Bax is a 21 kD pro-apoptotic protein known to regulate apoptosis. Bax is found in the cytoplasm, mitochondria, and nucleus and is highly expressed in hematopoietic stem cells, ovaries, and lymph nodes. Bax binds the anti-apoptotic protein Bcl-2 as a heterodimer or forms homodimers. The relative levels of pro-apoptotic proteins such as Bax and anti-apoptotic proteins such as Bcl-2 determines whether cell death will occur following an apoptotic stimulus. Bax accelerates the opening of mitochondrial VDAC altering membrane potential and allowing cytochrome c to pass out of the mitochondria into the cytosol to initiate downstream caspase activation. p53 can transcriptionally activate the Bax gene to induce apoptosis. Bax has been shown to be mutated in some human cancers.