Negative regulator of amyloid-beta peptide production. May inhibit the processing of APP by blocking its access to alpha- and beta-secretase. Binding to the beta-secretase-cleaved APP C-terminal fragment is negligible, suggesting that ITM2C is a poor gamma-secretase cleavage inhibitor. May play a role in TNF-induced cell death and neuronal differentiation (By similarity). Interacts with BACE1. Interacts with APP. Interacts with STMN2 (By similarity). Type I membrane-bound, as well as soluble, furin has a pre-eminent role in ITM2C proteolytic processing. PCSK7 and PCSK5 may also be involved although to a lesser extent. The soluble form of PCSK7 is incapable of processing ITM2C. Fails to undergo shedding by ADAM10 and intramembrane cleavage by SPPL2B (By similarity). Belongs to the ITM2 family.