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. In complex with ERLIN1, interacts with RNF170. Interacts with activated ITPR1, independently of the degree of ITPR1 polyubiquitination. Interacts with SCAP, INSIG1, SREBF1 and SREBF2 under cholesterol sufficiency conditions; indicative for an association with the SCAP-SREBP-INSIG complex. 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. Interacts with TMEM259 (By similarity). Interacts with TMEM41B (By similarity). Associated with lipid raft-like domains of the endoplasmic reticulum membrane. Belongs to the band 7/mec-2 family.