One key obstacle to crafting effective gene therapies is the ability to tailor dosing according to a patient’s needs. This can be tricky because even if protein production is successful, staying within the therapeutic window is paramount—too much of a protein could be toxic, and too little will not produce the desired effect. This balance is difficult to achieve with current technologies. In a study recently published in Nature Biotechnology, researchers at Baylor College of Medicine investigated a possible solution to this problem, engineering a molecular “on/off” switch that could regulate gene expression and maintain protein production at dose-dependent, therapeutic levels.
Most modulatory mechanisms that have been used to regulate gene expression in mammalian cells have not been approved for clinical applications because they involve the introduction of a foreign regulatory protein, which carries the risk of triggering an immune response. Cells that express the therapeutic protein would then be neutralized by the immune system, rendering the therapy ineffective.
New research has proposed something of a workaround: a pA regulator, or an RNA-based system that uses a synthetic polyadenylation signal (PAS) to modulate gene expression, together with the addition of an upstream binding site specific to tetracycline.
In normal gene expression, the PAS typically occurs during transcription and signals for the addition of a polyA tail to an mRNA sequence. This tail, a chain of adenine nucleotides, plays a crucial role in stabilizing the mRNA and protecting it from degradation as it is transported out of the nucleus. In this particular study, scientists have engineered RNA to include a synthetic PAS outside of where it is normally located within the RNA sequence. This placement disrupts protein production, setting the system’s default state to ‘off.’ Researchers also introduced a binding site upstream of this synthetic PAS that can specifically bind to a tetracycline molecule. Tetracycline interacts with this binding site, inhibiting the function of the synthetic PAS. This inhibition turns the switch ‘on’, allowing mRNA to be processed normally (including the addition of a polyA tail), thereby facilitating normal protein production.
In theory, different doses of tetracycline would lead to different levels of gene expression. A patient who only needs a small amount of the gene therapy would be given a smaller dose than someone who needs a larger amount, and the subsequent levels of gene expression would reflect these doses. This strategy represents a novel way to tune gene expression in response to different dosing requirements and has the potential to lead to more personalized and effective gene therapies.
- Liming Luo, Jocelyn Duen-Ya Jea, Yan Wang, Pei-Wen Chao, Laising Yen. Control of mammalian gene expression by modulation of polyA signal cleavage at 5′ UTR. Nature Biotechnology, 2024; DOI: 10.1038/s41587-023-01989-0
- Baylor College of Medicine. “A novel switch to turn genes on/off on cue, a promising step toward safer gene therapy.” ScienceDaily. ScienceDaily, 2 January 2024.
- A step closer to safe and efficient mammalian gene regulation | Nature Biotechnology
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