Expression and functional role of negative signalling regulators in tumour development and progression

Conditional Ablation of Spred1 and Spred2 in the Eye Lens Negatively Impacts Its Development and Growth

The development and growth of the eye depends on normal lens morphogenesis and its growth. This growth, in turn, is dependent on coordinated proliferation of the lens epithelial cells and their subsequent differentiation into fiber cells. These cellular processes are tightly regulated to maintain the precise cellular structure and size of the lens, critical for its transparency and refractive properties. Growth factor-mediated MAPK signaling driven by ERK1/2 has been reported as essential for regulating cellular processes of the lens, with ERK1/2 signaling tightly regulated by endogenous antagonists, including members of the Sprouty and related Spred families. Our previous studies have demonstrated the importance of both these inhibitory molecules in lens and eye development. In this study, we build on these findings to highlight the importance of Spreds in regulating early lens morphogenesis by modulating ERK1/2-mediated lens epithelial cell proliferation and fiber differentiation. Conditional loss of both Spred1 and Spred2 in early lens morphogenesis results in elevated ERK1/2 phosphorylation, hyperproliferation of lens epithelia, and an associated increase in the rate of fiber differentiation. This results in transient microphakia and microphthalmia, which disappears, owing potentially to compensatory Sprouty expression. Our data support an important temporal role for Spreds in the early stages of lens morphogenesis and highlight how negative regulation of ERK1/2 signaling is critical for maintaining lens proliferation and fiber differentiation in situ throughout life.

The negative regulatory Spred1 and Spred2 proteins are required for lens and eye morphogenesis

The transparent and refractive properties of the ocular lens are dependent on its precise cellular structure, supported by the regulation of lens cellular processes of proliferation and differentiation that are essential throughout life. The ERK/MAPK-signalling pathway plays a crucial role in regulating lens cell proliferation and differentiation, and in turn is regulated by inhibitory molecules including the Spred family of proteins to modulate and attenuate the impact of growth factor stimulation. Given Spreds are strongly and distinctly expressed in lens, along with their established inhibitory role in a range of different tissues, we investigated the role these antagonists play in regulating lens cell proliferation and differentiation, and their contribution to lens structure and growth. Using established mice lines deficient for either or both Spred 1 and Spred 2, we demonstrate their role in regulating lens development by negatively regulating ERK1/2 activity. Mice deficient for both Spred 1 and Spred 2 have impaired lens and eye development, displaying irregular lens epithelial and fibre cell activity as a result of increased levels of phosphorylated ERK1/2. While Spred 1 and Spred 2 do not appear to be necessary for induction and early stages of lens morphogenesis (prior to E11.5), nor for the formation of the primary fibre cells, they are required for the continuous embryonic growth and differentiation of the lens.

Drug resistance of BRAF-mutant melanoma: Review of up-to-date mechanisms of action and promising targeted agents

Melanoma onset and progression are associated with a high variety of activating mutations in the MAPK-pathway, most frequently involving BRAF (35-45%) and NRAS (15-25%) genes, but also c-KIT and PTEN. Targeted therapies with BRAF and MEK inhibitors showed promising results over the past years, but it is known that most responses are temporary, and almost all of patients develop a tumor relapse within one year. Different drug-resistance mechanisms underlie the progression of disease and activation of both MAPK and PI3K/AKT/mTOR pathways. Therefore, in this article we reviewed the main studies about clinical effects of several target inhibitors, describing properly the most prominent mechanisms of both intrinsic and acquired resistance. Furthermore, suggestive strategies for overcoming drug resistance and the most recent alternative combination therapies to optimize the use of MAPK pathway inhibitors were also discussed.

Spred negatively regulates lens growth by modulating epithelial cell proliferation and fiber differentiation

Spred, like Sprouty (Spry) and also Sef proteins, have been identified as important regulators of receptor tyrosine kinase (RTK)-mediated MAPK/ERK-signaling in various developmental systems, controlling cellular processes such as proliferation, migration and differentiation. Spreds are widely expressed during early embryogenesis, and in the eye lens, become more localised in the lens epithelium with later development, overlapping with other antagonists including Spry. Given the synexpression of Spreds and Spry in lens, in order to gain a better understanding of their specific roles in regulating growth factor mediated-signaling and cell behavior, we established and characterised lines of transgenic mice overexpressing Spred1 or Spred2, specifically in the lens. This overexpression of Spreds resulted in a small lens phenotype during ocular morphogenesis, retarding its growth by compromising epithelial cell proliferation and fiber differentiation. These in situ findings were shown to be dependent on the ability of Spreds to suppress MAPK-signaling, in particular FGF-induced ERK1/2-signaling in lens cells. This was validated in vitro using lens epithelial explants, that highlighted the overlapping role of Spreds with Spry2, but not Spry1. This study provides insights into the putative function of Spreds and Spry in situ, some overlapping and some distinct, and their importance in regulating lens cell proliferation and fiber differentiation contributing to lens and eye growth.

Hair follicle dermal condensation forms via Fgf20 primed cell cycle exit, cell motility, and aggregation

Mesenchymal condensation is a critical step in organogenesis, yet the underlying molecular and cellular mechanisms remain poorly understood. The hair follicle dermal condensate is the precursor to the permanent mesenchymal unit of the hair follicle, the dermal papilla, which regulates hair cycling throughout life and bears hair inductive potential. Dermal condensate morphogenesis depends on epithelial Fibroblast Growth Factor 20 (Fgf20). Here, we combine mouse models with 3D and 4D microscopy to demonstrate that dermal condensates form de novo and via directional migration. We identify cell cycle exit and cell shape changes as early hallmarks of dermal condensate morphogenesis and find that Fgf20 primes these cellular behaviors and enhances cell motility and condensation. RNAseq profiling of immediate Fgf20 targets revealed induction of a subset of dermal condensate marker genes. Collectively, these data indicate that dermal condensation occurs via directed cell movement and that Fgf20 orchestrates the early cellular and molecular events.

All mammal hair springs from hair follicles under the skin. These follicles sit in the dermis, beneath the outermost skin layer, the epidermis. In the embryo, hair follicles develop from unspecialized cells in two tissues, the epithelium and the mesenchyme, which will later develop into the dermis and epidermis, respectively. As development progresses, the cells of these tissues begin to cluster, and signals passing back and forth between the epithelium and mesenchyme instruct the cells what to do. In the mesenchyme, cells called fibroblasts squeeze up against their neighbors, forming patches called dermal condensates. These mature into so-called dermal papillae, which supply specific molecules called growth factors that regulate hair formation throughout lifetime.

Fibroblasts in the developing skin respond to a signal from the epithelium called fibroblast growth factor 20 (Fgf20), but we do not yet understand its effects. It is possible that Fgf20 tells the cells to divide, forming clusters of daughter cells around their current location. Or, it could be that Fgf20 tells the cells to move, encouraging them to travel towards one another to form groups.

To address this question, Biggs, Mäkelä et al. examined developing mouse skin grown in the laboratory. They traced cells marked with fluorescent tags to analyze their behavior as the condensates formed. This revealed that the Fgf20 signal acts as a rallying call, triggering fibroblast movement. The cells changed shape and moved towards one another, rather than dividing to create their own clusters. In fact, they switched off their own cell cycle as the condensates formed, halting their ability to divide. A technique called RNA sequencing revealed that Fgf20 also promotes the use of genes known to be active in dermal condensates.

Dermal papillae control hair growth, and transplanting them under the skin can form new hair follicles. However, these cells lose this ability when grown in the laboratory. Understanding how they develop could be beneficial for future hair growth therapy. Further work could also address fundamental questions in embryology. Condensates of cells from the mesenchyme also precede the formation of limbs, bones, muscles and organs. Extending this work could help us to understand this critical developmental step.

Cooperative Epigenetic Remodeling by TET2 Loss and NRAS Mutation Drives Myeloid Transformation and MEK Inhibitor Sensitivity

Mutations in epigenetic modifiers and signaling factors often co-occur in myeloid malignancies, including TET2 and NRAS mutations. Concurrent Tet2 loss and Nras^G12D expression in hematopoietic cells induced myeloid transformation, with a fully penetrant, lethal chronic myelomonocytic leukemia (CMML), which was serially transplantable. Tet2 loss and Nras mutation cooperatively led to decrease in negative regulators of mitogen-activated protein kinase (MAPK) activation, including Spry2, thereby causing synergistic activation of MAPK signaling by epigenetic silencing. Tet2/Nras double-mutant leukemia showed preferential sensitivity to MAPK kinase (MEK) inhibition in both mouse model and patient samples. These data provide insights into how epigenetic and signaling mutations cooperate in myeloid transformation and provide a rationale for mechanism-based therapy in CMML patients with these high-risk genetic lesions.

Crosstalk signaling in targeted melanoma therapy

Inhibition of the BRAF/MAPK pathway belongs to the standard therapies for patients with activating BRAF^V600E/K mutations. However, even in well-responding tumors, anti-tumorigenic effect and clinical benefit are only transient, and the original tumors often relapse. This demonstrates that there are remaining residual tumors, which have withstood therapy-induced apoptosis and which have the potential to resume growth. Although BRAF mutant melanoma cells seem to depend on BRAF/MAPK signaling, the inhibition of this pathway triggers several events, which modulate the tumor as well as the tumor niche. After a certain adaptation period, this can turn out to be beneficial for tumor growth and metastasis-even in cases of good initial tumor response. This review sheds light on the biology of BRAF/MEK inhibitor-sensitive melanoma cells, which survive targeted therapy and will address the crosstalk signaling events occurring in BRAF mutant melanomas when the BRAF/MAPK pathway is fully blocked. The knowledge of these events is important for potential future drug combinations, which enhance the inhibitory effect of BRAF/MEK inhibition, particularly in patients not eligible for immune therapy.

Loss of hSef promotes metastasis through upregulation of EMT in prostate cancer

We have previously reported that the negative signaling regulator Similar Expression to FGF (hSef) is downregulated in prostate cancer and its loss is associated with clinical metastasis. Here, we explored the mechanistic basis of this finding. We first confirmed our clinical observation by testing hSef manipulation in an in vivo metastasis model. hSef stable expressing cells (PC3M-hSef) or empty vector controls (PC3M-EV) were injected subcutaneously into the lateral thoracic walls of NOD-SCID gamma mice and lungs were harvested at autopsy. In this model, 6/7 PC3M-EV xenografts had definitive lung micro-metastasis whilst only 1/6 PC3M-hSef xenografts exhibited metastasis recapitulating the clinical scenario (p = 0.03). Gene expression studies revealed key perturbations in genes involved in cell motility and epithelial to mesenchymal transition (EMT) along with alterations in cognate signaling pathways. These results were validated in an EMT specific PCR array whereby hSef over-expression and silencing reciprocally altered E-Cadherin expression (p = <0.001) amongst other EMT markers. Immunohistochemistry of excised tumors from the xenografts also confirmed the effect of hSef in suppressing E-Cadherin expression at the protein level. Phosphokinase arrays further demonstrated a role for hSef in attenuating signaling of not only ERK-MAPK but also the JNK and p38 pathways as well. Taken together, these data suggest evidence that loss of hSef may be a critical event facilitating tumor dissemination of prostate cancer through alteration of EMT. Detection of downregulated hSef, along with other negative regulators, may therefore be a useful biomarker heralding a transition to a metastatic phenotype and warrants further exploration in this context.

Sprouty2 correlates with favorable prognosis of gastric adenocarcinoma via suppressing FGFR2-induced ERK phosphorylation and cancer progression

Fibroblast growth factor receptor 2 (FGFR2) has been identified as a predictive biomarker for unfavorable prognosis of gastric adenocarcinoma. As a well-defined antagonist in FGFR2-induced RAS/ERK activation, ectopic expression of sprouty (SPRY) family was reported in several kinds of cancers except gastric cancer. To explore the clinical significance of SPRY family and its correlation with FGFR2, we detected the expression of FGFR2 and SPRY family in 104 cases of gastric adenocarcinoma and subsequently analyzed their correlations with clinicopathological factors and overall survival rates by univariate and multivariate analysis. As the result, we demonstrated that both FGFR2 high-expression and SPRY2 low-expression indicated poorer prognosis of gastric adenocarcinoma. SPRY2 low-expression was significantly associated with FGFR2 high-expression, positive lymphatic invasion and metastasis. We further proved that SPRY2 could suppress FGFR2-induced ERK phosphorylation, cell proliferation and invasion with experiments in vitro and in vivo. In conclusion, we demonstrated that SPRY2 low-expression is a biomarker for unfavorable prognosis in gastric adenocarcinoma. SPRY2 can antagonize FGFR2-induced proliferation and invasion via suppressing ERK phosphorylation in gastric cancer cells, indicating SPRY2 as a potential therapeutic target for gastric adenocarcinoma treatment.

FGFs: crucial factors that regulate tumour initiation and progression

Fibroblast growth factors (FGFs) are crucial signalling molecules involved in normal cell growth, differentiation and proliferation. Over the past few decades, a large body of research has illustrated effects of individual FGFs on tumour initiation and progression. Tumour development is commonly accompanied with generation of new blood and lymph vessels, which support enhanced cell proliferation. Moreover, acquisition of tumour cells of the epithelial-mesenchymal transition (EMT) phenotype, enhances tumour cell migration and invasion potentials, crucial steps in tumour metastasis. This review summarizes recent findings concerning roles of FGFs in angiogenesis, lymphangiogenesis and EMT.

Regulation of BRAF protein stability by a negative feedback loop involving the MEK-ERK pathway but not the FBXW7 tumour suppressor

The ^V600EBRAF oncogenic mutation is detected in a wide range of human cancers and induces hyperactivation of the downstream MEK–ERK signalling cascade. Although output of the BRAF–MEK–ERK pathway is regulated by feed-forward RAF activity, feedback control also plays an important role. One such feedback pathway has been identified in Caenorhabditis elegans and involves ERK-mediated phosphorylation of BRAF within a CDC4 phosphodegron (CPD), targeting BRAF for degradation via CDC4 (also known as FBXW7), a component of the SKP1/CUL1/F-box (SCF) E3 ubiquitin ligase complex. Here we investigate this pathway in mammalian cells. Short-term expression of autochthonous ^V600EBRAF in mouse embryonic fibroblasts (MEFs) leads to down-regulation of BRAF protein levels in a proteasome-dependent manner and ^V600EBRAF has a reduced half-life compared to ^WTBRAF in HEK293^T cells. These effects were reversed by treatment with the MEK inhibitor PD184352. We have identified the equivalent CPD at residues 400–405 in human BRAF and have found that mutation of ERK phosphorylation sites at residues T401 and S405 in ^V600EBRAF increases the half-life of the protein. While BRAF and FBXW7 co-immunoprecipitated, the overexpression of FBXW7 did not influence the half-life of either ^WTBRAF or ^V600EBRAF. Furthermore, disruption of the substrate-binding site of mouse FBXW7 using the R482Q mutation did not affect the interaction with BRAF and the expression levels of ^WTBRAF and ^V600EBRAF were not altered in MEFs derived from mice with the homozygous knockin ^R482QFBXW7 mutation. Overall these data confirm the existence of a negative feedback pathway by which BRAF protein stability is regulated by ERK. However, unlike the situation in C. elegans, FBXW7 does not play a unique role in mediating subsequent BRAF degradation.

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Expression of oncogenic ^V600EBRAF down-regulates BRAF expression at the protein level.

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^V600EBRAF has a shorter half-life than ^WTBRAF.

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BRAF protein stability is subjected to feedback control by the MEK/ERK pathway.

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This feedback pathway is associated with the oncogene-induced senescence phenotype.

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ERK phosphorylation sites at T401 and S405 within a conserved CDC4 (FBXW7) phosphodegron of BRAF are involved in the feedback control pathway.

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The FBXW7 substrate recognition component of the SKP1/CUL1/F-box (SCF) complex binds to BRAF but is not uniquely involved in the regulation of its protein turnover.

KIAA1549: BRAF Gene Fusion and FGFR1 Hotspot Mutations Are Prognostic Factors in Pilocytic Astrocytomas

Up to 20% of patients with pilocytic astrocytoma (PA) experience a poor outcome. BRAF alterations and Fibroblast growth factor receptor 1 (FGFR1) point mutations are key molecular alterations in Pas, but their clinical implications are not established. We aimed to determine the frequency and prognostic role of these alterations in a cohort of 69 patients with PAs. We assessed KIAA1549:BRAF fusion by fluorescence in situ hybridization and BRAF (exon 15) mutations by capillary sequencing. In addition, FGFR1 expression was analyzed using immunohistochemistry, and this was compared with gene amplification and hotspot mutations (exons 12 and 14) assessed by fluorescence in situ hybridization and capillary sequencing. KIAA1549:BRAF fusion was identified in almost 60% of cases. Two tumors harbored mutated BRAF. Despite high FGFR1 expression overall, no cases had FGFR1 amplifications. Three cases harbored a FGFR1 p.K656E point mutation. No correlation was observed between BRAF and FGFR1 alterations. The cases were predominantly pediatric (87%), and no statistical differences were observed in molecular alterations–related patient ages. In summary, we confirmed the high frequency of KIAA1549:BRAF fusion in PAs and its association with a better outcome. Oncogenic mutations of FGFR1, although rare, occurred in a subset of patients with worse outcome. These molecular alterations may constitute alternative targets for novel clinical approaches, when radical surgical resection is unachievable.

Downregulation of Sprouty homolog 2 by microRNA-21 inhibits proliferation, metastasis and invasion, however promotes the apoptosis of multiple myeloma cells

The aim of the present study was to assess the effects of sprouty homolog 2 (SPRY2) gene regulation by miR-21 on the occurrence, development and tumor metastasis in multiple myeloma (MM). The miR-21 expression lentiviral vector (LV)-anti-miR-21 and a liposome transfection method were used to screen MM cell lines with stable silent SPRY2. Real-time quantitative polymerase chain reaction (PCR) and western blot analyses were used to detect SPRY2 expression and miR-21 protein expression levels. An MTT assay was used to assess cell proliferation. Flow cytometry was used for analysis of cell cycle. A scratch test/wound healing assay was used to detect the cell migration ability. A Transwell assay was used to detect the cell invasion ability. Real-time quantitative PCR and western blot analysis showed that in the MM cell lines with high endogenous miR-21 expression (RPMI8226 and KM3), SPRY2 expression was significantly lower. Conversely, in the U266 cell line with low endogenous miR-21 expression, SPRY2 expression was significantly higher, and the gray values of miR-21 and SPRY2 protein in the respective cell lines showed statistically significant differences (P<0.01). Following transfection of U266 cells, the expression of miR-21 in the U266/LV-anti-miR21 lentiviral multiplicity of infection (MOI) 20 group and -MOI 40 group decreased significantly compared with that in the untransfected U266 group (P<0.05). SPRY2 protein expression in U266 cells transfected with miR-21 mimics was significantly reduced compared with that in the non-transfected (untreated) group and the negative control-transfected group (P<0.01). An MTT assay showed that compared with the non-transfected and negative control groups, the cell growth rate as well as the proliferation rate were significantly decreased in the transfection group 48, 72 and 96 h after transfection (P<0.01). Flow cytometric analysis showed that 48 and 72 h after transfection of U266 cells with miR-21 mimics, the apoptotic rates were (24.7±1.97 and 38.6±1.56%) in the U266 group, (27.3±1.72 and 37.3±1.59%) in the siRNA group and (12.7±1.27 and 22.1±1.63%) in the U266/miR-21 group. Compared with the two control groups, the apoptotic rate in the U266/miR-21 group was significantly decreased and the G₀/G₁ phase cell population was significantly reduced (P<0.05). Scratch experiments showed that the cell migration ability was significantly reduced in the transfection group 24 and 48 h after transfection (P<0.05). A Transwell invasion assay confirmed that the number of U266 cells which migrated through a Matrigel-covered polyphosphate membrane significantly decreased in the transfection group 24 and 48 h after transfection. The cell-penetrating ability was also significantly decreased (P<0.05). In conclusion, the downregulation of SPRY2 gene expression mediated by miR-21 promotes the proliferation and invasion of MM cells in vitro, suggesting that miR-21 may be a novel potential molecular therapeutic target in the treatment of MM.

Therapeutic targets in pilocytic astrocytoma based on genetic analysis

Pilocytic astrocytoma (PA) is the most common astrocytic neoplasm of childhood. Patients have an extremely favorable prognosis after surgical resection, qualifying tumors for a grade I designation by the World Health Organization. The molecular data on PA support a key role for the BRAF oncogene in the pathogenesis of these tumors, with the KIAA1549-BRAF fusion being the most common alteration identified in sporadic cases, particularly those occurring in the posterior fossa. Constitutive activation of BRAF leads to downstream activation of the MEK/MAPK/ERK/p16 pathway, which interestingly is also used by cells to activate oncogene-induced senescence (OIS). In fact, the presence of an active OIS pathway might explain the periods of dormancy or spontaneous regression or both, that can be seen in PA. In addition to reviewing the historical evolution, clinicopathologic, predictive, prognostic, and molecular features of PA, we discuss current therapeutic strategies and the caveats that should be considered for the development of therapies that could be used to more effectively treat challenging cases. Individualized treatment requires identification of the type of MAPK alteration, as several alterations in BRAF have been described in addition to the KIAA1549-BRAF fusion. Combination regimens would also appear crucial to achieve tumor eradication and prevent the development of drug resistance. Balancing mitogen-activated protein kinases (MAPK) pathway inhibition with abrogation of an active OIS should be carefully considered as well to preserve any existing protective pathways. Importantly, PAs are largely indolent tumors, and care should be taken to avoid overtreatment, as aggressive therapy could cause more harm than good.

Spred2 modulates the erythroid differentiation induced by imatinib in chronic myeloid leukemia cells

Differentiation induction is currently considered as an alternative strategy for treating chronic myelogenous leukemia (CML). Our previous work has demonstrated that Sprouty-related EVH1 domainprotein2 (Spred2) was involved in imatinib mediated cytotoxicity in CML cells. However, its roles in growth and lineage differentiation of CML cells remain unknown. In this study, we found that CML CD34⁺ cells expressed lower level of Spred2 compared with normal hematopoietic progenitor cells, and adenovirus mediated restoration of Spred2 promoted the erythroid differentiation of CML cells. Imatinib could induce Spred2 expression and enhance erythroid differentiation in K562 cells. However, the imatinib induced erythroid differentiation could be blocked by Spred2 silence using lentiviral vector PLKO.1-shSpred2. Spred2 interference activated phosphorylated-ERK (p-ERK) and inhibited erythroid differentiation, while ERK inhibitor, PD98059, could restore the erythroid differentiation, suggesting Spred2 regulated the erythroid differentiation partly through ERK signaling. Furthermore, Spred2 interference partly restored p-ERK level leading to inhibition of erythroid differentiation in imatinib treated K562 cells. In conclusion, Spred2 was involved in erythroid differentiation of CML cells and participated in imatinib induced erythroid differentiation partly through ERK signaling.

The MAPK pathway across different malignancies: a new perspective

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

Molecular pathways: adaptive kinome reprogramming in response to targeted inhibition of the BRAF-MEK-ERK pathway in cancer

The central role of the BRAF-MEK-ERK pathway in controlling cell fate has made this pathway a primary target for deregulated activation in cancer. BRaf is activated by Ras proteins allowing Ras oncogenes to constitutively activate the pathway. Activating BRaf mutations are also frequent in several cancers, being the most common oncogenic mutation in thyroid carcinoma and melanoma. There are currently two inhibitors, vemurafenib and dabrafenib, approved for treatment of malignant melanoma having activating BRaf mutations. Concurrent administration of BRAF and MAP-ERK kinase (MEK) inhibitor (trametinib) is significantly more active in patients with BRAF-mutant melanoma than either single agent alone, but progression to resistance ultimately occurs by different mechanisms that increase the activation of extracellular signal-regulated kinase (ERK). Such adaptive changes in tumor cell signaling networks allow bypass of targeted oncoprotein inhibition. This is true with targeted inhibitors for BRaf and MEK as well as specific inhibitors for AKT, mTOR, and many receptor tyrosine kinases such as EGF receptor (EGFR) and HER2. It is this adaptive response to targeted kinase inhibitors that contributes to the failure of single-agent kinase inhibitors to have durable responses. This failure is seen in virtually all cancers treated with single-agent kinase inhibitors, most of which are not as dependent on a single signaling pathway such as BRaf-MEK-ERK in melanoma. Thus, understanding the breadth of adaptive reprogramming responses to specific targeted kinase inhibition will be critical to develop appropriate combination therapies for durable clinical responses.

Pilocytic astrocytomas of the optic nerve and their relation to pilocytic astrocytomas elsewhere in the central nervous system

Pilocytic astrocytoma is a low-grade glioma that affects mostly children and young adults and can occur anywhere in the central nervous system. Pilocytic astrocytoma of the optic nerve is an equally indolent subtype that is occasionally associated with neurofibromatosis type 1. In earlier studies, this subtype was considered within the larger category of 'optic pathway glioma,' which included infiltrating astrocytomas and other hypothalamic tumors. However, there have been suggestions that gliomas in the optic nerve, and especially pilocytic astrocytoma of the optic nerve, are biologically different from tumors within the hypothalamus and other parts of the optic tract. Furthermore, the recent discovery of BRAF duplication and fusion with the KIAA1549 gene is reported to be more typical for posterior fossa tumors, and the rate of this aberration is not well known in pilocytic astrocytoma of the optic nerve. To determine the distinction of pilocytic astrocytoma of the optic nerve from pilocytic astrocytoma of the posterior fossa and to investigate the prevalence of BRAF aberrations, we reviewed the clinicopathological and molecular features of all such patients in our institution. Our study demonstrates that BRAF duplication is more frequent in posterior fossa tumors compared with pilocytic astrocytoma of the optic nerve (P=0.011). However, the rates of phospho-MAPK1 and CDKN2A expression were high in both pilocytic astrocytoma of the optic nerve and posterior fossa pilocytic astrocytoma, suggesting that the MAPK pathway is active in these tumors. Our study supports the notion that BRAF duplication is more typical of posterior fossa pilocytic astrocytoma and that molecular alterations other than KIAA1549 fusion may underlie MAPK pathway activation in pilocytic astrocytoma of the optic nerve.

Complexity of receptor tyrosine kinase signal processing

Our knowledge of molecular mechanisms of receptor tyrosine kinase (RTK) signaling advances with ever-increasing pace. Yet our understanding of how the spatiotemporal dynamics of RTK signaling control specific cellular outcomes has lagged behind. Systems-centered experimental and computational approaches can help reveal how overlapping networks of signal transducers downstream of RTKs orchestrate specific cell-fate decisions. We discuss how RTK network regulatory structures, which involve the immediate posttranslational and delayed transcriptional controls by multiple feed forward and feedback loops together with pathway cross talk, adapt cells to the combinatorial variety of external cues and conditions. This intricate network circuitry endows cells with emerging capabilities for RTK signal processing and decoding. We illustrate how mathematical modeling facilitates our understanding of RTK network behaviors by unraveling specific systems properties, including bistability, oscillations, excitable responses, and generation of intricate landscapes of signaling activities.

Association between the SPRY1 gene polymorphism and obesity-related traits and osteoporosis in Korean women

BACKGROUND

Emerging evidence has revealed a close relationship between obesity and osteoporosis. It was reported recently that conditional knockout of the Spry1 gene in mice adipocytes causes an increase in body fat and a decrease in bone mass, and that these phenotypes are rescued by Spry1 overexpression in adipose tissue. In this study, we investigated whether genetic variation in the human SPRY1 gene is associated with obesity-related phenotypes and/or osteoporosis in humans.

METHODS

We performed a candidate gene association analysis between the four single nucleotide polymorphisms (SNPs) and 14 imputed SNPs in the SPRY1 gene and obesity-related traits and osteoporosis in a Korean women cohort (3013 subjects).

RESULTS

All four SPRY1 gene SNPs were significantly associated with either obesity-related traits or osteoporosis. The TGCC haplotype in the SRPY1 gene showed simultaneous association with an increased risk for obesity-related traits, percentage body fat (p=0.0087) and percentage abdominal fat (p=0.047), and osteoporosis (odds ratio=1.50; p=0.025) in the recessive genetic model.

CONCLUSIONS

Our results support a previous finding in conditional Spry1 gene knockout mice and suggest that the SPRY1 gene is an important genetic factor for determining the risk of both obesity and osteoporosis in humans.

Evidence for downregulation of the negative regulator SPRED2 in clinical prostate cancer

Background:

SPRED1 and 2 are key negative regulators of MAPK signalling in mammalian cells. Here, we investigate the expression and functional role of SPREDs in prostate cancer.

Methods:

A transcriptome bank of microdissected grade-specific primary cancers was constructed and interrogated for transcript expression of prostate cancer genes, known negative signalling regulators as well as SPRED1 and 2. The effect of SPRED2 manipulation was tested in in vitro assays.

Results:

In a panel of 5 benign glands and 15 tumours, we observed concomitant downregulation of the negative regulators SEF and DUSP1 in tumours with increasing Gleason grade. Profiling in the same cohorts revealed downregulation of SPRED2 mRNA in tumours compared with benign glands (P<0.05). By contrast, SPRED1 expression remained unchanged. This observation was further validated in two additional separate cohorts of microdissected tumours (total of n=10 benign and n=58 tumours) with specific downregulation of SPRED2 particularly in higher grade tumours. In functional assays, SPRED2 overexpression reduced ERK phosphorylation and inhibited prostate cancer cell proliferation and migration in response to different growth factors and full-media stimulation (P<0.001). Conversely, SPRED2 suppression by siRNA enhanced the mitogenic response to growth factors and full media (P<0.001).

Conclusion:

These data suggest first evidence that SPRED2 is downregulated in prostate cancer and warrants further investigation as a potential tumour-suppressor gene.

Role and expression of FRS2 and FRS3 in prostate cancer

Background

FGF receptor substrates (FRS2 and FRS3) are key adaptor proteins that mediate FGF-FGFR signalling in benign as well as malignant tissue. Here we investigated FRS2 and FRS3 as a means of disrupting global FGF signalling in prostate cancer.

Methods

FRS2 and FRS3 manipulation was investigated in vitro using over-expression, knockdown and functional assays. FRS2 and FRS3 expression was profiled in cell lines and clinical tumors of different grades.

Results

In a panel of cell lines we observed ubiquitous FRS2 and FRS3 transcript and protein expression in both benign and malignant cells. We next tested functional redundancy of FRS2 and FRS3 in prostate cancer cells. In DU145 cells, specific FRS2 suppression inhibited FGF induced signalling. This effect was not apparent in cells stably over-expressing FRS3. Indeed FRS3 over-expression resulted in enhanced proliferation (p = 0.005) compared to control cells. Given this functional redundancy, we tested the therapeutic principle of dual targeting of FRS2 and FRS3 in prostate cancer. Co-suppression of FRS2 and FRS3 significantly inhibited ERK activation with a concomitant reduction in cell proliferation (p < 0.05), migration and invasion (p < 0.05). Synchronous knockdown of FRS2 and FRS3 with exposure to cytotoxic irradiation resulted in a significant reduction in prostate cancer cell survival compared to irradiation alone (p < 0.05). Importantly, this synergistic effect was not observed in benign cells. Finally, we investigated expression of FRS2 and FRS3 transcript in a cohort of micro-dissected tumors of different grades as well as by immunohistochemistry in clinical biopsies. Here, we did not observe any difference in expression between benign and malignant biopsies.

Conclusions

These results suggest functional overlap of FRS2 and FRS3 in mediating mitogenic FGF signalling in the prostate. FRS2 and FRS3 are not over-expressed in tumours but targeted dual inhibition may selectively adversely affect malignant but not benign prostate cells.

Fibroblast growth factor signaling in non-small-cell lung cancer

Despite recent progress in the treatment on non-small cell lung cancer (NSCLC), outcomes remain suboptimal. Treatment advances that target the epidermal growth factor receptor (EGFR) and vascular endothelial growth factor (VEGF) signaling pathways highlight the need to understand the multiple convergent growth factor signaling pathways involved in the pathogenesis of NSCLC. Signaling through fibroblast growth factors (FGF), long recognized for its pro-angiogenic activity, has recently emerged as a contributing factor in the pathogenesis and progression of NSCLC through an autocrine signaling loop. In addition, this pathway may function as a mechanism of resistance to anti-EGFR and anti-VEGF treatment. Clinical experience with FGF receptor (FGFR) inhibitors is mounting, and more specific inhibitors of this signaling pathway are in development. This review describes the structure of the FGF signaling pathway, delineates its dual roles in angiogenesis and proliferation in NSCLC, evaluates FGF ligand and receptor expression as prognostic biomarkers in NSCLC, and discusses the development of FGF pathway inhibitors for the treatment of lung malignancies.