ABSTRACT
Comprehensive analyses of gene expression have been carried out by the development of microarrays and deep sequencers. However, it is difficult to obtain comprehensive information on gene expression from a small amount of ribonucleic acid (RNA). Therefore, we investigated the reproducibility and application of T7 RNA polymerase-mediated transcription, adaptor ligation and polymerase chain reaction (PCR) amplification, followed by T7 transcription (TALPAT), an efficient method for amplifying poly (A)-positive RNA, such as messenger RNA (mRNA). When amplified complementary RNA (cRNA) was electrophoresed, a large number of amplified cRNA was detected in the size of 0.2-0.5 kb. This indicates that the region up to 0.2-0.5 kb from the 3' end of the original mRNA was amplified by the TALPAT method. Seven housekeeping genes, glyceraldehyde-3-phosphate dehydrogenase (GAPDH), hydroxymethylbilane synthase (HMBS), hypoxanthine phosphoribosyltransferase (HPRT1), ribosomal protein L13a (RPL13A), succinate dehydrogenase complex (SDHA), TATA box-binding protein (TBP) and ubiquitin C (UBC), showed high reproducibility (square of the correlation coefficient, R2=0.9954), according to scatter plots of Ct values obtained in the real-time PCR analysis of amplified cRNA. In addition, relative expression ratios of amplified cRNA of the seven housekeeping genes were approximately equal to the ratio of the original RNA solution. Furthermore, cRNA was amplified from 20 pg total RNA. In the present study, we confirmed the characteristics of mRNA amplification using the TALPAT method. This method may be applicable to mRNA and poly (A)-positive non-coding RNA amplification, using a small amount of RNA from single, laser-captured and sorted cells, as well as exosomes from serum, urine and body fluids.
ABSTRACT
Exosomes are microvesicles that are released from various cells into the extracellular space. It has been reported that the components within exosomes vary according to the type of secreted cell. In the present study, we investigated the tetraspanin family proteins CD63, CD9 and CD81 as useful collection markers of exosomes derived from the three colorectal cancer (CRC) cell lines HCT-15, SW480 and WiDr. In addition, we aimed to detect the mRNAs, microRNAs and natural antisense RNAs within the exosomes secreted from the three CRC cell lines. Furthermore, we examined whether exosomes containing their RNAs were transferred into the hepatoma cell line HepG2 and lung cancer cell line A549. CD81 was detected in exosomes secreted from the three CRC cell lines. This result indicates that CD81 can be a collection marker of exosomes derived from the three CRC cell lines. When the RNA species within exosomes derived from the three CRC cell lines were examined, the mRNAs of housekeeping genes such as ACTB and GAPDH, the microRNAs such as miR-21, miR-192 and miR-221, and the natural antisense RNAs of LRRC24, MDM2 and CDKN1A genes, were detected. We discovered their natural antisense RNAs within exosomes for the first time in the present study. Furthermore, PKH67-labeled exosomes derived from the CRC cell lines were taken up into HepG2 and A549 cells. These findings indicate that the intracellular RNAs enclosed within exosomes are secreted to the outside, and exosomes derived from the CRC cell lines are transferred into HepG2 and A549 cells. In conclusion, we reveal that exosomes derived from the CRC cell lines contain mRNAs, microRNAs and natural antisense RNAs, and can be delivered into HepG2 and A549 cells. These findings indicate that exosomal RNAs can shuttle between cells, and may be involved in the regulation of gene expression in recipient cells.
