TSC1 and neoplasm: In its GTP-loaded state, Rheb activates mTORC1 (Saucedo et al., 2003; Yang et al., 2017), and this Rheb function is negatively regulated by the GTPase-activating protein (GAP) activity of the tumor-suppressing TSC complex composed of TSC1, TSC2, and TBC1D7 (Dibble et al., 2012).