Project description:The PARP family of proteins comprises 17 members, about two thirds of which are active mono- or poly(ADP-ribosyl)transferase enzymes that transfer the ADP-ribose moiety of NAD+ onto target proteins. In many cases, ADP-ribosylation, which plays critical roles in human diseases (e.g., cancer, heart disease, and neuropathies) is associated with abrogation of the molecular functions of the target. Discerning ADP-ribosylation events mediated by a specific PARP is challenging, since all PARPs use the same substrate (i.e., NAD+) and the available inhibitors lack the specificity needed to make such conclusions. In order to identify the direct and specific targets of individual PARP family members, we have developed a chemical and genetic approach known as analog sensitivity, in which alteration of a single conserved amino acid in the active site of the PARP protein creates a pocket that allows use of an unnatural NAD+ analog containing a steric moiety. We have functionalized the steric moiety with alkyne for use in click chemistry reactions. This approach, which is transferable to other PARP family members, creates substrate specificity where none previously existed, allowing PARP-specific post-translational modification followed by target visualization, or isolation of ADP-ribosylated targets using click chemistry techniques. We have used this technology in conjunction with mass spectrometry to identify hundreds of targets both unique to, as well as shared among, the nuclear PARP proteins, PARP-1, PARP-2, and PARP-3. We have also determined the genome-wide distribution of PARP-1-specific ADP-ribosylation by coupling this analog-sensitive PARP approach with chromatin cross-linking in method that we call “Click-ChIP-seq”. We observed that PARP-1-specific ADP-ribosylation is enriched at transcriptionally active promoters in proximity to sites of PARP-1 enrichment. In addition, we observed that NELF, an important regulator of RNA Polymerase II (Pol II) pausing, is not only a target of ADP-ribosylation by PARP-1 but also spatially correlated with chromatin-associated ADP-ribose and PARP-1 in Click-ChIP-seq and ChIP-seq assays, respectively. Given these observations, we hypothesized that ADP-ribosylation might modulate NELF function and result altered Pol II pausing. We have explored this possibility using global run-on coupled with deep sequencing (GRO-seq) in MCF-7 cells in which PARP-1 was depleted by RNAi-mediated knockdown. PARP-1 depletion caused an increase in Pol II pausing genome-wide. Taken together, these results suggest the intriguing possibility that ADP-ribosylation of NELF by PARP-1 may be an important and heretofore unknown step in the release of Pol II into productive elongation.

Project description:Poly(ADP-ribose) Polymerase 1 (PARP-1) is a nuclear enzyme that catalyse the transfer of ADP-ribose units from NAD+ to several target proteins involved in cellular stress responses. Using the cell line WRL68, we have previously shown that the activation of PARP-1 induced by oxidative stress after H2O2 treatment lead to depletion of cellular NAD+ and ATP, which promote cell death. In this work, we used LC-MS/MS based phosphoproteomics to show that the oxidative damage induced by H2O2 treatment modified the phosphorylation of several proteins in WRL68 cells, most of them related to transcription process. Interestingly, genetic or pharmacological inhibition of PARP-1 reduced the phosphorylation of YAP1, a transcriptional coactivator involved in cell survival, in WRL68 cells after H2O2 treatment. Inhibition of PARP-1 increased cell viability after oxidative treatment and diminished the degradation of YAP1; the elimination of YAP1 by gene silencing abrogated the protective effect of PARP-1 inhibition, indicating that YAP1 is important for the survival of WRL68 cells after oxidative damage. In the same way, the supplementation of NAD+, substrate of PARP-1, on WRL68 cells suffering oxidative damage reduced the phosphorylation of YAP1, suggesting that the loss of cellular NAD+ caused by PARP-1 activation after oxidative treatment is responsible for the phosphorylation of YAP1. Finally, PARP-1 silencing after oxidative treatment diminished the activation of AMPK, a master regulator of cell metabolism implicated in the restoration of energy balance during metabolic stress. Since NAD+ supplementation reduced the phosphorylation of some AMPK substrates in WRL68 cells after oxidative treatment, we hypothesize that the loss of cellular NAD+ after PARP-1 activation may induce a metabolic stress that activates AMPK. In summary, we showed a new crucial role of PARP-1 in the response to oxidative stress in WRL68 cells; PARP-1 activation reduces the cell viability by promoting the phosphorylation and degradation of YAP1, which is mediated by the energy stress caused by PARP-1 activation.

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Substrate Identification Using a Chemical Genetics Approach Reveals a Role for PARP-7-Mediated MARylation in Controlling Microtubule Stability in Ovarian Cancer Cells

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