The small GTPase Rab7 promotes fusion events between late endosomes and lysosomes. TBC domain family, member 15 (TAB1CD15) is ubiquitously expressed and localized predominantly to the cytosol. TBC1D15 stimulates the intrinsic GTPase activity of Rab7, reducing Rab7 binding to its effector protein RILP, fragmenting the lysosome, and conferring resistance to growth factor withdrawal-induced cell death (Zhang et al. 2005, Peralta et al. 2010).