Basic, simple and extendable kinetic model of protein synthesis

Protein synthesis is one of the most fundamental biological processes, which consumes a significant amount of cellular resources. Despite existence of multiple mathematical models of translation, varying in the level of mechanistical details, surprisingly, there is no basic and simple chemical kinetic model of this process, derived directly from the detailed kinetic model. One of the reasons for this is that the translation process is characterized by indefinite number of states, thanks to existence of polysomes. We bypass this difficulty by applying a trick consisting in lumping multiple states of translated mRNA into few dynamical variables and by introducing a variable describing the pool of translating ribosomes. The simplest model can be solved analytically under some assumptions. The basic and simple model can be extended, if necessary, to take into account various phenomena such as the interaction between translating ribosomes, limited amount of ribosomal units or regulation of translation by microRNA. The model can be used as a building block (translation module) for more complex models of cellular processes. We demonstrate the utility of the model in two examples. First, we determine the critical parameters of the single protein synthesis for the case when the ribosomal units are abundant. Second, we demonstrate intrinsic bi-stability in the dynamics of the ribosomal protein turnover and predict that a minimal number of ribosomes should pre-exists in a living cell to sustain its protein synthesis machinery, even in the absence of proliferation.Comment: 22 pages, 9 figure

Dynamical modeling of microRNA action on the protein translation process.

International audienceBACKGROUND: Protein translation is a multistep process which can be represented as a cascade of biochemical reactions (initiation, ribosome assembly, elongation, etc.), the rate of which can be regulated by small non-coding microRNAs through multiple mechanisms. It remains unclear what mechanisms of microRNA action are the most dominant: moreover, many experimental reports deliver controversial messages on what is the concrete mechanism actually observed in the experiment. Nissan and Parker have recently demonstrated that it might be impossible to distinguish alternative biological hypotheses using the steady state data on the rate of protein synthesis. For their analysis they used two simple kinetic models of protein translation. RESULTS: In contrary to the study by Nissan and Parker, we show that dynamical data allow discriminating some of the mechanisms of microRNA action. We demonstrate this using the same models as developed by Nissan and Parker for the sake of comparison but the methods developed (asymptotology of biochemical networks) can be used for other models. We formulate a hypothesis that the effect of microRNA action is measurable and observable only if it affects the dominant system (generalization of the limiting step notion for complex networks) of the protein translation machinery. The dominant system can vary in different experimental conditions that can partially explain the existing controversy of some of the experimental data. CONCLUSIONS: Our analysis of the transient protein translation dynamics shows that it gives enough information to verify or reject a hypothesis about a particular molecular mechanism of microRNA action on protein translation. For multiscale systems only that action of microRNA is distinguishable which affects the parameters of dominant system (critical parameters), or changes the dominant system itself. Dominant systems generalize and further develop the old and very popular idea of limiting step. Algorithms for identifying dominant systems in multiscale kinetic models are straightforward but not trivial and depend only on the ordering of the model parameters but not on their concrete values. Asymptotic approach to kinetic models allows putting in order diverse experimental observations in complex situations when many alternative hypotheses co-exist

miRNA Expression in Control and FSHD Fetal Human Muscle Biopsies

International audienceBackground :Facioscapulohumeral muscular dystrophy (FSHD) is an autosomal-dominant disorder and is one of the most common forms of muscular dystrophy. We have recently shown that some hallmarks of FSHD are already expressed in fetal FSHD biopsies, thus opening a new field of investigation for mechanisms leading to FSHD. As microRNAs (miRNAs) play an important role in myogenesis and muscle disorders, in this study we compared miRNAs expression levels during normal and FSHD muscle development. Methods :Muscle biopsies were obtained from quadriceps of both healthy control and FSHD1 fetuses with ages ranging from 14 to 33 weeks of development. miRNA expression profiles were analyzed using TaqMan Human MicroRNA Arrays. Results :During human skeletal muscle development, in control muscle biopsies we observed changes for 4 miRNAs potentially involved in secondary muscle fiber formation and 5 miRNAs potentially involved in fiber maturation. When we compared the miRNA profiles obtained from control and FSHD biopsies, we did not observe any differences in the muscle specific miRNAs. However, we identified 8 miRNAs exclusively expressed in FSHD1 samples (miR-330, miR-331-5p, miR-34a, miR-380-3p, miR-516b, miR-582-5p, miR-517* and miR-625) which could represent new biomarkers for this disease. Their putative targets are mainly involved in muscle development and morphogenesis. Interestingly, these FSHD1 specific miRNAs do not target the genes previously described to be involved in FSHD. Conclusions :This work provides new candidate mechanisms potentially involved in the onset of FSHD pathology. Whether these FSHD specific miRNAs cause deregulations during fetal development, or protect against the appearance of the FSHD phenotype until the second decade of life still needs to be investigated

Expression and cellular localization of microRNA-29b and RAX, an activator of the RNA-dependent protein kinase (PKR), in the retina of streptozotocin-induced diabetic rats

Purpose: The apoptosis of retinal neurons plays a critical role in the pathogenesis of diabetic retinopathy (DR), but the molecular mechanisms underlying this phenomenon remain unclear. The purpose of this study was to investigate the cellular localization and the expression of microRNA-29b (miR-29b) and its potential target PKR associated protein X (RAX), an activator of the pro-apoptotic RNA-dependent protein kinase (PKR) signaling pathway, in the retina of normal and diabetic rats. Methods: Retinas were obtained from normal and diabetic rats within 35 days after streptozotocin (STZ) injection. In silico analysis indicated that RAX is a potential target of miR-29b. The cellular localization of miR-29b and RAX was assessed by in situ hybridization and immunofluorescence, respectively. The expression levels of miR-29b and RAX mRNA were evaluated by quantitative reverse transcription PCR (qRT-PCR), and the expression of RAX protein was evaluated by western blot. A luciferase reporter assay and inhibition of endogenous RAX were performed to confirm whether RAX is a direct target of miR-29b as predicted by the in silico analysis. Results: We found that miR-29b and RAX are localized in the retinal ganglion cells (RGCs) and the cells of the inner nuclear layer (INL) of the retinas from normal and diabetic rats. Thus, the expression of miR-29b and RAX, as assessed in the retina by quantitative RT-PCR, reflects their expression in the RGCs and the cells of the INL. We also revealed that RAX protein is upregulated (more than twofold) at 3, 6, 16, and 22 days and downregulated (70%) at 35 days, whereas miR-29b is upregulated (more than threefold) at 28 and 35 days after STZ injection. We did not confirm the computational prediction that RAX is a direct target of miR-29b. Conclusions: Our results suggest that RAX expression may be indirectly regulated by miR-29b, and the upregulation of this miRNA at the early stage of STZ-induced diabetes may have a protective effect against the apoptosis of RGCs and cells of the INL by the pro-apoptotic RNA-dependent protein kinase (PKR) signaling pathway.FAPESP[08/58325-4]FAPESP[08/50294-2]Coordenacao de Aperfeicoamento de Pessoal de Nivel Superior (CAPES

Prognostic impact of vitamin B6 metabolism in lung cancer

Patients with non-small cell lung cancer (NSCLC) are routinely treated with cytotoxic agents such as cisplatin. Through a genome-wide siRNA-based screen, we identified vitamin B6 metabolism as a central regulator of cisplatin responses in vitro and in vivo. By aggravating a bioenergetic catastrophe that involves the depletion of intracellular glutathione, vitamin B6 exacerbates cisplatin-mediated DNA damage, thus sensitizing a large panel of cancer cell lines to apoptosis. Moreover, vitamin B6 sensitizes cancer cells to apoptosis induction by distinct types of physical and chemical stress, including multiple chemotherapeutics. This effect requires pyridoxal kinase (PDXK), the enzyme that generates the bioactive form of vitamin B6. In line with a general role of vitamin B6 in stress responses, low PDXK expression levels were found to be associated with poor disease outcome in two independent cohorts of patients with NSCLC. These results indicate that PDXK expression levels constitute a biomarker for risk stratification among patients with NSCLC.publishedVersio

Prix Nobel de Médecine 2006 Andrew Z. Fire et Craig C. Mello : Silence, on désactive les gènes

Andrew Z. Fire, Américain, est né le 27 avril 1959 à Palo Alto (Californie). Détenteur d’un Bachelor en mathématiques en 1978 (Université de Californie, Berkeley) à l’âge de 19 ans, il rejoint le Massachusetts Institute of Technology et obtient son PhD en biologie en 1983. Il effectue ensuite un post-doc dans le laboratoire de biologie moléculaire de Sydney Brenner (Prix Nobel 1992) à Cambridge (Royaume- Uni). De 1986 à 2003, il travaille à Baltimore, dans le département d’embryologie du Carnegie Institution, puis, à partir de 1989, occupe un poste de professeur associé dans le département de biologie de l’Université Johns Hopkins. Ensuite, en 2003, il est nommé professeur de pathologie et de génétique à l’école de médecine de l’Université de Stanford. Andrew Fire est également membre de la National Academy of Sciences et de l’American Academy of Arts and Science et participe au Board of Scientific Counselors et au National Center for Biotechnology. Craig C. Mello, Américain, né le 19 octobre 1960 à Worcester (Massachusetts), obtient un Bachelor of Science à la Brown University (Providence, Rhode Island) en 1982, puis son PhD à l’Université de Harvard en 1990. Il effectue ensuite un post-doc au Fred Hutchinson Cancer Research Center dans le laboratoire du Dr James Priess et devient Professeur de biologie moléculaire à l’University of Massachusetts Medical School de Worcester où il enseigne à la Faculté depuis 1994. C. Mello est aussi investigator au Howard Hughes Medical Institute depuis 2000. Il a été élu membre de la National Academy of Sciences en 2005 Andrew Z. Fire et Craig C. Mello avaient auparavant reçu (conjointement) : en 2003, le Prix de la National Academy of Sciences en Biologie moléculaire et le Wiley Prize en sciences biomédicales de l’Université Rockefeller ; en 2005, le Prix Brandeis University’s Lewis S. Rosenstiel, le Prix Gairdner Foundation International et le Prix Massry ; puis, en 2006, le Prix Paul Ehrlich et Ludwig Darmstaedter

Etude de l'acetylation du facteur de trancription myod par les coactivateurs transcriptionnels CBP, p300 et PCAF (caractéristiques, effet sur la transcription, et conséquences sur la différenciation musculaire)

LE KREMLIN-B.- PARIS 11-BU Méd (940432101) / SudocPARIS-BIUP (751062107) / SudocSudocFranceF

Etude de l'action des microARN (Mécanismes et cibles)

LE KREMLIN-B.- PARIS 11-BU Méd (940432101) / SudocSudocFranceF