Life Sciences Research for Lifelong Health

Publications biological-chemistry

Title / Authors / Details Open Access Download

Dynamics of mTORC1 activation in response to amino acids.
Manifava M, Smith M, Rotondo S, Walker S, Niewczas I, Zoncu R, Clark J, Ktistakis NT

Amino acids are essential activators of mTORC1 via a complex containing RAG GTPases, RAGULATOR and the vacuolar ATPase. Sensing of amino acids causes translocation of mTORC1 to lysosomes, an obligate step for activation. To examine the spatial and temporal dynamics of this translocation, we used live imaging of the mTORC1 component RAPTOR and a cell permeant fluorescent analogue of di-leucine methyl ester. Translocation to lysosomes is a transient event, occurring within 2 min of aa addition and peaking within 5 min. It is temporally coupled with fluorescent leucine appearance in lysosomes and is sustained in comparison to aa stimulation. Sestrin2 and the vacuolar ATPase are negative and positive regulators of mTORC1 activity in our experimental system. Of note, phosphorylation of canonical mTORC1 targets is delayed compared to lysosomal translocation suggesting a dynamic and transient passage of mTORC1 from the lysosomal surface before targetting its substrates elsewhere.

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eLife, 5, 2050-084X, , 2016

PMID: 27725083

Open Access

Application of virtual screening to the discovery of novel nicotinamide phosphoribosyltransferase (NAMPT) inhibitors with potential for the treatment of cancer and axonopathies.
Clark DE, Waszkowycz B, Wong M, Lockey PM, Adalbert R, Gilley J, Clark J, Coleman MP

NAMPT may represent a novel target for drug discovery in various therapeutic areas, including oncology and inflammation. Additionally, recent work has suggested that targeting NAMPT has potential in treating axon degeneration. In this work, publicly available X-ray co-crystal structures of NAMPT and the structures of two known NAMPT inhibitors were used as the basis for a structure- and ligand-based virtual screening campaign. From this, two novel series of NAMPT inhibitors were identified, one of which showed a statistically significant protective effect when tested in a cellular model of axon degeneration.

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Bioorganic & medicinal chemistry letters, , 1464-3405, , 2016

PMID: 27158141

Open Access

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

Investigating the effect of arachidonate supplementation on the phosphoinositide content of MCF10a breast epithelial cells.
Anderson KE, Juvin V, Clark J, Stephens LR, Hawkins PT

Phosphoinositides in primary mammalian tissue are highly enriched in a stearoyl/arachidonyl (C38:4) diacylgycerol backbone. However, mammalian cells grown in culture typically contain more diverse molecular species of phosphoinositides, characterised by a reduction in arachidonyl content in the sn-2 position. We have analysed the phosphoinositide species in MCF10a cells grown in culture by mass spectrometry. Under either serum or serum starved conditions the most abundant species of PI, PIP, PIP2 and PIP3 had masses which corresponded to C36:2, C38:4, C38:3, C38:2 and C36:1 diacylglycerol backbones and the relative proportions of each molecular species were broadly similar between each phosphoinositide class (approx. 50%, 25%, 10%, 10% and 10% respectively, for the species listed above). Supplementing the culture medium with BSA-loaded arachidonic acid promoted a rapid increase in the proportion of the C38:4 species in all phosphoinositide classes (from approx. 25%-60% of total species within 24 h), but the total amount of all combined species for each class remained remarkably constant. Stimulation of cells, cultured in either normal or arachidonate-enriched conditions, with 2 ng/ml EGF for 90 s caused substantial activation of Class I PI3K and accumulation of PIP3. Despite the increased proportion of C38:4 PIP3 under the arachidonate-supplemented conditions, the total amount of all combined PIP3 species accumulating in response to EGF was the same, with or without arachidonate supplementation; there were however small but significant preferences for the conversion of some PIP2 species to PIP3, with the polyunsaturated C38:4 and C38:3 species being more favoured over other species. These results suggest the enzymes which interconvert phosphoinositides are able to act on several different molecular species and homoeostatic mechanisms are in place to deliver similar phosphoinositide pool sizes under quite different conditions of arachidonate availability. They also suggest enzymes regulating PIP3 levels downstream of growth factor stimulation (i.e. PI3Ks and PIP3-phosphatases) show some acyl selectivity and further work should be directed at assessing whether different acyl species of PIP3 exhibit differing signalling potential.

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Advances in biological regulation, , 2212-4934, , 2015

PMID: 26639089

Open Access

Dictyostelium uses ether-linked inositol phospholipids for intracellular signalling.
Clark J,Kay RR,Kielkowska A,Niewczas I,Fets L,Oxley D,Stephens LR,Hawkins PT

Inositol phospholipids are critical regulators of membrane biology throughout eukaryotes. The general principle by which they perform these roles is conserved across species and involves binding of differentially phosphorylated inositol head groups to specific protein domains. This interaction serves to both recruit and regulate the activity of several different classes of protein which act on membrane surfaces. In mammalian cells, these phosphorylated inositol head groups are predominantly borne by a C38:4 diacylglycerol backbone. We show here that the inositol phospholipids of Dictyostelium are different, being highly enriched in an unusual C34:1e lipid backbone, 1-hexadecyl-2-(11Z-octadecenoyl)-sn-glycero-3-phospho-(1'-myo-inositol), in which the sn-1 position contains an ether-linked C16:0 chain; they are thus plasmanylinositols. These plasmanylinositols respond acutely to stimulation of cells with chemoattractants, and their levels are regulated by PIPKs, PI3Ks and PTEN. In mammals and now in Dictyostelium, the hydrocarbon chains of inositol phospholipids are a highly selected subset of those available to other phospholipids, suggesting that different molecular selectors are at play in these organisms but serve a common, evolutionarily conserved purpose.

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The EMBO journal, , 1460-2075, , 2014

PMID: 25180230

Structure of lipid kinase p110β/p85β elucidates an unusual SH2-domain-mediated inhibitory mechanism.
X Zhang, O Vadas, O Perisic, KE Anderson, J Clark, PT Hawkins, LR Stephens, RL Williams

Phosphoinositide 3-kinases (PI3Ks) are essential for cell growth, migration, and survival. The structure of a p110β/p85β complex identifies an inhibitory function for the C-terminal SH2 domain (cSH2) of the p85 regulatory subunit. Mutagenesis of a cSH2 contact residue activates downstream signaling in cells. This inhibitory contact ties up the C-terminal region of the p110β catalytic subunit, which is essential for lipid kinase activity. In vitro, p110β basal activity is tightly restrained by contacts with three p85 domains: the cSH2, nSH2, and iSH2. RTK phosphopeptides relieve inhibition by nSH2 and cSH2 using completely different mechanisms. The binding site for the RTK's pYXXM motif is exposed on the cSH2, requiring an extended RTK motif to reach and disrupt the inhibitory contact with p110β. This contrasts with the nSH2 where the pY-binding site itself forms the inhibitory contact. This establishes an unusual mechanism by which p85 SH2 domains contribute to RTK signaling specificities.

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Molecular cell, 41, 5, 567-78, 2011

PMID: 21362552
DOI: 10.1016/j.molcel.2011.01.026

Open Access

Quantification of PtdInsP3 molecular species in cells and tissues by mass spectrometry.
J Clark, KE Anderson, V Juvin, TS Smith, F Karpe, MJ Wakelam, LR Stephens, PT Hawkins

Class I phosphoinositide-3-kinase (PI3K) isoforms generate the intracellular signaling lipid, phosphatidylinositol(3,4,5)trisphosphate (PtdIns(3,4,5)P(3)). PtdIns(3,4,5)P(3) regulates major aspects of cellular behavior, and the use of both genetic and pharmacological intervention has revealed important isoform-specific roles for PI3Ks in health and disease. Despite this interest, current methods for measuring PtdIns(3,4,5)P(3) have major limitations, including insensitivity, reliance on radiolabeling, low throughput and an inability to resolve different fatty-acyl species. We introduce a methodology based on phosphate methylation coupled to high-performance liquid chromatography-mass spectrometry (HPLC-MS) to solve many of these problems and describe an integrated approach to quantify PtdIns(3,4,5)P(3) and related phosphoinositides (regio-isomers of PtdInsP and PtdInsP(2) are not resolved). This methodology can be used to quantify multiple fatty-acyl species of PtdIns(3,4,5)P(3) in unstimulated mouse and human cells (≥10(5)) or tissues (≥0.1 mg) and their increase upon appropriate stimulation.

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Nature methods, 8, 3, 267-72, 2011

PMID: 21278744
DOI: 10.1038/nmeth.1564

Open Access

PI3K p110delta regulates T-cell cytokine production during primary and secondary immune responses in mice and humans.
DR Soond, E Bjørgo, K Moltu, VQ Dale, DT Patton, KM Torgersen, F Galleway, B Twomey, J Clark, JS Gaston, K Taskén, P Bunyard, K Okkenhaug

We have previously described critical and nonredundant roles for the phosphoinositide 3-kinase p110delta during the activation and differentiation of naive T cells, and p110delta inhibitors are currently being developed for clinical use. However, to effectively treat established inflammatory or autoimmune diseases, it is important to be able to inhibit previously activated or memory T cells. In this study, using the isoform-selective inhibitor IC87114, we show that sustained p110delta activity is required for interferon-gamma production. Moreover, acute inhibition of p110delta inhibits cytokine production and reduces hypersensitivity responses in mice. Whether p110delta played a similar role in human T cells was unknown. Here we show that IC87114 potently blocked T-cell receptor-induced phosphoinositide 3-kinase signaling by both naive and effector/memory human T cells. Importantly, IC87114 reduced cytokine production by memory T cells from healthy and allergic donors and from inflammatory arthritis patients. These studies establish that previously activated memory T cells are at least as sensitive to p110delta inhibition as naive T cells and show that mouse models accurately predict p110delta function in human T cells. There is therefore a strong rationale for p110delta inhibitors to be considered for therapeutic use in T-cell-mediated autoimmune and inflammatory diseases.

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Blood, 115, 11, 2203-13, 2010

PMID: 20081091
DOI: 10.1182/blood-2009-07-232330

Open Access