ANTIGENE PROPERTY OF PNA CONJUGATED TO THE NUCLEAR LOCALIZATION SIGNAL PEPTIDE

Peptide nucleic acid (PNA) is a DNA mimic with antigene properties. To enhance its capacity to enter in the cell and internalize in the nucleus, PNA has been conjugated to the nuclear localization signal (NLS) peptide, PKKKRKV. PNA-NLS conjugates form stable hybrids with complementary DNA strands and poorly tolerate mismatched base pairing. Employed against cancer-associated genes, PNA-NLS exhibited a potent and specific antigene activity, suggesting exciting therapeutic approaches to cancer.     

A peptide nucleic acid-nuclear localization signal fusion that mediates nuclear transport of DNA.

We have combined a peptide nucleic acid (PNA) with the SV40 core nuclear localization signal (NLS), to create a bifunctional PNA-NLS peptide. The PNA-NLS peptide increased the nuclear uptake of oligonucleotides and enhanced the transfection efficacy of plasmids. Gene expression from an enhanced green fluorescent protein plasmid and a lacZ plasmid was preserved when hybridized to PNA-NLS. In combination with the transfection agent polyethyleneimine, we have improved both the nuclear translocation of fluorescence-marked oligonucleotides, and the efficacy of plasmid transfection, up to eightfold. The technique obviates the use of cumbersome coupling procedures of the vector due to DNA-PNA duplex formation or displacement of the antisense plasmid DNA strand by a PNA molecule.     

An introduction to peptide nucleic acid

Peptide Nucleic Acid (PNA) is a powerful new biomolecular tool with a wide range of important applications. PNA mimics the behaviour of DNA and binds complementary nucleic acid strands. The unique chemical, physical and biological properties of PNA have been exploited to produce powerful biomolecular tools, antisense and antigene agents, molecular probes and biosensors.     

Peptide nucleic acids specifically cause antigene effects in vivo by systemic injection

Peptide nucleic acids (PNAs) are uncharged DNA analogs that hybridize to complementary sequences with high affinity and stability. We previously showed that PNAs, after intraperitoneal injection into rats, are effective antisense compounds in vivo. The present study was designed to test whether PNAs also have antigene effects in vivo. The renin-angiotensin system is critical in the control of blood pressure. We designed and synthesized sense (antigene) PNAs to angiotensinogen, which is the precursor protein that leads to angiotensin I and II. Spontaneously hypertensive rats received intraperitoneal injections of either 20 mg/kg sense-angiotensinogen-PNA, mismatch-angiotensinogen PNA, or saline. Only the sense-angiotensinogen PNA treatment resulted in a significant decrease in plasma angiotensin I, systolic blood pressure, and liver and brain angiotensinogen mRNA levels. Thus, these results demonstrate on the molecular, protein, and physiological levels that antigene PNAs are effective in vivo upon systemic administration.     

Differential DNA and RNA sequence discrimination by PNA having charged side chains

PNA sequences modified with charged side chains were evaluated for base-pairing sequence selectivity under physiological conditions. PNA having negatively charged aspartic acid side chains shows higher selectivity with RNA, while PNA having positively charged lysine side chains shows higher selectivity with DNA. These observations provide insight into the binding selectivity of modified PNA in antisense and antigene applications.     

Quinoxaline antibiotics enhance peptide nucleic acid binding to double-stranded DNA

The effects of a wide range of DNA binding drugs on peptide nucleic acid (PNA) binding to double-stranded DNA by strand displacement have been investigated using a gel retardation assay. The bis-PNA [H-(Lys)-TTJTTJTTTT-(eg)(3)-TTTTCTTCTT-Lys-NH(2)] was used together with a 248 bp DNA fragment containing an appropriate target for the PNA. Most of the ligands that were studied, including DNA minor groove binders as well as intercalators and bis-intercalators, either have no effect or strongly inhibit PNA binding to DNA. By contrast, quinoxaline antibiotics facilitate PNA-DNA complex formation. The "PNA-helper" effect of echinomycin was studied in more detail using time and temperature dependence experiments to elucidate the mechanism. PNA binding to DNA follows pseudo-first-order kinetics, but the initial rate of binding is accelerated more than 10-fold in the presence of 10 microM echinomycin. The activation energy for PNA binding to dsDNA is lowered 2-fold by the antibiotic (45 vs 90 kJ/mol in the control). The reasons why quinoxalines promote the binding of PNA to DNA are not entirely clear but may well include distortions (opening) of the double helix that facilitate PNA invasion. This study establishes that the efficacy of DNA-targeted PNA antigene molecules could potentially be enhanced by judiciously adding certain DNA-interactive ligands.     

PNA monomers fully compatible with standard Fmoc-based solid-phase synthesis of pseudocomplementary PNA

Here we report the synthesis of new PNA monomers for pseudocomplementary PNA (pcPNA) that are fully compatible with standard Fmoc chemistry. The thiocarbonyl group of the 2-thiouracil (sU) monomer was protected with the 4-methoxy-2-methybenzyl group (MMPM), while the exocyclic amino groups of diaminopurine (D) were protected with Boc groups. The newly synthesized monomers were incorporated into a 10-mer PNA oligomer using standard Fmoc chemistry for solid-phase synthesis. Oligomerization proceeded smoothly and the HPLC and MALDI-TOF MS analyses indicated that there was no remaining MMPM on the sU nucleobase. The new PNA monomers reported here would facilitate a wide range of applications, such as antigene PNAs and DNA nanotechnologies.     

肽核酸在分子生物学技术中的应用

肽核酸(PNA)作为一种人工合成的核酸类似物,以中性的肽链酰胺2-氨基乙基甘氨酸键取代了DNA中的戊糖磷酸二酯键骨架,其余部分与DNA相同。PNA可通过Watson-Crick碱基配对的形式识别并结合DNA或RNA序列,形成稳定的双螺旋结构。与传统的DNA或RNA相比,PNA具有生物学稳定性高、杂交特异性强、杂合体的稳定性高和杂交速度快等明显优点,使PNA具有良好的物理化学性质和生物学特性,在检测目的核酸序列中单碱基突变、PCR基因分子诊断与检测、荧光原位杂交定量分析、基因芯片和生物传感器技术等调控水平和临床应用上有自己的特点。简要综述了近年来肽核酸在上述分子生物学技术中的运用以及应用前景的展望。     

Non-Watson-Crick interactions between PNA and DNA inhibit the ATPase activity of bacteriophage T4 Dda helicase

Peptide nucleic acid (PNA) is a DNA mimic in which the nucleobases are linked by an N-(2-aminoethyl) glycine backbone. Here we report that PNA can interact with single-stranded DNA (ssDNA) in a non-sequence-specific fashion. We observed that a 15mer PNA inhibited the ssDNA-stimulated ATPase activity of a bacteriophage T4 helicase, Dda. Surprisingly, when a fluorescein-labeled 15mer PNA was used in binding studies no interaction was observed between PNA and Dda. However, fluorescence polarization did reveal non-sequence-specific interactions between PNA and ssDNA. Thus, the inhibition of ATPase activity of Dda appears to result from depletion of the available ssDNA due to non-Watson–Crick binding of PNA to ssDNA. Inhibition of the ssDNA-stimulated ATPase activity was observed for several PNAs of varying length and sequence. To study the basis for this phenomenon, we examined self-aggregation by PNAs. The 15mer PNA readily self-aggregates to the point of precipitation. Since PNAs are hydrophobic, they aggregate more than DNA or RNA, making the study of this phenomenon essential for understanding the properties of PNA. Non-sequence-specific interactions between PNA and ssDNA were observed at moderate concentrations of PNA, suggesting that such interactions should be considered for antisense and antigene applications.     

Peptide nucleic acids as therapeutic agents.

Peptide nucleic acids (PNAs) have been around for more than seven years and it was hoped, at their introduction, that they would quickly enter the fields of antisense and antigene technology and drug development. Despite their extremely favorable hybridization and stability properties, as well as the encouraging antisense and antigene activity of PNA in cell-free systems, progress has been slow and experiments on cells in culture and in animals have been lacking. Judging from the very promising results published within the past year, however, there is every reason to believe that both PNA antisense and, possibly, PNA antigene research will strongly pick up momentum again. Specifically, it has been demonstrated that certain peptide-PNA conjugates are taken up very efficiently by, at least some, eukaryotic cells and that antisense down regulation of target genes in nerve cells in culture is attainable using such PNA conjugates. Perhaps even more exciting is that antisense-compatible effects have been reported using PNAs injected into the brain of rats. Finally, it has been shown that the bacterium Escherichia coli is susceptible to antisense gene regulation using PNA.     

Inhibition of multidrug resistance by SV40 pseudovirion delivery of an antigene peptide nucleic acid (PNA) in cultured cells

Peptide nucleic acid (PNA) is known to bind with extraordinarily high affinity and sequence-specificity to complementary nucleic acid sequences and can be used to suppress gene expression. However, effective delivery into cells is a major obstacle to the development of PNA for gene therapy applications. Here, we present a novel method for the in vitro delivery of antigene PNA to cells. By using a nucleocapsid protein derived from Simian virus 40, we have been able to package PNA into pseudovirions, facilitating the delivery of the packaged PNA into cells. We demonstrate that this system can be used effectively to suppress gene expression associated with multidrug resistance in cancer cells, as shown by RT-PCR, flow cytometry, Western blotting, and cell viability under chemotherapy. The combination of PNA with the SV40-based delivery system is a method for suppressing a gene of interest that could be broadly applied to numerous targets.