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.

Small extracellular vesicle-derived miR-574-5p regulates PGE2-biosynthesis via TLR7/8 in lung cancer.

Intercellular communication plays an essential role in lung cancer (LC). One of the major players in cell-cell-communication is small extracellular vesicles (sEV). SEV trigger various biological responses by transporting cellular cargo to target cells. One essential sEV component are microRNAs (miRs), whose transport has recently attracted increasing research interest. We report that prostaglandin E2 (PGE2 ), a key inflammatory lipid mediator, specifically induces the sorting of miR-574-5p in sEV of A549 and 2106T cells. We found that sEV-derived miR-574-5p activates Toll-like receptors (TLR) 7/8, thereby decreasing PGE2 -levels. In contrast, intracellular miR-574-5p induces PGE2 -biosynthesis. Consequently, the combination of intracellular and sEV-derived miR-574-5p controls PGE2 -levels via a feedback loop. This was only observed in adeno- but not in squamous cell carcinoma, indicating a cell-specific response to sEV-derived miRs, which might be due to unique tetraspanin compositions. Hence, we describe a novel function of miR-574-5p unique to adenocarcinoma. Intracellular miR-574-5p induces PGE2 and thus the secretion of sEV-derived miR-574-5p, which in turn decreases PGE2 -biosynthesis in recipient cells.