All living organisms are constantly faced with challenges to the integrity of their genomes from both exogenous sources, such as environmental exposures to genotoxic agents, and endogenous sources, such as exposures to reactive oxygen species (ROS) generated during metabolic processes and physiologic DNA breaks generated during recombination of antigen-receptor genes. To guard genomic integrity and to protect against cancer and other diseases associated with genomic instability, cells with DNA lesions activate a complex network of intersecting pathways referred to as the DNA damage response (DDR) that leads to either cell cycle arrest and repair of damage allowing for resumption of normal cellular processes or cell death if the damage is too severe. Central to the DDR are several key members of the PI3-kinase-related protein kinase family. These include the ATM protein kinase that is activated in response to the highly toxic DNA double stand break (DSB) and chromatin alterations, the ATR protein kinase that is activated by lesions that generate single strand DNA (ssDNA), and the DNA-dependent protein kinase catalytic subunit (DNA-PKcs) that is activated by DSBs and is required for non-homologous end-joining repair. We, and others, have demonstrated significant cross-talk between these key DDR protein kinases and their downstream signaling pathways. In particular, we have found that in response to ionizing radiation-generated DSBs in ATM-deficient cells, DNA-PKcs can contribute significantly to the G2 checkpoint response and protect against cell death. We are testing the hypothesis that disruption of the function of key members of the DDR, and in particular ATM, reveals cross-talk and network redundancies that are important in protecting genome integrity from adverse environmental exposures. We are testing this hypothesis by 1) determining molecular components of cross-talk in the DDR kinase signaling network initiated in response to DSBs in the presence and absence of ATM function and 2) determining cross-talk and redundancy in the network of ATM-dependent and ATMñindependent DDR global transcriptional responses to DSBs. We then are validating our findings by depleting, disrupting or inhibiting members in the compensatory pathways identified in cells. The impact of these studies will be to identify 1) protective compensatory signaling pathways that might be enhanced in individuals with genetic or epigenetic deficiencies in DDR function and exposed to environmental genotoxic agents, and 2) compensatory signaling pathways that could be targeted for disruption pharmacologically or epigenetically to improve therapeutic efficiencies for treatment regimens through synthetic lethality approaches when DDR signaling is found to be defective in tumors or other diseases arising from adverse environmental exposures.
In addition, we are integrating conventional studies of environmental stress and toxicity with global "omics" approaches, or toxicogenomics, in studies designed to relate alterations in global gene expression to adverse effects defined by conventional parameters of toxicity and pathology. Studies are designed to provide insight into mechanisms of injury and disease as well as to establish signatures of adverse effects to develop putative biomarkers. We have utilized microarray and NextGen sequence analyses for global gene expression and global microRNA expression profiling to examine genomic responses to environmental stresses. Analyses that implicate a critical role of a particular biological process or of a particular gene in an adverse response are followed up with additional experiments designed to test hypotheses concerning these roles.
Richard S. Paules, Ph.D., received his Ph.D. from the Department of Pathology at the University of North Carolina at Chapel Hill in 1984. Paules completed postdoctoral training in the laboratory group of George F. Vande Woude at the National Cancer Institute-Frederick Cancer Research Facility before joining NIEHS in 1990. At NIEHS, he heads the Environmental Stress and Cancer Group and directs the NIEHS Molecular Genomics Core within the Laboratory of Toxicology and Pharmacology. He also holds adjunct appointments in the Department of Pathology and Laboratory Medicine as well as in the Lineberger Comprehensive Cancer Center at UNC-CH. Paules currently serves as Associate Editor of Physiological Genomics and BMC Genomics and serves on the editorial review board of Environmental Heath Perspectives. Since joining the NIEHS, Paules has been recognized with four NIH Merit Awards, the NIH Director's Award as well as the Society of Toxicology's 2010 Leading Edge in Basic Science Award.