Variables affecting antisense RNA inhibition of gene expression

Evidence for a regulatory role of diatom silicon transporters in cellular silicon responses

The utilization of silicon by diatoms has both global and small-scale implications, from oceanic primary productivity to nanotechnological applications of their silica cell walls. The sensing and transport of silicic acid are key aspects of understanding diatom silicon utilization. At low silicic acid concentrations (<30 μM), transport mainly occurs through silicic acid transport proteins (SITs), and at higher concentrations it occurs through diffusion. Previous analyses of the SITs were done either in heterologous systems or without a distinction between individual SITs. In the present study, we examined individual SITs in Thalassiosira pseudonana in terms of transcript and protein abundance in response to different silicic acid regimes and examined knockdown lines to evaluate the role of the SITs in transport, silica incorporation, and lipid accumulation resulting from silicon starvation. SIT1 and SIT2 were localized in the plasma membrane, and protein levels were generally inversely correlated with cellular silicon needs, with a distinct response being found when the two SITs were compared. We developed highly effective approaches for RNA interference and antisense knockdowns, the first such approaches developed for a centric diatom. SIT knockdown differentially affected the uptake of silicon and the incorporation of silicic acid and resulted in the induction of lipid accumulation under silicon starvation conditions far earlier than in the wild-type cells, suggesting that the cells were artificially sensing silicon limitation. The data suggest that the transport role of the SITs is relatively minor under conditions with sufficient silicic acid. Their primary role is to sense silicic acid levels to evaluate whether the cell can proceed with its cell wall formation and division processes.

Antisense inhibition of amoebapore expression in Entamoeba histolytica causes a decrease in amoebic virulence

Amoebapores have been proposed to be a major pathogenicity factor of the protozoan parasite Entamoeba histolytica, which is responsible for the killing of target cells. These 77-residue peptides are structural and functional analogues of NK-lysin and granulysin of porcine and human cytotoxic lymphocytes. Inhibition of amoebapore gene expression in amoebae was obtained following transfection with a hybrid plasmid construct (pAP-R2) containing the Neo resistance gene and the gene coding for amoebapore A, including its 5' and 3' untranslated region (UTR) sequences, in reverse orientation under a promoter (g34) taken from one of the E. histolytica ribosomal protein (RP-L21) gene copies. Transfectants of virulent E. histolytica strain HM-1:IMSS, in which the expression of amoebapore was inhibited by approximately 60%, were significantly less pathogenic. Cytopathic and cytolytic activities of viable trophozoites against mammalian nucleated cells, as well as lysis of red blood cells, were markedly inhibited. Moreover, trophozoite extracts of pAP-R2 transfectant displayed lower pore-forming activity and were less potent in inhibiting bacterial growth compared with controls. Notably, liver abscess formation in hamsters by the pAP-R2 transfectant was substantially impaired. These results demonstrate for the first time that amoebapore is one of the pathogenicity factors by which trophozoites of E. histolytica exert their remarkable cytolytic and tissue destructive activity.

Modification of glucose and glutamine metabolism in hybridoma cells through metabolic engineering

The present work describes the genetic modification of a hybridoma cell line with the aim to change its metabolic behaviour, particularly reducing the amounts of ammonia and lactate produced by the cells. The cellular excretion of ammonia was eliminated by transfection of a cloned glutamine synthetase gene. The metabolic characterisation of the transformed cell line includes the analysis of the changes introduced in its intracellular metabolic fluxes by means of a stoichiometric model. Furthermore, the reduction of lactate accumulation was attempted through an antisense mRNA approach, aiming to generate a rate limiting step in the glycolytic pathway, thus lowering the glucose consumption rate. The physiological results obtained with the transformed cells are discussed. A maximum reduction of about 47% in the glucose consumption rate was obtained for one of the transformations. However a main drawback was the lack of stability of the transformed cells.

Inhibition of human squamous cell carcinoma growth in vivo by epidermal growth factor receptor antisense RNA transcribed from the U6 promoter

BACKGROUND

Squamous cell carcinomas of the head and neck (SCCHN), unlike normal mucosal squamous epithelial cells, overexpress epidermal growth factor receptor (EGFR) messenger RNA and protein. EGFR protein is required to sustain the proliferation of SCCHN cells in vitro. To determine whether EGFR expression contributes to tumor growth, we investigated the effect of suppressing EGFR expression in tumor xenografts through in situ expression of antisense oligonucleotides.

METHODS

Intratumoral cationic liposome-mediated gene transfer was used to deliver plasmids capable of expressing sense or antisense EGFR sequences into human head and neck tumors, which were grown as subcutaneous xenografts in nude mice. The oligonucleotides were expressed under the control of the U6 RNA promoter.

RESULTS

Direct inoculation of the EGFR antisense (but not the corresponding sense) plasmid construct into established SCCHN xenografts resulted in inhibition of tumor growth, suppression of EGFR protein expression, and an increased rate of apoptosis (programmed cell death). Sustained antitumor effects were observed for up to 2 weeks after the treatments were discontinued.

CONCLUSION

These results suggest that interference with EGFR expression, using an antisense-based gene therapy approach, may be an effective means of treating EGFR-overexpressing tumors, including SCCHN.

Suppression of c-fos induction in rat brain impairs retention of a brightness discrimination reaction

Recently, the induction of transcription factor-encoding immediate-early genes such as c-fos was observed in distinct brain regions of rats trained to acquire a footshock-motivated brightness discrimination in a Y-maze. The functional relevance of inducible transcription factors for learning and memory formation is, however, not clear. To address this question in the present study, we have used a synthetic antisense phosphorothioate oligodeoxynucleotide to suppress in vivo the expression of c-fos in rat brain. Intrahippocampal application of the oligodeoxynucleotide 10 hr and 2 hr before starting a brightness discrimination training drastically reduced the induction of c-Fos immunoreactivity normally observed in limbic and cortical areas after the training session. Acquisition of the discrimination reaction was not affected by this treatment. In a relearning test 24 hr after the first training, retention of the discrimination reaction was specifically impaired compared with rats pretreated with control oligodeoxynucleotide or saline. Our findings are consistent with the hypothesis that the inducible transcription factor c-Fos is involved in processes underlying the formation of long-term memory.

Analysis of gene function in Dictyostelium

Over the past ten years, powerful molecular genetic techniques have been developed to analyze gene function in Dictyostelium. DNA-mediated transformation using a variety of selections and vectors has allowed the introduction of wild-type or modified genes that are under various forms of transcriptional control. Homologous recombination is efficient and can be used to modify the genome in precise ways. In addition, it is now possible to clone genes based on their mutant phenotype alone, either by insertional mutagenesis, or by screening antisense expression cDNA libraries. Finally, a nearly complete physical map of the genome is available and so genes are easily mapped by physical techniques. We discuss many of these advances within the context of major research problems presently under study.

Transfection with bFGF sense and antisense cDNA resulting in modification of malignant glioma growth

Aberrant autocrine control by peptide growth factors is a possible mechanism by which disordered regulation of cell proliferation may occur. The authors used the C6 glioma cell line as a model to study the role of basic fibroblast growth factor (bFGF) in tumor growth by transfection with bFGF complementary deoxyribonucleic acid in both the sense and antisense orientation. Clones with high messenger ribonucleic acid expression of the sense construct have increased proliferation in cell culture and increased levels of intracellular and extracellular bFGF. Clones with high expression of the antisense construct show decreased proliferation in culture and reduced levels of immunologically detectable bFGF.

Systematic analysis of antisense RNA inhibition of myosin II heavy-chain gene expression in Dictyostelium discoideum

The powerful potential of antisense nucleotide inhibition of gene expression is presently being exploited in many biological systems. Although use of the technique is widespread, little is known about the variables that contribute to experimental success. We sought to define those variables that affect inhibition of myosin II heavy-chain (MIIHC) gene expression by stable nuclear-derived antisense RNAs in Dictyostelium discoideum. Different fragments of the MIIHC gene cloned in the antisense orientation into several transformation vectors were introduced into cells, and the accumulation of MIIHC protein and mRNA was examined. Inhibition of expression ranged from slight to virtually complete, and depended only on the specific gene fragment used to generate the antisense RNA. Fragments of the 3' end of the gene were the most effective and resulted in almost complete inhibition, whereas 5' fragments gave very little reduction. The severity of the morphological phenotypes associated with MIIHC depletion reflected the different levels of MIIHC in the transformants. Important implications for the design of antisense vectors suggested by these results are discussed.