Flow cytometric evaluation of cell‐cycle progression in ethyl methanesulfonate and methyl methanesulfonate‐exposed P3 Cells: Relationship to the induction of sister‐chromatid exchanges and cellular toxicity

Abstract

In order to determine the relationships among the reduction in relative cloning efficiency (RCE), sister-chromatid exchange (SCE) formation, and interference with progression through the cell-cycle, human teratocarcinoma-derived (P3) cells were exposed to either ethyl methanesulfonate or to methyl methanesulfonate. The relationship between SCE and toxicity was quantified, the progression through the cell-cycle was evaluated with flow cytometric methods, and the effects of these chemicals on cell growth and average generation time (AGT) were determined. A strong correlation existed between RCE and SCE (r = -0.978, p less than .001) which was accompanied by an inhibition of growth as evidenced by a significant (p less than .0001) negative linear effect of concentration on the relative cell count from 24 to 72 hours after exposure and by a concentration-dependent increase (p less than .0001) in the AGT. Delays in the transit through S-phase were evident 4 hours after exposure to toxic concentrations of either carcinogen and by 8 to 12 hours post-exposure at the lower concentrations. Increases in the percentage of nuclei in G2 + M, indicative of G2 arrest, occurred from 12 to 24 hours after exposure. One interpretation of these results is that those effects of EMS and MMS exposure which result in S-phase delay and G2 arrest may be those elements common to the induction of SCE and cellular toxicity.

A Chemical and Genetic Approach Together Define the Biological Consequences of 3-Methyladenine Lesions in the Mammalian Genome

“…3MeA DNA Lesions Induce S Phase Arrest-MMS is known to induce an S phase arrest in mammalian cells (24), and here we show that 3MeA DNA lesions contribute to that arrest. ( Fig.…”

“…However, it has also been proposed that SCEs result from strand switching at stalled replication forks for the following reasons: (i) cells that sustain damage in G 2 do not form SCEs, and (ii) DNA damage must be present during S phase to induce SCEs (33)(34)(35). Indeed, it was reported that the lowest dose of MMS that results in S phase arrest coincides with the lowest dose required for SCE induction (24). Our data support this model in that a more robust 3MeA-induced S phase arrest coincides with increased SCE induction.…”

Synchronization in mammalian system: An introduction

“…The effects of some of the mutagenic compounds such as EMS and NMS have also been shown to lead to 'S' phase delay, a common effect of toxicity and sister chromatid exchange [35]. Out of all these, the decreased amount of calcium leading to quiescence followed by increase in calcium concentration has been found to be very effective.…”