Exosomes in prostate cancer: putting together the pieces of a puzzle

Abstract

Exosomes have been shown to act as mediators for cell to cell communication and as a potential source of biomarkers for many diseases, including prostate cancer. Exosomes are nanosized vesicles secreted by cells and consist of proteins normally found in multivesicular bodies, RNA, DNA and lipids. As a potential source of biomarkers, exosomes have attracted considerable attention, as their protein content resembles that of their cells of origin, even though it is noted that the proteins, miRNAs and lipids found in the exosomes are not a reflective stoichiometric sampling of the contents from the parent cells. While the biogenesis of exosomes in dendritic cells and platelets has been extensively characterized, much less is known about the biogenesis of exosomes in cancer cells. An understanding of the processes involved in prostate cancer will help to further elucidate the role of exosomes and other extracellular vesicles in prostate cancer progression and metastasis. There are few methodologies available for general isolation of exosomes, however validation of those methodologies is necessary to study the role of exosomal-derived biomarkers in various diseases. In this review, we discuss "exosomes" as a member of the family of extracellular vesicles and their potential to provide candidate biomarkers for prostate cancer.

Figure 1

Schematic representation of exosome biogenesis. Extracellular molecules are endocytosed through various endocytic pathways such as clathrin mediated endocytosis or lipid rafts, and trafficked to early endosomes. The cargo and molecules are then recycled back to the plasma membrane; transferred to lysosome for degradation or secreted through exosome pathways. Evidence shows that the biogenesis of exosomes is mediated by intraluminal membrane budding at the Multi Vesicular Bodies (MVB) which are formed through an endosome maturation process. Both MVB and lysosome have been shown to be capable of fusing with the plasma membrane and releasing their contents, and some studies have highlighted the ability of MVB to fuse with the lysosome [1,73,74]. Classical soluble protein secretory pathways from Trans Golgi network (TGN) are also indicated. ER: endoplasmic reticulum.