Postsynthesis functionalization of oligonucleotides

Nucleic acid duplexes incorporating a dissociable covalent base pair

We have used molecular modeling techniques to design a dissociable covalently bonded base pair that can replace a Watson-Crick base pair in a nucleic acid with minimal distortion of the structure of the double helix. We introduced this base pair into a potential precursor of a nucleic acid double helix by chemical synthesis and have demonstrated efficient nonenzymatic template-directed ligation of the free hydroxyl groups of the base pair with appropriate short oligonucleotides. The nonenzymatic ligation reactions, which are characteristic of base paired nucleic acid structures, are abolished when the covalent base pair is reduced and becomes noncoplanar. This suggests that the covalent base pair linking the two strands in the duplex is compatible with a minimally distorted nucleic acid double-helical structure.

Regulation of cytokine-induced iNOS expression by a hairpin oligonucleotide in murine cerebral endothelial cells

Inducible nitric oxide synthase (iNOS) is expressed in response to cytokines by a number of cell types participating in CNS inflammation, including brain cerebral endothelial cells. NF-kappaB, a transcription factor, mediates effector actions of pro-inflammatory cytokines. A combination of tumor necrosis factor alpha (TNF-alpha) and interferon gamma (IFN-gamma) enhanced the expression of iNOS in murine cerebral endothelial cells (MCECs). In an attempt to modulate TNF-alpha+IFN-gamma induced expression of iNOS in MCECs, we designed a double-strand hairpin (hp) oligonucleotide carrying the NF-kappaB motif. This hp oligonucleotide inhibited NF-kappaB binding activity and decreased both iNOS mRNA and protein expression induced by TNF-alpha+IFN-gamma. As a control, a mutant hp oligonucleotide was without effect. The present study confirms the role of transcription factor NF-kappaB in iNOS expression induced by TNF-alpha+IFN-gamma in MCECs. More importantly, it demonstrates that an appropriately designed hp oligonucleotide is an effective tool to modulate iNOS expression and may be of potential pharmacological use.