Mediator of programmed cell death (apoptosis). Heterotetramer that consists of two anti-parallel arranged heterodimers, each one formed by a 20 kDa (p20) and a 10 kDa (p10) subunits. Up-regulated by bacterial lipopolysaccharides (LPS). Expressed in barely detectable amounts in most tissues except brain, highest levels being found in lung, liver and skeletal muscle. Belongs to the peptidase C14A family. 6 isoforms of the human protein are produced by alternative splicing. Note: This description may include information from UniProtKB.