Seminal prostasomes inhibit the angiogenesis activity of rat aortic rings

Communication between cells: exosomes as a delivery system in prostate cancer

Despite the considerable efforts in screening and diagnostic protocols, prostate cancer still represents the second leading cause of cancer-related death in men. Many patients with localized disease and low risk of recurrence have a favourable outcome. In a substantial proportion of patients, however, the disease progresses and becomes aggressive. The mechanisms that promote prostate cancer progression remain still debated. Many findings point to the role of cross-communication between prostate tumor cells and their surrounding microenvironment during the disease progression. Such a connection fosters survival, proliferation, angiogenesis, metastatic spreading and drug-resistance of prostate cancer. Recent years have seen a profound interest in understanding the way by which prostate cancer cells communicate with the surrounding cells in the microenvironment. In this regard, direct cell-to-cell contacts and soluble factors have been identified. Increasing evidence indicates that PC cells communicate with the surrounding cells through the release of extracellular vesicles, mainly the exosomes. By directly acting in stromal or prostate cancer epithelial cells, exosomes represent a critical intercellular communication system. By querying the public database (https://pubmed.ncbi.nlm.nih.gov) for the past 10 years, we have found more than four hundred papers. Among them, we have extrapolated the most relevant about the role of exosomes in prostate cancer malignancy and progression. Emerging data concerning the use of these vesicles in diagnostic management and therapeutic guidance of PC patients are also presented.

Extracellular Vesicles in Prostate Cancer Carcinogenesis, Diagnosis, and Management

Extracellular vesicles (EVs), especially exosomes, are now well recognized as major ways by which cancer cells interact with each other and stromal cells. The meaningful messages transmitted by the EVs are carried by all components of the EVs, i.e., the membrane lipids and the cargo (DNAs, RNAs, microRNAs, long non-coding RNAs, proteins). They are clearly part of the armed arsenal by which cancer cells obtain and share more and more advantages to grow and conquer new spaces. Identification of these messages offers a significant opportunity to better understand how a cancer occurs and then develops both locally and distantly. But it also provides a powerful means by which cancer progression can be detected and monitored. In the last few years, significant research efforts have been made to precisely identify how the EV trafficking is modified in cancer cells as compared to normal cells and how this trafficking is altered during cancer progression. Prostate cancer has not escaped this trend. The aim of this review is to describe the results obtained when assessing the meaningful content of prostate cancer- and stromal-derived EVs in terms of a better comprehension of the cellular and molecular mechanisms underlying prostate cancer occurrence and development. This review also deals with the use of EVs as powerful tools to diagnose non-indolent prostate cancer as early as possible and to accurately define, in a personalized approach, its present and potential aggressiveness, its response to treatment (androgen deprivation, chemotherapy, radiation, surgery), and the overall patients’ prognosis.

Prostasomes: extracellular vesicles from the prostate

The term 'prostasomes' is generally used to classify the extracellular vesicles (EVs) released into prostatic fluid by prostate epithelial cells. However, other epithelia within the male reproductive tract also release EVs that mix with 'true' prostasomes during semen emission or ejaculation. Prostasomes have been proposed to regulate the timing of sperm cell capacitation and induction of the acrosome reaction, as well as to stimulate sperm motility where all three are prerequisite processes for spermatozoa to attain fertilising capacity. Other proposed functions of prostasomes include interfering with the destruction of spermatozoa by immune cells within the female reproductive tract. On the other hand, it is unclear whether the distinct presumed functions are performed collectively by a single type of prostasome or by separate distinct sub-populations of EVs. Moreover, the exact molecular mechanisms through which prostasomes exert their functions have not been fully resolved. Besides their physiological functions, prostasomes produced by prostate tumour cells have been suggested to support prostate cancer spread development, and prostasomes in peripheral blood plasma may prove to be valuable biomarkers for prostate cancer.

Expression of tissue factor and tissue factor pathway inhibitor in microparticles and subcellular fractions of normal and malignant prostate cell lines

The association between cancer and thrombogenesis has been recognized since 1865, and tissue factor (TF) is important at various stages in the natural history of the disease. It is involved in cancer angiogenesis, growth and metastasis. TF pathway inhibitor (TFPI), being the major physiological regulator of the TF-dependent coagulation pathway, is also important in establishing net procoagulant potential. In this study, we determine TF and TFPI levels in three prostate epithelial cell lines, one of normal and two of malignant origin. Cells were grown in standard maintenance conditions and harvested at more than 90% confluence. These were fractionated into cytosol, membrane and nuclei for analysis. Microparticles secreted into the culture medium were also analysed. TF and TFPI levels were determined using an ELISA. TF expression in these cells was also visualized using immunocytochemistry. There was absence of TF and TFPI in nuclei of all cell lines. TF expression was higher in subcellular fractions and microparticles of normal prostate cells than cancer cells. In contrast, levels of TFPI (structurally resembling a secreted, rather than transmembrane protein) in microparticles of normal prostate cells were much lower than tumour cells. In conclusion, the activity of prostate cancer cells themselves is unlikely to be the source of hypercoagulability in patients, but might precipitate chains of events that would produce such an effect.

Mapping pro- and antiangiogenic factors on the surface of prostasomes of normal and malignant cell origin

BACKGROUND

Angiogenesis is the formation of new blood vessels by capillary sprouting from pre-existing vessels. Tumor growth is angiogenesis-dependent and the formation of new blood vessels is associated with the increased expression of angiogenic factors. Prostasomes are secretory granules produced, stored and released by the glandular epithelial cells of the prostate. We investigated the expression of selected angiogenic and anti-angiogenic factors on the surface of prostasomes of different origins as well as the direct effect of prostasomes on angiogenesis.

METHODS

VEGF, endothelin-1, endostatin, and thrombospondin-1 were determined on prostasomes from seminal fluid and human prostate cancer cell lines (DU145,PC-3,LNCaP) using different immunochemical techniques. Human dermal microvascular endothelial cells were incubated with seminal and DU145 cell-prostasomes and with radioactive thymidine. The effect of prostasomes on angiogenesis was judged by measuring the uptake of labeled thymidine. The presence of any deleterious effects of prostasomes on the endothelial cells was investigated using thymidine assay and confocal laser microscopy.

RESULTS

VEGF and endothelin-1 were determined on malignant cell-prostasomes (no difference between cell lines) but not determined on seminal prostasomes. The same applies for the expression of endostatin but with much higher expression on malignant cell-prostasomes with obvious differences between them. Seminal and DU145 cell-prostasomes were found to have anti-angiogenic effect which was more expressed by DU145 cell-prostasomes. No deleterious effect of prostasomes on endothelial function was detected using either thymidine assay or microscopy.

CONCLUSIONS

Prostasomes contain pro- and anti-angiogenic factors that function to counteract each other unless the impact from one side exceeds the other to bring about dysequilibrium.

Cholesterol regulates prostasome release from secretory lysosomes in PC-3 human prostate cancer cells

Prostasomes are vesicles secreted by epithelial cells of the prostate gland. However, little is known about the mechanism and the regulation of prostasome secretion. Since endocytic organelles may be involved in prostasome release, PC-3-derived prostasomes were investigated by Western blot analysis for the presence of marker proteins normally associated with these organelles. Prostasomes secreted by PC-3 cells contain clathrin, Tsg101, Hrs, Rab11, Rab5, LAMP-1, LAMP-2, LAMP-3/CD63, and annexin II. Moreover, electron microscopy of PC-3 cells revealed the presence of characteristic multivesicular body-like secretory lysosomes containing vesicles with the same size-distribution as released prostasomes. Ultrastructural immunogold labelling showed that LAMP-1, LAMP-2 and LAMP-3/CD63 were associated with these vesicles. In addition, we have investigated whether cholesterol plays a role in prostasome release by the human prostate cancer cell line PC-3. Interestingly, prostasome release was significantly increased when the cholesterol levels of PC-3 cells were reduced by the cholesterol-sequestering agent methyl-beta-cyclodextrin (MBCD), or by treatment with lovastatin and mevalonate. In conclusion, these studies indicate that cholesterol plays an important role in the release of prostasomes by the human prostate cancer PC-3 cells, and suggest that prostasomes may be released after fusion of secretory lysosomes with the plasma membrane.