The Ras-ERK pathway: understanding site-specific signaling provides hope of new anti-tumor therapies

ERK1/2 mitogen-activated protein kinase dimerization is essential for the regulation of cell motility

ERK1/2 mitogen-activated protein kinases (ERK) are key regulators of basic cellular processes, including proliferation, survival, and migration. Upon phosphorylation, ERK becomes activated and a portion of it dimerizes. The importance of ERK activation in specific cellular events is generally well documented, but the role played by dimerization is largely unknown. Here, we demonstrate that impeding ERK dimerization precludes cellular movement by interfering with the molecular machinery that executes the rearrangements of the actin cytoskeleton. We also show that a constitutively dimeric ERK mutant can drive cell motility per se, demonstrating that ERK dimerization is both necessary and sufficient for inducing cellular migration. Importantly, we unveil that the scaffold protein kinase suppressor of Ras 1 (KSR1) is a critical element for endowing external agonists, acting through tyrosine kinase receptors, with the capacity to induce ERK dimerization and, subsequently, to unleash cellular motion. In agreement, clinical data disclose that high KSR1 expression levels correlate with greater metastatic potential and adverse evolution of mammary tumors. Overall, our results portray both ERK dimerization and KSR1 as essential factors for the regulation of cell motility and mammary tumor dissemination.

Mechanism of lncRNA SNHG16 on kidney clear cell carcinoma cells by targeting miR-506-3p/ETS1/RAS/ERK molecular axis

Objective

This study aimed to investigate the mechanism of long noncoding ribonucleic acid (lncRNA) SNHG16 on kidney clear cell carcinoma (KIRC) cells by targeting miR-506-3p/ETS proto-oncogene 1, transcription factor (ETS1)/RAS/Extracellular regulated protein kinases (ERK) molecular axis, thus to provide reference for clinical diagnosis and treatment of KIRC in the future.

Methods

Thirty-six patients with KIRC were enrolled in this study, and their carcinoma tissues and adjacent tissues were obtained for the detection of SNHG16/miR-506-3p/ETS1/RAS/ERK expression. Then, over-expressed SNHG16 plasmid and silenced plasmid were transfected into KIRC cells to observe the changes of their biological behavior.

Results

SNHG16 and ETS1 were highly expressed while miR-506- 3p was low expressed in KIRC tissues; the RAS/ERK signaling pathway was significantly activated in KIRC tissues (P < 0.05). After SNHG16 silence, KIRC cells showed decreased proliferation, invasion and migration capabilities and increased apoptosis rate; correspondingly, increase in SNHG16 expression achieved opposite results (P < 0.05). Finally, in the rescue experiment, the effects of elevated SNHG16 on KIRC cells were reversed by simultaneous increase in miR-506-3p, and the effects of miR-506-3p were reversed by ETS1. Activation of the RAS/ERK pathway had the same effect as increase in ETS1, which further worsened the malignancy of KIRC. After miR-506-3p increase and ETS1 silence, the RAS/ERK signaling pathway was inhibited (P < 0.05). At last, the rescue experiment (co-transfection) confirmed that the effect of SNHG16 on KIRC cells is achieved via the miR-506-3p/ETS1/RAS/ERK molecular axis.

Conclusion

SNHG16 regulates the biological behavior of KIRC cells by targeting the miR-506-3p/ETS1/RAS/ERK molecular axis.

Cooperativity and oscillations: Regulatory mechanisms of K-Ras nanoclusters

K-Ras nanoclusters (NCs) concentrate all required molecules belonging to the extracellular signal-regulated kinase (ERK) mitogen-activated protein kinase (MAPK) pathway in a small area where signaling events take place, increasing efficiency and specificity of signaling. Such nanostructures are characterized by controlled sizes and lifetimes distributions, but there is a poor understanding of the mechanisms involved in their dynamics of growth/decay. Here, a minimum computational model is presented to analyze the behavior of K-Ras NCs as cooperative dynamic structures that self-regulate their growth and decay according to their size. Indeed, the proposed model reveals that the growth and the local production of a K-Ras nanocluster depend positively on its actual size, whilst its lifetime is inversely proportional to the root of its size. The cooperative binding between the structural constituents of the NC (K-Ras proteins) induces oscillations in the size distributions of K-Ras NCs allowing them to range within controlled values, regulating the growth/decay dynamics of these NCs. Thereby, the size of a K-Ras NC is proposed as a key factor to regulate cell signaling, opening a range of possibilities to develop strategies for use in chronic diseases and cancer.

Navigating the ERK1/2 MAPK Cascade

The RAS-ERK pathway is a fundamental signaling cascade crucial for many biological processes including proliferation, cell cycle control, growth, and survival; common across all cell types. Notably, ERK1/2 are implicated in specific processes in a context-dependent manner as in stem cells and pancreatic β-cells. Alterations in the different components of this cascade result in dysregulation of the effector kinases ERK1/2 which communicate with hundreds of substrates. Aberrant activation of the pathway contributes to a range of disorders, including cancer. This review provides an overview of the structure, activation, regulation, and mutational frequency of the different tiers of the cascade; with a particular focus on ERK1/2. We highlight the importance of scaffold proteins that contribute to kinase localization and coordinate interaction dynamics of the kinases with substrates, activators, and inhibitors. Additionally, we explore innovative therapeutic approaches emphasizing promising avenues in this field.

Scaffold coupling: ERK activation by trans-phosphorylation across different scaffold protein species

RAS-ERK (extracellular signal-regulated kinase) pathway signals are modulated by scaffold proteins that assemble the components of different kinase tiers into a sequential phosphorylation cascade. In the prevailing model scaffold proteins function as isolated entities, where the flux of phosphorylation events progresses downstream linearly, to achieve ERK phosphorylation. We show that different types of scaffold proteins, specifically KSR1 (kinase suppressor of Ras 1) and IQGAP1 (IQ motif-containing guanosine triphosphatase activating protein 1), can bind to each other, forming a complex whereby phosphorylation reactions occur across both species. MEK (mitogen-activated protein kinase kinase) bound to IQGAP1 can phosphorylate ERK docked at KSR1, a process that we have named "trans-phosphorylation." We also reveal that ERK trans-phosphorylation participates in KSR1-regulated adipogenesis, and it also underlies the modest cytotoxicity exhibited by KSR-directed inhibitors. Overall, we identify interactions between scaffold proteins and trans-phosphorylation as an additional level of regulation in the ERK cascade, with broad implications in signaling and the design of scaffold protein-aimed therapeutics.

40 Years of RAS-A Historic Overview

It has been over forty years since the isolation of the first human oncogene (HRAS), a crucial milestone in cancer research made possible through the combined efforts of a few selected research groups at the beginning of the 1980s. Those initial discoveries led to a quantitative leap in our understanding of cancer biology and set up the onset of the field of molecular oncology. The following four decades of RAS research have produced a huge pool of new knowledge about the RAS family of small GTPases, including how they regulate signaling pathways controlling many cellular physiological processes, or how oncogenic mutations trigger pathological conditions, including developmental syndromes or many cancer types. However, despite the extensive body of available basic knowledge, specific effective treatments for RAS-driven cancers are still lacking. Hopefully, recent advances involving the discovery of novel pockets on the RAS surface as well as highly specific small-molecule inhibitors able to block its interaction with effectors and/or activators may lead to the development of new, effective treatments for cancer. This review intends to provide a quick, summarized historical overview of the main milestones in RAS research spanning from the initial discovery of the viral RAS oncogenes in rodent tumors to the latest attempts at targeting RAS oncogenes in various human cancers.

Eccrine Sweat Gland and Its Regeneration: Current Status and Future Directions

Eccrine sweat glands (ESGs) play an important role in temperature regulation by secreting sweat. Insufficiency or dysfunction of ESGs in a hot environment or during exercise can lead to hyperthermia, heat exhaustion, heatstroke, and even death, but the ability of ESGs to repair and regenerate themselves is very weak and limited. Repairing the damaged ESGs and regenerating the lost or dysfunctional ESGs poses a challenge for dermatologists and bum surgeons. To promote and accelerate research on the repair and regeneration of ESGs, we summarized the development, structure and function of ESGs, and current strategies to repair and regenerate ESGs based on stem cells, scaffolds, and possible signaling pathways involved.

Noncanonical Cell Death Induction by Reassortant Reovirus

Triple-negative breast cancer (TNBC) constitutes 10 to 15% of all breast cancer and is associated with worse prognosis than other subtypes of breast cancer. Current therapies are limited to cytotoxic chemotherapy, radiation, and surgery, leaving a need for targeted therapeutics to improve outcomes for TNBC patients. Mammalian orthoreovirus (reovirus) is a nonenveloped, segmented, double-stranded RNA virus in the Reoviridae family. Reovirus preferentially kills transformed cells and is in clinical trials to assess its efficacy against several types of cancer. We previously engineered a reassortant reovirus, r2Reovirus, that infects TNBC cells more efficiently and induces cell death with faster kinetics than parental reoviruses. In this study, we sought to understand the mechanisms by which r2Reovirus induces cell death in TNBC cells. We show that r2Reovirus infection of TNBC cells of a mesenchymal stem-like (MSL) lineage downregulates the mitogen-activated protein kinase/extracellular signal-related kinase pathway and induces nonconventional cell death that is caspase-dependent but caspase 3-independent. Infection of different MSL lineage TNBC cells with r2Reovirus results in caspase 3-dependent cell death. We map the enhanced oncolytic properties of r2Reovirus in TNBC to epistatic interactions between the type 3 Dearing M2 gene segment and type 1 Lang genes. These findings suggest that the genetic composition of the host cell impacts the mechanism of reovirus-induced cell death in TNBC. Together, our data show that understanding host and virus determinants of cell death can identify novel properties and interactions between host and viral gene products that can be exploited for the development of improved viral oncolytics.IMPORTANCE TNBC is unresponsive to hormone therapies, leaving patients afflicted with this disease with limited treatment options. We previously engineered an oncolytic reovirus (r2Reovirus) with enhanced infective and cytotoxic properties in TNBC cells. However, how r2Reovirus promotes TNBC cell death is not known. In this study, we show that reassortant r2Reovirus can promote nonconventional caspase-dependent but caspase 3-independent cell death and that the mechanism of cell death depends on the genetic composition of the host cell. We also map the enhanced oncolytic properties of r2Reovirus in TNBC to interactions between a type 3 M2 gene segment and type 1 genes. Our data show that understanding the interplay between the host cell environment and the genetic composition of oncolytic viruses is crucial for the development of efficacious viral oncolytics.

RAS Subcellular Localization Inversely Regulates Thyroid Tumor Growth and Dissemination

Simple Summary

RAS mutations occur frequently in thyroid tumors, but the extent to which they are associated to tumor aggressiveness is still uncertain. HRAS proteins occupy different subcellular localizations, from which they regulate distinct biochemical processes. Herein, we demonstrate that the capacity of HRAS-transformed thyroid cells to extravasate and invade distant organs is orchestrated by HRAS subcellular localization, by a mechanism dependent on VEGF-B secretion. Interestingly, aggressiveness inversely correlates with tumor size. Moreover, we have identified the acyl protein thioesterase APT-1, a regulator of HRAS sublocalization, as a determinant of thyroid tumor growth versus dissemination. As such, alterations in APT-1 expression levels can dramatically affect the behavior of thyroid tumors. In this respect, APT-1 levels could serve as a biomarker that may help in the stratification of HRAS mutant thyroid tumors based on their aggressiveness.

Abstract

RAS mutations are the second most common genetic alteration in thyroid tumors. However, the extent to which they are associated with the most aggressive phenotypes is still controversial. Regarding their malignancy, the majority of RAS mutant tumors are classified as undetermined, which complicates their clinical management and can lead to undesired under- or overtreatment. Using the chick embryo spontaneous metastasis model, we herein demonstrate that the aggressiveness of HRAS-transformed thyroid cells, as determined by the ability to extravasate and metastasize at distant organs, is orchestrated by HRAS subcellular localization. Remarkably, aggressiveness inversely correlates with tumor size. In this respect, we also show that RAS site-specific capacity to regulate tumor growth and dissemination is dependent on VEGF-B secretion. Furthermore, we have identified the acyl protein thioesterase APT-1 as a determinant of thyroid tumor growth versus dissemination. We show that alterations in APT-1 expression levels can dramatically affect the behavior of thyroid tumors, based on its role as a regulator of HRAS sublocalization at distinct plasma membrane microdomains. In agreement, APT-1 emerges in thyroid cancer clinical samples as a prognostic factor. As such, APT-1 levels could serve as a biomarker that could help in the stratification of HRAS mutant thyroid tumors based on their aggressiveness.

Pleiotropic Roles of Calmodulin in the Regulation of KRas and Rac1 GTPases: Functional Diversity in Health and Disease

Calmodulin is a ubiquitous signalling protein that controls many biological processes due to its capacity to interact and/or regulate a large number of cellular proteins and pathways, mostly in a Ca²⁺-dependent manner. This complex interactome of calmodulin can have pleiotropic molecular consequences, which over the years has made it often difficult to clearly define the contribution of calmodulin in the signal output of specific pathways and overall biological response. Most relevant for this review, the ability of calmodulin to influence the spatiotemporal signalling of several small GTPases, in particular KRas and Rac1, can modulate fundamental biological outcomes such as proliferation and migration. First, direct interaction of calmodulin with these GTPases can alter their subcellular localization and activation state, induce post-translational modifications as well as their ability to interact with effectors. Second, through interaction with a set of calmodulin binding proteins (CaMBPs), calmodulin can control the capacity of several guanine nucleotide exchange factors (GEFs) to promote the switch of inactive KRas and Rac1 to an active conformation. Moreover, Rac1 is also an effector of KRas and both proteins are interconnected as highlighted by the requirement for Rac1 activation in KRas-driven tumourigenesis. In this review, we attempt to summarize the multiple layers how calmodulin can regulate KRas and Rac1 GTPases in a variety of cellular events, with biological consequences and potential for therapeutic opportunities in disease settings, such as cancer.

Nuclear Migration: An Indicator of Plant Salinity Tolerance in vitro

In order to understand the mechanisms underlying acquisition of tolerance to salinity, we recently produced callus tissues of tobacco and Medicago truncatula resistant to NaCl-induced salt stress following application of a step-up recurrent selection method. The effects of salinity on cell size are known, but those on cell morphometry including cell and nuclear surface area and position of nuclei within salt stress resistant cells were never studied before. This work fills that gap, using suspension cultured cells of M. truncatula A17 initiated from callus, and Nicotiana tabacum BY-2 cell line resistant to increasing NaCl concentrations up to 150 mM NaCl. The surface area of salinity resistant cells of M. truncatula A17 and N. tabacum BY2 and their nuclei, produced by step-up recurrent selection, were reduced, and cells elongated as NaCl increased, but these parameters proved to be unreliable in explaining cell survival and growth at high NaCl. Conversely, nuclei of resistant cells migrated from the center to the periphery of the cytoplasm close to the walls. Nuclear marginalization was for the first time observed as a result of salt stress in plant cells, and could be a novel helpful morphological marker of acquisition of salinity tolerance.

Regulators of the RAS-ERK pathway as therapeutic targets in thyroid cancer

Thyroid cancer is mostly an ERK-driven carcinoma, as up to 70% of thyroid carcinomas are caused by mutations that activate the RAS/ERK mitogenic signaling pathway. The incidence of thyroid cancer has been steadily increasing for the last four decades; yet, there is still no effective treatment for advanced thyroid carcinomas. Current research efforts are focused on impairing ERK signaling with small-molecule inhibitors, mainly at the level of BRAF and MEK. However, despite initial promising results in animal models, the clinical success of these inhibitors has been limited by the emergence of tumor resistance and relapse. The RAS/ERK pathway is an extremely complex signaling cascade with multiple points of control, offering many potential therapeutic targets: from the modulatory proteins regulating the activation state of RAS proteins to the scaffolding proteins of the pathway that provide spatial specificity to the signals, and finally, the negative feedbacks and phosphatases responsible for inactivating the pathway. The aim of this review is to give an overview of the biology of RAS/ERK regulators in human cancer highlighting relevant information on thyroid cancer and future areas of research.

The Modulatory Role of MicroRNA-873 in the Progression of KRAS-Driven Cancers

KRAS is one of the most frequently mutated proto-oncogenes in pancreatic ductal adenocarcinoma (PDAC) and aberrantly activated in triple-negative breast cancer (TNBC). A profound role of microRNAs (miRNAs) in the pathogenesis of human cancer is being uncovered, including in cancer therapy. Using in silico prediction algorithms, we identified miR-873 as a potential regulator of KRAS, and we investigated its role in PDAC and TNBC. We found that reduced miR-873 expression is associated with shorter patient survival in both cancers. miR-873 expression is significantly repressed in PDAC and TNBC cell lines and inversely correlated with KRAS levels. We demonstrate that miR-873 directly bound to the 3′ UTR of KRAS mRNA and suppressed its expression. Notably, restoring miR-873 expression induced apoptosis; recapitulated the effects of KRAS inhibition on cell proliferation, colony formation, and invasion; and suppressed the activity of ERK and PI3K/AKT, while overexpression of KRAS rescued the effects mediated by miR-873. Moreover, in vivo delivery of miR-873 nanoparticles inhibited KRAS expression and tumor growth in PDAC and TNBC tumor models. In conclusion, we provide the first evidence that miR-873 acts as a tumor suppressor by targeting KRAS and that miR-873-based gene therapy may be a therapeutic strategy in PDAC and TNBC.

Amphiphile-Mediated Depalmitoylation of Proteins in Living Cells

Post-translational S-palmitoylation plays a central role in protein localization, trafficking, stability, aggregation, and cell signaling. Dysregulation of palmitoylation pathways in cells can alter protein function and is the cause of several diseases. Considering the biological and clinical importance of S-palmitoylation, tools for direct, in vivo modulation of this lipid modification would be extremely valuable. Here, we describe a method for the cleavage of native S-palmitoyl groups from proteins in living cells. Using a cell permeable, cysteine-functionalized amphiphile, we demonstrate the direct depalmitoylation of cellular proteins. We show that amphiphile-mediated depalmitoylation (AMD) can effectively cleave S-palmitoyl groups from the native GTPase HRas and successfully depalmitoylate mislocalized proteins in an infantile neuronal ceroid lipofuscinosis (INCL) disease model. AMD enables direct and facile depalmitoylation of proteins in live cells and has potential therapeutic applications for diseases such as INCL, where native protein thioesterase activity is deficient.

Reactive Oxygen Species and Oncoprotein Signaling-A Dangerous Liaison

SIGNIFICANCE

There is evidence to implicate reactive oxygen species (ROS) in tumorigenesis and its progression. This has been associated with the interplay between ROS and oncoproteins, resulting in enhanced cellular proliferation and survival. Recent Advances: To date, studies have investigated specific contributions of the crosstalk between ROS and signaling networks in cancer initiation and progression. These investigations have challenged the established dogma of ROS as agents of cell death by demonstrating a secondary function that fuels cell proliferation and survival. Studies have thus identified (onco)proteins (Bcl-2, STAT3/5, RAS, Rac1, and Myc) in manipulating ROS level as well as exploiting an altered redox environment to create a milieu conducive for cancer formation and progression.

CRITICAL ISSUES

Despite these advances, drug resistance and its association with an altered redox metabolism continue to pose a challenge at the mechanistic and clinical levels. Therefore, identifying specific signatures, altered protein expressions, and modifications as well as protein-protein interplay/function could not only enhance our understanding of the redox networks during cancer initiation and progression but will also provide novel targets for designing specific therapeutic strategies.

FUTURE DIRECTIONS

Not only a heightened realization is required to unravel various gene/protein networks associated with cancer formation and progression, particularly from the redox standpoint, but there is also a need for developing more sensitive tools for assessing cancer redox metabolism in clinical settings. This review attempts to summarize our current knowledge of the crosstalk between oncoproteins and ROS in promoting cancer cell survival and proliferation and treatment strategies employed against these oncoproteins. Antioxid. Redox Signal.

RAS at the Golgi antagonizes malignant transformation through PTPRκ-mediated inhibition of ERK activation

RAS GTPases are frequently mutated in human cancer. H- and NRAS isoforms are distributed over both plasma-membrane and endomembranes, including the Golgi complex, but how this organizational context contributes to cellular transformation is unknown. Here we show that RAS at the Golgi is selectively activated by apoptogenic stimuli and antagonizes cell survival by suppressing ERK activity through the induction of PTPRκ, which targets CRAF for dephosphorylation. Consistently, in contrast to what occurs at the plasma-membrane, RAS at the Golgi cannot induce melanoma in zebrafish. Inactivation of PTPRκ, which occurs frequently in human melanoma, often coincident with TP53 inactivation, accelerates RAS-ERK pathway-driven melanomagenesis in zebrafish. Likewise, tp53 disruption in zebrafish facilitates oncogenesis driven by RAS from the Golgi complex. Thus, RAS oncogenic potential is strictly dependent on its sublocalization, with Golgi complex-located RAS antagonizing tumor development.

RAS isoforms are associated with the plasma membrane and endomembranes, but how their localization contributes to tumorigenesis is unclear. Here, the authors show that RAS signals from Golgi complex antagonize tumour formation by inducing apoptosis via ERK inhibition.

Characterisation of HRas local signal transduction networks using engineered site-specific exchange factors

Ras GTPases convey signals from different types of membranes. At these locations, different Ras isoforms, interactors and regulators generate different biochemical signals and biological outputs. The study of Ras localisation-specific signal transduction networks has been hampered by our inability to specifically activate each of these Ras pools. Here, we describe a new set of site-specific tethered exchange factors, engineered by fusing the RasGRF1 CDC25 domain to sub-localisation-defining cues, whereby Ras pools at specific locations can be precisely activated. We show that the CDC25 domain has a high specificity for activating HRas but not NRas and KRas. This unexpected finding means that our constructs mainly activate endogenous HRas. Hence, their use enabled us to identify distinct pathways regulated by HRas in endomembranes and plasma membrane microdomains. Importantly, these new constructs unveil different patterns of HRas activity specified by their subcellular localisation. Overall, the targeted GEFs described herein constitute ideal tools for dissecting spatially-defined HRas biochemical and biological functions.

GTPases Rac1 and Ras Signaling from Endosomes

The endocytic compartment is not only the functional continuity of the plasma membrane but consists of a diverse collection of intracellular heterogeneous complex structures that transport, amplify, sustain, and/or sort signaling molecules. Over the years, it has become evident that early, late, and recycling endosomes represent an interconnected vesicular-tubular network able to form signaling platforms that dynamically and efficiently translate extracellular signals into biological outcome. Cell activation, differentiation, migration, death, and survival are some of the endpoints of endosomal signaling. Hence, to understand the role of the endosomal system in signal transduction in space and time, it is therefore necessary to dissect and identify the plethora of decoders that are operational in the different steps along the endocytic pathway. In this chapter, we focus on the regulation of spatiotemporal signaling in cells, considering endosomes as central platforms, in which several small GTPases proteins of the Ras superfamily, in particular Ras and Rac1, actively participate to control cellular processes like proliferation and cell mobility.

miR-200c inhibits breast cancer proliferation by targeting KRAS

The microRNA, miR-200c, is involved in the tumorigenesis and progression of a variety of cancers. The purpose of this study was to investigate the expression, mechanism and prognostic roles of miR-200c in breast cancer. We found that miR-200c was downregulated in both breast cancer tissue and cell lines using quantitative real-time PCR (qRT-PCR). In situ hybridization (ISH) and microarrays showed that low miR-200c expression was associated with poor patient overall survival (OS) and disease free survival (DFS). We used luciferase reporter plasmids to find that miR-200c inhibited the AKT and ERK pathways by directly targeting KRAS. Repression of KRAS by miR-200c suppressed the proliferation and survival of breast cancer cells in vitro and in vivo. miR-200c also had an anti-tumor effect by negatively regulating KRAS in a xenograft mouse model. Our findings provide clues regarding the role of miR-200c as a tumor suppressor in breast cancer through the inhibition of KRAS translation both in vitro and in vivo. miR-200c could be a potential therapeutic target in breast cancer.

Defined spatiotemporal features of RAS-ERK signals dictate cell fate in MCF-7 mammary epithelial cells

Signals conveyed through the RAS-ERK pathway are essential for the determination of cell fate. It is well established that signal variability is achieved in the different microenvironments in which signals unfold. It is also known that signal duration is critical for decisions concerning cell commitment. However, it is unclear how RAS-ERK signals integrate time and space in order to elicit a given biological response. To investigate this, we used MCF-7 cells, in which EGF-induced transient ERK activation triggers proliferation, whereas sustained ERK activation in response to heregulin leads to adipocytic differentiation. We found that both proliferative and differentiating signals emanate exclusively from plasma membrane-disordered microdomains. Of interest, the EGF signal can be transformed into a differentiating stimulus by HRAS overexpression, which prolongs ERK activation, but only if HRAS localizes at disordered membrane. On the other hand, HRAS signals emanating from the Golgi complex induce apoptosis and can prevent heregulin-induced differentiation. Our results indicate that within the same cellular context, RAS can exert different, even antagonistic, effects, depending on its sublocalization. Thus cell destiny is defined by the ability of a stimulus to activate RAS at the appropriate sublocalization for an adequate period while avoiding switching on opposing RAS signals.

The dynamic subcellular localization of ERK: mechanisms of translocation and role in various organelles

The dynamic subcellular localization of ERK in resting and stimulated cells plays an important role in its regulation. In resting cells, ERK localizes in the cytoplasm, and upon stimulation, it translocates to its target substrates and organelles. ERK signaling initiated from different places in resting cells has distinct outcomes. In this review, we summarize the mechanisms of ERK1/2 translocation to the nucleus and mitochondria, and of ERK1c to the Golgi. We also show that ERK1/2 translocation to the nucleus is a useful anti cancer target. Unraveling the complex subcellular localization of ERK and its dynamic changes upon stimulation provides a better understanding of the regulation of ERK signaling and may result in the development of new strategies to combat ERK-related diseases.

HSF1: Guardian of Proteostasis in Cancer

Proteomic instability is causally related to human diseases. In guarding proteome stability, the heat shock factor 1 (HSF1)-mediated proteotoxic stress response plays a pivotal role. Contrasting with its beneficial role of enhancing cell survival, recent findings have revealed a compelling pro-oncogenic role for HSF1. However, the mechanisms underlying the persistent activation and function of HSF1 within malignancy remain poorly understood. Emerging evidence reveals that oncogenic signaling mobilizes HSF1 and that cancer cells rely on HSF1 to avert proteomic instability and repress tumor-suppressive amyloidogenesis. In aggregate, these new developments suggest that cancer cells endure chronic proteotoxic stress and that proteomic instability is intrinsically associated with the malignant state, a characteristic that could be exploited to combat cancer.

Small Molecule Inhibition of ERK Dimerization Prevents Tumorigenesis by RAS-ERK Pathway Oncogenes

Nearly 50% of human malignancies exhibit unregulated RAS-ERK signaling; inhibiting it is a valid strategy for antineoplastic intervention. Upon activation, ERK dimerize, which is essential for ERK extranuclear, but not for nuclear, signaling. Here, we describe a small molecule inhibitor for ERK dimerization that, without affecting ERK phosphorylation, forestalls tumorigenesis driven by RAS-ERK pathway oncogenes. This compound is unaffected by resistance mechanisms that hamper classical RAS-ERK pathway inhibitors. Thus, ERK dimerization inhibitors provide the proof of principle for two understudied concepts in cancer therapy: (1) the blockade of sub-localization-specific sub-signals, rather than total signals, as a means of impeding oncogenic RAS-ERK signaling and (2) targeting regulatory protein-protein interactions, rather than catalytic activities, as an approach for producing effective antitumor agents.

The thyroid hormone receptors as tumor suppressors

In addition to the well-known role of the thyroid hormone receptors (TRs) in growth, development and metabolism, there is increasing evidence that they have profound effects on cell proliferation and malignant transformation. TRs repress transcriptional induction of cyclin D1 by the ras oncogene and block transformation and tumor formation by Ras-transformed fibroblasts in nude mice. Mutant receptors that do not bind coactivators are able to display these actions, whereas receptors defective in corepressors binding are unable to antagonize the responses to the ras oncogene. Furthermore, expression of TRβ1 in hepatocarcinoma and breast cancer cells abolishes anchorage-independent growth and migration, blocks responses to growth factors and represses expression of prometastatic genes, reducing tumor growth and strongly inhibiting invasiveness, extravasation and metastasis formation in euthyroid mice. By contrast, when cells are inoculated into hypothyroid host, tumor growth is retarded, but tumors are more invasive and metastatic growth is enhanced. Increased aggressiveness and tumor growth retardation was also observed with parental cells that do not express TRs, showing that changes secondary to hypothyroidism can modulate tumor progression and metastatic growth independently of the presence of TRs on the tumor cells. Finally, increased malignancy of skin tumors is found in mice lacking TRs, further demonstrating the role of these receptors as inhibitors of tumor progression and suggesting that they represent a potential therapeutic target in cancer.

Oncolytic reovirus induces intracellular redistribution of Ras to promote apoptosis and progeny virus release

Reovirus is a naturally oncolytic virus that preferentially replicates in Ras-transformed cells and is currently undergoing clinical trials as a cancer therapeutic. Ras transformation promotes reovirus oncolysis by enhancing virion disassembly during entry, viral progeny production, and virus release through apoptosis; however, the mechanism behind the latter is not well understood. Here, we show that reovirus alters the intracellular location of oncogenic Ras to induce apoptosis of H-RasV12-transformed fibroblasts. Reovirus infection decreases Ras palmitoylation levels and causes accumulation of Ras in the Golgi through Golgi fragmentation. With the Golgi being the site of Ras palmitoylation, treatment of target cells with the palmitoylation inhibitor, 2-bromopalmitate (2BP), prompts a greater accumulation of H-RasV12 in the Golgi, and a dose-dependent increase in progeny virus release and subsequent spread. Conversely, tethering H-RasV12 to the plasma membrane (thereby preventing its movement to the Golgi) allows for efficient virus production, but results in basal levels of reovirus-induced cell death. Analysis of Ras downstream signaling reveals that cells expressing cycling H-RasV12 have elevated levels of phosphorylated JNK (c-Jun N-terminal kinase), and that Ras retained at the Golgi body by 2BP increases activation of the MEKK1/MKK4/JNK signaling pathway to promote cell death. Collectively, our data suggest that reovirus induces Golgi fragmentation of target cells, and the subsequent accumulation of oncogenic Ras in the Golgi body initiates apoptotic signaling events required for virus release and spread.

H-ras distribution and signaling in plasma membrane microdomains are regulated by acylation and deacylation events

H-Ras must adhere to the plasma membrane to be functional. This is accomplished by posttranslational modifications, including palmitoylation, a reversible process whereby H-Ras traffics between the plasma membrane and the Golgi complex. At the plasma membrane, H-Ras has been proposed to occupy distinct sublocations, depending on its activation status: lipid rafts/detergent-resistant membrane fractions when bound to GDP, diffusing to disordered membrane/soluble fractions in response to GTP loading. Herein, we demonstrate that H-Ras sublocalization is dictated by its degree of palmitoylation in a cell type-specific manner. Whereas H-Ras localizes to detergent-resistant membrane fractions in cells with low palmitoylation activity, it locates to soluble membrane fractions in lineages where it is highly palmitoylated. Interestingly, in both cases GTP loading results in H-Ras diffusing away from its original sublocalization. Moreover, tilting the equilibrium between palmitoylation and depalmitoylation processes can substantially alter H-Ras segregation and, subsequently, its biochemical and biological functions. Thus, the palmitoylation/depalmitoylation balance not only regulates H-Ras cycling between endomembranes and the plasma membrane but also serves as a key orchestrator of H-Ras lateral diffusion between different types of plasma membrane and thereby of H-Ras signaling.

Lysine methylation in cancer: SMYD3-MAP3K2 teaches us new lessons in the Ras-ERK pathway

Lysine methylation has been traditionally associated with histones and epigenetics. Recently, lysine methyltransferases and demethylases - which are involved in methylation of non-histone substrates - have been frequently found deregulated in human tumours. In this realm, a new discovery has unveiled the methyltransferase SMYD3 as an enhancer of Ras-driven cancer. SMYD3 is up-regulated in different types of tumours. SMYD3-mediated methylation of MAP3K2 increases mutant K-Ras-induced activation of ERK1/2. Methylation of MAP3K2 prevents it from binding to the phosphatase PP2A, thereby impeding the impact of this negative regulator on Ras-ERK1/2 signals, leading to the formation of lung and pancreatic adenocarcinomas. Furthermore, depletion of SMYD3 synergises with a MEK inhibitor, currently in clinical trials, to block Ras-driven pancreatic neoplasia. These results underscore the importance of lysine methylation in the regulation of signalling pathways relevant for tumourigenesis and endorse the development of drugs targeting unregulated lysine methylation as therapeutic agents in the struggle against cancer.

MicroRNA-493 suppresses tumor growth, invasion and metastasis of lung cancer by regulating E2F1

miRNAs have been proposed to be key regulators of progression and metastasis in cancer. However, an understanding of their roles and molecular mechanisms is needed to provide deeper insights for better therapeutic opportunities. In this study we investigated the role and mechanism of miR-493 in the development and progression of nonsmall-cell lung cancer (NSCLC). Our data indicated that the expression of miR-493 was markedly reduced in pulmonary carcinoma. The ectopic expression of miR-493 impaired cell growth and invasion in vitro and in vivo. Mechanically, miR-493 commonly directly targeted E2F1, which resulted in a robust reduction of the expression of mRNA and protein. This effect, in turn, decreased the growth, invasion and metastasis of lung cancer cells. Our findings highlight the importance of miR-493 dysfunction in promoting tumor progression, and implicate miR-493 as a potential therapeutic target in lung cancer.

Dynamics of KRas on endosomes: involvement of acidic phospholipids in its association

The endocytic compartment is emerging as a functional platform for controlling important cellular processes. We have found that ∼10 to 15% of total KRas, a protein that is frequently mutated in cancer, is present on endosomes, independent of its activation state. The dynamics of GFP-KRas wild-type (WT) and constitutively active or inactive mutants on endosomes were analyzed by fluorescence recovery after photobleaching (FRAP) microscopy. The measurements revealed an extraordinarily fast recovery of KRas WT [half-time (HT), ∼1.3 s] compared to HRas, Rab5, and EGFR, with the active KRasG12V mutant being significantly faster and more mobile (HT, ∼1 s, and ∼82% of exchangeable fraction) than the inactive KRasS17N (HT, ∼1.6 s, and ∼60% of exchangeable fraction). KRas rapidly switches from the cytoplasm to the endosomal membranes by an electrostatic interaction between its polybasic region and the endosomal acidic phospholipids, mainly phosphatidylserine.-Gelabert-Baldrich, M., Soriano-Castell, D., Calvo, M., Lu, A., Viña-Vilaseca, A., Rentero, C., Pol, A., Grinstein, S. Enrich, C., Tebar, F. Dynamics of KRas on endosomes: involvement of acidic phospholipids in its association.

The TRIM-FLMN protein TRIM45 directly interacts with RACK1 and negatively regulates PKC-mediated signaling pathway

The receptor for activated C-kinase (RACK1), a scaffolding protein that participates in the protein kinase C (PKC) signaling pathway, has an important role in shuttling active PKCs to its substrate. Indeed, recent studies have revealed that RACK1 has an important role in tumorigenesis and that enhancement of the feed-forward mechanism of the c-Jun N-terminal kinase (JNK)-Jun pathway via RACK1 is associated with constitutive activation of MEK (MAPK-ERK kinase)-ERK (extracellular signal-regulated kinase) signaling in human melanoma cells. Taken together, RACK1 additionally has a very important role in the mitogen-activated protein kinase (MAPK) signaling pathway. Here, we show that one of the tripartite motif-containing (TRIM) family ubiquitin ligases, TRIM45, is a novel RACK1-interacting protein and downregulates MAPK signal transduction. Importantly, the expression of TRIM45 is induced when growth-promoting extracellular stimuli activate the MAPK signaling pathway, resulting in attenuation of activation of the MAPK pathway. These findings suggest that TRIM45 functions as a member of the negative feedback loop of the MAPK pathway.

Research progress of ursolic acid's anti-tumor actions

Ursolic acid (UA) is a sort of pentacyclic triterpenoid carboxylic acid purified from natural plant. UA has a series of biological effects such as sedative, anti-inflammatory, anti-bacterial, anti-diabetic, antiulcer, etc. It is discovered that UA has a broad-spectrum anti-tumor effect in recent years, which has attracted more and more scholars' attention. This review explained anti-tumor actions of UA, including (1) the protection of cells' DNA from different damages; (2) the anti-tumor cell proliferation by the inhibition of epidermal growth factor receptor/mitogen-activated protein kinase signal or of FoxM1 transcription factors, respectively; (3) antiangiogenesis, (4) the immunological surveillance to tumors; (5) the inhibition of tumor cell migration and invasion; (6) the effect of UA on caspase, cytochromes C, nuclear factor kappa B, cyclooxygenase, tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) or mammalian target of rapamycin signal to induce tumor cell apoptosis respectively, and etc. Moreover, UA has selective toxicity to tumor cells, basically no effect on normal cells. With further studies, UA would be one of the potential anti-tumor agents.

Targeting the Ras-ERK pathway in pancreatic adenocarcinoma

Pancreatic ductal adenocarcinoma (PAC) stands as the poorest prognostic tumor of the digestive tract with limited therapeutic options. PAC carcinogenesis is associated with the loss of function of tumor suppressor genes such as INK4A, TP53, BRCA2, and DPC4, and only a few activated oncogenes among which K-RAS mutations are the most prevalent. The K-RAS mutation occurs early in PAC carcinogenesis, driving downstream activation of MEK and ERK1/2 which promote survival, invasion, and migration of cancer cells. In PAC models, inhibition of members of the Ras-ERK pathway blocks cellular proliferation and metastasis development. As oncogenic Ras does not appear to be a suitable drug target, inhibitors targeting downstream kinases including Raf and MEK have been developed and are currently under evaluation in clinical trials. In this review, we describe the role of the Ras-ERK pathway in pancreatic carcinogenesis and as a new therapeutic target for the treatment of PAC.

Key role of ERK1/2 molecular scaffolds in heart pathology

The ability of cardiomyocytes to detect mechanical and humoral stimuli is critical for adaptation of the myocardium in response to new conditions and for sustaining the increased workload during stress. While certain stimuli mediate a beneficial adaptation to stress conditions, others result in maladaptive remodelling, ultimately leading to heart failure. Specific signalling pathways activating either adaptive or maladaptive cardiac remodelling have been identified. Paradoxically, however, in a number of cases, the transduction pathways involved in such opposing responses engage the same signalling proteins. A notable example is the Raf-MEK1/2-ERK1/2 signalling pathway that can control both adaptive and maladaptive remodelling. ERK1/2 signalling requires a signalosome complex where a scaffold protein drives the assembly of these three kinases into a linear pathway to facilitate their sequential phosphorylation, ultimately targeting specific effector molecules. Interestingly, a number of different Raf-MEK1/2-ERK1/2 scaffold proteins have been identified, and their role in determining the adaptive or maladaptive cardiac remodelling is a promising field of investigation for the development of therapeutic strategies capable of selectively potentiating the adaptive response.

Isolation of a novel thioflavin S-derived compound that inhibits BAG-1-mediated protein interactions and targets BRAF inhibitor-resistant cell lines

Protein-protein interactions mediated through the C-terminal Bcl-2-associated athanogene (BAG) domain of BAG-1 are critical for cell survival and proliferation. Thioflavin S (NSC71948)-a mixture of compounds resulting from the methylation and sulfonation of primulin base-has been shown to dose-dependently inhibit the interaction between BAG-1 and Hsc70 in vitro. In human breast cancer cell lines, with high BAG-1 expression levels, Thioflavin S reduces the binding of BAG-1 to Hsc70, Hsp70, or CRAF and decreases proliferation and viability. Here, we report the development of a protocol for the purification and isolation of biologically active constituents of Thioflavin S and the characterization of the novel compound Thio-2. Thio-2 blocked the growth of several transformed cell lines, but had much weaker effects on untransformed cells. Thio-2 also inhibited the proliferation of melanoma cell lines that had become resistant to treatment with PLX4032, an inhibitor of mutant BRAF. In transformed cells, Thio-2 interfered with intracellular signaling at the level of RAF, but had no effect on the activation of AKT. Thio-2 decreased binding of BAG-1 to Hsc70 and to a lesser extent BRAF in vitro and in vivo, suggesting a possible mechanism of action. Given that tumors frequently develop resistance to kinase inhibitors during treatment, Thio-2 and related compounds may offer promising alternative strategies to currently available therapies.

Nuclear positioning

The nucleus is the largest organelle and is commonly depicted in the center of the cell. Yet during cell division, migration, and differentiation, it frequently moves to an asymmetric position aligned with cell function. We consider the toolbox of proteins that move and anchor the nucleus within the cell and how forces generated by the cytoskeleton are coupled to the nucleus to move it. The significance of proper nuclear positioning is underscored by numerous diseases resulting from genetic alterations in the toolbox proteins. Finally, we discuss how nuclear position may influence cellular organization and signaling pathways.

FOXM1 (Forkhead box M1) in tumorigenesis: overexpression in human cancer, implication in tumorigenesis, oncogenic functions, tumor-suppressive properties, and target of anticancer therapy

FOXM1 (Forkhead box M1) is a typical proliferation-associated transcription factor and is also intimately involved in tumorigenesis. FOXM1 stimulates cell proliferation and cell cycle progression by promoting the entry into S-phase and M-phase. Additionally, FOXM1 is required for proper execution of mitosis. In accordance with its role in stimulation of cell proliferation, FOXM1 exhibits a proliferation-specific expression pattern and its expression is regulated by proliferation and anti-proliferation signals as well as by proto-oncoproteins and tumor suppressors. Since these factors are often mutated, overexpressed, or lost in human cancer, the normal control of the foxm1 expression by them provides the basis for deregulated FOXM1 expression in tumors. Accordingly, FOXM1 is overexpressed in many types of human cancer. FOXM1 is intimately involved in tumorigenesis, because it contributes to oncogenic transformation and participates in tumor initiation, growth, and progression, including positive effects on angiogenesis, migration, invasion, epithelial-mesenchymal transition, metastasis, recruitment of tumor-associated macrophages, tumor-associated lung inflammation, self-renewal capacity of cancer cells, prevention of premature cellular senescence, and chemotherapeutic drug resistance. However, in the context of urethane-induced lung tumorigenesis, FOXM1 has an unexpected tumor suppressor role in endothelial cells because it limits pulmonary inflammation and canonical Wnt signaling in epithelial lung cells, thereby restricting carcinogenesis. Accordingly, FOXM1 plays a role in homologous recombination repair of DNA double-strand breaks and maintenance of genomic stability, that is, prevention of polyploidy and aneuploidy. The implication of FOXM1 in tumorigenesis makes it an attractive target for anticancer therapy, and several antitumor drugs have been reported to decrease FOXM1 expression.

Targeting GRB7/ERK/FOXM1 signaling pathway impairs aggressiveness of ovarian cancer cells

Ovarian cancer is a highly lethal disease with poor prognosis and especially in high-grade tumor. Emerging evidence has reported that aberrant upregulation and activation of GRB7, ERK as well as FOXM1 are closely associated with aggresivenesss of human cancers. However, the interplay between these factors in the pathogenesis of human cancers still remains unclear. In this study, we found that GRB7 (P<0.0001), ERK phosphorylation (P<0.0001) and FOXM1 (P = 0.001) were frequently increased and associated with high-grade tumors, as well as a high tendency in association with advanced stage ovarian cancer by immunohistochemical analysis. Intriguingly, the expressions of GRB7 (P<0.0001), ERK phosphorylation (P<0.001) and FOXM1 (P<0.001) showed a significant stepwise increase pattern along Grade 1 to Grade 3 ovarian cancers. Biochemical studies using western blot analysis demonstrated that enforced expression or knockdown of GRB7 showed GRB7 could elevate the levels of ERK phosphorylation and FOXM1, whereas enforced expression of FOXM1 could not alter levels of GRB7 and ERK phosphorylation. But inhibition of ERK signaling by U0126 or PD98059 could reduce the level of FOXM1 in GRB7-overexpressing ovarian cancer cells, suggesting that GRB7, ERK and FOXM1 are regulated orderly. Moreover, inhibition of ERK activity by U0126 or PD98059, or decreased FOXM1 expression by Thiostrepton significantly inhibited cell migration/invasion, tumor growth in vitro and in vivo. Collectively, our findings confer that targeting GRB7/ERK/FOXM1 signaling cascade may be a promising molecular therapeutic choice in combating ovarian cancer.

Ibandronate increases the expression of the pro-apoptotic gene FAS by epigenetic mechanisms in tumor cells

There is growing evidence that aminobisphosphonates like ibandronate show anticancer activity by an unknown mechanism. Biochemically, they prevent posttranslational isoprenylation of small GTPases, thus inhibiting their activity. In tumor cells, activated RAS-GTPase, the founding member of the gene family, down-regulates the expression of the pro-apoptotic gene FAS via epigenetic DNA-methylation by DNMT1. We compared ibandronate treatment in neoplastic human U-2 osteosarcoma and in mouse CCL-51 breast cancer cells as well as in the immortalized non-neoplastic MC3T3-E1 osteoblastic cells. Ibandronate attenuated cell proliferation in all cell lines tested. In the neoplastic cells we found up-regulation of caspases suggesting apoptosis. Further we found stimulation of FAS-expression as a result of epigenetic DNA demethylation that was due to down-regulation of DNMT1, which was rescued by re-isoprenylation by both geranylgeranyl-pyrophosphate and farnesylpyrophosphate. In contrast, ibandronate did not affect FAS and DNMT1 expression in MC3T3-E1 non-neoplastic cells. Data suggest that bisphosphonates via modulation of the activity of small-GTPases induce apoptosis in neoplastic cells by DNA-CpG-demethylation and stimulation of FAS-expression. In conclusion the shown epigenetic mechanism underlying the anti-neoplastic activity of farnesyl-transferase-inhibition, also explains the clinical success of other drugs, which target this pathway.

The natural compound Alizarin as an osteotropic drug for the treatment of bone tumors

Despite significant clinical improvements, conventional therapies for bone cancer treatment are limited by significant systemic toxicity and lack of specific targeting. In this study, we considered Alizarin, a natural hydroxyanthraquinone derived from madder root with high affinity to calcium and remarkable osteotropic features, as a novel approach for bone cancer treatment. Due to its antitumor properties, as demostrated in colon cancer cells, and to its tropism to bone, Alizarin may be an ideal drug to reduce bone tumor growth. We demonstrated that low dosages of Alizarin strongly inhibited the osteosarcoma (IC(50) for Saos-2, MG-63, and U-2 OS cells, 27.5, 29.0, and 69.9 µg/ml, respectively) and breast carcinoma (IC(50) for MDA-MB-231 cells, 62.1 µg/ml) cell proliferation in vitro. Importantly, Alizarin had a significantly lower inhibitory activity on normal cells (IC(50) for MSC, 828.6 µg/ml), thereby revealing a selective activity towards malignant cells. Furthermore, we found that Alizarin acted through the inhibition of ERK phosphorylation and cell cycle arrest in the S-phase. Finally, Alizarin significantly and strongly impaired both osteosarcoma and breast cancer tumorigenesis. Our results highlight a selective and effective inhibitory activity of Alizarin towards cancerous cells, laying the basis for further studies to investigate its application in bone cancer therapy.

MACC1: A potential molecule associated with pancreatic cancer metastasis and chemoresistance

It has been suggested that the newly identified metastasis-associated in colon cancer-1 (MACC1) oncogene is involved in the progression and metastasis of cancer. Several studies have indicated that MACC1 has potential as a novel biomarker. In this study, we aimed to investigate the functions and serum expression levels of MACC1 in pancreatic cancer patients. Blood serum samples from 60 cancer patients and 49 controls were analyzed for serum MACC1 by ELISA. The results revealed that high expression levels of MACC1 were correlated with lymph node metastasis, distant metastasis and a later TNM stage. Inhibition of MACC1 by siRNAs significantly suppressed pancreatic cancer cell proliferation and migration. Furthermore, it was found that the downregulation of MACC1 sensitized pancreatic cancer cells to gemcitabine treatment through the inhibition of the Ras/ERK signaling pathway. Our findings suggest that MACC1 may aid in the diagnosis of pancreatic cancer and serve as a potential therapeutic target.

pERK activation in esophageal carcinomas: clinicopathological associations

MAPK (mitogen-activated protein kinase) pathway is considered a control regulator in various malignant tumors but its role in esophageal carcinomas remains elusive. In our study, we examined the possible prognostic significance of MAPK pathway in human esophageal cancer. We searched for mutations in exons 18-21 of EGFR gene, codons 12 and 13 of K-RAS gene and exon 15 of B-RAF gene by high resolution melting analysis (HRMA) and pyrosequencing in 44 esophageal carcinomas. Immunohistochemistry was performed in 29 cases in order to evaluate expression levels of pERK (extracellular-signal regulated kinase). In one laser microdissected squamous cell carcinoma, a somatic K-RAS mutation at codon 12 was detected, whereas none of the cases displayed mutations in EGFR and B-RAF genes. Elevated nuclear as well as cytoplasmic pERK expression (100% and 62% of cases respectively) was observed independently of EGFR and B-RAF mutational status. Increasing pERK nuclear and cytoplasmic expression as well as the intensity of nuclear staining was found to be significantly correlated with tumor grade in univariate and multivariate statistical analysis. Our findings depict the presence of activated ERK despite the low frequency of upstream alterations, implicating ERK activation in the acquisition of a more aggressive phenotype in esophageal cancer.

miR-216b suppresses tumor growth and invasion by targeting KRAS in nasopharyngeal carcinoma

MicroRNAs (miRNAs) are small noncoding RNAs that are involved in various diseases, including cancer. In the present study, we found that miR-216b was downregulated in nasopharyngeal carcinoma (NPC) cell lines and specimens. Decreased expression of miR-216b was directly related to advanced clinical stage and lymph node metastasis. miR-216b levels correlated inversely with levels of KRAS protein during nasopharyngeal tumorigenesis. Furthermore, we demonstrated that miR-216b can bind to the 3' untranslated region (UTR) of KRAS and inhibit expression of the KRAS protein. Both in vitro and in vivo assays revealed that miR-216b attenuated NPC cell proliferation, invasion and tumor growth in nude mice. miR-216b exerts its tumor suppressor function through inhibition of the KRAS-related AKT and ERK pathways. Our findings provide, for the first time, significant clues regarding the role of miR-216b as a tumor suppressor by targeting KRAS in NPC.

Inhibition and Termination of Physiological Responses by GTPase Activating Proteins

Physiological processes are strictly organized in space and time. However, in cell physiology research, more attention is given to the question of space rather than to time. To function as a signal, environmental changes must be restricted in time; they need not only be initiated but also terminated. In this review, we concentrate on the role of one specific protein family involved in biological signal termination. GTPase activating proteins (GAPs) accelerate the endogenously low GTP hydrolysis rate of monomeric guanine nucleotide-binding proteins (GNBPs), limiting thereby their prevalence in the active, GTP-bound form. We discuss cases where defective or excessive GAP activity of specific proteins causes significant alteration in the function of the nervous, endocrine, and hemopoietic systems, or contributes to development of infections and tumors. Biochemical and genetic data as well as observations from human pathology support the notion that GAPs represent vital elements in the spatiotemporal fine tuning of physiological processes.