A research team led by Nigel W. Fraser, PhD, Professor of Microbiology, has found that herpes simplex virus-1 (HSV-1), the virus that causes cold sores and ocular keratitis, produces an miRNA molecule. This miRNA is encoded by the Latency-Associated Transcript gene (LAT) in the viral genome and works through a process called RNA interference to prevent normal cell death or apoptosis. Thus, the latent viral infection is maintained for the lifetime of the individual because the latently infected cell does not die.
"Although miRNAs encoded by cellular genes are known to be an important mechanism for controlling gene expression, this is one of the first miRNA found to be encoded by a viral genome," says Fraser. "Our study helps show how HSV-1 can maintain a latent infection for the lifetime of an infected individual."
The LAT gene was discovered by Fraser and colleagues in 1984, but a protein product from this gene has never been found. This caused Fraser and his research team to hypothesize that LAT may work through an miRNA molecule, which is a small piece of the LAT gene. It interferes with the translation of two cell proteins that are required for cell death: TGF-b and SMAD-3. The LAT miRNA binds to specific sequences of messenger RNA from these two genes and causes them to be degraded. Thus, the amount of TGF-b and SMAD-3 protein is reduced in the cell and apoptosis is prevented. Because the latent virus is not producing any viral proteins the immune system of the infec
Source:University of Pennsylvania School of Medicine