Component of the ERLIN1/ERLIN2 complex which mediates the endoplasmic reticulum-associated degradation (ERAD) of inositol 1,4,5-trisphosphate receptors (IP3Rs) such as ITPR1 (PubMed:19240031, PubMed:17502376). Promotes sterol-accelerated ERAD of HMGCR probably implicating an AMFR/gp78-containing ubiquitin ligase complex (PubMed:21343306). Involved in regulation of cellular cholesterol homeostasis by regulation the SREBP signaling pathway. May promote ER retention of the SCAP-SREBF complex (PubMed:24217618). Forms a heteromeric complex with ERLIN1. In complex with ERLIN1, interacts with RNF170 (PubMed:19240031, PubMed:21610068). Interacts with activated ITPR1, independently of the degree of ITPR1 polyubiquitination (By similarity). Interacts with SCAP, INSIG1, SREBF1 and SREBF2 under cholesterol sufficiency conditions; indicative for an association with the SCAP-SREBP-INSIG complex (PubMed:24217618). Probably part of an AMFR/gp78 and INSIG1-containing ubiquitin ligase complex involved in ERAD of HMGCR. Interacts with TMUB1; TMUB1 bridges the association with AMFR. Interacts with SYVN1 and RNF139 (PubMed:21343306). Interacts with TMEM259 (By similarity). Interacts with TMEM41B (PubMed:30352685). Associated with lipid raft-like domains of the endoplasmic reticulum membrane. Ubiquitous. The disease is caused by variants affecting the gene represented in this entry. Belongs to the band 7/mec-2 family.