Modulated glycosylation of proteoglycans during differentiation of human B lymphocytes.
Proteoglycans are mediators of cellular adhesion and regulate growth factor activities. Proteoglycans of B lymphocytes undergo structural changes during B cell ontogeny which may correspond to the specific requirements of the respective microenvironment of the maturing cell. We analyzed three human B cell lines representing pre-B cells (Nalm-6), activated B cells (Jok-1) and plasma cells (U266) for their cellular proteoglycans. Gel filtration of the 35S-labeled macromolecules of the three cell lines revealed an increase in size in the order Nalm-6 < Jok-1 < U266. In Jok-1 and U266 cells the major pool of proteoglycans consisted of proteochondroitin sulfates of 50 to 90 kDa. These proteolglycans carried a protein core of approx. 30 kDa to which 1 to 3 glycosaminoglycan chains in the range of 28 to 32 kDa were attached. In Nalm-6 cells only free chondroitin sulfate chains of 23 kDa, but no intact proteoglycans, were detected. Chondroitin sulfate chains were predominantly composed of chondroitin-4-sulfate, those of Nalm-6 and U266 cells additionally contained 10-20% of unsulfated disaccharides. In U266 cells 30% of glycosaminoglycans consisted of heparan sulfate either bound to pure proteoheparan sulfate or to chondroitin sulfate/heparan sulfate hybrid-proteoglycans. Earlier, syndecan-1 was described as a hybrid proteoglycan containing heparan sulfate/chondroitin sulfate chains which is transcribed by murine B cells at early and late maturation stages. In order to see whether syndecan is transcribed by the human B cell lines used here, we measured expression of syndecan mRNA by the reverse transcriptase polymerase chain reaction. Similar to murine lymphocytes, syndecan-specific mRNA was detected in Nalm-6 and U266 cells, equivalent to early and late B cells, but not in lymphoblastoid Jok-1 cells. However, Nalm-6 cells do not produce proteoheparan sulfate. In these cells, syndecan synthesis may be blocked at the translational level. Also, the proteoglycans of U266 are different from syndecan-1 in their composition of glycosaminoglycans and in size of protein cores. Together, these results indicate that the major pool of proteoglycans produced by human B cells consists of proteochondroitin sulfate and additionally in later stages of a smaller proportion of proteoheparan sulfate which is not identical to syndecan-1. During distinct phases of B cell differentiation, modulations in the glycosaminoglycan moiety concerning size and sulfation of glycosaminoglycan chains were also found.
Engelmann
S
S
Tumor Immunology Program, German Cancer Research Center, Heidelberg.
Ebeling
O
O
Schwartz-Albiez
R
R
D001402:B-Lymphocytes / Q000166:cytology / Q000378:metabolism*; D002454:Cell Differentiation; D002460:Cell Line; D011508:Chondroitin Sulfate Proteoglycans / Q000737:chemistry; D002810:Chondroitinases and Chondroitin Lyases; D006025:Glycosaminoglycans / Q000737:chemistry; D006031:Glycosylation; D006801:Humans; D008562:Membrane Glycoproteins / Q000235:genetics; D011509:Proteoglycans / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D012333:RNA, Messenger / Q000032:analysis; D053668:Syndecan-1; D053667:Syndecans
D011508:Chondroitin Sulfate Proteoglycans; D006025:Glycosaminoglycans; D008562:Membrane Glycoproteins; D011509:Proteoglycans; D012333:RNA, Messenger; C508241:SDC1 protein, human; D053668:Syndecan-1; D053667:Syndecans; D002810:Chondroitinases and Chondroitin Lyases