Oxysterol-binding protein that mediates feedback control of cholesterol synthesis by controlling both endoplasmic reticulum to Golgi transport of SCAP and degradation of HMGCR (PubMed:12242332, PubMed:16606821, PubMed:32322062). Acts as a negative regulator of cholesterol biosynthesis by mediating the retention of the SCAP-SREBP complex in the endoplasmic reticulum, thereby blocking the processing of sterol regulatory element-binding proteins (SREBPs) SREBF1/SREBP1 and SREBF2/SREBP2 (PubMed:32322062). Binds oxysterol, including 22-hydroxycholesterol, 24-hydroxycholesterol, 25-hydroxycholesterol and 27-hydroxycholesterol, regulating interaction with SCAP and retention of the SCAP-SREBP complex in the endoplasmic reticulum (PubMed:26160948, PubMed:17428920, PubMed:32322062). In presence of oxysterol, interacts with SCAP, retaining the SCAP-SREBP complex in the endoplasmic reticulum, thereby preventing SCAP from escorting SREBF1/SREBP1 and SREBF2/SREBP2 to the Golgi (PubMed:32322062). Sterol deprivation or phosphorylation by PCK1 reduce oxysterol-binding, disrupting the interaction between INSIG2 and SCAP, thereby promoting Golgi transport of the SCAP-SREBP complex, followed by processing and nuclear translocation of SREBF1/SREBP1 and SREBF2/SREBP2 (PubMed:32322062). Also regulates cholesterol synthesis by regulating degradation of HMGCR: initiates the sterol-mediated ubiquitin-mediated endoplasmic reticulum-associated degradation (ERAD) of HMGCR via recruitment of the reductase to the ubiquitin ligase RNF139 (PubMed:16606821, PubMed:22143767). Interacts with SCAP; interaction is direct and only takes place in the presence of sterols; it prevents interaction between SCAP and the coat protein complex II (COPII) (PubMed:12242332, PubMed:17428920, PubMed:26160948, PubMed:32322062). Associates with the SCAP-SREBP complex (composed of SCAP and SREBF1/SREBP1 or SREBF2/SREBP2); association is mediated via its interaction with SCAP and only takes place in the presence of sterols (PubMed:12242332, PubMed:32322062). Interacts with RNF139 (PubMed:20068067, PubMed:22143767). Interacts with RNF145 (PubMed:29374057). Binds oxysterols in a pocket within their transmembrane domains and interacts with SCAP via transmembrane domains 3 and 4. The KxHxx motif mediates association with the coatomer complex. Phosphorylation at Ser-151 by PCK1 reduces binding to oxysterol, disrupting the interaction between INSIG2 and SCAP, thereby promoting nuclear translocation of SREBP proteins (SREBF1/SREBP1 or SREBF2/SREBP2) and subsequent transcription of downstream lipogenesis-related genes. Polyubiquitinated by AMFR/gp78 at Cys-215 in some tissues such as adipose tissues, undifferentiated myoblasts and liver, leading to its degradation (PubMed:31953408). In differentiated myotubes, Cys-215 oxidation prevents ubiquitination at the same site, resulting in protein stabilization (PubMed:31953408). Oxidized at Cys-215 in differentiated myotubes, preventing ubiquitination at the same site, and resulting in protein stabilization. Belongs to the INSIG family. A study showed that INSIG2 is not ubiquitinated by AMFR/gp78 (PubMed:17043353). However, another paper showed that it is ubiquitinated on Cys-215, and that ubiquitination takes place in some tissues only and depends on the differentiation state (PubMed:31953408).