Characterization of cell surface-expressed proteochondroitin sulfate of pre-B Nalm-6 cells and its possible role in laminin adhesion.

Cell surface-expressed proteoglycans mediate contacts to extracellular matrix (ECM). Human B lymphocytes produce a species of a proteochondroitin sulfate (CSPG) with an approximate molecular mass of 135-150 kDa. Using a monoclonal antibody (mAb) against B cell CSPG in flow cytometry we found that this CSPG is expressed on tumor cells of patients with CD19+ common acute lymphoblastic leukemia and on the corresponding cell lines Nalm-6, Reh and KM3. The CSPG is also present on hairy cell leukemia JOK-1 cells and weakly on the myeloma line U266. Concomitant with CSPG expression, Nalm-6 cells express the integrins alpha 5/beta 1 (CD49e/CD29) and alpha 6/beta 1 (CD49f/CD29), adhesion receptors for fibronectin and laminin, in contrast to the other two cell lines tested. Expression patterns of these adhesion receptors and CSPG were paralleled by strong adhesion of Nalm-6 to fibronectin and laminin. Adhesion of Nalm-6 to fibronectin was inhibited by the alpha 5-specific antibody SAM 1 by 80% whereas the alpha 6-specific antibody GoH3 reduced binding to laminin only by 20%. A possible involvement of surface-expressed CSPG in adhesion to ECM components was investigated by 24 h incubation of Nalm-6 cells with p-nitrophenyl-beta-D-xyloside, an inhibitor of proteoglycan glycosylation. By this treatment, both adhesion of Nalm-6 to laminin and expression of CSPG were reduced by 40-50%. Furthermore, addition of chondroitin-6-sulfate, a structural element of Nalm-6 CSPG, reduced adhesion of Nalm-6 to laminin by 60%. Chondroitin-4-sulfate, heparin and heparan sulfate did not effectively inhibit the adhesion process. These observations suggest that surface-expressed CSPG may be involved in binding of Nalm-6 cells to laminin and that the specific sulfation pattern of chondroitin-6-sulfate may be essential in this regard.