Erk5 participates in neuregulin signal transduction and is constitutively active in breast cancer cells overexpressing ErbB2

Kinome profiling reveals breast cancer heterogeneity and identifies targeted therapeutic opportunities for triple negative breast cancer

Our understanding of breast cancer heterogeneity at the protein level is limited despite proteins being the ultimate effectors of cellular functions. We investigated the heterogeneity of breast cancer (41 primary tumors and 15 breast cancer cell lines) at the protein and phosphoprotein levels to identify activated oncogenic pathways and developing targeted therapeutic strategies. Heterogeneity was observed not only across histological subtypes, but also within subtypes. Tumors of the Triple negative breast cancer (TNBC) subtype distributed across four different clusters where one cluster (cluster ii) showed high deregulation of many proteins and phosphoproteins. The majority of TNBC cell lines, particularly mesenchymal lines, resembled the cluster ii TNBC tumors. Indeed, TNBC cell lines were more sensitive than non-TNBC cell lines when treated with targeted inhibitors selected based on upregulated pathways in cluster ii. In line with the enrichment of the upregulated pathways with onco-clients of Hsp90, we found synergy in combining Hsp90 inhibitors with several kinase inhibitors, particularly Erk5 inhibitors. The combination of Erk5 and Hsp90 inhibitors was effective in vitro and in vivo against TNBC leading to upregulation of pro-apoptotic effectors. Our studies contribute to proteomic profiling and improve our understanding of TNBC heterogeneity to provide therapeutic opportunities for this disease.

ERK5 pathway regulates transcription factors important for monocytic differentiation of human myeloid leukemia cells

Mitogen-activated protein kinases (MAPKs) are important transducers of external signals for cell growth, survival, and other cellular responses including cell differentiation. Several MAPK cascades are known with the MEK1/2-ERK1/2, JNK, and p38MAPKs receiving most attention, but the role of MEK5-ERK5 in intracellular signaling deserves more scrutiny, as this pathway transmits signals that can complement ERK/2 signaling. We hypothesized that the ERK5 pathway plays a role in the control of monocytic differentiation, which is disturbed in myeloid leukemia. We therefore examined the cellular phenotype and key molecular events which occur when human myeloid leukemia cells, acute (AML) or chronic (CML), are forced to differentiate by vitamin D derivatives (VDDs). This study was performed using established cell lines HL60 and U937, and primary cultures of blasts from 10 patients with ML. We found that ERK5 and its direct downstream target transcription factor MEF2C are upregulated by 1,25D in parallel with monocytic differentiation. Further, inhibition of ERK5 activity by specific pharmacological agents BIX02189 and XMD8-92 alters the phenotype of these cells by reducing the abundance of the VDD-induced surface monocytic marker CD14, and concomitantly increasing surface expression of the general myeloid marker CD11b. Similar results were obtained when the expression of ERK5 was reduced by siRNA or short hairpin (sh) RNA. ERK5 inhibition resulted in an expected decrease in MEF2C activation. We also found that in AML cells the transcription factor C/EBPβ is positively regulated, while C/EBPα is negatively regulated by ERK5. These findings provide new understanding of dysregulated differentiation in human myeloid leukemia.

Role of ERK1, 2, and 5 in dopamine neuron survival during aging

Extracellular signal-regulated kinases (ERKs) 1, 2, and 5 have been shown to play distinct roles in proliferation, differentiation, and neuronal viability. In this study, we examined ERK1, 2, and 5 expression and activation in the substantia nigra (SN), striatum (STR), and ventral tegmental area (VTA) during aging. An age-related decrease in phosphorylated ERK5 was observed in the SN and STR, whereas an increase in total ERK1 was observed in all 3 regions. In primary cultures of the SN and VTA, inhibition of ERK5 but not ERK1 and 2 decreased dopamine neuronal viability significantly. These data suggest that ERK5 is essential for the basal survival of SN and VTA dopaminergic neurons. This is the first study to examine ERK1, 2, and 5 expression and activation in the SN, STR, and VTA during aging, and the relative roles of ERK1, 2, and 5 in basal survival of SN and VTA dopaminergic neurons. These data raise the possibility that a decline in ERK5 signaling may play a role in age-related impairments in dopaminergic function.

ErbB2 upregulates the Na+,HCO3(-)-cotransporter NBCn1/SLC4A7 in human breast cancer cells via Akt, ERK, Src, and Kruppel-like factor 4

Misregulation of acid-base transport plays central roles in cancer development. We previously demonstrated the strong up-regulation of the Na(+),HCO3(-) cotransporter NBCn1 (SLC4A7) in MCF-7 breast cancer cells by a truncated, constitutively active ErbB2 (HER2) receptor, ΔNErbB2, and showed that NBCn1 expression and activity are increased in breast cancer tissue from patients. Here, we present the first in-depth characterization of an SLC4A7 promoter and identify its minimal ΔNErbB2-sensitive region. Inhibition or siRNA-mediated knockdown of PI3K, Akt1, ERK1/2, or Src decreased the NBCn1 protein level in ΔNErbB2-expressing MCF-7 cells by ~50, 60, 30 and 35%, respectively. Further, knockdown of the transcription factor Krüppel-like factor 4 (KLF4) reduced NBCn1 protein expression by ~40%, and KLF4 overexpression increased NBCn1 expression by 50-80%. In contrast, knockdown of the closely related transcription factor specificity protein 1 (Sp1) or transfection with dominant-negative Sp1 increased NBCn1 expression by ~35 and ~50%, respectively. NBCn1 expression was also increased by stimulation of full-length ErbB1, -2, and -3 receptors in SKBr3 cells (1.5- and 2-fold by NRG1 or EGF, respectively) or after their exogenous expression in MCF-7 cells. Finally, stimulation with NRG1 or EGF more than doubled acid extrusion capacity in SKBr3 cells. In conclusion, NBCn1 is strongly upregulated by ErbB receptor signaling in a manner involving opposite effects of KLF4 and Sp1, transcription factors with central roles in cancer development. ErbB-induced up-regulation of NBCn1-mediated acid extrusion may play important physiological and pathophysiological roles in the breast epithelium and other tissues with high ErbB receptor levels.

Modulation of dorsal root ganglion development by ErbB signaling and the scaffold protein Sorbs3

The multipotent cells of the vertebrate neural crest (NC) arise at the dorsal aspect of the neural tube, then migrate throughout the developing embryo and differentiate into diverse cell types, including the sensory neurons and glia of the dorsal root ganglia (DRG). As multiple cell types are derived from this lineage, it is ideal for examining mechanisms of fate restriction during development. We have isolated a mutant, ouchless, that specifically fails to develop DRG neurons, although other NC derivatives develop normally. This mutation affects the expression of Sorbs3, a scaffold protein known to interact with proteins involved in focal adhesions and several signaling pathways. ouchless mutants share some phenotypic similarities with mutants in ErbB receptors, EGFR homologs that are implicated in diverse developmental processes and associated with several cancers; and ouchless interacts genetically with an allele of erbb3 in DRG neurogenesis. However, the defect in ouchless DRG neurogenesis is distinct from ErbB loss of function in that it is not associated with a loss of glia. Both ouchless and neurogenin1 heterozygous fish are sensitized to the effects of ErbB chemical inhibitors, which block the development of DRG in a dose-dependent manner. Inhibitors of MEK show similar effects on DRG neurogenesis. We propose a model in which Sorbs3 helps to integrate ErbB signals to promote DRG neurogenesis through the activation of MAPK and upregulation of neurogenin1.

Role of p90(RSK) in regulating the Crabtree effect: implications for cancer

High glucose inhibits mitochondrial respiration, known as the 'Crabtree effect', in cancer cells and possibly other cell types. The upstream pathways regulating this phenomenon are poorly understood. In diabetes, where glucose levels are elevated, the p90(RSK) (p90 ribosomal S6 kinase) has received much attention as a potential upstream mediator of the effects of high glucose. Evidence is also emerging that p90(RSK) may play a role in cancer cell signalling, although the role of p90(RSK) in regulating cancer cell metabolism is unclear. In the present paper, we provide an overview of the Crabtree effect and its relationship to mitochondrial metabolism. Furthermore, preliminary data are presented suggesting a role for p90(RSK) and its upstream components, the ERK (extracellular-signal-regulated kinase) family of MAPKs (mitogen-activated protein kinases), in the Crabtree effect.

MEK and the inhibitors: from bench to bedside

Four distinct MAP kinase signaling pathways involving 7 MEK enzymes have been identified. MEK1 and MEK2 are the prototype members of MEK family proteins. Several MEK inhibitors are in clinical trials. Trametinib is being evaluated by FDA for the treatment of metastatic melanoma with BRAF V600 mutation. Selumetinib has been studied in combination with docetaxel in phase II randomized trial in previously treated patients with advanced lung cancer. Selumetinib group had better response rate and progression-free survival. This review also summarized new MEK inhibitors in clinical development, including pimasertib, refametinib, PD-0325901, TAK733, MEK162 (ARRY 438162), RO5126766, WX-554, RO4987655 (CH4987655), GDC-0973 (XL518), and AZD8330.

Potent antimyeloma activity of a novel ERK5/CDK inhibitor

PURPOSE

To analyze the antimyeloma potential of TG02, an ERK5/CDK inhibitory drug.

EXPERIMENTAL DESIGN

Utilizing different multiple myeloma cell lines we determined the effect of TG02 over viability by MTT assays. The apoptotic effect over multiple myeloma patient samples was studied ex vivo by cytometry. The mechanism of action of TG02 was analyzed in the cell line MM1S, studying its effect on the cell cycle, the induction of apoptosis, and the loss of mitochondrial membrane potential by cytometry and Western blot. Two models of multiple myeloma xenograft were utilized to study the in vivo action of TG02.

RESULTS

TG02 potently inhibited proliferation and survival of multiple myeloma cell lines, even under protective bone marrow niche conditions, and selectively induced apoptosis of primary patient-derived malignant plasma cells. TG02 displayed significant single-agent activity in two multiple myeloma xenograft models, and enhanced the in vivo activity of bortezomib and lenalidomide. Signaling analyses revealed that the drug simultaneously blocked the activity of CDKs 1, 2, and 9 as well as the MAP kinase ERK5 in MM1S cells, leading to cell-cycle arrest and rapid commitment to apoptosis. TG02 induced robust activation of both the intrinsic and extrinsic pathways of apoptosis, and depletion of XIAP and the key multiple myeloma survival protein Mcl-1.

CONCLUSIONS

TG02 is a promising new antimyeloma agent that is currently in phase I clinical trials in leukemia and multiple myeloma patients.

Canonical and kinase activity-independent mechanisms for extracellular signal-regulated kinase 5 (ERK5) nuclear translocation require dissociation of Hsp90 from the ERK5-Cdc37 complex

The mitogen-activated protein (MAP) kinase extracellular signal-regulated kinase 5 (ERK5) plays a crucial role in cell proliferation, regulating gene transcription. ERK5 has a unique C-terminal tail which contains a transcriptional activation domain, and activates transcription by phosphorylating transcription factors and acting itself as a transcriptional coactivator. However, the molecular mechanisms that regulate its nucleocytoplasmatic traffic are unknown. We have used tandem affinity purification to identify proteins that interact with ERK5. We show that ERK5 interacts with the Hsp90-Cdc37 chaperone in resting cells, and that inhibition of Hsp90 or Cdc37 results in ERK5 ubiquitylation and proteasomal degradation. Interestingly, activation of cellular ERK5 induces Hsp90 dissociation from the ERK5-Cdc37 complex, leading to ERK5 nuclear translocation and activation of transcription, by a mechanism which requires the autophosphorylation at its C-terminal tail. Consequently, active ERK5 is no longer sensitive to Hsp90 or Cdc37 inhibitors. Cdc37 overexpression also induces Hsp90 dissociation and the nuclear translocation of a kinase-inactive form of ERK5 which retains transcriptional activity. This is the first example showing that ERK5 transcriptional activity does not require kinase activity. Since Cdc37 cooperates with ERK5 to promote cell proliferation, Cdc37 overexpression (as happens in some cancers) might represent a new, noncanonical mechanism by which ERK5 regulates tumor proliferation.

The extracellular-regulated protein kinase 5 (ERK5) promotes cell proliferation through the down-regulation of inhibitors of cyclin dependent protein kinases (CDKs)

Activation of the extracellular-regulated protein kinase 5 (ERK5) has been associated with mitogenic signal transduction. However, conflicting findings have challenged the idea that ERK5 is a critical regulator of cell proliferation. We have addressed this issue by testing the effect of the conditional loss of ERK5 in primary fibroblasts. We have discovered that ERK5 suppressed the expression of the cyclin dependent protein kinase (CDKs) inhibitors, p21 and p27, by decreasing mRNA and protein stability, respectively. As a result, low level CDK2 activity detected in ERK5-deficient cells correlated with a defect in G1 to S phase transition of the cell cycle. Similarly, we found that the malignant MDA-MB-231 human breast cancer cell line was dependent on ERK5 to proliferate. We propose that ERK5 blocks p21 expression in MDA-MB-231 cells via a mechanism that implicates c-Myc-dependent transcriptional regulation of the miR-17-92 cluster. Together with evidence that cancer patients with poor prognosis display a high level of expression of components of the ERK5 signaling pathway, these findings support the hypothesis that ERK5 can be a potential target for cancer therapy.

BMK1 is involved in the regulation of p53 through disrupting the PML-MDM2 interaction

Promyelocytic leukemia protein (PML) modulates the p53 tumor suppressor through its interaction with p53 and MDM2. We found that activated BMK1 preferentially associates with PML isoform IV and disrupts PML-MDM2 interaction. Doxorubicin, a common chemotherapeutic agent, is known to promote PML-mediated p53 activation in part by promoting PML-dependent MDM2 nucleolar sequestration. We discovered that BMK1 deactivation coupled with doxorubicin synergistically enhanced MDM2 nucleolar sequestration and, consequently, promoted PML-mediated p53 up-regulation leading to tumor cell apoptosis in vitro and tumor regression in vivo. Collectively, these results not only suggest that BMK1 activity plays a role in suppressing p53 by blocking the interaction between PML and MDM2 but also implicate that pharmacological BMK1 inhibitor should significantly enhance the anti-cancer capacity of doxorubicin-based chemotherapy.

ERK5: structure, regulation and function

Extracellular signal-regulated kinase 5 (ERK5), also termed big mitogen-activated protein kinase-1 (BMK1), is the most recently identified member of the mitogen-activated protein kinase (MAPK) family and consists of an amino-terminal kinase domain, with a relatively large carboxy-terminal of unique structure and function that makes it distinct from other MAPK members. It is ubiquitously expressed in numerous tissues and is activated by a variety of extracellular stimuli, such as cellular stresses and growth factors, to regulate processes such as cell proliferation and differentiation. Targeted deletion of Erk5 in mice has revealed that the ERK5 signalling cascade plays a critical role in cardiovascular development and vascular integrity. Recent data points to a potential role in pathological conditions such as cancer and tumour angiogenesis. This review focuses on the physiological and pathological role of ERK5, the regulation of this kinase and the recent development of small molecule inhibitors of the ERK5 signalling cascade.

Targeted deletion of ERK5 MAP kinase in the developing nervous system impairs development of GABAergic interneurons in the main olfactory bulb and behavioral discrimination between structurally similar odorants

ERK5 MAP kinase is highly expressed in the developing nervous system and has been implicated in promoting the survival of immature neurons in culture. However, its role in the development and function of the mammalian nervous system has not been established in vivo. Here, we report that conditional deletion of the erk5 gene in mouse neural stem cells during development reduces the number of GABAergic interneurons in the main olfactory bulb (OB). Our data suggest that this is due to a decrease in proliferation and an increase in apoptosis in the subventricular zone and rostral migratory stream of ERK5 mutant mice. Interestingly, ERK5 mutant mice have smaller OB and are impaired in odor discrimination between structurally similar odorants. We conclude that ERK5 is a novel signaling pathway regulating developmental OB neurogenesis and olfactory behavior.

ERK5 and its role in tumour development

The MEK5 [MAPK (mitogen-activated protein kinase)/ERK (extracellular-signal-regulated kinase) kinase 5]/ERK5 pathway is the least well studied MAPK signalling module. It has been proposed to play a role in the pathology of cancer. In the present paper, we review the role of the MEK5/ERK5 pathway using the 'hallmarks of cancer' as a framework and consider how this pathway is deregulated. As well as playing a key role in endothelial cell survival and tubular morphogenesis during tumour neovascularization, ERK5 is also emerging as a regulator of tumour cell invasion and migration. Several oncogenes can stimulate ERK5 activity, and protein levels are increased by a novel amplification at chromosome locus 17p11 and by down-regulation of the microRNAs miR-143 and miR-145. Together, these finding underscore the case for further investigation into understanding the role of ERK5 in cancer.

Expression of the phosphorylated MEK5 protein is associated with TNM staging of colorectal cancer

BACKGROUND

Activation of MEK5 in many cancers is associated with carcinogenesis through aberrant cell proliferation. In this study, we determined the level of phosphorylated MEK5 (pMEK5) expression in human colorectal cancer (CRC) tissues and correlated it with clinicopathologic data.

METHODS

pMEK5 expression was examined by immunohistochemistry in a tissue microarray (TMA) containing 335 clinicopathologic characterized CRC cases and 80 cases of nontumor colorectal tissues. pMEK5 expression of 19 cases of primary CRC lesions and paired with normal mucosa was examined by Western blotting. The relationship between pMEK5 expression in CRC and clinicopathologic parameters, and the association of pMEK5 expression with CRC survival were analyzed respectively.

RESULTS

pMEK5 expression was significantly higher in CRC tissues (185 out of 335, 55.2%) than in normal tissues (6 out of 80, 7.5%; P < 0.001). Western blotting demonstrated that pMEK5 expression was upregulated in 12 of 19 CRC tissues (62.1%) compared to the corresponding adjacent nontumor colorectal tissues. Overexpression of pMEK5 in CRC tissues was significantly correlated to the depth of invasion (P = 0.001), lymph node metastasis (P < 0.001), distant metastasis (P < 0.001) and high preoperative CEA level (P < 0.001). Consistently, the pMEK5 level in CRC tissues was increased following stage progression of the disease (P < 0.001). Analysis of the survival curves showed a significantly worse 5-year disease-free (P = 0.002) and 5-year overall survival rate (P < 0.001) for patients whose tumors overexpressed pMEK5. However, in multivariate analysis, pMEK5 was not an independent prognostic factor for CRC (DFS: P = 0.139; OS: P = 0.071).

CONCLUSIONS

pMEK5 expression is correlated with the staging of CRC and its expression might be helpful to the TNM staging system of CRC.

The colony-stimulating factor-1 (CSF-1) receptor sustains ERK1/2 activation and proliferation in breast cancer cell lines

Breast cancer is the second leading cause of cancer-related deaths in western countries. Colony-Stimulating Factor-1 (CSF-1) and its receptor (CSF-1R) regulate macrophage and osteoclast production, trophoblast implantation and mammary gland development. The expression of CSF-1R and/or CSF-1 strongly correlates with poor prognosis in several human epithelial tumors, including breast carcinomas. We demonstrate that CSF-1 and CSF-1R are expressed, although at different levels, in 16/17 breast cancer cell lines tested with no differences among molecular subtypes. The role of CSF-1/CSF-1R in the proliferation of breast cancer cells was then studied in MDAMB468 and SKBR3 cells belonging to different subtypes. CSF-1 administration induced ERK1/2 phosphorylation and enhanced cell proliferation in both cell lines. Furthermore, the inhibition of CSF-1/CSF-1R signaling, by CSF-1R siRNA or imatinib treatment, impaired CSF-1 induced ERK1/2 activation and cell proliferation. We also demonstrate that c-Jun, cyclin D1 and c-Myc, known for their involvement in cell proliferation, are downstream CSF-1R in breast cancer cells. The presence of a proliferative CSF-1/CSF-1R autocrine loop involving ERK1/2 was also found. The wide expression of the CSF-1/CSF-1R pair across breast cancer cell subtypes supports CSF-1/CSF-1R targeting in breast cancer therapy.

MEK5/ERK5 pathway: the first fifteen years

While conventional MAP kinase pathways are one of the most highly studied signal transduction molecules, less is known about the MEK5 signaling pathway. This pathway has been shown to play a role in normal cell growth cycles, survival and differentiation. The MEK5 pathway is also believed to mediate the effects of a number of oncogenes. MEK5 is the upstream activator of ERK5 in many epithelial cells. Activation of the MEK-MAPK pathway is a frequent event in malignant tumor formation and contributes to chemoresistance and anti-apoptotic signaling. This pathway may be involved in a number of more aggressive, metastatic varieties of cancer due to its role in cell survival, proliferation and EMT transitioning. Further study of this pathway may lead to new prognostic factors and new drug targets to combat more aggressive forms of cancer.

Cross-talk and modulation of signaling between somatostatin and growth factor receptors

The process of homo- and/or heterodimerization of G-protein coupled receptors (GPCRs) and receptor tyrosine kinase (RTK) families are crucial for implicating the fundamental properties of receptor proteins including receptor expression, trafficking, and desensitization as well as signal transduction. The members of GPCR and RTK family constitute largest cell surface receptor proteins and regulate physiological functions of cells in response to external and internal stimuli. Notably, GPCRs and RTKs play major role in regulation of several key cellular functions which are associated with several pathological conditions including cancer biology, neurodegenerative and cardiovascular diseases. The focus of this review is to highlight the recent findings on the possible cross-talk between somatostatin receptors (members of GPCR family) and growth factor receptors like epidermal growth factor receptors (members of RTK family). Furthermore, functional consequences of such an interaction in modulation of signaling pathways linked to pathological conditions specifically in cancer are discussed.

MEK5/ERK5/mef2: a novel signaling pathway affected by hepatitis C virus non-enveloped capsid-like particles

Hepatitis C virus (HCV) is an RNA positive strand virus, member of the Flaviviridae family. The viral particle is composed of a capsid containing the genome, surrounded by E1 and E2 proteins, however different forms of viral particles have been observed including non-enveloped particles. Previous reports have proposed that hepatitis C non-enveloped capsid-like particles (HCVne) enter cells of hepatic origin via clathrin-mediated endocytosis, during which different signaling events occur. In this report we show that HCVne particles are capable of inducing the recently discovered ERK5 pathway, in a dose dependent way. The ERK5 pathway can be activated by growth factors and other extracellular signals. This specific activation occurs through a well characterized upstream kinase, MEK5, and is capable of inducing gene regulation of mef2. In contrast, when HCV core structural and NS5A non-structural proteins were expressed endogenously no activation of this pathway was detected. These cell signaling events could be of critical importance and might give clues for the elucidation of cellular manifestations associated with HCV infection.

Targeting the BMK1 MAP kinase pathway in cancer therapy

The big mitogen activated protein kinase 1 (BMK1) pathway is the most recently discovered and least-studied mammalian mitogen-activated protein (MAP) kinase cascade, ubiquitously expressed in all types of cancer cells tested so far. Mitogens and oncogenic signals strongly activate this cellular MAP kinase pathway, thereby passing down proliferative, survival, chemoresistance, invasive, and angiogenic signals in tumor cells. Recently, several pharmacologic small molecule inhibitors of this pathway have been developed. Among them, the BMK1 inhibitor XMD8-92 blocks cellular BMK1 activation and significantly suppresses tumor growth in lung and cervical tumor models and is well tolerated in animals. On the other hand, MEK5 inhibitors, BIX02188, BIX02189, and compound 6, suppress cellular MEK5 activity, but no data exist to date on their effectiveness in animals.

Transautocrine signaling by membrane neuregulins requires cell surface targeting, which is controlled by multiple domains

The neuregulins (NRGs) play important roles in animal development and homeostasis, and their deregulation has been linked to diseases such as cancer and schizophrenia. The NRGs belong to the epidermal growth factor (EGF) family of transmembrane growth factors. Although NRGs may be synthesized as transmembrane proteins (the pro-NRGs), some of them lack an N-terminal signal sequence, raising the question of how these pro-NRGs are directed to the plasma membrane. Here we have explored the domains of pro-NRGs that are required for their membrane anchoring, cell surface exposure, and biological activity. We show that an internal hydrophobic region acts as a membrane-anchoring domain, but other regions of pro-NRG are required for proper sorting to the plasma membrane. Using mutants that are located in different subcellular compartments, we show that only plasma membrane-exposed pro-NRG is biologically active. At this location, the pro-NRGs may act as transautocrine molecules (i.e. as membrane factors able to activate receptors present in cells that are in physical contact with the pro-NRG-producing cells (in trans) or capable of activating receptors present in the pro-NRG-producing cells (in cis)).

Apoptotic cell-derived factors induce arginase II expression in murine macrophages by activating ERK5/CREB

Apoptotic cell (AC)-derived factors alter the physiology of macrophages (MΦs) towards a regulatory phenotype, characterized by reduced nitric oxide (NO) production. Impaired NO formation in response to AC-conditioned medium (CM) was facilitated by arginase II (ARG II) expression, which competes with inducible NO synthase for L-arginine. Here we explored signaling pathways allowing CM to upregulate ARG II in RAW264.7 MΦs. Sphingosine-1-phosphate (S1P) was required and acted synergistically with a so far unidentified factor to elicit high ARG II expression. S1P activated S1P(2), since S1P(2) knockdown prevented ARG II upregulation. Furthermore, ERK5 knockdown attenuated CM-mediated ARG II protein induction. CREB was implicated as shown by EMSA analysis and decoy-oligonucleotides scavenging CREB in RAW264.7 MΦs, which blocked ARG II expression. We conclude that AC-derived S1P binds to S1P(2) and acts synergistically with other factors to activate ERK5 and concomitantly CREB. This signaling cascade shapes an anti-inflammatory MΦ phenotype by ARG II induction.

Discovery of a benzo[e]pyrimido-[5,4-b][1,4]diazepin-6(11H)-one as a Potent and Selective Inhibitor of Big MAP Kinase 1

Kinome-wide selectivity profiling of a collection of 2-amino-pyrido[2,3-d]pyrimidines followed by cellular structure−activity relationship-guided optimization resulted in the identification of moderately potent and selective inhibitors of BMK1/ERK5 exemplified by 11, 18, and 21. For example, 11 possesses a dissociation constant (K_d) for BMK1 of 19 nM, a cellular IC₅₀ for inhibiting epidermal growth factor induced BMK1 autophosphorylation of 0.19 ± 0.04 μM, and an Ambit KINOMEscan selectivity score (S₅) of 0.035. Inhibitors 18 and 21 are also potent BMK1 inhibitors and possess favorable pharmacokinetic properties which enable their use as pharmacological probes of BMK1-dependent phenomena as well as starting points for further optimization efforts.

Dissociation of epidermal growth factor receptor and ErbB2 heterodimers in the presence of somatostatin receptor 5 modulate signaling pathways

Epidermal growth factor through the stimulation of epidermal growth factor receptor (EGFR) plays a critical role in the activation of MAPKs and phosphatidylinositol-3-protein kinase/AKT cell survival pathways attributed in many pathological conditions. At the cellular level, such functions involve EGFR overactivation and phosphorylation. In the present study, we describe that human embryonic kidney-293 cells transfected with somatostatin (SST) receptor 5 (SSTR5) exhibit inhibition of EGFR phosphorylation and modulate MAPK and phosphatidylinositol-3-protein kinase/AKT cell survival signaling. Furthermore, suppression of EGFR by using small interference RNA and an antagonist (AG1478) potentiates the SST effect via activation of SSTR5 on signaling molecules. In wild-type human embryonic kidney-293 cells, EGFR/ErbB2 exists as constitutive heterodimers. The presence of SSTR5 leads to the dissociation of the heteromeric complex of EGFR/ErbB2 and display preferential heterodimerization between SSTR5 and EGFR in an agonist-dependent manner. These findings highlight a new undiscovered mechanism and potential role of SSTR5 to attenuate the EGFR-mediated signaling pathways involved in tumorigenesis. Our data indicate that the activation and/or overexpression of SST receptors along with the inhibition of EGFR will serve as an important therapeutic approach in the treatment of ErbB-positive tumors.

P-Rex1 participates in Neuregulin-ErbB signal transduction and its expression correlates with patient outcome in breast cancer

The Neuregulins and their receptors, the ErbB/HER subfamily of receptor tyrosine kinases, have critical roles in animal physiology, and their deregulation is frequent in cancer. Here we report the identification of the guanine nucleotide exchange factor, phosphatidylinositol 3,4,5-triphosphate-dependent Rac exchanger 1 (P-Rex1), as a novel mediator in signalling by ErbB/HER receptors. P-Rex1 was formerly described as a phosphoinositide 3-kinase and Gβγ activated protein that regulates Rac function. We define how ErbB/HER receptors regulate P-Rex1 function, which involves dephosphorylation of inhibitory residues, and phosphorylation of activating residues of P-Rex. The net balance resulting from activation of this phosphorylation/dephosphorylation cycle of P-Rex1 favours Rac activation. Molecular and biological studies indicated that P-Rex1 phosphorylation regulated the proliferation of breast cancer cells, and P-Rex1 knockdown affected their migration or invasiveness, as well as their in vivo tumourigenic potential. Moreover, as we found correlation between high P-Rex1 expression and poor patient outcome in breast cancer, P-Rex1 targeting may be therapeutically relevant in cancer.

Multisite phosphorylation of Erk5 in mitosis

The MAP kinase Erk5 plays important roles in cellular proliferation, and has recently been implicated in the regulation of mitosis. The classic pathway of Erk5 activation involves dual phosphorylation at its TEY microdomain by the upstream regulating kinase MEK5. Here we describe a second pathway that controls Erk5 phosphorylation. This pathway is activated in mitotic cells and involves kinase activities distinct from MEK5. Studies aimed at identifying these kinases suggested that CDK1 activity is required to sustain Erk5 phosphorylation in mitosis, as treatment with RO3306, a CDK1 inhibitor, reversed mitotic phosphorylation of Erk5. Moreover, CDK1 co-precipitated with Erk5 in mitotic cells. The mitotic phosphorylation of Erk5 occurs at multiple sites located at its unique C-terminal region, within an Erk5 subdomain that has formerly been implicated in the control of the subcellular location of Erk5. Furthermore, molecular studies indicated that phosphorylation at these sites may participate in the control of the transit of Erk5 between the cytosol and the nucleus, in addition to regulating its transcriptional activity. Together, our results demonstrate the existence of a second Erk5 phosphorylation pathway, that is activated in mitosis, and that may participate in the regulation of Erk5 functions.

Pharmacological inhibition of BMK1 suppresses tumor growth through promyelocytic leukemia protein

BMK1 is activated by mitogens and oncogenic signals and, thus, is strongly implicated in tumorigenesis. We found that BMK1 interacted with promyelocytic leukemia protein (PML), and inhibited its tumor-suppressor function through phosphorylation. Furthermore, activated BMK1 notably inhibited PML-dependent activation of p21. To further investigate the BMK-mediated inhibition of the tumor suppressor activity of PML in tumor cells, we developed a small-molecule inhibitor of the kinase activity of BMK1, XMD8-92. Inhibition of BMK1 by XMD8-92 blocked tumor cell proliferation in vitro and significantly inhibited tumor growth in vivo by 95%, demonstrating the efficacy and tolerability of BMK1-targeted cancer treatment in animals.

Effect of multikinase inhibitors on caspase-independent cell death and DNA damage in HER2-overexpressing breast cancer cells

BACKGROUND

The receptor tyrosine kinase, HER2, is overexpressed in approximately 25% of patients with breast cancer and is implicated in the aggressiveness of cancer. Targeting of HER2 signaling with trastuzumab, a monoclonal antibody that inhibits HER2 activity, has demonstrated clinical benefits.

METHODS

We investigated whether the antitumor activity of trastuzumab can be potentiated by dasatinib, a small-molecule tyrosine kinase inhibitor, on breast cancer cell lines that overexpress HER2 (BT474 and SKBR3) or have normal HER2 expression (MCF7 and T47D). Functional, biochemical, and gene expression microarray studies were performed to test the effect of trastuzumab, dasatinib, or a combination of trastuzumab and dasatinib on cell proliferation; HER activation; cell cycle; DNA damage; and apoptosis. The effect of drugs on mice (n = 6 per group) bearing xenograft tumors originating from HER2-overexpressing BT474 cells was assessed, and tumors were evaluated for an effect on volume, HER signaling, and DNA damage. All statistical tests were two-sided.

RESULTS

Trastuzumab and dasatinib combination showed a synergistic effect on the proliferation of HER2-overexpressing breast cancer cells (combination index = 0.44, 95% confidence interval = 0.30 to 0.58). The drug combination also induced a stronger inhibitory effect on HER2 activation than the individual drugs, decreased the level of proteins involved in DNA damage response, induced DNA double-strand breaks, cell cycle arrest, and caspase-independent apoptosis. Mice (n = 6 per group) bearing xenograft tumors originating from HER2-overexpressing BT474 cells showed statistically significantly reduced tumor volume on day 28 when treated with the drug combination (control vs trastuzumab and dasatinib combination; mean volume = 2.6 vs 0.5 cm(3), difference = 2.1 cm(3), 95% confidence interval = 0.76 to 3.51 cm(3), P = .01) and total regression of tumors by day 36 with no later relapse.

CONCLUSIONS

Results showed that HER2 and dasatinib-sensitive tyrosine kinases act in a synergistic manner to safeguard the breast cancer cells from DNA damage. The therapeutic targeting of multikinase inhibition opens new avenues for the treatment of HER2-positive breast cancer patients.

Breast tumor kinase and extracellular signal-regulated kinase 5 mediate Met receptor signaling to cell migration in breast cancer cells

Introduction

Breast tumor kinase (Brk/protein tyrosine kinase 6 (PTK6)) is a nonreceptor, soluble tyrosine kinase overexpressed in the majority of breast tumors. Previous work has placed Brk downstream of epidermal growth factor receptor (ErbB) activation and upstream of extracellular signal-regulated kinase 5 (ERK5) and p38 mitogen-activated protein (MAP) kinases. Herein we investigate the regulation of Brk kinase activity and cell migration in response to treatment of keratinocytes (HaCaT cells) and breast cancer cell lines (MDA-MB-231 and T47D cells) with hepatocyte growth factor (HGF) and macrophage stimulating protein (MSP), peptide ligands for Met and Ron receptors, respectively.

Methods

In vitro kinase assays were performed to directly measure Brk kinase activity in response to MET and RON ligands. Transfection of Brk-targeted RNAi was used to knock down endogenous Brk or ERK5 in multiple cell lines. Kinase activities (downstream of MET signaling) were assayed by Western blotting using total and phospho-specific antibodies. Boyden chamber assays were used to measure cell migration in response to manipulation of Brk and downstream MET effectors. Rescue experiments were performed by knock down of endogenous Brk using RNAi (targeting the untranslated region (3′-UTR)) and transient transfection (re-expression) of either wild-type or kinase-inactive Brk.

Results

Brk gene silencing revealed that HGF, but not MSP, induced robust Brk-dependent cell migration. Brk and ERK5 copurified in HGF-induced protein complexes, and Brk/ERK5 complexes formed independently of Brk kinase activity. ERK5 was required for breast cancer cell but not keratinocyte cell migration, which became ERK1/2-dependent upon ERK5 knockdown. Notably, rescue experiments indicated that the kinase activity of Brk was not required for HGF-induced cell migration. Further, expression of either wild-type or kinase-inactive Brk in Brk-null MDA-MB-435 cells activated ERK5 and conferred increased HGF-induced cell migration.

Conclusions

These results have identified Brk and ERK5 as important downstream effectors of Met signaling to cell migration. Targeting ERK5 kinase activity or inhibiting the formation of Brk/ERK5 complexes may provide an additional means of blocking cell migration associated with breast cancer progression to metastasis.

Key signalling nodes in mammary gland development and cancer. Mitogen-activated protein kinase signalling in experimental models of breast cancer progression and in mammary gland development

Seven classes of mitogen-activated protein kinase (MAPK) intracellular signalling cascades exist, four of which are implicated in breast disease and function in mammary epithelial cells. These are the extracellular regulated kinase (ERK)1/2 pathway, the ERK5 pathway, the p38 pathway and the c-Jun N-terminal kinase (JNK) pathway. In some forms of human breast cancer and in many experimental models of breast cancer progression, signalling through the ERK1/2 pathway, in particular, has been implicated as being important. We review the influence of ERK1/2 activity on the organised three-dimensional association of mammary epithelial cells, and in models of breast cancer cell invasion. We assess the importance of epidermal growth factor receptor family signalling through ERK1/2 in models of breast cancer progression and the influence of ERK1/2 on its substrate, the oestrogen receptor, in this context. In parallel, we consider the importance of these MAPK-centred signalling cascades during the cycle of mammary gland development. Although less extensively studied, we highlight the instances of signalling through the p38, JNK and ERK5 pathways involved in breast cancer progression and mammary gland development.

RSK in tumorigenesis: connections to steroid signaling

The Ser/Thr kinase family, RSK, has been implicated in numerous types of hormone-dependent and -independent cancers. However, there has been little consideration of RSKs as downstream mediators of steroid hormone non-genomic effects or of their ability to facilitate steroid receptor-mediated gene expression. Steroid hormone signaling can directly stimulate the MEK/ERK/RSK pathway to regulate cellular proliferation and survival in transformed cells. To date, multiple mechanisms of RSK and steroid hormone receptor-mediated proliferation/survival have been elucidated. For example, RSK enhances proliferation of breast and prostate cancer cells via its ability to control the levels of the estrogen receptor co-activator, cyclin D1. While in lung and other tumors RSK may control apoptosis via estrogen-mediated regulation of mitochondrial integrity. Thus the RSKs could be important anti-cancer therapeutic targets in many different transformed tissues. The recent discovery of RSK-specific inhibitors will advance our current understanding of RSK in transformation and drive these studies into animal and clinical models. In this review we explore the mechanisms associated with RSK in tumorigenesis and their relationship to steroid hormone signaling.

Astrocytes express Mxi2, a splice isoform of p38MAPK

Mitogen-activated protein kinases (MAPKs) are a superfamily of cytoplasmic serine/threonine kinases that transduce many types of extracellular stimuli into cellular responses. p38MAPK is a member of this family with its active form in a diphosphorylated state (p38MAPKdiP). Two strong anti-p38MAPKdiP immunoreactive bands (apparent molecular weight 38 and 34 kDa) were detected by Western blotting in cultured astrocytes. Using a specific antibody and employing immunoprecipitation procedures and SELDI-TOF analysis, the 34 kDa band was found to correspond to Mxi2, a splice variant of p38MAPK; cultured astrocytes therefore express Mxi2. Separate protein extractions of different subcellular fractions, and fluorescent immunovisualisation employing confocal microscopy, showed Mxi2 to have a non-nuclear, cytosolic distribution in the studied cells. ERK1/2, protein whose intracellular distribution is influenced by Mxi2, showed the same cytoplasmic pattern than Mxi2.

Extracellular signal regulated kinase 5 mediates signals triggered by the novel tumor promoter palytoxin

Palytoxin is classified as a non-12-O-tetradecanoylphorbol-13-acetate (TPA)-type skin tumor because it does not bind to or activate protein kinase C. Palytoxin is thus a novel tool for investigating alternative signaling pathways that may affect carcinogenesis. We previously showed that palytoxin activates three major members of the mitogen activated protein kinase (MAPK) family, extracellular signal regulated kinase 1 and 2 (ERK1/2), c-Jun N-terminal kinase (JNK), and p38. Here we report that palytoxin also activates another MAPK family member, called ERK5, in HeLa cells and in keratinocytes derived from initiated mouse skin (308 cells). By contrast, TPA does not activate ERK5 in these cell lines. The major cell surface receptor for palytoxin is the Na+,K+-ATPase. Accordingly, ouabain blocked the ability of palytoxin to activate ERK5. Ouabain alone did not activate ERK5. ERK5 thus represents a divergence in the signaling pathways activated by these two agents that bind to the Na+,K+-ATPase. Cycloheximide, okadaic acid, and sodium orthovanadate did not mimic the effect of palytoxin on ERK5. These results indicate that the stimulation of ERK5 by palytoxin is not simply due to inhibition of protein synthesis or inhibition of serine/threonine or tyrosine phosphatases. Therefore, the mechanism by which palytoxin activates ERK5 differs from that by which it activates ERK1/2, JNK, and p38. Finally, studies that used pharmacological inhibitors and shRNA to block ERK5 action indicate that ERK5 contributes to palytoxin-stimulated c-Fos gene expression. These results suggest that ERK5 can act as an alternative mediator for transmitting diverse tumor promoter-stimulated signals.

ERK2, but not ERK1, mediates acquired and "de novo" resistance to imatinib mesylate: implication for CML therapy

Resistance to Imatinib Mesylate (IM) is a major problem in Chronic Myelogenous Leukaemia management. Most of the studies about resistance have focused on point mutations on BCR/ABL. However, other types of resistance that do not imply mutations in BCR/ABL have been also described. In the present report we aim to study the role of several MAPK in IM resistance not associate to BCR/ABL mutations. Therefore we used an experimental system of resistant cell lines generated by co-culturing with IM (K562, Lama 84) as well as primary material from resistant and responder patient without BCR/ABL mutations. Here we demonstrate that Erk5 and p38MAPK signaling pathways are not implicated in the acquired resistance phenotype. However, Erk2, but not Erk1, is critical for the acquired resistance to IM. In fact, Bcr/Abl activates preferentially Erk2 in transient transfection in a dose dependent fashion through the c-Abl part of the chimeric protein. Finally, we present evidences demonstrating how constitutive activation of Erk2 is a de novo mechanism of resistance to IM. In summary our data support the use of therapeutic approaches based on Erk2 inhibition, which could be added to the therapeutic armamentarium to fight CML, especially when IM resistance develops secondary to Erk2 activation.

ERK1/2, but not ERK5, is necessary and sufficient for phosphorylation and activation of c-Fos

Growth factor-stimulated expression and activation of c-Fos is regulated by the ERK1/2 pathway. However, recent reports have also suggested a prominent role for the closely related ERK5 pathway in regulating the expression, transcriptional activation and nuclear localization of c-Fos. Here we have compared the role of ERK1/2 and ERK5 in regulating c-Fos using a combination of conditional protein kinases, selective biochemical inhibitors and ERK5 null fibroblasts. We demonstrate that activation of the ERK1/2 pathway, but not ERK5, is sufficient for c-Fos phosphorylation and transcriptional activation. Furthermore, growth factor-dependent expression of c-Fos is blocked by low doses of PD184352 that selectively inhibit the ERK1/2 pathway but proceeds normally in ERK5-/- 3T9 cells; in addition, nuclear localization of c-Fos is normal in ERK5-/- cells. ERK5-/- cells are, however, defective for c-Jun expression but this is reversed by re-expression of ERK5. In addition to ERK5, neither the JNK nor p38 pathways can substitute for ERK1/2 in the regulation of c-Fos transcriptional activity. These results demonstrate that c-Fos transcriptional activity is not regulated by the ERK5 pathway; rather, of all the MAPKs and SAPKs, c-Fos activation appears to be predominantly linked to the ERK1/2 pathway.

Expression of Erk5 in early stage breast cancer and association with disease free survival identifies this kinase as a potential therapeutic target

Background

Breast cancer is the most common neoplasia in women. Even though advances in its treatment have improved disease outcome, some patients relapse. Therefore, attempts to better define the molecular determinants that drive breast cancer cell proliferation may help in defining potential therapeutic targets. Mitogen-activated protein kinases (MAPK) play important roles in tumorigenesis. One of them, Erk5, has been linked to the proliferation of breast cancer cells in vitro. Here we have investigated the expression and prognostic value of Erk5 in human breast cancer.

Methodology/Principal Findings

Animal and cellular models were used to study Erk5 expression and function in breast cancer. In 84 human breast tumours the expression of Erk5 was analyzed by immunohistochemistry. Active Erk5 (pErk5) was studied by Western blotting. Correlation of Erk5 with clinicopathological parameters and with disease-free survival in early stage breast cancer patients was analyzed. Expression of Erk5 was detected in most patients, and overexpression was found in 20%. Active Erk5 was present in a substantial number of samples, as well as in tumours from an animal breast cancer model. Overexpression of Erk5 was associated with a decrease in disease-free survival time, which was independent of other clinicopathological parameters of prognosis. Transient transfection of a short hairpin RNA (shRNA) targeting Erk5, and a stable cell line expressing a dominant negative form of Erk5 (Erk5^AEF), were used to investigate the influence of Erk5 on drugs used in the clinic to treat breast tumours. We found that inhibition of Erk5 decreased cancer cell proliferation and also sensitized these cells to the action of anti-HER2 therapies.

Conclusions/Significance

Overexpression of Erk5 is an independent predictor of disease-free survival in breast cancer, and may represent a future therapeutic target.

ERK5 is a target for gene amplification at 17p11 and promotes cell growth in hepatocellular carcinoma by regulating mitotic entry

Using high-density oligonucleotide microarrays, we investigated DNA copy-number aberrations in cell lines derived from hepatocellular carcinomas (HCCs) and detected a novel amplification at 17p11. To identify the target of amplification at 17p11, we defined the extent of the amplicon and examined HCC cell lines for expression of all seven genes in the 750-kb commonly amplified region. Mitogen-activated protein kinase (MAPK) 7, which encodes extracellular-regulated protein kinase (ERK) 5, was overexpressed in cell lines in which the gene was amplified. An increase in MAPK7 copy number was detected in 35 of 66 primary HCC tumors. Downregulation of MAPK7 by small interfering RNA suppressed the growth of SNU449 cells, the HCC cell line with the greatest amplification and overexpression of MAPK7. ERK5, phosphorylated during the G2/M phases of the cell cycle, regulated entry into mitosis in SNU449 cells. In conclusion, our results suggest that MAPK7 is likely the target of 17p11 amplification and that the ERK5 protein product of MAPK7 promotes the growth of HCC cells by regulating mitotic entry.

Isolation of intrinsically active (MEK-independent) variants of the ERK family of mitogen-activated protein (MAP) kinases

MAPKs are key components of cell signaling pathways with a unique activation mechanism: i.e. dual phosphorylation of neighboring threonine and tyrosine residues. The ERK enzymes form a subfamily of MAPKs involved in proliferation, differentiation, development, learning, and memory. The exact role of each Erk molecule in these processes is not clear. An efficient strategy for addressing this question is to activate individually each molecule, for example, by expressing intrinsically active variants of them. However, such molecules were not produced so far. Here, we report on the isolation, via a specifically designed genetic screen, of six variants (each carries a point mutation) of the yeast MAPK Mpk1/Erk that are active, independent of upstream phosphorylation. One of the activating mutations, R68S, occurred in a residue conserved in the mammalian Erk1 (Arg-84) and Erk2 (Arg-65) and in the Drosophila ERK Rolled (Arg-80). Replacing this conserved Arg with Ser rendered these MAPKs intrinsically active to very high levels when tested in vitro as recombinant proteins. Combination of the Arg to Ser mutation with the sevenmaker mutation (producing Erk2(R65S+D319N) and Rolled(R80S+D334N)) resulted in even higher activity (45 and 70%, respectively, in reference to fully active dually phosphorylated Erk2 or Rolled). Erk2(R65S) and Erk2(R65S+D319N) were found to be spontaneously active also when expressed in human HEK293 cells. We further revealed the mechanism of action of the mutants and show that it involves acquisition of autophosphorylation activity. Thus, a first generation of Erk molecules that are spontaneously active in vitro and in vivo has been obtained.

ERK5/MAPK is activated by TGFbeta in hepatocytes and required for the GSK-3beta-mediated Snail protein stabilization

Extracellular signal-regulated protein kinase 5 (ERK5) is a mitogen-activated protein kinase, specifically activated by MEK5, and involved in the regulation of many cellular functions including proliferation, survival, differentiation and apoptosis. MEK5/ERK5 module is an important element of different signal transduction pathways. The aim of this study was to investigate whether ERK5 participates to the signalling of the multifunctional cytokine TGFbeta, known to play an important role in the regulation of hepatic growth. Here, we reported that ERK5 is phosphorylated and activated by TGFbeta in hepatocytes, with a rapid and sustained kinetic, through a Src-dependent pathway. Moreover, we demonstrated that ERK5 participates to the TGFbeta-induced Snail protein regulation being required for its stabilization. We also found that the functional inactivation of ERK5 impedes the TGFbeta-mediated glycogen synthase kinase-3beta inactivation suggesting this as mechanism responsible for ERK5-mediated Snail stabilization. Thus, results presented in this study uncovered for the first time a role for ERK5 in the TGFbeta-induced cellular responses.

Synergic antitumoral effect of an IGF-IR inhibitor and trastuzumab on HER2-overexpressing breast cancer cells

BACKGROUND

Receptor tyrosine kinases play an important role in breast cancer. One of them, the type I insulin-like growth factor, has been linked to resistance to trastuzumab (Herceptin), an agent that targets human epidermal growth factor receptor 2. Here, we show that the insulin-like growth factor-I receptor (IGF-IR) antagonist NVP-AEW541 inhibits proliferation of breast cancer cells and synergizes with trastuzumab.

PATIENTS AND METHODS

Patient samples and breast cancer cell lines were evaluated for IGF-IR expression or activation by western blotting. 1-(4,5-Dimethylthiazol-2-yl)-3,5-diphenylformazan (MTT) uptake assays and Annexin V staining were used for the analyses of cell proliferation/apoptosis. Biochemical and genomic studies were carried out to gain insights into the mechanism of action of NVP-AEW541.

RESULTS

The IGF-IR was expressed above normal levels in a number of breast cancer samples. Activation of this receptor was inhibited by NVP-AEW541 that also decreased cell proliferation and increased apoptosis. NVP-AEW541 decreased the amount of pAkt and increased the level of p27. Combination studies with several drugs used in the breast cancer clinic showed that NVP-AEW541 synergistically increased the action of trastuzumab.

CONCLUSIONS

Our results show the anti-breast cancer action of NVP-AEW541 and support the clinical development of anti-IGF-IR agents, especially in combination with trastuzumab.

Characterization of contractile 5-hydroxytryptamine receptor subtypes in the in situ autoperfused kidney in the anaesthetized rat

Using several 5-hydroxytryptamine (5-HT) agonists and antagonists, we attempted to characterize the receptor subtypes involved in the contractile response to 5-HT in the in situ autoperfused rat kidney. An intra-arterial (i.a.) bolus injection of 5-HT (0.00000125 to 0.1 microg/kg) increased renal perfusion pressure in a dose-dependent way but did not affect the systemic blood pressure. The selective 5-HT2 receptor agonist alpha-methyl-5-HT (alpha-methyl-5-hydroxytryptamine) and the non-selective 5-HT2C receptor agonist (1-(3-chlorophenyl)piperazine), m-CPP, caused a local vasoconstrictor effect in the autoperfused rat kidney, whereas BW723C86, a selective 5-HT2B receptor agonist, the 5-HT1 receptor agonist 5-carboxamidotryptamine, 5-CT, and the selective 5-HT3 receptor agonist m-CPBG (1-(m-chlorophenyl)-biguanide) did not modify the renal perfusion pressure. The vasoconstrictor effect elicited by alpha-methyl-5-HT and m-CPP was significantly decreased by ritanserin (a 5-HT2 receptor antagonist), SB 206553 (3,5-Dihydro-5-methyl-N-3pyridinylbenzo[1,2.b:4,5-b']dipyrrole(1H)-carboxamide hydrochloride), a selective 5-HT2B/2C receptor antagonist and enalapril, but was not modified by pretreatment with spiperone (a 5-HT2A receptor antagonist). The results of protein expression analyses allow us to postulate that 5HT-SRC (a 5-HT2C receptor protein) is expressed in renal tissue and differentially expressed in renal artery. Our data suggest also that the serotonergic vasoconstrictor response induced in the in situ autoperfused rat kidney would be mediated by local 5-HT2C receptor activation.