title: Developing a Gene Biomarker at the Tipping Point of Adaptive and Adverse Responses in Human Bronchial Epithelial Cells.
abstract: Determining mechanism-based biomarkers that distinguish adaptive and adverse cellular processes is critical to understanding the health effects of environmental exposures. Shifting from in vivo, low-throughput toxicity studies to high-throughput screening (HTS) paradigms and risk assessment based on in vitro and in silico testing requires utilizing toxicity pathway information to distinguish adverse outcomes from recoverable adaptive events. Little work has focused on oxidative stresses in human airway for the purposes of predicting adverse responses. We hypothesize that early gene expression-mediated molecular changes could be used to delineate adaptive and adverse responses to environmentally-based perturbations. Here, we examined cellular responses of the tracheobronchial airway to zinc (Zn) exposure, a model oxidant. Airway derived BEAS-2B cells exposed to 2-10 μM Zn2+ elicited concentration- and time-dependent cytotoxicity. Normal, adaptive, and cytotoxic Zn2+ exposure conditions were determined with traditional apical endpoints, and differences in global gene expression around the tipping point of the responses were used to delineate underlying molecular mechanisms. Bioinformatic analyses of differentially expressed genes indicate early enrichment of stress signaling pathways, including those mediated by the transcription factors p53 and NRF2. After 4 h, 154 genes were differentially expressed (p < 0.01) between the adaptive and cytotoxic Zn2+ concentrations. Nearly 40% of the biomarker genes were related to the p53 signaling pathway with 30 genes identified as likely direct targets using a database of p53 ChIP-seq studies. Despite similar p53 activation profiles, these data revealed widespread dampening of p53 and NRF2-related genes as early as 4 h after exposure at higher, unrecoverable Zn2+ exposures. Thus, in our model early increased activation of stress response pathways indicated a recoverable adaptive event. Overall, this study highlights the importance of characterizing molecular mechanisms around the tipping point of adverse responses to better inform HTS paradigms.
authors.affiliation: Oak Ridge Institute for Science and Education at U.S. Environmental Protection Agency, Research Triangle Park, North Carolina, United States of America.
authors.forename: Jenna M
authors.initials: JM
authors.lastname: Currier
authors.affiliation: Oak Ridge Institute for Science and Education at U.S. Environmental Protection Agency, Research Triangle Park, North Carolina, United States of America.
authors.forename: Wan-Yun
authors.initials: WY
authors.lastname: Cheng
authors.affiliation: Genome Integrity & Structural Biology Laboratory, National Institute of Environmental Health Sciences, NIH, Research Triangle Park, North Carolina, United States of America.
authors.forename: Daniel
authors.initials: D
authors.lastname: Menendez
authors.affiliation: National Health and Environmental Effects Research Laboratory, U.S. Environmental Protection Agency, Research Triangle Park, North Carolina, United States of America.
authors.forename: Rory
authors.initials: R
authors.lastname: Conolly
authors.affiliation: National Health and Environmental Effects Research Laboratory, U.S. Environmental Protection Agency, Research Triangle Park, North Carolina, United States of America.
authors.forename: Brian N
authors.initials: BN
authors.lastname: Chorley
mesh_terms: D017209:Apoptosis; D015415:Biomarkers / Q000378:metabolism*; D001980:Bronchi / Q000166:cytology*; D002460:Cell Line; D002470:Cell Survival; D004847:Epithelial Cells / Q000378:metabolism*; D020869:Gene Expression Profiling; D005786:Gene Expression Regulation; D005819:Genetic Markers; D005978:Glutathione / Q000378:metabolism; D006801:Humans; D007118:Immunoassay; D051267:NF-E2-Related Factor 2 / Q000378:metabolism; D020411:Oligonucleotide Array Sequence Analysis; D018384:Oxidative Stress; D025341:Principal Component Analysis; D018570:Risk Assessment; D015398:Signal Transduction; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism; D015032:Zinc / Q000737:chemistry
chemical_list: D015415:Biomarkers; D005819:Genetic Markers; D051267:NF-E2-Related Factor 2; C495635:NFE2L2 protein, human; C495901:TP53 protein, human; D016159:Tumor Suppressor Protein p53; D005978:Glutathione; D015032:Zinc