Regulates cell growth, proliferation and survival via inhibition of the activity of the mammalian target of rapamycin complex 1 (mTORC1). Inhibition of mTORC1 is mediated by a pathway that involves ddit4/redd1, akt1, the tsc1-tsc2 complex and the GTPase rheb. Plays an important role in responses to cellular energy levels and cellular stress, including responses to hypoxia and DNA damage, via its effect on mTORC1 activity. Plays a role in neuronal differentiation, neuron migration during embryonic brain development and in neuronal cell death (By similarity). Belongs to the DDIT4 family.