Ras--a versatile cellular switch

Molecular divergence with major morphological consequences: development and evolution of organ size and shape

Understanding the causes of the morphological diversity among organisms is a topic of great interest to evolutionary developmental biologists. Although developmental biologists have had great success in identifying the developmental mechanisms and molecular processes that specify organ size and shape within species, only relatively recently have the molecular tools become available to study how variation in these mechanisms gives rise to the phenotypic differences that are observed among closely related species. In addition to these technological advances, researchers interested in understanding how molecular variation gives rise to phenotypic variation have used three primary strategies to identify the molecular differences underlying species-specific traits: the candidate gene approach, differential gene expression screens, and between-species genetic mapping experiments. In this review, we discuss how these approaches have been successful in identifying the genes and the cellular mechanisms by which they specify variation in one of the most recognizable examples of the evolution of organ size, the adaptive variation in beak morphology among Darwin's finches. We also discuss insect reproductive structures as a model with great potential to advance our understanding of the specification and evolution of organ size and shape differences among species. The results from these two examples, and those from other species, show that species-specific variation in organ size and shape typically evolves via changes in the timing, location, and amount of gene/protein expression that act on tissue growth processes.

Episodes of Rapid Recovery of the Functional Activity of the ras85D Gene in the Evolutionary History of Phylogenetically Distant Drosophila Species

As assemblies of genomes of new species with varying degrees of relationship appear, it becomes obvious that structural rearrangements of the genome, such as inversions, translocations, and transposon movements, are an essential and often the main source of evolutionary variation. In this regard, the following questions arise. How conserved are the regulatory regions of genes? Do they have a common evolutionary origin? And how and at what rate is the functional activity of genes restored during structural changes in the promoter region? In this article, we analyze the evolutionary history of the formation of the regulatory region of the ras85D gene in different lineages of the genus Drosophila, as well as the participation of mobile elements in structural rearrangements and in the replacement of specific areas of the promoter region with those of independent evolutionary origin. In the process, we substantiate hypotheses about the selection of promoter elements from a number of frequently repeated motifs with different degrees of degeneracy in the ancestral sequence, as well as about the restoration of the minimum required set of regulatory sequences using a conversion mechanism or similar.

Recent insights of T cell receptor-mediated signaling pathways for T cell activation and development

T cell activation requires extracellular stimulatory signals that are mainly mediated by T cell receptor (TCR) complexes. The TCR recognizes antigens on major histocompatibility complex molecules with the cooperation of CD4 or CD8 coreceptors. After recognition, TCR-induced signaling cascades that propagate signals via various molecules and second messengers are induced. Consequently, many features of T cell-mediated immune responses are determined by these intracellular signaling cascades. Furthermore, differences in the magnitude of TCR signaling direct T cells toward distinct effector linages. Therefore, stringent regulation of T cell activation is crucial for T cell homeostasis and proper immune responses. Dysregulation of TCR signaling can result in anergy or autoimmunity. In this review, we summarize current knowledge on the pathways that govern how the TCR complex transmits signals into cells and the roles of effector molecules that are involved in these pathways.

The basics of epithelial-mesenchymal transition (EMT): A study from a structure, dynamics, and functional perspective

Epithelial-mesenchymal transition (EMT) is a key step in transdifferentiation process in solid cancer development. Forthcoming evidence suggest that the stratified program transforms polarized, immotile epithelial cells to migratory mesenchymal cells associated with enhancement of breast cancer stemness, metastasis, and drug resistance. It involves primarily several signaling pathways, such as transforming growth factor-β (TGF-β), cadherin, notch, plasminogen activator protein inhibitor, urokinase plasminogen activator, and WNT/beta catenin pathways. However, current understanding on the crosstalk of multisignaling pathways and assemblies of key transcription factors remain to be explored. In this review, we focus on the crosstalk of signal transduction pathways linked to the current therapeutic and drug development strategies. We have also performed the computational modeling on indepth the structure and conformational dynamic studies of regulatory proteins and analyze molecular interactions with their associate factors to understand the complicated process of EMT in breast cancer progression and metastasis. Electrostatic potential surfaces have been analyzed that help in optimization of electrostatic interactions between the protein and its ligand. Therefore, understanding the biological implications underlying the EMT process through molecular biology with biocomputation and structural biology approaches will enable the development of new therapeutic strategies to sensitize tumors to conventional therapy and suppress their metastatic phenotype.

Fgf8 signaling for development of the midbrain and hindbrain

In this paper, we review how midbrain and hindbrain are specified. Otx2 and Gbx2 are expressed from the early phase of development, and their expression abuts at the midbrain hindbrain boundary (MHB), where Fgf8 expression is induced, and functions as an organizing molecule for the midbrain and hindbrain. Fgf8 induces En1 and Pax2 expression at the region where Otx2 is expressed to specify midbrain. Fgf8 activates Ras-ERK pathway to specify hindbrain. Downstream of ERK, Pea3 specifies isthmus (rhombomere 0, r0), and Irx2 may specify r1, where the cerebellum is formed.

Epithelial-mesenchymal Transition---A Hallmark of Breast Cancer Metastasis

Epithelial-mesenchymal transition (EMT) is a highly conserved cellular program that converts polarized, immotile epithelial cells to migratory mesenchymal cells. In addition, EMT was initially recognized as a key step for morphogenesis during embryonic development. Emerging evidences indicate that this important developmental program promotes metastasis, drug resistance, and tumor recurrence, features that are associated with a poor clinical outcome for patients with breast cancer. Therefore, better understanding of regulation and signaling pathways in EMT is essential to develop novel targeted therapeutics. In this review, we present updated developments underlying EMT in tumor progression and metastasis, and discuss the challenges remaining in breast cancer research.

Epithelial-mesenchymal transition in breast cancer progression and metastasis

Breast cancer is the most common cancer in women, and approximately 90% of breast cancer deaths are caused by local invasion and distant metastasis of tumor cells. Epithelial-mesenchymal transition (EMT) is a vital process for large-scale cell movement during morphogenesis at the time of embryonic development. Tumor cells usurp this developmental program to execute the multi-step process of tumorigenesis and metastasis. Several transcription factors and signals are involved in these events. In this review, we summarize recent advances in breast cancer researches that have provided new insights in the molecular mechanisms underlying EMT regulation during breast cancer progression and metastasis. We especially focus on the molecular pathways that control EMT.

Epigenetic inactivation of the NORE1 gene correlates with malignant progression of colorectal tumors

Background

NORE1 (RASSF5) is a newly described member of the RASSF family with Ras effector function. NORE1 expression is frequently inactivated by aberrant promoter hypermethylation in many human cancers, suggesting that NORE1 might be a putative tumor suppressor. However, expression and mutation status of NORE1 and its implication in colorectal tumorigenesis has not been evaluated.

Methods

Expression, mutation, and methylation status of NORE1A and NORE1B in 10 cancer cell lines and 80 primary tumors were characterized by quantitative PCR, SSCP, and bisulfite DNA sequencing analyses. Effect of NORE1A and NORE1B expression on tumor cell growth was evaluated using cell number counting, flow cytometry, and colony formation assays.

Results

Expression of NORE1A and NORE1B transcript was easily detectable in all normal colonic epithelial tissues, but substantially decreased in 7 (70%) and 4 (40%) of 10 cancer cell lines and 31 (38.8%) and 25 (31.3%) of 80 primary carcinoma tissues, respectively. Moreover, 46 (57.6%) and 38 (47.5%) of 80 matched tissue sets exhibited tumor-specific reduction of NORE1A and NORE1B, respectively. Abnormal reduction of NORE1 was more commonly observed in advanced stage and high grade tumors compared to early and low grade tumors. While somatic mutations of the gene were not identified, its expression was re-activated in all low expressor cells after treatment with the demethylating agent 5-aza-dC. Bisulfite DNA sequencing analysis of 31 CpG sites within the promoter region demonstrated that abnormal reduction of NORE1A is tightly associated with promoter CpG sites hypermethylation. Moreover, transient expression and siRNA-mediated knockdown assays revealed that both NORE1A and NORE1B decrease cellular growth and colony forming ability of tumor cells and enhance tumor cell response to apoptotic stress.

Conclusion

Our data indicate that epigenetic inactivation of NORE1 due to aberrant promoter hypermethylation is a frequent event in colorectal tumorigenesis and might be implicated in the malignant progression of colorectal tumors.

Genetic analysis of Ras signalling pathways in cell proliferation, migration and survival

We have used mouse embryonic fibroblasts (MEFs) devoid of Ras proteins to illustrate that they are essential for proliferation and migration, but not for survival, at least in these cells. These properties are unique to the Ras subfamily of proteins because ectopic expression of other Ras-like small GTPases, even when constitutively active, could not compensate for the absence of Ras proteins. Only constitutive activation of components of the Raf/Mek/Erk pathway was sufficient to sustain normal proliferation and migration of MEFs devoid of Ras proteins. Activation of the phosphatidylinositol 3-kinase (PI3K)/PTEN/Akt and Ral guanine exchange factor (RalGEF)/Ral pathways, either alone or in combination, failed to induce proliferation or migration of Rasless cells, although they cooperated with Raf/Mek/Erk signalling to reproduce the full response mediated by Ras signalling. In contrast to current hypotheses, Ras signalling did not induce proliferation by inducing expression of D-type Cyclins. Rasless MEFs had normal levels of Cyclin D1/Cdk4 and Cyclin E/Cdk2. However, these complexes were inactive. Inactivation of the pocket proteins or knock down of pRb relieved MEFs from their dependence on Ras signalling to proliferate.

Epigenetic regulation of the ras effector/tumour suppressor RASSF2 in breast and lung cancer

RASSF2 is a recently identified member of a class of novel tumour suppressor genes, all containing a ras-association domain. RASSF2 resides at 20p13, a region frequently lost in human cancers. In this report we investigated methylation status of the RASSF2 promoter CpG island in a series of breast, ovarian and non-small cell lung cancers (NSCLC). RASSF2 was frequently methylated in breast tumour cell lines (65%, 13/20) and in primary breast tumours (38%, 15/40). RASSF2 expression could be switched back on in methylated breast tumour cell lines after treatment with 5'-aza-2'deoxycytidine. RASSF2 was also frequently methylated in NSCLC tumours (44%, (22/50). The small number of corresponding normal breast and lung tissue DNA samples analysed were unmethylated. We also did not detect RASSF2 methylation in ovarian tumours (0/17). Furthermore no mutations were found in the coding region of RASSF2 in these ovarian tumours. We identified a highly conserved putative bipartite nuclear localization signal (NLS) and demonstrated that endogenous RASSF2 localized to the nucleus. Mutation of the putative NLS abolished the nuclear localization. RASSF2 suppressed breast tumour cell growth in vitro and in vivo, while the ability of NLS-mutant RASSF2 to suppress growth was much diminished. Hence we demonstrate that RASSF2 has a functional NLS that is important for its tumour suppressor gene function. Our data from this and a previous report indicate that RASSF2 is frequently methylated in colorectal, breast and NSCLC tumours. We have identified RASSF2 as a novel methylation marker for multiple malignancies and it has the potential to be developed into a valuable marker for screening several cancers in parallel using promoter hypermethylation profiles.

The origin of breast cancer

Biological studies confirm that breast cancer is the result of an accumulation of a large number of individual genetic mutations that collectively alter elements of the complex internal signaling system of a cell. These aberrant genetic alterations, when assembled in a single breast cell, disrupt the control system to the extent that the cell functions autonomously in an erratic and irregular manner. Continual replication of a corrupted cell results in the formation of a colony of abnormal cells that may accumulate other aberrant mutations to eventually initiate cancer. What causes these mutations has been the topic of debate over a number of years, but because so many genetic alterations are involved, it is now conceded that one single factor could not possibly initiate all the changes. One plausible explanation involves a sequence of random, accidental, spontaneous mutations during normal stem cell replication. Some of these mutations may be an advantage to the host and their creation advances the functional ability of the breast, whereas abnormal mutations are usually deleted after activation of the complex apoptotic and inhibitory signaling system. When the defense system is corrupted, cells carrying the abnormal genes are able to avoid elimination, eventually passing abnormal mutations from one cell generation to the next. Accumulation of genetic abnormalities, over time, leads to development of a colony of cells that are pathologically abnormal. Biological studies confirm that cultured stem cells are capable of undergoing spontaneous mutations during mitosis, that sex hormones control the rate of mitosis, and that estrogen and progesterone therefore influence the rate that mutations occur. Accumulating the large number of mutations that eventually cause breast cancer can be achieved only if chromosomal abnormalities are carried from one generation of cells to the next to combine with genetic alterations generated spontaneously during stem cell mitosis.

Molecular Biology for the Radiation Oncologist: the 5Rs of Radiobiology meet the Hallmarks of Cancer

Recent advances in our understanding of the biology of cancer have provided enormous opportunities for the development of novel therapies against specific molecular targets. It is likely that most of these targeted therapies will have only modest single agent activities but may have the potential to accentuate the therapeutic effects of ionising radiation. In this introductory review, the 5Rs of classical radiobiology are interpreted in terms of their relationship to the hallmarks of cancer. Future articles will focus on the specific hallmarks of cancer and will highlight the opportunities that exist for designing new combination treatment regimens.

A MAPK docking site is critical for downregulation of Capicua by Torso and EGFR RTK signaling

Early Drosophila development requires two receptor tyrosine kinase (RTK) pathways: the Torso and the Epidermal growth factor receptor (EGFR) pathways, which regulate terminal and dorsal-ventral patterning, respectively. Previous studies have shown that these pathways, either directly or indirectly, lead to post-transcriptional downregulation of the Capicua repressor in the early embryo and in the ovary. Here, we show that both regulatory effects are direct and depend on a MAPK docking site in Capicua that physically interacts with the MAPK Rolled. Capicua derivatives lacking this docking site cause dominant phenotypes similar to those resulting from loss of Torso and EGFR activities. Such phenotypes arise from inappropriate repression of genes normally expressed in response to Torso and EGFR signaling. Our results are consistent with a model whereby Capicua is the main nuclear effector of the Torso pathway, but only one of different effectors responding to EGFR signaling. Finally, we describe differences in the modes of Capicua downregulation by Torso and EGFR signaling, raising the possibility that such differences contribute to the tissue specificity of both signals.

The histone acetyltransferases CBP/p300 are degraded in NIH 3T3 cells by activation of Ras signalling pathway

The CBP [CREB (cAMP-response-element-binding protein)-binding protein]/p300 acetyltransferases function as transcriptional co-activators and play critical roles in cell differentiation and proliferation. Accumulating evidence shows that alterations of the CBP/p300 protein levels are linked to human tumours. In the present study, we show that the levels of the CBP/p300 co-activators are decreased dramatically by continuous PDGF (platelet-derived growth factor) and Ras signalling pathway activation in NIH 3T3 fibroblasts. This effect occurs by reducing the expression levels of the CBP/p300 genes. In addition, CBP and p300 are degraded by the 26 S proteasome pathway leading to an overall decrease in the levels of the CBP/p300 proteins. Furthermore, we provide evidence that Mdm2 (murine double minute 2), in the presence of active H-Ras or N-Ras, induces CBP/p300 degradation in NIH 3T3 cells. These findings support a novel mechanism for modulating other signalling transduction pathways that require these common co-activators.

Molecular prognostic markers in resectable colorectal liver metastases: A systematic review

BACKGROUND

Determination of prognosis in patients with resectable colorectal liver metastases (CLM) is desirable in order to improve case selection for surgery and tailor adjuvant treatment according to individual recurrence risk. Conventional clinicopathological factors lack the sensitivity to accurately achieve this goal. Consideration of tumour biology and the identification of molecular prognostic markers may allow more accurate risk stratification.

METHOD

This systematic review examines evidence from published manuscripts looking at molecular markers in resectable colorectal liver metastases and their correlation with disease recurrence and survival following hepatectomy.

RESULTS

Studies have yielded promising results in the search for prognostic molecular markers of CLM. Molecular biomarkers from varied aspects of tumour biology have been examined and a number of these, including proliferation indices, telomerase, thymidylate synthase, microvessel density and thrombospondin-1 appear to have prognostic utility in this context. Validation of other markers, notably p53, has been limited by a failure of methodologies to account for their biological complexity.

CONCLUSIONS

A biomarker-based approach may yield significant benefits through informed treatment of resectable metastatic colorectal malignancy. Standardised retrospective analyses are necessary to confirm preliminary findings and identify existing and novel markers for inclusion into prospective studies. Assessment and verification of multiple molecular markers in this manner may allow molecular profiling of metastases and tailoring of therapy according to the biological aggressiveness of individual tumours. The advent of genomic- and proteomic-based technologies will allow the simultaneous analysis of multiple molecular markers and the derivation of disease profiles associated with disease recurrence and poor survival.

Fgf8 is required for anterior heart field development

In the mouse embryo, the splanchnic mesodermal cells of the anterior heart field (AHF) migrate from the pharynx to contribute to the early myocardium of the outflow tract (OT) and right ventricle (RV). Recent studies have attempted to distinguish the AHF from other precardiac populations, and to determine the genetic and molecular mechanisms that regulate its development. Here, we have used an Fgf8lacZ allele to demonstrate that Fgf8is expressed within the developing AHF. In addition, we use both a hypomorphic Fgf8 allele (Fgf8neo) and Cre-mediated gene ablation to show that Fgf8 is essential for the survival and proliferation of the AHF. Nkx2.5Cre is expressed in the AHF, primary heart tube and pharyngeal endoderm, while TnT-Cre is expressed only within the specified heart tube myocardium. Deletion of Fgf8 by Nkx2.5Cre results in a significant loss of the Nkx2.5Cre lineage and severe OT and RV truncations by E9.5, while the remaining heart chambers (left ventricle and atria) are grossly normal. These defects result from significant decreases in cell proliferation and aberrant cell death in both the pharyngeal endoderm and splanchnic mesoderm. By contrast, ablation of Fgf8 in the TnT-Cre domain does not result in OT or RV defects, providing strong evidence that Fgf8 expression is crucial in the pharyngeal endoderm and/or overlying splanchnic mesoderm of the AHF at a stage prior to heart tube elongation. Analysis of downstream signaling components, such as phosphorylated-Erk and Pea3, identifies the AHF splanchnic mesoderm itself as a target for Fgf8 signaling.

Effect of neurofibromatosis type I mutations on a novel pathway for adenylyl cyclase activation requiring neurofibromin and Ras

Neurofibromatosis type I (NFI) is a common genetic disorder that causes nervous system tumors, and learning and memory defects in humans, and animal models. We identify a novel growth factor stimulated adenylyl cyclase (AC) pathway in the Drosophila brain, which is disrupted by mutations in the epidermal growth factor receptor (EGFR), neurofibromin (NF1) and Ras, but not Galpha(s). This is the first demonstration in a metazoan that a receptor tyrosine kinase (RTK) pathway, acting independently of the heterotrimeric G-protein subunit Galpha(s), can activate AC. We also show that Galpha(s) is the major Galpha isoform in fly brains, and define a second AC pathway stimulated by serotonin and histamine requiring NF1 and Galpha(s), as well as a third, classical Galpha(s)-dependent AC pathway, which is stimulated by Phe-Met-Arg-Phe-amide (FMRFamide) and dopamine. Using mutations and deletions of the human NF1 protein (hNF1) expressed in Nf1 mutant flies, we show that Ras activation by hNF1 is essential for growth factor stimulation of AC activity. Further, we demonstrate that sequences in the C-terminal region of hNF1 are sufficient for NF1/Galpha(s)-dependent neurotransmitter stimulated AC activity, and for rescue of body size defects in Nf1 mutant flies.

Role of svp in Drosophila pericardial cell growth

The Drosophila dorsal vessel is a segmentally repeated linear organ, in which seven-up (svp) is expressed in two pairs of cardioblasts and two pairs of pericardial cells in each segment. Under the control of hedgehog (hh) signaling from the dorsal ectoderm, svp participates in diversifying cardioblast identities within each segment. In this experiment, the homozygous embryos of svp mutants exhibited an increase in cell size of Eve positive pericardial cells (EPCs) and a disarranged expression pattern, while the cardioblasts pattern of svp-lacZ expression was normal. In the meantime, the DAI muscle founders were absent in some segments in svp mutant embryos, and the dorsal somatic muscle patterning was also severely damaged in the late stage mutant embryos, suggesting that svp is required for the differentiation of Eve-positive pericardial cells and DA1 muscle founders and may have a role in EPC cell growth.

Combined signaling through ERK, PI3K/AKT, and RAC1/p38 is required for met-triggered cortical neuron migration

Cell migration is a complex biological process playing a key role in physiological and pathological conditions. During central nervous system development, positioning and function of cortical neurons is tightly regulated by cell migration. Recently, signaling events involving the urokinase-type plasminogen activator receptor, which is a key regulator for the activation of hepatocyte growth factor (HGF), have been implicated in modulating cortical neuron migration. However, the intracellular pathways controlling neuronal migration triggered by the HGF receptor Met have not been elucidated. By combining pharmacological and genetic approaches, we show here that the Ras/ERK pathway and phosphatidylinositol 3-kinase (PI3K) are both required for cortical neuron migration. By dissecting the downstream signals necessary for this event, we found that Rac1/p38 and Akt are required, whereas the c-Jun N-terminal kinase (JNK) and mTOR/p70(s6k) pathways are dispensable. This study demonstrates that concomitant activation of the Ras/ERK, PI3K/Akt, and Rac1/p38 pathways is required to achieve full capacity of cortical neurons to migrate upon HGF stimulation.

Isthmus organizer for midbrain and hindbrain development

Classical transplantation studies showed that the isthmus has an organizing activity upon the tectum and cerebellum. Since Fgf8 is expressed in the isthmus and mimics functionally isthmic grafts, it is accepted that Fgf8 plays pivotal role in the isthmic organizing activity. The fate of brain vesicles is determined by the combinations of transcription factors. The neural tube region where Otx2, Pax2, and En1 are expressed early on acquires midbrain identity. Pax3/7 forces the midbrain to differentiate into tectum. En1/2, Pax2/5, and Fgf8 form a positive feedback loop for their expression, thus misexpression of one of these molecules turns on the loop and forces presumptive diencephalon to differentiate into tectum. The isthmic organizer signal, Fgf8, stabilizes or changes the expression of the transcription factors in mid/hindbrain region. A strong Fgf8 signal activates the Ras-ERK signaling pathway, which in turn activates Irx2 in a rostrodorsal part of the hindbrain, and forces this tissue to differentiate into cerebellum.

Se-methylselenocysteine inhibits phosphatidylinositol 3-kinase activity of mouse mammary epithelial tumor cells in vitro

Introduction

Se-methylselenocysteine (MSC), a naturally occurring selenium compound, is a promising chemopreventive agent against in vivo and in vitro models of carcinogen-induced mouse and rat mammary tumorigenesis. We have demonstrated previously that MSC induces apoptosis after a cell growth arrest in S phase in a mouse mammary epithelial tumor cell model (TM6 cells) in vitro. The present study was designed to examine the involvement of the phosphatidylinositol 3-kinase (PI3-K) pathway in TM6 tumor model in vitro after treatment with MSC.

Methods

Synchronized TM6 cells treated with MSC and collected at different time points were examined for PI3-K activity and Akt phosphorylation along with phosphorylations of Raf, MAP kinase/ERK kinase (MEK), extracellular signal-related kinase (ERK) and p38 mitogen-activated protein kinase (MAPK). The growth inhibition was determined with a [³H]thymidine incorporation assay. Immunoblotting and a kinase assay were used to examine the molecules of the survival pathway.

Results

PI3-K activity was inhibited by MSC followed by dephosphorylation of Akt. The phosphorylation of p38 MAPK was also downregulated after these cells were treated with MSC. In parallel experiments MSC inhibited the Raf–MEK–ERK signaling pathway.

Conclusion

These studies suggest that MSC blocks multiple signaling pathways in mouse mammary tumor cells. MSC inhibits cell growth by inhibiting the activity of PI3-K and its downstream effector molecules in mouse mammary tumor cells in vitro.

How does Fgf signaling from the isthmic organizer induce midbrain and cerebellum development?

The mesencephalic/rhombomere 1 border (isthmus) is an organizing center for early development of midbrain and cerebellum. In this review, we summarize recent progress in studies of Fgf signaling in the isthmus and discuss how the isthmus instructs the differentiation of the midbrain versus cerebellum. Fgf8 is shown to play a pivotal role in isthmic organizer activity. Only a strong Fgf signal mediated by Fgf8b activates the Ras-extracellular signal-regulated kinase (ERK) pathway, and this is sufficient to induce cerebellar development. A lower level of signaling transduced by Fgf8a, Fgf17 and Fgf18 induce midbrain development. Numerous feedback loops then maintain appropriate mesencephalon/rhombomere1 and organizer gene expression.

Suppression of MEK/ERK signalling by Myc: role of Bin-1

We report for the first time that over-expression of Myc suppresses mitogen-activated ERK kinase (MEK)/extracellular regulated kinase (ERK) signalling in chick embryo fibroblasts (CEF). Myc does not interfere with individual components of the signalling cascade, since efficient signal propagation via MEK and ERK in Myc-infected CEF can be seen. However, using the Myc-binding domain (MBD) of Bin-1, which binds to and negatively regulates the activity of Myc, we selectively suppressed Myc-induced apoptosis, without affecting its transforming properties. This was accompanied by a restoration in MEK/ERK signalling, suggesting a critical role for this pathway in regulating apoptosis in these cells. This was also confirmed using a specific pharmacological inhibitor of MEK. Experiments with conditioned media suggest that over-expression of Myc may inhibit autocrine growth factor production, which can be restored by co-expression of MBD. Although the identity of the growth factor(s) is not known, we propose a feedback mechanism whereby Myc interferes with growth factor signalling.

Oncogenic K-ras stimulates Wnt signaling in colon cancer through inhibition of GSK-3beta

BACKGROUND & AIMS

Two key genetic events underlying the development of colon cancer are activation of the K-ras and Wnt signaling pathways. We have previously shown that these 2 pathways can cooperate to regulate vascular endothelial growth factor (VEGF) gene expression. The goal of this study was to define the molecular basis for this interaction.

METHODS

The effects of K-ras(Val12) on VEGF and T-cell factor 4 (TCF-4) promoter activity, nuclear levels of beta-catenin and beta-catenin/TCF-4 complexes, glycogen synthase kinase 3beta (GSK-3beta) phosphorylation, and GSK-3beta kinase activity were measured. LY294002 and PD98059 were used to define the role of specific ras effector pathways.

RESULTS

Oncogenic K-ras up-regulated the activity of the VEGF promoter, and selective mutagenesis of TCF-4 binding sites significantly blocked this induction. K-ras(Val12) also induced the activity of a heterologous TCF-4 reporter construct in Caco-2 and HeLa cells. LY294002 and dominant negative phosphatidylinositol 3-kinase nearly completely blocked this induction. K-ras(Val12) increased the stability of beta-catenin, the levels of nuclear beta-catenin, and the formation of nuclear beta-catenin/TCF-4 complexes, and these effects were also blocked by LY294002. Finally, K-ras(Val12) inhibited the kinase activity of total cellular GSK-3beta and GSK-3beta complexed with Axin. This effect was not mediated through phosphorylation at serine 9 but did depend on phosphatidylinositol 3-kinase.

CONCLUSIONS

Our results suggest a unique cooperative interaction between 2 critical oncogenic pathways in colorectal tumorigenesis and highlight the pivotal role of GSK-3beta.

CNK1 is a scaffold protein that regulates Src-mediated Raf-1 activation

Raf-1 is a regulator of cellular proliferation, differentiation, and apoptosis. Activation of the Raf-1 kinase activity is tightly regulated and involves targeting to the membrane by Ras and phosphorylation by various kinases, including the tyrosine kinase Src. Here we demonstrate that the connector enhancer of Ksr1, CNK1, mediates Src-dependent tyrosine phosphorylation and activation of Raf-1. CNK1 binds preactivated Raf-1 and activated Src and forms a trimeric complex. CNK1 regulates the activation of Raf-1 by Src in a concentration-dependent manner typical for a scaffold protein. Down-regulation of endogenously expressed CNK1 by small inhibitory RNA interferes with Src-dependent activation of ERK. Thus, CNK1 allows cross-talk between Src and Raf-1 and is essential for the full activation of Raf-1.

Integration of Ras subeffector signaling in TGF-beta mediated late stage hepatocarcinogenesis

Immortalized p19(ARF) null hepatocytes (MIM) feature a high degree of functional differentiation and are susceptible to transforming growth factor (TGF)-beta driven growth arrest and apoptosis. In contrast, polarized MIM hepatocytes expressing hyperactive Ha-Ras continue proliferation in cooperation with TGF-beta, and adopt an invasive phenotype by executing an epithelial to mesenchymal transition (EMT). In this study, we analyzed the involvement of Ras subeffectors in TGF-beta mediated hepatocellular EMT by employing MIM hepatocytes, which express Ras mutants allowing selective activation of either mitogen-activated protein kinase (MAPK) signaling (V12-S35) or phosphoinositide 3-OH (PI3)3 kinase (PI3K) signaling (V12-C40). We found that MAPK signaling in MIM-S35 hepatocytes was necessary and sufficient to promote resistance to TGF-beta mediated inhibition of proliferation in vitro and in vivo. MIM-S35 hepatocytes showed also PI3K activation during EMT, however, MAPK signaling on its own protected hepatocytes from apoptosis. Yet, MIM-C40 hepatocytes failed to form tumors and required additional MAPK stimulation to overcome TGF-beta mediated growth arrest. In vivo, the collaboration of MAPK signaling and TGF-beta activity drastically accelerated the cell-cycle progression of the hepatocytes, leading to vast tumor formation. From these data we conclude that MAPK is crucial for the cooperation with TGF-beta to regulate the proliferation as well as the survival of hepatocytes during EMT, and causes the fatal increase in hepatocellular tumor progression.

RASSF4/AD037 is a potential ras effector/tumor suppressor of the RASSF family

Activated Ras proteins interact with a broad range of effector proteins to induce a diverse series of biological consequences. Although typically associated with enhanced growth and transformation, activated Ras may also induce growth antagonistic effects such as senescence or apoptosis. It is now apparent that some of the growth-inhibitory properties of Ras are mediated via the RASSF family of Ras effector/tumor suppressors. To date, four members of this family have been identified (Nore1, RASSF1, RASSF2, and RASSF3). We now identify a fifth member of this group, RASSF4 (AD037). RASSF4 shows approximately 25% identity with RASSF1A and 60% identity with RASSF2. RASSF4 binds directly to activated K-Ras in a GTP-dependent manner via the effector domain, thus exhibiting the basic properties of a Ras effector. Overexpression of RASSF4 induces Ras-dependent apoptosis in 293-T cells and inhibits the growth of human tumor cell lines. Although broadly expressed in normal tissue, RASSF4 is frequently down-regulated by promoter methylation in human tumor cells. Thus, RASSF4 appears to be a new member of the RASSF family of potential Ras effector/tumor suppressors.

The Fgf8 signal causes cerebellar differentiation by activating the Ras-ERK signaling pathway

The mes/metencephalic boundary (isthmus) is an organizing center for the optic tectum and cerebellum. Fgf8 is accepted as a crucial organizing signal. Previously, we reported that Fgf8b could induce cerebellum in the mesencephalon, while Fgf8a transformed the presumptive diencephalon into mesencephalon. Since lower doses of Fgf8b exerted similar effects to those of Fgf8a, the type difference could be attributed to the difference in the strength of the signal. It is of great interest to uncover mechanisms of signal transduction pathways downstream of the Fgf8 signal in tectal and cerebellar development, and in this report we have concentrated on the Ras-ERK pathway. In normal embryos,extracellular-signal-regulated kinase (ERK) is activated at the site where Fgf8 mRNA is expressed. Fgf8b activated ERK while Fgf8a or a lower dose of Fgf8b did not activate ERK in the mes/metencephalon. Disruption of the Ras-ERK signaling pathway by a dominant negative form of Ras (RasS17N) changed the fate of the metencephalic alar plate from cerebellum to tectum. RasS17N canceled the effects of Fgf8b, while co-transfection of Fgf8a and RasS17N exerted additive effects. Disruption of Fgf8b, not Fgf8a, by siRNA resulted in posterior extension of the Otx2 expression domain. Our results indicate that the presumptive metencephalon receives a strong Fgf8 signal that activates the Ras-ERK pathway and differentiates into the cerebellum.

RARgamma acts as a tumor suppressor in mouse keratinocytes

All-trans retinoic acid (RA), the principle biologically active form of vitamin A, is essential for many developmental process as well as homeostasis in the adult. Many lines of evidence also suggest that RA, acting through the RA receptors (RARs), can also suppress growth of tumors of diverse origin. To assess directly the role of the RARs in a model of epidermal tumorigenesis, we investigated the incidence of tumor formation using keratinocytes lacking specific RAR types. Our data suggest that loss of RARgamma, but not RARalpha, predisposed keratinocytes to v-Ha-Ras-induced squamous cell carcinoma. We also found that ablation of RARgamma, but not RARalpha, abolished RA-induced cell cycle arrest and apoptosis in these keratinocytes. Reconstitution of receptor expression into RAR-null cells restored sensitivity to RA, and reversed the tumorigenic potential of receptor-deficient keratinocytes. These data strongly support a tumor suppressor effect for the RARs, in particular endogenous RARgamma, in murine keratinocytes.

Rhomboid 3 orchestrates Slit-independent repulsion of tracheal branches at the CNS midline

EGF-receptor ligands act as chemoattractants for migrating epithelial cells during organogenesis and wound healing. We present evidence that Rhomboid 3/EGF signalling, which originates from the midline of the Drosophila ventral nerve cord, repels tracheal ganglionic branches and prevents them from crossing it. rho3 acts independently from the main midline repellent Slit, and originates from a different sub-population of midline cells: the VUM neurons. Expression of dominant-negative Egfr or Ras induces midline crosses, whereas activation of the Egfr or Ras in the leading cell of the ganglionic branch can induce premature turns away from the midline. This suggests that the level of Egfr intracellular signalling, rather than the asymmetric activation of the receptor on the cell surface, is an important determinant in ganglionic branch repulsion. We propose that Egfr activation provides a necessary switch for the interpretation of a yet unknown repellent function of the midline.

Molecular aspects of epithelial cell plasticity: implications for local tumor invasion and metastasis

Carcinomas arising from epithelial cells represent the most prevalent malignancies in humans, and metastasis is the major cause for the death of carcinoma patients. The breakdown of epithelial cell homeostasis leading to aggressive cancer progression has been correlated with the loss of epithelial characteristics and the acquisition of a migratory phenotype. This phenomenon, referred to as epithelial to mesenchymal transition (EMT), is considered as a crucial event in late stage tumorigenesis. Here we summarize the multitude of EMT models derived from different tissues, and review the diversity of molecular mechanisms contributing to the plasticity of epithelial cells. In particular, the synergism between activation of Ras, provided by the aberrant stimulation of receptor tyrosine kinases, and transforming growth factor (TGF)-beta signaling plays a pivotal role in inducing EMT of various epithelial cell types. Cytokines such as TGF-beta and extracellular matrix molecules are thought to fundamentally contribute to the microenvironmental interaction between stromal and malignant cells, and provide the basis for a broad repertoire of epithelial differentiation. Investigations of EMT tumor models, which represent in vitro correlates to local invasion and metastasis in vivo, facilitate the identification of diagnostic markers for a more accurate and faithful clinical and pathological assessment of epithelial tumors. In addition, the analysis of molecular mechanisms involved in EMT might yield novel therapeutic targets for the specific treatment of aggressive carcinomas.

RASSF2 is a novel K-Ras-specific effector and potential tumor suppressor

Ras proteins regulate a wide range of biological processes by interacting with a broad assortment of effector proteins. Although activated forms of Ras are frequently associated with oncogenesis, they may also provoke growth-antagonistic effects. These include senescence, cell cycle arrest, differentiation, and apoptosis. The mechanisms that underlie these growth-inhibitory activities are relatively poorly understood. Recently, two related novel Ras effectors, NORE1 and RASSF1, have been identified as mediators of apoptosis and cell cycle arrest. Both of these proteins exhibit many of the properties normally associated with tumor suppressors. We now identify a novel third member of this family, designated RASSF2. RASSF2 binds directly to K-Ras in a GTP-dependent manner via the Ras effector domain. However, RASSF2 only weakly interacts with H-Ras. Moreover, RASSF2 promotes apoptosis and cell cycle arrest and is frequently down-regulated in lung tumor cell lines. Thus, we identify RASSF2 as a new member of the RASSF1 family of Ras effectors/tumor suppressors that exhibits a specificity for interacting with K-Ras.

The cyclopentenone 15-deoxy-delta 12,14-prostaglandin J2 binds to and activates H-Ras

The cyclopentenone 15-deoxy-Delta(12,14)-prostaglandin J(2) (15d-PGJ(2)) induces cell proliferation and mitogen-activated protein kinase activation. Here, we describe that these effects are mediated by 15d-PGJ(2)-elicited H-Ras activation. We demonstrate that this pathway is specific for H-Ras through the formation of a covalent adduct of 15d-PGJ(2) with Cys-184 of H-Ras, but not with N-Ras or K-Ras. Mutation of C184 inhibited H-Ras modification and activation by 15d-PGJ(2), whereas serum-elicited stimulation was not affected. These results describe a mechanism for the activation of the Ras signaling pathway, which results from the chemical modification of H-Ras by formation of a covalent adduct with cyclopentenone prostaglandins.

Ethylene regulates monomeric GTP-binding protein gene expression and activity in Arabidopsis

Ethylene rapidly and transiently up-regulates the activity of several monomeric GTP-binding proteins (monomeric G proteins) in leaves of Arabidopsis as determined by two-dimensional gel electrophoresis and autoradiographic analyses. The activation is suppressed by the receptor-directed inhibitor 1-methylcyclopropene. In the etr1-1 mutant, constitutive activity of all the monomeric G proteins activated by ethylene is down-regulated relative to wild type, and ethylene treatment has no effect on the levels of activity. Conversely, in the ctr1-1 mutant, several of the monomeric G proteins activated by ethylene are constitutively up-regulated. However, the activation profile of ctr1-1 does not exactly mimic that of ethylene-treated wild type. Biochemical and molecular evidence suggested that some of these monomeric G proteins are of the Rab class. Expression of the genes for a number of monomeric G proteins in response to ethylene was investigated by reverse transcriptase-PCR. Rab8 and Ara3 expression was increased within 10 min of ethylene treatment, although levels fell back significantly by 40 min. In the etr1-1 mutant, expression of Rab8 was lower than wild type and unaffected by ethylene; in ctr1-1, expression of Rab8 was much higher than wild type and comparable with that seen in ethylene treatments. Expression in ctr1-1 was also unaffected by ethylene. Thus, the data indicate a role for monomeric G proteins in ethylene signal transduction.

The molecular and genetic basis of colon cancer

Remarkable progress has been accomplished in understanding the molecular basis of genetic colon cancer syndromes including FAP and HNPCC, and their variants; of sporadic colon cancer; and of the rare hamartomatous polyp syndromes. This molecular progress now has to be translated into clinical progress in molecular diagnosis, and in pharmacologic therapy for colonic polyps and cancers. It is hoped that such progress will impact on the frequency and mortality of this very common and frequently fatal cancer.

Identification of Ras and Its Downstream Signaling Elements and Their Potential Role in Hamster Sperm Motility1

Ras, a member of the small G-protein family, regulates multiple signaling pathways in somatic cells. The objectives of the present study included the characterization and localization of Ras and the identification of its downstream effectors in hamster spermatozoa. Immunoblot analysis with a pan-Ras monoclonal antibody localized Ras to the particulate fraction of sonicated testicular and caput and cauda epididymal spermatozoa. However, Ras was present in both the particulate and soluble fractions of spermatocytes and round spermatids, suggesting that its membrane recruitment is completed during spermiogenesis. Immunoblots of plasma membrane fractions demonstrated that hamster spermatozoa express both N-Ras and K-Ras. Indirect immunofluorescence with pan-Ras antibody localized Ras to the flagellum. Immunoblot analysis of sperm plasma membrane fractions demonstrated the presence of phosphatidylinositol 3-kinase (PI3-kinase) and protein kinase C zeta (PKCzeta), the downstream targets of Ras, and coimmunoprecipitation analysis demonstrated their interaction with Ras. Inhibitors of PI3-kinase (wortmannin and 2-(4- morpholinyl)-8-phenyl-4H-1-benzopyran-4-one) and PKCzeta (staurosporine) inhibited the hyperactivation of sperm motility during capacitation in a dose-dependent manner, indicating that both PI3-kinase and PKCzeta are associated with development of this motility pattern. The interaction of Ras with both PI3-kinase and PKCzeta suggests that Ras may regulate several signaling pathways in spermatozoa.

Interactions between Ras1, dMyc, and dPI3K signaling in the developing Drosophila wing

The Ras GTPase links extracellular signals to intracellular mechanisms that control cell growth, the cell cycle, and cell identity. An activated form of Drosophila Ras (Ras(V12)) promotes these processes in the developing wing, but the effector pathways involved are unclear. Here, we present evidence indicating that Ras(V12) promotes cell growth and G(1)/S progression by increasing dMyc protein levels and activating dPI3K signaling, and that it does so via separate effector pathways. We also show that endogenous Ras is required to maintain normal levels of dMyc, but not dPI3K signaling during wing development. Finally, we show that induction of dMyc and regulation of cell identity are separable effects of Raf/MAPK signaling. These results suggest that Ras may only affect PI3K signaling when mutationally activated, such as in Ras(V12)-transformed cells, and provide a basis for understanding the synergy between Ras and other growth-promoting oncogenes in cancer.

Activation of Ras and the mitogen-activated protein kinase pathway promotes protein degradation in muscle cells of Caenorhabditis elegans

To discover and study intracellular signals that regulate proteolysis in muscle, we have employed transgenic strains of Caenorhabditis elegans that produce a soluble LacZ reporter protein limited to body-wall and vulval muscles. This reporter protein is stable in well-fed wild-type animals, but its degradation is triggered upon a shift to 25 degrees C in a strain carrying a temperature-sensitive activating mutation in the Ras oncogene homologue let-60. These mutants are not physiologically starved, inasmuch as growth rates are normal at 25 degrees C. Ras-induced degradation is not prevented by the presence of cycloheximide added at or before the temperature shift and thus uses preexisting proteolytic systems and signaling components. Furthermore, degradation is triggered when adult animals are shifted to conditions of 25 degrees C, confirming that Ras acutely promotes protein degradation in muscles whose developmental history is normal. Reduction-of-function mutations in the downstream protein kinase Raf (lin-45), MEK (mek-2), or mitogen-activated protein kinase (MAPK) (mpk-1) prevent Ras-induced protein degradation, whereas activated MPK-1 is sufficient to trigger degradation, indicating that this kinase cascade is the principal route by which Ras signaling triggers protein degradation in muscle. This pathway is activated in hypodermal cells by the LET-23 epidermal growth factor receptor homologue, but an activating mutation in let-23 does not promote proteolysis in muscle. Starvation-induced LacZ reporter degradation is unaffected by reduction-of-function mutations in Ras, Raf, MEK, or MAPK, implying that Ras activation and starvation trigger proteolysis by mechanisms that are at least partially independent. This is the first evidence that Ras-Raf-MEK-MAPK signaling activates protein degradation in differentiated muscle.

Hepatocytes convert to a fibroblastoid phenotype through the cooperation of TGF-β1 and Ha-Ras: steps towards invasiveness

In hepatocarcinogenesis, it is an open question whether transforming growth factor (TGF)-β1 provides a tumor-suppressive or a tumor-promoting role. To address this question, we employed immortalized murine hepatocytes, which display a high degree of differentiation and, expectedly, arrest in the G1 phase under exposure to TGF-β1. These hepatocytes maintain epithelial polarization upon expression of oncogenic Ha-Ras. However, Ras-transformed hepatocytes rapidly convert to a spindle-shaped, fibroblastoid morphology upon treatment with TGF-β1, which no longer inhibits proliferation. This epithelial to fibroblastoid conversion (EFC) is accompanied by disruption of intercellular contacts and remodeling of the cytoskeletal framework. Fibroblastoid derivatives form elongated branching cords in collagen gels and grow to severely vascularized tumors in vivo, indicating their increased malignancy and even invasive phenotype. Additionally, fibroblastoid cells secrete strongly enhanced levels of TGF-β1, suggesting an autocrine regulation of TGF-β signaling. Expression profiling further revealed that the loss of the adhesion component E-cadherin correlates with the upregulation of its transcriptional repressor Snail in fibroblastoid cells. Moreover, the phosphoinositide 3-OH (PI3) kinase pathway was required for the maintenance of EFC, as inhibition of PI3 kinase reverted fibroblastoid cells to an epithelial-like phenotype. Taken together, these data indicate a dual role of TGF-β1 in hepatocytes: it induces proliferation arrest but provides a crucial function in promoting late malignant events in collaboration with activated Ha-Ras.

Ras and TGF[beta] cooperatively regulate epithelial cell plasticity and metastasis: dissection of Ras signaling pathways

Multistep carcinogenesis involves more than six discrete events also important in normal development and cell behavior. Of these, local invasion and metastasis cause most cancer deaths but are the least well understood molecularly. We employed a combined in vitro/in vivo carcinogenesis model, that is, polarized Ha-Ras-transformed mammary epithelial cells (EpRas), to dissect the role of Ras downstream signaling pathways in epithelial cell plasticity, tumorigenesis, and metastasis. Ha-Ras cooperates with transforming growth factor beta (TGFbeta) to cause epithelial mesenchymal transition (EMT) characterized by spindle-like cell morphology, loss of epithelial markers, and induction of mesenchymal markers. EMT requires continuous TGFbeta receptor (TGFbeta-R) and oncogenic Ras signaling and is stabilized by autocrine TGFbeta production. In contrast, fibroblast growth factors, hepatocyte growth factor/scatter factor, or TGFbeta alone induce scattering, a spindle-like cell phenotype fully reversible after factor withdrawal, which does not involve sustained marker changes. Using specific inhibitors and effector-specific Ras mutants, we show that a hyperactive Raf/mitogen-activated protein kinase (MAPK) is required for EMT, whereas activation of phosphatidylinositol 3-kinase (PI3K) causes scattering and protects from TGFbeta-induced apoptosis. Hyperactivation of the PI3K pathway or the Raf/MAPK pathway are sufficient for tumorigenesis, whereas EMT in vivo and metastasis required a hyperactive Raf/MAPK pathway. Thus, EMT seems to be a close in vitro correlate of metastasis, both requiring synergism between TGFbeta-R and Raf/MAPK signaling.

Control of growth and organ size in Drosophila

Transplantation experiments have shown that developing metazoan organs carry intrinsic information about their size and shape. Organ and body size are also sensitive to extrinsic cues provided by the environment, such as the availability of nutrients. The genetic and molecular pathways that contribute to animal size and shape are numerous, yet how they cooperate to control growth is mysterious. The recent identification and characterization of several mutations affecting growth in Drosophila melanogaster promises to provide insights. Many of these mutations affect the extrinsic control of animal size; others affect the organ-intrinsic control of pattern and size. In this review, we summarize the characteristics of some of these mutations and their roles in growth and size control. In addition, we speculate about possible connections between the extrinsic and intrinsic pathways controlling growth and pattern.

Specificity of FGF signaling in cell migration inDrosophila

We wanted to investigate the relationship between receptor tyrosine kinase (RTK) activated signaling pathways and the induction of cell migration. Using Drosophila tracheal and mesodermal cell migration as model systems, we find that the intracellular domain of the fibroblast growth factor receptors (FGFRs) Breathless (Btl) and Heartless (Htl) can be functionally replaced by the intracellular domains of Torso (Tor) and epidermal growth factor receptor (EGFR). These hybrid receptors can also rescue cell migration in the absence of Downstream of FGFR (Dof), a cytoplasmic protein essential for FGF signaling. These results demonstrate that tracheal and mesodermal cells respond during a specific time window to a receptor tyrosine kinase (RTK) signal with directed migration, independent of the presence or absence of Dof. We discuss our findings in the light of the recent findings that RTKs generate a generic signal that is interpreted in responding cells according to their developmental history.

Analysis of corkscrew signaling in the Drosophila epidermal growth factor receptor pathway during myogenesis

The Drosophila nonreceptor protein tyrosine phosphatase, Corkscrew (Csw), functions positively in multiple receptor tyrosine kinase (RTK) pathways, including signaling by the epidermal growth factor receptor (EGFR). Detailed phenotypic analyses of csw mutations have revealed that Csw activity is required in many of the same developmental processes that require EGFR function. However, it is still unclear where in the signaling hierarchy Csw functions relative to other proteins whose activities are also required downstream of the receptor. To address this issue, genetic interaction experiments were performed to place csw gene activity relative to the EGFR, spitz (spi), rhomboid (rho), daughter of sevenless (DOS), kinase-suppressor of ras (ksr), ras1, D-raf, pointed (pnt), and moleskin. We followed the EGFR-dependent formation of VA2 muscle precursor cells as a sensitive assay for these genetic interaction studies. First, we established that Csw has a positive function during mesoderm development. Second, we found that tissue-specific expression of a gain-of-function csw construct rescues loss-of-function mutations in other positive signaling genes upstream of rolled (rl)/MAPK in the EGFR pathway. Third, we were able to infer levels of EGFR signaling in various mutant backgrounds during myogenesis. This work extends previous studies of Csw during Torso and Sevenless RTK signaling to include an in-depth analysis of the role of Csw in the EGFR signaling pathway.

Modulation of the Ras/MAPK signalling pathway by the redox function of selenoproteins in Drosophila melanogaster

Modulation of reactive oxygen species (ROS) plays a key role in signal transduction pathways. Selenoproteins act controlling the redox balance of the cell. We have studied how the alteration of the redox balance caused by patufet (selD(ptuf)), a null mutation in the Drosophila melanogaster selenophosphate synthetase 1 (sps1) gene, which codes for the SelD enzyme of the selenoprotein biosynthesis, affects the Ras/MAPK signalling pathway. The selD(ptuf) mutation dominantly suppresses the phenotypes in the eye and the wing caused by hyperactivation of the Ras/MAPK cassette and the activated forms of the Drosophila EGF receptor (DER) and Sevenless (Sev) receptor tyrosine kinases (RTKs), which signal in the eye and wing, respectively. No dominant interaction is observed with sensitized conditions in the Wnt, Notch, Insulin-Pi3K, and DPP signalling pathways. Our current hypothesis is that selenoproteins selectively modulate the Ras/MAPK signalling pathway through their antioxidant function. This is further supported by the fact that a selenoprotein-independent increase in ROS caused by the catalase amorphic Cat(n1) allele also reduces Ras/MAPK signalling. Here, we present the first evidence for the role of intracellular redox environment in signalling pathways in Drosophila as a whole organism.

Differential expression of ras signal transduction mediators in verrucous and squamous cell carcinomas of the upper aerodigestive tract

CONTEXT

ras gene mutations and expression of its gene product have been described in verrucous and squamous cell carcinomas. Other downstream signal-transduction mediators, extracellular signal-regulated kinases 1 and 2 (ERK-1 and ERK-2) and Raf-1, have not yet been as extensively studied.

OBJECTIVE

To determine patterns of expression of ERK-1, ERK-2, and Raf-1 in verrucous and squamous cell carcinomas of the upper aerodigestive tract.

DESIGN

Seventeen verrucous carcinomas and 10 squamous cell carcinomas of the upper aerodigestive tract were examined for the immunohistochemical expression of ERK-1, ERK-2, and Raf-1 product.

RESULTS

Raf-1 expression was intensely expressed in the most basal portions of the epithelium in verrucous carcinomas, but was minimally expressed in the suprabasalar areas. Anti-Raf-1 staining of the squamous cell carcinomas was diffuse and patchy throughout the tumor cells and was weak in intensity. There was no geographic preference of staining. The cytoplasmic expression of both ERK-1 and ERK-2 was predominantly negative in the most basal layers of the epithelium in the verrucous carcinomas, but was positive in the suprabasalar region of the epithelium. Immunohistochemical expression of ERK-1 and ERK-2 in the squamous carcinomas was diffuse throughout the tumor.

CONCLUSION

There is strong correlation of the geographic expression of these mediators of ras signal transduction in verrucous and squamous carcinomas, but the cause of these differences remains unclear at present. The expression of these mediator proteins may have potential for diagnosis, as well as in understanding the biologic behavior of these lesions.

The chemical biology of Ras lipidation

In this review, we summarize the successful interplay between three disciplines, organic synthesis, biophysics and cell biology, in the study of protein lipidation and its relevance to targeting of proteins to the plasma membrane of cells in molecular detail. Highlighting the example of the Ras proteins, we show how the development of new synthetic methodologies paved the road to the synthesis of lipidated peptides and--by a combination of chemical and molecular biological techniques--lipidated proteins as molecular tools. We further give an overview of the results of the biophysical properties and biological activities of the molecules synthesized by means of this interdisciplinary approach. This successful combination of different disciplines led to a better understanding of the selective targeting of Ras and related lipoproteins to the plasma membrane.