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. Promotes sterol-accelerated ERAD of HMGCR probably implicating an AMFR/gp78-containing ubiquitin ligase complex. Involved in regulation of cellular cholesterol homeostasis by regulation the SREBP signaling pathway. May promote ER retention of the SCAP-SREBF complex (By similarity). Forms a heteromeric complex with ERLIN1 (By similarity). In complex with ERLIN1, interacts with RNF170 (PubMed:21610068). Interacts with activated ITPR1, independently of the degree of ITPR1 polyubiquitination (PubMed:17502376). Interacts with SCAP, INSIG1, SREBF1 and SREBF2 under cholesterol sufficiency conditions; indicative for an association with the SCAP-SREBP-INSIG complex (By similarity). Probably part of an AMFR/gp78 and INSIG1-containing ubiquitin ligase complex involved in ERAD of HMGCR (By similarity). Interacts with TMUB1; TMUB1 bridges the association with AMFR (By similarity). Interacts with SYVN1 and RNF139 (By similarity). Interacts with TMEM259 (PubMed:25977983). Interacts with TMEM41B (By similarity). Associated with lipid raft-like domains of the endoplasmic reticulum membrane. Belongs to the band 7/mec-2 family.