ATF4 and central nervous system cancer: However, ATF4 also drives CHOP/GADD153 expression resulting in engagement of apoptotic signaling pathways, but since glioma cells are remarkably resistant to apoptosis [67], this arm of the UPR seems to have minimal effect in these tumor cells despite clear expression of CHOP (although it is somewhat variable, Figures 1, 2 and 8, Table 3).