The bromodomain protein Brd4 insulates chromatin from DNA damage signalling.

DNA damage activates a signalling network that blocks cell-cycle progression, recruits DNA repair factors and/or triggers senescence or programmed cell death. Alterations in chromatin structure are implicated in the initiation and propagation of the DNA damage response. Here we further investigate the role of chromatin structure in the DNA damage response by monitoring ionizing-radiation-induced signalling and response events with a high-content multiplex RNA-mediated interference screen of chromatin-modifying and -interacting genes. We discover that an isoform of Brd4, a bromodomain and extra-terminal (BET) family member, functions as an endogenous inhibitor of DNA damage response signalling by recruiting the condensin II chromatin remodelling complex to acetylated histones through bromodomain interactions. Loss of this isoform results in relaxed chromatin structure, rapid cell-cycle checkpoint recovery and enhanced survival after irradiation, whereas functional gain of this isoform compacted chromatin, attenuated DNA damage response signalling and enhanced radiation-induced lethality. These data implicate Brd4, previously known for its role in transcriptional control, as an insulator of chromatin that can modulate the signalling response to DNA damage.

MAPKAP Kinase-2 phosphorylation of PABPC1 controls its interaction with 14-3-3 proteins after DNA damage: A combined kinase and protein array approach.

14-3-3 proteins play critical roles in controlling multiple aspects of the cellular response to stress and DNA damage including regulation of metabolism, cell cycle progression, cell migration, and apoptotic cell death by binding to protein substrates of basophilic protein kinases following their phosphorylation on specific serine/threonine residues. Although over 200 mammalian proteins that bind to 14-3-3 have been identified, largely through proteomic studies, in many cases the relevant protein kinase responsible for conferring 14-3-3-binding to these proteins is not known. To facilitate the identification of kinase-specific 14-3-3 clients, we developed a biochemical approach using high-density protein filter arrays and identified the translational regulatory molecule PABPC1 as a substrate for Chk1 and MAPKAP Kinase-2 (MK2) in vitro, and for MK2 in vivo, whose phosphorylation results in 14-3-3-binding. We identify Ser-470 on PABPC1 within the linker region connecting the RRM domains to the PABC domain as the critical 14-3-3-binding site, and demonstrate that loss of PABPC1 binding to 14-3-3 results in increased cell proliferation and decreased cell death in response to UV-induced DNA damage.

Implementation of the Connective Tissue Screening Questionnaire in northeast Pennsylvania to identify comorbidities of connective tissue diseases in subjects with systemic lupus erythematosus.

Previous studies have described an increased risk of developing an additional connective tissue disease (CTD) when one such ailment is present. We examine here the likelihood that individuals with systemic lupus erythematosus (SLE) screen positive for one or more of the following five autoimmune CTDs: Sjögren's syndrome, scleroderma, rheumatoid arthritis, dermatomyositis/polymyositis, and mixed connective tissue disorder. Five hundred SLE-diagnosed subjects were asked to complete a CTD screening questionnaire (CSQ). The results were analyzed according to the set of diagnostic criteria given by the American College of Rheumatology to identify probable cases of each CTD. Significant standardized prevalence ratios and comorbidities indicate an increased risk for the other autoimmune CTDs. In all, 96% of the subjects screened positive for at least one additional CTD, and 13% screened positive for at least two additional CTDs. We see that the SLE-diagnosed population may benefit from further attention regarding the presence of additional CTDs, which may further inform treatment strategies. We also see the application of the CSQ as a potentially important tool for clinical practice, and we describe the present study's limitations along with possible ways that these can be addressed.