EFFECT OF DNA-DAMAGING AGENTS IN QUIESCENT CELLS
Joaquin Garcia, Lindsey Long, Mary Ann Osley.
The University of New Mexico, Albuquerque, NM.
DNA damage occurs in all organisms. Cells in different stages of the cell cycle (G1, S, G2, and M phases) may respond differently to DNA damage. When deprived of essential nutrients, many cells can exit the cell cycle and enter a state called G0 or quiescence. We tested the response of quiescent Saccharomyces cerevisiae (budding yeast) cells to DNA damaging agents (DDAs). The DDAs we used were ultraviolet light (UV) and 4-nitroquinoline (4NQO), which lead to DNA adducts. When Q cells encounter DNA damage they must repair it so the damage will not be propagated to future generations. To analyze the effect of the DDAs on G0 cells, we used a combination of assays. Our results show that 4NQO and UV result in a decreased reproductive capacity in quiescent G0 cells when compared to G1-arrested cells. By western blotting, we found that phospho-H2A is induced in G0 cells but not in G1 cells during 4NQO exposure. This implies that the signal to recruit the DNA damage repair machinery is present in quiescent cells. Using a canavanine viability assay, we found that 4NQO exposure increases the frequency of DNA mutations in Q cells. From these data, we conclude that G0 and G1 cells respond differently to 4NQO exposure, and that the reduced reproductive capacity of Q cells may be a consequence of the increased frequency of DNA mutations produced by the DDAs. Our experiments could lead to a greater understanding of how quiescent cells in eukaryotes respond to DNA damage.