Differential release of proteoglycans during human B lymphocyte maturation

Proteoglycans interact with soluble proteins such as growth factors and thereby regulate extracellular signals. During B lymphocyte maturation, secretion of proteoglycans may be functionally related to the different requirements of the respective maturation stage. In order to address this question we compared structures of proteoglycans released by three B lymphocyte lines which correspond to different maturation stages. Plasma-cell type U266 cells secreted the largest proteoglycans (150 kDa), followed by mature B cells JOK-1 (130 kDa) and pre-B cells Nalm 6 (90 kDa). On average, secreted proteoglycans carried four glycosaminoglycan chains with molecular masses ranging each from 32 kDa (U266) to 23 kDa (Nalm 6). All three cell lines secreted more than 90% of their proteoglycans possessing chondroitin sulfate chains having chondroitin-4-sulfate (delta Di-4S) as the prevalent disaccharide unit. In these proteochondroitin sulfates, unsulfated chondroitin (delta Di-0S) was present in smaller quantities and chondroitin-6-sulfate (delta Di-6S)-containing proteoglycan was released only by Nalm 6 and U266 cells. Cell line Nalm 6 exclusively produced proteochondroitin sulfate, whereas in culture medium of JOK-1 and U266 a small amount of proteoheparan sulfate was found also. In all three cell lines, treatment with chondroitinase ABC released a protein of 30 kDa and chemical deglycosylation resulted in a core protein of 21 kDa. In addition to pure proteochondroitin sulfate, a small portion of proteoheparan sulfate with a protein moiety of 30 kDa was detected after heparitinase treatment in supernatants of JOK-1 and U266. Thus, our results indicate that released proteoglycans may undergo modulations in their glycosaminoglycan moieties during B-cell differentiation. This may have functional consequences at the level of growth factor regulation.