Replication of Human Endogenous Retroviruses in Modern Humans
Human endogenous retroviruses make up 8% of the human genome, but are generally thought to be genomic “fossils” no longer capable of replication. Our group has evidence that one of these viruses, HERV-K, might still be capable of active replication in modern humans, and is found at high levels in the blood of certain patients with cancer. As these viruses contain oncogenes, active replication could be involved in the pathogenesis of some malignancies, and would have potentially serious consequences for the human blood supply. However, ascertaining the replicative capability of these viruses, which are an innate part of all human cells, is difficult and requires new and multi-disciplinary approaches. Here we propose several complementary pathways to examine whether the HERV-K endogenous retrovirus is indeed capable of replication in modern humans. In Aim I, we use classical virology methods to explore whether HERV-K can be taken from the blood of cancer patients and grown in the laboratory. Animal cells are used as a target, as it is very difficult to differentiate between new and old infection in human cells. In Aim III, we again assess whether HERV-K from the blood of patients can be passaged in the laboratory, but this time we use genetic engineering to create a system where viral replication can be assessed by antibiotic resistance. This system allows us to detect new HERV-K infection in human cells. We will also use nuclear magnetic resonance (NMR) with labeled viruses (red) to examine HERV-K replication in human and non-human cells. In Aim II, we use the tools of very rapid DNA sequencing (deep sequencing) and computer analysis (bioinformatics) to look for the presence of infectious HERV-K genetic material (DNA) in the cells of cancer patients. These methods, as well as direct cloning of cDNAs derived from viral RNAs in the blood, will also be used to generate an infectious clone of modern HERV-K. If HERV-K does indeed replicate, this finding will cast new light on a significant part of the human genome, be relevant to cancer biology and perhaps therapy, and suggest the possibility that the blood supply will need to be screened for these viruses.
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