Ancient viral elements embedded in human genome not from fossil retrovirus

The ancient retrovirus moves around our genome and may be a risk for regenerative medicine

Date:: May 27, 2022
Source:: Kumamoto University
Summary:: 许多种类的动物,包括人类,是否成功lly coexist with retroviruses, and we know that ancient retrovirus viral elements can even be found within our genome. We also know that these endogenous retroviruses can be utilized for development and evolution. However, uncontrolled endogenous retroviruses may be a cause of disease in the human body. Now, researchers have discovered that endogenous retroviruses in our genome may pose a risk in regenerative medicine.
Share:: Facebook Twitter Pinterest LinkedIN Email

FULL STORY

Using a next generation sequencing analysis to examine human endogenous retrovirus (HERV) integration sites, researchers from Kumamoto University, the National Institute of Genetics (Japan), and the University of Michigan (USA) have discovered that these ancient retroviruses can undergo retrotransposition (DNA sequence insertion with RNA mediation) into iPS cells. The team believes that their discovery places a spotlight on a possible risk that HERVs pose when using iPS cells in regenerative medicine.

The study of ancient retroviruses embedded in our genome requires knowledge about our coexistence with viral threats throughout history. We know that HERVs occupy approximately 8% of the human genome and obtain mutations and deletions over long periods. HERVs are also expressed in early embryos and play several physiological roles in human development. For example, HERV-W and HERV-FRD Env proteins are important for placental formation, and HERV-K is thought to protect host cells from exogenous retrovirus infection. However, uncontrollable HERV-K expression is also thought to be associated with various diseases, including various cancers and neurological diseases, but the details of this association is not well known in humans.

因为还没有人发现复制竞争ent HERVs in our genome, it is thought that they are from an extinct (fossil) virus. In their current work, the research team from Japan and the US discovered that HERV-K is expressed in SOX2-expressing cells, such as those in early embryos, cancer stem cells and iPS cells. They also found that some HERV-K are newly integrated into the host genome in the absence of Env, the viral envelope glycoprotein. This integration was dependent on reverse transcriptase, integrase and protease, thus the researchers hypothesized that the HERV-K embedded in our genome is actually not from a fossil virus, but moves on the genome through the synthesis of proviral DNA reverse transcription. Interestingly, when the researchers compared the HERV-K integration sites between iPS and fibroblast cells from the same donor, they found new HERV-K integration sites in iPS cells. However, the new integration sites were rarely preserved and disappeared during long-term culturing. HERV-K is likely to be randomly integrated into genome, thus the possibility remains that HERV-K retrotransposed-cells predominantly survive depending on their integration site.

The movement of HERV-K on the genome might cause cancer and neurological diseases by altering the gene expression profile. The researchers believe that the risk of HERV-K transposition is low in iPS cells but suggest that monitoring HERV-K integration sites should be seriously considered to improve the safety of regenerative medicine using iPS cells.

This research was published online on 14 April 2022 in theJournal of Virology.