Identification of Siglec-9 as the receptor for MUC16 on human NK cells, B cells, and monocytes

Abstract

BackgroundMUC16 is a cell surface mucin expressed at high levels by epithelial ovarian tumors. Following proteolytic cleavage, cell surface MUC16 (csMUC16) is shed in the extracellular milieu and is detected in the serum of cancer patients as the tumor marker CA125. csMUC16 acts as an adhesion molecule and facilitates peritoneal metastasis of ovarian tumors. Both sMUC16 and csMUC16 also protect cancer cells from cytotoxic responses of natural killer (NK) cells. In a previous study we demonstrated that sMUC16 binds to specific subset of NK cells. Here, we identify the csMUC16/sMUC16 binding partner expressed on immune cells.ResultsAnalysis of immune cells from the peripheral blood and peritoneal fluid of ovarian cancer patients indicates that in addition to NK cells, sMUC16 also binds to B cells and monocytes isolated from the peripheral blood and peritoneal fluid. I-type lectin, Siglec-9, is identified as the sMUC16 receptor on these immune cells. Siglec-9 is expressed on approximately 30-40% of CD16pos/CD56dim NK cells, 20-30% of B cells and >95% of monocytes. sMUC16 binds to the majority of the Siglec-9pos NK cells, B cells and monocytes. sMUC16 is released from the immune cells following neuraminidase treatment. Siglec-9 transfected Jurkat cells and monocytes isolated from healthy donors bind to ovarian tumor cells via Siglec-9-csMUC16 interaction.ConclusionsRecent studies indicate that csMUC16 can act as an anti-adhesive agent that blocks tumor-immune cell interactions. Our results demonstrate that similar to other mucins, csMUC16 can also facilitate cell adhesion by interacting with a suitable binding partner such as mesothelin or Siglec-9. Siglec-9 is an inhibitory receptor that attenuates T cell and NK cell function. sMUC16/csMUC16-Siglec-9 binding likely mediates inhibition of anti-tumor immune responses.

Difference in mesothelin‐binding ability of serum CA125 between patients with endometriosis and epithelial ovarian cancer

“…8 These carbohydrate chains are involved in the binding of CA125 to mesothelin, siglec-9, galectin-1 and selectins. [9][10][11][12][13] Although the latter three lectins bind not only to CA125 but also to various other glycoconjugates, mesothelin binds to CA125 with high specificity, suggesting that the expression and/or precise positioning of unique carbohydrate chain(s) on the core protein of this mucin may be responsible for its binding to mesothelin. 9,10 Mesothelin is a glycosylphosphatidylinositol-linked cell surface glycoprotein that is expressed in mesothelial cells lining the body cavity.…”

Potential Tumor Biomarkers for Ovarian Cancer

“…Adhesion of ovarian cancer cells to the peritoneum is in part facilitated by the binding of cleaved cell surface MUC16 to mesothelin (Rump et al, 2004). Muc-16 additionally dampens immune response by binding to the inhibitory siglec-9 receptor on a wide range of cells involved in both innate and adaptive immunity, allowing growing tumors to evade immune system surveillance (Belisle et al, 2010). The CA125 assay displays a superior sensitivity of 95% in tumors positive for the cell surface antigen in human serum (Cramer et al, 2011).…”

CA-125 of fetal origin can act as a ligand for dendritic cell-specific ICAM-3-grabbing non-integrin

“…Distinct types of human lectin with different specificities and binding requirements were demonstrated to recognize CA-125. The siglecs (sialic-acid Ig-like lectins), which are a subgroup of I-type lectins, and the galectins (beta-galactoside-binding lectins) were found to interact with MUC16 [9][10][11][12]. Specifically, siglec-9 was identified as a ligand for MUC16 on human NK cells, B cells, and monocytes [11].…”

“…In addition, MUC16 expressed by metastatic pancreatic cancer cells was identified as a ligand for E-and L-selectin [13]. MUC16/CA-125 interactions with lectins are conferred by the specific glycan structures and depend on sialic acid, i.e., on the type and level of sialylation, and on lactosamine structures [11,12,14,15]. In addition, recognition of high mannose glycans or blood type group Lewis x antigen (Le x ) or Lewis y antigen (Le y ) on the CA-125 moiety is seen as a possibility, but experimental data are still lacking [16].…”

“…The siglecs (sialic-acid Ig-like lectins), which are a subgroup of I-type lectins, and the galectins (beta-galactoside-binding lectins) were found to interact with MUC16 [9][10][11][12]. Specifically, siglec-9 was identified as a ligand for MUC16 on human NK cells, B cells, and monocytes [11]. Galectin-1 (gal-1) and galectin-3 (gal-3) were shown to be receptors for MUC16 on membrane-associated fragments of HeLa cell lysates and on the ocular epithelial cell surface [9,10].…”