Exposure of alpha2,6-sialylated lactosaminic chains marks apoptotic and necrotic death in different cell types

Many observations have reported glycosylation changes associated with apoptosis in different biological systems, although none of these has shown any general significance. In this work we show that in cell lines from different histological origin, (colon, breast, pancreas, and bladder cancer) as well as in normal human and mice neutrophils, apoptosis is accompanied by the exposure of sugar chains recognized by the lectin from Sambucus nigra (SNA), specific for Sia2,6Gal/GalNAc structures. Also cells undergoing primary necrosis induced by heat treatment (56 °C 30 min) expose specifically binding sites for SNA. While this modification is recognized also by the lectin from the mushroom Polyporus squamosus, which is highly specific for 2,6 -sialylated lactosamine, no significant changes were detected in the binding of lectins specific for other carbohydrate structures, such as those from Phaseolus vulgaris, Arachis hypogea and Maackia amurensis. The binding of SNA to apoptotic/necrotic cells is inhibited by neuraminidase treatment and by 2,6-sialylated compounds. In apoptotic, but not in necrotic SW948 cells, SNA reactivity is specifically associated with 65, 69 and 87 kDa glycoproteins. The exposure of SNA-reactive chains by apoptotic/necrotic cells occurs also in cells not expressing sialyltransferases ST6Gal.1 or ST6Gal.2 and is largely independent of the presence of 2,6-sialylated lactosaminic chains on the surface of pre -apoptotic cells. In neutrophils from ST6Gal.1 knock out mice, the apoptosis-related increase of SNA reactivity is reduced but not abolished. These data demonstrate that apoptosis and primary necrosis induce a specific glycosylation change independent of the cell type and nature of the stimulus.