Project description:Ultraviolet (UV) light radiation induces the formation of bulky photoproducts in the DNA that interfere with replication and transcription. Recent studies showed that exposure of human cells to UV light globally affects transcription and alternative splicing, however, the signaling pathways and mechanisms that link UV light-induced DNA damage to RNA metabolism regulation remain poorly understood. Here, we provide a systems view on protein phosphorylation patterns induced by UV light, and uncover the dependencies of phosphorylation events on the canonical DNA damage signaling mediated by ATM/ATR or p38 MAP kinase pathway. We identify RNA binding proteins as primary targets and 14-3-3 family as direct readers of p38-MK2-dependent phosphorylation induced by UV light. Moreover, we show that MK2 phosphorylates the RNA binding subunit of the NELF complex NELFE on S115. NELFE phosphorylation promotes the recruitment of 14-3-3 and rapid dissociation of the NELF complex from chromatin that is accompanied with an increase in transcriptional elongation.
Project description:Ultraviolet (UV) light radiation induces the formation of bulky photoproducts in the DNA that globally affect transcription and splicing. However, the signaling pathways and mechanisms that link UV light-induced DNA damage to changes in RNA metabolism remain poorly understood. Here, we employ quantitative phosphoproteomics and protein kinase inhibition to provide a systems view on protein phosphorylation patterns induced by UV light, and uncover the dependencies of phosphorylation events on the canonical DNA damage signaling by ATM/ATR and the p38 MAP kinase pathway. We identify RNA binding proteins as primary substrates and 14-3-3 as direct readers of p38-MK2-dependent phosphorylation induced by UV light. Mechanistically, we show that MK2 phosphorylates the RNA binding subunit of the NELF complex NELFE on Serine 115. NELFE phosphorylation promotes the recruitment of 14-3-3 and rapid dissociation of the NELF complex from chromatin, which is accompanied by RNA polymerase II elongation.
Project description:Mechanistic model of the Post-Replication Repair (PRR), the pathway involved in the bypass
of DNA lesions induced by sunlight exposure and UV radiation. PRR acts through two different mechanisms,
activated by mono- and poly-ubiquitylation of the DNA sliding clamp, called Proliferating Cell Nuclear Antigen (PCNA).
This model has been defined according to the stochastic formulation of chemical kinetics [Gillespie DT, J Phys Chem 1977, 81(25):2340-2361],
which requires to specify the set of molecular species occurring in the pathway and their respective interactions,
formally described as a set of biochemical reactions.
The volume considered for this system is 1.666667e-17L; this value can be used to convert the model into the deterministic formulation.
Project description:We have published results demonstrating that UV-C induces apoptotic-like changes in Arabidopsis (Danon and Gallois FEBS lett (1998) 437: 131-136). The Programmed Cell Death "phenotype" of nucleus shape, DNA laddering caspase-like activity is similar to what has been described in other plant PCD. This demonstrates that UV-C is an appropriate and controllable trigger to study PCD in plants. Using selected mutants and a set of chosen conditions we are aiming at identifying genes that are part of the PCD pathways in plants and filter out the general stress response. We are asking for a medium size experiment knowing that additional microarray analysis are likely to be required to refine the results obtained. We are currently awaiting the results of Affymetrix RNAs hybridisation of PCD-induced wild type that will define the appropriate single time point of the proposed analysis. The rationale is to vary treatments in order to distinguish changes in gene transcription arising from general cellular stress responses to the trigger used from those specific to PCD: 1. We will use wild-type Arabidopsis seedlings as a negative control to provide the basal gene expression pattern. 2. A dose of UV-C radiation of 1KJ/m2. We will irradiate wild type with this non PCD-inducing dose of UV-C radiation to identify sets of genes that respond to UV-induced damage but whose expression is not linked to cell death. 3. A dose of UV-C radiation of 50 KJ/m2. We will irradiate wild type with a PCD-inducing dose of UV-C radiation to identify sets of genes that respond to UV-induced damage and cell death. 4. We have shown that the cell death induced by UV is light dependant, the control, sub-inducing dose and inducing dose treatments will be repeated and the plants kept in the dark until RNA sampling. In those conditions there is no PCD.
Project description:Recent observations show that the single-cell response of p53 to ionizing radiation (IR) is “digital” in that it is the number of oscillations rather than the amplitude of p53 that shows dependence on the radiation dose. We present a model of this phenomenon. In our model, double-strand break (DSB) sites induced by IR interact with a limiting pool of DNA repair proteins, forming DSB–protein complexes at DNA damage foci. The persisting complexes are sensed by ataxia telangiectasia mutated (ATM), a protein kinase that activates p53 once it is phosphorylated by DNA damage. The ATM-sensing module switches on or off the downstream p53 oscillator, consisting of a feedback loop formed by p53 and its negative regulator, Mdm2. In agreement with experiments, our simulations show that by assuming stochasticity in the initial number of DSBs and the DNA repair process, p53 and Mdm2 exhibit a coordinated oscillatory dynamics upon IR stimulation in single cells, with a stochastic number of oscillations whose mean increases with IR dose. The damped oscillations previously observed in cell populations can be explained as the aggregate behavior of single cell