Functional prostate-specific membrane antigen is enriched in exosomes from prostate cancer cells

Abstract

Developing simple and effective approaches to detect tumor markers will be critical for early diagnosis or prognostic evaluation of prostate cancer treatment. Prostate-specific membrane antigen (PSMA) has been validated as an important tumor marker for prostate cancer progression including angiogenesis and metastasis. As a type II membrane protein, PSMA can be constitutively internalized from the cell surface into endosomes. Early endosomes can fuse with multivesicular bodies (MVB) to form and secrete exosomes (40–100 nm) into the extracellular environment. Herein, we tested whether some of the endosomal PSMA could be transferred to exosomes as an extracellular resource for PSMA. Using PSMA-positive LNCaP cells, the secreted exosomes were collected and isolated from the cultured media. The vesicular structures of exosomes were identified by electron microscopy, and exosomal marker protein CD9 and tumor susceptibility gene (TSG 101) were confirmed by western blot analysis. Our present data demonstrate that PSMA can be enriched in exosomes, exhibiting a higher content of glycosylation and partial proteolysis in comparison to cellular PSMA. An in vitro enzyme assay further confirmed that exosomal PSMA retains functional enzymatic activity. Therefore, our data may suggest a new role for PSMA in prostate cancer progression, and provide opportunities for developing non-invasive approaches for diagnosis or prognosis of prostate cancer.

Tumor-Derived Exosomal Long Noncoding RNAs as Promising Diagnostic Biomarkers for Prostate Cancer

“…Our results show that the dual-antibody capture system can effectively capture tumor-derived exosomes from total exosomes. EpCAM and PSMA are marker proteins that are frequently overexpressed in PCa exosomes [30, 44]. EpCAM is a ubiquitous cancer marker expressed exclusively in epithelial cells and epithelium-originated tumors, and it has been used as a specific antibody to isolate tumor-derived exosomes to avoid the interference of exosomes from nonepithelial tissues [44, 45].…”

“…EpCAM is a ubiquitous cancer marker expressed exclusively in epithelial cells and epithelium-originated tumors, and it has been used as a specific antibody to isolate tumor-derived exosomes to avoid the interference of exosomes from nonepithelial tissues [44, 45]. PSMA is generally regarded as a biomarker enriched in exosomes from PCa cells, and its levels were significantly increased in plasma-derived exosomes from PCa patients compared with healthy individuals [30, 40]. Recent studies suggest that the expression level of PSMA is even higher than EpCAM in exosomes from PCa cell lines [40].…”

“…They are released into the extracellular space upon fusion of multivesicular bodies with the plasma membrane [20, 21] and play important roles as cellular messengers to trigger diverse physiological and pathological responses and achieve cross-talk without direct contact with one another [22]. They have been found in a variety of biological fluids, such as blood [19], urine [23], saliva [24], milk [25] and bronchoalveolar lavage fluid [26] and are secreted by platelet [27], normal [28, 29] and tumor cells [30, 31]. Analyzing exosomes in the peripheral blood can therefore provide important information on the characteristics of parental cancer cells.…”

The emerging role of extracellular vesicles as biomarkers for urogenital cancers

“…For instance, several proteomic studies have revealed the presence of urinary extracellular vesicles that contain candidate proteins unique to cancer types that include a broad range of urogenital diseases. 25,26,29,102,110,112,147,157,162 Such tumour-specific vesicles are easily captured from urine using established isolation procedures, which enables repeated tissue sampling.…”

Therapeutic and diagnostic applications of extracellular vesicles

“…), EVs derived from cancerous cells have shown to carry a panel of known (e.g. CEA, GP100, HER2, melan-A, PSMA) [32,195] and likely to date unknown tumor antigens. This is not only of interest from a diagnostic point of view but also makes tumor-derived EVs, which have shown to outperform free antigens [193,196] and whole tumor lysate [197,198], an attractive candidate to evaluate as a cell-free vaccine.…”