Downregulation of Exosomal miR-26a-5p Promotes Lymphangiogenesis and Lymphatic Metastasis in Endometrial Cancer

Abstract Background: Endometrial cancer (EC) patients with lymph node (LN) metastasis have poor prognosis. However, the potential biomarkers that predict LN metastasis and the molecular mechanism of tumor-induced peritumoral lymphangiogenesis have not been well explored. Cancer-secreted exosomal miRNAs are emerging mediators of cell-cell communication in the tumor environment.Methods: Exosomes were isolated with a differential centrifugation method and confirmed by Transmission electron microscopy, NanoSight analysis, and Western blot. MicroRNA (miRNA) sequencing of exosomes derived from EC patients and healthy donors were performed. FISH and qRT-PCR were used to detect the indicated miRNA expression. Exosomal miRNA transferred to cells were confirmed by immunofluorescence and confocal microscope. siRNA and plasmid transfections as well as viral infection were performed to manipulate gene expression. A series of in vitro and in vivo phenotype experiments (tube formation, migration, and popliteal LN metastasis model) were performed to investigate the role of indicated miRNA in EC. RNA sequencing was used to select the underlying transcription factor, and luciferase activity assay and chromatin immunoprecipitation were performed to elucidate the molecular mechanisms. Results: Our data showed that serum exosomal miR-26a-5p was significantly reduced in EC patients, and its level was positively associated with LN metastasis. Loss of miR-26a-5p promoted the migratory and invasive abilities of EC cells, and miR-26a-5p could be transferred from EC cells-secreted exosomes into human lymphatic endothelial cell (HLEC). Mechanistically, miR-26a-5p could regulate LEF1/c-myc/VEGFA axis via binding to its direct downstream target lymphoid enhancer binding factor 1 (LEF1), consequently promoting HLEC tube formation and migration in vitro, facilitating lymphangiogenesis and LN metastasis in vivo. Re-expression and knockdown of LEF1 could respectively promote and rescue the effects induced by exosomal miR-26a-5p. Moreover, we demonstrated that transcriptional factor EB (TFEB) directly induced miR-26a-5p expression.Conclusions: Our results show that exosomal miR-26a-5p/LEF1/c-myc/VEGFA axis is dysregulated and plays a critical role in LN metastasis and exosomal miR-26a-5p may be used as a blood-based biomarker for EC patients with LN metastasis.