Cavin‐1/PTRF alters prostate cancer cell‐derived extracellular vesicle content and internalization to attenuate extracellular vesicle‐mediated osteoclastogenesis and osteoblast proliferation

<jats:sec><jats:title>Background</jats:title><jats:p>Tumour‐derived extracellular vesicles (EVs) play a role in tumour progression; however, the spectrum of molecular mechanisms regulating EV secretion and cargo selection remain to be fully elucidated. We have reported that cavin‐1 expression in prostate cancer PC3 cells reduced the abundance of a subset of EV proteins, concomitant with reduced xenograft tumour growth and metastasis.</jats:p></jats:sec><jats:sec><jats:title>Methods</jats:title><jats:p>We examined the functional outcomes and mechanisms of cavin‐1 expression on PC3‐derived EVs (PC3‐EVs).</jats:p></jats:sec><jats:sec><jats:title>Results</jats:title><jats:p>PC3‐EVs were internalized by osteoclast precursor RAW264.7 cells and primary human osteoblasts (hOBs) <jats:italic>in vitro</jats:italic>, stimulating osteoclastogenesis 37‐fold and hOB proliferation 1.5‐fold, respectively. Strikingly, EVs derived from cavin‐1‐expressing PC3 cells (cavin‐1‐PC3‐EVs) failed to induce multinucleate osteoblasts or hOB proliferation. Cavin‐1 was not detected in EVs, indicating an indirect mechanism of action. EV morphology, size and quantity were also not affected by cavin‐1 expression, suggesting that cavin‐1 modulated EV cargo recruitment rather than release. While cavin‐1‐EVs had no osteoclastogenic function, they were internalized by RAW264.7 cells but at a reduced efficiency compared to control EVs. EV surface proteins are required for internalization of PC3‐EVs by RAW264.7 cells, as proteinase K treatment abolished uptake of both control and cavin‐1‐PC3‐EVs. Removal of sialic acid modifications by neuraminidase treatment increased the amount of control PC3‐EVs internalized by RAW264.7 cells, without affecting cavin‐1‐PC3‐EVs. This suggests that cavin‐1 expression altered the glycosylation modifications on PC3‐EV surface. Finally, cavin‐1 expression did not affect EV <jats:italic>in vivo</jats:italic> tissue targeting as both control and cavin‐1‐PC3‐EVs were predominantly retained in the lung and bone 24 hours after injection into mice.</jats:p></jats:sec><jats:sec><jats:title>Discussion</jats:title><jats:p>Taken together, our results reveal a novel pathway for EV cargo sorting, and highlight the potential of utilizing cavin‐1‐mediated pathways to attenuate metastatic prostate cancer.</jats:p></jats:sec>