Specificity and regulation of the endoplasmic reticulum-associated degradation machinery

The endoplasmic reticulum-associated degradation (ERAD) machinery selects native and misfolded polypeptides for dislocation across the ER membrane and proteasomal degradation. Regulated degradation of native proteins is an important aspect of cell physiology. For example, it contributes to the control of lipid biosynthesis, calcium homeostasis and ERAD capacity by setting the turnover rate of crucial regulators of these pathways. In contrast, degradation of native proteins has pathologic relevance when caused by viral or bacterial infections, or when it occurs as a consequence of dysregulated ERAD activity. The efficient disposal of misfolded proteins prevents toxic depositions and persistent sequestration of molecular chaperones that could induce cellular stress and perturb maintenance of cellular proteostasis. In the first section of this review, we survey the available literature on mechanisms of selection of native and non-native proteins for degradation from the ER and on how pathogens hijack them. In the second section, we highlight the mechanisms of ERAD activity adaptation to changes in the ER environment with a particular emphasis on the post-translational regulatory mechanisms collectively defined as ERAD tuning.