REDD1 (regulated in development and DNA damage response 1) is a direct transcriptional target of HIF. It plays a role in the TSC/mTOR pathway as a regulator upstream of the TSC1/2 complex. In response to both hypoxia and energy stress, REDD1 inhibitsmTOR activity in a TSC-dependent manner. Alternative names for REDD1 include DDIT4, DNA-damage-inducible transcript 4 protein, and RTP801.