MTP18 (mitochondrial 18 kDa protein), also known as HSPC242, is a 166 amino acid protein essential for cell viability. MTP18 may also have a role in maintaining the integrity of the mitochondrial network. Localized to the mitochonrion, expression of MTP18 is regulated by the PI 3-kinase pathway. Loss of function of MTP18 results in the release of cytochrome c, which subsequently activates the caspase cascade and leads to apoptosis.