Hypoxic tumor-derived exosomal miR-21 induces cancer-associated fibroblast activation to promote head and neck squamous cell carcinoma metastasis

Background: Both microRNA-21-5p (miR-21) and the tumor microenvironment, including hypoxia and cancerassociated fibroblasts (CAFs), play a vital role in head and neck squamous cell carcinoma (HNSCC), but whether there is an interaction and the specific regulatory mechanism between them in the process of metastasis is still unclear. In this study, we aimed to elucidate the connection and regulatory mechanism of miR-21, hypoxia, and CAFs in HNSCC metastasis.Methods: The underlying mechanisms of hypoxia inducible factor 1 subunit alpha (HIF1a) regulating miR-21 transcription, promoting exosome secretion, CAFs activation, tumor invasion, and lymph node metastasis were determined through quantitative real-time PCR, immunoblotting, transwell, wound healing, immunofluorescence, ChIP, electron microscopy, nanoparticle tracking analysis, dual-luciferase reporter assay, co-culture model and xenografts experiments.Results: MiR-21 promoted the invasion and metastasis of HNSCC in vitro and in vivo, whereas HIF1a knockdown inhibited these processes. HIF1a upregulated transcription of miR-21 and promoted the release of exosomes from HNSCC cells. Exosomes derived from hypoxic tumor cells were rich in miR-21, which induced NFs activation towards CAFs by targeting YOD1. Knockdown the expression level of miR-21 in CAFs prevented lymph node metastasis in HNSCC.Conclusion: Hypoxic tumor cell-derived exosomal miR-21 might be a therapeutic target to prevent or delay HNSCC invasion and metastasis.