Use of bicistronic vectors in combination with flow cytometry to screen for effective small interfering RNA target sequences

MicroRNA-92 regulates vascular smooth muscle cell function by targeting KLF4 during vascular restenosis and injury

MicroRNAs (miRNAs) contribute to multiple cellular processes in embryonic development and disorders. Several miRNAs are strongly associated with the progression of peripheral vascular disease. Recently, it was reported that miRNA (miR)-92 is one of the most upregulated miRNAs in vascular injury after intervention in the lower extremities; however, the function of miR-92 during proliferative vascular diseases remains unclear and the potential targets of miR-92 are poorly characterized. In this study, we investigated the expression of miR-92 in vitro and in vivo, and explored the associated underlying mechanism. qRT-PCR analysis showed that miR-92 expression was highly upregulated in patients with artery restenosis compared to those without restenosis. Platelet-derived growth factor (PDGF)-BB is regarded as a critical regulator of the phenotypic switch of VSMCs. miR-92 expression was significantly upregulated in PDGF-BB-stimulated VSMCs. Introducing an miR-92 mimic into VSMCs enhanced cell proliferation and migration, and induced S-phase arrest. The luciferase reporter assay revealed that KLF4 is a downstream target gene of miR-92. In vivo, miR-92 overexpression promoted neointimal formation, and thus resulted in a dramatic increase in intimal-medial area and thickness. These results reveal that miR-92 regulates VSMC function by directly targeting KLF4, which may be an important finding useful for the diagnosis and treatment of vascular restenosis and injury, arteriosclerosis, and other proliferative vascular diseases.

A novel siRNA validation system for functional screening of effective RNAi targets in mammalian cells and development of a derivative lentivirus delivery system

RNA interference technology is a widely used tool for the regulation of gene expression at the post-transcriptional level. One major challenge is to find the effective short interfering (si)RNA for target gene rapidly and easily, and then to deliver the siRNA into cells or tissues with high efficiency. Here, we designed a novel siRNA validation vector using a dual luciferase reporter system for the functional screening of effective RNAi targets in mammalian cells. Then, based on a siRNA expression cassette, we developed a derivative lentivirus delivery system to infect the appropriate cells or tissues for the efficient knockdown of target gene expression. Based on this system, we used human IRF7 gene, a key regulatory factor for the differentiation of monocytes to macrophages, as an example. We screened for the optimal siRNA, then packaged it into a lentiviral siRNA expression system. Then, monocytes were infected and we confirmed the knockdown of IRF7 expression could inhibit the differentiation of monocytes to macrophages. To validate our method further, we also screened and identified optimal siRNA for human TLR4 gene. In summary, we developed a novel siRNA validation system to identify optimal siRNA to target genes rapidly. In addition, the lentivirus system is an efficient tool for siRNA delivery for the further study of target gene function. Taken together, this represents an efficient and user-friendly strategy to validate and deliver siRNAs.

Cyclic AMP responsive element binding proteins are involved in 'emergency' granulopoiesis through the upregulation of CCAAT/enhancer binding protein β

In contrast to the definitive role of the transcription factor, CCAAT/Enhancer binding protein α (C/EBPα), in steady-state granulopoiesis, previous findings have suggested that granulopoiesis during emergency situations, such as infection, is dependent on C/EBPβ. In this study, a novel lentivirus-based reporter system was developed to elucidate the molecular switch required for C/EBPβ-dependency. The results demonstrated that two cyclic AMP responsive elements (CREs) in the proximal promoter region of C/EBPβ were involved in the positive regulation of C/EBPβ transcription during granulocyte-macrophage colony-stimulating factor (GM-CSF)–induced differentiation of bone marrow cells. In addition, the transcripts of CRE binding (CREB) family proteins were readily detected in hematopoietic stem/progenitor cells. CREB was upregulated, phosphorylated and bound to the CREs in response to GM-CSF stimulation. Retroviral transduction of a dominant negative CREB mutant reduced C/EBPβ mRNA levels and significantly impaired the proliferation/differentiation of granulocyte precursors, while a constitutively active form of CREB facilitated C/EBPβ transcription. These data suggest that CREB proteins are involved in the regulation of granulopoiesis via C/EBPβ upregulation.

Fluorescence-based evaluation of shRNA efficacy

RNA interference is a cellular mechanism regulating levels of mRNAs. It has been widely exploited to knock down specific protein targets. The selected interfering RNA sequence greatly influences its ability to knock down the target. Here we present a method for constructing multiple testing plasmids which express small hairpin RNAs (shRNA) targeting different regions of an mRNA. A simple fluorescence test in cultured cells allows convenient evaluation of mRNA knockdown by many different shRNAs on 96-well plates. We show that software predicted shRNAs have varying efficacies and only 2 of the 7 tested shRNAs significantly knocked down their targets.

Guide to red fluorescent proteins and biosensors for flow cytometry

Since the discovery of the first red fluorescent protein (RFP), named DsRed, 12 years ago, a wide pallet of red-shifted fluorescent proteins has been cloned and biotechnologically developed into monomeric fluorescent probes for optical microscopy. Several new types of monomeric RFPs that change the emission wavelength either with time, called fluorescent timers, or after a brief irradiation with violet light, known as photoactivatable proteins, have been also engineered. Moreover, RFPs with a large Stokes shift of fluorescence emission have been recently designed. Because of their distinctive excitation and fluorescence detection conditions developed specifically for microscopy, these fluorescent probes can be suboptimal for flow cytometry. Here, we have selected and summarized the advanced orange, red, and far-red fluorescent proteins with the properties specifically required for the flow cytometry applications. Their effective brightness was calculated for the laser sources available for the commercial flow cytometers and sorters. Compatibility of the fluorescent proteins of different colors in a multiparameter flow cytometry was determined. Novel FRET pairs, utilizing RFPs, RFP-based intracellular biosensors, and their application to a high-throughput screening, are also discussed.