Exosomal particles secreted by prostate cancer cells are potent mRNA and protein vehicles for the interference of tumor and tumor environment

BackgroundRemodeling of the tumor environment and the modulation of tumor associated non-malignant cells are essential events in tumor progression. Exosomes are small membranous vesicles of 50-150nm in diameter, which are secreted into the extracellular space and supposedly serve as vehicles for signal and effector molecules to modulate adjacent target cells. We characterized the mRNA and protein composition as well as cellular functions of prostate cancer cell-derived exosomes. MethodsExosomes were prepared from prostate cancer cell culture supernatant by ultracentrifugation and subsequently characterized by dynamic light scattering and electron microscopy. Exosomal mRNA and protein composition were analyzed by DNA microarrays and gel electrophoresis coupled with mass spectrometry. Physiological effects of exosomes were studied by means of 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide and lactate dehydrogenase release cell assays. Using a SILAC approach, putative uptake of exosomal human proteins in canine cells and canine de novo synthesis of proteins specified by exosome-transferred human mRNA was analyzed in MDCK cells via mass spectrometry. ResultsPreparations of exosomes revealed typical cup shaped particles of 150nm in diameter. Analysis of mRNA and protein composition of exosomes exhibited a wide range of mRNA and protein species. Interestingly, the packaging of at least small proteins into exosomes was apparently unspecific, as shown with the example of two model proteins. In cell culture incubation experiments exosomal preparations of prostate cancer cells caused anti-proliferative effects. MS analysis revealed the uptake of exosomal human proteins into canine cells after 6hr of incubation. ConclusionsThe results reveal a distinct exosomal functionality in the modulation of the prostatic tumor adjacent environment. The multitude of translocated factors implies the induction of numerous effects in tumor-associated target cells, including impact on cellular growth. Prostate 76:409-424, 2016. (c) 2015 Wiley Periodicals, Inc.