Deleted in breast cancer gene 1 protein (DBC1) was originally identified by its localization to a region of chromosome 8p21 that is homozygously deleted in breast cancer. DBC1 is a large, nuclear protein with multiple functions in cell survival. It binds directly to the estrogen receptor ? (ER?) hormone-binding domain in a ligand-independent manner and may be a key determinant of ligand-independent ER? expression and survival in human breast cancer cells . DBC1 can promote p53-mediated apoptosis by binding to and inhibiting the deacetylase activity of SirT1, resulting in increased p53 acetylation levels and activity . DBC1 may be an important regulator of heterochromatin formation as it binds SUV39H1 and inhibits its histone methyltransferase activity . Caspase-dependent processing activates the pro-apoptotic activity of DBC1 during Tumor Necrosis Factor-? (TNF-?)-mediated cell death signaling. This processing of DBC1 in response to TNF-? is an early event in the onset of apoptosis and results in relocalization of DBC1 to the cytoplasm. Overexpression of the processed, cytoplasmic form of DBC1 results in mitochondrial clustering and matrix condensation and sensitizes cells to TNF-?-mediated apoptosis.