Sialic acids linked to glycoconjugates of Fas regulate the caspase-9-dependent and mitochondria-mediated pathway of Fas-induced apoptosis in Jurkat T cell lymphoma

To clarify the functions of sialic acids linked to glycoconjugates of Fas in Fas-induced apoptosis, Jurkat T cells, untreated and treated with neuraminidase, were incubated with anti-Fas monoclonal antibody, CH11. Apoptosis of Jurkat T cells induced by incubation with CH11 was enhanced by the pre-treatment with neuraminidase. By flow cytometry sialylated glycoconjugates were detected on the cell surface of Jurkat T cells using LFA lectin, which specifically reacts with sialic acid, and pre-treatment with Vibrio Cholerae neuraminidase resulted in desialylation of Jurkat cell surface glycoconjugates. The enhancement of Fas-induced apoptosis by pre-treatment with neuraminidase was inhibited by z-VAD-fmk, a broad caspase inhibitor, and Ac-LEHD-CHO, an inhibitor of caspase-9, but not by Ac-IETD-CHO an inhibitor of caspase-8 or 6, imipramine, an inhibitor of acidic sphingomyelinase, glutathione, an inhibitor of neutral sphingomyelinase and Fumonisin B1, an inhibitor of ceramide synthase. Mitochondrial membrane potentials (Δψm) measured with a Mitocapture assay kit demonstrated that the loss of Δψm involved in Fas-induced apoptosis was enhanced by pre-treatment with neuraminidase. Furthermore, Western blot analysis using polyclonal antibody (C-20) against Fas detected Fas at about 45 kDa, and pre-treatment with neuraminidase resulted in a reduction of the molecular weight of Fas of about 8 kDa. These data suggest that the enhancement of Fas-induced apoptosis by pre-treatment with neuraminidase was mediated by a caspase-9 dependent pathway closely associated with the loss of Δψm, not by activation of caspase-8, -6 or acidic and neutral sphingomyelinases, and that sialic acid linked to glycoconjugates of Fas may regulate Fas-induced apoptosis in human T cell lymphoma.