Antonopoulos, A

Barthel, SR

Bhattacharyya, N

Dimitroff, CJ

Geddes-Sweeney, J

Giovannone, N

Haslam, SM

Liang, J

Pochebit, SM

Widlund, HR

Glycobiology

English

Spiral - Imperial College Digital Repository

ST3Gal1 truncates O-glycans and augments galectin-3binding to CD45 in human B cellsNicholas Giovannone1,4, Jenna Geddes-Sweeney1,4, JenniferLiang1, Aristotelis Antonopoulos2, Stephen M. Pochebit3,4,Neil Bhattacharyya5,6, Steven R. Barthel1, Hans R.Widlund1, Stuart M. Haslam2, Charles J. Dimitroff1,41Department of Dermatology, Brigham and Women’sHospital, Boston, MA, USA; 2Department of Life Sciences,Imperial College London, London, United Kingdom;3Department of Pathology, Brigham and Women’sHospital, MA, USA; 4Harvard Medical School, Boston, MA,USA; 5Department of Surgery, Division of Otolaryngology,Brigham and Women’s Hospital, Boston, MA, USA;6Department of Otology and Laryngology, HarvardMedical School, Boston, MA, USALymphocyte activation is commonly accompanied by structural remodeling of glycans on membrane glycoproteins. On T cells, activation and differentiation lead to alterations in glycosylation that influence binding of endogenous lectins, including regulators of T cell survival (galectins) and trafficking (selectins). Based on these studies, we hypothesized B cells similarly undergo glycan restructuring during activation and differentiation that modulates endogenous lectin binding. To test this, we profiled human tonsil naive, germinal center (GC), memory, and plasmablast (PB) B cells by flow cytometry and immunohistochemistry with plant lectins. We found GC B cells show 4-fold increased expression of polylactosamine (polyLN) compared to naive, memory, and PB B cells, as measured by STA and LEA lectin binding. We further observed that GC B cells display more asialylated Core 1 O-glycans (PNA binding), consistent with numerous reports. Because polyLN and Core 1 sialylation can be simultaneously controlled by the Core 1 α2,3 sialyltransferase ST3Gal1 in T cells, we sought to test whether decreased ST3Gal1 expression may explain augmented polyLN levels in GC B cells. Indeed, we found that GC B cells express 4-fold less ST3Gal1 than naive and memory B cells. Furthermore, we observed that enforced ST3Gal1 expression in GC-like Ramos B cells ablates Core 2 polyLNs in both flow cytometric and MALDI-TOF MS analyses. As polyLNs are high affinity ligands for galectin-3 (Gal-3), a regulator of B lymphoma cell apoptosis, we tested whether GC B cells demonstrate increased Gal-3 binding. Unexpectedly, GC B cells bound significantly less Gal-3 compared to naive (4- fold) and memory (2-fold) B cells, and ST3Gal1 overexpression in Ramos B cells enhanced Gal-3 binding by >10-fold. Co-immunoprecipitation studies revealed the primary glycoprotein receptor of Gal-3 on Naive B cells to be CD45. Collectively, these studies implicate ST3Gal1 as a regulator of O-glycan polyLN and Gal-3 binding to B cells, primarily to CD45. Ongoing studies are focused on understanding the mechanism of altered Gal-3 binding, and how Gal-3 may influence CD45 activity. Because CD45 is a major receptor tyrosine phosphatase central to B cell receptor signaling, altered Gal-3/CD45 dynamics may have important consequences for development of high-affinity antibody responses in GCs.

ST3Gal1 truncates O-glycans and augments galectin-3 binding to CD45 in human B cells

http://spiral.imperial.ac.uk/bitstream/10044/1/44462/2/ST3Gal1%20truncates%20O.docx

ST3Gal1 truncates O-glycans and augments galectin-3 binding to CD45 in human B cells

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