Newly Discovered Virology Principle Helps Guide Vaccine Development
Viruses that infect humans and other mammals are classified into 22 distinct families. Six of these families are classically persistent — that is once infected by one of these viruses, the individual will have the infection for life. These persistent families include the herpesviruses and HIV, the virus that causes Acquired Immune Deficiency Syndrome (AIDS).
A new study by researchers at the Miller School of Medicine describes for the first time a new general principal of virology — that all members of the six persistent families use an unusual strategy to stringently regulate, in a time-ordered fashion, the expression of the proteins that make up the virus particle. This is called temporal regulation of viral protein expression. The findings are shared online in the journal Proceedings of the National Academy of Sciences.
This new discovery may have important applications for the development of vaccines that could protect against and even cure previously refractory infections, such as HIV. The findings may also have implications for the use of viral vectors to correct hereditary disorders.
“This finding is fundamental new knowledge of how viruses do what they do,” said Ronald C. Desrosiers, Ph.D., professor of pathology and principal investigator of this project. “Basic fundamental observations like this are important over the long term for increasing our understanding and the armamentarium that can be applied to treat and/or prevent human diseases.”
Every protein is made up of amino acid building blocks. There are 20 amino acids. A protein’s ability to function is determined by the specific sequence of amino acids that make up an individual protein. That sequence is encoded in the DNA by units of genetic information called codons, where each codon specifies a particular amino acid. The precursor protein for the viral encoded proteins of the HIV and the SIV is called gp160.
The new findings show that the six persistent virus families employ a highly unusual codon usage to make the proteins of the virus particle. The molecules that turn on, or induce, the genes for making protein are expressed early in the replication cycle of the virus. However, the actual proteins of the virus particle are made late in the cycle.
Richard J. Cote, M.D., Professor and Joseph R. Coulter Chair of the Department of Pathology, professor of biochemistry and molecular biology, Chief of Pathology at Jackson Memorial Hospital, and Director of BioNIUM, concurs on the significance of the current findings for the field of virology and the potential development of persistent vaccines.
“This latest discovery is a stunning finding of a new general principal of virology,” Cote said. “Besides its fundamental importance to understanding viral biology, this discovery will very likely have practical applications, especially in vaccine therapy. In fact, the Desrosiers lab has already shown that altered codon usage has allowed, for the first time, anti-gp160 antibody responses in their herpesvirus vector system, suggesting use of this finding in generating persistent immune responses to HIV and other viruses.”
The study looked at the molecules that turn on, or induce, the genes for making the viral proteins. Rev is the natural trans-inducer for HIV and SIV, and Orf57 is the natural trans-inducer for RRV, the herpesvirus of the rhesus monkey. Both are early viral products.
In order to analyze the influence of codon usage, researchers changed the sequence of each virus in the lab, in such a way that the herpesvirus coding sequence for proteins resembled more the codon sequence of the AIDS virus and vice versa.
“Remarkably, the findings show that trans-induction of the AIDS virus and the herpesvirus can be flipped, simply by imparting distinctive changes in codon usage,” Desrosiers said. “In other words, rev dependence of gp160 expression can be flipped to orf57 dependence, simply by manipulating the nature of the codon usage of the target gene.”
The researchers are continuing to increase the level of detailed understanding by extending their observations to other families of viruses and the details of how this temporal regulation is achieved.
The study is titled “Importance of Codon Usage for the Temporal Regulation of Viral Gene Expression.” Collaborating authors from the Department of Pathology are Young C. Shin, Ph.D., assistant scientist, Georg F. Bischof, research associate, and William A. Lauer, lab manager.