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Biomedical subjects

Douglas A Lauffenburger

Publications and source records attributed to Douglas A Lauffenburger.

At least 19 recordsLinked to original sources

A scalable, low-cost, sample hashing workflow for multiomic single-cell analysis using the Seq-Well S3 platform.

In-depth analyses of clinical samples have the potential to provide unparalleled insights into the cellular mechanisms that underlie both health and disease, as well as therapeutic and prophylactic responses. However, these specimens are often paucicellular, necessitating the use of workflows that maximize the amount of information that can be learned. Here we provide a detailed protocol for generating and analyzing single-cell multiomic data from low-input samples with the Seq-Well S3 platform. We further describe a matched pipeline for sample hashing that reduces costs and sources of technical variation in the resulting data while also enhancing throughput. In brief, our streamlined and efficient methodology involves: (1) optionally staining single-cell suspensions with antibody-oligonucleotide conjugates for cell surface protein quantification and/or sample multiplexing; (2) generating Seq-Well S3 sequencing libraries; (3) optionally producing bulk-RNA sequencing libraries via SMART-seq2 to support genetic demultiplexing; and (4) computationally analyzing the resulting data. Each step herein has been designed to leverage readily available reagents and standard laboratory equipment, substantially lowering barriers to entry for researchers. The overall Protocol can yield high-quality multiomic insights from samples in under a week.

Single-Cell Analysis↗

Quantitative analysis of Akt phosphorylation and activity in response to EGF and insulin treatment.

The protein kinase Akt is a critical regulator of cell function and its overexpression and activation have been functionally linked to numerous pathologies such as cancer. Previous reports regarding the mechanism-regulating Akt's activation have revealed two phosphorylation events, at threonine 308 (T308) and serine 473 (S473), as necessary for the full activation of the kinase in response to insulin. For this reason and because of the availability of phospho-specific antibodies to both T308 and S473, many studies that focus on Akt's role in governing cell function rely on the measurement of these two sites to understand changes in kinase activity. Recent evidence, however, suggests the involvement of other phosphorylation sites; for example, in Src-transformed and epidermal growth factor (EGF)-treated cells, tyrosine phosphorylation has been found important for full kinase activation. In this study, we probed the quantitative reliability of using S473 and/or T308 phosphorylation as surrogates for Akt kinase activity across diverse treatment conditions. We performed quantitative Western blots and kinase activity assays on lysates generated during a 2h time course from two cell lines treated with either EGF or insulin. From the resulting approximately 250 quantitative measurements of phosphorylation and activity, we found that both T308 and S473 phosphorylation accurately captured quantitative changes in EGF-stimulated cells, but not in insulin-stimulated cells. Moreover, in all but one condition studied, we found a tight correlation between the onset of phosphorylation and dephosphorylation for both sites, despite the fact that they do not share common kinase- or phosphatase-mediated regulation. In sum, using a quantitative approach to study Akt activation identified ligand-dependent limits for the use of T308 or S473 as proxies for kinase activity and suggests the coregulation of Akt phosphorylation and dephosphorylation.

Dose-Response Relationship, Drug↗

Modeling HER2 effects on cell behavior from mass spectrometry phosphotyrosine data.

Cellular behavior in response to stimulatory cues is governed by information encoded within a complex intracellular signaling network. An understanding of how phenotype is determined requires the distributed characterization of signaling processes (e.g., phosphorylation states and kinase activities) in parallel with measures of resulting cell function. We previously applied quantitative mass spectrometry methods to characterize the dynamics of tyrosine phosphorylation in human mammary epithelial cells with varying human epidermal growth factor receptor 2 (HER2) expression levels after treatment with epidermal growth factor (EGF) or heregulin (HRG). We sought to identify potential mechanisms by which changes in tyrosine phosphorylation govern changes in cell migration or proliferation, two behaviors that we measured in the same cell system. Here, we describe the use of a computational linear mapping technique, partial least squares regression (PLSR), to detail and characterize signaling mechanisms responsible for HER2-mediated effects on migration and proliferation. PLSR model analysis via principal component inner products identified phosphotyrosine signals most strongly associated with control of migration and proliferation, as HER2 expression or ligand treatment were individually varied. Inspection of these signals revealed both previously identified and novel pathways that correlate with cell behavior. Furthermore, we isolated elements of the signaling network that differentially give rise to migration and proliferation. Finally, model analysis identified nine especially informative phosphorylation sites on six proteins that recapitulated the predictive capability of the full model. A model based on these nine sites and trained solely on data from a low HER2-expressing cell line a priori predicted migration and proliferation in a HER2-overexpressing cell line. We identify the nine signals as a "network gauge," meaning that when interrogated together and integrated according to the quantitative rules of the model, these signals capture information content in the network sufficiently to predict cell migration and proliferation under diverse ligand treatments and receptor expression levels. Examination of the network gauge in the context of previous literature indicates that endocytosis and activation of phosphoinositide 3-kinase (PI3K)-mediated pathways together represent particularly strong loci for the integration of the multiple pathways mediating HER2's control of mammary epithelial cell proliferation and migration. Thus, a PLSR modeling approach reveals critical signaling processes regulating HER2-mediated cell behavior.

Cell Line↗

Understanding effects of matrix protease and matrix organization on directional persistence and translational speed in three-dimensional cell migration.

Recent studies have shown significant differences in migration mechanisms between two- and three-dimensional environments. While experiments have suggested a strong dependence of in vivo migration on both structure and proteolytic activity, the underlying biophysics of such dependence has not been studied adequately. In addition, the existing models of persistent random walk migration are primarily based on two-dimensional movement and do not account for the effect of proteolysis or matrix inhomogeneity. Using lattice Monte Carlo methods, we present a model to study the role of matrix metallo-proteases (MMPs) on directional persistence and speed. The simulations account for a given cell's ability to deform as well as to digest the matrix as the cell moves in three dimensions. Our results show a bimodal dependence of speed and persistence on matrix pore size and suggest high sensitivity on MMP activity, which is in very good agreement with experimental studies carried out in 3D matrices.

Cell Movement↗

Effects of HER2 overexpression on cell signaling networks governing proliferation and migration.

Although human epidermal growth factor receptor 2 (HER2) overexpression is implicated in tumor progression for a variety of cancer types, how it dysregulates signaling networks governing cell behavioral functions is poorly understood. To address this problem, we use quantitative mass spectrometry to analyze dynamic effects of HER2 overexpression on phosphotyrosine signaling in human mammary epithelial cells stimulated by epidermal growth factor (EGF) or heregulin (HRG). Data generated from this analysis reveal that EGF stimulation of HER2-overexpressing cells activates multiple signaling pathways to stimulate migration, whereas HRG stimulation of these cells results in amplification of a specific subset of the migration signaling network. Self-organizing map analysis of the phosphoproteomic data set permitted elucidation of network modules differentially regulated in HER2-overexpressing cells in comparison with parental cells for EGF and HRG treatment. Partial least-squares regression analysis of the same data set identified quantitative combinations of signals within the networks that strongly correlate with cell proliferation and migration measured under the same battery of conditions. Combining these modeling approaches enabled association of epidermal growth factor receptor family dimerization to activation of specific phosphorylation sites, which appear to most critically regulate proliferation and/or migration.

Algorithms↗

Adenoviral vector saturates Akt pro-survival signaling and blocks insulin-mediated rescue of tumor necrosis-factor-induced apoptosis.

Recombinant adenoviruses are used extensively as delivery vectors in clinical gene therapy and in molecular biology, but little is known about how the viral carrier itself contributes to cellular responses. Here we show that infection with an E1/E3-deleted adenoviral vector (Adv) sensitizes human epithelial cells to tumor necrosis factor (TNF)-induced apoptosis. To explore the mechanism of Adv-mediated sensitization, we measured activity time courses for three protein kinases (MK2, IKK and JNK1) centrally involved in the TNF-receptor signaling network, as well as two kinases (Akt and ERK) activated by growth factors. Both the pro-apoptotic signal MK2 and the anti-apoptotic signal Akt were upregulated when Adv-infected cells were stimulated with TNF, and MK2 and Akt each contributed significantly to TNF-induced cell fate. Surprisingly, further activation of Akt in Adv-infected cells via insulin treatment did not significantly reduce apoptosis or MK2 activity. We show that the ineffectiveness of insulin-mediated anti-apoptotic signaling through Akt is due to saturation of Akt-effector substrate phosphorylation in Adv-infected cells. Normalizing Akt signaling relative to its Adv-induced baseline activity identified a global dose-response curve that relates Akt signaling to cellular survival. Thus, the background Akt activity induced by Adv limits the transmission of anti-apoptotic signals in response to further cytokine or growth-factor stimulation. The phenotypic and intracellular synergy between Adv and TNF may have implications for interpreting cellular responses in gene-therapy and laboratory applications.

Adenoviridae↗

Integrated mechanistic and data-driven modelling for multivariate analysis of signalling pathways.

Mathematical models of highly interconnected and multivariate signalling networks provide useful tools to understand these complex systems. However, effective approaches to extracting multivariate regulation information from these models are still lacking. In this study, we propose a data-driven modelling framework to analyse large-scale multivariate datasets generated from mathematical models. We used an ordinary differential equation based model for the Fas apoptotic pathway as an example. The first step in our approach was to cluster simulation outputs generated from models with varied protein initial concentrations. Subsequently, decision tree analysis was applied, in which we used protein concentrations to predict the simulation outcomes. Our results suggest that no single subset of proteins can determine the pathway behaviour. Instead, different subsets of proteins with different concentrations ranges can be important. We also used the resulting decision tree to identify the minimal number of perturbations needed to change pathway behaviours. In conclusion, our framework provides a novel approach to understand the multivariate dependencies among molecules in complex networks, and can potentially be used to identify combinatorial targets for therapeutic interventions.

Apoptosis↗

Migration of tumor cells in 3D matrices is governed by matrix stiffness along with cell-matrix adhesion and proteolysis.

Cell migration on 2D surfaces is governed by a balance between counteracting tractile and adhesion forces. Although biochemical factors such as adhesion receptor and ligand concentration and binding, signaling through cell adhesion complexes, and cytoskeletal structure assembly/disassembly have been studied in detail in a 2D context, the critical biochemical and biophysical parameters that affect cell migration in 3D matrices have not been quantitatively investigated. We demonstrate that, in addition to adhesion and tractile forces, matrix stiffness is a key factor that influences cell movement in 3D. Cell migration assays in which Matrigel density, fibronectin concentration, and beta1 integrin binding are systematically varied show that at a specific Matrigel density the migration speed of DU-145 human prostate carcinoma cells is a balance between tractile and adhesion forces. However, when biochemical parameters such as matrix ligand and cell integrin receptor levels are held constant, maximal cell movement shifts to matrices exhibiting lesser stiffness. This behavior contradicts current 2D models but is predicted by a recent force-based computational model of cell movement in a 3D matrix. As expected, this 3D motility through an extracellular environment of pore size much smaller than cellular dimensions does depend on proteolytic activity as broad-spectrum matrix metalloproteinase (MMP) inhibitors limit the migration of DU-145 cells and also HT-1080 fibrosarcoma cells. Our experimental findings here represent, to our knowledge, discovery of a previously undescribed set of balances of cell and matrix properties that govern the ability of tumor cells to migration in 3D environments.

Cell Adhesion↗

A high-throughput migration assay reveals HER2-mediated cell migration arising from increased directional persistence.

Human epidermal growth factor receptor 2 (HER2) overexpression has been associated with increased invasiveness in mammalian breast cancer cell lines, but the effects of overexpression on key underlying cell migration properties such as translational speed and directional persistence are not understood. Moreover, the differential effect of HER2 activation through heterodimerization with epidermal growth factor receptor versus human epidermal growth factor receptor 3 (HER3) on cell speed and persistence has not been studied. To investigate these issues, we developed a high-throughput wound closure assay in which individual cell locomotion and wound closure kinetics were quantified in human mammary epithelial cells with varying levels of HER2 under epidermal growth factor or heregulin (a HER3 ligand) stimulation. Increasing levels of HER2 elevated wound closure with closure kinetics dependent on ligand treatment. Cell speed increased with HER2 levels under epidermal growth factor treatment, but decreased under heregulin treatment. In contrast, directional persistence increased with HER2 levels under both ligand treatments. Increasing persistence quantitatively accounted for observed elevated wound closure, as measured by the effective diffusion of the cells. Taken together, the data show that the HER2 overexpression mediates cell migration through differential control of translational speed and directional persistence dependent on epidermal growth factor receptor-HER2 versus HER2-HER3 heterodimerization. Observed consistent increases in persistence associated with HER2 overexpression indicate a prospective mechanism for invasiveness previously documented in HER2-overexpressing human breast tumors.

Biological Assay↗

Multiple signaling pathways mediate compaction of collagen matrices by EGF-stimulated fibroblasts.

Fibroblasts stimulated by EGF within collagen matrices generate contraction forces that are likely of importance to cell migration and matrix compaction during wound healing. We have employed an in vitro fibroblast-embedded collagen matrix compaction assay to ascertain signaling pathway components downstream of EGFR activation leading to generation and transmission of contractile force. EGF compacts this floating collagen matrix to a similar extent as PDGF. We demonstrate that compaction requires EGFR kinase activity, yet is maximal in magnitude at intermediate EGF concentrations. This suggests that transmission of EGFR-induced contractile force to the matrix can be mitigated by consequent anti-adhesive effects of EGFR signaling in a dose-dependent manner. Treatment with pharmacological inhibitors demonstrated involvement of the signaling components extracellular signal-regulated kinase (ERK), Rho kinase, and myosin light chain kinase (MLCK) in the force generation and/or transmission process. Moreover, treatment with the pan-calpain inhibitor ALLN and isoform-specific downregulation of m-calpain (CAPN2) using RNA interference determined m-calpain to be a key component of the EGF-induced force response. ALLN treatment modulated the compaction response in a biphasic manner, enhancing matrix deformation to the greatest extent at intermediate concentrations. Our findings have thus identified key signals downstream of EGFR, which integrate in a complex manner to generate and transmit contractile forces to yield matrix deformation.

Animals↗

The response of human epithelial cells to TNF involves an inducible autocrine cascade.

Tumor necrosis factor (TNF) is a proinflammatory cytokine that induces conflicting pro- and antiapoptotic signals whose relative strengths determine the extent of cell death. TNF receptor (TNFR) has been studied in considerable detail, but it is not known how crosstalk among antagonistic pro- and antiapoptotic signals is achieved. Here we report an experimental and computational analysis of crosstalk between prodeath TNF and prosurvival growth factors in human epithelial cells. By applying classifier-based regression to a cytokine-signaling compendium of approximately 8000 intracellular protein measurements, we demonstrate that cells respond to TNF both directly, via activated TNF receptor, and indirectly, via the sequential release of transforming growth factor-alpha (TGF-alpha), interleukin-1alpha (IL-1alpha), and IL-1 receptor antagonist (IL-1ra). We refer to the contingent and time-varying series of extracellular signals induced by TNF as an "autocrine cascade." Time-dependent crosstalk of synergistic and antagonistic autocrine circuits may serve to link cellular responses to the local environment.

Autocrine Communication↗

A biological approach to computational models of proteomic networks.

Computational modeling is useful as a means to assemble and test what we know about proteins and networks. Models can help address key questions about the measurement, definition and function of proteomic networks. Here, we place these biological questions at the forefront in reviewing the computational strategies that are available to analyze proteomic networks. Recent examples illustrate how models can extract more information from proteomic data, test possible interactions between network proteins and link networks to cellular behavior. No single model can achieve all these goals, however, which is why it is critical to prioritize biological questions before specifying a particular modeling approach.

Computer Simulation↗

Applying computational modeling to drug discovery and development.

Computational models of cells, tissues and organisms are necessary for increased understanding of biological systems. In particular, modeling approaches will be crucial for moving biology from a descriptive to a predictive science. Pharmaceutical companies identify molecular interventions that they predict will lead to therapies at the organism level, suggesting that computational biology can play a key role in the pharmaceutical industry. We discuss pharmaceutically-relevant computational modeling approaches currently used as predictive tools. Specific examples demonstrate how companies can employ these computational models to improve the efficiency of transforming targets into therapies.

Animals↗

Physicochemical modelling of cell signalling pathways.

Physicochemical modelling of signal transduction links fundamental chemical and physical principles, prior knowledge about regulatory pathways, and experimental data of various types to create powerful tools for formalizing and extending traditional molecular and cellular biology.

Algorithms↗

Right on cue.

Explore the source record for details and available documents.

Animals↗

Collecting and organizing systematic sets of protein data.

Systems biology, particularly of mammalian cells, is data starved. However, technologies are now in place to obtain rich data, in a form suitable for model construction and validation, that describes the activities, states and locations of cell-signalling molecules. The key is to use several measurement technologies simultaneously and, recognizing each of their limits, to assemble a self-consistent compendium of systematic data.

Animals↗

Motility signaled from the EGF receptor and related systems.

Cell motility is now recognized as central to many biological processes. Growth factors, such as those that activate the epidermal growth factor receptor (EGFR), drive biochemically and biologically distinct subsets of migration critical for (neo)organogenesis and tumor invasion. Thus, modulation of these events requires an understanding of the controls of EGFR-mediated motility. Deconstruction of motility into its component events enables this deeper insight. Herein we describe methods that measure the overall motility and its parameters as well as the biophysical processes extension, de-adhesion/retraction, and contraction.

Animals↗