| RalA binding protein 1 (RALBP1/RLIP76) is a multifunctional, ubiquitously expressed protein that serves both as a downstream effector of Ral and R‑Ras small GTPases and as an ATP‑dependent transporter for glutathione conjugates and xenobiotic toxins, integrating signaling, endocytosis and detoxification processes in proliferating and stressed cells. Structurally, RALBP1 contains domains that mediate binding to active, GTP‑loaded RALA and RALB and a region with GTPase‑activating protein activity toward CDC42 and RAC1, allowing it to inactivate these Rho family GTPases by stimulating their GTP hydrolysis and thereby modulate cytoskeletal reorganization and vesicle trafficking. As a Ral pathway effector, RALBP1 participates in receptor‑mediated endocytosis by regulating ligand‑dependent internalization of EGFR and insulin receptor and acts as a mitotic scaffold: during mitosis, it recruits cyclin B–CDK1 to EPSIN/EPN1 to block endocytosis, and to mitochondria via RALA to promote CDK1‑mediated phosphorylation and activation of dynamin‑related protein DNM1L, controlling mitochondrial fission during cell division. In parallel, RALBP1 functions as a primary ATP‑dependent transporter for glutathione conjugates of electrophilic lipid peroxidation products and a wide range of xenobiotics, including anthracyclines and vinca alkaloids, contributing to multidrug resistance by lowering intracellular concentrations of pro‑apoptotic oxidized lipids and chemotherapeutic agents. Overexpression of RALBP1 has been documented in multiple cancers, and in colorectal cancer, high RALBP1 protein levels correlate significantly with advanced UICC stage, nodal involvement, recurrence and death; multivariate analysis identifies RALBP1 overexpression as an independent predictor of shorter disease‑free and overall survival in stage‑stratified cohorts. Functional studies in tumor models show that depletion or inhibition of RALBP1 reduces migration and invasion, suppresses tumor growth and metastasis in prostate, bladder and colorectal cancer models, and in human lung and colon xenografts, antisense knockdown or inhibitory anti‑RALBP1 IgG alone induces rapid, complete and sustained tumor regression, while also enhancing the efficacy of cisplatin–vinorelbine chemotherapy. RALBP1 also mediateds transport of glutathione conjugates and xenobiotics and serves as a key effector function for cancer cell survival and chemoresistance, and RALBP1’s roles in Ral/Ras–Rho signaling, receptor endocytosis and mitotic mitochondrial dynamics couple upstream oncogenic pathways to changes in drug handling, oxidative stress tolerance and metastatic behavior. |
