A. MAITI1,3, R. Wu1, L. Yan4, Y. Wu2, J.T. Lau3, N.C. Hait1,3 1Roswell Park Cancer Institute, Surgical Oncology, Buffalo, NY, USA 2University at Buffalo, Biomedical Engineering, Buffalo, NY, USA 3Roswell Park Cancer Institute, Molecular And Cellular Biology, Buffalo, NY, USA 4Roswell Park Cancer Institute, Biostatistics And Bioinformatics, Buffalo, NY, USA
Introduction:
There is substantial literature correlating ST6GAL1, the sialyltransferase mediating the construction of α2,6- linked sialic acid linkages, with a wide-ranging array of pathologic conditions such as inflammation, immunity, hematology, and malignancy. ST6GAL1 action is presumed to be an intracellular, cell-autonomous process where the sialyltransferase resides within the ER-Golgi secretory apparatus and glycosylates nascent glycoconjugates in biosynthetic transit. ST6GAL1 is also present extracellularly in abundance, but the significance of extracellular ST6GAL1 (exoST6) is understudied and not considered. Here, we investigate the novel concept that exoST6, which can be released cell-natively in exosome vesicles or from distal sources, e.g., the liver in cytosolic form, is a principal driver of tumor cell biology. We utilize breast cancer cells as a model, and this study examines the never-considered mechanism of exoST6 in regulating cancer pathobiology. This is a pioneering investigation into extracellular glycosyltransferases as systemic regulators of tumor cell function.
Methods:
Protein and mRNA analysis of functional ST6GAL1 were performed in TNBC and ER+ breast cancer cells. Tumor cells released exosome characterization for functionally active ST6GAL1 expression and correlation with aggressive disease of breast cancer patients. Extracellular ST6GAL1 in triple-negative breast cancer (TNBC) 3D spheroid cell phenotypes and growth analysis.
Results:
We hypothesize that ST6GAL1 action is the combined native sialyltransferase acting cell-autonomously within the ER-Golgi complex and extracellular ST6GAL1 acting to remodel cellular glycans. Extracellular ST6GAL1, coordinated by co-factors in exosomes from cancer cells, modify and shape pathobiologic progression. Analysis using TCGA and METABRIC cohorts revealed that elevated ST6GAL1 is associated with enrichment in gene networks associated with cancer stemness (Hedgehog), epithelial-mesenchymal transition (EMT), and hypoxia pathways. Functional ST6GAL1 is heterogeneously expressed in cultured breast cancer cells and clinical tissue specimens. Breast cancer cells release functionally active ST6GAL1 in exosome vesicles and compensate for cell-native ST6GAL1 functions in tumor cell growth and invasive phenotypes. Breast cancer patients have elevated circulatory functional ST6GAL1 in exosomes associated with disease severity vs. healthy control clinical specimens.
Conclusion:
Our data support the novel concept that the extracellular pool, which can be cell-natively released or from non-native origins, is the principal driver of tumor cell invasive phenotypes and growth. Breast cancer cells as a model, the study examines the never-considered mechanism of extracellular ST6GAL1 in regulating cancer pathobiology. This study is also a pioneering investigation into an entirely new aspect of glycoscience of extracellular glycosyltransferases as systemic regulators of cell function.