Alteration of Cell Cycle Mediated by Zinc in Human Bronchial Epithelial Cells In Vitro
Citation:
Keshava, A., B. Chorley, AND J. Currier. Alteration of Cell Cycle Mediated by Zinc in Human Bronchial Epithelial Cells In Vitro. The Society of Toxicology 55th Annual Meeting and ToxExpo, New Orleans, LA, March 13 - 16, 2016.
Impact/Purpose:
Determining molecular biomarkers that differentiate adaptive and adverse cellular processes is critical to understanding the health effects of hazardous environmental exposures. As a case study, we focused on the adaptive and adverse responses of tracheobronchial airway cells to zinc (Zn) exposure. Zn is a ubiquitous contaminant of ambient air that presents an oxidant challenge to the human lung in environmental settings and has been linked to various adverse health effects. Saturation of intracellular Zn2+ increases free cytosolic Zn2+ which mediates the oxidative-linked effects of this heavy metal, including activation of stress signaling pathways and programmed cell death. To delineate underlying molecular mechanisms mediating this switch in normal human bronchial epithelial cell culture (BEAS-2B), we utilized a systems biology approach to determine research parameters using a computational model and validate these predictions in vitro. This pilot study was conducted by a high school student as part of a summer research project experience. The cell cycle analysis of the model zinc exposure system supported work conducted by ORISE fellow, Jenna Currier.
Description:
Zinc (Zn2+), a ubiquitous ambient air contaminant, presents an oxidant challenge to the human lung and is linked to adverse human health effects. To further elucidate the adaptive and apoptotic cellular responses of human airway cells to Zn2+, we performed pilot studies to examine cell cycle perturbation upon exposure using a normal human bronchial epithelial cell culture (BEAS-2B). BEAS-2B cells were treated with low (0, 1, 2 µM) and apoptotic (3 µM) doses of Zn2+ plus 1 µM pyrithione, a Zn2+-specific ionophore facilitating cellular uptake, for up to 24 h. Fixed cells were then stained with propidium iodine (PI) and cell cycle phase was determined by fluorescent image cytometry. Initial results report the percentage of cells in the S phase after 18 h exposure to 1, 2, and 3 µM Zn2+ were similar (8%, 7%, and 12%, respectively) compared with 7% in controls. Cells exposed to 3 µM Zn2+ increased cell populations in G2/M phase (76% versus 68% in controls). Interestingly, exposure to 1 µM Zn2+ resulted in decreased (59%) cells in G2/M. While preliminary, these pilot studies suggest Zn2+ alters cell cycle in BEAS-2B cells, particularly in the G2/M phase. The G2/M checkpoint maintains DNA integrity by enabling initiation of DNA repair or apoptosis. Our findings suggest that the adaptive and apoptotic responses to Zn2+ exposure may be mediated via perturbation of the cell cycle at the G2/M checkpoint. This work was a collaborative summer student project. The studies do not necessarily reflect the policies of the US EPA.