ATF4 and neoplasm: Glutamine serves not only as a vital carbon and nitrogen source for rapidly proliferating tumor cells, but also contributes to redox balance maintenance, antioxidant synthesis (such as glutathione), and supports the TCA cycle and energy production (Elucidation of an mTORC2-PKC-NRF2 pathway that sustains the ATF4 stress response and identification of Sirt5 as a key ATF4 effector).