Lectin binding to surface Ig variable regions provides a universal persistent activating signal for follicular lymphoma cells

• Published in: Blood Vol. 126; no. 16; pp. 1902 - 1910
• Main Authors: Linley, Adam, Krysov, Sergey, Ponzoni, Maurilio, Johnson, Peter W., Packham, Graham, Stevenson, Freda K.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 15.10.2015
• Subjects: B-Lymphocytes - immunology; B-Lymphocytes - metabolism; B-Lymphocytes - pathology; Calcium Signaling; Cell Adhesion Molecules - immunology; Cell Adhesion Molecules - metabolism; Female; Humans; Immunoglobulin G - immunology; Immunoglobulin G - metabolism; Immunoglobulin M - immunology; Immunoglobulin M - metabolism; Immunoglobulin Variable Region - immunology; Immunoglobulin Variable Region - metabolism; Lectins, C-Type - immunology; Lectins, C-Type - metabolism; Lymphoma, Follicular - immunology; Lymphoma, Follicular - metabolism; Lymphoma, Follicular - pathology; Male; MAP Kinase Signaling System; Mitogen-Activated Protein Kinase 1 - immunology; Mitogen-Activated Protein Kinase 1 - metabolism; Mitogen-Activated Protein Kinase 3 - immunology; Mitogen-Activated Protein Kinase 3 - metabolism; Phospholipase C gamma - immunology; Phospholipase C gamma - metabolism; Proto-Oncogene Proteins c-akt - immunology; Proto-Oncogene Proteins c-akt - metabolism; Proto-Oncogene Proteins c-myc - immunology; Proto-Oncogene Proteins c-myc - metabolism; Receptors, Cell Surface - immunology; Receptors, Cell Surface - metabolism; Receptors, CXCR4 - immunology; Receptors, CXCR4 - metabolism; Tumor Cells, Cultured
• ISSN: 0006-4971; 1528-0020
• DOI: 10.1182/blood-2015-04-640805

The vast majority of cases of follicular lymphoma (FL), but not normal B cells, acquire N-glycosylation sites in the immunoglobulin variable regions during somatic hypermutation. Glycans added to sites are unusual in terminating at high mannoses. We showed previously that the C-type lectins, dendritic cell–specific intercellular adhesion molecule-3 grabbing non-integrin (DC-SIGN) and mannose receptor, bound to FL surface immunoglobulin (sIg), generating an intracellular Ca2+ flux. We have now mapped further intracellular pathways activated by DC-SIGN in a range of primary FL cells with detection of phosphorylated ERK1/2, AKT, and PLCγ2. The SYK inhibitor (tamatinib) or the BTK inhibitor (ibrutinib) each blocked phosphorylation. Activation by DC-SIGN occurred in both IgM+ and IgG+ cases and led to upregulation of MYC expression, with detection in vivo observed in lymph nodes. Unlike cells of chronic lymphocytic leukemia, FL cells expressed relatively high levels of sIg, unchanged by long-term incubation in vitro, indicating no antigen-mediated downregulation in vivo. In contrast, expression of CXCR4 increased in vitro. Engagement of sIg in FL cells or normal B cells by anti-Ig led to endocytosis in vitro as expected, but DC-SIGN, even when cross-linked, did not lead to significant endocytosis of sIg. These findings indicate that lectin binding generates signals via sIg but does not mediate endocytosis, potentially maintaining a supportive antigen-independent signal in vivo. Location of DC-SIGN in FL tissue revealed high levels in sinusoidlike structures and in some colocalized mononuclear cells, suggesting a role for lectin-expressing cells at this site. •Unusual sugars on the tips of sIg of FL cells interact with a tissue lectin to activate tumor-specific signaling.•Activating lectin does not allow endocytosis of sIg, leading to persistent, essential, and targetable antigen-independent stimulation.