Life Sciences Research for Lifelong Health

Publications simon-cook

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Control of cell death and mitochondrial fission by ERK1/2 MAP Kinase signalling.
Cook SJ, Stuart K, Gilley R, Sale MJ

The ERK1/2 signalling pathway is best known for its role in connecting activated growth factor receptors to changes in gene expression due to activated ERK1/2 entering the nucleus and phosphorylating transcription factors. However, active ERK1/2 also translocate to a variety of other organelles including the endoplasmic reticulum, endosomes, golgi and mitochondria to access specific substrates and influence cell physiology. In this article we review two aspects of ERK1/2 signalling at the mitochondria that are involved in regulating cell fate decisions. First, we describe the prominent role of ERK1/2 in controlling the BCL2-regulated, cell-intrinsic apoptotic pathway. In most cases ERK1/2 signalling promotes cell survival by activating pro-survival BCL2 proteins (BCL2, BCL-xL and MCL1) and repressing pro-death proteins (BAD, BIM, BMF and PUMA). This pro-survival signalling is co-opted by oncogenes to confer cancer cell-specific survival advantages and we describe how this information has been used to develop new drug combinations. However, ERK1/2 can also drive the expression of the pro-death protein NOXA to control 'autophagy or apoptosis' decisions during nutrient starvation. We also describe recent studies demonstrating a link between ERK1/2 signalling, DRP1 and the mitochondrial fission machinery and how this may influence metabolic reprogramming during tumorigenesis and stem cell reprogramming. With advances in sub-cellular proteomics it is likely that new roles for ERK1/2, and new substrates, remain to be discovered at the mitochondria and other organelles. This article is protected by copyright. All rights reserved.

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The FEBS journal, , 1742-4658, , 2017

PMID: 28548464

Visualisation of Endogenous ERK1/2 in Cells with a Bioorthogonal Covalent Probe.
Sipthorp J, Lebraud H, Gilley R, Kidger A, Okkenhaug H, Saba-El-Leil MK, Meloche S, Caunt CJ, Cook S, Heightman TD

The RAS-RAF-MEK-ERK pathway has been intensively studied in oncology with RAS known to be mutated in ~30% of all human cancers. The recent emergence of ERK1/2 inhibitors and their ongoing clinical investigation demands a better understanding of ERK1/2 behaviour following small molecule inhibition. Although fluorescent fusion proteins and fluorescent antibodies are well-established methods to visualise proteins, we show that ERK1/2 can be visualised via a less invasive approach based on a two-step process using Inverse Electron Demand Diels-Alder cycloaddition. Our previously reported TCO-tagged covalent ERK1/2 inhibitor was used in a series of imaging experiments following a click reaction with a tetrazine-tagged fluorescent dye. Although limitations were encountered with this approach, endogenous ERK1/2 was successfully imaged in cells and 'on target' staining was confirmed by overexpressing DUSP5, a nuclear ERK1/2 phosphatase which anchors ERK1/2 in the nucleus.

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Bioconjugate chemistry, , 1520-4812, , 2017

PMID: 28449575

RNA-binding proteins ZFP36L1 and ZFP36L2 promote cell quiescence.
Galloway A, Saveliev A, Łukasiak S, Hodson DJ, Bolland D, Balmanno K, Ahlfors H, Monzón-Casanova E, Mannurita SC, Bell LS, Andrews S, Díaz-Muñoz MD, Cook SJ, Corcoran A, Turner M

Progression through the stages of lymphocyte development requires coordination of the cell cycle. Such coordination ensures genomic integrity while cells somatically rearrange their antigen receptor genes [in a process called variable-diversity-joining (VDJ) recombination] and, upon successful rearrangement, expands the pools of progenitor lymphocytes. Here we show that in developing B lymphocytes, the RNA-binding proteins (RBPs) ZFP36L1 and ZFP36L2 are critical for maintaining quiescence before precursor B cell receptor (pre-BCR) expression and for reestablishing quiescence after pre-BCR-induced expansion. These RBPs suppress an evolutionarily conserved posttranscriptional regulon consisting of messenger RNAs whose protein products cooperatively promote transition into the S phase of the cell cycle. This mechanism promotes VDJ recombination and effective selection of cells expressing immunoglobulin-μ at the pre-BCR checkpoint.

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Science (New York, N.Y.), 352, 1095-9203, 453-9, 2016

PMID: 27102483

Tumor cells with KRAS or BRAF mutations or ERK5/MAPK7 amplification are not addicted to ERK5 activity for cell proliferation.
Lochhead PA, Clark J, Wang LZ, Gilmour L, Squires M, Gilley R, Foxton C, Newell DR, Wedge SR, Cook SJ

ERK5, encoded by MAPK7, has been proposed to play a role in cell proliferation, thus attracting interest as a cancer therapeutic target. While oncogenic RAS or BRAF cause sustained activation of the MEK1/2-ERK1/2 pathway, ERK5 is directly activated by MEK5. It has been proposed that RAS and RAF proteins can also promote ERK5 activation. Here we investigated the interplay between RAS-RAF-MEK-ERK and ERK5 signaling and studied the role of ERK5 in tumor cell proliferation in 2 disease-relevant cell models. We demonstrate that although an inducible form of CRAF (CRAF:ER*) can activate ERK5 in fibroblasts, the response is delayed and reflects feed-forward signaling. Additionally, oncogenic KRAS and BRAF do not activate ERK5 in epithelial cells. Although KRAS and BRAF do not couple directly to MEK5-ERK5, ERK5 signaling might still be permissive for proliferation. However, neither the selective MEK5 inhibitor BIX02189 or ERK5 siRNA inhibited proliferation of colorectal cancer cells harbouring KRAS(G12C/G13D) or BRAF(V600E). Furthermore, there was no additive or synergistic effect observed when BIX02189 was combined with the MEK1/2 inhibitor Selumetinib (AZD6244), suggesting that ERK5 was neither required for proliferation nor a driver of innate resistance to MEK1/2 inhibitors. Finally, even cancer cells with MAPK7 amplification were resistant to BIX02189 and ERK5 siRNA, showing that ERK5 amplification does not confer addiction to ERK5 for cell proliferation. Thus ERK5 signaling is unlikely to play a role in tumor cell proliferation downstream of KRAS or BRAF or in tumor cells with ERK5 amplification. These results have important implications for the role of ERK5 as an anti-cancer drug target.

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Cell cycle (Georgetown, Tex.), 15, 1551-4005, 506-18, 2016

PMID: 26959608

Open Access

Maternal DNA Methylation Regulates Early Trophoblast Development.
Branco MR, King M, Perez-Garcia V, Bogutz AB, Caley M, Fineberg E, Lefebvre L, Cook SJ, Dean W, Hemberger M, Reik W

Critical roles for DNA methylation in embryonic development are well established, but less is known about its roles during trophoblast development, the extraembryonic lineage that gives rise to the placenta. We dissected the role of DNA methylation in trophoblast development by performing mRNA and DNA methylation profiling of Dnmt3a/3b mutants. We find that oocyte-derived methylation plays a major role in regulating trophoblast development but that imprinting of the key placental regulator Ascl2 is only partially responsible for these effects. We have identified several methylation-regulated genes associated with trophoblast differentiation that are involved in cell adhesion and migration, potentially affecting trophoblast invasion. Specifically, trophoblast-specific DNA methylation is linked to the silencing of Scml2, a Polycomb Repressive Complex 1 protein that drives loss of cell adhesion in methylation-deficient trophoblast. Our results reveal that maternal DNA methylation controls multiple differentiation-related and physiological processes in trophoblast via both imprinting-dependent and -independent mechanisms.

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Developmental cell, 36, 1878-1551, 152-63, 2016

PMID: 26812015

Open Access

MEK1 and MEK2 inhibitors and cancer therapy: the long and winding road.
Caunt CJ, Sale MJ, Smith PD, Cook SJ

The role of the ERK signalling pathway in cancer is thought to be most prominent in tumours in which mutations in the receptor tyrosine kinases RAS, BRAF, CRAF, MEK1 or MEK2 drive growth factor-independent ERK1 and ERK2 activation and thence inappropriate cell proliferation and survival. New drugs that inhibit RAF or MEK1 and MEK2 have recently been approved or are currently undergoing late-stage clinical evaluation. In this Review, we consider the ERK pathway, focusing particularly on the role of MEK1 and MEK2, the 'gatekeepers' of ERK1/2 activity. We discuss their validation as drug targets, the merits of targeting MEK1 and MEK2 versus BRAF and the mechanisms of action of different inhibitors of MEK1 and MEK2. We also consider how some of the systems-level properties (intrapathway regulatory loops and wider signalling network connections) of the ERK pathway present a challenge for the success of MEK1 and MEK2 inhibitors, discuss mechanisms of resistance to these inhibitors, and review their clinical progress.

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Nature reviews. Cancer, 15, 1474-1768, 577-92, 2015

PMID: 26399658

Identification of DYRK1B as a substrate of ERK1/2 and characterisation of the kinase activity of DYRK1B mutants from cancer and metabolic syndrome.
Ashford AL, Dunkley TP, Cockerill M, Rowlinson RA, Baak LM, Gallo R, Balmanno K, Goodwin LM, Ward RA, Lochhead PA, Guichard S, Hudson K, Cook SJ

The dual-specificity tyrosine-phosphorylation-regulated kinase, DYRK1B, is expressed de novo during myogenesis, amplified or mutated in certain cancers and mutated in familial cases of metabolic syndrome. DYRK1B is activated by cis auto-phosphorylation on tyrosine-273 (Y273) within the activation loop during translation but few other DYRK1B phosphorylation sites have been characterised to date. Here, we demonstrate that DYRK1B also undergoes trans-autophosphorylation on serine-421 (S421) in vitro and in cells and that this site contributes to DYRK1B kinase activity. Whilst a DYRK1B(S421A) mutant was completely defective for p-S421 in cells, DYRK1B inhibitors caused only a partial loss of p-S421 suggesting the existence of an additional kinase that could also phosphorylate DYRK1B S421. Indeed, a catalytically inactive DYRK1B(D239A) mutant exhibited very low levels of p-S421 in cells but this was increased by KRAS(G12V). In addition, selective activation of the RAF-MEK1/2-ERK1/2 signalling pathway rapidly increased p-S421 in cells whereas activation of the stress kinases JNK or p38 could not. S421 resides within a Ser-Pro phosphoacceptor motif that is typical for ERK1/2 and recombinant ERK2 phosphorylated DYRK1B at S421 in vitro. Our results show that DYRK1B is a novel ERK2 substrate, uncovering new links between two kinases involved in cell fate decisions. Finally, we show that DYRK1B mutants that have recently been described in cancer and metabolic syndrome exhibit normal or reduced intrinsic kinase activity.

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Cellular and molecular life sciences : CMLS, , 1420-9071, , 2015

PMID: 26346493

Open Access

DYRK1A-mediated Cyclin D1 Degradation in Neural Stem Cells Contributes to the Neurogenic Cortical Defects in Down Syndrome.
Najas S, Arranz J, Lochhead PA, Ashford AL, Oxley D, Delabar JM, Cook SJ, Barallobre MJ, Arbonés ML

Alterations in cerebral cortex connectivity lead to intellectual disability and in Down syndrome, this is associated with a deficit in cortical neurons that arises during prenatal development. However, the pathogenic mechanisms that cause this deficit have not yet been defined. Here we show that the human DYRK1A kinase on chromosome 21 tightly regulates the nuclear levels of Cyclin D1 in embryonic cortical stem (radial glia) cells, and that a modest increase in DYRK1A protein in transgenic embryos lengthens the G1 phase in these progenitors. These alterations promote asymmetric proliferative divisions at the expense of neurogenic divisions, producing a deficit in cortical projection neurons that persists in postnatal stages. Moreover, radial glial progenitors in the Ts65Dn mouse model of Down syndrome have less Cyclin D1, and Dyrk1a is the triplicated gene that causes both early cortical neurogenic defects and decreased nuclear Cyclin D1 levels in this model. These data provide insights into the mechanisms that couple cell cycle regulation and neuron production in cortical neural stem cells, emphasizing that the deleterious effect of DYRK1A triplication in the formation of the cerebral cortex begins at the onset of neurogenesis, which is relevant to the search for early therapeutic interventions in Down syndrome.

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EBioMedicine, 2, 2352-3964, 120-34, 2015

PMID: 26137553

Open Access

Epigenetic memory of the first cell fate decision prevents complete ES cell reprogramming into trophoblast.
F Cambuli, A Murray, W Dean, D Dudzinska, F Krueger, S Andrews, CE Senner, S Cook, M Hemberger

Embryonic (ES) and trophoblast (TS) stem cells reflect the first, irrevocable cell fate decision in development that is reinforced by distinct epigenetic lineage barriers. Nonetheless, ES cells can seemingly acquire TS-like characteristics upon manipulation of lineage-determining transcription factors or activation of the extracellular signal-regulated kinase 1/2 (Erk1/2) pathway. Here we have interrogated the progression of reprogramming in ES cell models with regulatable Oct4 and Cdx2 transgenes or conditional Erk1/2 activation. Although trans-differentiation into TS-like cells is initiated, lineage conversion remains incomplete in all models, underpinned by the failure to demethylate a small group of TS cell genes. Forced expression of these non-reprogrammed genes improves trans-differentiation efficiency, but still fails to confer a stable TS cell phenotype. Thus, even ES cells in ground-state pluripotency cannot fully overcome the boundaries that separate the first cell lineages but retain an epigenetic memory of their ES cell origin.

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Nat Commun., 26, 5, 5538, 2014

PMID: 25423963

Open Access

Intrinsic and acquired resistance to MEK1/2 inhibitors in cancer.
Sale MJ, Cook SJ

Recent clinical data with BRAF and MEK1/2 [MAPK (mitogen-activated protein kinase)/ERK (extracellular-signal-regulated kinase) kinase 1/2] inhibitors have demonstrated the remarkable potential of targeting the RAF-MEK1/2-ERK1/2 signalling cascade for the treatment of certain cancers. Despite these advances, however, only a subset of patients respond to these agents in the first instance, and, of those that do, acquired resistance invariably develops after several months. Studies in vitro have identified various mechanisms that can underpin intrinsic and acquired resistance to MEK1/2 inhibitors, and these frequently recapitulate those observed clinically. In the present article, we review these mechanisms and also discuss recent advances in our understanding of how MEK1/2 inhibitor activity is influenced by pathway feedback.

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Biochemical Society transactions, 42, 1470-8752, 776-83, 2014

PMID: 25109957

The increase in BIK expression following ERK1/2 pathway inhibition is a consequence of G₁ cell-cycle arrest and not a direct effect on BIK protein stability.
Sale MJ, Cook SJ

BIK (BCL2-interacting killer) is a pro-apoptotic BH3 (BCL2 homology domain 3)-only protein and a member of the BCL2 protein family. It was proposed recently that BIK abundance is controlled by ERK1/2 (extracellular-signal-regulated kinase 1/2)-catalysed phosphorylation, which targets the protein for proteasome-dependent destruction. In the present study, we examined ERK1/2-dependent regulation of BIK, drawing comparisons with BIM(EL) (BCL2-interacting mediator of cell death; extra long), a well-known target of ERK1/2. In many ERK1/2-dependent tumour cell lines, inhibition of BRAF(V600E) (v-raf murine sarcoma viral oncogene homologue B1, V600E mutation) or MEK1/2 (mitogen-activated protein kinase/ERK kinase 1/2) had very little effect on BIK expression, whereas BIM(EL) was strongly up-regulated. In some cell lines we observed a modest increase in BIK expression; however, this was not apparent until ~16 h or later, whereas BIM(EL) expression increased rapidly within a few hours. Although BIK was degraded by the proteasome, we found no evidence that this was regulated by ERK1/2 signalling. Rather, the delayed increase in BIK expression was prevented by actinomycin D, and was accompanied by increases in BIK mRNA. Finally, the delayed increase in BIK expression following ERK1/2 inhibition was phenocopied by a highly selective CDK4/6 (cyclin-dependent kinases 4 and 6) inhibitor, which caused a strong G₁ cell-cycle arrest without inhibiting ERK1/2 signalling. In contrast, BIM(EL) expression was induced by ERK1/2 inhibition, but not by CDK4/6 inhibition. We conclude that BIK expression is not subject to direct regulation by the ERK1/2 pathway; rather, we propose that BIK expression is cell-cycle-dependent and increases as a consequence of the G₁ cell-cycle arrest which results from inhibition of ERK1/2 signalling.

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The Biochemical journal, 459, 1470-8728, 513-24, 2014

PMID: 24527759

Oncogenic K-Ras suppresses IP3-dependent Ca2+ release through remodeling of IP3Rs isoform composition and ER luminal Ca2+ levels in colorectal cancer cell lines.
C Pierro, SJ Cook, TC Foets, MD Bootman, HL Roderick

The GTPase Ras is a molecular switch engaged downstream of G-protein coupled receptors and receptor tyrosine kinases that controls multiple cell fate-determining signalling pathways. Ras signalling is frequently deregulated in cancer underlying associated changes in cell phenotype. Although Ca(2+) signalling pathways control some overlapping functions with Ras, and altered Ca(2+) signalling pathways are emerging as important players in oncogenic transformation, how Ca(2+) signalling is remodelled during transformation and whether it has a causal role remains unclear. We have investigated Ca(2+) signalling in two human colorectal cancer cell lines and their isogenic derivatives in which the mutated K-Ras allele (G13D) has been deleted by homologous recombination. We show that agonist-induced Ca(2+) release from intracellular stores is enhanced by loss of K-Ras(G13D) through an increase in the ER store content and a modification of IP3R subtype abundance. Consistently, uptake of Ca(2+) into mitochondria and sensitivity to apoptosis was enhanced as a result of K-Ras(G13D) loss. These results suggest that suppression of Ca(2+) signalling is a common response to naturally occurring levels of K-Ras(G13D) that contributes to a survival advantage during oncogenic transformation.

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Journal of cell science, , , , 2014

PMID: 24522186
DOI: 10.1242/jcs.141408

Open Access

The role of MAPK signalling pathways in the response to endoplasmic reticulum stress.
NJ Darling, SJ Cook

Perturbations in endoplasmic reticulum (ER) homeostasis, including depletion of Ca(2+) or altered redox status, induce ER stress due to protein accumulation, misfolding and oxidation. This activates the unfolded protein response (UPR) to re-establish the balance between ER protein folding capacity and protein load, resulting in cell survival or, following chronic ER stress, promotes cell death. The mechanisms for the transition between adaptation to ER stress and ER stress-induced cell death are still being understood. However, the identification of numerous points of cross-talk between the UPR and mitogen-activated protein kinase (MAPK) signalling pathways may contribute to our understanding of the consequences of ER stress. Indeed, the MAPK signalling network is known to regulate cell cycle progression and cell survival or death responses following a variety of stresses. In this article, we review UPR signalling and the activation of MAPK signalling pathways in response to ER stress. In addition, we highlight components of the UPR that are modulated in response to MAPK signalling and the consequences of this cross-talk. We also describe several diseases, including cancer, type II diabetes and retinal degeneration, where activation of the UPR and MAPK signalling contribute to disease progression and highlight potential avenues for therapeutic intervention. This article is part of a Special Issue entitled: Calcium Signaling In Health and Disease.

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Biochimica et biophysica acta, , , , 2014

PMID: 24440275
DOI: 10.1016/j.bbamcr.2014.01.009

Adaptation to mTOR kinase inhibitors by amplification of eIF4E to maintain cap-dependent translation.
CL Cope, R Gilley, K Balmanno, MJ Sale, KD Howarth, M Hampson, PD Smith, SM Guichard, SJ Cook

The mechanistic target of rapamycin (mTOR) protein kinase coordinates responses to nutrients and growth factors and is an anti-cancer drug target. To anticipate how cells will respond and adapt to chronic mTOR complex (mTORC)1 and mTORC2 inhibition, we have generated SW620 colon cancer cells with acquired resistance to the ATP-competitive mTOR kinase inhibitor AZD8055 (SW620:8055R). AZD8055 inhibited mTORC1 and mTORC2 signalling and caused a switch from cap-dependent to internal ribosome entry site (IRES)-dependent translation in parental SW620 cells. In contrast, SW620:8055R cells exhibited a loss of S6K signalling, an increase in expression of the eukaryotic translation initiation factor eIF4E and increased cap-dependent mRNA translation. As a result, the expression of CCND1 and MCL1, proteins encoded by eIF4E-sensitive and cap-dependent transcripts, was refractory to AZD8055 in SW620:8055R cells. RNAi-mediated knockdown of eIF4E reversed acquired resistance to AZD8055 in SW620:8055R cells; furthermore, increased expression of eIF4E was sufficient to reduce sensitivity to AZD8055 in a heterologous cell system. Finally, although the combination of MEK1/2 inhibitors with mTOR inhibitors is an attractive rational drug combination, SW620:8055R cells were actually cross-resistant to the MEK1/2 inhibitor selumetinib (AZD6244). These results exemplify the convergence of ERK1/2 and mTOR signalling at eIF4E, and the key role of eIF4E downstream of mTOR in maintaining cell proliferation. They also have important implications for therapeutic strategies based around mTOR and the MEK1/2-ERK1/2 pathway.

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Journal of cell science, 127, Pt 4, 788-800, 2014

PMID: 24363449
DOI: 10.1242/jcs.137588

Open Access

A novel DYRK1B inhibitor AZ191 demonstrates that DYRK1B acts independently of GSK3β to phosphorylate cyclin D1 at Thr(286), not Thr(288).
AL Ashford, D Oxley, J Kettle, K Hudson, S Guichard, SJ Cook, PA Lochhead

DYRK1B (dual-specificity tyrosine phosphorylation-regulated kinase 1B) is amplified in certain cancers and may be an oncogene; however, our knowledge of DYRK1B has been limited by the lack of selective inhibitors. In the present study we describe AZ191, a potent small molecule inhibitor that selectively inhibits DYRK1B in vitro and in cells. CCND1 (cyclin D1), a key regulator of the mammalian G1-S-phase transition, is phosphorylated on Thr(286) by GSK3β (glycogen synthase kinase 3β) to promote its degradation. DYRK1B has also been proposed to promote CCND1 turnover, but was reported to phosphorylate Thr(288) rather than Thr(286). Using in vitro kinase assays, phospho-specific immunoblot analysis and MS in conjunction with AZ191 we now show that DYRK1B phosphorylates CCND1 at Thr(286), not Thr(288), in vitro and in cells. In HEK (human embryonic kidney)-293 and PANC-1 cells (which exhibit DYRK1B amplification) DYRK1B drives Thr(286) phosphorylation and proteasome-dependent turnover of CCND1 and this is abolished by AZ191 or DYRK1B RNAi, but not by GSK3β inhibitors or GSK3β RNAi. DYRK1B expression causes a G1-phase cell-cycle arrest, but overexpression of CCND1 (wild-type or T286A) fails to overcome this; indeed, DYRK1B also promotes the expression of p21CIP1 (21 kDa CDK-interacting protein 1) and p27KIP1 (CDK-inhibitory protein 1). The results of the present study demonstrate for the first time that DYRK1B is a novel Thr(286)-CCND1 kinase that acts independently of GSK3β to promote CCND1 degradation. Furthermore, we anticipate that AZ191 may prove useful in defining further substrates and biological functions of DYRK1B.

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The Biochemical journal, 457, 1, 43-56, 2014

PMID: 24134204
DOI: 10.1042/BJ20130461

MEK Inhibitor U0126 Reverses Protection of Axons from Wallerian Degeneration Independently of MEK-ERK Signaling.
C Evans, SJ Cook, MP Coleman, J Gilley

Wallerian degeneration is delayed when sufficient levels of proteins with NMNAT activity are maintained within axons after injury. This has been proposed to form the basis of 'slow Wallerian degeneration' (Wld (S)), a neuroprotective phenotype conferred by an aberrant fusion protein, Wld(S). Proteasome inhibition also delays Wallerian degeneration, although much less robustly, with stabilization of NMNAT2 likely to play a key role in this mechanism. The pan-MEK inhibitor U0126 has previously been shown to reverse the axon-protective effects of proteasome inhibition, suggesting that MEK-ERK signaling plays a role in delayed Wallerian degeneration, in addition to its established role in promoting neuronal survival. Here we show that whilst U0126 can also reverse Wld(S)-mediated axon protection, more specific inhibitors of MEK1/2 and MEK5, PD184352 and BIX02189, have no significant effect on the delay to Wallerian degeneration in either situation, whether used alone or in combination. This suggests that an off-target effect of U0126 is responsible for reversion of the axon protective effects of Wld(S) expression or proteasome inhibition, rather than inhibition of MEK1/2-ERK1/2 or MEK5-ERK5 signaling. Importantly, this off-target effect does not appear to result in alterations in the stabilities of either Wld(S) or NMNAT2.

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PloS one, 8, 10, e76505, 2013

PMID: 24124570
DOI: 10.1371/journal.pone.0076505

Open Access

Adaptation to chronic mTOR inhibition in cancer and in aging.
R Gilley, K Balmanno, CL Cope, SJ Cook

The mTOR [mammalian (or mechanistic) target of rapamycin] protein kinase co-ordinates catabolic and anabolic processes in response to growth factors and nutrients and is a validated anticancer drug target. Rapamycin and related allosteric inhibitors of mTORC1 (mTOR complex 1) have had some success in specific tumour types, but have not exhibited broad anticancer activity, prompting the development of new ATP-competitive mTOR kinase inhibitors that inhibit both mTORC1 and mTORC2. In common with other targeted kinase inhibitors, tumours are likely to adapt and acquire resistance to mTOR inhibitors. In the present article, we review studies that describe how tumour cells adapt to become resistant to mTOR inhibitors. mTOR is a central signalling hub which responds to an array of signalling inputs and activates a range of downstream effector pathways. Understanding how this signalling network is remodelled and which pathways are invoked to sustain survival and proliferation in the presence of mTOR inhibitors can provide new insights into the importance of the various mTOR effector pathways and may suggest targets for intervention to combine with mTOR inhibitors. Finally, since chronic mTOR inhibition by rapamycin can increase lifespan and healthspan in nematodes, fruitflies and mice, we contrast these studies with tumour cell responses to mTOR inhibition.

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Biochemical Society transactions, 41, 4, 956-61, 2013

PMID: 23863163
DOI: 10.1042/BST20130080

FGF Signaling Inhibition in ESCs Drives Rapid Genome-wide Demethylation to the Epigenetic Ground State of Pluripotency.
G Ficz, TA Hore, F Santos, HJ Lee, W Dean, J Arand, F Krueger, D Oxley, YL Paul, J Walter, SJ Cook, S Andrews, MR Branco, W Reik

Genome-wide erasure of DNA methylation takes place in primordial germ cells (PGCs) and early embryos and is linked with pluripotency. Inhibition of Erk1/2 and Gsk3β signaling in mouse embryonic stem cells (ESCs) by small-molecule inhibitors (called 2i) has recently been shown to induce hypomethylation. We show by whole-genome bisulphite sequencing that 2i induces rapid and genome-wide demethylation on a scale and pattern similar to that in migratory PGCs and early embryos. Major satellites, intracisternal A particles (IAPs), and imprinted genes remain relatively resistant to erasure. Demethylation involves oxidation of 5-methylcytosine (5mC) to 5-hydroxymethylcytosine (5hmC), impaired maintenance of 5mC and 5hmC, and repression of the de novo methyltransferases (Dnmt3a and Dnmt3b) and Dnmt3L. We identify a Prdm14- and Nanog-binding cis-acting regulatory region in Dnmt3b that is highly responsive to signaling. These insights provide a framework for understanding how signaling pathways regulate reprogramming to an epigenetic ground state of pluripotency.

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Cell stem cell, 13, 3, 351-9, 2013

PMID: 23850245
DOI: 10.1016/j.stem.2013.06.004

Open Access

That which does not kill me makes me stronger; combining ERK1/2 pathway inhibitors and BH3 mimetics to kill tumour cells and prevent acquired resistance.
MJ Sale, SJ Cook

Oncogenic mutations in RAS or BRAF can drive the inappropriate activation of the ERK1/2. In many cases, tumour cells adapt to become addicted to this deregulated ERK1/2 signalling for their proliferation, providing a therapeutic window for tumour-selective growth inhibition. As a result, inhibition of ERK1/2 signalling by BRAF or MEK1/2 inhibitors is an attractive therapeutic strategy. Indeed, the first BRAF inhibitor, vemurafenib, has now been approved for clinical use, while clinical evaluation of MEK1/2 inhibitors is at an advanced stage. Despite this progress, it is apparent that tumour cells adapt quickly to these new targeted agents so that tumours with acquired resistance can emerge within 6-9 months of primary treatment. One of the major reasons for this is that tumour cells typically respond to BRAF or MEK1/2 inhibitors by undergoing a G1 cell cycle arrest rather than dying. Indeed, although inhibition of ERK1/2 invariably increases the expression of pro-apoptotic BCL2 family proteins, tumour cells undergo minimal apoptosis. This cytostatic response may simply provide the cell with the opportunity to adapt and acquire resistance. Here we discuss recent studies that demonstrate that combination of BRAF or MEK1/2 inhibitors with inhibitors of pro-survival BCL2 proteins is synthetic lethal for ERK1/2-addicted tumour cells. This combination effectively transforms the cytostatic response of BRAF and MEK1/2 inhibitors into a striking apoptotic cell death response. This not only augments the primary efficacy of BRAF and MEK1/2 inhibitors but delays the onset of acquired resistance to these agents, validating their combination in the clinic.

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British journal of pharmacology, 169, 8, 1708-22, 2013

PMID: 23647573
DOI: 10.1111/bph.12220

Open Access

The BH3 mimetic ABT-263 synergizes with the MEK1/2 inhibitor selumetinib/AZD6244 to promote BIM-dependent tumour cell death and inhibit acquired resistance.
MJ Sale, SJ Cook

Tumour cells typically exhibit a G(1) cell cycle arrest in response to the MEK1/2 [mitogen-activated protein kinase/ERK (extracellular-signal-regulated kinase) kinase 1/2] inhibitor selumetinib, but do not die, and thus they acquire resistance. In the present study we examined the effect of combining selumetinib with the BH3 [BCL2 (B-cell lymphoma 2) homology domain 3]-mimetic BCL2 inhibitor ABT-263. Although either drug alone caused little tumour cell death, the two agents combined to cause substantial caspase-dependent cell death and inhibit long-term clonogenic survival of colorectal cancer and melanoma cell lines with BRAF(V600E) or RAS mutations. This cell death absolutely required BAX (BCL2-associated X protein) and was inhibited by RNAi (RNA interference)-mediated knockdown of BIM (BCL2-interacting mediator of cell death) in the BRAF(V600E)-positive COLO205 cell line. When colorectal cancer cell lines were treated with selumetinib plus ABT-263 we observed a striking reduction in the incidence of cells emerging with acquired resistance to selumetinib. Similar results were observed when we combined ABT-263 with the BRAF(V600E)-selective inhibitor PLX4720, but only in cells expressing BRAF(V600E). Finally, cancer cells in which acquired resistance to selumetinib arises through BRAF(V600E) amplification remained sensitive to ABT-263, whereas selumetinib-resistant HCT116 cells (KRAS(G13D) amplification) were cross-resistant to ABT-263. Thus the combination of a BCL2 inhibitor and an ERK1/2 pathway inhibitor is synthetic lethal in ERK1/2-addicted tumour cells, delays the onset of acquired resistance and in some cases overcomes acquired resistance to selumetinib.

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The Biochemical journal, 450, 2, 285-94, 2013

PMID: 23234544
DOI: 10.1042/BJ20121212

Tumour cell responses to new fibroblast growth factor receptor tyrosine kinase inhibitors and identification of a gatekeeper mutation in FGFR3 as a mechanism of acquired resistance.
V Chell, K Balmanno, AS Little, M Wilson, S Andrews, L Blockley, M Hampson, PR Gavine, SJ Cook

Fibroblast growth factor receptors (FGFRs) can act as driving oncoproteins in certain cancers, making them attractive drug targets. Here we have characterized tumour cell responses to two new inhibitors of FGFR1-3, AZ12908010 and the clinical candidate AZD4547, making comparisons with the well-characterized FGFR inhibitor PD173074. In a panel of 16 human tumour cell lines, the anti-proliferative activity of AZ12908010 or AZD4547 was strongly linked to the presence of deregulated FGFR signalling, indicating that addiction to deregulated FGFRs provides a therapeutic opportunity for selective intervention. Acquired resistance to targeted tyrosine kinase inhibitors is a growing problem in the clinic but has not yet been explored for FGFR inhibitors. To assess how FGFR-dependent tumour cells adapt to long-term FGFR inhibition, we generated a derivative of the KMS-11 myeloma cell line (FGFR(Y373C)) with acquired resistance to AZ12908010 (KMS-11R cells). Basal phosphorylated FGFR and FGFR-dependent downstream signalling were constitutively elevated and refractory to drug in KMS-11R cells. Sequencing of FGFR3 in KMS-11R cells revealed the presence of a heterozygous mutation at the gatekeeper residue, encoding FGFR3(V555M); consistent with this, KMS-11R cells were cross-resistant to AZD4547 and PD173074. These results define the selectivity and efficacy of two new FGFR inhibitors and identify a secondary gatekeeper mutation as a mechanism of acquired resistance to FGFR inhibitors that should be anticipated as clinical evaluation proceeds.

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Oncogene, 32, 25, 3059-70, 2013

PMID: 22869148
DOI: 10.1038/onc.2012.319

Mechanisms of acquired resistance to ERK1/2 pathway inhibitors.
AS Little, PD Smith, SJ Cook

The ERK1/2 (extracellular signal-regulated kinase 1 and 2) pathway, comprising the protein kinases RAF (v-raf-1 murine leukemia viral oncogene homolog 1), MEK1/2 (mitogen-activated protein kinase or ERK kinase 1 and 2) and ERK1/2 is frequently de-regulated in human cancers, due to mutations in RAS or BRAF (v-raf-1 murine leukemia viral oncogene homolog B1). New, highly selective inhibitors of BRAF and MEK1/2 have shown promise in clinical trials, including in previously intractable diseases such as melanoma. However, drug-resistant tumour cells invariably emerge leading to disease progression. It is important to understand the mechanisms underlying such acquired resistance since this may lead to the development of rational strategies either to delay its onset or to overcome it once established. It also offers unique insights into the plasticity of signalling pathways, which may in turn inform our understanding of the basic biology of these pathways and lead to the validation of new drug targets. Several recent reports have identified diverse mechanisms of acquired resistance to MEK1/2 or BRAF inhibitors. In this article, we review these studies, discuss the different mechanisms, identify common themes and consider their therapeutic implications.

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Oncogene, 32, 10, 1207-15, 2013

PMID: 22562245
DOI: 10.1038/onc.2012.160

ERK5 and its role in tumour development.
PA Lochhead, R Gilley, SJ Cook

The MEK5 [MAPK (mitogen-activated protein kinase)/ERK (extracellular-signal-regulated kinase) kinase 5]/ERK5 pathway is the least well studied MAPK signalling module. It has been proposed to play a role in the pathology of cancer. In the present paper, we review the role of the MEK5/ERK5 pathway using the 'hallmarks of cancer' as a framework and consider how this pathway is deregulated. As well as playing a key role in endothelial cell survival and tubular morphogenesis during tumour neovascularization, ERK5 is also emerging as a regulator of tumour cell invasion and migration. Several oncogenes can stimulate ERK5 activity, and protein levels are increased by a novel amplification at chromosome locus 17p11 and by down-regulation of the microRNAs miR-143 and miR-145. Together, these finding underscore the case for further investigation into understanding the role of ERK5 in cancer.

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Biochemical Society transactions, 40, 1, 251-6, 2012

PMID: 22260700
DOI: 10.1042/BST20110663

Tumour cell responses to MEK1/2 inhibitors: acquired resistance and pathway remodelling.
AS Little, K Balmanno, MJ Sale, PD Smith, SJ Cook

The Raf/MEK1/2 [mitogen-activated protein kinase/ERK (extracellular-signal-regulated kinase) kinase 1/2]/ERK1/2 signalling pathway is frequently activated in human tumours due to mutations in BRAF or KRAS. B-Raf and MEK1/2 inhibitors are currently undergoing clinical evaluation, but their ultimate success is likely to be limited by acquired drug resistance. We have used colorectal cancer cell lines harbouring mutations in B-Raf or K-Ras to model acquired resistance to the MEK1/2 inhibitor selumetinib (AZD6244). Selumetinib-resistant cells were refractory to other MEK1/2 inhibitors in cell proliferation assays and exhibited a marked increase in MEK1/2 and ERK1/2 activity and cyclin D1 abundance when assessed in the absence of inhibitor. This was driven by a common mechanism in which resistant cells exhibited an intrachromosomal amplification of their respective driving oncogene, B-Raf V600E or K-RasG13D. Despite the increased signal flux from Raf to MEK1/2, resistant cells maintained in drug actually exhibited the same level of ERK1/2 activity as parental cells, indicating that the pathway is remodelled by feedback controls to reinstate the normal level of ERK1/2 signalling that is required and sufficient to maintain proliferation in these cells. These results provide important new insights into how tumour cells adapt to new therapeutics and highlight the importance of homoeostatic control mechanisms in the Raf/MEK1/2/ERK1/2 signalling cascade.

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Biochemical Society transactions, 40, 1, 73-8, 2012

PMID: 22260668
DOI: 10.1042/BST20110647

Regulation of MEK/ERK pathway output by subcellular localization of B-Raf.
C Andreadi, C Noble, B Patel, H Jin, MM Aguilar Hernandez, K Balmanno, SJ Cook, C Pritchard

The strength and duration of intracellular signalling pathway activation is a key determinant of the biological outcome of cells in response to extracellular cues. This has been particularly elucidated for the Ras/Raf/MEK [mitogen-activated growth factor/ERK (extracellular-signal-regulated kinase) kinase]/ERK signalling pathway with a number of studies in fibroblasts showing that sustained ERK signalling is a requirement for S-phase entry, whereas transient ERK signalling does not have this capability. A major unanswered question, however, is how a cell can sustain ERK activation, particularly when ERK-specific phosphatases are transcriptionally up-regulated by the pathway itself. A major point of ERK regulation is at the level of Raf, and, to sustain ERK activation in the presence of ERK phosphatases, sustained Raf activation is a requirement. Three Raf proteins exist in mammals, and the activity of all three is induced following growth factor stimulation of cells, but only B-Raf activity is maintained at later time points. This observation points to B-Raf as a regulator of sustained ERK activation. In the present review, we consider evidence for a link between B-Raf and sustained ERK activation, focusing on a potential role for the subcellular localization of B-Raf in this key physiological event.

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Biochemical Society transactions, 40, 1, 67-72, 2012

PMID: 22260667
DOI: 10.1042/BST20110621