Functional component of endoplasmic reticulum-associated degradation (ERAD) for misfolded lumenal proteins. Forms homotetramers which encircle a large channel traversing the endoplasmic reticulum (ER) membrane. This allows the retrotranslocation of misfolded proteins from the ER into the cytosol where they are ubiquitinated and degraded by the proteasome. The channel has a lateral gate within the membrane which provides direct access to membrane proteins with no need to reenter the ER lumen first. May mediate the interaction between VCP and the misfolded protein. Also involved in endoplasmic reticulum stress-induced pre-emptive quality control, a mechanism that selectively attenuates the translocation of newly synthesized proteins into the endoplasmic reticulum and reroutes them to the cytosol for proteasomal degradation. By controlling the steady-state expression of the IGF1R receptor, indirectly regulates the insulin-like growth factor receptor signaling pathway. Homotetramer. The four subunits of the tetramer are arranged in a twofold symmetry. Forms homo- and heterooligomers with DERL2 and DERL3; binding to DERL3 is poorer than that between DERL2 and DERL3. Interacts (via SHP-box motif) with VCP. Interacts with AMFR, SELENOS, SEL1L, SELENOK and SYVN1, as well as with SEL1L-SYVN1 and VCP-SELENOS protein complexes; this interaction is weaker than that observed between DERL2 and these complexes. Interacts with NGLY1 and YOD1. Does not bind to EDEM1. Interacts with DNAJB9. Interacts with RNF103. Interacts with HM13. Interacts with XBP1 isoform 1 (via luminal/ectodomain domain); the interaction obviates the need for ectodomain shedding prior HM13/SPP-mediated XBP1 isoform 1 cleavage. Interacts with the signal recognition particle/SRP and the SRP receptor; in the process of endoplasmic reticulum stress-induced pre-emptive quality control. May interact with UBXN6. Interacts with ZFAND2B; probably through VCP. Interacts with CCDC47. Interacts with C18orf32. May interact with TRAM1. Belongs to the derlin family.