Involved in endoplasmic reticulum-associated protein degradation (ERAD). Acts as a platform to recruit both UBQLN1 and VCP to the ER during ERAD. Directly interacts with VCP. Interacts with UBQLN1. Forms a complex with VCP and UBQLN1. Both the N- and the C-terminus face the cytosol. Also found in the nucleus envelope contiguous to the ER. Expressed in many tissues, including brain, heart, kidney, liver, muscle and spleen (at protein level). The UBX domain is required for interaction with VCP. The intramembrane domain also contains the signal for ER targeting.