Metal impurities cause false positives in high-throughput screening campaigns

Organic impurities in compound libraries are known to often cause false-positive signals in screening campaigns for new leads, but organic impurities do not fully account for all false-positive results. We discovered inorganic impurities in our screening library that can also cause positive signals for a variety of targets and/or readout systems, including biochemical and biosensor assays. We investigated in depth the example of zinc for a specific project and in retrospect in various HTS screens at Roche and propose a straightforward counter screen using the chelator TPEN to rule out inhibition caused by zinc.

Ras-induced ROS upregulation affecting cell proliferation is connected with cell type-specific alterations of HSF1/SESN3/p21Cip1/WAF1 pathways

Oncogenes of the RAS family regulate many of the cell's activities, including proliferation, survival and differentiation. Activating mutations in these genes are common events for many types of cancer. One of the contradictory points concerning the biological significance of Ras activation is its dual effect (pro- or anti-proliferative) on cell reproduction. One of mechanisms by which Ras proteins influence cell growth is a regulation of intracellular level of reactive oxygen species (ROS), second messengers affecting variety of cellular processes including cell proliferation. Recently it was shown that repression of SESN1 and SESN3 genes, whose protein products control regeneration of peroxiredoxins, can play a critical role in Ras-induced ROS upregulation. In the present study we have found that Ras-induced repression of SESN3 expression and ROS upregulation is mediated via the modifications of transcriptional activity of HSF1. Interestingly, mutant Ras overexpression altered the activity of HSF1 in opposite directions in different cell contexts, in particular in human normal fibroblasts and HaCaT immortalized keratinocytes, but these opposite changes caused similar repression of SESN3 expression followed by elevation of ROS content and inhibition of cell proliferation in corresponding cell types. The inhibitory effect on cell proliferation was mediated by upregulation of p21(Cip1/WAF1). Thus, HSF1/SESN3/ROS/p21(Cip1/WAF1)-mediated deceleration of cell growth may contribute to cell defense systems protecting the organism from excessive proliferation of cells that overexpress activated Ras oncoproteins.

Neurofibromatosis type 1 (NF1): diagnosis and management

Neurofibromatosis 1 (NF1) is an inherited neurocutaneous disease that has a major impact on the nervous system, eye, skin, and bone. Individuals with NF1 have a predisposition to benign and malignant tumor formation and the hallmark lesion is the neurofibroma, a benign peripheral nerve sheath tumor. The gene for NF1 was cloned on chromosome 17q11.2 and neurofibromin, the NF1 protein, controls cell growth and proliferation by regulating the proto-oncogene Ras and cyclic adenosine monophosphate (AMP). Advances in molecular biology and mouse models of disease have enhanced our understanding of the pathogenesis of NF1 complications and facilitated targeted therapy. Progress has been made in developing robust clinical and radiological outcome measures and clinical trials are underway for children with learning difficulties and for individuals with symptomatic plexiform neurofibromas.

MK2 Regulates Ras Oncogenesis through Stimulating ROS Production

Ras signals through both mitogenic and stress pathways and studies of Ras regulatory effects of stress pathways hold great promise to control Ras-dependent malignancies. Our previous work showed Ras activation of a stress kinase (MAPK-activated protein kinase 2 [MK2]), and here, we examine regulatory effects of MK2 on Ras oncogenesis. MK2 knockout was shown to increase Ras transformation in mouse embryonic fibroblasts (MEFs) in vitro and to enhance the resultant tumor growth in mice, indicating a tumor suppressor activity. In Ras-dependent and -independent human colon cancer, however, MK2-forced expression increases and MK2 depletion decreases the malignant growth, suggesting its oncogenic activity. The oncogenic activity of MK2 couples with its activation by both stress and mitogenic signals through extracellular signal-regulated kinase and p38α pathways, whereas its tumor-suppressing effect links to its stimulation only by stress downstream of p38α. Of interest, MK2 was shown to decrease intracellular levels of reactive oxygen species (ROS) in MEFs but increase its production in human colon cancer cells, and experiments with antioxidants revealed that ROS is required for Ras oncogenesis in both systems. These results indicate that MK2 can increase or decrease Ras oncogenesis dependent of its ROS regulatory activities.

The scat mouse model highlights RASA3, a GTPase activating protein, as a key regulator of vertebrate erythropoiesis and megakaryopoiesis

Although significant progress has been made in the past decades in our understanding of bone marrow failure syndromes and anemia, many pathological conditions of unknown origin remain. Mouse models have significantly contributed to our understanding of normal erythropoiesis and the pathogenesis of erythroid disorders. Recently, we identified in the scat (severe combined anemia and thrombocytopenia) mouse model a missense mutation (G125V) in the Rasa3 gene, encoding a Ras GTPase activating protein (GAP). RASA3 is lost during reticulocyte maturation through the exosomal pathway and is therefore absent in mature erythrocytes. In wild-type reticulocytes, RASA3 is bound to the plasma membrane, a prerequisite for its GAP activity, but is mislocalized to the cytosol in scat. This mislocalization leads to RASA3 loss of function and higher levels of Ras-GTP, the active form of Ras, are consistently found in scat mature red cells. Finally, RASA3 function is conserved among vertebrates, since erythropoiesis and thrombopoiesis are impaired in zebrafish in which rasa3 is knocked-down by morpholinos, and RASA3 is expressed in human erythroleukemia cells as well as in primary cells. In this commentary, we highlight the critical, conserved and non-redundant function of RASA3 in the context of vertebrate erythropoiesis and megakaryopoiesis. We notably discuss the mechanism of RASA3 downregulation and speculate on the most intriguing part of the phenotype observed in scat; the transient remission period.

The gain of function of p53 mutant p53S in promoting tumorigenesis by cross-talking with H-RasV12

The loss of wild type p53 tumor suppressive function and oncogenic gain-of-function of p53 mutants have been showing important implications in tumorigenesis. The p53^N236S (p53^N239S in human, p53S) mutation has been shown to lose wild type p53 function by yeast assay. However, its gain of function is still not clear. By gel shift assay, we showed that mutant p53S had lost its DNA binding ability to its target promoters. Further real-time PCR data confirmed that p53S had lost the function of regulating the transcription of p21 ^Cip1/Waf1, cyclin G, PUMA, and Bax in response to 10Gy irradiation. These data confirmed the loss of function of p53S in mammalian cells. By xenograft assay, we showed that the p53S per se was not oncogenic enough to form tumor, however, cooperating with H-RasV12, p53S could dramatically promote tumorigenesis in p53 null MEFs. Further study showed that co-expression of p53S and H-RasV12 could increase the expression level of H-RasV12 and partially eliminate the elevation of stress response proteins such as Chk2, γ-H2AX, Hsp70, Rb, p16^Ink4a caused by either p53S or H-RasV12. These data suggested that p53S cross-talked with H-RasV12 and reduced the cellular stress response to oncogenic signals, which facilitated the cell growth and tumorigenesis. Together these data provided the molecular basis for the cooperation of p53S and H-RasV12 and revealed the gain of function of p53S in cross-talking with H-RasV12. This study revealed an important aspect of gain of function for p53 mutant, therefore might shed light on the clinical strategy in targeting p53 mutant.

Ras-Mediated Signal Transduction and Virulence in Human Pathogenic Fungi

Signal transduction pathways regulating growth and stress responses are areas of significant study in the effort to delineate pathogenic mechanisms of fungi. In-depth knowledge of signal transduction events deepens our understanding of how a fungal pathogen is able to sense changes in the environment and respond accordingly by modulation of gene expression and re-organization of cellular activities to optimize fitness. Members of the Ras protein family are important regulators of growth and differentiation in eukaryotic organisms, and have been the focus of numerous studies exploring fungal pathogenesis. Here, the current data regarding Ras signal transduction are reviewed for three major pathogenic fungi: Cryptococcus neoformans, Candida albicans and Aspergillus fumigatus. Particular emphasis is placed on Ras-protein interactions during control of morphogenesis, stress response and virulence.

RASSF1A and the rs2073498 Cancer Associated SNP

RASSF1A is one of the most frequently inactivated tumor suppressors yet identified in human cancer. It is pro-apoptotic and appears to function as a scaffolding protein that interacts with a variety of other tumor suppressors to modulate their function. It can also complex with the Ras oncoprotein and may serve to integrate pro-growth and pro-death signaling pathways. A SNP has been identified that is present in approximately 29% of European populations [rs2073498, A(133)S]. Several studies have now presented evidence that this SNP is associated with an enhanced risk of developing breast cancer. We have used a proteomics based approach to identify multiple differences in the pattern of protein/protein interactions mediated by the wild type compared to the SNP variant protein. We have also identified a significant difference in biological activity between wild type and SNP variant protein. However, we have found only a very modest association of the SNP with breast cancer predisposition.

Ras-ERK Signaling in Behavior: Old Questions and New Perspectives

The role of Ras–ERK signaling in behavioral plasticity is well established. Inhibition studies using the blood–brain barrier permeable drug SL327 have conclusively demonstrated that this neuronal cell signaling cascade is a crucial component of the synaptic machinery implicated in the formation of various forms of long-term memory, from spatial learning to fear and operant conditioning. However, abnormal Ras–ERK signaling has also been linked to a number of neuropsychiatric conditions, including mental retardation syndromes (“RASopathies”), drug addiction, and l-DOPA induced dyskinesia (LID). The work recently done on these brain disorders has pointed to previously underappreciated roles of Ras–ERK in specific subsets of neurons, like GABAergic interneurons of the hippocampus or the cortex, as well as in the medium spiny neurons of the striatum. Here we will highlight the open questions related to Ras–ERK signaling in these behavioral manifestations and propose crucial experiments for the future.

Regulation and Function of the RasGRP Family of Ras Activators in Blood Cells

Ras guanyl nucleotide releasing proteins (RasGRPs) are guanyl nucleotide exchange factors that activate Ras and related GTPases such as Rap. Like Sos proteins, RasGRPs have a catalytic region composed of a Ras exchange motif (REM) and a CDC25 domain. RasGRPs also possess a pair of atypical EF hands that may bind calcium in vivo and a C1 domain resembling the diacylglycerol (DAG)-binding domain of protein kinase C. DAG directly activates RasGRPs by a membrane recruitment mechanism as well as indirectly by PKC-mediated phosphorylation. RasGRPs are prominently expressed in blood cells. RasGRP1 acts downstream of TCR, while RasGRP1 and RasGRP3 both act downstream of BCR. Together, they regulate Ras in adaptive immune cells. RasGRP2, through Rap, plays a role in controlling platelet adhesion, while RasGRP4 controls Ras activation in mast cells. RasGRP malfunction likely contributes to autoimmunity and may contribute to blood malignancies. RasGRPs might prove to be viable drug targets. The intracellular site of RasGRP action and the relationship between RasGRPs and other Ras regulatory mechanisms are subjects of lively debate.

Synthetic Lethality Induced by Loss of PKC δ and Mutated Ras

Synthetic lethal interaction between oncogenic Ha-ras and loss of PKC has been demonstrated. Recently, the authors reported that the concurrent knockdown of PKC α and β, via upregulating PKC δ, sensitizes cells with aberrant Ras signaling to apoptosis. As a continuation of the study, using shRNA, the authors demonstrate that loss of PKC δ causes a lethal reaction in NIH3T3/Hras or prostate cancer DU145 cells that overexpress JNK. In this apoptotic process, PKC α and β are upregulated and then associated with RACK1 (an adaptor for activated PKC) and JNK. Immunoblotting analysis shows that JNK is phosphorylated, accompanied with caspase 8 cleavage. The inhibition of JNK abrogates this apoptotic process triggered by PKC δ knockdown. Interestingly, without blocking PKC δ, the concurrent overexpression of wt- or CAT-PKC α and β is insufficient to induce apoptosis in the cells. Together with the authors' previous findings, the data suggest that PKC α/β and δ function oppositely to maintain a balance that supports cells expressing v-ras to survive and prevents them from being eliminated through oncogenic stress-induced apoptosis.

Mammalian son of sevenless Guanine nucleotide exchange factors: old concepts and new perspectives

The Son of Sevenless (Sos) factors were originally discovered 2 decades ago as specialized Ras activators in signaling pathways controlling the process of R7 cell development in the eye of Drosophila melanogaster. The 2 known members of the mammalian Sos family (Sos1 and Sos2) code for ubiquitously expressed, highly homologous (69% overall) proteins involved in coupling signals originated by cell surface receptor tyrosine kinases (RTKs) to downstream, Ras-dependent mitogenic signaling pathways. Mechanistically, the Sos proteins function as enzymatic factors interacting with Ras proteins in response to upstream stimuli to promote guanine nucleotide exchange (GDP/GTP) and subsequent formation of the active Ras-GTP complex. In this review, we summarize current knowledge on structural, regulatory, and functional aspects of the Sos family, focusing on specific aspects of Sos biology such as structure-function relationship, crosstalk with different signaling pathways, and in vivo functional significance as deduced from phenotypic characterization of Sos knockout mice and human genetic syndromes caused by germline hSos1 mutations.

Emerging Roles for SSeCKS/Gravin/AKAP12 in the Control of Cell Proliferation, Cancer Malignancy, and Barriergenesis

Emerging data suggest that SSeCKS/Gravin/AKAP12 ("AKAP12"), originally identified as an autoantigen in cases of myasthenia gravis, controls multiple biological processes through its ability to scaffold key signaling proteins such as protein kinase (PK) C and A, calmodulin, cyclins, phosphoinositides, "long" β-1,4 galactosyltransferase (GalTase) isoform, Src, as well as the actin cytoskeleton in a spatiotemporal manner. Specialized functions attributed to AKAP12 include the suppression of cancer malignancy, especially aspects of metastatic progression, regulation of blood-brain and blood-retina barrier formation, and resensitization of β2-adrenergic pain receptors. Recent data identify a direct role for AKAP12 in cytokinesis completion, further suggesting a function as a negative regulator of cell senescence. The current review will discuss the emerging knowledge base of AKAP12-related biological roles and how the factors that affect AKAP12 expression or that interact with AKAP12 at the protein level control cancer progression and blood-tissue barrier formation.

Functional specificity of ras isoforms: so similar but so different

H-ras, N-ras, and K-ras are canonical ras gene family members frequently activated by point mutation in human cancers and coding for 4 different, highly related protein isoforms (H-Ras, N-Ras, K-Ras4A, and K-Ras4B). Their expression is nearly ubiquitous and broadly conserved across eukaryotic species, although there are quantitative and qualitative differences of expression depending on the tissue and/or developmental stage under consideration. Extensive functional studies have determined during the last quarter century that these Ras gene products are critical components of signaling pathways that control eukaryotic cell proliferation, survival, and differentiation. However, because of their homology and frequent coexpression in various cellular contexts, it remained unclear whether the different Ras proteins play specific or overlapping functional roles in physiological and pathological processes. Initially, their high degree of sequence homology and the observation that all Ras isoforms share common sets of downstream effectors and upstream activators suggested that they were mostly redundant functionally. In contrast, the notion of functional specificity for each of the different Ras isoforms is supported at present by an increasing body of experimental observations, including 1) the fact that different ras isoforms are preferentially mutated in specific types of tumors or developmental disorders; 2) the different transforming potential of transfected ras genes in different cell contexts; 3) the distinct sensitivities exhibited by the various Ras family members for modulation by different GAPs or GEFs; 4) the demonstration that different Ras isoforms follow distinct intracellular processing pathways and localize to different membrane microdomains or subcellular compartments; 5) the different phenotypes displayed by genetically modified animal strains for each of the 3 ras loci; and 6) the specific transcriptional networks controlled by each isoform in different cellular settings.

Regulation of Neuronal Function by Ras-GRF Exchange Factors

Ras-GRF1 (GRF1) and Ras-GRF2 (GRF2) constitute a family of guanine nucleotide exchange factors (GEFs). The main isoforms, p140-GRF1 and p135-GRF2, have 2 GEF domains that give them the capacity to activate both Ras and Rac GTPases in response to signals from a variety of neurotransmitter receptors. GRF1 and GRF2 proteins are found predominantly in adult neurons of the central nervous system, although they can also be detected in a limited number of other tissues. p140-GRF1 and p135-GRF2 contain calcium/calmodulin-binding IQ domains that allow them to act as calcium sensors to mediate the actions of NMDA-type and calcium-permeable AMPA-type glutamate receptors. p140-GRF1 also mediates the action of dopamine receptors that signal through cAMP. Although p140-GRF1 and p135-GRF2 have similar functional domains, studies of GRF knockout mice show that they can play strikingly different roles in regulating MAP kinase family members, neuronal synaptic plasticity, specific forms of learning and memory, and behavioral responses to psychoactive drugs. In addition, the function of GRF proteins may vary in different regions of the brain. Alternative splice variants yielding smaller GRF1 gene isoforms with fewer functional domains also exist; however, their distinct roles in neurons have not been revealed. Continuing studies of these proteins should yield important insights into the biochemical basis of brain function as well as novel concepts to explain how complex signal transduction proteins, like Ras-GRFs, integrate multiple upstream signals into specific downstream outputs to control brain function.

Therapeutic strategies for targeting ras proteins

Ras genes are frequently activated in cancer. Attempts to develop drugs that target mutant Ras proteins have, so far, been unsuccessful. Tumors bearing these mutations, therefore, remain among the most difficult to treat. Most efforts to block activated Ras have focused on pathways downstream. Drugs that inhibit Raf kinase have shown clinical benefit in the treatment of malignant melanoma. However, these drugs have failed to show clinical benefit in Ras mutant tumors. It remains unclear to what extent Ras depends on Raf kinase for transforming activity, even though Raf proteins bind directly to Ras and are certainly major effectors of Ras action in normal cells and in development. Furthermore, Raf kinase inhibitors can lead to paradoxical activation of the MAPK pathway. MEK inhibitors block the Ras-MAPK pathway, but often activate the PI3'-kinase, and have shown little clinical benefit as single agents. This activation is mediated by EGF-R and other receptor tyrosine kinases through relief of a negative feedback loop from ERK. Drug combinations that target multiple points within the Ras signaling network are likely to be necessary to achieve substantial clinical benefit. Other effectors may also contribute to Ras signaling and provide a source of targets. In addition, unbiased screens for genes necessary for Ras transformation have revealed new potential targets and have added to our understanding of Ras cancer biology.

Ras, an actor on many stages: posttranslational modifications, localization, and site-specified events

Among the wealth of information that we have gathered about Ras in the past decade, the introduction of the concept of space in the field has constituted a major revolution that has enabled many pieces of the Ras puzzle to fall into place. In the early days, it was believed that Ras functioned exclusively at the plasma membrane. Today, we know that within the plasma membrane, the 3 Ras isoforms-H-Ras, K-Ras, and N-Ras-occupy different microdomains and that these isoforms are also present and active in endomembranes. We have also discovered that Ras proteins are not statically associated with these localizations; instead, they traffic dynamically between compartments. And we have learned that at these localizations, Ras is under site-specific regulatory mechanisms, distinctively engaging effector pathways and switching on diverse genetic programs to generate different biological responses. All of these processes are possible in great part due to the posttranslational modifications whereby Ras proteins bind to membranes and to regulatory events such as phosphorylation and ubiquitination that Ras is subject to. As such, space and these control mechanisms act in conjunction to endow Ras signals with an enormous signal variability that makes possible its multiple biological roles. These data have established the concept that the Ras signal, instead of being one single, homogeneous entity, results from the integration of multiple, site-specified subsignals, and Ras has become a paradigm of how space can differentially shape signaling.

Requirement of Cdk4 for v-Ha-ras-Induced Breast Tumorigenesis and Activation of the v-ras-Induced Senescence Program by the R24C Mutation

Activating mutations in CDK4 and inactivation of its key kinase inhibitor, p16INK4A, have been implicated in the genesis and progression of human cancer. Previous work has demonstrated that CDK4 expression is required for Neu-induced but not Wnt-induced breast tumorigenesis in mice. However, the role that CDK4 plays in ras-mediated breast tumor development is not well defined. To gain an understanding of the role of Cdk4 in ras-induced breast tumorigenesis, MMTV-v-Ha-ras transgenic mice were bred with Cdk4(+/neo) and Cdk4(R24C/R24C) mice to generate Cdk4(neo/neo):MMTV-v-Ha-ras, Cdk4(+/+):MMTV-v-Ha-ras, and Cdk4(R24C/R24C):MMTV-v-Ha-ras mice. The studies presented here demonstrate that Cdk4 expression is essential for Ras-mediated breast tumorigenesis. Surprisingly, the results also show that coexpression of mutant ras and Cdk4R24C genes in breast epithelial cells leads to an activation of senescent pathways that delay tumorigenesis. Analysis of the phosphorylated form of H2AX, a marker for DNA damage, indicated its increased presence in the tumors of Cdk4(R24C/R24C):MMTV-v-Ha-ras mice. These observations indicate that the increased apoptosis and senescence seen in breast tumors of these mice might be due to increased DNA damage response in cells expressing activated forms of ras and Cdk4(R24C).

H-ras localizes to cell nuclei and varies with the cell cycle

H-Ras functions as a signal switch molecule in numerous signaling pathways in the cytoplasm, requiring H-Ras localization to the inner surface of the cytoplasmic membrane, and H-Ras is considered to be a cytoplasmic protein. Immunoblot studies of cells transformed by overexpression of c-H-ras indicated that H-Ras protein was present in both cytoplasmic and nuclear extracts, suggesting a possible correlation of nuclear H-Ras and cellular transformation. Unexpectedly, additional studies revealed that H-Ras protein was also present in the nuclei of nontransformed and primary mouse cells, which do not overexpress H-Ras. Mouse fibroblast NIH 3T3 cells, L cells, and a primary fibroblast line all had H-Ras present in both cytoplasmic and nuclear extracts. Nuclear extracts of cells synchronized by growth without serum displayed an increasing amount of H-Ras and cyclin D1 as cells grew after serum addition. Treatment with farnesyltransferase inhibitor caused loss of H-Ras from the nucleus. Immunofluorescence in situ studies of nuclei from synchronized cultures showed that H-Ras protein appeared in and disappeared from the nuclei as the cells moved through the growth cycle. This cycling occurred in both nontransformed and ras-transformed cells. Flow cytometry measurements on parallel cultures revealed that the time point at which the greatest percentage of cells were in S phase, for each line, corresponded to appearance of a noticeably stronger in situ signal for H-Ras. H-Ras may participate in nuclear signaling pathways associated with replication in addition to its cytoplasmic signaling functions.

RAS Interaction with PI3K: More Than Just Another Effector Pathway

RAS PROTEINS ARE SMALL GTPASES KNOWN FOR THEIR INVOLVEMENT IN ONCOGENESIS: around 25% of human tumors present mutations in a member of this family. RAS operates in a complex signaling network with multiple activators and effectors, which allows them to regulate many cellular functions such as cell proliferation, differentiation, apoptosis, and senescence. Phosphatidylinositol 3-kinase (PI3K) is one of the main effector pathways of RAS, regulating cell growth, cell cycle entry, cell survival, cytoskeleton reorganization, and metabolism. However, it is the involvement of this pathway in human tumors that has attracted most attention. PI3K has proven to be necessary for RAS-induced transformation in vitro, and more importantly, mice with mutations in the PI3K catalytic subunit p110α that block its ability to interact with RAS are highly resistant to endogenous oncogenic KRAS-induced lung tumorigenesis and HRAS-induced skin carcinogenesis. These animals also have a delayed development of the lymphatic vasculature. Many PI3K inhibitors have been developed that are now in clinical trials. However, it is a complex pathway with many feedback loops, and interactions with other pathways make the results of its inhibition hard to predict. Combined therapy with another RAS-regulated pathway such as RAF/MEK/ERK may be the most effective way to treat cancer, at least in animal models mimicking the human disease. In this review, we will summarize current knowledge about how RAS regulates one of its best-known effectors, PI3K.

Ras in cancer and developmental diseases

Somatic, gain-of-function mutations in ras genes were the first specific genetic alterations identified in human cancer about 3 decades ago. Studies during the last quarter century have characterized the Ras proteins as essential components of signaling networks controlling cellular proliferation, differentiation, or survival. The oncogenic mutations of the H-ras, N-ras, or K-ras genes frequently found in human tumors are known to throw off balance the normal outcome of those signaling pathways, thus leading to tumor development. Oncogenic mutations in a number of other upstream or downstream components of Ras signaling pathways (including membrane RTKs or cytosolic kinases) have been detected more recently in association with a variety of cancers. Interestingly, the oncogenic Ras mutations and the mutations in other components of Ras/MAPK signaling pathways appear to be mutually exclusive events in most tumors, indicating that deregulation of Ras-dependent signaling is the essential requirement for tumorigenesis. In contrast to sporadic tumors, separate studies have identified germline mutations in Ras and various other components of Ras signaling pathways that occur in specific association with a number of different familial, developmental syndromes frequently sharing common phenotypic cardiofaciocutaneous features. Finally, even without being a causative force, defective Ras signaling has been cited as a contributing factor to many other human illnesses, including diabetes and immunological and inflammatory disorders. We aim this review at summarizing and updating current knowledge on the contribution of Ras mutations and altered Ras signaling to development of various tumoral and nontumoral pathologies.

Anti-apoptotic effect of Tax: an NF-κB path or a CREB way?

The NF-κB pathway is intimately linked to the survival of mammalian cells, and its activation by Tax has consequently been considered important for human T-cell leukemia/lymphoma virus type 1 (HTLV-1)-infected cell resistance to death. Very little emphasis has been given to other mechanisms, although Tax regulates the expression and activity of several cellular genes. The finding that CREB protein is activated in HTLV-1 infected cells underlines the possibility that other mechanisms of survival may be implicated in HTLV-1 infection. Indeed, CREB activation or overexpression plays a role in normal hematopoiesis, as well as in leukemia development, and CREB is considered as a survival factor in various cell systems. A better understanding of the different molecular mechanisms used by Tax to counteract cell death will also help in the development of new therapeutic strategies for HTLV-1 associated diseases.

The beneficial effects of physical activity on impaired adult neurogenesis and cognitive performance

Neurogenesis occurs in two neurogenic zones in the adult brain: new neurons are born at the subventricular zone of the lateral ventricles and then migrate to the olfactory bulb, and at the subgranular zone to integrate the granular cell layer of the dentate gyrus. The hippocampus is involved in learning and memory and the generation of new hippocampal neurons has been suggested to be a new form of plasticity implicated in these processes. In the last decades, diverse intrinsic and epigenetic factors have been identified to influence adult neurogenesis but the underlying mechanisms remain unclear. In a recent study, Lafenetre et al. (2010) showed the beneficial influence of physical voluntary activity on adult neurogenesis and cognitive performance in a transgenic mouse, the synRas mouse via brain-derived neurotrophic factor. Here we review how hippocampal neurogenesis can be regulated by environmental factors and the possible role of the newly generated cells in learning and memory.

Somatic mutations of the EGF receptor and their signal transducers affect the efficacy of EGF receptor-specific tyrosine kinase inhibitors

Non-small cell lung cancer (NSCLC) is a major subtype of lung cancer that has been the most common and most fatal cancer worldwide. Gefitinib (Iressa) and erlotinib (Tarceva) specific tyrosine kinase inhibitors (TKI) for the epidermal growth factor receptor (EGFR), have been demonstrated to be effective for some NSCLC patients and are pioneering molecular-targeted drugs used in the clinic for cancer. Because many studies indicate that only some patient populations benefit from these drugs, there has been an urgent need to develop diagnostic methods to select appropriate patients for whom treatment with these drugs will be beneficial. Moreover, problems of acquired resistance after long-term treatment with the drugs have emerged. In this review, I summarize the current understanding of the EGFR-activated signal transduction pathway, which plays important roles in tumorigenesis, and of the molecular mechanisms that determine the sensitivity toward EGFR-TKI.

Statins and prostate cancer: role of cholesterol inhibition vs. prevention of small GTP-binding proteins

Prostate cancer (PCa) is initially regulated by androgens, such as testosterone and dihydrotestosterone, which regulates cell proliferation and survival by activating the androgen receptor (AR), but later progresses to an aggressive, metastatic, androgen-independent stage for which, currently, there is no cure. Here, we argue that prevention of PCa progression is a better strategy compared to trying to cure the disease once it has already progressed. Statins inhibit the mevalonate pathway, thus preventing the synthesis of cholesterol, geranylgeranyl pyrophosphate and farnesyl pyrophosphate. Multiple clinical studies have shown an inverse relationship between statin use and PCa risk, especially the risk for developing advanced metastatic cancer. Biochemical investigations have largely corroborated the positive effect of statins on PCa risk, showing that statins inhibited cell proliferation, induced apoptosis, and decreased cell migration and invasion in PCa cells in vitro. However, investigations of the biochemical mechanism of statin action in preventing advanced/high risk PCa remains inconclusive, as statins can act through cholesterol, geranylgeranyl, or farnesyl mediated signals. This review discusses the current clinical and biochemical findings on the use of statins in preventing PCa. Evidence of statin action through cholesterol as well as geranylgeranylation and farnesylation has been discussed. As cholesterol is a precursor of androgen production, it can reduce PCa risk by decreasing the levels of circulating testosterone, which in turn reduces the levels of interprostatic dihydrotestosterone, a strong ligand for the AR. Cholesterol was also shown to accumulate in lipid rafts and regulate the activation of the phosphatidylinositol 3-kinase/Akt pathway. However, clinical evidence from multiple studies also point to the existence of cholesterol-independent pathways mediating statin action in PCa patients. In particular, ligand-activated AR activation is seen in early stage PCa and activation of the cholesterol pathway did not indicate an effect on metastasis. Cell migration and invasion, on the other hand, is regulated strongly by members of the Ras superfamily of small GTPases, especially the Rho family, which is geranylgeranylated. This review, therefore, also compares the effects of statins on both cholesterol and geranylgeranylated and farnesylated small GTPases regulating tumor progression and metastasis in biochemical and clinical studies.