Figure 2

The effect of K1 expression on resistance to apoptosis, ROS generation, DNA damage and DNA damage response. (A) Under genotoxic conditions, mock cells showed a significant increase in the number of apoptotic cells, whereas AK1 cells demonstrated a smaller number of apoptotic cells. CK1 cells exhibited intermediate resistance. Magnification, 400×. (B) Under serum-free treatment, all cell lines showed increased ROS levels, with no differences among them. However, under non-genotoxic conditions, mock cells showed little ROS generation, whereas both AK1 and CK1 cells demonstrated slight increased levels of ROS generation compared with those under genotoxic conditions. Magnification, 400×. (C) An eightfold increase in DNA damage was observed in mock cells under genotoxic stress; however, AK1 and CK1 cells demonstrated a moderate induction of DNA damage (within twofold). Magnification, 400× *p < 0.05. (D) Although siRNA con-treated AK1 cells showed DNA damage, K1 knockdown demonstrated very little DNA damage. Magnification, 400×. (E,F) Under genotoxic stress, increased apoptotic cells in K1 knocked down AK1 were demonstrated by both TUNEL (E) and flowcytometry (F) analyses. (E) Magnification, 400×. (G) Under genotoxic conditions, AK1 cells strongly suppressed the induction of DDR proteins, including ATM, ATR, and Chk1, whereas CK1 cells showed only mild suppression of ATM and Chk2.