Cyclophilin D (also known as peptidylpropyl isomerase D, PPID) is a member of peptidyl-propyl cis-trans isomerase (PPIase) family, which catalyzes the cis-trans isomerization of proline imidic peptide bonds in oligopeptides and accelerates the folding of proteins. This protein can bind to the immunosuppressant cyclosporine A and was known that its overexpression suppresses the apoptosis in cancer cells.