High-Throughput Analysis Reveals miRNA Upregulating α-2,6-Sialic Acid through Direct miRNA-mRNA Interactions

Chemical biology has revealed the importance of sialic acids as a major signal in physiology and disease. The terminal modification alpha-2,6-sialic acid is controlled by the enzymes ST6GAL1 and ST6GAL2. Dysregulation of this glycan impacts immunological recognition and cancer development. microRNAs (miRNA, miR), noncoding RNAs that downregulate protein expression, are important regulators of glycosylation. Using our recently developed high-throughput fluorescence assay (miRFluR), we comprehensively mapped the miRNA regulatory landscape of alpha-2,6-sialyltransferases ST6GAL1 and ST6GAL2. We found, contrary to expectations, the majority of miRNAs upregulate ST6GAL1 and alpha-2,6-sialylation in a variety of cancer cells. In contrast, miRNAs that regulate ST6GAL2 were predominantly downregulatory. Mutational analysis identified direct binding sites in the 3 '-untranslated region (UTR) responsible for upregulation, confirming it is a direct effect. The miRNA binding proteins AGO2 and FXR1 were required for upregulation. Our results upend common assumptions surrounding miRNA, arguing that upregulation by these noncoding RNA is common. Indeed, for some proteins, upregulation may be the dominant function of miRNA. Our work also suggests that upregulatory miRNAs enhance overexpression of ST6GAL1 and alpha-2,6-sialylation, providing another potential pathway to explain the dysregulation observed in cancer and other disease states.

Automated summary

Chemical biology has revealed the significance of sialic acids as important signals in physiology and disease. miRNAs, noncoding RNAs that downregulate protein expression, have been shown to play a role in regulating glycosylation. Contrary to expectations, our study found that the majority of miRNAs upregulate ST6GAL1 and alpha-2,6-sialylation in cancer cells, while miRNAs that regulate ST6GAL2 were predominantly downregulatory. This challenges previous assumptions about miRNA and suggests a potential pathway for explaining the dysregulation of sialylation observed in cancer and other diseases.