Project description:Cultured human pluripotent stem cells (hPSCs) grow as colonies that require breakdown into small clumps for further propagation. Although cell death mechanism by single-cell dissociation of hPSCs has been well defined, how hPSCs respond to the deadly stimulus and recover the original status remains unclear. Here we show that dissociation of hPSCs immediately activates ERK, which subsequently activates RSK and induces DUSP6, an ERK-specific phosphatase. Although the activation is transient, DUSP6 expression persists days after passaging. DUSP6 depletion using the CRISPR/Cas9 system reveals that DUSP6 suppresses the ERK activity over the long term. Elevated ERK activity by DUSP6 depletion increases both viability of hPSCs after single-cell dissociation and differentiation propensity towards mesoderm and endoderm lineages. These findings provide new insights into how hPSCs respond to dissociation in order to maintain pluripotency.
Project description:Yamanaka reprogramming is a stochastic process resulting in only a small fraction of somatic cells successfully converting into iPSCs. The molecular and cellular basis underlying this stochasticity remains elusive. Here we demonstrate that this stochasticity can be eliminated when ERK activity is tuned within a narrow range. This tuning can be accomplished by one tenth the concentration of MEK inhibitor in the 2i media. In the absence of pharmacologic ERK inhibition, cells fine tune ERK by morphological changes, growing taller by allocating more actin into their nucleus. A minimal cell height of 10 m is required for pluripotency, a cell geometric feature underlying the “dome-shaped” colony morphology of naïve pluripotent stem cells. Nuclear actin tunes ERK activity by binding to and immobilizing TFII-I, a transcription factor that binds and mediates ERK’s nuclear activation. This work uncovers a mechanistic link for how cell morphology controls cell identity. Insights into these fundamentally coupled processes provide effective approaches to overcome the stochasticity in reprogramming into pluripotency.
Project description:Schilling2009 - ERK distributive
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This model is described in the article:
Theoretical and experimental
analysis links isoform-specific ERK signalling to cell fate
decisions.
Schilling M, Maiwald T, Hengl S,
Winter D, Kreutz C, Kolch W, Lehmann WD, Timmer J,
Klingmüller U.
Mol. Syst. Biol. 2009; 5: 334
Abstract:
Cell fate decisions are regulated by the coordinated
activation of signalling pathways such as the extracellular
signal-regulated kinase (ERK) cascade, but contributions of
individual kinase isoforms are mostly unknown. By combining
quantitative data from erythropoietin-induced pathway
activation in primary erythroid progenitor (colony-forming unit
erythroid stage, CFU-E) cells with mathematical modelling, we
predicted and experimentally confirmed a distributive ERK
phosphorylation mechanism in CFU-E cells. Model analysis showed
bow-tie-shaped signal processing and inherently transient
signalling for cytokine-induced ERK signalling. Sensitivity
analysis predicted that, through a feedback-mediated process,
increasing one ERK isoform reduces activation of the other
isoform, which was verified by protein over-expression. We
calculated ERK activation for biochemically not addressable but
physiologically relevant ligand concentrations showing that
double-phosphorylated ERK1 attenuates proliferation beyond a
certain activation level, whereas activated ERK2 enhances
proliferation with saturation kinetics. Thus, we provide a
quantitative link between earlier unobservable signalling
dynamics and cell fate decisions.
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Project description:Here we report that NONO, a nuclear para-speckle component, instead functions as a chromatin regulator in mESCs acting in the ERK signaling pathway to regulate the balance between ground state versus mESCs primed for differentiation. NONO loss increases a \u201cground-like\u201d population of mESCs favoring self-renewal and more resist to differentiation, partially mimicking the effects of 2i. Mechanistically, NONO and ERK mainly co-binds a subset of development related, bivalent genes. Importantly, NONO and ERK reciprocally regulate one another, i.e. NONO regulates ERK activation while ERK controls NONO chromatin association, forming a self-reinforcing feedback loop. Our findings thus reveal a cell intrinsic mechanism involving NONO and ERK, which impact the balance between self-renewal and differentiation, respectively.
Project description:Activation of the AKT and ERK signaling pathway is a major contributor to cell proliferation. However, the integrated regulation of this multistep process, involving signal processing, cell growth and cell-cycle progression, is poorly understood. Here we study three cell types of hematopoietic origin, in which AKT and ERK signaling is triggered by erythropoietin (Epo). We find that the different cell types exhibit distinct proliferative responses, despite sharing the molecular network for pro-proliferative signaling. Iterating quantitative experiments and mathematical modeling, we show that the cell-type-specific regulation of proliferation emerges from two sources: (1) the protein abundance patterns of signaling components that cause differential flow of signals along the AKT and ERK pathways, and (2) the differential impact of the downstream regulators for protein synthesis and for cell-cycle progression on proliferation. Our integrated mathematical model of Epo-driven proliferation explains cell-type-specific effects of targeted AKT and ERK inhibitors and correctly predicts whether their combined application results in synergy.
Project description:Acting downstream of many growth factors, extracellular signal-regulated kinase (ERK) plays a pivotal role in regulating cell proliferation and tumorigenesis, where its spatiotemporal dynamics, as well as its strength, determine cellular responses. Here, we uncover the ERK activity dynamics in intestinal epithelial cells (IECs) and their association with tumour characteristics. In vivo imaging identified two distinct modes of ERK activity, sustained and pulse-like activity, in IECs. The sustained and pulse-like activity depended on ErbB2 and EGFR, respectively. Notably, deregulated activation of Wnt signalling, the earliest event in intestinal tumorigenesis, augmented EGFR signalling and exalted it to a dominant driver of ERK activity dynamics, which rendered IECs addicted to EGFR signalling. Furthermore, the frequency of ERK activity pulses was also increased to promote cell proliferation. Thus, ERK activity dynamics are defined by composite inputs from EGFR and ErbB2 signalling in IECs and their alterations underlie tumour-specific sensitivity to pharmacological EGFR inhibition. In this microarray analysis, we aimed to elucidate molecular mechanisms that mediate Wnt signalling activation-induced alterations in EGFR-ERK signalling dynamics.
Project description:Signaling through the AKT and ERK pathways controls cell proliferation. However, the integrated regulation of this multistep process, involving signal processing, cell growth and cell-cycle progression, is poorly understood. Here we study different murine hematopoietic cell types, in which AKT and ERK signaling is triggered by erythropoietin (Epo). Although these cell types share the molecular network topology for pro-proliferative Epo signaling, they exhibit distinct proliferative responses. Iterating quantitative experiments and mathematical modeling, we identify two molecular sources for cell-type-specific proliferation. First, cell-type-specific protein abundance patterns cause differential signal flow along the AKT and ERK pathways. Second, downstream regulators of both pathways have differential effects on proliferation, suggesting that protein synthesis is rate-limiting for faster-cycling cells while slower cell-cycles are controlled at the G1-S progression. The integrated mathematical model of Epo-driven proliferation explains cell-type-specific effects of targeted AKT and ERK inhibitors and faithfully predicts based on the protein abundance anti-proliferative effects of inhibitors in primary human erythroid progenitor cells. Our findings suggest that the effectiveness of targeted cancer therapy might become predictable from protein abundance patterns.
Project description:Cavin-3 is a tumor suppressor protein of unknown function. Using a combination of in vivo knockout and in vitro gain/loss of function approaches, we show that cavin-3 dictates the balance between ERK and Akt signaling. Loss of cavin-3 increases Akt signaling at the expense of ERK, while gain of cavin-3 increases ERK signaling at the expense Akt. Cavin-3 facilitates signal transduction to ERK by anchoring caveolae, a lipid-raft specialization that contains an ERK activation module, to the membrane skeleton of the plasma membrane. Loss of cavin-3 reduces the number of caveolae, thereby separating this ERK activation module from signaling receptors. Loss of cavin-3 promotes Akt signaling through suppression of EGR1 and PTEN. The in vitro consequences of the loss of cavin-3 include induction of Warburg metabolism (aerobic glycolysis), accelerated cell proliferation and resistance to apoptosis. The in vivo consequences of cavin-3 loss are increased lactate production and cachexia. 9 total samples, consisting of 3 cavin-3 siRNA groups (0 days, 3 days and 8 days) one set was untreated, one set was serum starved, one set was serum starved and then treated with EGF for 1 hr.
Project description:Amplification and activation of the Met receptor tyrosine kinase occurs up to 23% of gastric cancers, suggesting that Met is a therapeutic target in these cancers. However, the steady-state signaling events that occur during chronic Met activation, and mechanisms for resistance to Met small-molecule inhibitors, are poorly understood. Here we show that multiple gastric cancer cell lines harboring MET amplifications are dependent on Met signaling for proliferation and anchorage-independent growth. In these cells, short-term inhibition of Met leads to coordinated changes in gene expression; these include a rapid loss in expression of immediate-early genes, followed by decreased expression of genes involved in cell cycle and proliferation. Activation of Ras-Erk, PI3K-Akt and STAT3 pathways is attenuated by acute Met inhibition. STAT3 inhibition alone, but not individual inhibition of Mek or Akt, is sufficient to abrogate Met-dependent growth of these cells. However, following chronic Met inhibition, reactivation of Mek-dependent Erk phosphorylation occurs even in the presence of Met inhibitor corresponding with a downregulation of Erk negative regulators DUSP4/6. This provides a mechanism for the emergence of drug resistance. Our findings provide insights into innate resistance to a small-molecule Met inhibitor and highlight rational combination therapies that could be evaluated in clinical trials. Time series experiment, four cell lines, 2 treatments