ATF4 and cancer: Elevated levels of ATF4 also correlate with resistance to chemotherapeutic agents, including DNA damaging agents (ionizing radiation, aphidicolin, hydroxyurea, cytarabine, etoposide, doxorubicin, and mafosfamide), celecoxib (a nonsteroidal anti-inflammatory drug), and bortezomib, in different cancers [181–186].