Serglycin inhibits the classical and lectin pathways of complement via its glycosaminoglycan chains: Implications for multiple myeloma

Abstract

Serglycin (SG) is a proteoglycan expressed by hematopoietic cells and is constitutively secreted by multiple myeloma (MM) cells. SG participates in the regulation of various inflammatory events. We found that SG secreted by human MM cell lines inhibits both the classical and lectin pathways of complement, without influencing alternative pathway activity. The inhibitory effect of SG is due to direct interactions with C1q and mannosebinding lectin (MBL). C1q-binding is mediated through the glycosaminoglycan moieties of SG, whereas MBL binds additionally to SG protein core. Interactions between SG and C1q as well as MBL are diminished in the presence of chondroitin sulfate type E. In addition, we localized the SG-binding site to the collagen-like stalk of C1q. Interactions between SG and C1q as well as MBL are ionic in character and only the interaction with MBL was found to be partially dependent on the presence of calcium. We found the serum levels of SG to be elevated in patients with MM compared to healthy controls. Moreover, we found that SG expressed from myeloma plasma cells protects these cells from complement activation induced by treatment with anti-thymocyte immunoglobulins. This might protect myeloma cells during immunotherapy and promote survival of malignant cells.Keywords: Complement . Multiple myeloma . Serglycin Introduction Serglycin (SG) is a proteoglycan with a 17 kDa protein moiety containing a characteristic domain rich in serine/glycine repeats, which serves as the attachment site for glycosaminoglycan (GAG) chains [1]. SG is mainly expressed by cells of hematopoietic origin and is a key intracellular proteoglycan [2,3]. SG can carry eight GAG chains, which depending on cell-type, can be either chondroitin sulfate (CS), dermatan sulfate (DS), heparan sulfate (HS), and heparin [3,4]. SG is constitutively secreted from monocytes [5] and macrophages [6] into the extracellular matrix and the secretion increases upon activation of these cells. The Eur. J. Immunol. 2011. 41: 437-449 DOI 10.1002 Innate immunity 437 biological function of SG is not fully elucidated, but the results obtained from studies with SG-knockout mice suggest a role for SG in the delivery of proteins into secretory granules and/or directing the secretion of these molecules [2]. It appears that SG interacts with a plethora of molecules, playing a role in the delivery of these components into secretory vesicles and further into their targets via its highly negatively charged GAG chains.Other studies have demonstrated that SG plays a key role in the storage of mast cell proteases and granzyme B and the maturation of secretory granules of mast cells and cytotoxic T-cells [7,8]. Furthermore, SG plays a crucial role in cytotoxic T-cells, as part of a multimolecular complex with perforin and granzyme B, in the delivery of the latter to the target cells during cytotoxic cell-granule-mediated cell death [9]. SG is constitutively secreted but also present on the cell surface of myeloma plasma cells and affects bone mineralization [1...

Serglycin: A Structural and Functional Chameleon with Wide Impact on Immune Cells

“…On a different angle, it was recently shown that serglycin isolated from multiple myeloma cells can inhibit both the classical and lectin pathway of complement, through direct effects on C1q and mannose-binding lectin, respectively (61). These findings support the earlier reported ability of serglycinlike proteoglycans to inhibit complement activation (62).…”

Insights into the key roles of proteoglycans in breast cancer biology and translational medicine

“…Serglycin isolated from myeloma and breast cancer cells inhibits the classical and the lectin pathways of complement system via direct binding to C1q and MBL, respectively, and protects tumor cells from complement system attack [33, 353]. Only those CS-4S chains with a high proportion of 4-sulfated disaccharides interact efficiently with complement proteins [353]. CS-E and in a lower extent heparin compete with CS-4 chains of serglycin for binding to C1q, whereas only CS-E competes for binding to MBL.…”

“…Binding of serglycin to C1q or/and C1 inhibits the cleavage of C4 in the classical pathway. In the lectin pathway, binding of serglycin to MBL either competes out MBL-associated proteases (MASPs) from the stalk region of MBL or sterically hinders cleavage of C2 and C4 by MASPs [353]. The inhibition of complement is a great limitation during immunotherapy against several types of cancer.…”

Review on complement analysis method and the roles of glycosaminoglycans in the complement system

“…Due to different sulfation groups there are many kinds of CS such as CS-A, CS-C, CS-D and CS-E (Lamari & Karamanos, 2006). The roles of CSs playing in complement system were investigated by Skliris et al (2011). They incubated CS-A, CS-C, CS-D and CS-E with NHS and added them to IgG coated plates for C4b determination in CP.…”