The interaction between Siglec-15 and tumor-associated sialyl-Tn antigen enhances TGF-  secretion from monocytes/macrophages through the DAP12-Syk pathway

Abstract

We previously demonstrated that Siglec-15, a member of the Siglec family of glycan-recognition proteins, is expressed on a subset of macrophages and preferentially recognizes the sialyl-Tn (sTn) antigen, a tumor-associated glycan structure. In this study, we report on the biological significance of the Siglec-15-mediated interaction between monocytes/macrophages and cancer cells. Siglec-15 is expressed on tumor-associated macrophages (TAMs) in various human tumor tissues. We further demonstrated that its expression is substantially elevated in macrophage colony-stimulating factor-induced M2-like macrophages, which produced more transforming growth factor-β (TGF-β) in response to sTn-positive cells than to negative cells. We designed a co-culture model of THP-1 (human monocytic leukemia) cells and H157 (human lung carcinoma) cells mimicking the interaction between monocytes/macrophages and cancer cells that recapitulated the enhanced TGF-β production in Siglec-15 expressing THP-1 cells by the cellular interaction with sTn expressing H157 cells. The enhanced TGF-β production required a direct interaction between the two cell lines through sialic acids. Siglec-15 associates with adaptor protein DNAX activation protein of 12 kDa (DAP12) at the binding determinant Lys(274) in the transmembrane domain and transduces a signal to spleen tyrosine kinase (Syk). The enhanced TGF-β secretion was significantly attenuated by Syk inhibitor treatment of THP-1 cells or by substitution of the Siglec-15 Lys(274) to Ala, which disrupts the molecular interaction between Siglec15 and DAP12. These findings indicate that Siglec-15 recognizes the tumoral sTn antigen and transduces a signal for enhanced TGF-β secretion in TAMs and further suggest that Siglec-15 on macrophages may contribute to tumor progression by the TGF-β-mediated modulation of intratumoral microenvironments.

Macrophage-inducible C-type lectin underlies obesity-induced adipose tissue fibrosis

“…Stimulation of Mincle with TDM activates Syk in macrophages to increase expression of fibrosis-related genes as well as proinflammatory cytokines. These observations are consistent with previous studies that activation of Syk can induce TGFb production in macrophages and dendritic cells 27,28 . On the other hand, Mincle is selectively expressed in proinflammatory M1 macrophages and localized to some of the macrophages constituting CLS in obese adipose tissue, whereas antiinflammatory M2 macrophages, not M1 macrophages, are considered to contribute to tissue repair and remodelling.…”

Variation in Carbohydrates between Cancer and Normal Cell Membranes Revealed by Super‐Resolution Fluorescence Imaging

“…In fact, the interactions of carbohydrates with CBPs can affect tumor cell interactions with normal cells or with the extracellular matrix during metastatic spread and growth. These bindings of carbohydrate ligands and endogenous lectins not only occur in the formation of carbohydrate patterns on cell membranes (i.e., via galectins on tumor cells),21 but also in interactions of tumor cells and local microenvironment (via selectins on the endothelial surface,22 or via siglecs on macrophages23) in various metastasis processes. As known, carbohydrate‐related molecular interactions are generally weak and of low affinity, thus multivalent bindings between CBPs and carbohydrates via clustering together carbohydrates ligands of glycoconjugates are reported to be typically necessary in various cellular processes 24, 25, 26.…”

Induction of Siglec-1 by Endotoxin Tolerance Suppresses the Innate Immune Response by Promoting TGF-β1 Production

“…Most Siglecs inhibit immune responses via the recruitment of tyrosine phosphatases such as SHP1 and SHP2 by their cytoplasmic immunoreceptor tyrosine-based inhibitory motifs (ITIM) domain. Siglecs which lack an ITIM domain (such as Siglec-14, 15, and 16) associate with DAP12 via a positively charged amino acid in their transmembrane region to activate receptors through the recruitment of Syk (15,40). Siglec-1, the first discovered member of Siglecs, has been shown to play an important role in sialylated pathogen uptake (17,19,(53)(54)(55), antigen presentation (56,57), lymphocyte proliferation (58), self-tolerance (59,60) and antiviral immune response (47).…”

“…Syk, a 72-kDa non-receptor tyrosine kinase, is most highly expressed by hematopoietic cells and plays a crucial role in signal transduction via its two SRC homology 2 (SH2) domains (38,39). Recently it was shown that Syk plays an important role in TGF-␤1 production both in monocytes/macrophages (40) and epithelial cells (41). It was shown that the expression of Syk is negatively regulated by the E3 ubiquitin ligase Casitas B-lineage lymphoma (CBl), leading to ubiquitylation and degradation of SYK (42)(43)(44).…”