Alejandro Colman-Lerner
Facultad de Ciencias Exactas y Naturales
Network
Latest external collaboration on country level. Dive into details by clicking on the dots.
Publication
Featured researches published by Alejandro Colman-Lerner.
Science Signaling | 2010
Bernd Bodenmiller; Stefanie Wanka; Claudine Kraft; Joerg Urban; David G. Campbell; Patrick G A Pedrioli; Bertran Gerrits; Paola Picotti; Henry H N Lam; Olga Vitek; Mi-Youn Brusniak; Bernd Roschitzki; Chao Zhang; Kevan M. Shokat; Ralph Schlapbach; Alejandro Colman-Lerner; Garry P. Nolan; Alexey I. Nesvizhskii; Matthias Peter; Robbie Loewith; Christian von Mering; Ruedi Aebersold
A system-wide analysis of protein phosphorylation in yeast reveals robustness in the network of kinases and phosphatases. Holistic Approach Protein kinases and phosphatases make attractive targets for therapies. Although various such enzymes have been characterized individually in vitro, an understanding of their roles in vivo, in the context of the entire network of kinases and phosphatases, is lacking. Indeed, inadequate knowledge of the downstream, indirect consequences of targeting a particular enzyme has led to the discontinuation of potential therapies. Bodenmiller et al. (listen to the accompanying Podcast) individually targeted most of the kinases and phosphatases in yeast, and they performed phosphoproteomic analysis of the effects of these deletions or mutations on the cellular phosphorylation network. They found that the network was surprisingly robust to perturbations in individual enzymes and that a large number of changes occurred in phosphoproteins that were not direct substrates of the targeted kinase or phosphatase. This approach should serve as a starting point toward understanding the complexity of phosphorylation regulation in yeast and other organisms. The phosphorylation and dephosphorylation of proteins by kinases and phosphatases constitute an essential regulatory network in eukaryotic cells. This network supports the flow of information from sensors through signaling systems to effector molecules and ultimately drives the phenotype and function of cells, tissues, and organisms. Dysregulation of this process has severe consequences and is one of the main factors in the emergence and progression of diseases, including cancer. Thus, major efforts have been invested in developing specific inhibitors that modulate the activity of individual kinases or phosphatases; however, it has been difficult to assess how such pharmacological interventions would affect the cellular signaling network as a whole. Here, we used label-free, quantitative phosphoproteomics in a systematically perturbed model organism (Saccharomyces cerevisiae) to determine the relationships between 97 kinases, 27 phosphatases, and more than 1000 phosphoproteins. We identified 8814 regulated phosphorylation events, describing the first system-wide protein phosphorylation network in vivo. Our results show that, at steady state, inactivation of most kinases and phosphatases affected large parts of the phosphorylation-modulated signal transduction machinery—and not only the immediate downstream targets. The observed cellular growth phenotype was often well maintained despite the perturbations, arguing for considerable robustness in the system. Our results serve to constrain future models of cellular signaling and reinforce the idea that simple linear representations of signaling pathways might be insufficient for drug development and for describing organismal homeostasis.
Nature | 2008
Richard C. Yu; C. Gustavo Pesce; Alejandro Colman-Lerner; Larry Lok; David Pincus; Eduard Serra; Mark Holl; Kirsten Benjamin; Andrew Gordon; Roger Brent
Haploid Saccharomyces cerevisiae yeast cells use a prototypic cell signaling system to transmit information about the extracellular concentration of mating pheromone secreted by potential mating partners. The ability for cells to respond distinguishably to different pheromone concentrations depends on how much information about pheromone concentration the system can transmit. Here we show that the MAPK Fus3 mediates fast-acting negative feedback that adjusts the dose-response of downstream system response to match that of receptor-ligand binding. This “dose-response alignment”, defined by a linear relationship between receptor occupancy and downstream response, can improve the fidelity of information transmission by making downstream responses corresponding to different receptor occupancies more distinguishable and reducing amplification of stochastic noise during signal transmission. We also show that one target of the feedback is a novel signal-promoting function of the RGS protein Sst2. Our work suggests that negative feedback is a general mechanism used in signaling systems to align dose-responses and thereby increase the fidelity of information transmission.Haploid Saccharomyces cerevisiae yeast cells use a prototypic cell signalling system to transmit information about the extracellular concentration of mating pheromone secreted by potential mating partners. The ability of cells to respond distinguishably to different pheromone concentrations depends on how much information about pheromone concentration the system can transmit. Here we show that the mitogen-activated protein kinase Fus3 mediates fast-acting negative feedback that adjusts the dose response of the downstream system response to match the dose response of receptor-ligand binding. This ‘dose–response alignment’, defined by a linear relationship between receptor occupancy and downstream response, can improve the fidelity of information transmission by making downstream responses corresponding to different receptor occupancies more distinguishable and reducing amplification of stochastic noise during signal transmission. We also show that one target of the feedback is a previously uncharacterized signal-promoting function of the regulator of G-protein signalling protein Sst2. Our work suggests that negative feedback is a general mechanism used in signalling systems to align dose responses and thereby increase the fidelity of information transmission.
Molecular Systems Biology | 2012
Jörg Schaber; Rodrigo Baltanás; Alan Bush; Edda Klipp; Alejandro Colman-Lerner
The high osmolarity glycerol (HOG) pathway in yeast serves as a prototype signalling system for eukaryotes. We used an unprecedented amount of data to parameterise 192 models capturing different hypotheses about molecular mechanisms underlying osmo‐adaptation and selected a best approximating model. This model implied novel mechanisms regulating osmo‐adaptation in yeast. The model suggested that (i) the main mechanism for osmo‐adaptation is a fast and transient non‐transcriptional Hog1‐mediated activation of glycerol production, (ii) the transcriptional response serves to maintain an increased steady‐state glycerol production with low steady‐state Hog1 activity, and (iii) fast negative feedbacks of activated Hog1 on upstream signalling branches serves to stabilise adaptation response. The best approximating model also indicated that homoeostatic adaptive systems with two parallel redundant signalling branches show a more robust and faster response than single‐branch systems. We corroborated this notion to a large extent by dedicated measurements of volume recovery in single cells. Our study also demonstrates that systematically testing a model ensemble against data has the potential to achieve a better and unbiased understanding of molecular mechanisms.
Science Signaling | 2013
Rodrigo Baltanás; Alan Bush; Alicia S. Couto; Lucia Durrieu; Stefan Hohmann; Alejandro Colman-Lerner
Crosstalk between MAPK pathways activated by a single sensory input enhances yeast responses to multiple simultaneous stimuli. Crosstalk for Adaptability Yeast use different mitogen-activated protein kinase (MAPK) pathways to respond to distinct stimuli, such as mating pheromone, high external osmolarity, and cell wall integrity. Baltanás et al. investigated how yeast cells respond to simultaneous distinct stimuli that activate different MAPK pathways. In cells adapted to high osmolarity, the MAPK that is normally responsive only to high osmolarity was further activated by pheromone in bursts that coincided with times when yeast cells underwent a mating-related shape change. This activation process required a third MAPK with a role in the cell wall integrity pathway. Thus, crosstalk between three MAPK pathways enhances the response of yeast to an external stress (such as high osmolarity) when exposed to a sensory stimulus (such as mating pheromone). Environmental and internal conditions expose cells to a multiplicity of stimuli whose consequences are difficult to predict. We investigate the response to mating pheromone of yeast cells adapted to high osmolarity. Events downstream of pheromone binding involve two mitogen-activated protein kinase (MAPK) cascades: the pheromone response (PR) and the cell wall integrity (CWI) response. Although the PR MAPK pathway shares components with a third MAPK pathway, the high osmolarity (HOG) response, each one is normally only activated by its cognate stimulus, a phenomenon called insulation. We found that in cells adapted to high osmolarity, PR activated the HOG pathway in a pheromone- and osmolarity-dependent manner. Activation of HOG by the PR was not due to loss of insulation, but rather a response to a reduction in internal osmolarity, which resulted from an increase in glycerol release caused by the PR. By analyzing single-cell time courses, we found that stimulation of HOG occurred in discrete bursts that coincided with the “shmooing” morphogenetic process. Activation required the polarisome, the CWI MAPK Slt2, and the aquaglyceroporin Fps1. HOG activation resulted in high glycerol turnover, which improved adaptability to rapid changes in osmolarity. Our work shows how a differentiation signal can recruit a second, unrelated sensory pathway to fine-tune yeast response in a complex environment.
PLOS ONE | 2013
Matías Blaustein; Daniela Pérez-Munizaga; Manuel Alejandro Sánchez; Carolina Urrutia; Alicia Grande; Guillermo Risso; Anabella Srebrow; Jennifer Alfaro; Alejandro Colman-Lerner
The unfolded protein response (UPR) and the Akt signaling pathway share several regulatory functions and have the capacity to determine cell outcome under specific conditions. However, both pathways have largely been studied independently. Here, we asked whether the Akt pathway regulates the UPR. To this end, we used a series of chemical compounds that modulate PI3K/Akt pathway and monitored the activity of the three UPR branches: PERK, IRE1 and ATF6. The antiproliferative and antiviral drug Akt-IV strongly and persistently activated all three branches of the UPR. We present evidence that activation of PERK/eIF2α requires Akt and that PERK is a direct Akt target. Chemical activation of this novel Akt/PERK pathway by Akt-IV leads to cell death, which was largely dependent on the presence of PERK and IRE1. Finally, we show that hypoxia-induced activation of eIF2α requires Akt, providing a physiologically relevant condition for the interaction between Akt and the PERK branch of the UPR. These data suggest the UPR and the Akt pathway signal to one another as a means of controlling cell fate.
Cell | 2015
Andreas Doncic; Oguzhan Atay; Ervin Valk; Alicia Grande; Alan Bush; Gustavo Vasen; Alejandro Colman-Lerner; Mart Loog; Jan M. Skotheim
Cells make accurate decisions in the face of molecular noise and environmental fluctuations by relying not only on present pathway activity, but also on their memory of past signaling dynamics. Once a decision is made, cellular transitions are often rapid and switch-like due to positive feedback loops in the regulatory network. While positive feedback loops are good at promoting switch-like transitions, they are not expected to retain information to inform subsequent decisions. However, this expectation is based on our current understanding of network motifs that accounts for temporal, but not spatial, dynamics. Here, we show how spatial organization of the feedback-driven yeast G1/S switch enables the transmission of memory of past pheromone exposure across this transition. We expect this to be one of many examples where the exquisite spatial organization of the eukaryotic cell enables previously well-characterized network motifs to perform new and unexpected signal processing functions.
Biophysical Journal | 2013
Alan Bush; Alejandro Colman-Lerner
Microscope cytometry provides a powerful means to study signaling in live cells. Here we present a quantitative method to measure protein relocalization over time, which reports the absolute fraction of a tagged protein in each compartment. Using this method, we studied an essential step in the early propagation of the pheromone signal in Saccharomyces cerevisiae: recruitment to the membrane of the scaffold Ste5 by activated Gβγ dimers. We found that the dose response of Ste5 recruitment is graded (EC50 = 0.44 ± 0.08 nM, Hill coefficient = 0.8 ± 0.1). Then, we determined the effective dissociation constant (K(de)) between Ste5 and membrane sites during the first few minutes when the negative feedback from the MAPK Fus3 is first activated. K(de) changed during the first minutes from a high affinity of < 0.65 nM to a steady-state value of 17 ± 9 nM. During the same period, the total number of binding sites decreased slightly, from 1940 ± 150 to 1400 ± 200. This work shows how careful quantification of a protein relocalization dynamic can give insight into the regulation mechanisms of a biological system.
Cell Cycle | 2013
Guillermo Risso; Federico Pelisch; Berta Pozzi; Pablo Mammi; Matías Blaustein; Alejandro Colman-Lerner; Anabella Srebrow
Akt/PKB is a key signaling molecule in higher eukaryotes and a crucial protein kinase in human health and disease. Phosphorylation, acetylation, and ubiquitylation have been reported as important regulatory post-translational modifications of this kinase. We describe here that Akt is modified by SUMO conjugation, and show that lysine residues 276 and 301 are the major SUMO attachment sites within this protein. We found that phosphorylation and SUMOylation of Akt appear as independent events. However, decreasing Akt SUMOylation levels severely affects the role of this kinase as a regulator of fibronectin and Bcl-x alternative splicing. Moreover, we observed that the Akt mutant (Akt E17K) found in several human tumors displays increased levels of SUMOylation and also an enhanced capacity to regulate fibronectin splicing patterns. This splicing regulatory activity is completely abolished by decreasing Akt E17K SUMO conjugation levels. Additionally, we found that SUMOylation controls Akt regulatory function at G₁/S transition during cell cycle progression. These findings reveal SUMO conjugation as a novel level of regulation for Akt activity, opening new areas of exploration related to the molecular mechanisms involved in the diverse cellular functions of this kinase.
BMC Systems Biology | 2015
Markus Karlsson; David L.I. Janzén; Lucia Durrieu; Alejandro Colman-Lerner; Maria C. Kjellsson; Gunnar Cedersund
BackgroundStudies of cell-to-cell variation have in recent years grown in interest, due to improved bioanalytical techniques which facilitates determination of small changes with high uncertainty. Like much high-quality data, single-cell data is best analysed using a systems biology approach. The most common systems biology approach to single-cell data is the standard two-stage (STS) approach. In STS, data from each cell is analysed in a separate sub-problem, meaning that only data from the same cell is used to calculate the parameter values within that cell. Because only parts of the data are considered, problems with parameter unidentifiability are exaggerated in STS. In contrast, a related approach to data analysis has been developed for the studies of patient-to-patient variations. This approach, called nonlinear mixed-effects modelling (NLME), makes use of all data, when estimating the patient-specific parameters. NLME would therefore be advantageous compared to STS also for the study of cell-to-cell variation. However, no such systematic evaluation of the two approaches exists.ResultsHerein, such a systematic comparison between STS and NLME has been performed. Different examples, both linear and nonlinear, and both simulated and real experimental data, have been examined. With informative data, there is no significant difference in the results for either parameter or noise estimation. However, when data becomes uninformative, NLME is significantly superior to STS. These results hold independently of whether the loss of information is due to a low signal-to-noise ratio, too few data points, or a bad input signal. The improvement is shown to come from both the consideration of a joint likelihood (JLH) function, describing all parameters and data, and from an a priori postulated form of the population parameters. Finally, we provide a small tutorial that shows how to use NLME for single-cell analysis, using the free and user-friendly software Monolix.ConclusionsWhen considering uninformative single-cell data, NLME yields more accurate parameter and noise estimates, compared to more traditional approaches, such as STS and JLH.
Physical Biology | 2014
Edgar Altszyler; Alejandra C. Ventura; Alejandro Colman-Lerner; Ariel Chernomoretz
Much work has been done on the study of the biochemical mechanisms that result in ultrasensitive behavior of simple biochemical modules. However, in a living cell, such modules are embedded in a bigger network that constrains the range of inputs that the module will receive as well as the range of the modules outputs that network will be able to detect. Here, we studied how the effective ultrasensitivity of a modular system is affected by these restrictions. We use a simple setup to explore to what extent the dynamic range spanned by upstream and downstream components of an ultrasensitive module impact on the effective sensitivity of the system. Interestingly, we found for some ultrasensitive motifs that dynamic range limitations imposed by downstream components can produce effective sensitivities much larger than that of the original module when considered in isolation.