Osteoblasts express, produce, and secrete certain SLRPs. Protein and mRNA were extracted from MSCs before and after differentiation into osteoblasts (OB). (A) Global gene expression profiling demonstrated the expression of various SLRPs and proteoglycans. (B) Expression levels of decorin and lumican were validated by qRT-PCR. (C) Decorin was detected in cell lysates by Western blot. The core protein of decorin had a molecular weight less than 50 kDa, whereas the other bands reflected monomers and the binding of the core protein to different glycosaminoglycan chains. (D) Osteoblast lysate was digested with chondroitinase ABC before Western blotting for decorin was performed. It is noteworthy that only the core protein was detected after enzymatic digestion, confirming the specificity of the assay. (E) Decorin was detected in the serum-free conditioned media of osteoblasts. (F) By qRT-PCR, decorin was shown to be expressed in myeloma cells lines (MM cell lines), primary myeloma plasma cells (MM PC, n = 12), normal plasma cells (Normal PC), osteoclasts (OC), osteoblasts (OB), and MSCs. Note that decorin was expressed in normal plasma cells but not in myeloma plasma cells or osteoclasts. MSCs and osteoblasts served as positive controls.