Getting a first clue about SPRED functions

Activation of Ras requires the ERM-dependent link of actin to the plasma membrane

BACKGROUND

Receptor tyrosine kinases (RTKs) participate in a multitude of signaling pathways, some of them via the small G-protein Ras. An important component in the activation of Ras is Son of sevenless (SOS), which catalyzes the nucleotide exchange on Ras.

PRINCIPAL FINDINGS

We can now demonstrate that the activation of Ras requires, in addition, the essential participation of ezrin, radixin and/or moesin (ERM), a family of actin-binding proteins, and of actin. Disrupting either the interaction of the ERM proteins with co-receptors, down-regulation of ERM proteins by siRNA, expression of dominant-negative mutants of the ERM proteins or disruption of F-actin, abolishes growth factor-induced Ras activation. Ezrin/actin catalyzes the formation of a multiprotein complex consisting of RTK, co-receptor, Grb2, SOS and Ras. We also identify binding sites for both Ras and SOS on ezrin; mutations of these binding sites destroy the interactions and inhibit Ras activation. Finally, we show that the formation of the ezrin-dependent complex is necessary to enhance the catalytic activity of SOS and thereby Ras activation.

CONCLUSIONS

Taking these findings together, we propose that the ERM proteins are novel scaffolds at the level of SOS activity control, which is relevant for both normal Ras function and dysfunction known to occur in several human cancers.

Sprouty genes prevent excessive FGF signalling in multiple cell types throughout development of the cerebellum

Fibroblast growth factors (FGFs) and regulators of the FGF signalling pathway are expressed in several cell types within the cerebellum throughout its development. Although much is known about the function of this pathway during the establishment of the cerebellar territory during early embryogenesis, the role of this pathway during later developmental stages is still poorly understood. Here, we investigated the function of sprouty genes (Spry1, Spry2 and Spry4), which encode feedback antagonists of FGF signalling, during cerebellar development in the mouse. Simultaneous deletion of more than one of these genes resulted in a number of defects, including mediolateral expansion of the cerebellar vermis, reduced thickness of the granule cell layer and abnormal foliation. Analysis of cerebellar development revealed that the anterior cerebellar neuroepithelium in the early embryonic cerebellum was expanded and that granule cell proliferation during late embryogenesis and early postnatal development was reduced. We show that the granule cell proliferation deficit correlated with reduced sonic hedgehog (SHH) expression and signalling. A reduction in Fgfr1 dosage during development rescued these defects, confirming that the abnormalities are due to excess FGF signalling. Our data indicate that sprouty acts both cell autonomously in granule cell precursors and non-cell autonomously to regulate granule cell number. Taken together, our data demonstrate that FGF signalling levels have to be tightly controlled throughout cerebellar development in order to maintain the normal development of multiple cell types.

Short mandible, maxilla and cranial base are common in patients with neurofibromatosis 1

Neurofibromatosis type 1 (NF1) is an autosomal-dominant neuro-cutaneous-skeletal syndrome. Neurofibromatosis type 1 is one of the Rasopathies, and at the cellular level NF1 results in a hyperactive Ras pathway. In the current investigation, our aim was to study lateral skull X-rays (cephalograms) to assess NF1-related craniofacial morphology. A total of 85 Finnish patients with NF1, including four patients with plexiform neurofibroma of the 5th cranial nerve, and their age- and gender-matched controls, were enrolled in the study. The results showed that patients with NF1 typically had a short mandible, maxilla, and cranial base compared with healthy controls, irrespective of age, but the results were statistically significant only in adults. The length of the mandible, the maxilla and the cranial base correlated with the height of patients under 19 yr of age, but this correlation was absent in adult patients. Thus, a tall adult patient with NF1 may have short jaws and a short cranial base. In conclusion, the NF1 gene apparently influences the growth of craniofacial bones, thus contributing to the craniofacial morphology in NF1.

The genetic determination of skin pigmentation: KITLG and the KITLG/c-Kit pathway as key players in the onset of human familial pigmentary diseases

Cutaneous pigmentation is regulated by a complex melanogenic network in which skin cells synthesize growth factors and cytokines. Mutations in genes encoding these regulators modify their expression and/or functionality, leading to altered signaling pathways and contributing to altered skin phenotypes. In this issue, Amyere et al. report a genome-wide analysis of seven families with familial progressive hyperpigmentation and hypopigmentation, identifying three new mutations in KITLG. The study underlines the relevance of investigating candidate genes implicated in the onset of pigmentary disorders. Furthermore, Amyere et al. suggest that different pigmentary diseases can result from the same mutation or different mutations in the same gene, and they offer hope for the development of new and efficacious treatment strategies.

Biology using engineering tools: the negative feedback amplifier

Negative feedback is an ubiquitous feature of biological networks. Recent work from Sturm and colleaguespresents experimental evidence that biological negative feedback can serve the same function as it does for engineered systems: robustness to perturbations within the feedback loop. Such behavior has important implications for how to attack deregulated signaling networks containing negative feedback in diseases such as cancer.

Interaction of the receptor FGFRL1 with the negative regulator Spred1

FGFRL1 is a member of the fibroblast growth factor receptor family. It plays an essential role during branching morphogenesis of the metanephric kidneys, as mice with a targeted deletion of the Fgfrl1 gene show severe kidney dysplasia. Here we used the yeast two-hybrid system to demonstrate that FGFRL1 binds with its C-terminal, histidine-rich domain to Spred1 and to other proteins of the Sprouty/Spred family. Members of this family are known to act as negative regulators of the Ras/Raf/Erk signaling pathway. Truncation experiments further showed that FGFRL1 interacts with the SPR domain of Spred1, a domain that is shared by all members of the Sprouty/Spred family. The interaction could be verified by coprecipitation of the interaction partners from solution and by codistribution at the cell membrane of COS1 and HEK293 cells. Interestingly, Spred1 increased the retention time of FGFRL1 at the plasma membrane where the receptor might interact with ligands. FGFRL1 and members of the Sprouty/Spred family belong to the FGF synexpression group, which also includes FGF3, FGF8, Sef and Isthmin. It is conceivable that FGFRL1, Sef and some Sprouty/Spred proteins work in concert to control growth factor signaling during branching morphogenesis of the kidneys and other organs.

Sprouty2 and Spred1-2 proteins inhibit the activation of the ERK pathway elicited by cyclopentenone prostanoids

Sprouty and Spred proteins have been widely implicated in the negative regulation of the fibroblast growth factor receptor-extracellular regulated kinase (ERK) pathway. In considering the functional role of these proteins, we explored their effects on ERK activation induced by cyclopentenone prostanoids, which bind to and activate Ras proteins. We therefore found that ectopic overexpression in HeLa cells of human Sprouty2, or human Spred1 or 2, inhibits ERK1/2 and Elk-1 activation triggered by the cyclopentenone prostanoids PGA₁ and 15d-PGJ₂. Furthermore, we found that in HT cells that do not express Sprouty2 due to hypermethylation of its gene-promoter, PGA₁-provoked ERK activation was more intense and sustained compared to other hematopoietic cell lines with unaltered Sprouty2 expression. Cyclopentenone prostanoids did not induce Sprouty2 tyrosine phosphorylation, in agreement with its incapability to activate tyrosine-kinase receptors. However, Sprouty2 Y55F, which acts as a defective mutant upon tyrosine-kinase receptor stimulation, did not inhibit cyclopentenone prostanoids-elicited ERK pathway activation. In addition, Sprouty2 did not affect the Ras-GTP levels promoted by cyclopentenone prostanoids. These results unveil both common and differential features in the activation of Ras-dependent pathways by cyclopentenone prostanoids and growth factors. Moreover, they provide the first evidence that Sprouty and Spred proteins are negative regulators of the ERK/Elk-1 pathway activation induced not only by growth-factors, but also by reactive lipidic mediators.

Multiple genetic loci modulate lung adenocarcinoma clinical staging

PURPOSE

The main prognostic factor of lung cancer patient outcome is clinical stage, a parameter of tumor aggressiveness. Our study was conducted to test whether germ line variations modulate individual differences in clinical stage.

EXPERIMENTAL DESIGN

We conducted a case-only genome-wide association study (GWAS) using a 620,901 single-nucleotide polymorphism (SNP) array in a first series of 600 lung adenocarcinoma (ADCA) patients and in a replication series of 317 lung ADCA patients.

RESULTS

GWAS identified 54 putatively associated SNPs, 3 of which were confirmed in the replication series. Joint analysis of the two series pointed to 22 statistically associated (P < 0.01) genetic variants that together explained about 20% of the phenotypic variation in clinical staging (P < 2 × 10(-16)) and showed a statistically significant difference in overall survival (P = 8.0 × 10(-8)). The strongest statistical association was observed at rs10278557 (P = 1.1 × 10(-5)), located in the mesenchyme homeobox 2 (MEOX2) gene.

CONCLUSION

These data point to the role of germ line variations involving multiple loci in modulating clinical stage and, therefore, prognosis in lung ADCA patients.

Disorders of dysregulated signal traffic through the RAS-MAPK pathway: phenotypic spectrum and molecular mechanisms

RAS GTPases control a major signaling network implicated in several cellular functions, including cell fate determination, proliferation, survival, differentiation, migration, and senescence. Within this network, signal flow through the RAF-MEK-ERK pathway-the first identified mitogen-associated protein kinase (MAPK) cascade-mediates early and late developmental processes controlling morphology determination, organogenesis, synaptic plasticity, and growth. Signaling through the RAS-MAPK cascade is tightly controlled; and its enhanced activation represents a well-known event in oncogenesis. Unexpectedly, in the past few years, inherited dysregulation of this pathway has been recognized as the cause underlying a group of clinically related disorders sharing facial dysmorphism, cardiac defects, reduced postnatal growth, ectodermal anomalies, variable cognitive deficits, and susceptibility to certain malignancies as major features. These disorders are caused by heterozygosity for mutations in genes encoding RAS proteins, regulators of RAS function, modulators of RAS interaction with effectors, or downstream signal transducers. Here, we provide an overview of the phenotypic spectrum associated with germline mutations perturbing RAS-MAPK signaling, the unpredicted molecular mechanisms converging toward the dysregulation of this signaling cascade, and major genotype-phenotype correlations.

Sprouty2 downregulates angiogenesis during mouse skin wound healing

Angiogenesis is regulated by signals received by receptor tyrosine kinases such as vascular endothelial growth factor receptors. Mammalian Sprouty (Spry) proteins are known to function by specifically antagonizing the activation of the mitogen-activated protein kinase signaling pathway by receptor tyrosine kinases, a pathway known to promote angiogenesis. To examine the role of Spry2 in the regulation of angiogenesis during wound repair, we used a model of murine dermal wound healing. Full-thickness excisional wounds (3 mm) were made on the dorsum of anesthetized adult female FVB mice. Samples were harvested at multiple time points postwounding and analyzed using real-time RT-PCR, Western blot analysis, and immunofluorescent histochemistry. Spry2 mRNA and protein levels in the wound bed increased significantly during the resolving phases of healing, coincident with the onset of vascular regression in this wound model. In another experiment, intracellular levels of Spry2 or its dominant-negative mutant (Y55F) were elevated by a topical application to the wounds of controlled-release gel containing cell permeable, transactivator of transcription-tagged Spry2, Spry2Y55F, or green fluorescent protein (as control). Wound samples were analyzed for vascularity using CD31 immunofluorescent histochemistry as well as for total and phospho-Erk1/2 protein content. The treatment of wounds with Spry2 resulted in a significant decrease in vascularity and a reduced abundance of phospho-Erk1/2 compared with wounds treated with the green fluorescent protein control. In contrast, the wounds treated with the dominant-negative Spry2Y55F exhibited a moderate increase in vascularity and elevated phospho-Erk1/2 content. These results indicate that endogenous Spry2 functions to downregulate angiogenesis in the healing murine skin wound, potentially by inhibiting the mitogen-activated protein kinase signaling pathway.

Direct association of Sprouty-related protein with an EVH1 domain (SPRED) 1 or SPRED2 with DYRK1A modifies substrate/kinase interactions

The mammalian SPRED (Sprouty-related protein with an EVH1 domain) proteins include a family of three members, SPRED1-3. Currently, little is known about their biochemistry. The best described, SPRED1, has been shown to inhibit the Ras/ERK pathway downstream of Ras. All three SPREDs have a cysteine-rich domain (CRD) that has high homology to the CRD of the Sprouty family of proteins, several of which are also Ras/ERK inhibitors. In the belief that binding partners would clarify SPRED function, we assayed for their associated proteins. Here, we describe the direct and endogenous interaction of SPRED1 and SPRED2 with the novel kinase, DYRK1A. DYRK1A has become the subject of recent research focus as it plays a central role in Caenorhabditis elegans oocyte maturation and egg activation, and there is strong evidence that it could be involved in Down syndrome in humans. Both SPRED1 and SPRED2 inhibit the ability of DYRK1A to phosphorylate its substrates, Tau and STAT3. This inhibition occurs via an interaction of the CRD of the SPREDs with the kinase domain of DYRK1A. DYRK1A substrates must bind to the kinase to enable phosphorylation, and SPRED proteins compete for the same binding site to modify this process. Our accumulated evidence indicates that the SPRED proteins are likely physiological modifiers of DYRK1A.

Dact2 is expressed in the developing ureteric bud/collecting duct system of the kidney and controls morphogenetic behavior of collecting duct cells

The overall pattern of the developing kidney is set in large part by the developing ureteric bud/collecting duct system, and dysgenesis of this system accounts for a variety of clinically significant renal diseases. Understanding how the behavior of cells in the developing ureteric bud/collecting duct is controlled is therefore important to understanding the normal and abnormal kidney. Dact proteins have recently been identified as cytoplasmic regulators of intracellular signaling. Dact1 inhibits Wnt signaling, and Dact2 inhibits transforming growth factor (TGF)-β signaling. Here, we report that Dact2 is expressed in developing and adult mouse kidneys, specifically in the ureteric bud/collecting duct epithelium, a structure whose morphogenesis is controlled partially by TGF-β. When small interfering RNA is used to knock down Dact2 expression in collecting duct cells, they show some constitutive phospho-Smad2, undetectable in controls, and elevated phospho-Smad2 in response to TGF-β. They also show defective migration and, in a monolayer wound-healing assay, they fail to assemble a leading edge “cable” of actomyosin and advance instead as a disorganized mass of lamellipodium-bearing cells. This effect is seriously exacerbated by exogenous TGF-β, although control cells tolerate it well. In three-dimensional culture, Dact2 knockdown cells form cysts and branching tubules, but the outlines of the cysts made by knockdown cells are ragged rather than smooth and the branching tubules are decorated with many fine spikes not seen in controls. These data suggest Dact2 plays a role in regulating morphogenesis by renal collecting duct cells, probably by protecting cells from overly strong TGF-β pathway activation.

Spred2 inhibits TGF-beta1-induced urokinase type plasminogen activator expression, cell motility and epithelial mesenchymal transition

TGF-beta1 is a potent inductor of malignance in cancer cells. TGF-beta1 stimulates the expression of extracellular matrix degrading proteases, cell migration and it is also involved in the epithelial-mesenchymal transition (EMT). In the present work, we analyzed the role of Spred2 in the urokinase-type plasminogen activator (uPA) stimulation, EMT and cell migration by TGF-beta1. We found that both the expression of mRNA and the protein level of Spred2 were lower in transformed keratinocytes PDV compared with immortalized keratinocytes MCA-3D. The transient ectopic expression of Spred2 in PDV cells inhibited the TGF-beta1-transactivated SRE-Luc reporter which is related with the ERK1,2 signal. The stable ectopic expression of Spred2 in PDV cells (SP cells) led to the loss of ERK 1,2 activation by TGF-beta1, although Smad2 activation was not affected, and the knockdown of Spred2 enhanced the activation of ERK1,2 signal by TGF-beta1. The increment of uPA expression induced by TGF-beta1 was suppressed in SP cells. In contrast, the stimulus on PAI-1 expression was not affected and comparable to parental PDV cells. SP cells under TGF-beta1 treatment were unable to display the EMT, since the overexpression of Spred2 abolished the TGF-beta1-induced disruption of the E-cadherin cell to cell interactions, reorganization of the actin cytoskeleton and upregulation of the mesenchymal marker vimentin. Finally, SP cells could not respond to the TGF-beta1 stimulus on cell migration. Taken together, the data in the present study suggests that Spred2 is a regulator of TGF-beta1-induced malignance in transformed keratinocytes.

The dual-specificity MAP kinase phosphatases: critical roles in development and cancer

Intracellular signaling by mitogen-activated protein (MAP) kinases (MAPK) is involved in many cellular responses and in the regulation of various physiological and pathological conditions. Tight control of the localization and duration of extracellular-regulated kinase (ERK), c-Jun NH(2)-terminal kinase (JNK), or p38 MAPK activity is thus a fundamental aspect of cell biology. Several members of the dual-specificity phosphatase (DUSPs) family are able to dephosphorylate MAPK isoforms with different specificity, cellular, and tissue localization. Understanding how these phosphatases are themselves regulated during development or in physiological and pathological conditions is therefore fundamental. Over the years, gene deletion and knockdown studies have completed initial in vitro studies and shed a new light on the global and specific roles of DUSPs in vivo. Whereas DUSP1, DUSP2, and DUSP10 appear as crucial players in the regulation of immune responses, other members of the family, like the ERK-specific DUSP6, were shown to play a major role in development. Recent findings on the involvement of DUSPs in cancer progression and resistance will also be discussed.

Spred2 is involved in imatinib-induced cytotoxicity in chronic myeloid leukemia cells

Spreds, a recently established class of negative regulators of the Ras-ERK (extracellular signal-regulated kinase) pathway, are involved in hematogenesises, allergic disorders and tumourigenesis. However, their role in hematologic neoplasms is largely unknown. Possible effects of Spreds on other signal pathways closely related to Ras-ERK have been poorly investigated. In this study, we investigated the in vitro effects of Spred2 on chronic myeloid leukemia (CML) cells. In addition to inhibiting the well-established Ras-ERK cascade, adenovirus-mediated Spred2 over-expression inhibits constitutive and stem cell factor (SCF)-stimulated sphingosine kinase-1 (SPHK1) and Mcl-1 expression, as well as inhibiting proliferation and inducing apoptosis in CML cells. In K562 cells and primary CML cells, imatinib induces endogenous Spred2 expression. Spred2 silencing by stable RNA interference partly protects K562 cells against imatinib-induced apoptosis. Together, these data implicate Spred2 in imatinib-induced cytotoxicity in CML cells, possibly by inhibiting the Ras-ERK cascade and the pro-survival signaling molecules SPHK1 and Mcl-1. These findings reveal potential targets for selective therapy of CML.

Spred1, a negative regulator of Ras-MAPK-ERK, is enriched in CNS germinal zones, dampens NSC proliferation, and maintains ventricular zone structure

Neural stem cells (NSCs) have great potential for self-renewal, which must be tightly regulated to generate appropriate cell numbers during development and to prevent tumor formation. The Ras-MAPK-ERK pathway affects mitogen-stimulated proliferation, and negative regulators are likely to be important for keeping self-renewal in check. Sprouty-related protein with an EVH1 domain (Spred1) is a recently discovered negative Ras-MAPK-ERK regulator linked to a neurofibromatosis 1 (NF-1)-like human syndrome; however, its role in CNS development has not been explored. We show that Spred1 is highly enriched in CNS germinal zones during neurogenesis. Spred1 knockdown increases NSC self-renewal and progenitor proliferation cell-autonomously, and overexpression causes premature differentiation. Surprisingly, Spred1 knockdown in vivo in the embryonic mouse forebrain frequently resulted in periventricular heterotopia, developmental abnormalities often associated with mutations in genes in the vesicular trafficking pathway that cause disruption of germinal zones and impair cell migration. In cortical progenitor cells, Spred1 localizes within distinct vesicles, indicating a potential role in transport. Spred1 knockdown gradually leads to disruption of the apical ventricular zone and loss of radial glia alignment. This impairs late neuronal migration, resulting in the formation of periventricular masses. Thus, Spred1 is critical for normal cortical development, as it modulates progenitor self-renewal/proliferation and helps maintain the integrity and organization of germinal zones.

From synapse to nucleus: novel targets for treating depression

The need for newer compounds to treat depression is an ever-growing concern due to the enormous societal and financial ramifications of this disorder. Here, we review some of the candidate systems that could potentially be involved in depression, or an inherent resistance to depression termed resilience, and the numerous protein targets for these systems. A substantial body of literature provides strong evidence that neurotrophic factors, glutamate receptors, hypothalamic feeding peptides, nuclear hormone receptors, and epigenetic mechanisms, among others, will make for interesting targets when examining depressive behavior or resilience in preclinical models, and eventually clinical trials. Although some of these targets for depression already appear promising, new waves of more selective compounds for any molecular system should promote a better understanding of this complex disease and perhaps improved treatments.

Similar expression to FGF (Sef) inhibits fibroblast growth factor-induced tumourigenic behaviour in prostate cancer cells and is downregulated in aggressive clinical disease

Background:

The fibroblast growth factor (FGF) axis is an important mitogenic stimulus in prostate carcinogenesis. We have previously reported that transcript level of human similar expression to FGF (hSef), a key regulator of this pathway, is downregulated in clinical prostate cancer. In this study we further analysed the role of hSef in prostate cancer.

Methods:

hSef function was studied in in vitro and in vivo prostate cancer models using stable over-expression clones. Protein expression of hSef was studied in a comprehensive tissue microarray.

Results:

Stable over-expression of hSef resulted in reduced in vitro cancer cell proliferation, migration and invasive potential. In an in vivo xenograft model, the expression of hSef significantly retarded prostate tumour growth as compared with empty vector (P=0.03) and non-transfected (P=0.0001) controls. Histological examination further showed a less invasive tumour phenotype and reduced numbers of proliferating cells (P=0.0002). In signalling studies, hSef inhibited FGF-induced ERK phosphorylation, migration to the nucleus and activation of a reporter gene. Constitutively active Ras, however, was able to reverse these effects, suggesting that hSef exerts an effect either above or at the level of Ras in prostate cancer cells. In a large tissue microarray, we observed a significant loss of hSef protein in high-grade (P<0.0001) and metastatic (P<0.0001) prostate cancer.

Conclusions:

Considered together, the role of hSef in attenuating FGF signalling and evidence of downregulation in advanced tumours argue strongly for a tumour suppressor function in human prostate cancer.

Identification of LATS transcriptional targets in HeLa cells using whole human genome oligonucleotide microarray

Human LATS1 and LATS2) (LATS1/2) are tumor suppressors that have been shown to be mutated or downregulated in several human cancers including leukemia, lung, prostate and breast cancers. However, the precise mechanisms and the proteins modulated by LATS1/2 that are responsible for these events remain largely unknown. To elucidate potential signaling pathways, the current study investigated the expression profile in HeLa cells with reduced expression of LATS1/2. Using RNA-mediated interference, both LATS1 and LATS2 were substantially knocked-down, and accordingly, this lead to an increase in multiple phenotypes associated with tumor progression, including enhanced cell proliferation, resistance to drug-induced cell death, and increased cell migration. Using whole human genome Oligo (60-mer) arrays (Agilent), genes modulated by loss of LATS1/2 were identified and functionally grouped into categories including cell proliferation, cell death, cell adhesion and motility, as well as cell communication. Selected genes, including known tumor suppressor genes and oncogenes such as CDKN1A, WISP2, SLIT2, TP53INP1, BIRC4BP, SPRY2, SPRY4, SPRED1, FAT4, and CYR61 were confirmed by qRT-PCR to be significantly differentially expressed. Importantly, the collection of genes identified suggests that LATS1/2 function through diverse mechanisms and multiple signaling pathways including the Hippo signaling pathway, as well as the p53, Ras-ERK, or WNT networks, to inhibit tumor progression.

Ras signaling and therapies

More than 25 years have passed since activating mutations in Ras genes were identified in DNA from human tumors. In this time, it has been established beyond doubt that these mutations play a direct role in causing cancer, and do so in collaboration with a number of other oncogenes and tumor suppressors. Oncogenic mutant Ras proteins are resistant to downregulation by GAP-mediated hydrolysis of bound GTP, and therefore signal persistently. Efforts to develop therapies that block Ras oncoprotein function directly have failed. The high affinity of Ras proteins for GTP has discouraged attempts to identify GTP-analogs. Ras processing enzymes have been targeted, but unfortunately, K-Ras, the Ras protein that plays the major role in human cancer, has proven refractory to these approaches. Further progress has been made with drugs that block downstream signaling: the approved drug Sorafenib inhibits Raf kinase, and its clinical benefits in liver cancer are greatest in patients in which the mitogen activated protein kinase (MAPK) signaling pathway is hyperactive. Other Raf kinase inhibitors, as well as drugs that block mitogen-activated protein kinase / extracellular signal-regulated kinase kinase (MEK) and various steps in the PI 3' kinase pathway, are under development. Here we will discuss the complexities of Ras signaling and their effects on targeting the Ras pathway in the future.

The solution structure of pGolemi, a high affinity Mena EVH1 binding miniature protein, suggests explanations for paralog-specific binding to Ena/VASP homology (EVH) 1 domains

Ena/VASP homology 1 (EVH1) domains are polyproline binding domains that are present in a wide range of adaptor proteins, among them Ena/VASP proteins involved in actin remodeling and axonal guidance. The interaction of ActA, a transmembrane protein from the food-borne pathogen Listeria monocytogenes, with EVH1 domains has been shown to be crucial for recruitment of the host's actin skeleton and, as a consequence, for the infectivity of this bacterium. We present the structure of a synthetic high-affinity Mena EVH1 ligand, pGolemi, capable of paralog-specific binding, solved by NMR spectroscopy. This peptide shares the common pancreatic peptide fold with its scaffold, avian pancreatic peptide, but shows pivotal differences in the amino-terminus. The interplay of spatial fixation and flexibility appears to be the reason for its high affinity towards Mena EVH1. Combined with earlier investigations, our structural data shed light on the specificity determinants of pGolemi and the importance of additional binding epitopes around the residues Thr74 and Phe32 on EVH1 domains regulating paralog specificity. Our results are expected to facilitate the design of other high-affinity, paralog-specific EVH1 domain ligands, and serve as a fundament for the investigation of the molecular mode of action of EVH1 domains.

Intermolecular interactions of Sprouty proteins and their implications in development and disease

Receptor tyrosine kinase (RTK) signaling is spatially and temporally regulated by a number of positive and negative regulatory mechanisms. These regulatory mechanisms control the amplitude and duration of the signals initiated at the cell surface to have a normal or aberrant biological outcome in development and disease, respectively. In the past decade, the Sprouty (Spry) family of proteins has been identified as modulators of RTK signaling in normal development and disease. This review summarizes recent advances concerning the biological activities modulated by Spry family proteins, their interactions with signaling proteins, and their involvement in cardiovascular diseases and cancer. The diversity of mechanisms in the regulation of Spry expression and activity in cell systems emphasizes the crucial role of Spry proteins in development and growth across the animal kingdom.

A severe form of Noonan syndrome and autosomal dominant café-au-lait spots - evidence for different genetic origins

AIM

The clinical overlap among Noonan syndrome (NS), cardio-facio-cutaneous (CFC), LEOPARD and Costello syndromes as well as Neurofibromatosis type 1 is extensive, which complicates the process of diagnosis. Further genotype-phenotype correlations are required to facilitate future diagnosis of these patients. Therefore, investigations of the genetic cause of a severe phenotype in a patient with NS and the presence of multiple café-au-lait spots (CAL) spots in the patient and four members of the family were performed.

METHODS

Mutation analyses of candidate genes, PTPN11, NF1, SPRED1 and SPRED2, associated with these syndromes, were conducted using DNA sequencing.

RESULTS

A previously identified de novo mutation, PTPN11 F285L and an inherited NF1 R1809C substitution in the index patient were found. However, neither PTPN11 F285L, NF1 R1809C, SPRED1 nor SPRED2 segregated with CAL spots in the family. The results indicate that the familial CAL spots trait in this family is caused by a mutation in another gene, distinct from previous genes associated with CAL spots in these syndromes.

CONCLUSION

We suggest that the atypical severe symptoms in the index patient may be caused by an additive effect on the F285L mutation in PTPN11 by another mutation, for example the NF1 R1809C or alternatively, the not yet identified gene mutation associated with CAL spots in this family.

Genetic modifier loci linked to intima formation induced by low flow in the mouse carotid

OBJECTIVE

Previously we found dramatic strain-dependent differences in a low flow model of vascular remodeling. Specifically, intima formation in the left common carotid artery was approximately 30-fold greater in SJL compared to C3HeB/Fe (C3H/F) mice. We hypothesized that a few genes control intima formation in response to low flow. A C3H/F and SJL backcross resulted in broad range of N2 intima phenotypes.

METHODS AND RESULTS

Using genome-wide scan we identified two highly significant quantitative trait loci (QTLs) for intima, Im1 (intima modifier 1 locus) on chromosome 2 (Chr2; 77.6 cM, LOD=6.4), and Im2 on Chr11 (17 cM, LOD=5.3). One significant QTL Im3 was found on Chr18 (6 cM, LOD=3.0), and two suggestive QTLs (LOD=1.5 and 1.8) were identified on Chr7 and Chr17, respectively. Interestingly, the intima/media ratio trait mapped to the same QTLs as the intima trait. Haplotype mapping predicted 40 candidate genes. Six of these genes contained SNPs that differed between C3H/F and SJL.

CONCLUSIONS

We have successfully mapped 3 QTLs (Im1, Im2, and Im3) that are associated with carotid intima formation in response to low blood flow. These results may be important in identifying genes that influence carotid intima-media thickening and predict cardiovascular disease in humans.

Epigenetic inactivation of the ERK inhibitor Spry2 in B-cell diffuse lymphomas

Spry2 has been characterized as a negative regulator of the extracellular-regulated kinase (ERK) pathway. In this study we analysed whether epigenetic alterations of hSpry2 promoter occur in human lymphoid/hematopoietic malignancies. Our results revealed that hSpry2 promoter was hypermethylated in the HT cell line derived from a B-cell diffuse lymphoma, which correlated with decreased hSpry2 expression. We detected deregulation of the ERK pathway in these cells, but not in other blood cell lines expressing hSpry2. In addition, the ectopic overexpression of hSpry2 in HT cells drastically reduced the activation of ERK upon phorbol 12-myristate-13-acetate stimulation. Nude mice inoculated with HT mock cells developed tumors seven times larger than those from HT-hSpry2-transfected cells. We found hypermethylation of hSpry2 promoter in 37% (26 cases out of 71) of primary tumors from patients with B-cell diffuse lymphoma but none in normal B lymphocytes from 37 healthy individuals. Finally, we detected that hSpry2 promoter hypermethylation was associated with a significant decrease in the 5-year survival rate. These data suggest that hSpry2 could be important in lymphoid malignancies.

Sprouty proteins, masterminds of receptor tyrosine kinase signaling

Angiogenesis relies on endothelial cells properly processing signals from growth factors provided in both an autocrine and a paracrine manner. These mitogens bind to their cognate receptor tyrosine kinases (RTKs) on the cell surface, thereby activating a myriad of complex intracellular signaling pathways whose outputs include cell growth, migration, and morphogenesis. Understanding how these cascades are precisely controlled will provide insight into physiological and pathological angiogenesis. The Sprouty (Spry) family of proteins is a highly conserved group of negative feedback loop modulators of growth factor-mediated mitogen-activated protein kinase (MAPK) activation originally described in Drosophila. There are four mammalian orthologs (Spry1-4) whose modulation of RTK-induced signaling pathways is growth factor- and cell context-dependent. Endothelial cells are a group of highly differentiated cell types necessary for defining the mammalian vasculature. These cells respond to a plethora of growth factors and express all four Spry isoforms, thus highlighting the complexity that is required to form and maintain vessels in mammals. This review describes Spry functions in the context of endothelial biology and angiogenesis, and provides an update on Spry-interacting proteins and Spry mechanisms of action.