Ran-binding protein 2 (Ranbp2) is a molecular hub for nucleocytoplasmic transport. Ran-GTP-binding domains (RBDs) of Ranbp2 destabilize Ran-GTP from its cargoes, whereas small molecules against the cyclophilin domain (CY) regulate Ranbp2 CY's moonlighting activity on client substrates. Ranbp2 haploinsufficiency protects retinal pigment epithelium and photoreceptors against phototoxicity, whereas Ranbp2 loss in motoneurons triggers amyotrophic lateral sclerosis-like behavior (e.g., paralysis).

Nucleocytoplasmic transport comprises the multistep assembly, transport, and disassembly of protein and RNA cargoes entering and exiting nuclear pores. Accruing evidence supports that impairments to nucleocytoplasmic transport are a hallmark of neurodegenerative diseases. These impairments cause dysregulations in nucleocytoplasmic partitioning and proteostasis of nuclear transport receptors and client substrates that promote intracellular deposits – another hallmark of neurodegeneration. Disturbances in liquid–liquid phase separation (LLPS) between dense and dilute phases of biomolecules implicated in nucleocytoplasmic transport promote micrometer-scale coacervates, leading to proteinaceous aggregates. This Review provides historical and emerging principles of LLPS at the interface of nucleocytoplasmic transport, proteostasis, aging and noxious insults, whose dysregulations promote intracellular aggregates. E3 SUMO-protein ligase Ranbp2 constitutes the cytoplasmic filaments of nuclear pores, where it acts as a molecular hub for rate-limiting steps of nucleocytoplasmic transport. A vignette is provided on the roles of Ranbp2 in nucleocytoplasmic transport and at the intersection of proteostasis in the survival of photoreceptor and motor neurons under homeostatic and pathophysiological environments. Current unmet clinical needs are highlighted, including therapeutics aiming to manipulate aggregation-dissolution models of purported neurotoxicity in neurodegeneration.