Specific locus mutagenesis of human mammary epithelial cells by ultraviolet radiation

The stress response resolution assay. I. Quantitative assessment of environmental agent/condition effects on cellular stress resolution outcomes in epithelium

The events or factors that lead from normal cell function to conditions and diseases such as aging or cancer reflect complex interactions between cells and their environment. Cellular stress responses, a group of processes involved in homeostasis and adaptation to environmental change, contribute to cell survival under stress and can be resolved with damage avoidance or damage tolerance outcomes. To investigate the impact of environmental agents/conditions upon cellular stress response outcomes in epithelium, a novel quantitative assay, the "stress response resolution" (SRR) assay, was developed. The SRR assay consists of pretreatment with a test agent or vehicle followed later by a calibrated stress conditions exposure step (here, using 6-thioguanine). Pilot studies conducted with a spontaneously-immortalized murine mammary epithelial cell line pretreated with vehicle or 20 µg N-ethyl-N-nitrososurea/ml medium for 1 hr, or two hTERT-immortalized human bronchial epithelial cell lines pretreated with vehicle or 100 µM zidovudine/lamivudine for 12 days, found minimal alterations in cell morphology, survival, or cell function through 2 weeks post-exposure. However, when these pretreatments were followed 2 weeks later by exposure to calibrated stress conditions of limited duration (for 4 days), significant alterations in stress resolution were observed in pretreated cells compared with vehicle-treated control cells, with decreased damage avoidance survival outcomes in all cell lines and increased damage tolerance outcomes in two of three cell lines. These pilot study results suggest that sub-cytotoxic pretreatments with chemical mutagens have long-term adverse impact upon the ability of cells to resolve subsequent exposure to environmental stressors.

Epithelial and fibroblast cell lines cultured from the transgenic BigBlue rat: an in vitro mutagenesis assay

We have isolated, cultured, and immortalised three new BigBlue transgenic rat cell lines for the study of mutation induction in vitro. The two epithelial cell lines, from the mammary gland and oral cavity, were designated BBR/ME and BBR/OE, respectively, and the third is a mammary fibroblast line designated BBR/MFib. We have characterised these cell lines with respect to chromosome number and the expression of some cell-specific antigens. The clonogenic survival and cII transgene mutation induction responses of these three cell lines to N-ethyl-N-nitrosourea (ENU) treatment were determined. Both epithelial cell lines were much more sensitive to ENU toxicity than was the fibroblast cell line. However, all cell lines showed similar ENU dose-dependent increases in mutant frequency. We hope that cell lines such as these will extend the power of the BigBlue assay to in vitro studies.

The role of the lens epithelium in development of UV cataract

In view of renewed interest in the lens epithelium as the initiation site for cataract development, it seemed timely to review recent studies which appear to establish UV damage in the lens epithelium as the cause of UV cataract. While UV photons can and do interact with lens proteins in the cortex and nucleus, experimental results from cultured lenses and tissue cultured epithelial cells also demonstrate both mutagenic and cytotoxic effects in the epithelium. This minireview examines UV-induced changes in lens physiology that appear to follow epithelial cell damage, including inactivation of critical enzymes of transport and metabolic processes. Changes in membrane function include altered cation transport, increased permeability, and altered biosynthesis. One potential scenario for the propagation of damage from the epithelium to the underlying fiber cells includes calcium elevation, an early event in cataract development and critical to many physiological processes.

Application of the standard mutagenesis assay results in underestimation of ethyl methanesulphonate-induced mutations to ouabain-resistance in Chinese hamster cells

Chinese hamster V79 cells were exposed to ethyl methanesulphonate (EMS) and the incidence of mutant cells resistant to 8-azaguanine (8AZG), 6-thioguanine (6TG) or ouabain (OUA) was determined both by the respreading and the in situ techniques. In the former assay, the mutagen-treated cultures were grown for several days to permit the expression of mutations after which the cells were trypsinized, replated (10(5) cells/100-mm dish), and grown in medium supplemented with a selective agent. In the in situ assay, cultures were left undisturbed between EMS treatment and incubation in the presence of the selective agents. The yield of 8AZG-resistant mutants observed at optimal expression times after EMS treatment was comparable for both techniques; the induced mutation frequency (corrected for spontaneous mutation frequency) was estimated to be 82 x 10(-6) mutations per viable cell per unit dose (mM) of EMS. The frequency of 6TG-resistant mutants equalled 45 and 4 x 10(-6)/mM EMS as determined by the respreading and the in situ assays, respectively. In sharp contrast to that observed with 6TG, the frequency of OUA-resistant mutants scored by the in situ assay (30 x 10(-6)/mM EMS) proved to be an order of magnitude greater than that determined by the respreading assay (3 x 10(-6)/mM EMS). Our data therefore indicate that, when OUA is used for mutant selection, the application of the respreading technique, which has been widely adopted as the standard mammalian mutational assay over the past decade, may result in a marked underestimation of the actual mutation frequency (approximately 10-fold in V79 cells).