Pincheira J, López-Sáez J F
Departamento de Biología Celular y Genética, Facultad de Medicina, Universidad de Chile, Santiago.
Mutat Res. 1991 Nov;251(1):71-7. doi: 10.1016/0027-5107(91)90216-b.
The effect of caffeine and cycloheximide during the G2 phase on frequency of chromosomal aberrations and G2 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 G2 duration in control and X-ray-irradiated lymphocytes (40 R). Both caffeine effects are reversed by 0.5 micrograms/ml cycloheximide in combination treatments. Cycloheximide treatments alone prolong G2 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, G2 delay has generally been associated with certain genome damage. The fact that the caffeine and cycloheximide effects on X-irradiated lymphocytes are also present in control lymphocytes (without X-rays) suggests that control of the G2 duration constitutes one of the mechanisms involved in DNA repair operating during the G2 phase.
在体外培养的对照及经X射线照射的人淋巴细胞中，研究了G2期咖啡因和放线菌酮对染色体畸变频率及G2期持续时间的影响。单独使用咖啡因处理可增加对照及经X射线照射（40伦琴）淋巴细胞的染色单体断裂频率，并缩短平均G2期持续时间。在联合处理中，0.5微克/毫升放线菌酮可逆转咖啡因的这两种作用。单独使用放线菌酮处理可延长对照及经X射线照射淋巴细胞的G2期持续时间，不过在我们的实验条件下，未观察到这种蛋白质合成抑制剂对染色体修复有改善作用。我们认为，放线菌酮的作用与进入有丝分裂所需的有丝分裂因子水平较低有关，而单独使用咖啡因处理时该因子水平维持在较高水平。最后，G2期延迟通常与某些基因组损伤有关。咖啡因和放线菌酮对经X射线照射淋巴细胞的作用在对照淋巴细胞（未照射X射线）中也存在，这一事实表明，控制G2期持续时间是G2期DNA修复过程中涉及的机制之一。
