Moreover, PA28γ was shown to be involved in the ubiquitin- and ATP-independent degradation of a number of cell-cycle regulatory proteins, such as the cyclin-dependent inhibitor p21, or the steroid receptor coactivator 3 (SRC-3), which is an oncogene often amplified in breast cancer and involved in cell growth [181,182]. This evidence concerns the gene NCOA3 and breast cancer.