APEX1 and glioblastoma: To examine whether the chromosome fusions caused by Ape1 deficiency can be rescued by Chk2 depletion in the glioblastoma cells, we analyzed the metaphase chromosomes of the Ape1- and/or Chk2-depleted U251-MG cells, and observed that depletion of Ape1 causes massive chromosome fusions in U251-MG cells, and that is further augmented by TMZ (Fig. 3A,B).