Anticancer activity of an adenoviral vector expressing short hairpin RNA against BK virus T-ag

A review on current status of antiviral siRNA

Viral diseases like influenza, AIDS, hepatitis, and Ebola cause severe epidemics worldwide. Along with their resistant strains, new pathogenic viruses continue to be discovered so creating an ongoing need for new antiviral treatments. RNA interference is a cellular gene‐silencing phenomenon in which sequence‐specific degradation of target mRNA is achieved by means of complementary short interfering RNA (siRNA) molecules. Short interfering RNA technology affords a potential tractable strategy to combat viral pathogenesis because siRNAs are specific, easy to design, and can be directed against multiple strains of a virus by targeting their conserved gene regions. In this review, we briefly summarize the current status of siRNA therapy for representative examples from different virus families. In addition, other aspects like their design, delivery, medical significance, bioinformatics resources, and limitations are also discussed.

The role of Merkel cell polyomavirus and other human polyomaviruses in emerging hallmarks of cancer

Polyomaviruses are non-enveloped, dsDNA viruses that are common in mammals, including humans. All polyomaviruses encode the large T-antigen and small t-antigen proteins that share conserved functional domains, comprising binding motifs for the tumor suppressors pRb and p53, and for protein phosphatase 2A, respectively. At present, 13 different human polyomaviruses are known, and for some of them their large T-antigen and small t-antigen have been shown to possess oncogenic properties in cell culture and animal models, while similar functions are assumed for the large T- and small t-antigen of other human polyomaviruses. However, so far the Merkel cell polyomavirus seems to be the only human polyomavirus associated with cancer. The large T- and small t-antigen exert their tumorigenic effects through classical hallmarks of cancer: inhibiting tumor suppressors, activating tumor promoters, preventing apoptosis, inducing angiogenesis and stimulating metastasis. This review elaborates on the putative roles of human polyomaviruses in some of the emerging hallmarks of cancer. The reciprocal interactions between human polyomaviruses and the immune system response are discussed, a plausible role of polyomavirus-encoded and polyomavirus-induced microRNA in cancer is described, and the effect of polyomaviruses on energy homeostasis and exosomes is explored. Therapeutic strategies against these emerging hallmarks of cancer are also suggested.

Use of herpes simplex virus type 1-based amplicon vector for delivery of small interfering RNA

Silencing of gene expression by small interfering RNAs (siRNAs) is rapidly becoming a powerful tool for genetic analysis of mammalian cells. The use of DNA-based plasmid vectors to achieve transient and stable expression of siRNA has been developed to avoid the problems of double-stranded oligonucleotides transfection. These vectors direct the transcription of small hairpin RNAs (shRNAs) from a polymerase-III (H1 or U6)-RNA gene promoter. However, numerous disadvantages remain, including low transfection efficiency and difficulty in transfecting primary cells. To overcome some of these problems, the use of viral vectors for siRNA delivery has been described. Retroviral, adenoviral, adeno-associated and herpes viral shRNAs delivery systems have been successfully used to silence genes, in vitro and in vivo. The use of a herpes simplex virus type 1 (HSV-1)-based amplicon vector for siRNA delivery into mammalian cells, using human polyomavirus BK (BKV)-transformed cells as a model system is described. The results demonstrate the ability of amplicon vectors to inhibit the expression of BKV T-Ag and tumorigenicity of BKV-transformed cells. We show that the use of the amplicon vector is highly efficient for the delivery of siRNA molecules. The unique ability of these vectors to deliver multiple copies of siRNA may provide a useful tool in the development of novel anticancer therapy.