MicroRNA (miRNA) mimics are innovative biomolecules useful for research in gene targeting, antisense and cell reprogramming approches
miRNA mimics are innovative molecules designed for gene silencing approaches. miRNA mimics contain nonnatural or artificial double stranded miRNA-like RNA fragments. These RNA fragments are constructed to contain a sequence motif on its 5’-end that is partially complementary to the target sequence in the 3’UTR.
The three prime untranslated region or 3’-UTR is the sequence section of messenger RNAs (mRNAs) immediately following the translation termination codon of a gene. The mRNA molecule is transcribed from the DNA sequence that is later translated into a protein. Several sequence regions of the mRNA molecule are not translated into proteins including the cap on the 5’, the 5’ untranslated region, the 3’ untranslated region, and the poly(A) tail. Several regulatory regions involved in post-transcriptional gene expression are often found within the 3′-UTR.
Illustration of the mRNA structure where the median length of 3’UTR is approximately 700 nucleotides.
Once these RNA fragments are introduced into cells the miRNA mimics can bind specifically to the targeted gene. The result is posttranscriptional repression or more specifically translational inhibition of the gene. miR-Mimics will act in a gene-specific fashion allowing for “miRNA-targeting” and “miRNA-gain-of-function” approaches that are presently primarily used as exogenous tools to study gene function by targeting mRNA through miRNA-like actions in mammalian cells.
Zhang et al. recently used BNA (LNA) modified oligonucleotides to inhibit miRNAs to study the function of miR-126/miR-126* for their role in metastasis. The researchers report that miR-126/miR-126*, a microRNA pair derived from a single precursor, independently suppress the sequential recruitment of mesenchymal stem cells and inflammatory monocytes into the tumour stroma to inhibit lung metastasis by breast tumour cells in a mouse xenograft model. The scientists found that miR-126/miR-126* directly inhibit stromal cell-derived factor-1 alpha (Sdf-1α) expression, and indirectly suppress the expression of chemokine (C-C motif) ligand 2 (Ccl2) by cancer cells in an Sdf-1α-dependent manner. Furthermore the miR-126/miR-126* expression was found to be downregulated in cancer cells by promoter methylation of their host gene Egfl7. The result is that pri-miR-126 may suppress the metastasis process through different mechanism in different subsets of breast cancer patients by targeting Sdf-1α.
The microRNA pair appears to alter the composition of the primary tumour microenvironment to favor breast cancer metastasis. This paper demonstrated a correlation between miR-126/126* downregulation and poor metastasis-free survival of breast cancer patients.
[Yun Zhang, Pengyuan Yang, Tao Sun, Dong Li, Xin Xu, Yaocheng Rui, Chaoran Li, Mengyang Chong, Toni Ibrahim, Laura Mercatali, Dino Amadori, Xincheng Lu, Dong Xie, Qi-Jing Li, and Xiao-Fan Wang; miR-126 and miR-126* repress recruitment of mesenchymal stem cells and inflammatory monocytes to inhibit breast cancer metastasis. Nat Cell Biol. 2013 Mar;15(3):284-94. doi: 10.1038/ncb2690. Epub 2013 Feb 10.]
Translational control mechanisms result from the interaction of RNA-binding proteins with 5′- or 3′-untranslated regions (UTRs) of mRNA in organisms ranging from viruses to humans. Protein-mediated interactions between transcript termini result in the formation of an RNA loop. It is thought that such RNA ‘circularization‘ increase translational efficiency and permits its regulation by novel mechanisms.
Two general mechanisms of translational inhibition by 3’-UTR-binding proteins have been proposed:
1: One in which mRNA closure is disrupted, and
2: Another one in which mRNA closure is required.
The study of interferon-gamma-mediated translational silencing of ceruloplasmin expression in monocytic cells provides support for the second mechanism. Furthermore, multi-species analysis has shown that 3′-UTRs are substantially longer than their 5′ counterparts in most vertebrates. Scientists now think that this type of regulation contributes to the complexity of organisms.
A more detailed description of the molecular mechanism of translational control can be found in the following paper: Fátima Gebauer & Matthias W. Hentze; Molecular mechanisms of translational contro.l Nature Reviews Molecular Cell Biology 5, 827-835 (October 2004) | doi:10.1038/nrm1488. http://www.nature.com/nrm/journal/v5/n10/execsumm/nrm1488.html.
News from the AACR 2013 Meeting in Washington DC.
A poster about BNA modified oligonucleotides for cell reprogramming
During the recent AACR 2013 Meeting in Washington DC Dr. Masamitsu Konno together with Dr. Satoshi Obika’s group used synthetic oligonucleotides modified with bridged nucleic acids (BNAs) to study their potential in the use for the reprogramming of cells. The poster reported the successful reprogramming of mouse and human cells to pluripotency by direct transfection using mature double-stranded microRNAs. The miRNA hsa-mir369-3P was chosen as the target. This research aims to reprogram tumorigenic cells that are resistant to other drug treatment regiments by hopefully exterminating the cancer altogether.
The reported approach gives hope to usher in a new era of cancer treatments not presently available. It is hoped that approches like this will allow to interfere with the cancer development cycle at critical checkpoints to halt the development and spread of cancers altogether.
Picture of the poster.
Picture of Drs. Konno and Castro in front of Dr. Konno’s poster.
Dr. Castro is the CEO and President of Biosynthesis Inc. Lewisville, Texas.
Biosynthesis is providing its third generation Bridged Nucleic Acids (BNA) also known as BNA3TM to researchers in academia and industry to enhance their research. This new technology is based on multi-functional synthetic RNA analogues that can be used in place of the first generation bridged nucleic acids known as Locked Nucleic Acids (LNA). These RNA analogues can be synthesized and spiked with DNA or RNA in order to modify the formation of nucleic acid helices. Also, when compared to Peptide Nucleic Acids (PNA), BNA3 allows for better base-pair stacking and a high stability of the resulting oligonucleotide complexes, making BNA based oligonucleotides an ideal solution for the detection of small or highly similar DNA or RNA targets.
Furthermore, Bio-Synthesis Inc. is now providing synthetic oligonucleotides containing BNA3 which are deprotected, desalted or HPLC purified. All oligonucleotides are quality checked by MALDI-TOF Mass Spectrometry.