Plays a regulatory role in the processing of the amyloid-beta A4 precursor protein (APP) and acts as an inhibitor of the amyloid-beta peptide aggregation and fibrils deposition. Plays a role in the induction of neurite outgrowth. Functions as a protease inhibitor by blocking access of secretases to APP cleavage sites. Mature BRI2 (mBRI2) functions as a modulator of the amyloid-beta A4 precursor protein (APP) processing leading to a strong reduction in the secretion of secretase-processed amyloid-beta protein 40 and amyloid-beta protein 42. Bri23 peptide prevents aggregation of APP amyloid-beta protein 42 into toxic oligomers. Homodimer; disulfide-linked. Interacts with SPPL2A and SPPL2B. Interacts with APP. Mature BRI2 (mBRI2) interacts with the APP amyloid-beta A4 protein; the interaction occurs at the cell surface and in the endocytic compartments and enable alpha- and beta-secretase-induced APP cleavage inhibition. Mature BRI2 (mBRI2) interacts with the APP C99; the interaction occurs in the endocytic compartments and enable gamma-secretase-induced C99 cleavage inhibition. May form heterodimers with Bri23 peptide and APP amyloid-beta protein 40. Immature BRI2 (imBRI2) is cleaved by furin in the Golgi into mBRI2 and a Bri23 peptide. mBRI2 is transported to the plasma membrane and Bri23 peptide is secreted. Mature BRI2 (mBRI2) needs to be transported from the endoplasmic reticulum compartment to the cell membrane in order to be able to inhibit APP processing. Detected in the cerebral spinal fluid (CSF). Ubiquitous. Expressed in brain. The ectodomain C-terminal part of the imBRI2 is processed by furin producing a secreted Bri23 peptide and a mature BRI2, membrane form (mBRI2). The remaining part of the ectodomain of mBRI2 containing the BRICHOS domain is cleaved by ADAM10 and is secreted (BRI2C, soluble form). The membrane-bound N-terminal fragment (BRI2C, membrane form) is further proteolytically processed by SPPL2A and SPPL2B through regulated intramembrane proteolysis producing a secreted C-peptide and a BRI2 intracellular domain (BRI2 ICD) released in the cytosol. Shedding by ADAM10 facilitates intramembrane cleavage but is not absolutely required for BRI2 ICD generation. Glycosylation at Asn-170 is important for cell surface localization, but doesn't affect furin- and ADAM10-induced proteolytic processing. The disease is caused by variants affecting the gene represented in this entry. A single base substitution at the stop codon of ITM2B generates a 277-residue precursor that is cleaved at the normal furin processing site to generate the ABri amyloidogenic peptide (PubMed:10391242). ABri accumulates in the brain and produces amyloid fibrils responsible for neuronal dysfunction and dementia. ABri peptide variant forms fibrils in vitro (PubMed:10526337). The disease is caused by variants affecting the gene represented in this entry. A decamer duplication in the 3' region of ITM2B results in the production of the ADan amyloidogenic peptide (PubMed:10781099). ADan is generated by cleavage of the mutated precursor at the normal furin processing site. ADan accumulates in the brain and produces amyloid fibrils responsible for neuronal dysfunction and dementia. The disease is caused by variants affecting the gene represented in this entry. Belongs to the ITM2 family.