The T/Tn-Specific Helix pomatia Lectin Induces Cell Death in Lymphoma Cells Negative for T/Tn Antigens

Abstract

Morniga G is a T/Tn-specific lectin, inducing cell death in Tn-positive leukemias but not in healthy lymphocytes. Helix pomatia lectin (HPA) is another T/Tn-specific lectin, currently used as tool for cancer diagnostics. The HPA-mediated tumor cell death was evaluated on human leukemia and mouse lymphoma cells, and compared to the effect of Morniga G. Both lectins induced an equivalent percentage of cell death in Tn-positive Jurkat human leukemia. In contrast, EL4 mouse lymphoma resisted Morniga G-mediated cytotoxicity but were killed by HPA at concentrations of 2.5 μg/mL (0.032 nM) and higher. In both malignant cells, HPA-mediated cell death showed features compatible with apoptosis (annexin-externalization, caspase-activation, mitochondrial membrane depolarization, and ROS production). Cytometry analysis indicated that EL4 cells are T/Tn-negative. Because previous results showed a high amount of N-acetylgalactosamine (GalNAc, sugar present in Tn antigen) on EL4 cell surface, this GalNAc could be involved in the formation of truncated O-glycans other than the T/Tn residues. When compared to Morniga G, bioinformatic analysis suggested that HPA benefits from an extended carbohydrate-binding site, better adapted than Morniga G to the accommodation of more complex branched and truncated O-glycans (such as core 2). Finally, HPA killed EL4 cells but not healthy lymphocytes in a mixture of lymphoma cells + lymphocytes, suggesting that HPA selectively triggers tumor cell death.