Serglycin Constitutively Secreted by Myeloma Plasma Cells Is a Potent Inhibitor of Bone Mineralization in Vitro

Abstract

Although the biological significance of proteoglycans (PGs) has previously been highlighted in multiple myeloma (MM), little is known about serglycin, which is a hematopoietic cell granule PG. In this study, we describe the expression and highly constitutive secretion of serglycin in several MM cell lines. Serglycin messenger RNA was detected in six MM cell lines. PGs were purified from conditioned medium of four MM cell lines, and serglycin substituted with 4-sulfated chondroitin sulfate was identified as the predominant PG. Flow cytometry and confocal microscopy showed that serglycin was also present intracellularly and on the cell surface, and attachment to the cell surface was at least in part dependent on intact glycosaminoglycan side chains. Immunohistochemical staining of bone marrow biopsies showed the presence of serglycin both in benign and malignant plasma cells. Immunoblotting in bone marrow aspirates from a limited number of patients with newly diagnosed MM revealed highly increased levels of serglycin in 30% of the cases. Serglycin isolated from myeloma plasma cells was found to influence the bone mineralization process through inhibition of the crystal growth rate of hydroxyapatite. This rate reduction was attributed to adsorption and further blocking of the active growth sites on the crystal surface. The apparent order of the crystallization reaction was found to be n ‫؍‬ 2, suggesting a surface diffusion-controlled spiral growth mechanism. Our findings suggest that serglycin release is a constitutive process, which may be of fundamental biological importance in the study of MM.

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

“…marrow microenvironment [10]. Now we show that complement attack induced by ATG on U266, JJN3, and CAG cells is significantly reduced in the presence of SG.…”

“…Proteins and sera SG was purified from MM cell lines as described [10]. 125 I-labelling of SG was performed using the chloramine T [34,35].…”

“…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 [10]. Multiple myeloma (MM) is a B-cell malignancy characterized by clonal proliferation of plasma cells within the bone marrow and excessive production of non-functional immunoglobulins.…”

“…2G). SG secreted from MM cells carries CS of particular structure that is constituted by 4-sulfated disaccharides (92.5%), low amounts of six-sulfated disaccharides (4.5%) and only trace amounts of non-sulfated (1.5%) and (4,6)-disulfated units (1.5%) [10]. In order to evaluate whether individual GAG chains display similar complement inhibitory abilities as CS isolated from SG, C4b deposition was studied in the presence of CS-4, CS-6, CS-D, CS-E, dermatan sulfate (DS, also called CS-B), HS, heparin and keratan sulfate (KS) isolated from various sources (Materials and methods).…”

Glycotranscriptome study reveals an enzymatic switch modulating glycosaminoglycan synthesis during B‐cell development and activation

“…Except for the in vitro biochemical characterization of several enzymes, the precise in vivo regulation of CS and HS biogenesis and their respective functions are still incompletely understood. In lymphoid cells, while the global amount of GAGs is very low and escape detection by direct biochemical methods, a variety of PG core polypeptides were indirectly shown to carry HS/CS chains and are differentially expressed, including syndecans, glypican, serglycin and CD44-HS [18][19][20][21][22].…”