Riboregulation of human Serine Hydroxymethyltransferase activity in cellular metabolism

In the past, a number of metabolic enzymes were solely recognized for their primary metabolic function, but it is now evident that the vast majority of them are engaged in other activities. These moonlighting traits often involve non-standard interactions with other proteins or nucleic acids. In this context, there are proteins that bind and control the fate of an RNA molecule. Nonetheless, it is essential to acknowledge the presence of a phenomenon known as riboregulation, a mechanism by which RNA molecules can influence the protein to which they bind, hence regulating their enzymatic activity and/or location. In this scenario SHMT proteins offer a paradigmatic example: they have a key role in the One Carbon Metabolism for the control of the redox balance of the cells and production of nucleotides. In the meantime, SHMTs can bind RNA; the RNA-SHMT1 (the cytosolic isoform) interaction not only control RNA translation but also the catalytic activity of the enzyme. Due to the role of SHMT proteins in OCM and the importance of this pathway for highly proliferating cells, the lack of effective inhibitors that block the activity of these enzymes represents a significant problem. The objective of this thesis is to demonstrate that riboregulation of the mitochondrial SHMT2 isoform also occurs, and to propose that the RNA-binding feature of SHMT2 might be utilized to target this protein through the production of an RNA-based inhibitor (iRNA). This research represents a starting point for understanding how metabolic enzymes are riboregulated and provides the proof-of-concept for the development of a unique RNA-based approach to inhibit cancer cell growth, a novel potentially effective tool for patients chemotherapy.