In what could be a major step forward for gene therapy, an RNA-based switch to regulate gene expression has been developed by researchers at Baylor College of Medicine. The pA regulator, as it is called, turns genes on at different levels using small molecules at FDA-approved doses. Although gene therapy has been going forward at a rapid pace, the ability to regulate therapeutic genes has been a significant impediment.
The study appears today in Nature Biotechnology. The lead authors are Baylor’s Liming Luo and Jocelyn Duen-Ya Jea.
“Although there are several gene regulation systems used in mammalian cells, none has been approved by the U.S. Food and Drug Administration [FDA] for clinical applications, mainly because those systems use a regulatory protein that is foreign to the human body, which triggers an immune response against it,” said the study’s corresponding author Laising Yen, associate professor of pathology and immunology and of molecular and cellular biology at Baylor.
“The solution we found does not involve a foreign regulatory protein that will evoke an immune response in patients. Instead, we use small molecules to interact with RNA, which typically do not trigger an immune response,” Yen said. “We were able to engineer our system in such a way that it works at the FDA-approved dosage.”
The RNA-based switch controls mammalian gene expression through modulation of a synthetic polyA signal (PAS) cleavage introduced into the 5′ UTR of a transgene. RNA is first engineered to contain an extra polyA signal to mark the end of a gene. When the cell’s machinery detects a polyA signal in the RNA, it automatically makes a cut and defines the cut point as the end of the RNA.
“In our system, we use the added polyA signal, not at the end, but at the beginning of the RNA, so the cut destroys the RNA and therefore the default is no protein production. It is turned off until we turn it on with the small molecule,” Yen said.
To turn on the gene at the desired level, the team modified a section of the RNA near the polyA signal such that it can now bind to a small molecule—tetracycline, which has long been FDA-approved. “When tetracycline binds to that section that functions as a sensor on the RNA, it masks off the polyA signal, and the RNA will now be translated into protein,” Yen said.
Such a tool could allow physicians to control the production of therapeutic proteins. If the patient only requires a small amount of the therapeutic protein, then only a small dose of tetracycline will be administered, which will turn on the therapeutic gene only a little. If the patient needs more therapeutic protein, then more tetracycline will be given. To stop production of the therapeutic protein altogether, the patient just stops taking tetracycline.
“This strategy allows us to be more precise in the control of gene expression of a therapeutic protein. It enables us to adjust its production according to disease’s stages or tune to the patients’ specific needs, all using the FDA-approved tetracycline dose,” Yen said. “Our approach is not disease-specific, it can theoretically be used for regulating the expression of any protein, and potentially has many therapeutic applications. In addition, this system is more compact and easier to implement than the existing technologies. Therefore, it also can be very useful in the lab to turn a gene of interest on or off to study its function.”
