Effects of ATM-ATR inhibitors on the surface expressions of NKG2D ligands in A549 cells. The surface protein expressions of NKG2D ligands on A549 cells, MICA, were unaffected by KU-55933 or caffeine (A); caffeine significantly decreased the surface expression of MICA. The induction of NKG2D ligands surface protein by ionizing radiation was blocked by ATM-ATR inhibitors in A549 cells, although difference of ULBP2 was not significant. (B). The induction of the surface expressions of NKG2D ligands by HDAC inhibitors was not blocked by ATM-ATR inhibitors in A549 cells, with the exception of MICA in cells treated with caffeine (C).