Showing papers on "Cell growth published in 2011"

RAS oncogenes: weaving a tumorigenic web

Abstract: RAS proteins are essential components of signalling pathways that emanate from cell surface receptors. Oncogenic activation of these proteins owing to missense mutations is frequently detected in several types of cancer. A wealth of biochemical and genetic studies indicates that RAS proteins control a complex molecular circuitry that consists of a wide array of interconnecting pathways. In this Review, we describe how RAS oncogenes exploit their extensive signalling reach to affect multiple cellular processes that drive tumorigenesis.

AMP-activated protein kinase—an energy sensor that regulates all aspects of cell function

Abstract: AMP-activated protein kinase (AMPK) is a sensor of energy status that maintains cellular energy homeostasis. It arose very early during eukaryotic evolution, and its ancestral role may have been in the response to starvation. Recent work shows that the kinase is activated by increases not only in AMP, but also in ADP. Although best known for its effects on metabolism, AMPK has many other functions, including regulation of mitochondrial biogenesis and disposal, autophagy, cell polarity, and cell growth and proliferation. Both tumor cells and viruses establish mechanisms to down-regulate AMPK, allowing them to escape its restraining influences on growth.

The JAK2/STAT3 signaling pathway is required for growth of CD44+CD24– stem cell–like breast cancer cells in human tumors

Abstract: Intratumor heterogeneity is a major clinical problem because tumor cell subtypes display variable sensitivity to therapeutics and may play different roles in progression. We previously characterized 2 cell populations in human breast tumors with distinct properties: CD44+CD24- cells that have stem cell-like characteristics, and CD44-CD24+ cells that resemble more differentiated breast cancer cells. Here we identified 15 genes required for cell growth or proliferation in CD44+CD24- human breast cancer cells in a large-scale loss-of-function screen and found that inhibition of several of these (IL6, PTGIS, HAS1, CXCL3, and PFKFB3) reduced Stat3 activation. We found that the IL-6/JAK2/Stat3 pathway was preferentially active in CD44+CD24- breast cancer cells compared with other tumor cell types, and inhibition of JAK2 decreased their number and blocked growth of xenografts. Our results highlight the differences between distinct breast cancer cell types and identify targets such as JAK2 and Stat3 that may lead to more specific and effective breast cancer therapies.

Hippo pathway regulation by cell morphology and stress fibers

Abstract: The Hippo signaling pathway plays an important role in regulation of cell proliferation. Cell density regulates the Hippo pathway in cultured cells; however, the mechanism by which cells detect density remains unclear. In this study, we demonstrated that changes in cell morphology are a key factor. Morphological manipulation of single cells without cell-cell contact resulted in flat spread or round compact cells with nuclear or cytoplasmic Yap, respectively. Stress fibers increased in response to expanded cell areas, and F-actin regulated Yap downstream of cell morphology. Cell morphology- and F-actin-regulated phosphorylation of Yap, and the effects of F-actin were suppressed by modulation of Lats. Our results suggest that cell morphology is an important factor in the regulation of the Hippo pathway, which is mediated by stress fibers consisting of F-actin acting upstream of, or on Lats, and that cells can detect density through their resulting morphology. This cell morphology (stress-fiber)-mediated mechanism probably cooperates with a cell-cell contact (adhesion)-mediated mechanism involving the Hippo pathway to achieve density-dependent control of cell proliferation.

Caspase 3-mediated stimulation of tumor cell repopulation during cancer radiotherapy

Abstract: In cancer treatment, apoptosis is a well-recognized cell death mechanism through which cytotoxic agents kill tumor cells. Here we report that dying tumor cells use the apoptotic process to generate potent growth-stimulating signals to stimulate the repopulation of tumors undergoing radiotherapy. Furthermore, activated caspase 3, a key executioner in apoptosis, is involved in the growth stimulation. One downstream effector that caspase 3 regulates is prostaglandin E(2) (PGE(2)), which can potently stimulate growth of surviving tumor cells. Deficiency of caspase 3 either in tumor cells or in tumor stroma caused substantial tumor sensitivity to radiotherapy in xenograft or mouse tumors. In human subjects with cancer, higher amounts of activated caspase 3 in tumor tissues are correlated with markedly increased rate of recurrence and death. We propose the existence of a cell death-induced tumor repopulation pathway in which caspase 3 has a major role.

E2F1 regulates cellular growth by mTORC1 signaling.

Abstract: During cell proliferation, growth must occur to maintain homeostatic cell size. Here we show that E2F1 is capable of inducing growth by regulating mTORC1 activity. The activation of cell growth and mTORC1 by E2F1 is dependent on both E2F1's ability to bind DNA and to regulate gene transcription, demonstrating that a gene induction expression program is required in this process. Unlike E2F1, E2F3 is unable to activate mTORC1, suggesting that growth activity could be restricted to individual E2F members. The effect of E2F1 on the activation of mTORC1 does not depend on Akt. Furthermore, over-expression of TSC2 does not interfere with the effect of E2F1, indicating that the E2F1-induced signal pathway can compensate for the inhibitory effect of TSC2 on Rheb. Immunolocalization studies demonstrate that E2F1 induces the translocation of mTORC1 to the late endosome vesicles, in a mechanism dependent of leucine. E2F1 and leucine, or insulin, together affect the activation of S6K stronger than alone suggesting that they are complementary in activating the signal pathway. From these studies, E2F1 emerges as a key protein that integrates cell division and growth, both of which are essential for cell proliferation.

E-cadherin mediates contact inhibition of proliferation through Hippo signaling-pathway components

Abstract: Contact inhibition of cell growth is essential for embryonic development and maintenance of tissue architecture in adult organisms, and the growth of tumors is characterized by a loss of contact inhibition of proliferation. The recently identified Hippo signaling pathway has been implicated in contact inhibition of proliferation as well as organ size control. The modulation of the phosphorylation and nuclear localization of Yes-associated protein (YAP) by the highly conserved kinase cascade of the Hippo signaling pathway has been intensively studied. However, cell-surface receptors regulating the Hippo signaling pathway in mammals are not well understood. In this study, we show that Hippo signaling pathway components are required for E-cadherin–dependent contact inhibition of proliferation. Knockdown of the Hippo signaling components or overexpression of YAP inhibits the decrease in cell proliferation caused by E-cadherin homophilic binding at the cell surface, independent of other cell–cell interactions. We also demonstrate that the E-cadherin/catenin complex functions as an upstream regulator of the Hippo signaling pathway in mammalian cells. Expression of E-cadherin in MDA-MB-231 cells restores the density-dependent regulation of YAP nuclear exclusion. Knockdown of β-catenin in densely cultured MCF10A cells, which mainly depletes E-cadherin–bound β-catenin, induces a decrease in the phosphorylation of S127 residue of YAP and its nuclear accumulation. Moreover, E-cadherin homophilic binding independent of other cell interactions is sufficient to control the subcellular localization of YAP. Therefore, Our results indicate that, in addition to its role in cell–cell adhesion, E-cadherin-mediated cell–cell contact directly regulates the Hippo signaling pathway to control cell proliferation.

Transcriptional mechanisms regulating skeletal muscle differentiation, growth and homeostasis

Abstract: Skeletal muscle is the dominant organ system in locomotion and energy metabolism. Postnatal muscle grows and adapts largely by remodelling pre-existing fibres, whereas embryonic muscle grows by the proliferation of myogenic cells. Recently, the genetic hierarchies of the myogenic transcription factors that control vertebrate muscle development - by myoblast proliferation, migration, fusion and functional adaptation into fast-twitch and slow-twitch fibres - have become clearer. The transcriptional mechanisms controlling postnatal hypertrophic growth, remodelling and functional differentiation redeploy myogenic factors in concert with serum response factor (SRF), JUNB and forkhead box protein O3A (FOXO3A). It has also emerged that there is extensive post-transcriptional regulation by microRNAs in development and postnatal remodelling.

GSK1120212 (JTP-74057) Is an Inhibitor of MEK Activity and Activation with Favorable Pharmacokinetic Properties for Sustained In Vivo Pathway Inhibition

Abstract: Purpose: Despite their preclinical promise, previous MEK inhibitors have shown little benefit for patients. This likely reflects the narrow therapeutic window for MEK inhibitors due to the essential role of the P42/44 MAPK pathway in many nontumor tissues. GSK1120212 is a potent and selective allosteric inhibitor of the MEK1 and MEK2 (MEK1/2) enzymes with promising antitumor activity in a phase I clinical trial (ASCO 2010). Our studies characterize GSK11202129 enzymatic, cellular, and in vivo activities, describing its unusually long circulating half-life. Experimental Design: Enzymatic studies were conducted to determine GSK1120212 inhibition of recombinant MEK, following or preceding RAF kinase activation. Cellular studies examined GSK1120212 inhibition of ERK1 and 2 phosphorylation (p-ERK1/2) as well as MEK1/2 phosphorylation and activation. Further studies explored the sensitivity of cancer cell lines, and drug pharmacokinetics and efficacy in multiple tumor xenograft models. Results: In enzymatic and cellular studies, GSK1120212 inhibits MEK1/2 kinase activity and prevents Raf-dependent MEK phosphorylation (S217 for MEK1), producing prolonged p-ERK1/2 inhibition. Potent cell growth inhibition was evident in most tumor lines with mutant BRAF or Ras. In xenografted tumor models, GSK1120212 orally dosed once daily had a long circulating half-life and sustained suppression of p-ERK1/2 for more than 24 hours; GSK1120212 also reduced tumor Ki67, increased p27 Kip1/CDKN1B , and caused tumor growth inhibition in multiple tumor models. The largest antitumor effect was among tumors harboring mutant BRAF or Ras. Conclusions: GSK1120212 combines high potency, selectivity, and long circulating half-life, offering promise for successfully targeting the narrow therapeutic window anticipated for clinical MEK inhibitors. Clin Cancer Res; 17(5); 989–1000. ©2011 AACR .

NADPH Oxidase-Mediated Redox Signaling: Roles in Cellular Stress Response, Stress Tolerance, and Tissue Repair

Abstract: NADPH oxidase (Nox) has a dedicated function of generating reactive oxygen species (ROS). Accumulating evidence suggests that Nox has an important role in signal transduction in cellular stress responses. We have reviewed the current evidence showing that the Nox system can be activated by a collection of chemical, physical, and biological cellular stresses. In many circumstances, Nox activation fits to the cellular stress response paradigm, in that (1) the response can be initiated by various forms of cellular stresses; (2) Nox-derived ROS may activate mitogen-activated protein kinases (extracellular signal-regulated kinase, p38) and c-Jun NH 2 -terminal kinase, which are the core of the cell stress-response signaling network; and (3) Nox is involved in the development of stress cross-tolerance. Activation of the cell survival pathway by Nox may promote cell adaptation to stresses, whereas Nox may also convey signals toward apoptosis in irreversibly injured cells. At later stage after injury, Nox is involved in tissue repair by modulating cell proliferation, angiogenesis, and fibrosis. We suggest that Nox may have an integral role in cell stress responses and the subsequent tissue repair process. Understanding Nox-mediated redox signaling mechanisms may be of prominent significance at the crossroads of directing cellular responses to stress, aiming at either enhancing the stress resistance (in such situations as preventing ischemia-reperfusion injuries and accelerating wound healing) or sensitizing the stress-induced cytotoxicity for proliferative diseases such as cancer. Therefore, an optimal outcome of interventions on Nox will only be achieved when this is dealt with in a timely and disease-and stage-specific manner.

Brusatol enhances the efficacy of chemotherapy by inhibiting the Nrf2-mediated defense mechanism

Abstract: The major obstacle in cancer treatment is the resistance of cancer cells to therapies. Nrf2 is a transcription factor that regulates a cellular defense response and is ubiquitously expressed at low basal levels in normal tissues due to Keap1-dependent ubiquitination and proteasomal degradation. Recently, Nrf2 has emerged as an important contributor to chemoresistance. High constitutive expression of Nrf2 was found in many types of cancers, creating an environment conducive for cancer cell survival. Here, we report the identification of brusatol as a unique inhibitor of the Nrf2 pathway that sensitizes a broad spectrum of cancer cells and A549 xenografts to cisplatin and other chemotherapeutic drugs. Mechanistically, brusatol selectively reduces the protein level of Nrf2 through enhanced ubiquitination and degradation of Nrf2. Consequently, expression of Nrf2-downstream genes is reduced and the Nrf2-dependent protective response is suppressed. In A549 xenografts, brusatol and cisplatin cotreatment induced apoptosis, reduced cell proliferation, and inhibited tumor growth more substantially when compared with cisplatin treatment alone. Additionally, A549-K xenografts, in which Nrf2 is expressed at very low levels due to ectopic expression of Keap1, do not respond to brusatol treatment, demonstrating that brusatol-mediated sensitization to cisplatin is Nrf2 dependent. Moreover, a decrease in drug detoxification and impairment in drug removal may be the primary mechanisms by which brusatol enhances the efficacy of chemotherapeutic drugs. Taken together, these results clearly demonstrate the effectiveness of using brusatol to combat chemoresistance and suggest that brusatol can be developed into an adjuvant chemotherapeutic drug.

Dying for a cause: NETosis, mechanisms behind an antimicrobial cell death modality

Abstract: Neutrophil extracellular traps (NETs) are chromatin structures loaded with antimicrobial molecules. They can trap and kill various bacterial, fungal and protozoal pathogens, and their release is one of the first lines of defense against pathogens. In vivo, NETs are released during a form of pathogen-induced cell death, which was recently named NETosis. Ex vivo, both dead and viable neutrophils can be stimulated to release NETs composed of either nuclear or mitochondrial chromatin, respectively. In certain pathological conditions, NETs are associated with severe tissue damage or certain auto-immune diseases. This review describes the recent progress made in the identification of the mechanisms involved in NETosis and discusses its interplay with autophagy and apoptosis.

Fighting neurodegeneration with rapamycin: mechanistic insights

Abstract: A growing number of studies point to rapamycin as a pharmacological compound that is able to provide neuroprotection in several experimental models of neurodegenerative diseases, including Alzheimer's disease, Parkinson's disease, Huntington's disease and spinocerebellar ataxia type 3. In addition, rapamycin exerts strong anti-ageing effects in several species, including mammals. By inhibiting the activity of mammalian target of rapamycin (mTOR), rapamycin influences a variety of essential cellular processes, such as cell growth and proliferation, protein synthesis and autophagy. Here, we review the molecular mechanisms underlying the neuroprotective effects of rapamycin and discuss the therapeutic potential of this compound for neurodegenerative diseases.

Harnessing the biology of IL-7 for therapeutic application

Abstract: Interleukin-7 (IL-7) is required for T cell development and for maintaining and restoring homeostasis of mature T cells. IL-7 is a limiting resource under normal conditions, but it accumulates during lymphopaenia, leading to increased T cell proliferation. The administration of recombinant human IL-7 to normal or lymphopenic mice, non-human primates and humans results in widespread T cell proliferation, increased T cell numbers, modulation of peripheral T cell subsets and increased T cell receptor repertoire diversity. These effects raise the prospect that IL-7 could mediate therapeutic benefits in several clinical settings. This Review summarizes the biology of IL-7 and the results of its clinical use that are available so far to provide a perspective on the opportunities for clinical application of this cytokine.

E-cadherin mediates contact inhibition of proliferation through Hippo signaling-pathway components

Abstract: Contact inhibition of cell growth is essential for embryonic development and maintenance of tissue architecture in adult organisms, and the growth of tumors is characterized by a loss of contact inhibition of proliferation. The recently identified Hippo signaling pathway has been implicated in contact inhibition of proliferation as well as organ size control. The modulation of the phosphorylation and nuclear localization of Yes-associated protein (YAP) by the highly conserved kinase cascade of the Hippo signaling pathway has been intensively studied. However, cell-surface receptors regulating the Hippo signaling pathway in mammals are not well understood. In this study, we show that Hippo signaling pathway components are required for E-cadherin–dependent contact inhibition of proliferation. Knockdown of the Hippo signaling components or overexpression of YAP inhibits the decrease in cell proliferation caused by E-cadherin homophilic binding at the cell surface, independent of other cell–cell interactions. We also demonstrate that the E-cadherin/catenin complex functions as an upstream regulator of the Hippo signaling pathway in mammalian cells. Expression of E-cadherin in MDA-MB-231 cells restores the density-dependent regulation of YAP nuclear exclusion. Knockdown of β-catenin in densely cultured MCF10A cells, which mainly depletes E-cadherin–bound β-catenin, induces a decrease in the phosphorylation of S127 residue of YAP and its nuclear accumulation. Moreover, E-cadherin homophilic binding independent of other cell interactions is sufficient to control the subcellular localization of YAP. Therefore, Our results indicate that, in addition to its role in cell–cell adhesion, E-cadherin-mediated cell–cell contact directly regulates the Hippo signaling pathway to control cell proliferation.

Mechanical signaling through the cytoskeleton regulates cell proliferation by coordinated focal adhesion and Rho GTPase signaling.

Abstract: The notion that cell shape and spreading can regulate cell proliferation has evolved over several years, but only recently has this been linked to forces from within and upon the cell. This emerging area of mechanical signaling is proving to be wide-spread and important for all cell types. The microenvironment that surrounds cells provides a complex spectrum of different, simultaneously active, biochemical, structural and mechanical stimuli. In this milieu, cells probe the stiffness of their microenvironment by pulling on the extracellular matrix (ECM) and/or adjacent cells. This process is dependent on transcellular cell–ECM or cell–cell adhesions, as well as cell contractility mediated by Rho GTPases, to provide a functional linkage through which forces are transmitted through the cytoskeleton by intracellular force-generating proteins. This Commentary covers recent advances in the underlying mechanisms that control cell proliferation by mechanical signaling, with an emphasis on the role of 3D microenvironments and in vivo extracellular matrices. Moreover, as there is much recent interest in the tumor–stromal interaction, we will pay particular attention to exciting new data describing the role of mechanical signaling in the progression of breast cancer.

3D microfilter device for viable circulating tumor cell (CTC) enrichment from blood

Abstract: Detection of circulating tumor cells has emerged as a promising minimally invasive diagnostic and prognostic tool for patients with metastatic cancers. We report a novel three dimensional microfilter device that can enrich viable circulating tumor cells from blood. This device consists of two layers of parylene membrane with pores and gap precisely defined with photolithography. The positions of the pores are shifted between the top and bottom membranes. The bottom membrane supports captured cells and minimize the stress concentration on cell membrane and sustain cell viability during filtration. Viable cell capture on device was investigated with scanning electron microscopy, confocal microscopy, and immunofluorescent staining using model systems of cultured tumor cells spiked in blood or saline. The paper presents and validates this new 3D microfiltration concept for circulation tumor cell enrichment application. The device provides a highly valuable tool for assessing and characterizing viable enriched circulating tumor cells in both research and clinical settings.

The role of Bcl-2 and its pro-survival relatives in tumourigenesis and cancer therapy.

Abstract: Tumour development requires a combination of defects that allow nascent neoplastic cells to become self-sufficient for cell proliferation and insensitive to signals that normally restrain cell growth Among the latter, evasion of programmed cell death (apoptosis) has proven to be critical for the development and sustained growth of many, perhaps all, cancers Apoptotic cell death is regulated by complex interactions between pro-survival members and two subgroups of pro-apoptotic members of the B-cell lymphoma-2 (Bcl-2) protein family In this invited review article, we reminisce on the discovery of Bcl-2, the first regulator of cell death identified, we discuss the mechanisms that control apoptotic cell death, focussing on how defects in this process promote the development and sustained growth of tumours and also affect their responses to anticancer therapeutics and, finally, we describe how current knowledge of the regulatory networks of apoptosis is exploited to develop novel approaches for cancer therapy