N-Linked Glycosylation Regulates CD22 Organization and Function

Frontiers in Immunology

卷:10

Bebhinn Treanor²  Myuran Yoganathan²  Fathima Hifza Mohamed Buhari³  Laabiah Wasim⁴  Taylor Sicard⁵  June Ereño-Orbea⁵  Jean-Philippe Julien⁵ 

[1] Department of Biochemistry, University of Toronto, Toronto, ON, Canada;

[2] Department of Biological Sciences, University of Toronto Scarborough, Toronto, ON, Canada;

[3] Department of Cell and Systems Biology, University of Toronto, Toronto, ON, Canada;

[4] Department of Immunology, University of Toronto, Toronto, ON, Canada;

[5] The Hospital for Sick Children Research Institute, Toronto, ON, Canada;

关键词: B cell receptor;    B cell activation;    signaling;    CD22;    glycosylation;    galectin-9;   

DOI  :  10.3389/fimmu.2019.00699

来源: DOAJ

【 摘 要 】

The organization and clustering of cell surface proteins plays a critical role in controlling receptor signaling; however, the biophysical mechanisms regulating these parameters are not well understood. Elucidating these mechanisms is highly significant to our understanding of immune function in health and disease, given the importance of B cell receptor (BCR) signaling in directing B cells to produce antibodies for the clearance of pathogens, and the potential deleterious effects of dysregulated BCR signaling, such as in B cell malignancies or autoimmune disease. One of main inhibitory co-receptors on B cells is CD22, a sialic-acid binding protein, which interacts homotypically with other sialylated CD22 molecules, as well as heterotypically with IgM and CD45. Although the importance of CD22 in attenuating BCR signaling is well established, we still do not fully understand what mediates CD22 organization and association to BCRs. CD22 is highly glycosylated, containing 12 N-linked glycosylation sites on its extracellular domain, the function of which remain to be resolved. We were interested in how these glycosylation sites mediate homotypic vs. heterotypic interactions. To this end, we mutated five out of the six N-linked glycosylation residues on CD22 localized closest to the sialic acid binding site. Glycan site N101 was not mutated as this resulted in lack of CD22 expression. We used dual-color super-resolution imaging to investigate the impact of altered glycosylation of CD22 on the nanoscale organization of CD22 and its association with BCR. We show that mutation of these five glycosylation sites increased the clustering tendency of CD22 and resulted in higher density CD22 nanoclusters. Consistent with these findings of altered CD22 organization, we found that mutation of N-glycan sites attenuated CD22 phosphorylation upon BCR stimulation, and consequently, increased BCR signaling. Importantly, we identified that these sites may be ligands for the soluble secreted lectin, galectin-9, and are necessary for galectin-9 mediated inhibition of BCR signaling. Taken together, these findings implicate N-linked glycosylation in the organization and function of CD22, likely through regulating heterotypic interactions between CD22 and its binding partners.

【 授权许可】

Unknown