The mitochondrial protein BCL-2 family are critical in apoptosis. They are structurally related and can be classified as a functional and structural. Can be subdivided into multidomain proapoptotic proteins (such as BAX and BAK), multidomain antiapoptotic proteins (such as BCL-2), and BH3-only proteins (such as BID or BIM). All these lead to the regulated permeability of the mitochondrial outer membrane with release of cytochrome c and activation of effector caspases. They may also have other functions in other subcellular compartments.

Currently known to exert a role in maintaining the level of endoplasmic reticulum (ER), controlling the Ca 2 + homeostasis and in regulating the response of the protein is not folded (UPR: unfolded protein response) on a non-apoptotic. The ER and mitochondria are physically and functionally connected. It has accepted that the mitochondrial expression of BAX and BAK was sufficient to initiate apoptosis and it was unclear if the corresponding ER BAK and BAX could have similar potential.

Using cells expressing BAK only in reticulum, the Pimentel-Muiños group, Center for Cancer Research at the University of Salamanca, has identified the proapoptotic protein BCL-2 family that can activate the mitochondrial pathway of death also when are restricted only in the ER. This means that with the involvement of protein mediators of type BH3-only (Puma and Bim) can produce apoptosis of multidomain BAK using lattice. This paper shows how through cascades unconventional space restriction is overcome by cellular signaling components, plus the discovery that mitochondria and ER can communicate during apoptosis, provides new insights into the regulation of cell death.