Prostate cancer sheds the αvβ3 integrin in vivo through exosomes

The alpha v beta 3 integrin has been shown to promote aggressive phenotypes in many types of cancers, including prostate cancer. We show that GFP-labeled alpha v beta 3 derived from cancer cells circulates in the blood and is detected in distant lesions in NOD scid gamma (NSG) mice. We, therefore, hypothesized that alpha v beta 3 travels through exosomes and tested its levels in pools of vesicles, which we designate extracellular vesicles highly enriched in exosomes (ExVs), and in exosomes isolated from the plasma of prostate cancer patients. Here, we show that the alpha v beta 3 integrin is found in patient blood exosomes purified by sucrose or iodixanol density gradients. In addition, we provide evidence that the alpha v beta 3 integrin is transferred through ExVs isolated from prostate cancer patient plasma to beta 3-negative recipient cells. We also demonstrate the intracellular localization of beta 3-GFP transferred via cancer cell-derived ExVs. We show that the ExVs present in plasma from prostate cancer patients contain higher levels of alpha v beta 3 and CD9 as compared to plasma ExVs from age-matched subjects who are not affected by cancer. Furthermore, using PSMA antibody-bead mediated immunocapture, we show that the alpha v beta 3 integrin is expressed in a subset of exosomes characterized by PSMA, CD9, CD63, and an epithelial-specific marker, Trop-2. Finally, we present evidence that the levels of alpha v beta 3, CD63, and CD9 remain unaltered in ExVs isolated from the blood of prostate cancer patients treated with enzalutamide. Our results suggest that detecting exosomal alpha v beta 3 integrin in prostate cancer patients could be a clinically useful and non-invasive biomarker to follow prostate cancer progression. Moreover, the ability of alpha v beta 3 integrin to be transferred from ExVs to recipient cells provides a strong rationale for further investigating the role of alpha v beta 3 integrin in the pathogenesis of prostate cancer and as a potential therapeutic target. (C) 2018 Elsevier B.V. All rights reserved.