Component of the ESCRT-I complex, a regulator of vesicular trafficking process. Required for the sorting of endocytic ubiquitinated cargos into multivesicular bodies. May be involved in the ligand-mediated internalization and down-regulation of EGF receptor. . This is the function of MVB12A (multivesicular body subunit 12A, Ensembl gene identifier ENSG00000141971).