treatment of U0126, an inhibitor of MEK/ERK signaling pathway, partially sensitized OVCAR-3/CDDP cells to cisplatin; (2) pretreatment of OVCAR-3 cells with phorbol 12-myristate 13-acetate (PMA), an activator of ERK, induced nuclear translocation of activated ERK2, which led to the suppression of cisplatin-induced apoptosis.

CONCLUSIONS

These results collectively indicate that prelocalization of activated ERK2 in the nuclei contribute to cisplatin resistance in OVCAR-3/CDDP cells.

c-Abl Expression in Chronic Lymphocytic Leukemia Cells: Clinical and Therapeutic Implications

c-Abl is important for normal B-cell development, but little is known about the function of this nonreceptor tyrosine kinase in chronic lymphocytic leukemia (CLL). Therefore, the aim of the present study was to examine the clinical, therapeutic, and pathogenetic importance of c-Abl in this disease. We show that the malignant cells of CLL predominantly express the type 1b splice variant of c-Abl and that the expression of c-Abl protein is higher in CLL cells than in normal peripheral blood B cells. Moreover, we show that the levels of c-Abl protein expression correlate positively with tumor burden and disease stage, and negatively with IgVH mutation. We also show that STI-571, an inhibitor of c-Abl kinase activity, induces apoptosis of CLL cells with high c-Abl expression levels through a mechanism involving inhibition of nuclear factor κB. We conclude that overexpression of c-Abl is likely to play a pathogenetic role in CLL and that STI-571 may be of potential use in the treatment of this disease. (Cancer Res 2006; 66(15): 7801-9)

Gene-mediated osteogenic differentiation of stem cells by bone morphogenetic proteins-2 or -6

Bone marrow-derived mesenchymal stem cells (BMDMSC) hold promise for targeted osteogenic differentiation and can be augmented by delivery of genes encoding bone morphogenetic proteins (BMP). The feasibility of promoting osteogenic differentiation of BMDMSC was investigated using two BMP genes in monolayer and three-dimensional alginate culture systems. Cultured BMDMSC were transduced with E1-deleted adenoviral vectors containing either human BMP2 or BMP6 coding sequence under cytomegalovirus (CMV) promoter control [17:1 multiplicities of infection (moi)] and either sustained in monolayer or suspended in 1 mL 1.2% alginate beads for 22 days. Adenovirus (Ad)-BMP-2 and Ad-BMP-6 transduction resulted in abundant BMP-2 and BMP-6 mRNA and protein expression in monolayer culture and BMP-2 protein expression in alginate cultures. Ad-BMP-2 and Ad-BMP-6 transduced BMDMSC in monolayer had earlier and robust alkaline phosphatase-positive staining and mineralization and were sustained for a longer duration with better morphology scores than untransduced or Ad-beta-galactosidase-transduced cells. Ad-BMP-2- and, to a lesser degree, Ad-BMP-6-transduced BMDMSC suspended in alginate demonstrated greater mineralization than untransduced cells. Gene expression studies at day 2 confirmed an inflammatory response to the gene delivery process with upregulation of interleukin 8 and CXCL2. Upregulation of genes consistent with response to BMP exposure and osteogenic differentiation, specifically endochondral ossification and extracellular matrix proteins, occurred in BMP-transduced cells. These data support that transduction of BMDMSC with Ad-BMP-2 or Ad-BMP-6 can accelerate osteogenic differentiation and mineralization of stem cells in culture, including in three-dimensional culture. BMP-2-transduced stem cells suspended in alginate culture may be a practical carrier system to support bone formation in vivo. BMP-6 induced a less robust cellular response than BMP-2, particularly in alginate culture.

Contrasting actions of prolonged mitogen-activated protein kinase activation on cell survival

Activation of the ERK mitogen-activated protein kinase pathway has been implicated in pro-survival and cellular protective mechanisms, so that chronic ERK activation may be a useful therapeutic strategy. Here, we further explored the consequences of prolonged ERK activation following expression of constitutively active form of MEK, MEK-EE, in cardiac myocytes. We confirmed that chronic MEK-EE overexpression halved myocyte death following glucose deprivation, but surprisingly this was not associated with preserved intracellular ATP levels. Whilst activities of a number of antioxidant enzymes were not altered upon MEK-EE expression, paradoxically Cu/Zn superoxide dismutase activity was almost halved upon MEK-EE expression. When we then exposed myocytes to the superoxide generator menadione, we observed significantly higher death of MEK-EE expressing myocytes. Pre-incubation with U0126 inhibited menadione-induced death. Our results are the first to show that MEK-ERK signalling can act to increase or decrease cell survival, the outcome depending on the form of stress stimulus encountered.

Phospho-proteomic immune analysis by flow cytometry: from mechanism to translational medicine at the single-cell level

Understanding a molecular basis for cellular function is a common goal of biomedicine. The complex and dynamic cellular processes underlying physiological processes become subtly or grossly perturbed in human disease. A primary objective is to demystify this complexity by creating and establishing relevant model systems to study important aspects of human disease. Although significant technological advancements over the last decade in both genomic and proteomic arenas have enabled progress, accessing the complexity of cellular interactions that occur in vivo has been a difficult arena in which to make progress. Moreover, there are extensive challenges in translating research tools to clinical applications. Flow cytometry, over the course of the last 40 years, has revolutionized the field of immunology, in both the basic science and clinical settings, as well as having been instrumental to new and exciting areas of discovery such as stem cell biology. Multiparameter machinery and systems exist now to access the heterogeneity of cellular subsets and enable phenotypic characterization and functional assays to be performed on material from both animal models and humans. This review focuses primarily on the development and application of using activation-state readouts of intracellular activity for phospho-epitopes. We present recent work on how a flow cytometric platform is used to obtain mechanistic insight into cellular processes as well as highlight the clinical applications that our laboratory has explored. Furthermore, this review discusses the challenges faced with processing high-content multidimensional and multivariate data sets. Flow cytometry, as a platform that is well situated in both the research and clinical settings, can contribute to drug discovery as well as having utility for both biomarker and patient-stratification.

Regulation of CXCR4-mediated nuclear translocation of extracellular signal-related kinases 1 and 2

Activation of the chemokine receptor CXCR4 by its agonist stromal cell-derived factor 1 (SDF-1) has been associated with cell migration and proliferation in many cell types, but the intracellular signaling cascades are incompletely defined. Here we show that CXCR4-dependent extracellular signal-regulated kinases 1 and 2 (ERK1/2) phosphorylation was mediated through the Ras/Raf pathway, as demonstrated with a dominant-negative Ras mutant and pharmacological inhibitors. The Src inhibitor 4-amino-5-methylphenyl-7-(t-butyl)pyrazolo[3,4-d] pyrimidine (PP1) and the Rho-kinase (ROCK) inhibitor N-(4-pyridyl)-4-(1-aminoethyl)cyclohexanecarboxamide dihydrochloride (Y27632) also attenuated SDF-1-induced ERK1/2 phosphorylation. Involvement of Src could furthermore be demonstrated by Src phosphorylation and by the shortened ERK1/2 phosphorylation in SYF cells, which are Src/Yes/Fyn-deficient compared with Src-reconstituted Src(++) cells. Membrane translocation of RhoA could be detected similarly. A large portion of the SDF-1-mediated ERK phosphorylation was detected in the nucleus, as shown by Western blotting and confocal microscopy, and resulted in the phosphorylation of the transcription factor Elk. It is interesting that the nuclear accumulation of ERK1/2 and Elk phosphorylation was completely blocked by dominant-negative Rho, Y27632, PP1, and latrunculin B, indicating that the Rho/ROCK pathway, Src kinase, and the actin cytoskeleton were required in this process. In accordance, neither nuclear ERK phosphorylation nor Elk phosphorylation were observed in SYF cells stimulated with SDF-1 but were reconstituted in Src(++) cells. In summary, these results demonstrate that Src, Rho/ROCK, and an intact cytoskeleton contribute to overall ERK1/2 activation in SDF-1-stimulated cells and are indispensable for nuclear translocation of ERK1/2 and activation of transcription factors.

Automated Interpretation of Protein Subcellular Location Patterns

Proteomics is a major current focus of biomedical research, and location proteomics is the important branch of proteomics that systematically studies the subcellular distributions for all proteins expressed in a given cell type. Fluorescence microscopy of labeled proteins is currently the main methodology to obtain location information. Traditionally, microscope images are analyzed by visual inspection, which suffers from inefficiency and inconsistency. Automated and objective interpretation approaches are therefore needed for location proteomics. In this article, we briefly review recent advances in automated imaging interpretation tools, including supervised classification (which assigns location pattern labels to previously unseen images), unsupervised clustering (which groups proteins based on the similarity among their subcellular distributions), and additional statistical tools that can aid cell and molecular biologists who use microscopy in their work.

Polycystin-2 regulates proliferation and branching morphogenesis in kidney epithelial cells

Autosomal dominant polycystic kidney disease (ADPKD) is characterized by the formation of multiple fluid-filled cysts that expand over time and destroy the renal architecture. Loss or mutation of polycystin-1 or polycystin-2, the respective proteins encoded by the ADPKD genes PKD1 and PKD2, is associated with most cases of ADPKD. Thus, the polycystin proteins likely play a role in cell proliferation and morphogenesis. Recent studies indicate that polycystin-1 is involved in these processes, but little is known about the role played by polycystin-2. To address this question, we created a number of related cell lines variable in their expression of polycystin-2. We show that the basal and epidermal growth factor-stimulated rate of cell proliferation is higher in cells that do not express polycystin-2 versus those that do, indicating that polycystin-2 acts as a negative regulator of cell growth. In addition, cells not expressing polycystin-2 exhibit significantly more branching morphogenesis and multicellular tubule formation under basal and hepatocyte growth factor-stimulated conditions than their polycystin-2-expressing counterparts, suggesting that polycystin-2 may also play an important role in the regulation of tubulogenesis. Cells expressing a channel mutant of polycystin-2 proliferated faster than those expressing the wild-type protein, but exhibited blunted tubule formation. Thus, the channel activity of polycystin-2 may be an important component of its regulatory machinery. Finally, we show that polycystin-2 regulation of cell proliferation appears to be dependent on its ability to prevent phosphorylated extracellular-related kinase from entering the nucleus. Our results indicate that polycystin-2 is necessary for the proper growth and differentiation of kidney epithelial cells and suggest a possible mechanism for the cyst formation seen in ADPKD2.

Actin cytoskeleton regulates extracellular matrix-dependent survival signals in glomerular epithelial cells

Adhesion of rat glomerular epithelial cells (GEC) to collagen activates focal adhesion kinase (FAK) and the Ras-extracellular signal-regulated kinase (ERK) pathway and supports survival (prevents apoptosis). The present study addresses the relationship between actin organization and the survival phenotype. Parental GEC (adherent to collagen) and GEC stably transfected with constitutively active mutants of mitogen-activated protein kinase kinase (R4F-MEK) or FAK (CD2-FAK) (on plastic) showed ERK activation, low levels of apoptosis, and a cortical distribution of F-actin. Parental GEC adherent to plastic showed increased apoptosis, disorganization of cortical F-actin, and formation of prominent stress fibers. Assembly of cortical F-actin was, at least in part, mediated via ERK. However, disruption of the actin cytoskeleton with cytochalasin D or latrunculin B in parental GEC (on collagen) and in GEC that express R4F-MEK or CD2-FAK (on plastic) decreased ERK activation and increased apoptosis. Expression of a constitutively active RhoA (L(63)RhoA) induced assembly of cortical F-actin, promoted ERK activation, and supplanted the requirement of collagen for survival. Adhesion of GEC to collagen increased phosphatidylinositol-4,5-bisphosphate (PIP(2)). Downregulation or sequestration of PIP(2) by transfection with an inositol 5'-phosphatase or the plextrin-homology domain of phospholipase C-delta1 decreased F-actin content and survival. Moreover, overexpression of wild-type or K256E mutant alpha-actinin-4 with increased affinity for F-actin increased apoptosis. These results demonstrate a reciprocal relationship between collagen-induced cortical F-actin assembly and collagen-dependent survival signaling, including ERK activation. Appropriate remodeling of the actin cytoskeleton may be necessary for facilitating survival, as both disassembly and excessive crosslinking affect survival adversely.

Cytoplasmic retention of peroxide-activated ERK provides survival in primary cultures of rat hepatocytes

Reactive oxygen species (ROS) are implicated in tissue damage causing primary hepatic dysfunction following ischemia/reperfusion injury and during inflammatory liver diseases. A potential role of extracellular signal-regulated kinase (ERK) as a mediator of survival signals during oxidative stress was investigated in primary cultures of hepatocytes exposed to ROS. Hydrogen peroxide (H(2)O(2)) induced a dose-dependent activation of ERK, which was dependent on MEK activation. The ERK activation pattern was transient compared with the ERK activation seen after stimulation with epidermal growth factor (EGF). Nuclear accumulation of ERK was found after EGF stimulation, but not after H(2)O(2) exposure. A slow import/rapid export mechanism was excluded through the use of leptomycin B, an inhibitor of nuclear export sequence-dependent nuclear export. Reduced survival of hepatocytes during ROS exposure was observed when ERK activation was inhibited. Ribosomal S6 kinase (RSK), a cytoplasmic ERK substrate involved in cell survival, was activated and located in the nucleus of H(2)O(2)-exposed hepatocytes. The activation was abolished when ERK was inhibited with U0126. In conclusion, our results indicate that activity of ERK in the cytoplasm is important for survival during oxidative stress in hepatocytes and that RSK is activated downstream of ERK. Supplementary material for this article can be found on the HEPATOLOGY website (http://www.interscience.wiley.com/jpages/0270-9139/suppmat/index.html).

Co-activation of ERK, NF-kappaB, and GADD45beta in response to ionizing radiation

NF-kappaB has been well documented to play a critical role in signaling cell stress reactions. The extracellular signal-regulated kinase (ERK) regulates cell proliferation and survival. GADD45beta is a primary cell cycle element responsive to NF-kappaB activation in anti-apoptotic responses. The present study provides evidence demonstrating that NK-kappaB, ERK and GADD45beta are co-activated by ionizing radiation (IR) in a pattern of mutually dependence to increase cell survival. Stress conditions generated in human breast cancer MCF-7 cells by the administration of a single exposure of 5 Gy IR resulted in the activation of ERK but not p38 or JNK, along with an enhancement of the NF-kappaB transactivation and GADD45beta expression. Overexpression of dominant negative Erk (DN-Erk) or pre-exposure to ERK inhibitor PD98059 inhibited NF-kappaB. Transfection of dominant negative mutant IkappaB that blocks NF-kappaB nuclear translocation, inhibited ERK activity and GADD45beta expression and increased cell radiosensitivity. Interaction of p65 and ERK was visualized in living MCF-7 cells by bimolecular fluorescence complementation analysis. Antisense inhibition of GADD45beta strikingly blocked IR-induced NF-kappaB and ERK but not p38 and JNK. Overall, these results demonstrate a possibility that NF-kappaB, ERK, and GADD45beta are able to coordinate in a loop-like signaling network to defend cells against the cytotoxicity induced by ionizing radiation.

Bisphosphonates and estrogens inhibit osteocyte apoptosis via distinct molecular mechanisms downstream of extracellular signal-regulated kinase activation

Both estrogens and bisphosphonates attenuate osteocyte apoptosis by activating the extracellular signal-regulated kinases (ERKs). However, whereas estrogens activate ERKs via an extranuclear function of the estrogen receptor, bisphosphonates do so by opening connexin 43 hemichannels. Here, we demonstrated that the signaling events downstream of ERKs induced by these two stimuli are also distinct. Inhibition of osteocyte apoptosis by estrogens requires nuclear accumulation of ERKs and activation of downstream transcription factors. On the other hand, anti-apoptosis induced by bisphosphonates requires neither transcription nor ERK-dependent transcription factors. Instead, the effect of bisphosphonates is abolished when ERKs are restricted to the nucleus by blocking CRM1/exportin1-mediated nuclear protein export or by expressing nuclear-anchored ERKs, but it is unaffected in cells expressing cytoplasmic-anchored ERKs. Connexin 43/ERK-mediated anti-apoptosis induced by bisphosphonates requires the kinase activity of the cytoplasmic target of ERKs, p90(RSK), which in turn phosphorylates the pro-apoptotic protein BAD and C/EBPbeta. Phosphorylation of BAD renders it inactive, whereas phosphorylation of C/EBPbeta leads to binding of pro-caspases, thus inhibiting apoptosis independently of the transcriptional activity of this transcription factor. Consistent with the evidence that estrogens and bisphosphonates phosphorylate diverse targets of ERKs, probably resulting from activation of spatially distinct pools of these kinases, the two agents had additive effects on osteocyte survival.

Myc antagonizes Ras-mediated growth arrest in leukemia cells through the inhibition of the Ras-ERK-p21Cip1 pathway

Even though RAS usually acts as a dominant transforming oncogene, in primary fibroblasts and some established cell lines Ras inhibits proliferation. This can explain the virtual absence of RAS mutations in some types of tumors, such as chronic myeloid leukemia (CML). We report that in the CML cell line K562 Ras induces p21Cip1 expression through the Raf-MEK-ERK pathway. Because K562 cells are deficient for p15INK4b, p16INK4a, p14ARF, and p53, this would be the main mechanism whereby Ras up-regulates p21 expression in these cells. Accordingly, we also found that Ras suppresses K562 growth by signaling through the Raf-ERK pathway. Because c-Myc and Ras cooperate in cell transformation and c-Myc is up-regulated in CML, we investigated the effect of c-Myc on Ras activity in K562 cells. c-Myc antagonized the induction of p21Cip1 mediated by oncogenic H-, K-, and N-Ras and by constitutively activated Raf and ERK2. Activation of the p21Cip1 promoter by Ras was dependent on Sp1/3 binding sites in K562. However, mutational analysis of the p21 promoter and the use of a Gal4-Sp1 chimeric protein strongly suggest that c-Myc affects Sp1 transcriptional activity but not the binding of Sp1 to the p21 promoter. c-Myc-mediated impairment of Ras activity on p21 expression required a transactivation domain, a DNA binding region, and a Max binding region. Moreover, the effect was independent of Miz1 binding to c-Myc. Consistent with its effect on p21Cip1 expression, c-Myc rescued cell growth inhibition induced by Ras. The data suggest that in particular tumor types, such as those associated with CML, c-Myc contributes to tumorigenesis by inhibiting Ras antiproliferative activity.