Negatively regulates vacuolar (H+)-ATPase (V-ATPase) activity by interacting with members of V-ATPase V0 complex and hence inhibiting V1-V0 complex assembly. Required for multinucleation during osteoclast differentiation. . This is the function of ENSG00000145107 (TM4SF19, transmembrane 4 L six family member 19).