Intracellular expression of the T-cell factor-1 RNA aptamer as an intramer

The Research Advances of Aptamers in Hematologic Malignancies

Currently, research for hematological malignancies is very intensive, with many breakthroughs. Among them, aptamer-based targeted therapies could be counted. Aptamer is a targeting tool with many unique advantages (easy synthesis, low toxicity, easy modification, low immunogenicity, nano size, long stability, etc.), therefore many experts screened corresponding aptamers in various hematological malignancies for diagnosis and treatment. In this review, we try to summarize and provide the recent progress of aptamer research in the diagnosis and treatment of hematologic malignancies. Until now, 29 aptamer studies were reported in hematologic malignancies, of which 12 aptamers were tested in vivo and the remaining 17 aptamers were only tested in vitro. In this case, 11 aptamers were combined with chemotherapeutic drugs for the treatment of hematologic malignancies, 4 aptamers were used in combination with nanomaterials for the diagnosis and treatment of hematologic malignancies, and some studies used aptamers for the targeted transportation of siRNA and miRNA for targeted therapeutic effects. Their research provides multiple approaches to achieve more targeted goals. These findings show promising and encouraging future for both hematological malignancies basic and clinical trials research.

Identifying novel interactions of the colon-cancer related APC protein with Wnt-pathway nuclear transcription factors

BACKGROUND

Colon cancer is often driven by mutations of the adenomatous polyposis coli (APC) gene, an essential tumor suppressor gene of the Wnt β-catenin signaling pathway. APC and its cytoplasmic interactions have been well studied. However, various groups have also observed its presence in the nucleus. Identifying novel interactions of APC in the Wnt pathway will provide an opportunity to understand APC's nuclear role better and ultimately identify potential cancer treatment targets.

METHODS

We used the all-vs-all sequencing (AVA-Seq) method to interrogate the interactome of protein fragments spanning most of the 60 Wnt β-catenin pathway proteins. Using protein fragments identified the interacting regions between the proteins with more resolution than a full-length protein approach. Pull-down assays were used to validate a subset of these interactions.

RESULTS

74 known and 703 novel Wnt β-catenin pathway protein-protein interactions were recovered in this study. There were 8 known and 31 novel APC protein-protein interactions. Novel interactions of APC and nuclear transcription factors TCF7, JUN, FOSL1, and SOX17 were particularly interesting and confirmed in validation assays.

CONCLUSION

Based on our findings of novel interactions between APC and transcription factors and previous evidence of APC localizing to the nucleus, we suggest APC may compete and repress CTNNB1. This would occur through APC binding to the transcription factors (JUN, FOSL1, TCF7) to regulate the Wnt signaling pathway including through enhanced marking of CTNNB1 for degradation in the nucleus by APC binding with SOX17. Additional novel Wnt β-catenin pathway protein-protein interactions from this study could lead researchers to novel drug designs for cancer.

Recent advances in understanding oligonucleotide aptamers and their applications as therapeutic agents

The innovative discovery of aptamers was based on target-specific treatment in clinical diagnostics and therapeutics. Aptamers are synthetic, single-stranded oligonucleotides, simply described as chemical antibodies, which can bind to diverse targets with high specificity and affinity. Aptamers are synthesized by the SELEX technique, and possess distinctive properties as small size (10-50 kDa), higher stability, easy manufacture and less immunogenicity. These oligonucleotides are easily degraded by nucleases, so require some important modifications like capping and incorporation of modified nucleotides. RNA aptamers can be modified chemically on 2' positions using -NH3, -F, -deoxy, or -OMe groups to enhance their nuclease resistance. Aptamers have been employed for multiple purposes, as direct drugs or aptamer-drug conjugates targeted against different diseased cells. Different aptamer-conjugated nanovehicles (e.g., micelles, liposomes, silica nano-shells) have been designed to transport diverse anticancer-drugs like doxorubicin and cisplatin in bulk to minimize systemic cytotoxicity. Some drug-loaded nanovehicles (up to 97% loading capacity) and conjugated with specific aptamer resulted in more than 60% tumor inhibition as compared to unconjugated drug-loaded nanovehicles which showed only 31% cancer inhibition. In addition, aptamers have been widely used in basic research, food safety, environmental monitoring, clinical diagnostics and therapeutics. Different FDA-approved RNA and DNA aptamers are now available in the market, used for the treatment of diverse diseases, especially cancer. These aptamers include Macugen, Pegaptanib, etc. Despite a good progress in aptamer use, the present-day chemotherapeutics and drug targeting systems still face great challenges. Here in this review article, we are discussing nucleic acid aptamers, preparation, role in the transportation of different nanoparticle vehicles and their applications as therapeutic agents.

At the Intersection of Biomaterials and Gene Therapy: Progress in Non-viral Delivery of Nucleic Acids

Biomaterials play a critical role in technologies intended to deliver therapeutic agents in clinical settings. Recent explosion of our understanding of how cells utilize nucleic acids has garnered excitement to develop a range of older (e.g., antisense oligonucleotides, plasmid DNA and transposons) and emerging (e.g., short interfering RNA, messenger RNA and non-coding RNAs) nucleic acid agents for therapy of a wide range of diseases. This review will summarize biomaterials-centered advances to undertake effective utilization of nucleic acids for therapeutic purposes. We first review various types of nucleic acids and their unique abilities to deliver a range of clinical outcomes. Using recent advances in T-cell based therapy as a case in point, we summarize various possibilities for utilizing biomaterials to make an impact in this exciting therapeutic intervention technology, with the belief that this modality will serve as a therapeutic paradigm for other types of cellular therapies in the near future. We subsequently focus on contributions of biomaterials in emerging nucleic acid technologies, specifically focusing on the design of intelligent nanoparticles, deployment of mRNA as an alternative to plasmid DNA, long-acting (integrating) expression systems, and in vitro/in vivo expansion of engineered T-cells. We articulate the role of biomaterials in these emerging nucleic acid technologies in order to enhance the clinical impact of nucleic acids in the near future.

Therapeutic aptamers in discovery, preclinical and clinical stages

The aptamer field witnessed steady growth during the past 28 years as evident from the exponentially increasing number of related publications. The field is "coming of age", but like other biomedical research areas facing a global push towards translational research to carry ideas from bench- to bedside, there is pressure to show impact for aptamers at the clinical end. Being easy-to-make, non-immunogenic, stable and high-affinity nano-ligands, aptamers are perfectly poised to move in this direction. They can specifically bind targets ranging from small molecules to complex multimeric structures, making them potentially useful in a limitless variety of therapeutic approaches. This review will summarize efforts made to accomplish the therapeutic promise of aptamers, with a focus on aptamers directly acting as therapeutic molecules, rather than those used in targeted delivery of other drugs. The review will showcase representative examples at various stages of development, covering different disease categories.

Selection and Application of Aptamers and Intramers

Aptamers are auspicious nucleic acid ligands for targeting different molecules, such as small molecules, peptides, proteins, or even whole living cells. They are short single-stranded DNA or RNA oligonucleotides, which can fold into complex three-dimensional structures and bind selectively their targets. Using the combinatorial chemistry process SELEX (Systematic Evolution of Ligands by EXponential Enrichment), target specific aptamers can be selected. These aptamers have a variety of application possibilities and can be used as sensors, diagnostic, imaging or therapeutic agents, and in the field of regenerative medicine for tissue engineering.

Aptamers as Valuable Molecular Tools in Neurosciences

Aptamers are short nucleic acids that interact with a variety of targets with high affinity and specificity. They have been shown to inhibit biological functions of cognate target proteins, and they are identifiable by an in vitro selection process, also termed SELEX (Systematic Evolution of Ligands by EXponential enrichment). Being nucleic acids, aptamers can be synthesized chemically or enzymatically. The latter renders RNA aptamers compatible with the cell's own transcription machinery and, thus, expressable inside cells. The synthesis of aptamers by chemical approaches opens up the possibility of producing aptamers on a large scale and enables a straightforward access to introduce modifications in a site-specific manner (e.g., fluorophores or photo-labile groups). These characteristics make aptamers broadly applicable (e.g., as an analytical, diagnostic, or separation tool). In this TechSight, we provide a brief overview on aptamer technology and the potential of aptamers as valuable research tools in neurosciences.

3D Cell-SELEX: Development of RNA aptamers as molecular probes for PC-3 tumor cell line

Human prostate cancer (PCa) is a highly heterogeneous and multifactorial disease. Current clinical biomarkers are not sufficiently accurate, thus being unable to predict the clinical outcome. Therefore, searching for new biomarkers aiming to improve diagnosis, prognosis and therapy is still required. In this study, we performed 3D Cell-SELEX against PC-3 prostate cancer cell line, a novel strategy to select specific nucleic acid ligands against spheroid cells in 3D cell culture. This original system combines Cell-SELEX, a process that exploits the cellular structure to generate specific ligands, and 3D cell culture, an approach that mimics the tissue microenvironment in vitro. In the first round of 3D Cell-SELEX, a negative selection against RWPE-1, non-tumor cell line, was performed to subtract non-tumor specific aptamers. The supernatant was used in eight additional rounds of selection, which were performed against PC-3 cell line. After nine selection cycles, eight PC-3 specific RNA aptamers were selected and sequenced. The aptamers presented sizes between 20 and 50 nucleotides-long, with low free energy (∆G<-13.6), which contributed for their spontaneous folding and high stability. Furthermore, our results showed the aptamer A4 as a specific ligand to prostate tumor cells, with dissociation constant in the nanomolar scale. Therefore, the novel 3D Cell-SELEX procedure improved the selection of PCa cell-surface ligands and the aptamer A4 has shown potential for the identification of prostate tumor cells, suggesting the application of this molecule in further screening assays for PCa.

Roles of transcriptional factor 7 in production of inflammatory factors for lung diseases

Lung disease is the major cause of death and hospitalization worldwide. Transcription factors such as transcription factor 7 (TCF7) are involved in the pathogenesis of lung diseases. TCF7 is important for T cell development and differentiation, embryonic development, or tumorogenesis. Multiple TCF7 isoforms can be characterized by the full-length isoform (FL-TCF7) as a transcription activator, or dominant negative isoform (dn-TCF7) as a transcription repressor. TCF7 interacts with multiple proteins or target genes and participates in several signal pathways critical for lung diseases. TCF7 is involved in pulmonary infection, allergy or asthma through promoting T cells differentiating to Th2 or memory T cells. TCF7 also works in tissue repair and remodeling after acute lung injury. The dual roles of TCF7 in lung cancers were discussed and it is associated with the cellular proliferation, invasion or metastasis. Thus, TCF7 plays critical roles in lung diseases and should be considered as a new therapeutic target.

Nucleic Acid Aptamers: An Emerging Tool for Biotechnology and Biomedical Sensing

Detection of small molecules or proteins of living cells provides an exceptional opportunity to study genetic variations and functions, cellular behaviors, and various diseases including cancer and microbial infections. Our aim in this review is to give an overview of selected research activities related to nucleic acid-based aptamer techniques that have been reported in the past two decades. Limitations of aptamers and possible approaches to overcome these limitations are also discussed.

Blocking the maturation of OncomiRNAs using pri-miRNA-17∼92 aptamer in retinoblastoma

The miR-17∼92. or oncomiR-1, cluster encodes oncogenic microRNAs (miRNAs), and it also promotes retinoblastoma (RB) tumor formation. Antagomir and miRNA mimics based approaches are widely tried against oncogenic and tumor suppressive miRNAs. Other methods for targeting cancer related miRNAs are still under development. In the current study, we focused on the pri-miRNA-17∼92 aptamer (pri-apt), which can potentially replace the mix of five antagomirs by one aptamer that function to abrogate the maturation of miR-17, miR-18a, and miR-19b (P<0.05) for targeting RB. We used RB cell lines WERI-Rb1 and Y79 as an in vitro model. Cellular changes upon transfecting the pri-apt led to S-phase arrest in WERI-Rb1 cells and onset of apoptosis in both Y79 and WERI-Rb1 cell lines. There was increased cytotoxicity as measured by lactate dehydrogenase activity in pri-apt treated Y79 cells (P<0.05), and significant inhibition of cell proliferation was observed in both of the cell lines. Thus we showed the antiproliferative property of pri-apt in RB cell lines, which can be readily modified by developing appropriate vectors for the delivery of the aptamer specifically to cancer cells.

Recent progress in generating intracellular functional antibody fragments to target and trace cellular components in living cells

In biomedical research there is an ongoing demand for new technologies, which help to elucidate disease mechanisms and provide the basis to develop novel therapeutics. In this context a comprehensive understanding of cellular processes and their pathophysiology based on reliable information on abundance, localization, posttranslational modifications and dynamic interactions of cellular components is indispensable. Besides their significant impact as therapeutic molecules, antibodies are arguably the most powerful research tools to study endogenous proteins and other cellular components. However, for cellular diagnostics their use is restricted to endpoint assays using fixed and permeabilized cells. Alternatively, live cell imaging using fluorescent protein-tagged reporters is widely used to study protein localization and dynamics in living cells. However, only artificially introduced chimeric proteins are visualized, whereas the endogenous proteins, their posttranslational modifications as well as non-protein components of the cell remain invisible and cannot be analyzed. To overcome these limitations, traceable intracellular binding molecules provide new opportunities to perform cellular diagnostics in real time. In this review we summarize recent progress in the generation of intracellular and cell penetrating antibodies and their application to target and trace cellular components in living cells. We highlight recent advances in the structural formulation of recombinant antibody formats, reliable screening protocols and sophisticated cellular targeting technologies and propose that such intrabodies will become versatile research tools for real time cell-based diagnostics including target validation and live cell imaging. This article is part of a Special Issue entitled: Recent advances in molecular engineering of antibody.

Aptamer-based affinity labeling of proteins

A most able label: Labeled aptamers can be cross-linked to their target structures in a light-dependent and highly specific manner as a result of a new strategy termed aptamer-based affinity labeling (ABAL) of proteins. The aptamer-protein complexes can be enriched in vitro, from a cellular lysate and from the surface of living cells, opening new ways to study aptamer interactions in biological contexts.

Cell-specific aptamers as emerging therapeutics

Aptamers are short nucleic acids that bind to defined targets with high affinity and specificity. The first aptamers have been selected about two decades ago by an in vitro process named SELEX (systematic evolution of ligands by exponential enrichment). Since then, numerous aptamers with specificities for a variety of targets from small molecules to proteins or even whole cells have been selected. Their applications range from biosensing and diagnostics to therapy and target-oriented drug delivery. More recently, selections using complex targets such as live cells have become feasible. This paper summarizes progress in cell-SELEX techniques and highlights recent developments, particularly in the field of medically relevant aptamers with a focus on therapeutic and drug-delivery applications.

Aptamers for allosteric regulation

Aptamers are useful for allosteric regulation because they are nucleic acid-based structures in which ligand binding induces conformational changes that may alter the function of a connected oligonucleotide at a distant site. Through this approach, a specific input is efficiently converted into an altered output. This property makes these biomolecules ideally suited to function as sensors or switches in biochemical assays or inside living cells. The ability to select oligonucleotide-based recognition elements in vitro in combination with the availability of nucleic acids with enzymatic activity has led to the development of a wide range of engineered allosteric aptasensors and aptazymes. Here, we discuss recent progress in the screening, design and diversity of these conformational switching oligonucleotides. We cover their application in vitro and for regulating gene expression in both prokaryotes and eukaryotes.

NF-κB p65 represses β-catenin-activated transcription of cyclin D1

Signaling crosstalk between the β-catenin and NF-κB pathways represents a functional network. To test whether the crosstalk also occurs on their common target genes, the cyclin D1 promoter was used as a model because it contains binding sites for both proteins. β-catenin activated transcription from the cyclin D1 promoter, while co-expression of NF-κB p65 reduced β-catenin-induced transcription. Chromatin immunoprecipitation revealed lithium chloride-induced binding of β-catenin on one of the T-cell activating factor binding sites. More interestingly, β-catenin binding was greatly reduced by NF-κB p65, possibly by the protein-protein interaction between the two proteins. Such a dynamic and complex binding of β-catenin and NF-κB on promoters might contribute to the regulated expression of their target genes.

Bioimaging of nucleolin aptamer-containing 5-(N-benzylcarboxyamide)-2'-deoxyuridine more capable of specific binding to targets in cancer cells

Chemically modified nucleotides have been developed and applied into SELEX procedure to find a novel type of aptamers to fit with targets of interest. In this study, we directly performed chemical modification of 5-(N-benzylcarboxyamide)-2'-deoxyuridine (called 5-BzdU) in the AS1411 aptamer, which binds to the nucleolin protein expressed in cancer cells. Forty-seven compounds of AS1411-containing Cy3-labeled 5-BzdU (called Cy3-(5-BzdU)-modified-AS1411) were synthesized by randomly substituting thymidines one to twelve in AS1411 with Cy3-labeled 5-BzdU. Both statistically quantified fluorescence measurements and confocal imaging analysis demonstrated at least three potential compounds of interest: number 12, 29 and 41 that significantly increased the targeting affinity to cancer cells but no significant activity from normal healthy cells. These results suggest that the position and number of substituents in AS1411 are critical parameters to improve the aptamer function. In this study, we demonstrated that chemical modification of the existing aptamers enhanced the binding and targeting affinity to targets of interest without additional SELEX procedures.

Modulation of transcription by the peroxisome proliferator-activated receptor delta--binding RNA aptamer in colon cancer cells

Peroxisome proliferator-activated receptor delta (PPAR-delta), one of three PPAR subtypes, is a lipid-sensing nuclear receptor that has been implicated in multiple processes, including inflammation and cancer. To directly establish the role of PPAR-delta in colon cancer development and progression, we selected high-affinity RNA aptamers and expressed them in several colon cancer cell lines. Nuclear-expressed aptamers efficiently inhibited PPAR-delta-dependent transcription from a synthetic peroxisome proliferator response element-driven luciferase reporter. PPAR-delta-specific aptamers suppressed transcription from natural promoters of vascular endothelial cell growth factor-A and cyclooxygenase-2. Moreover, vascular endothelial cell growth factor-A and cyclooxygenase-2 mRNA levels were significantly reduced by the PPAR-delta-specific aptamers in colon cancer cells. Most significantly, HCT116 colon cancer cells with high-level expression of PPAR-delta-specific aptamers exhibited a striking loss of tumorigenic potential. Further study on these RNA aptamers could provide an opportunity to modulate PPAR-delta-mediated colon cancer development and progression. Taken together, our results establish an important role for PPAR-delta in transcription of tumor-promoting genes, which can be specifically modulated by high-affinity RNA intramers in colon cancer cells. The RNA intramers may be further developed as specific inhibitors for cancer therapeutic strategies.

Use of RNA aptamers for the modulation of cancer cell signaling

Aptamers are in vitro evolved molecules that bind to target proteins with high affinity and specificity by adapting three-dimensional structures upon binding. Because cancer cells exhibit the activation of signaling pathways that are not usually activated in normal cells, RNA aptamers against such a cancer cell-specific signal can be useful lead molecules for cancer gene therapy. The Wnt/beta-catenin signaling pathway plays important roles in a critical initiating event in the formation of various human cancers. Because mutations in beta-catenin have been found to be responsible for human tumorigenesis, beta-catenin is the molecular target for effective anticancer therapies. Here, we describe the selection of RNA aptamers against beta-catenin/T-Cell Factor (TCF) proteins and their intracellular expression as intramers. The RNA aptamers acted as central inhibitory players for multiple oncogenic functions of beta-catenin in colon cancer cells. These data provide the proof-of-principle for the use of RNA aptamers for an effective anticancer gene therapy.

The chemical biology of aptamers

Aptamers are small single-stranded nucleic acids that fold into a well-defined three-dimensional structure. They show a high affinity and specificity for their target molecules and inhibit their biological functions. Aptamers belong to the nucleic acids family and can be synthesized by chemical or enzymatic procedures, or a combination of the two. They can, therefore, be considered as both chemical and biological substances. This Review summarizes the most convenient approaches to their preparation and new developments in the field of aptamers. The application of aptamers in chemical biology is also discussed.

The RNA aptamer disrupts protein-protein interaction between beta-catenin and nuclear factor-kappaB p50 and regulates the expression of C-reactive protein

Transcription is activated by signal-induced protein-protein interaction between transcription factors on regulatory elements positioned near their target genes. Here, we tested the utility of the beta-catenin binding RNA aptamer as a tool for studying protein-protein interaction within transcription complex and for modulating expression of a target gene. The RNA aptamer bound Armadillo repeats of beta-catenin and was effective in disrupting protein-protein interaction between beta-catenin and nuclear factor-kappaB (NF-kappaB) p50. In addition, the RNA aptamer effectively reduced tumor necrosis factor-alpha induced transcription from the promoter of C-reactive protein regulated by beta-catenin and NF-kappaB p50. Taken together, beta-catenin binding RNA aptamer was an effective regulator of beta-catenin and NF-kappaB p50 mediated transcription.

Nanotechnology and aptamers: applications in drug delivery

Nucleic acid ligands, also known as aptamers, are a class of macromolecules that are being used in several novel nanobiomedical applications. Aptamers are characterized by high affinity and specificity for their target, a versatile selection process, ease of chemical synthesis and a small physical size, which collectively make them attractive molecules for targeting diseases or as therapeutics. These properties will enable aptamers to facilitate innovative new nanotechnologies with applications in medicine. In this review, we will highlight recent developments in using aptamers in nanotechnology solutions for treating and diagnosing disease.

Selection and characterization of anti-NF-kappaB p65 RNA aptamers

NF-kappaB transcription factors include a group of five mammalian proteins that form hetero- or homodimers and regulate hundreds of target genes involved in acute inflammation, HIV-1 transcription activation, and resistance to cancer therapy. We previously used in vitro selection to develop a small RNA aptamer (anti-p50) that binds the DNA-binding domain of NF-kappaB p50(2) with low nanomolar affinity but does not bind NF-kappaB p65(2). Here, we report the in vitro selection of anti-NF-kappaB p65 RNA aptamers using parallel in vitro selections with either a fully randomized RNA library or a degenerate RNA library based on the primary sequence of the 31-nucleotide anti-p50 RNA aptamer. We report the characterization of these aptamers with respect to NF-kappaB target specificity, affinity, minimal sequence requirements, secondary structure, and competition with DNA kappaB sites. These results expand opportunities for artificial inhibition of NF-kappaB transcription factor dimers containing p65 subunits.

Visualization of RNA using fluorescence complementation triggered by aptamer-protein interactions (RFAP) in live bacterial cells

This unit describes a method allowing RNA visualization in live cells. The method is based on fluorescent protein complementation regulated by RNA-aptamer/RNA-binding protein interactions. Based on these two principles, a fluorescent ribonucleoprotein complex is assembled inside the cell only in response to the presence of the aptamer sequence on the target RNA.

beta-catenin regulates multiple steps of RNA metabolism as revealed by the RNA aptamer in colon cancer cells

Nuclear beta-catenin forms a transcription complex with TCF-4, which is implicated in colon cancer development and progression. Recently, we and others have shown that beta-catenin could be a regulator of RNA splicing and it also stabilizes the cyclooxygenase-2 (COX-2) mRNA. Here, we further explored the role of beta-catenin in the RNA metabolism in colon cancer cells. To specifically modulate the subcellular functions of beta-catenin, we expressed the RNA aptamer in the form of RNA intramers with unique cellular localizations. The nucleus-expressed RNA intramer proved to be effective in reducing the protein-protein interaction between beta-catenin and TCF-4, thus shown to be a specific regulator of beta-catenin-activated transcription. It could also regulate the alternative splicing of E1A minigene in diverse colon cancer cell lines. In addition, we tested whether beta-catenin could stabilize any other mRNAs and found that cyclin D1 mRNA was also bound and stabilized by beta-catenin. Significantly, the cytoplasm-expressed RNA intramer reverted the beta-catenin-induced COX-2 and cyclin D1 mRNA stabilization. We show here that beta-catenin regulated multiple steps of RNA metabolism in colon cancer cells and might be the protein factor coordinating RNA metabolism. We suggest that the RNA intramers could provide useful ways for inhibiting beta-catenin-mediated transcription and RNA metabolism, which might further enhance the antitumorigenic effects of these molecules in colon cancer cells.

Anti-innexin 2 aptamers specifically inhibit the heterologous interaction of the innexin 2 and innexin 3 carboxyl-termini in vitro

We recently demonstrated that heteromerization of innexins 2 and 3 from Drosophila melanogaster (Dm) is crucial for epithelial organization and polarity of the embryonic epidermis. Both innexins are thought to interact via their C-terminal cytoplasmic domains during the assembly of heteromeric gap junction channels. However, the mechanisms that control heteromeric versus homomeric channel formation are still largely unknown. Here we report the isolation of both non-modified and 2'-fluoro-2'-deoxy-modified RNA anti-innexin 2 aptamers by in vitro selection. The aptamers bind to a proximal epitope on the carboxyl-tail of Dm innexin 2 protein and specifically inhibit the heterologous interaction of innexin 2 and innexin 3 carboxyl-termini in vitro. These domain-specific inhibitors represent the first step towards functional studies focusing on the activity of these domains in vivo.

An RNA aptamer that recognizes a specific conformation of the protein calsenilin

The generation of molecules that selectively recognize specific conformations of a protein is an important component of the elucidation protein function. We have used SELEX (Systematic Evolution of Ligands by EXponential enrichment) technology to produce aptamers that bind in a conformationally selective manner to calsenilin, which involved in Ca(2+)-mediated apoptotic signaling. Since the conformations of calsenilin are quite different in the presence and absence of Ca(2+), aptamers were selected against the dimeric protein both under calcium-bound and calcium-free conditions. We have found that aptamer-12 selectively binds to the dimeric form of the protein in the presence of calcium ion, while the binding of aptamer-2 does not discriminate between the Ca(2+) bound and unbound protein. Data obtained from biochemical and biophysical experiments suggest that a dominant conformation of calcium-bound calsenilin exists in one dominant conformation and that one aptamer can be generated to recognize this conformation. In addition, observation made in this effort that aptamers selected against the two different conformations of calsenilin have different characteristics suggest that aptamers can serve as a plausible tool for recognizing various conformations of proteins, even those caused by interactions with small molecules or ions such as Ca(2+).

Gene therapy progress and prospects: RNA aptamers

Aptamers are oligonucleotides evolved in vitro or in nature to bind target ligands with high affinity and specificity. They are emerging as powerful tools in the fields of therapeutics, drug development, target validation and diagnostics. Aptamers are attractive alternatives to antibody- and small-molecule-based therapeutics owing to their stability, low toxicity, low immunogenicity and improved safety. With the recent approval of the first aptamer drug Macugen by the US FDA, there is great impetus to develop therapeutic aptamers that can target a wide array of disease states. The recent demonstration that aptamer activity can be reversed by the administration of a simple antidote greatly enhances the potential value of aptamers as therapeutic agents.

Modulation of oncogenic transcription and alternative splicing by beta-catenin and an RNA aptamer in colon cancer cells

Activated beta-catenin regulates the transcription of oncogenic target genes and is critical for tumorigenesis. Because nuclear functions are frequently coupled, we investigated whether it also has a role in alternative splicing of oncogenic genes. We showed that stabilized beta-catenin caused alternative splicing of estrogen receptor-beta pre-mRNA in colon cancer cells. To establish a direct role of beta-catenin in regulated splicing, we selected a high-affinity RNA aptamer that associated with beta-catenin in vivo. Nuclear localized aptamer inhibited beta-catenin-dependent transcription of cyclin D1 and c-myc in colon cancer cells; thus, cells stably expressing the aptamer exhibited cell cycle arrest and reduced tumor forming potential. Most significantly, the aptamer prevented the alternative splicing induced by stabilized beta-catenin. Taken together, our results establish that beta-catenin has an important role in both transcription and splicing, and that its action can be modulated by a high-affinity RNA aptamer. The RNA aptamer could be further developed as a specific inhibitor for cancer therapeutics.