Partners in dicing

Target-responsive DNA/RNA nanomaterials for microRNA sensing and inhibition: the jack-of-all-trades in cancer nanotheranostics?

microRNAs (miRNAs) show high potential for cancer treatment, however one of the most significant bottlenecks in enabling miRNA effect is the need for an efficient vehicle capable of selective targeting to tumor cells without disrupting normal cells. Even more challenging is the ability to detect and silence multiple targets simultaneously with high sensitivity while precluding resistance to the therapeutic agents. Focusing on the pervasive role of miRNAs, herein we review the multiple nanomaterial-based systems that encapsulate DNA/RNA for miRNA sensing and inhibition in cancer therapy. Understanding the potential of miRNA detection and silencing while overcoming existing limitations will be critical to the optimization and clinical utilization of this technology.

Beta-cell specific deletion of Dicer1 leads to defective insulin secretion and diabetes mellitus

Mature microRNAs (miRNAs), derived through cleavage of pre-miRNAs by the Dicer1 enzyme, regulate protein expression in many cell-types including cells in the pancreatic islets of Langerhans. To investigate the importance of miRNAs in mouse insulin secreting β-cells, we have generated mice with a β-cells specific disruption of the Dicer1 gene using the Cre-lox system controlled by the rat insulin promoter (RIP). In contrast to their normoglycaemic control littermates (RIP-Cre^+/− Dicer1^Δ/wt), RIP-Cre^+/−Dicer1^flox/flox mice (RIP-Cre Dicer1^Δ/Δ) developed progressive hyperglycaemia and full-blown diabetes mellitus in adulthood that recapitulated the natural history of the spontaneous disease in mice. Reduced insulin gene expression and concomitant reduced insulin secretion preceded the hyperglycaemic state and diabetes development. Immunohistochemical, flow cytometric and ultrastructural analyses revealed altered islet morphology, marked decreased β-cell mass, reduced numbers of granules within the β-cells and reduced granule docking in adult RIP-Cre Dicer1^Δ/Δ mice. β-cell specific Dicer1 deletion did not appear to disrupt fetal and neonatal β-cell development as 2-week old RIP-Cre Dicer1^Δ/Δ mice showed ultrastructurally normal β-cells and intact insulin secretion. In conclusion, we have demonstrated that a β-cell specific disruption of the miRNAs network, although allowing for apparently normal β-cell development, leads to progressive impairment of insulin secretion, glucose homeostasis and diabetes development.

Distinct RNA-dependent RNA polymerases are required for RNAi triggered by double-stranded RNA versus truncated transgenes in Paramecium tetraurelia

In many eukaryotes, RNA-dependent RNA polymerases (RdRPs) play key roles in the RNAi pathway. They have been implicated in the recognition and processing of aberrant transcripts triggering the process, and in amplification of the silencing response. We have tested the functions of RdRP genes from the ciliate Paramecium tetraurelia in experimentally induced and endogenous mechanisms of gene silencing. In this organism, RNAi can be triggered either by high-copy, truncated transgenes or by directly feeding cells with double-stranded RNA (dsRNA). Surprisingly, dsRNA-induced silencing depends on the putatively functional RDR1 and RDR2 genes, which are required for the accumulation of both primary siRNAs and a distinct class of small RNAs suggestive of secondary siRNAs. In contrast, a third gene with a highly divergent catalytic domain, RDR3, is required for siRNA accumulation when RNAi is triggered by truncated transgenes. Our data further implicate RDR3 in the accumulation of previously described endogenous siRNAs and in the regulation of the surface antigen gene family. While only one of these genes is normally expressed in any clonal cell line, the knockdown of RDR3 leads to co-expression of multiple antigens. These results provide evidence for a functional specialization of Paramecium RdRP genes in distinct RNAi pathways operating during vegetative growth.

The ubiquitin/26S proteasome system in plant-pathogen interactions: a never-ending hide-and-seek game

The ubiquitin/26S proteasome system (UPS) plays a central role in plant protein degradation. Over the past few years, the importance of this pathway in plant-pathogen interactions has been increasingly highlighted. UPS is involved in almost every step of the defence mechanisms in plants, regardless of the type of pathogen. In addition to its proteolytic activities, UPS, through its 20S RNase activity, may be part of a still unknown antiviral defence pathway. Strikingly, UPS is not only a weapon used by plants to defend themselves, but also a target for some pathogens that have evolved mechanisms to inhibit and/or use this system for their own purposes. This article attempts to summarize the current knowledge on UPS involvement in plant-microbe interactions, a complex scheme that illustrates the never-ending arms race between hosts and microbes.

Role of Dicer in posttranscriptional RNA silencing

Dicer, an RNase III type endonuclease, is the key enzyme involved in RNA interference (RNAi) and microRNA (miRNA) pathways. It is required for biogenesis of miRNAs and small interfering RNAs (siRNAs), and also plays an important role in an effector step of RNA silencing, the RNA-induced silencing complex (RISC) assembly. In this article we describe different functions of Dicer in posttranscriptional regulation. We review the current knowledge about Dicers in different organisms and the functions of individual domains of the enzyme. We also discuss information about Dicer-associated proteins and their role in the biogenesis of small RNAs and assembly of RISC.

Protocols for gene silencing in schistosomes

Schistosomes are parasitic platyhelminths that infect over 200 million people globally. In recent years there have been many advances in schistosome genomics and proteomics and in the development of molecular tools for use with these parasites. Among the more promising methodologies is RNA interference (RNAi) which is a mechanism by which gene-specific double-stranded RNA (dsRNA) triggers degradation of homologous mRNA transcripts. We aim to develop effective protocols utilizing RNAi for use in the intra-mammalian life stages of Schistosoma mansoni. In this work, the gene encoding alkaline phosphatase (SmAP) was targeted by exposing the parasites to dsRNA encoding part of the SmAP coding region. SmAP is known to be expressed in a variety of parasite tissues. We report that both long dsRNAs as well as synthetic short inhibitory RNAs (siRNAs) are effective at eliciting SmAP gene suppression in cultured schistosomula and in adult males and females. Electroporation as a mode of dsRNA delivery is more efficient than simply soaking the parasites in an equivalent dose. Relative SmAP RNA levels >90% lower than controls were routinely detected, when measured 2 days after treatment by electroporation, using quantitative real-time PCR. Commensurate with this decline in SmAP RNA, relative alkaline phosphatase enzyme activity levels >70% lower than controls were detected, 5 days after treatment. Protocols described here that result in the robust suppression of target genes in intravascular schistosomes may have wide applicability and promote functional schistosome genomics.

Up-regulation of dicer, a component of the MicroRNA machinery, in prostate adenocarcinoma

MicroRNAs are small noncoding 18- to 24-nt RNAs that are predicted to regulate expression of as many as 30% of protein-encoding genes. In prostate adenocarcinoma, 39 microRNAs are up-regulated, and six microRNAs are down-regulated. Production and function of microRNA requires coordinated processing by proteins of the microRNA machinery. Dicer, an RNase III endonuclease, is an essential component of the microRNA machinery. From a gene array analysis of 16 normal prostate tissue samples, 64 organ-confined, and four metastatic prostate adenocarcinomas, we identified an up-regulation of major components of the microRNA machinery, including Dicer, in metastatic prostate adenocarcinoma. Immunohistochemical studies on a tissue microarray consisting of 232 prostate specimens confirmed up-regulation of Dicer in prostatic intraepithelial neoplasia and in 81% of prostate adenocarcinoma. The increased Dicer level in prostate adenocarcinoma correlated with clinical stage, lymph node status, and Gleason score. Western blot analysis of benign and neoplastic prostate cell lines further confirmed Dicer up-regulation in prostate adenocarcinoma. Dicer up-regulation may explain an almost global increase of microRNA expression in prostate adenocarcinoma. The presence of up-regulated microRNA machinery may predict the susceptibility of prostate adenocarcinoma to RNA interference-based therapy.