G-Quadruplex and i-Motif Structures in the SHMT1 5'UTR Modulate Gene Expression

Multiple sclerosis (MS) is a fatal neurodegenerative disease that progresses by eroding the myelin sheath and exposing the neuron, leading to neuronal degradation and death. While MS remains without an effective treatment or cure, studies have identified genes that are dysregulated in MS patients and predicted to be involved with disease progression. These genes are primarily involved in controlling DNA methylation: a process required for regulating gene expression, which is critical for cellular health. Having identified potential genetic risk factors, research is focused on how to manipulate the expression of these genes by offsetting DNA methylation errors in patients through the targeting of DNA and RNA secondary structure formation. Serine hydroxy methyltransferase 1 (SHMT1), a key player in DNA methylation, was determined to be upregulated in MS patients. Here, we identified and characterized a hybrid 3+1 G-quadruplex (GQ) and i-motif (iM) structures in the SHMT1 DNA 5' untranslated region and a parallel GQ in the corresponding mRNA. Additionally, we found that the GQ/iM structures suppress the mRNA levels and protein expression of a reporter gene. Together, these data suggest that GQ/iM structures are necessary for SHMT1 regulation, which could serve as a target for therapeutic intervention for MS patients.