Decreased MCM2-6 in Drosophila S2 Cells Does Not Generate Significant DNA Damage or Cause a Marked Increase in Sensitivity to Replication Interference

A reduction in the level of some MCM proteins in human cancer cells (MCM5 in U20S cells or MCM3 in Hela cells) causes a rapid increase in the level of DNA damage under normal conditions of cell proliferation and a loss of viability when the cells are subjected to replication interference. Here we show that Drosophila S2 cells do not appear to show the same degree of sensitivity to MCM2-6 reduction. Under normal cell growth conditions a reduction of >95% in the levels of MCM3, 5, and 6 causes no significant short term alteration in the parameters of DNA replication or increase in DNA damage. MCM depleted cells challenged with HU do show a decrease in the density of replication forks compared to cells with normal levels of MCM proteins, but this produces no consistent change in the levels of DNA damage observed. In contrast a comparable reduction of MCM7 levels has marked effects on viability, replication parameters and DNA damage in the absence of HU treatment.

在人类癌细胞中，部分微型染色体维持蛋白（Mini-Chromosome Maintenance, MCM）的丰度下调（如U20S细胞中的MCM5或海拉细胞（Hela）中的MCM3），会在细胞增殖的正常生理条件下快速引发DNA损伤水平升高，且当细胞受到复制干扰时会导致细胞活力丧失。本研究显示，果蝇（Drosophila）S2细胞对MCM2-6蛋白丰度下调的敏感程度并未达到人类癌细胞的水平。在正常细胞生长条件下，将MCM3、5、6的蛋白丰度下调95%以上，并不会对DNA复制相关参数造成显著的短期改变，也不会引发DNA损伤水平的上升。经羟基脲（Hydroxyurea, HU）处理的MCM敲低细胞，与MCM蛋白水平正常的细胞相比，其复制叉密度确实有所下降，但并未使观测到的DNA损伤水平出现一致性变化。与之形成鲜明对比的是，在未经过HU处理的条件下，将MCM7蛋白丰度下调至相近水平，会对细胞活力、复制参数及DNA损伤水平产生显著影响。