Tumor‐derived exosomal BCYRN1 activates WNT5A/VEGF‐C/VEGFR3 feedforward loop to drive lymphatic metastasis of bladder cancer

BACKGROUND: Patients with lymph node (LN) metastatic bladder cancer (BCa) present with extremely poor prognosis. BCa‐derived exosomes function as crucial bioactive cargo carriers to mediate the signal transduction in tumor microenvironment triggering tumor metastasis. However, the mechanisms underlying exosome‐mediated LN metastasis in BCa are unclear. METHODS: We conducted the high‐throughput sequencing to explore the expression profile of long noncoding RNA (lncRNA) in urinary exosomes (urinary‐EXO) from patients with BCa and further evaluated the clinical relevance of exosomal lncRNA BCYRN1 in a larger 210‐case cohort. The functional role of exosomal BCYRN1 was evaluated through the migration and tube formation assays in vitro and the footpad‐popliteal LN metastasis model in vivo. RNA pull‐down assays, luciferase assays, and actinomycin assays were conducted to detect the regulatory mechanism of exosomal BCYRN1. RESULTS: LncRNA BCYRN1 was substantially upregulated in urinary‐EXO from patients with BCa, and associated with the LN metastasis of BCa. We demonstrated that exosomal BCYRN1 markedly promoted tube formation and migration of human lymphatic endothelial cells (HLECs) in vitro and lymphangiogenesis and LN metastasis of BCa in vivo. Mechanistically, BCYRN1 epigenetically upregulated WNT5A expression by inducing hnRNPA1‐associated H3K4 trimethylation in WNT5A promoter, which activated Wnt/β‐catenin signaling to facilitate the secretion of VEGF‐C in BCa. Moreover, exosomal BCYRN1 was transmitted to HLECs to stabilize the VEGFR3 mRNA and thus formed an hnRNPA1/WNT5A/VEGFR3 feedforward regulatory loop, ultimately promoting the lymphatic metastasis of BCa. Importantly, blocking VEGFR3 with specific inhibitor, SAR131675 significantly impaired exosomal BCYRN1‐induced the LN metastasis in vivo. Clinically, exosomal BCYRN1 was positively associated with the shorter survival of BCa patients and identified as a poor prognostic factor of patients. CONCLUSION: Our results uncover a novel mechanism by which exosomal BCYRN1 synergistically enhances VEGF‐C/VEGFR3 signaling‐induced lymphatic metastasis of BCa, indicating that BCYRN1 may serve as an encouraging therapeutic target for patients with BCa.