In control KB-3 cells, Bcl-xL interacts with Bax in the cytosol, and vinblastine induces JNK-dependent Bax mitochondrial translocation. JNK may also directly phosphorylate Bax, and a kinase distinct from JNK phosphorylates Bcl-xL (15). At the mitochondria, Bax induces cell death which is antagonized by Bcl-xL overexpression. GFP-Bax when transiently expressed in KB-3 localizes to the mitochondria and induces cell death, and this too is antagonized by Bcl-xL overexpression.