Persistent histone modifications at the BDNF and Cdk-5 promoters following extinction of nicotine-seeking in rats.

Drugs of addiction lead to a wide range of epigenetic changes at the promoter regions of genes directly implicated in learning and memory processes. We have previously shown that the histone deactylase inhibitor, sodium butyrate (NaB), accelerates the extinction of nicotine-seeking and provides resistance to relapse. Here, we explore the potential molecular mechanisms underlying this effect. Rats received intravenous nicotine or saline self-administration, followed by 6 days of extinction training, with each extinction session followed immediately by treatment with NaB or vehicle. On the last day of extinction, rats were killed and the medial ventral prefrontal cortex retained for chromatin immunoprecipitation and quantitative polymerase chain reaction (qPCR). A history of nicotine exposure significantly decreased H3K14 acetylation at the brain-derived neurotrophic factor (BDNF) exon IV promoter, and this effect was abolished with NaB treatment. In contrast, nicotine self-administration alone, resulted in a significant decrease in histone methylation at the H3K27me3 and H3K9me2 marks in the promoter regions of BDNF exon IV and cyclin-dependent kinase 5 (Cdk-5). Quantitative PCR-identified changes in several genes associated with NaB treatment that were independent of nicotine exposure; however, an interaction of nicotine history and NaB treatment was detected only in the expression of BDNF IV and BDNF IX. Together these results suggest that nicotine self-administration leads to a number of epigenetic changes at both the BDNF and Cdk-5 promoters, and that these changes may contribute to the enhanced extinction of nicotine-seeking by NaB.

Antiviral applications of RNAi.

RNA interference is a natural mechanism by which small interfering (si)RNA operates to specifically and potently down-regulate the expression of a target gene. This down-regulation has been thought to predominantly function at the level of the messenger (m)RNA, post-transcriptional gene silencing (PTGS). Recently, the discovery that siRNAs can function to suppress a gene's expression at the level of transcription, i.e., transcriptional gene silencing (TGS), has created a major paradigm shift in mammalian RNAi. These recent findings significantly broaden the role RNA, specifically siRNAs and potentially microRNAs, plays in the regulation of gene expression as well as the breadth of potential siRNA target sites. Indeed, the specificity and simplicity of design makes the use of siRNAs to target and suppress virtually any gene or gene promoter of interest a realized technology. Furthermore, since siRNAs are a small nucleic acid reagent, they are unlikely to elicit an immune response, making them a theoretically good future therapeutic. This review will focus on the development, delivery, and potential therapeutic use of antiviral siRNAs in treating viral infections as well as emerging viral threats.

Lentiviral-mediated delivery of siRNAs for antiviral therapy.

Lentiviral vectors portend a promising system to deliver antiviral genes for treating viral infections such as HIV-1 as they are capable of stably transducing both dividing and nondividing cells. Recently, small interfering RNAs (siRNAs) have been shown to be quite efficacious in silencing target genes. RNA interference is a natural mechanism, conserved in nature from Yeast to Humans, by which siRNAs operate to specifically and potently down regulate the expression of a target gene either transcriptionally (targeted to DNA) or post-transcriptionally (targeted to mRNA). The specificity and relative simplicity of siRNA design insinuate that siRNAs will prove to be favorable therapeutic agents. Since siRNAs are a small nucleic acid reagents, they are unlikely to elicit an immune response and genes encoding these siRNAs can be easily manipulated and delivered by lentiviral vectors to target cells. As such, lentiviral vectors expressing siRNAs represent a potential therapeutic approach for the treatment of viral infections such as HIV-1. This review will focus on the development, lentiviral based delivery, and the potential therapeutic use of siRNAs in treating viral infections.

siRNA-mediated transcriptional gene silencing: the potential mechanism and a possible role in the histone code.

Epigenetics is the study of meiotically and mitotically heritable changes in gene expression which are not coded for in the DNA. Three distinct mechanisms appear intricately related in initiating and sustaining epigenetic modifications: RNA-associated silencing, DNA methylation and histone modification. Recently, in human cells small-interfering RNAs (siRNAs) have been shown to mediate transcriptional gene silencing (TGS). The observation that siRNAs can function to suppress gene expression at the level of transcription has created a major paradigm shift in mammalian RNA interference. The putative mechanism(s) of siRNA-mediated TGS in both yeast and human cells will be discussed. Undoubtedly, the ramifications from this paradigm shift in which RNA has demonstrated a potent and specific capability to regulate the expression of the gene are immeasurable both therapeutically (i. e. directed control of gene expression) and biologically in understanding the evolution of the cell.