Profiling of microRNAs in exosomes released from PC-3 prostate cancer cells

Exosomes are small extracellular vesicles released to the extracellular milieu through fusion of multivesicular bodies with the plasma membrane. These vesicles contain microRNAs and might therefore be vehicles transferring genetic information between cells. The aim of this study was to investigate whether there was a sorting of microRNAs into exosomes in the prostate cancer cell line PC-3. In addition, microRNAs in PC-3 cells and in the non-cancerous prostate cell line RWPE-1 were compared. Exosomes were isolated from the conditioned media from PC-3 cells by ultracentrifugation and inspected by electron microscopy. Total RNA was isolated and microRNAs were analyzed by microarray analysis and real time RT-PCR. MicroRNA microarray analysis revealed that the microRNA profile of PC-3 released exosomes was similar to the profile of the corresponding parent cells. Nevertheless, a sorting of certain microRNAs into exosomes was observed, and low number microRNAs (microRNAs with a low number in their name) were found to be underrepresented in these vesicles. Moreover, the miRNA profile of PC-3 cells resembled the miRNA profile of RWPE-1 cells, though some miRNAs were found to be differently expressed in these cell lines. These results show that exosomes from PC-3 cells, in agreement with previous reports from other cell types, contain microRNAs. Furthermore, this study supports the idea that there is a sorting of microRNAs into exosomes and adds a new perspective by pointing at the underrepresentation of low number miRNAs in PC-3 released exosomes.