Furthermore, specific 20S core subunits may be replaced by alternative variants in the immunoproteasome for antigen peptide processing (with emerging, but yet unclear specific roles in neoplasia), whereas regulatory particle 19S can be substituted by 11S proteasome activators PA28αβ (11Sαβ) or PA28γ (11Sγ, a hexamer of REGγ/PSME3 proteins) [122]. Here, PSME3 is linked to neoplasm.