The multiple functions of miR-574-5p in the neuroblastoma tumor microenvironment

Neuroblastoma is the most common extracranial solid tumor in childhood and arises from neural crest cells of the developing sympathetic nervous system. Prostaglandin E₂ (PGE₂) has been identified as a key pro-inflammatory mediator of the tumor microenvironment (TME) that promotes neuroblastoma progression. We report that the interaction between the microRNA miR-574-5p and CUG-binding protein 1 (CUGBP1) induces the expression of microsomal prostaglandin E₂ synthase 1 (mPGES-1) in neuroblastoma cells, which contributes to PGE₂ biosynthesis. PGE₂ in turn specifically induces the sorting of miR-574-5p into small extracellular vesicles (sEV) in neuroblastoma cell lines. sEV are one of the major players in intercellular communication in the TME. We found that sEV-derived miR-574-5p has a paracrine function in neuroblastoma. It acts as a direct Toll-like receptor 7/8 (TLR7/8) ligand and induces α-smooth muscle actin (α-SMA) expression in fibroblasts, contributing to fibroblast differentiation. This is particularly noteworthy as it has an opposite function to that in the TME of lung carcinoma, another PGE₂ dependent tumor type. Here, sEV-derived miR-574-5p has an autokrine function that inhibits PGE₂ biosynthesis in lung cancer cells. We report that the tetraspanin composition on the surface of sEV is associated with the function of sEV-derived miR-574-5p. This suggests that the vesicles do not only transport miRs, but also appear to influence their mode of action.