Effects of caffeine and cycloheximide during G 2 prophase in control and X-ray-irradiated human lymphocytes

Abstract

The effect of caffeine and cycloheximide during the G 2 phase on frequency of chromosomal aberrations and G 2 duration was studied in control and X-ray-irradiated human lymphocytes in vitro. Caffeine treatments alone increase the frequencies of chromatid breakage and decrease the average G 2 duration in control and X-ray-irradiated lymphocytes (40 R). Both caffeine effects are reversed by 0.5 μg/ml cycloheximide in combination treatments. Cycloheximide treatments alone prolong G 2 duration in control as well as in X-ray-irradiated lymphocytes although no improvement in chromosome repairing by this inhibitor of protein synthesis was observed under the conditions of our experiments. We propose that the cycloheximide effect is associated with a low level of mitotic factors, required for the entrance into mitosis, which is maintained at a higher level in caffeine treatment alone. Finally, G 2 delay has generally been associated with certain genome damage. The fact that the caffeine and cycloheximide effects on X-irraduated lymphocytes are also present in control lymphocytes (without X-rays) suggests that control of the G 2 duration constitutes one of the mechanisms involved in DNA repair operating during the G 2 phase.