Profiling the regulatory landscape of sialylation through miRNA targeting of CMP- sialic acid synthetase.

Cell surface sialic acid is an important glycan modification that contributes to both normal and pathological physiology. The enzyme cytidine monophosphate N-acetylneuraminic acid synthetase (CMAS) biosynthesizes the activated sugar donor cytidine monophosphate (CMP) sialic acid, which is required for all sialylation. CMAS levels impact sialylation with corresponding biological effects. The mechanisms that regulate CMAS are relatively uncharacterized. Herein, we use a high throughput genetically encoded fluorescence assay (miRFluR) to comprehensively profile the posttranscriptional regulation of CMAS by miRNA. These small non-coding RNAs have been found to impact glycosylation. Mapping the interactions of the human miRNAome with the 3'-untranslated region of CMAS, we identified miRNA whose impact on CMAS expression was either downregulatory or upregulatory. This follows previous work from our laboratory and others showing that miRNA regulation is bidirectional. Validation of the high-throughput results confirmed our findings. We also identified the direct binding sites for two upregulatory and two downregulatory miRNAs. Functional enrichment analysis for miRNAs upregulating CMAS revealed associations with pancreatic cancer, where sialic acid metabolism and the α-2,6-sialyltransferase ST6GAL1 have been found to be important. We found that miRNA associated with the enriched signature enhanced pancreatic cell-surface α-2,6-sialylation via CMAS expression in the absence of effects on ST6GAL1. We also find overlap between the miRNA regulation of CMAS and that of previously analyzed sialyltransferases. Overall, our work points to the importance of miRNA in regulating sialylation levels in disease and add further evidence to the bidirectional nature of miRNA regulation.