FK506-binding protein 38 (FKBP38), a member of the immunophilin family, has been implicated to play an important role in apoptosis throμgh its involvement in the mechanism that targets Bcl-2 and Bcl-xL to the outer mitochondrial membrane (OMM). Suppression of endogenous FKBP38 by RNAi or transfection of a mutant FKBK38 missing the transmembrane domain necessary for mitochondrial insertion, resulted in the translocation of Bcl-2 and Bcl-xL from the OMM to the cytosol. It has also been sμggested that FKBP38 may play a role in the cross-talk between the Bcl-2 and the Calcineurin/NF-AT apoptosis signaling pathways and in cell size regulation throμgh interactions with tuberous sclerosis genes.