{"type": "root", "children": [{"type": "p", "children": [{"type": "t", "text": "\nRanBP3 is a multifunctional Ran‐interacting protein that plays critical roles in nucleocytoplasmic transport. It functions as an essential cofactor in the selective nuclear export of specific signaling molecules. For instance, RanBP3 directly binds to dephosphorylated Smad2/3—key mediators in the TGF‑β pathway—and facilitates their export from the nucleus in a Ran-dependent manner, thereby modulating the intensity and duration of TGF‑β signaling."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "1"}]}, {"type": "t", "text": " Additionally, its activity is fine‐tuned by phosphorylation events mediated by the Ras/ERK/RSK and PI3K/Akt pathways, highlighting its role as an integrator of major cell-fate signaling cascades."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "2"}]}, {"type": "t", "text": "\n"}]}, {"type": "t", "text": "\n\n"}, {"type": "p", "children": [{"type": "t", "text": "\nBeyond its role in modulating TGF‑β signaling, RanBP3 also contributes to the assembly of export complexes. It acts as a scaffold by binding both to the small GTPase Ran and to RCC1, the Ran-specific guanine nucleotide exchange factor, thereby promoting the catalytic loading of Ran·GTP on export receptors such as CRM1."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "3"}]}, {"type": "t", "text": " This scaffolding function is further implicated in viral mRNA export processes as RanBP3 is necessary for efficient nuclear export of influenza virus ribonucleoproteins, and its interaction with CRM1 also overlaps with domains that determine Rex multimerization in human T-cell leukemia virus type 1, underscoring potential species-specific regulatory mechanisms."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "4"}]}, {"type": "t", "text": "\n"}]}, {"type": "t", "text": "\n\n"}, {"type": "p", "children": [{"type": "t", "text": "\nStructural studies of RanBP3 have revealed unique characteristics that distinguish its function from other Ran-binding proteins. Its relatively low affinity for Ran and its ability to stabilize CRM1-containing export complexes explain how it not only enhances the affinity of CRM1 for Ran·GTP and NES-bearing cargos but also alters the cargo selectivity—favoring the export of proteins like HIV-1 Rev while deterring others such as the import adaptor Snurportin1."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "6"}]}, {"type": "t", "text": " Moreover, RanBP3’s own nucleocytoplasmic shuttling is regulated by interactions with importin-α isoforms, a process that is sensitive to phosphorylation at Ser58 and is critical for its participation in both CRM1-dependent and -independent export pathways (e.g., β-catenin and Smad proteins)."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "7"}]}, {"type": "t", "text": "\n"}]}, {"type": "t", "text": "\n\n"}, {"type": "p", "children": [{"type": "t", "text": "\nIn the context of disease, alterations in RanBP3 function have significant cellular consequences. In melanoma cells, for example, downregulation of RanBP3 leads to nuclear retention of extracellular signal-regulated kinase (ERK), which reactivates tumor-suppressive pathways such as the TGF‑β–Smad2/3–p21^Cip1 axis and promotes apoptosis, suggesting that abnormal RanBP3 activity contributes to oncogenic signaling."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "8"}]}, {"type": "t", "text": " Additionally, its expression in human testes and preferential localization in spermatogonia and spermatocytes indicate a role in spermatogenesis, with decreased levels correlating with disorders such as maturation arrest and Sertoli cell-only syndrome, potentially impacting male fertility."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "9"}]}, {"type": "t", "text": "\n"}]}, {"type": "rg", "children": [{"type": "r", "ref": 1, "children": [{"type": "t", "text": "Fangyan Dai, Xia Lin, Chenbei Chang, et al. 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