Lentivirus-mediated long-term overexpression of specific microRNA in mammalian cells

The establishment of a method that would overexpress or suppress of specific microRNA activity is essential for the functional analysis of these molecules and for the development of miRNA therapeutic applications. There already exist excellent ways to inhibit miRNA function in vitro and in vivo by overexpressing miRNA target sequences, which include miRNA decoys, sponges, or antagomirs that are complementary to an miRNA seed region. Conversely, no methods to induce stable gain-of-function phenotypes for specific miRNAs have, as yet, been reported. Furthermore, the discovery of complementary miRNA pairs raises suspicion regarding the existing methods used for miRNA overexpression. In our study, we will study whether the traditional methods for miRNA overexpression can be used for specific miRNA overexpression while complementary miRNA pairs exist. In addition, we test various miRNA-expression cassettes that were designed to efficiently overexpress specific miRNA through the shRNA lentivirus expression system. We report the optimal conditions that were established for the design of such miRNA-expression cassettes. We finally demonstrate that the miRNA-expression cassettes achieve efficient and long-term overexpression of specific miRNAs. Meanwhile, our results also support the notion that miRNA-miRNA interactions are implicated in potential, mutual regulatory patterns and beyond the seed sequence of miRNA, extensive pairing interactions between a miRNA and its target also lead to target-directed miRNA degradation. Our results indicate that our method offers a simple and efficient means to over-express the specific miRNA with long-term which will be very useful for future studies in miRNA biology, as well as contributed to the development of miRNA-based therapy for clinical applications.