ALTERATIONS IN PROTEIN GLYCOSYLATION IN PMA-DIFFERENTIATED U-937 CELLS EXPOSED TO MINERAL PARTICLES

Carbohydrate moieties of cell glycoconjugates play a pivotal role in m olecular recognition phenomena involved in the regulation of most biol ogical systems and the changes observed in cell surface carbohydrates during cell activation or differentiation frequently modulate certain cell functions. Consequently, some aspects of macrophage response to p article exposure might conceivably result from alterations in glycosyl ation. Therefore, the effect of mineral particles on protein glycosyla tion was investigated in phorbol myristate acetate (PMA)-differentiate d U-937. Jacalin, a lectin specific for O-glycosylated structures, sho wed a global increase in O-glycosylation in particle-treated cells. In contrast, no significant modifications were observed with concanavali n A, a lectin that recognizes certain N-glycosylated structures. The s ialic acid-specific lectins Sambucus nigra agglutinin and Maackia amur ensis agglutinin and the galactose-specific lectin Ricinus communis ag glutinin revealed a complex pattern of alterations in glycoprotein gly cosylation after crystalline silica or manganese dioxide treatments. E xpression of sialyl Lewis(x), a glycosylated structure implicated in l eukocyte trafficking, could not be detected in control or treated cell s. This finding was consistent with the decrease in sialyl Lewis(x) ex pression observed during PMA-induced differentiation. In conclusion, v arious treatments used in this study induced quantitative as well as q ualitative changes in protein glycosylation. Whether these changes are due to glycosidase release or to an alteration in glycosyltransferase expression remains to be determined. The potential functional implica tions of these changes are currently under investigation.