Bcl-2/E1B 19kDa-interacting protein 3-like protein (Bnip3L) interacts with Bcl-2/Bcl-xL and induces apoptosis by altering mitochondrial membrane permeability

We have previously reported on cloning of the human gene encoding Bcl-2/adenovirus E1B 19 kDa-interacting protein 3-like protein (Bnip3L) and its growth inhibitory effect on cancer cells. Here we show that Bnip3L contains a motif similar to the BH3 domain which is conserved in Bcl-2 family proteins as well as containing a membrane-anchoring domain, and that Bnip3L interacts with Bcl-2 and Bcl-x(L). Immunofluorescence microscopy revealed that Bnip3L was localized in the mitochondria, when in the presence of the membrane-anchoring domain. Transient expression of Bnip3L induced apoptosis of Rat-1 and HeLa cells and mutational analysis revealed that the BH3 domain and the membrane-anchoring domain were required for Bnip3L to induce cell death. Addition of recombinant Bnip3L to isolated mitochondria induced membrane potential loss and cytochrome c release both of which hale been suggested to be prerequisite for apoptotic cell death, These results suggest that Bnip3L is one of the BH3-containing proapoptotic proteins and that it targets the mitochondria when inducing apoptosis.