Question

How might differences between the kinetics of mRNA suppression and protein half-life affect the timing of the observed therapeutic effect?

Answer 1

The development of mRNA therapeutics received a significant boost following studies that demonstrated dendritic cells (DCs) pulsed with mRNA in vitro could become potent antigen-presenting cells in vivo. Various delivery methods were explored to ascertain the most efficient method to transfect DCs with mRNA. Ex vivo approaches to vaccination using autologous blood-derived DCs electroporated with tumor mRNA were developed and translated into clinical studies in patients with cancer. As a rapidly emerging class of nucleic acid therapeutics, there are key benefits in using mRNA over plasmid DNA for vaccine or therapeutic applications. First, mRNA contains no viral promoters (e.g. CMV) and bacterial sequences that can cause toxicity. Second, mRNA does not integrate into the host genome, which may lead to deleterious mutation. Third, gene expression via mRNA is relatively transient and therefore safer to use compared to DNA. Last but not least, as mRNA does not need to cross the nuclear envelope, it increases the chances of successfully transfecting quiescent cells such as DCs.

Precise control of protein turnover is essential for cellular homeostasis. The ubiquitin-proteasome system is well established as a major regulator of protein degradation, but an understanding of how inherent structural features influence the lifetimes of proteins is lacking. We report that yeast, mouse, and human proteins with terminal or internal intrinsically disordered segments have significantly shorter half-lives than proteins without these features. The lengths of the disordered segments that affect protein half-life are compatible with the structure of the proteasome. Divergence in a terminal and internal disordered segments in yeast proteins originating from gene duplication leads to significantly altered half-life. Many paralogs that are affected by such changes participate in signaling, where altered protein half-life will directly impact cellular processes and function. Thus, natural variation in the length and position of disordered segments may affect protein half-life and could serve as an underappreciated source of genetic variation with important phenotypic consequences.