5-Ethynylcytidine as a new agent for detecting RNA synthesis in live cells by "click" chemistry.

Detection of RNA synthesis in cells to measure the rate of total transcription is an important experimental technique. To screen the best nucleoside analogue for labeling RNA synthesis, a series of alkyne-modified nucleoside analogues, including 5-ethynylcytidine (EC) and 8-ethynyladenosine (EA), were successfully synthesized by the Sonogashira coupling reaction. The synthesis of RNA or DNA was assayed based on the biosynthetic incorporation of these analogues into newly transcribed RNA or replicating DNA. Analogue-labeled cellular RNA or DNA was detected quickly and with high sensitivity via "click" chemistry with fluorescent azides, followed by fluorescence microscopic imaging. The results showed that EC was efficiently incorporated into RNA, but not into DNA, in seven cell lines, as also previously shown for 5-ethynyluridine (EU). Moreover, EC was able to assay transcription rates of various tissues in animals and the rate of metabolism of EC was much faster than that of EU.

MicroRNA-192 targeting retinoblastoma 1 inhibits cell proliferation and induces cell apoptosis in lung cancer cells.

microRNAs play an important roles in cell growth, differentiation, proliferation and apoptosis. They can function either as tumor suppressors or oncogenes. We found that the overexpression of miR-192 inhibited cell proliferation in A549, H460 and 95D cells, and inhibited tumorigenesis in a nude mouse model. Both caspase-7 and the PARP protein were activated by the overexpression of miR-192, thus suggesting that miR-192 induces cell apoptosis through the caspase pathway. Further studies showed that retinoblastoma 1 (RB1) is a direct target of miR-192. Over-expression of miR-192 decreased RB1 mRNA and protein levels and repressed RB1-3'-UTR reporter activity. Knockdown of RB1 using siRNA resulted in a similar cell morphology as that observed for overexpression of miR-192. Additionally, RB1-siRNA treatment inhibited cell proliferation and induced cell apoptosis in lung cancer cells. Analysis of miRNA expression in clinical samples showed that miR-192 is significantly downregulated in lung cancer tissues compared to adjacent non-cancerous lung tissues. In conclusion, our results demonstrate that miR-192 is a tumor suppressor that can target the RB1 gene to inhibit cell proliferation and induce cell apoptosis in lung cancer cells. Furthermore, miR-192 was expressed at low levels in lung cancer samples, indicating that it might be a promising therapeutic target for lung cancer treatment.

5-Ethynyl-2'-deoxycytidine as a new agent for DNA labeling: detection of proliferating cells.

The labeling of newly synthesized DNA in cells to identify cell proliferation is an important experimental technique. The most accurate methods incorporate [(3)H]thymidine or 5-bromo-2'-deoxyruidine (BrdU) into dividing cells during S phase, which is subsequently detected by autoradiography or immunohistochemistry, directly measuring the newly synthesized DNA. Recently, a novel method was developed to detect DNA synthesis in proliferating cells based on a novel thymidine analog, 5-ethynyl-2'-deoxyuridine (EdU). EdU is incorporated into DNA and subsequently detected with a fluorescent azide via "click" chemistry. This novel technique is highly sensitive and does not require DNA denaturation. However, it was also found that EdU exhibits time-dependent inhibition effects on cell growth. Therefore, here we report a novel deoxycytidine analog, 5-ethynyl-2'-deoxycytidine (EdC), that can be used to detect DNA synthesis in vitro and in vivo at a similar sensitivity level compared with EdU. Furthermore, the EdC-induced cytotoxicity is much less than that of EdU when combined with thymidine. This will be a potential application for the long-term detection of proliferating cells.