Regulation of signal transduction and signal diversity by receptor oligomerization

The Plasminogen-Apple-Nematode (PAN) domain suppresses JA/ET defense pathways in plants

Suppression of immune response is a phenomenon that enables biological processes such as gamete fertilization, cell growth, cell proliferation, endophyte recruitment, parasitism, and pathogenesis. Here, we show for the first time that the Plasminogen-Apple-Nematode (PAN) domain present in G-type lectin receptor-like kinases is essential for immunosuppression in plants. Defense pathways involving jasmonic acid and ethylene are critical for plant immunity against microbes, necrotrophic pathogens, parasites, and insects. Using two Salix purpurea G-type lectin receptor kinases, we demonstrated that intact PAN domains suppress jasmonic acid and ethylene signaling in Arabidopsis and tobacco. Variants of the same receptors with mutated residues in this domain could trigger induction of both defense pathways. Assessment of signaling processes revealed significant differences between receptors with intact and mutated PAN domain in MAPK phosphorylation, global transcriptional reprogramming, induction of downstream signaling components, hormone biosynthesis and resistance to Botrytis cinerea . Further, we demonstrated that the domain is required for oligomerization, ubiquitination, and proteolytic degradation of these receptors. These processes were completely disrupted when conserved residues in the domain were mutated. Additionally, we have tested the hypothesis in recently characterized Arabidopsis mutant which has predicted PAN domain and negatively regulates plant immunity against root nematodes. ern1.1 mutant complemented with mutated PAN shows triggered immune response with elevated WRKY33 expression, hyperphosphorylation of MAPK and resistant to necrotrophic fungus Botrytis cinerea . Collectively, our results suggest that ubiquitination and proteolytic degradation mediated by the PAN domain plays a role in receptor turn-over to suppress jasmonic acid and ethylene defense signaling in plants.

Shifting the Focus of Signaling Abnormalities in Colon Cancer

Simple Summary

The major signaling pathways in colon cancer are WNT, RAS, and TGF-β. Components of these pathways are mutated in the majority of colon cancers, resulting in aberrantly high or low activity of the pathway. The functional consequences of the mutations reflect the behavior of these signaling pathways in intestinal stem cells. To better understand the roles of each pathway, we cover the basic function as well as points of intersection between the different pathways, to describe how they function individually, as well as together, to regulate cell proliferation.

Abstract

Colon cancer tumorigenesis occurs incrementally. The process involves the acquisition of mutations which typically follow an established pattern: activation of WNT signaling, activation of RAS signaling, and inhibition of TGF-β signaling. This arrangement recapitulates, to some degree, the stem cell niche of the intestinal epithelium, which maintains WNT and EGF activity while suppressing TGF-β. The resemblance between the intestinal stem cell environment and colon cancer suggests that the concerted activity of these pathways generates and maintains a potent growth-inducing stimulus. However, each pathway has a myriad of downstream targets, making it difficult to identify which aspects of these pathways are drivers. To address this, we utilize the cell cycle, the ultimate regulator of cell proliferation, as a foundation for cross-pathway integration. We attempt to generate an overview of colon cancer signaling patterns by integrating the major colon cancer signaling pathways in the context of cell replication, specifically, the entrance from G₁ into S-phase.

Kaempferol Regulates the Expression of Airway MUC5AC Mucin Gene via IκBα-NF-κB p65 and p38-p44/42-Sp1 Signaling Pathways

In the present study, kaempferol, a flavonoidal natural compound found in Polygonati Rhizoma, was investigated for its potential effect on the gene expression and production of airway MUC5AC mucin. A human respiratory epithelial NCI-H292 cells was pretreated with kaempferol for 30 min and stimulated with epidermal growth factor (EGF) or phorbol 12-myristate 13-acetate (PMA), for the following 24 h. The effect on PMA-induced nuclear factor kappa B (NF-κB) signaling pathway or EGF-induced mitogen-activated protein kinase (MAPK) signaling pathway was investigated. Kaempferol suppressed the production and gene expression of MUC5AC mucins, induced by PMA through the inhibition of degradation of inhibitory kappa Bα (IκBα), and NF-κB p65 nuclear translocation. Also, kaempferol inhibited EGF-induced gene expression and production of MUC5AC mucin through regulating the phosphorylation of EGFR, phosphorylation of p38 MAPK and extracellular signal-regulated kinase (ERK) 1/2 (p44/42), and the nuclear expression of specificity protein-1 (Sp1). These results suggest kaempferol regulates the gene expression and production of mucin through regulation of NF-κB and MAPK signaling pathways, in human airway epithelial cells.

Interactions between Ligand-Bound EGFR and VEGFR2

In this work, we put forward the provocative hypothesis that the active, ligand-bound RTK dimers from unrelated subfamilies can associate into heterooligomers with novel signaling properties. This hypothesis is based on a quantitative FRET study that monitors the interactions between EGFR and VEGFR2 in the plasma membrane of live cells in the absence of ligand, in the presence of either EGF or VEGF, and in the presence of both ligands. We show that direct interactions occur between EGFR and VEGFR2 in the absence of ligand and in the presence of the two cognate ligands. However, there are not significant heterointeractions between EGFR and VEGFR2 when only one of the ligands is present. Since RTK dimers and RTK oligomers are believed to signal differently, this finding suggests a novel mechanism for signal diversification.

Identification of Predictive ERBB Mutations by Leveraging Publicly Available Cell Line Databases

Although targeted therapies can be effective for a subgroup of patients, identification of individuals who benefit from the treatments is challenging. At the same time, the predictive significance of the majority of the thousands of mutations observed in the cancer tissues remains unknown. Here, we describe the identification of novel predictive biomarkers for ERBB-targeted tyrosine kinase inhibitors (TKIs) by leveraging the genetic and drug screening data available in the public cell line databases: Cancer Cell Line Encyclopedia, Genomics of Drug Sensitivity in Cancer, and Cancer Therapeutics Response Portal. We assessed the potential of 412 ERBB mutations in 296 cell lines to predict responses to 10 different ERBB-targeted TKIs. Seventy-six ERBB mutations were identified that were associated with ERBB TKI sensitivity comparable with non-small cell lung cancer cell lines harboring the well-established predictive EGFR L858R mutation or exon 19 deletions. Fourteen (18.4%) of these mutations were classified as oncogenic by the cBioPortal database, whereas 62 (81.6%) were regarded as novel potentially predictive mutations. Of the nine functionally validated novel mutations, EGFR Y1069C and ERBB2 E936K were transforming in Ba/F3 cells and demonstrated enhanced signaling activity. Mechanistically, the EGFR Y1069C mutation disrupted the binding of the ubiquitin ligase c-CBL to EGFR, whereas the ERBB2 E936K mutation selectively enhanced the activity of ERBB heterodimers. These findings indicate that integrating data from publicly available cell line databases can be used to identify novel, predictive nonhotspot mutations, potentially expanding the patient population benefiting from existing cancer therapies.

Eph receptors as cancer targets for antibody-based therapy

Receptor tyrosine kinases (RTKs) are integral membrane sensors that govern cell differentiation, proliferation and mobility, and enable rapid communication between cells and their environment. Of the 20 RTK subfamilies currently known, Eph receptors are the largest group. Together with their corresponding ephrin ligands, Eph receptors regulate a diverse array of physiologic processes including axonal guidance, bone remodeling, and immune cell development and trafficking. Deregulation of Eph signaling pathways is linked to cancer and other proliferative diseases and, because RTKs play critical roles in cancer development, the specific targeting of these molecules in malignancies provides a promising treatment approach. Monoclonal antibodies targeting RTKs represent a potentially attractive modality for pharmaceutical development due to their relatively high target specificity and low off-target binding rates. Therefore, new technologies to generate antibodies able to target RTKs in their native in vivo context are likely to facilitate pre-clinical and clinical development of antibody-based therapies. Our group has recently reported a platform discovery methodology termed Selection of Phage-displayed Accessible Recombinant Targeted Antibodies (SPARTA). SPARTA is a novel and robust stepwise method, which combines the attributes of in vitro screenings of a naïve human recombinant antibody library against known tumor targets with those features of in vivo selections based on tumor-homing capabilities of a pre-enriched antibody pool. This unique approach overcomes several rate-limiting challenges to generate human monoclonal antibodies amenable to rapid translation into medical applications.

Molecular-Biology-Driven Treatment for Metastatic Colorectal Cancer

BACKGROUND

Metastatic CRC (mCRC) is a molecular heterogeneous disease. The aim of this review is to give an overview of molecular-driven treatment of mCRC patients.

METHODS

A review of clinical trials, retrospective studies and case reports was performed regarding molecular biomarkers with therapeutic implications.

RESULTS

RAS wild-type status was confirmed as being crucial for anti-epidermal growth factor receptor (EGFR) monoclonal antibodies and for rechallenge strategy. Antiangiogenic therapies improve survival in first- and second-line settings, irrespective of RAS status, while tyrosine kinase inhibitors (TKIs) remain promising in refractory mCRC. Promising results emerged from anti-HER2 drugs trials in HER2-positive mCRC. Target inhibitors were successful for BRAFV600E mutant mCRC patients, while immunotherapy was successful for microsatellite instability-high/defective mismatch repair (MSI-H/dMMR) or DNA polymerase epsilon catalytic subunit (POLE-1) mutant patients. Data are still lacking on NTRK, RET, MGMT, and TGF-β, which require further research.

CONCLUSION

Several molecular biomarkers have been identified for the tailored treatment of mCRC patients and multiple efforts are currently ongoing to increase the therapeutic options. In the era of precision medicine, molecular-biology-driven treatment is the key to impro patient selection and patient outcomes. Further research and large phase III trials are required to ameliorate the therapeutic management of these patients.

Targeting EGFR pathway in metastatic colorectal cancer- tumour heterogeniety and convergent evolution

Despite significant progress in management of metastatic colorectal cancer (mCRC) pertaining to better screening procedures and amelioration of the therapeutic armamentarium with targeted therapies, prognosis remains poor. Targeting epidermal growth factor receptor (EGFR) has been of particular interest owing to favourable efficacy benefits demonstrated by monoclonal antibodies (cetuximab and panitumumab) in various clinical settings and development of predictive biomarkers informing treatment decisions respectively. In spite of optimal patient selection based on RAS mutation status, primary and secondary resistance to monoclonal antibodies is higher than desired. Further research into predictive biomarkers is therefore essential, but has, to date, been conducted with considerable limitations. Whilst molecular heterogeneity has been demonstrated by several studies in mCRC, for incomprehensible reasons, multiple resistant genetic alterations that emerge under the selective pressure of EGFR-targeted therapies are somehow able to influence the biological and clinical behaviour of cancer cells, despite being detectable at extremely low frequencies. Intriguingly, these subclonal events largely seem to converge on RAS/RAF/MAPK pathway in patients treated with EGFR-targeted monoclonal antibodies. This review describes the clinical and biological evolution and development of EGFR targeted therapies in mCRC, the challenges in the presence of molecular complexities, the role of cell free (cf)-DNA and future strategies that could lead to further optimal discovery of clinically meaningful biomarkers and application of precision medicine.

Fibroblast Growth Factor Receptors Function Redundantly During Zebrafish Embryonic Development

Fibroblast growth factor (Fgf) signaling regulates many processes during development. In most cases, one tissue layer secretes an Fgf ligand that binds and activates an Fgf receptor (Fgfr) expressed by a neighboring tissue. Although studies have identified the roles of specific Fgf ligands during development, less is known about the requirements for the receptors. We have generated null mutations in each of the five fgfr genes in zebrafish. Considering the diverse requirements for Fgf signaling throughout development, and that null mutations in the mouse Fgfr1 and Fgfr2 genes are embryonic lethal, it was surprising that all zebrafish homozygous mutants are viable and fertile, with no discernable embryonic defect. Instead, we find that multiple receptors are involved in coordinating most Fgf-dependent developmental processes. For example, mutations in the ligand fgf8a cause loss of the midbrain-hindbrain boundary, whereas, in the fgfr mutants, this phenotype is seen only in embryos that are triple mutant for fgfr1a;fgfr1b;fgfr2, but not in any single or double mutant combinations. We show that this apparent fgfr redundancy is also seen during the development of several other tissues, including posterior mesoderm, pectoral fins, viscerocranium, and neurocranium. These data are an essential step toward defining the specific Fgfrs that function with particular Fgf ligands to regulate important developmental processes in zebrafish.

Regulation of RhoB Gene Expression during Tumorigenesis and Aging Process and Its Potential Applications in These Processes

RhoB, a member of the Ras homolog gene family and GTPase, regulates intracellular signaling pathways by interfacing with epidermal growth factor receptor (EGFR), Ras, and phosphatidylinositol 3-kinase (PI3K)/Akt to modulate responses in cellular structure and function. Notably, the EGFR, Ras, and PI3K/Akt pathways can lead to downregulation of RhoB, while simultaneously being associated with an increased propensity for tumorigenesis. Functionally, RhoB, part of the Rho GTPase family, regulates intracellular signaling pathways by interfacing with EGFR, RAS, and PI3K/Akt/mammalian target of rapamycin (mTOR), and MYC pathways to modulate responses in cellular structure and function. Notably, the EGFR, Ras, and PI3K/Akt pathways can lead to downregulation of RhoB, while simultaneously being associated with an increased propensity for tumorigenesis. RHOB expression has a complex regulatory backdrop consisting of multiple histone deacetyltransferase (HDACs 1 and 6) and microRNA (miR-19a, -21, and -223)-mediated mechanisms of modifying expression. The interwoven nature of RhoB’s regulatory impact and cellular roles in regulating intracellular vesicle trafficking, cell motion, and the cell cycle lays the foundation for analyzing the link between loss of RhoB and tumorigenesis within the context of age-related decline in RhoB. RhoB appears to play a tissue-specific role in tumorigenesis, as such, uncovering and appreciating the potential for restoration of RHOB expression as a mechanism for cancer prevention or therapeutics serves as a practical application. An in-depth assessment of RhoB will serve as a springboard for investigating and characterizing this key component of numerous intracellular messaging and regulatory pathways that may hold the connection between aging and tumorigenesis.

Epidermal Growth Factor Receptor and c-erbB-2 Contents in Unresectable (UICC R1 or R2) Gastric Cancer

Background

Epidermal growth factor receptor (EGFR) and c-erbB-2 are membrane receptors expressed in a variety of solid human cancers and directly correlated with poor prognosis. The objective of this work was to evaluate the EGFR and c-erbB-2 levels in non-resectable gastric carcinomas, their possible relationship with a variety of clinicopathological tumor parameters, and their prognostic significance.

Methods

This was a prospective analysis of 65 patients with unresectable gastric carcinomas (UICC R1 or R2), who underwent palliative surgery and were followed up for a median period of 13 months. Membranous EGFR levels were examined by radioligand binding assays and cytosolic c-erbB-2 levels by means of an immunoenzymatic assay.

Results

There was a wide variability in EGFR (80.3-2910 fmol/mg of protein) and c-erbB-2 (0.4-10071 NHU/mg of protein) levels in neoplastic tissues from patients with unresectable gastric carcinomas. Median c-erbB2 was significantly higher in tumors of the intestinal type than in tumors of the diffuse type (p=0.035) and in R2 than in R1 tumors (p=0.016). Statistical analysis showed that there was no relationship between tumor c-erbB-2 or EGFR content and any other patient or tumor characteristics. However, high levels of EGFR were significantly associated with a shorter overall survival (p=0.01).

Conclusion

Our data suggest a role of both transmembrane proteins in the progression of gastric cancer. EGFR and c-erbB-2 contents in unresectable gastric cancer could be utilized as appropriate biological markers for selecting candidates for treatment based on EGFR and/or c-erbB-2 inhibition.

PLCγ1: Potential arbitrator of cancer progression

Phospholipase C (PLC) is an essential mediator of cellular signaling. PLC regulates multiple cellular processes by generating bioactive molecules such as inositol-1,4,5-triphosphate (IP₃) and diacylglycerol (DAG). These products propagate and regulate cellular signaling via calcium (Ca²⁺) mobilization and activation of protein kinase C (PKC), other kinases, and ion channels. PLCγ1, one of the primary subtypes of PLC, is directly activated by membrane receptors, including receptor tyrosine kinases (RTKs), and adhesion receptors such as integrin. PLCγ1 mediates signaling through direct interactions with other signaling molecules via SH domains, as well as its lipase activity. PLCγ1 is frequently enriched and mutated in various cancers, and is involved in the processes of tumorigenesis, including proliferation, migration, and invasion. Although many studies have suggested that PLCγ functions in cell mobility rather than proliferation in cancer, questions remain as to whether PLCγ regulates mitogenesis and whether PLCγ promotes or inhibits proliferation. Moreover, how PLCγ regulates cancer-associated cellular processes and the interplay among other proteins involved in cancer progression have yet to be fully elucidated. In this review, we discuss the current understanding of the role of PLCγ1 in cancer mobility and proliferation.

Inferring and Using Protein Quaternary Structure Information from Crystallographic Data

A precise knowledge of the quaternary structure of proteins is essential to illuminate both their function and their evolution. The major part of our knowledge on quaternary structure is inferred from X-ray crystallography data, but this inference process is hard and error-prone. The difficulty lies in discriminating fortuitous protein contacts, which make up the lattice of protein crystals, from biological protein contacts that exist in the native cellular environment. Here, we review methods devised to discriminate between both types of contacts and describe resources for downloading protein quaternary structure information and identifying high-confidence quaternary structures. The use of high-confidence datasets of quaternary structures will be critical for the analysis of structural, functional, and evolutionary properties of proteins.

Gefitinib (ZD1839) in Previously Treated Advanced Non-Small-Cell Lung Cancer: Experience from a Single Institution

BACKGROUND

We conducted an analysis of gefitinib in patients with advanced non-small-cell lung cancer (NSCLC) to assess the antitumor efficacy of this epidermal growth factor receptor tyrosine kinase inhibitor.

METHODS

Our single-center, prospective landmark analysis included 183 patients with advanced NSCLC who received 250 mg of gefitinib orally once daily in an expanded-use program at our institution. Thirty-three of the 183 patients were previously untreated. The patients included in this analysis had all received at least 12 weeks of gefitinib.

RESULTS

The objective tumor response rate was 3.8%, but an additional 53.5% of patients experienced clinically meaningful disease stabilization. Median progression-free survival time was 3.6 months, and median overall survival time was 8.8 months. The 1-year survival rate for the entire cohort was 35%. Predictors of longer survival included female gender, adenocarcinoma or bronchoalveolar carcinoma histology, and an Eastern Cooperative Oncology Group performance status of 0 or 1. Adverse events were generally mild (grade 1 or 2) and consisted mainly of skin reactions and diarrhea.

CONCLUSIONS

In this single-center experience, gefitinib demonstrated clinically significant antitumor activity and provided good palliation in a predominantly pretreated group of patients. Our results, which are likely to be reproducible in a community setting, demonstrated a 1-year survival rate of 35% in a cohort of patients who were able to take the drug for at least 12 weeks.

Live cell imaging shows hepatocyte growth factor-induced Met dimerization

The canonical model of receptor tyrosine kinase (RTK) activation assumes that ligand-induced dimerization of inactive receptor monomers is a prerequisite for autophosphorylation. For several RTK families, recent results of fluorescence microscopy provided evidence for preformed receptor dimers that may or may not require ligand binding for kinase activity. Here we report, for the first time, the application of advanced quantitative fluorescence microscopy techniques to study changes in the oligomerization state of the RTK Met in response to stimulation by its endogenous ligand hepatocyte growth factor (HGF). We used inducible C-terminal fusions between Met and enhanced green fluorescent protein (EGFP) or red fluorescent protein (RFP) in combination with fluorescence resonance energy transfer (FRET)-based fluorescence-lifetime imaging microscopy (FLIM) and fluorescence correlation spectroscopy (FCS). A small fraction of HGF-independent Met dimers appeared to be present in cells even at low receptor density. At high receptor density, both the fraction of Met dimers and the level of Met autophosphorylation increased in the absence of HGF. Stimulation with HGF at low receptor density significantly increased the fraction of Met dimers on live cells. We found no indications of Met oligomers larger than dimers. Our findings thus confirm a model of Met activation through HGF-induced dimerization and at the same time they support previous reports of Met dimers in unstimulated cells. The tools established in this work will be useful to further characterize the mechanism of Met activation and to define the contribution of co-receptors.

Targeted therapy in gastroesophageal cancers: past, present and future

Gastroesophageal cancer is a significant global problem that frequently presents at an incurable stage and has very poor survival with standard chemotherapy approaches. This review will examine the epidemiology and molecular biology of gastroesophageal cancer and will focus on the key deregulated signaling pathways that have been targeted in the clinic. A comprehensive overview of clinical data highlighting successes and failures with targeted agents will be presented. Most notably, HER2-targeted therapy with the monoclonal antibody trastuzumab has proven beneficial in first-line therapy and has been incorporated into standard practice. Targeting the VEGF pathway has also proven beneficial, and the VEGFR-targeted monoclonal antibody ramucirumab is now approved for second-line therapy. In contrast to these positive results, agents targeting the EGFR and MET pathways have been evaluated extensively in gastroesophageal cancer but have repeatedly failed to show benefit. An increased understanding of the molecular predictors of response to targeted therapies is sorely needed. In the future, improved molecular pathology approaches should subdivide this heterogeneous disease entity to allow individualization of cancer therapy based on integrated and global identification of deregulated signaling pathways. Better patient selection, rational combinations of targeted therapies and incorporation of emerging immunotherapeutic approaches should further improve the treatment of this deadly disease.

Targeting Protein Kinase C Downstream of Growth Factor and Adhesion Signalling

The signaling outputs of Receptor Tyrosine Kinases, G-protein coupled receptors and integrins converge to mediate key cell process such as cell adhesion, cell migration, cell invasion and cell proliferation. Once activated by their ligands, these cell surface proteins recruit and direct a diverse range of proteins to disseminate the appropriate response downstream of the specific environmental cues. One of the key groups of proteins required to regulate these activities is the family of serine/threonine intracellular kinases called Protein Kinase Cs. The activity and subcellular location of PKCs are mediated by a series of tightly regulated events and is dependent on several posttranslational modifications and the availability of second messengers. Protein Kinase Cs exhibit both pro- and anti-tumorigenic effects making them an interesting target for anti-cancer treatment.

Ligand binding alters dimerization and sequestering of urokinase receptors in raft-mimicking lipid mixtures

Lipid heterogeneities, such as lipid rafts, are widely considered to be important for the sequestering of membrane proteins in plasma membranes, thereby influencing membrane protein functionality. However, the underlying mechanisms of such sequestration processes remain elusive, in part, due to the small size and often transient nature of these functional membrane heterogeneities in cellular membranes. To overcome these challenges, here we report the sequestration behavior of urokinase receptor (uPAR), a glycosylphosphatidylinositol-anchored protein, in a planar model membrane platform with raft-mimicking lipid mixtures of well-defined compositions using a powerful optical imaging platform consisting of confocal spectroscopy XY-scans, photon counting histogram, and fluorescence correlation spectroscopy analyses. This methodology provides parallel information about receptor sequestration, oligomerization state, and lateral mobility with single molecule sensitivity. Most notably, our experiments demonstrate that moderate changes in uPAR sequestration are not only associated with modifications in uPAR dimerization levels, but may also be linked to ligand-mediated allosteric changes of these membrane receptors. Our data show that these modifications in uPAR sequestration can be induced by exposure to specific ligands (urokinase plasminogen activator, vitronectin), but not via adjustment of the cholesterol level in the planar model membrane system. Good agreement of our key findings with published results on cell membranes confirms the validity of our model membrane approach. We hypothesize that the observed mechanism of receptor translocation in the presence of raft-mimicking lipid mixtures is also applicable to other glycosylphosphatidylinositol-anchored proteins.

ERK1/2 mediates sperm acrosome reaction through elevation of intracellular calcium concentration

Mammalian sperm acquire fertilization capacity after residing in the female reproductive tract for a few hours in a process called capacitation. Only capacitated sperm can bind the zona pellucida (ZP) of the egg and undergo the acrosome reaction, a process that allows penetration and fertilization. Extracellular signal regulated kinase (ERK1/2) mediates signalling in many cell types, however its role in sperm function is largely unknown. Here we show that ERK1/2 is highly phosphorylated/activated after a short incubation of mouse sperm under capacitation conditions and that this phosphorylation is reduced after longer incubation. Further phosphorylation was observed upon addition of crude extract of egg ZP or epidermal growth factor (EGF). The mitogen-activated ERK-kinase (MEK) inhibitor U0126 abolished ERK1/2 phosphorylation, in vitro fertilization rate and the acrosome reaction induced by ZP or EGF but not by the Ca2+-ionophore A23187. Moreover, inhibition of ERK1/2 along the capacitation process diminished almost completely the sperm's ability to go through the acrosome reaction, while inhibition at the end of capacitation attenuated the acrosome reaction rate by only 45%. The fact that the acrosome reaction, induced by the Ca2+ -ionophore A23187, was not inhibited by U0126 suggests that ERK1/2 mediates the acrosome reaction by activating Ca2+ transport into the cell. Direct determination of intracellular [Ca2+] revealed that Ca2+ influx induced by EGF or ZP was completely blocked by U0126. Thus, it has been established that the increase in ERK1/2 phosphorylation/activation in response to ZP or by activation of the EGF receptor (EGFR) by EGF, is a key event for intracellular Ca2+ elevation and the subsequent occurrence of the acrosome reaction.

Isomerase-catalyzed binding of interleukin-1 receptor-associated kinase 1 to the EVH1 domain of vasodilator-stimulated phosphoprotein

Interleukin-1 receptor-associated kinase 1 (IRAK1) is a crucial signaling kinase in the immune system, involved in Toll-like receptor signaling. Vasodilator-stimulated phosphoprotein (VASP) is a central player in cell migration that regulates actin polymerization and connects signaling events to cytoskeletal remodeling. A VASP–IRAK1 interaction is thought to be important in controlling macrophage migration in response to protein kinase C-ε activation. We show that the monomeric VASP EVH1 domain directly binds to the 168WPPPP172 motif in the IRAK1 undefined domain (IRAK1-UD) with moderate affinity (KDApp = 203 ± 3 μM). We further show that this motif adopts distinct cis and trans isomers for the Trp168–Pro169 peptide bond with nearly equal populations, and that binding to the VASP EVH1 domain is specific for the trans isomer, coupling binding to isomerization. Nuclear magnetic resonance line shape analysis and tryptophan fluorescence experiments reveal the complete kinetics and thermodynamics of the binding reaction, showing diffusion-limited binding to the trans isomer followed by slow, isomerization-dependent binding. We further demonstrate that the peptidyl-prolyl isomerase cyclophilin A (CypA) catalyzes isomerization of the Trp168–Pro169 peptide bond and accelerates binding of the IRAK1-UD to the VASP EVH1 domain. We propose that binding of IRAK1 to tetrameric VASP is regulated by avidity through the assembly of IRAK1 onto receptor-anchored signaling complexes and that an isomerase such as CypA may modulate IRAK1 signaling in vivo. These studies demonstrate a direct interaction between IRAK1 and VASP and suggest a potential mechanism for how this interaction might be regulated by both assembly of IRAK1 onto an activated signaling complex and PPIase enzymes.

Bi-domain protein tyrosine phosphatases reveal an evolutionary adaptation to optimize signal transduction

SIGNIFICANCE

The bi-domain protein tyrosine phosphatases (PTPs) exemplify functional evolution in signaling proteins for optimal spatiotemporal signal transduction. Bi-domain PTPs are products of gene duplication. The catalytic activity, however, is often localized to one PTP domain. The inactive PTP domain adopts multiple functional roles. These include modulation of catalytic activity, substrate specificity, and stability of the bi-domain enzyme. In some cases, the inactive PTP domain is a receptor for redox stimuli. Since multiple bi-domain PTPs are concurrently active in related cellular pathways, a stringent regulatory mechanism and selective cross-talk is essential to ensure fidelity in signal transduction.

RECENT ADVANCES

The inactive PTP domain is an activator for the catalytic PTP domain in some cases, whereas it reduces catalytic activity in other bi-domain PTPs. The relative orientation of the two domains provides a conformational rationale for this regulatory mechanism. Recent structural and biochemical data reveal that these PTP domains participate in substrate recruitment. The inactive PTP domain has also been demonstrated to undergo substantial conformational rearrangement and oligomerization under oxidative stress.

CRITICAL ISSUES AND FUTURE DIRECTIONS

The role of the inactive PTP domain in coupling environmental stimuli with catalytic activity needs to be further examined. Another aspect that merits attention is the role of this domain in substrate recruitment. These aspects have been poorly characterized in vivo. These lacunae currently restrict our understanding of neo-functionalization of the inactive PTP domain in the bi-domain enzyme. It appears likely that more data from these research themes could form the basis for understanding the fidelity in intracellular signal transduction.

The intracellular juxtamembrane domain of discoidin domain receptor 2 (DDR2) is essential for receptor activation and DDR2-mediated cancer progression

Discoidin domain receptors (DDRs) are unusual receptor tyrosine kinases (RTKs) that are activated by fibrillar collagens instead of soluble growth factors. DDRs play an important role in various cellular functions and disease processes, including malignant progression. Compared to other RTKs, DDRs have relatively long juxtamembrane domains, which are believed to contribute to receptor function. Despite this possibility, the function and mechanism of the juxtamembrane domain of DDRs have not yet been fully elucidated. In this study, we found that the cytoplasmic juxtamembrane 2 (JM2) region of DDR2 contributed to receptor dimerization, which is critical for receptor activation in response to collagen stimulation. A collagen-binding assay showed that JM2 was required for efficient binding of collagen to the discoidin (DS) domain. Immunohistochemical analysis of DDR2 expression using a tissue microarray demonstrated that DDR2 was overexpressed in several carcinoma tissues, including bladder, testis, lung, kidney, prostate and stomach. In H1299 cells, inhibition of DDR2 activity by overexpressing the juxtamembrane domain containing JM2 suppressed collagen-induced colony formation, cell proliferation and invasion via the inhibition of matrix metalloproteinase-2 and matrix metalloproteinase-9. Taken together, our results suggest that JM2-mediated dimerization is likely to be essential for DDR2 activation and cancer progression. Thus, inhibition of DDR2 function using a JM2-containing peptide might be a useful strategy for the treatment of DDR2-positive cancers.

Role of receptor tyrosine kinases and their ligands in glioblastoma

Glioblastoma multiforme is the most frequent, aggressive and fatal type of brain tumor. Glioblastomas are characterized by their infiltrating nature, high proliferation rate and resistance to chemotherapy and radiation. Recently, oncologic therapy experienced a rapid evolution towards “targeted therapy,” which is the employment of drugs directed against particular targets that play essential roles in proliferation, survival and invasiveness of cancer cells. A number of molecules involved in signal transduction pathways are used as molecular targets for the treatment of various tumors. In fact, inhibitors of these molecules have already entered the clinic or are undergoing clinical trials. Cellular receptors are clear examples of such targets and in the case of glioblastoma multiforme, some of these receptors and their ligands have become relevant. In this review, the importance of glioblastoma multiforme in signaling pathways initiated by extracellular tyrosine kinase receptors such as EGFR, PDGFR and IGF-1R will be discussed. We will describe their ligands, family members, structure, activation mechanism, downstream molecules, as well as the interaction among these pathways. Lastly, we will provide an up-to-date review of the current targeted therapies in cancer, in particular glioblastoma that employ inhibitors of these pathways and their benefits.

The EGFR family: not so prototypical receptor tyrosine kinases

The epidermal growth factor receptor (EGFR) was among the first receptor tyrosine kinases (RTKs) for which ligand binding was studied and for which the importance of ligand-induced dimerization was established. As a result, EGFR and its relatives have frequently been termed "prototypical" RTKs. Many years of mechanistic studies, however, have revealed that--far from being prototypical--the EGFR family is quite unique. As we discuss in this review, the EGFR family uses a distinctive "receptor-mediated" dimerization mechanism, with ligand binding inducing a dramatic conformational change that exposes a dimerization arm. Intracellular kinase domain regulation in this family is also unique, being driven by allosteric changes induced by asymmetric dimer formation rather than the more typical activation-loop phosphorylation. EGFR family members also distinguish themselves from other RTKs in having an intracellular juxtamembrane (JM) domain that activates (rather than autoinhibits) the receptor and a very large carboxy-terminal tail that contains autophosphorylation sites and serves an autoregulatory function. We discuss recent advances in mechanistic aspects of all of these components of EGFR family members, attempting to integrate them into a view of how RTKs in this important class are regulated at the cell surface.

Apigenin and Wogonin Regulate Epidermal Growth Factor Receptor Signaling Pathway Involved in MUC5AC Mucin Gene Expression and Production from Cultured Airway Epithelial Cells

Background

We investigated whether wogonin and apigenin significantly affect the epidermal growth factor receptor (EGFR) signaling pathway involved in MUC5AC mucin gene expression, and production from cultured airway epithelial cells; this was based on our previous report that apigenin and wogonin suppressed MUC5AC mucin gene expression and production from human airway epithelial cells.

Methods

Confluent NCI-H292 cells were pretreated with wogonin or apigenin for 15 minutes or 24 hours and then stimulated with epidermal growth factor (EGF) for 24 hours or the indicated periods.

Results

We found that incubation of NCI-H292 cells with wogonin or apigenin inhibited the phosphorylation of EGFR. The downstream signals of EGFR such as phosphorylation of MEK1/2 and ERK1/2 were also inhibited by wogonin or apigenin.

Conclusion

The results suggest that wogonin and apigenin inhibits EGFR signaling pathway, which may explain how they inhibit MUC5AC mucin gene expression and production induced by EGF.

The Atlantic salmon protein tyrosine kinase Tyk2: molecular cloning, modulation of expression and function

Tyk2, a member of the Janus Kinase (JAK) family of protein tyrosine kinases, is required for interferon-α/β binding and signaling in higher vertebrates. Currently, little is known about the role of the different JAKs in signaling responses to interferon (IFN) in lower vertebrates including fish. In this paper we report the identification and characterization of Atlantic salmon (Salmo salar) Tyk2. Four cDNA sequences, two containing an open reading frame encoding full-length Tyk protein and two with an up-stream in frame stop codon, were identified. The deduced amino acid sequences of the salmon full-length Tyk2 proteins showed highest identity with Tyk2 from other species and their transcripts were ubiquitously expressed. Like in mammals the presented data suggests that salmon Tyk2 is auto-phosporylated when ectopically expressed in cells. In our experiments, full-length salmon Tyk2 overexpressed in CHSE-cells phosphorylated itself, while both a kinase-deficient mutant and the truncated Tyk2 (Tyk-short) were inactive. Interestingly, the overexpression of full length Tyk2 was shown to up-regulate the transcript levels of the IFN induced gene Mx, thus indicating the involvement of salmon Tyk2 in the salmon IFN I pathway.

Something old, something new and something borrowed: emerging paradigm of insulin-like growth factor type 1 receptor (IGF-1R) signaling regulation

The insulin-like growth factor type 1 receptor (IGF-1R) plays a key role in the development and progression of cancer; however, therapeutics targeting it have had disappointing results in the clinic. As a receptor tyrosine kinase (RTK), IGF-1R is traditionally described as an ON/OFF system, with ligand stabilizing the ON state and exclusive kinase-dependent signaling activation. Newly added to the traditional model, ubiquitin-mediated receptor downregulation and degradation was originally described as a response to ligand/receptor interaction and thus inseparable from kinase signaling activation. Yet, the classical model has proven over-simplified and insufficient to explain experimental evidence accumulated over the last decade, including kinase-independent signaling, unbalanced signaling, or dissociation between signaling and receptor downregulation. Based on the recent findings that IGF-1R “borrows” components of G-protein coupled receptor (GPCR) signaling, including β-arrestins and G-protein-related kinases, we discuss the emerging paradigm for the IGF-1R as a functional RTK/GPCR hybrid, which integrates the kinase signaling with the IGF-1R canonical GPCR characteristics. The contradictions to the classical IGF-1R signaling concept as well as the design of anti-IGF-1R therapeutics treatment are considered in the light of this paradigm shift and we advocate recognition of IGF-1R as a valid target for cancer treatment.

Targeting tumor micro-environment for design and development of novel anti-angiogenic agents arresting tumor growth

Angiogenesis: a process of generation of new blood vessels has been proved to be necessary for sustained tumor growth and cancer progression. Inhibiting angiogenesis pathway has long been remained a significant hope for the development of novel, effective and target orientated antitumor agents arresting the tumor proliferation and metastasis. The process of neoangiogenesis as a biological process is regulated by several pro- and anti-angiogenic factors, especially vascular endothelial growth factor, fibroblast growth factor, epidermal growth factor, hypoxia inducible factor 1 and transforming growth factor. Every endothelial cell destined for vessel formation is equipped with receptors for these angiogenic peptides. Moreover, numerous other angiogenic cytokines such as platelet derived growth factor (PGDF), placenta growth factor (PGF), nerve growth factor (NGF), stem-cell factor (SCF), and interleukins-2, 4, 6 etc. These molecular players performs critical role in regulating the angiogenic switch. Couple of decade's research in molecular aspects of tumor biology has unraveled numerous structural and functional mysteries of these angiogenic peptides. In present article, a detailed update on the functional and structural peculiarities of the various angiogenic peptides is described focusing on structural opportunities made available that has potential to be used to modulate function of these angiogenic peptides in developing therapeutic agents targeting neoplastic angiogenesis. The data may be useful in the mainstream of developing novel anticancer agents targeting tumor angiogenesis. We also discuss major therapeutic agents that are currently used in angiogenesis associated therapies as well as those are subject of active research or are in clinical trials.

The fall and rise of pharmacology--(re-)defining the discipline?

Pharmacology is an integrative discipline that originated from activities, now nearly 7000 years old, to identify therapeutics from natural product sources. Research in the 19th Century that focused on the Law of Mass Action (LMA) demonstrated that compound effects were dose-/concentration-dependent eventually leading to the receptor concept, now a century old, that remains the key to understanding disease causality and drug action. As pharmacology evolved in the 20th Century through successive biochemical, molecular and genomic eras, the precision in understanding receptor function at the molecular level increased and while providing important insights, led to an overtly reductionistic emphasis. This resulted in the generation of data lacking physiological context that ignored the LMA and was not integrated at the tissue/whole organism level. As reductionism became a primary focus in biomedical research, it led to the fall of pharmacology. However, concerns regarding the disconnect between basic research efforts and the approval of new drugs to treat 21st Century disease tsunamis, e.g., neurodegeneration, metabolic syndrome, etc. has led to the reemergence of pharmacology, its rise, often in the semantic guise of systems biology. Against a background of limited training in pharmacology, this has resulted in issues in experimental replication with a bioinformatics emphasis that often has a limited relationship to reality. The integration of newer technologies within a pharmacological context where research is driven by testable hypotheses rather than technology, together with renewed efforts in teaching pharmacology, is anticipated to improve the focus and relevance of biomedical research and lead to novel therapeutics that will contain health care costs.

Homodimerization of the Wnt receptor DERAILED recruits the Src family kinase SRC64B

Ryk pseudokinase receptors act as important transducers of Wnt signals, particularly in the nervous system. Little is known, however, of their interactions at the cell surface. Here, we show that a Drosophila Ryk family member, DERAILED (DRL), forms cell surface homodimers and can also heterodimerize with the two other fly Ryks, DERAILED-2 and DOUGHNUT ON 2. DERAILED homodimerization levels increase significantly in the presence of its ligand, WNT5. In addition, DERAILED displays ligand-independent dimerization mediated by a motif in its transmembrane domain. Increased dimerization of DRL upon WNT5 binding or upon the replacement of DERAILED's extracellular domain with the immunoglobulin Fc domain results in an increased recruitment of the Src family kinase SRC64B, a previously identified downstream pathway effector. Formation of the SRC64B/DERAILED complex requires SRC64B's SH2 domain and DERAILED's PDZ-binding motif. Mutations in DERAILED's inactive tyrosine kinase-homologous domain also disrupt the formation of DERAILED/SRC64B complexes, indicating that its conformation is likely important in facilitating its interaction with SRC64B. Finally, we show that DERAILED's function during embryonic axon guidance requires its Wnt-binding domain, a putative juxtamembrane extracellular tetrabasic cleavage site, and the PDZ-binding domain, indicating that DERAILED's activation involves a complex set of events including both dimerization and proteolytic processing.

Targeting mutant KRAS for anticancer therapeutics: a review of novel small molecule modulators

The RAS proteins play a role in cell differentiation, proliferation, and survival. Aberrant RAS signaling has been found to play a role in 30% of all cancers. KRAS, a key member of the RAS protein family, is an attractive cancer target, as frequent point mutations in the KRAS gene render the protein constitutively active. A number of attempts have been made to target aberrant KRAS signaling by identifying small molecule compounds that (1) are synthetic lethal to mutant KRAS, (2) block KRAS/GEF interactions, (3) inhibit downstream KRAS effectors, or (4) inhibit the post-translational processing of RAS proteins. In addition, inhibition of novel targets outside the main KRAS signaling pathway, specifically the cell cycle related kinase PLK1, has been shown have an effect in cells that harbor mutant KRAS. Herein we review the use of various high-throughput screening assays utilized to identify new small-molecule compounds capable of targeting mutant KRAS-driven cancers.

Controversies in antiepidermal growth factor receptor therapy in metastatic colorectal cancer

The randomized first-line trials, including the CRYSTAL trial, the OPUS trial, and the PRIME trial, have demonstrated the significant efficacy of cetuximab or panitumumab in patients with v-Ki-ras2 Kirsten rat sarcoma viral oncogene homolog (KRAS) wild-type tumors. The addition of an antiepidermal growth factor receptor (anti-EGFR)-directed monoclonal antibody to chemotherapy for these patients significantly improved progression-free survival, response rates, and R0 resection rates to a greater extent than overall survival compared with patients who received chemotherapy alone. However, 2 recent randomized phase 3 trials, the MRC COIN trial and the Nordic VII trial, reported an unexpected lack of benefit from the addition of cetuximab to chemotherapy in the first-line setting. In addition, recent retrospective analyses performed on a pooled data set from major clinical trials added more complexity, reporting an unexpected association of KRAS G13D mutation with a better clinical outcome compared with patients who had other KRAS mutations in the first-line and salvage settings, whereas the other independent analysis failed to demonstrate a benefit from panitumumab in patients with the same KRAS G13D mutation. The anti-EGFR monoclonal antibody-associated skin toxicity and the controversial strategies of management also are discussed. In this review, the authors analyze the previous randomized clinical trials and more critically re-evaluate recent trials and subgroup analyses to derive 3 factors that need to be taken into consideration regarding the addition of EGFR-directed monoclonal antibodies to chemotherapy: the preclinical data on mechanisms of action between chemotherapy and anti-EGFR antibodies along with mechanisms of resistance to anti-EGFR antibodies, the role of cross-over events in overall survival data, and the significant dose reductions of chemotherapeutic agents when combined with anti-EGFR agents.

Partial rescue of geldanamycin-induced TrkA depletion by a proteasome inhibitor in PC12 cells

In this work we tried to identify mechanisms that could explain how chemical inhibition of heat-shock protein 90 reduces nerve growth factor signaling in rat pheochromocytoma PC12 cells. Geldanamycin is an antibiotic originally discovered based on its ability to bind heat-shock protein 90. This interaction can lead to the disruption of heat-shock protein 90-containing multimolecular complexes. It can also induce the inhibition or even degradation of partner proteins dissociated from the 90 kDa chaperone and, eventually, can cause apoptosis, for instance, in PC12 cells. Before the onset of initial apoptotic events, however, a marked decrease in the activity of extracellular signal-regulated kinases ERK 1/2 and protein kinase B/Akt can be observed together with reduced expression of the high affinity nerve growth factor receptor, tropomyosine-related kinase, TrkA, in this cell type. The proteasome inhibitor MG-132 can effectively counteract the geldanamycin-induced reduction of TrkA expression and it can render TrkA and ERK1/2 phosphorylation but not that of protein kinase B/Akt by nerve growth factor again inducible. We have found altered intracellular distribution of TrkA in geldanamycin-treated and proteasome-inhibited PC12 cells that may, at least from the viewpoint of protein localization explain why nerve growth factor remains without effect on protein kinase B/Akt. The lack of protein kinase B/Akt stimulation by nerve growth factor in turn reveals why nerve growth factor treatment cannot save PC12 cells from geldanamycin-induced programmed cell death. Our observations can help to better understand the mechanism of action of geldanamycin, a compound with strong human therapeutical potential.

MAPK/ERK Signaling Pathway Analysis in Primary Osteoblasts From Patients With Nonsyndromic Sagittal Craniosynostosis

OBJECTIVE

The MAPK/ERK signaling pathway has been implicated in several craniosynostosis syndromes and represents a plausible target for therapeutic management of craniosynostosis. The causes of sagittal nonsyndromic craniosynostosis (sNSC) have not been well understood and the role that MAPK/ERK signaling cascade plays in this condition warrants an investigation. We hypothesized that MAPK-signaling is misregulated in calvarial osteoblasts derived from patients with sNSC.

METHODS

In order to analyze if the MAPK/ERK pathway is perturbed in sNSC, we established primary calvarial osteoblast cell lines from patients undergoing surgery for correction of this congenital anomaly. Appropriate negative and positive control cell lines were used for comparison, and we examined the levels of phosphorylated ERK by immunoblotting.

RESULTS

Primary osteoblasts from patients with sNSC showed no difference in ERK1/2 phosphorylation with or without FGF2 stimulation as compared with control osteoblasts.

CONCLUSION

Under the described test conditions, we did not observe convincing evidence that MAPK/ERK signaling contributes to the development of sNSC.

Clopidogrel delays gastric ulcer healing in rats

Clopidogrel is not safe enough for the gastric mucosa in patients with high risk of peptic ulcer. This study aimed to explore if clopidogrel delays gastric ulcer healing and elucidate the involved mechanisms. Gastric ulcer was induced in rats and the ulcer size, mucosal epithelial cell proliferation of the ulcer margin, expression of growth factors [epidermal growth factor (EGF), basic fibroblast growth factor] and their receptors, and signal transduction pathways for cell proliferation were measured and compared between the clopidogrel-treated group and untreated controls. For the in vitro part, rat gastric mucosal epithelial cell line (RGM-1 cells) was used to establish EGF receptor over-expressed cells. Cell proliferation and molecular change under EGF treatment (10ng/ml) with and without clopidogrel (10(-6)M) were demonstrated. Ulcer size was significantly larger in the clopidogrel-treated group compared to the control and mucosal epithelial cell proliferation of the ulcer margin was significantly decreased in the clopidogrel-treated group (P<0.05). Clopidogrel (2mg and 10mg/kg/day) significantly decreased ulcer-induced gastric epithelial cell proliferation and ulcer-stimulated expressions of EGF receptor and phosphorylated extracellular signal-regulated kinase (PERK) at the ulcer margin (P<0.05). Clopidogrel (10(-6)M) also inhibited EGF-stimulated EGF receptor, PERK expression, and cell proliferation in RGM-1 cells (P<0.05), and caused much less inhibition of EGF-stimulated cell proliferation in EGF receptor over-expressed RGM-1 cells than in RGM-1 cells (22% vs. 32% reduction). In conclusion, clopidogrel delays gastric ulcer healing in rats via inhibiting gastric epithelial cell proliferation, at least by inhibition of the EGF receptor-ERK signal transduction pathway.

The epidermal growth factor receptor as a therapeutic target in epithelial ovarian cancer

A majority of patients with ovarian carcinoma who receive conventional treatment of surgical staging and platinum-based chemotherapy recur and ultimately succumb to their diseases. Novel therapies that target specific pathways involved in ovarian tumorigenesis are rapidly emerging. The epidermal growth factor receptor (EGFR) is overexpressed in 30-98% of epithelial ovarian carcinoma (EOC), and the signaling cascades activated are related with cell proliferation, migration and invasion, and angiogenesis, as well as resistance to cell apoptosis. Various trials are ongoing focusing on EGFR as an attractive target in treatment of EOC. Anti-EGFR monoclonal antibodies (MAbs), cetuximab and panitumumab, and tyrosine kinase inhibitors (TKIs), erlotinib and gefitinib, are the most advanced in clinical development. The available data suggests that MAbs and TKIs only show marginal activity when they are used alone, but combination with platinum-based chemotherapy can induce elevated overall response rate in recurrent EOC patients. Consequently, mechanisms for intrinsic and extrinsic resistance have been explored due to the poor clinical response to EGFR-targeted therapy. Careful consideration of these clinical studies and the possible mechanisms involved in resistance can provide evidence for improvements in subsequent research. Identification of responder profiles and development of rational regimen of combination therapy of EGFR-targeted therapy with other effective treatment modalities may eventually bring about substantial progress in the treatment of epithelial ovarian cancers.

Leucine-rich repeat, immunoglobulin-like and transmembrane domain 3 (LRIT3) is a modulator of FGFR1

Fibroblast growth factor receptors (FGFRs) play critical roles in craniofacial and skeletal development via multiple signaling pathways including MAPK, PI3K/AKT, and PLC-?. FGFR-mediated signaling is modulated by several regulators. Proteins with leucine-rich repeat (LRR) and/or immunoglobulin (IG) superfamily domains have been suggested to interact with FGFRs. In addition, fibronectin leucine-rich repeat transmembrane protein 3 (FLRT3) has been shown to modulate the FGFR-mediated signaling via the fibronectin type III (FNIII) domain. Therefore proteins with LRR, IG, and FNIII are candidate regulators of the FGFRs. Here we identify leucine-rich repeat, immunoglobulin-like and transmembrane domain 3 (LRIT3) as a regulator of the FGFRs.

Molecular imaging with activatable reporter systems

Molecular imaging is a newly emerged multiple disciplinary field that aims to visualize, characterize and quantitatively measure biological processes at cellular and molecular levels in humans and other living systems. A reporter gene is a piece of DNA encoding reporter protein, which presents as a readily measurable phenotype that can be distinguished easily from the background of endogenous protein. After being transferred into cells of organ systems (transgenes), the reporter gene can be utilized to visualize transcriptional and posttranscriptional regulation of gene expression, protein-protein interactions, or trafficking of proteins or cells in living subjects. Herein, we review previous classification of reporter genes and regroup the reporter gene based imaging as basic, inducible and activatable, based on the regulation of reporter gene transcription and post-translational modification of reporter proteins. We then focus on activatable reporters, in which the signal can be activated at the posttranslational level for visualizing protein-protein interactions, protein phosphorylation or tertiary structure changes. The applications of several types of activatable reporters will also be summarized. We conclude that activatable reporter imaging can benefit both basic biomedical research and drug development.

Treatment of recurrent metastatic head and neck cancer: focus on cetuximab

EGFR belongs to the ErbB family of receptor tyrosine kinases and is associated with worse prognosis in head and neck squamous cell carcinoma (HNSCC). Cetuximab is a monoclonal antibody to the extracellular domain of EGFR and inhibits its downstream actions via multiple mechanisms. Besides its proven efficacy in locally advanced and incurable HNSCC, cetuximab has the distinct advantage of having a relatively tolerable side effect profile and not potentiating radiation toxicity. Though therapies for advanced HNSCC are evolving, locoregional recurrence and/or distant metastases occur in a large percentage of patients. Though some patients can be salvaged with surgery or radiation therapy, the majority are incurable, and are treated palliatively with systemic therapy. In the setting of first line therapy for recurrent/metastatic HNSCC, the EXTREME trial provided level 1 evidence that cetuximab improves overall survival when combined with cisplatinum and 5 FU. Following progression on first line chemotherapy, several phase II trials suggest that cetuximab monotherapy is a reasonable choice in this setting. Future studies should concentrate on clinical and molecular markers that may allow more personalized approaches to treating HNSCC, and combining EGFR inhibitors with other agents in a synergistic approach.

L1 cell adhesion molecule and epidermal growth factor receptor activation confer cisplatin resistance in intrahepatic cholangiocarcinoma cells

Intrahepatic cholangiocarcinoma (ICC) is refractory to conventional chemotherapy. We previously generated chemoresistant ICC (SCK(R)) cells and showed that AKT and ERK signaling conferred cisplatin resistance. Here, we report that epidermal growth factor receptor (EGFR) signaling and L1 cell adhesion molecule (L1CAM) conferred cisplatin resistance in SCK(R) cells in an additive fashion. Activation of EGFR connected to AKT and ERK signaling pathways may induce anti-apoptosis and promote cell proliferation, while L1CAM promoted cell proliferation by mainly activating ERK signaling. Inhibition of EGFR activation or L1ACM greatly sensitized the cells to cisplatin. EGFR and L1CAM may be important targets for ICC therapy.

Agonist-induced formation of FGFR1 homodimers and signaling differ among members of the FGF family

Fibroblast growth factor receptor 1 (FGFR1) is known to be activated by homodimerization in the presence of both the FGF agonist ligand and heparan sulfate glycosaminoglycan. FGFR1 homodimers in turn trigger a variety of downstream signaling cascades via autophosphorylation of tyrosine residues in the cytoplasmic domain of FGFR1. By means of Bioluminescence Energy Resonance Transfer (BRET) as a sign of FGFR1 homodimerization, we evaluated in HEK293T cells the effects of all known FGF agonist ligands on homodimer formation. A significant correlation between BRET(2) signaling and ERK1/2 phosphorylation was observed, leading to a further characterization of the binding and signaling properties of the FGF subfamilies. FGF agonist ligand-FGFR1 binding interactions appear as the main mechanism for the control of FGFR1 homodimerization and MAPK signaling which demonstrated a high correlation. The bioinformatic analysis demonstrates the interface of the two pro-triplets SSS (Ser-Ser-Ser) and YGS (Tyr-Gly-Ser) located in the extracellular and intracellular domain of the FGFR1. These pro-triplets are postulated participate in the FGFR1 homodimerization interface interaction. The findings also reveal that FGF agonist ligands within the same subfamily of the FGF gene family produced similar increases in FGFR1 homodimer formation and MAPK signaling. Thus, the evolutionary relationship within this gene family appears to have a distinct functional relevance.

Defining the cancer master switch

BACKGROUND

Recent research has focused on signaling cascades and their interactions yielding considerable insight into which genetic pathways are targeted and how they tend to be altered in tumors. Therapeutic interventions now can be designed based on the knowledge of pathways vital to tumor growth and survival. These critical targets for intervention, master switches for cancer, are termed so because the tumor attempts to "flip the switch" in a way that promotes its survival, whereas molecular therapy aims to "switch off" signals important for tumor-related processes.

METHODS

Literature review.

CONCLUSIONS

Defining useful targets for therapy depends on identifying pathways that are crucial for tumor growth, survival, and metastasis. Because not all signaling cascades are created equal, selecting master switches or targets for intervention needs to be done in a systematic fashion. This discussion proposes a set of criteria to define what it means to be a cancer master switch and provides examples to illustrate their application.

Oxidative stress-induced oligomerization inhibits the activity of the non-receptor tyrosine phosphatase STEP61

The neuron-specific tyrosine phosphatase STriatal Enriched Phosphatase (STEP) is emerging as an important mediator of glutamatergic transmission in the brain. STEP is also thought to be involved in the etiology of neurodegenerative disorders that are linked to oxidative stress such as Alzheimer's disease and cerebral ischemia. However, the mechanism by which oxidative stress can modulate STEP activity is still unclear. In this study, we have investigated whether dimerization may play a role in regulating the activity of STEP. Our findings show that STEP(61), the membrane associated isoform, can undergo homodimerization under basal conditions in neurons. Dimerization of STEP(61) involves intermolecular disulfide bond formation between two cysteine residues (Cys 65 and Cys 76 respectively) present in the hydrophobic region at the N-terminus specific to STEP(61). Oxidative stress induced by hydrogen peroxide leads to a significant increase in the formation of dimers and higher-order oligomers of STEP(61). Using two substrates, para-nitrophenylphosphate and extracellular-regulated kinase MAPK we further demonstrate that oligomerization leads to a significant reduction in its enzymatic activity.

The SCHOOL of nature: III. From mechanistic understanding to novel therapies

Protein-protein interactions play a central role in biological processes and thus represent an appealing target for innovative drug design and development. They can be targeted by small molecule inhibitors, modulatory peptides and peptidomimetics, which represent a superior alternative to protein therapeutics that carry many disadvantages. Considering that transmembrane signal transduction is an attractive process to therapeutically control multiple diseases, it is fundamentally and clinically important to mechanistically understand how signal transduction occurs. Uncovering specific protein-protein interactions critical for signal transduction, a general platform for receptor-mediated signaling, the signaling chain homooligomerization (SCHOOL) platform, suggests these interactions as universal therapeutic targets. Within the platform, the general principles of signaling are similar for a variety of functionally unrelated receptors. This suggests that global therapeutic strategies targeting key protein-protein interactions involved in receptor triggering and transmembrane signal transduction may be used to treat a diverse set of diseases. This also assumes that clinical knowledge and therapeutic strategies can be transferred between seemingly disparate disorders, such as T cell-mediated skin diseases and platelet disorders or combined to develop novel pharmacological approaches. Intriguingly, human viruses use the SCHOOL-like strategies to modulate and/or escape the host immune response. These viral mechanisms are highly optimized over the millennia, and the lessons learned from viral pathogenesis can be used practically for rational drug design. Proof of the SCHOOL concept in the development of novel therapies for atopic dermatitis, rheumatoid arthritis, cancer, platelet disorders and other multiple indications with unmet needs opens new horizons in therapeutics.

The SCHOOL of nature: II. Protein order, disorder and oligomericity in transmembrane signaling

Recent reports have revealed that many proteins that do not adopt globular structures under native conditions, thus termed intrinsically disordered proteins (IDPs), are involved in cell signaling. Intriguingly, physiologically relevant oligomerization of IDPs has been recently observed and shown to exhibit unique biophysical characteristics, including the lack of significant changes in chemical shift and peak intensity upon binding. In this work, I summarize several distinct features of protein disorder that are especially important as related to receptor-mediated transmembrane signal transduction. I also hypothesize that interactions of IDPs with their protein or lipid partners represent a general biphasic process with the "no disorder-to-order" fast interaction which, depending on the interacting partner, may or may not be accompanied by the slow formation of a secondary structure. Further, I suggest signaling-related functional connections between protein order, disorder, and oligomericity and hypothesize that receptor oligomerization induced or tuned upon ligand binding outside the cell is translated across the membrane into protein oligomerization inside the cell, thus providing a general platform, the Signaling Chain HOmoOLigomerization (SCHOOL) platform, for receptor-mediated signaling. This structures our current multidisciplinary knowledge and views of the mechanisms governing the coupling of recognition to signal transduction and cell response. Importantly, this approach not only reveals previously unrecognized striking similarities in the basic mechanistic principles of function of numerous functionally diverse and unrelated surface membrane receptors, but also suggests the similarity between therapeutic targets, thus opening new horizons for both fundamental and clinically relevant studies.