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.