May be a regulator of the duration of MAPK8 activity in response to various stress stimuli. Facilitates degradation of misfolded endoplasmic reticulum (ER) luminal proteins through the recruitment of components of the proteasome and endoplasmic reticulum-associated degradation (ERAD) system. Interacts with RNF5 and MAPK8, but not with MAPK9. Binding to MAPK8 occurs before and after exposure to stress, such as UV irradiation. After exposure to stress, interacts with phosphorylated MAPK8. Competes with DUSP10 for MAPK8 binding. Associates with multiple components of the proteasome and with ERAD regulatory proteins, including AMFR/GP78, CANX, PSMC1, PSMC2, PSMC3/TBP1, PSMC5, PSMC6, PSMD8, SEC61-ALPHA and UFD1. Expressed in numerous tissues, including brain, spleen, thymus, liver, kidney and testis. Elevated expression in medulloblastoma. By ER stress. Ubiquitinated by RNF5 via 'Lys-63'-linked ubiquitin linkage in a UBE2N-dependent manner. Ubiquitination decreases association with components of the proteasome and ERAD.