K11- and K48-Linked Ubiquitin Chains Interact with p97 during Endoplasmic Reticulum-Associated Degradation

The AAA+ ATPase p97 has a critical function in the cytoplasmic degradation of proteins misfolded in the endoplasmic reticulum through a mechanism known as ER-associated degradation (ERAD). During this process, p97 binds polyubiquitinated ERAD substrates and couples ATP hydrolysis to their dislocation from the ER as a prerequisite to destruction by the proteasome. The ubiquitin signals important for this process are not fully understood. Here we report that p97 interacts with lysine 11 (K11) and K48-linked ubiquitin polymers, but not those containing K63 linkages. Disruption of p97 through siRNA-mediated depletion, dominant negative over-expression, or chemical inhibition results in the accumulation of K11 and K48 ubiquitin chains predominantly at the ER membrane, and is associated with ER stress induction. We show that a catalytically inactive deubiquitinating enzyme and p97 cofactor YOD1 enhances the accumulation of K11- and K48-linked polyubiquitin in the cytoplasm, at the ER membrane, and bound to p97. In addition to general effects on p97-associated ubiquitin polymers, the ERAD substrate CD3δ is modified with both K11- and K48-ubiquitin chains prior to p97-dependent dislocation. Collectively, our data are consistent with a major role for p97 in the recognition of K11 and K48 polyubiquitinated proteins prior to their degradation by the proteasome.

Source: BJ Signal - January 14, 2014 Category: Biochemistry Authors: M Locke, J Irene Toth, M David Petroski Tags: BJ Signal Source Type: research