{"type": "root", "children": [{"type": "p", "children": [{"type": "t", "text": "\nRab27B is a member of the Rab family of small GTPases that regulates vesicle trafficking and exosome secretion, thereby orchestrating the delivery of a wide variety of cargoes in distinct cell types. In several studies, Rab27B has been shown to control the release of tumor‐suppressive or proinvasive microRNAs (e.g., miR23b and miR921) via exosomes, as well as to mediate the export of regulatory RNAs in endothelial cells, contribute to acid secretion in gastric parietal cells, and even participate in intracellular transport during spermiogenesis."}, {"type": "fg", "children": [{"type": "fg_fs", "start_ref": "1", "end_ref": "5"}]}, {"type": "t", "text": "\n"}]}, {"type": "t", "text": "\n\n"}, {"type": "p", "children": [{"type": "t", "text": "\nIn the context of cancer, Rab27B exhibits multifaceted roles that vary according to tumor type. In estrogen receptor–positive breast cancer, studies have demonstrated that increased Rab27B expression promotes cell cycle progression, proliferation, invasiveness, and metastasis by targeting the peripheral distribution of secretory vesicles containing proinvasive regulators such as heat‐shock protein 90α and matrix metalloprotease‐2 activators. In osteosarcoma, Rab27B is directly targeted by specific microRNAs, and its downregulation correlates with a suppression of metastatic behaviors. By contrast, in colorectal cancer, positive expression of Rab27B has been associated with less aggressive phenotypes and better differentiation, while in pancreatic cancer, non–small cell lung cancer, high‐grade glioma, and renal cell carcinoma its aberrant expression is linked to a more aggressive biological behavior and poorer prognosis. Furthermore, in liver cancer, the upregulation of Rab27B contributes to chemoresistance by enhancing exosome secretion, and in bladder carcinoma its activity supports invasive growth."}, {"type": "fg", "children": [{"type": "fg_fs", "start_ref": "6", "end_ref": "16"}, {"type": "fg_f", "ref": "1"}]}, {"type": "t", "text": "\n"}]}, {"type": "t", "text": "\n\n"}, {"type": "p", "children": [{"type": "t", "text": "\nBeyond cancer, Rab27B functions in diverse physiological and pathophysiological settings. It can functionally compensate for Rab27A in specialized cells, as observed in models of Griscelli syndrome. In the reproductive system, hypoxia‐inducible factor–regulated Rab27B mediates vesicle trafficking events that promote luminal epithelial remodeling and vascular network formation during embryo implantation. In neurological contexts, Rab27B contributes to the release and clearance of α‑synuclein, thereby influencing autophagic flux and the progression of synucleinopathies, while in the urinary tract Rab27B expression is upregulated by NRF2 to facilitate the exocytosis of vesicles that aid in bacterial expulsion."}, {"type": "fg", "children": [{"type": "fg_fs", "start_ref": "17", "end_ref": "20"}]}, {"type": "t", "text": "\n"}]}, {"type": "rg", "children": [{"type": "r", "ref": 1, "children": [{"type": "t", "text": "Marie Stampe Ostenfeld, Dennis K Jeppesen, Jens R Laurberg, et al. 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