Rapid proteasomal degradation of the stress response protein REDD2 is mediated by the E3 ligase HUWE1

The stress response proteins regulated in development and DNA damage (REDD)1 and REDD2 act as negative regulators of mechanistic target of rapamycin complex 1 (mTORC1). Prior studies support that REDD1 is rapidly degraded via both chaperone-mediated autophagy (CMA) and the ubiquitin proteasome system (UPS). Compared to REDD1, relatively little is known regarding the regulation of REDD2. The objective here was to investigate the molecular mechanisms that control the cellular abundance of REDD2. Genetic and pharmacologic interventions were used to manipulate protein synthesis and proteolysis. We found that both REDD1 and REDD2 were rapidly degraded with half-lives of <20 min. Interestingly, REDD2 expression reduced the rate of REDD1 degradation, suggesting that the molecular mechanism through which they are degraded overlaps. However, in contrast with REDD1, CMA activation did not promote REDD2 degradation, despite the conservation of a putative KFERQ-like motif sequence in REDD2. Instead, we provide evidence that the rapid degradation of REDD2 was mediated by the UPS, the E3 ligase HUWE1, and K119/K120 of REDD2. The findings support that the cellular abundance of both REDD1 and REDD2 are controlled at the level of protein stability.