calcimycin and Lymphoma--B-Cell

We have investigated whether the increases in ceramide levels that occur during apoptosis in SKW 6.4 cells induced by anti-Fas antibody depend on the activation of caspases. Using cells prelabelled to equilibrium with [14C]acetate, it was shown that the amount of ceramide approximately doubled after 24 h incubation with anti-Fas, but the time course of ceramide changes was slower than that of anti-Fas-induced cell death. Complete inhibition of the effects of anti-Fas on cell death and on ceramide production was observed when the caspase inhibitor N-benzyloxycarbonyl-Val-Ala-Asp-(O-methyl)fluoromethane (zVAD.fmk) was added together with anti-Fas, but N-benzyloxycarbonyl-Phe-Ala-fluoromethane (a structurally similar cathepsin B inhibitor) had no effect. Treatment of cells with the Ca2+-ionophore A23187 also doubled ceramide levels, but in this case the effect was complete within 2 h, was not blocked by zVAD.fmk and was not associated with increases in nuclear fragmentation. These results suggest that ceramide is not an upstream messenger in Fas-mediated apoptosis and may instead be produced as a consequence of processes downstream of the activation of caspases and increases in cytosolic calcium concentration.

Topics: Acetates; Amino Acid Chloromethyl Ketones; Antibodies; Apoptosis; Calcimycin; Calcium; Ceramides; Cysteine Endopeptidases; Cysteine Proteinase Inhibitors; fas Receptor; Humans; Kinetics; Leukemia, Promyelocytic, Acute; Lymphoma, B-Cell; Signal Transduction; Time Factors; Tumor Cells, Cultured

HLA-class II molecules can be induced in low-grade non-Hodgkin B lymphoma cells by either membrane IgM cross-linking or phorbolester stimulation. The ability of phorbolesters to substitute for anti-IgM antibodies in the activation of normal and malignant human B cells has been taken as evidence for the involvement of protein kinase C (PKC) in signals transduced through membrane IgM receptors (mIgR). Here we report on freshly isolated lymphoma B cells from different patients; the cells show a distinct regulation of HLA-class II expression. In certain lymphoma cases phorbol-myristate-acetate (PMA) not only fails to up-regulate HLA-class II molecules but also inhibits anti-IgM or interleukin-4 induced class II expression. This negative signal induced by PMA seems to operate specifically in HLA-class II regulation because PMA can induce other anti-IgM mediated events like blast transformation and induction of IL-4 responsiveness at the same time. Therefore these cells support the concept of functional heterogeneity in low-grade non-Hodgkin lymphoma and may represent a differentiation stage where anti-IgM antibodies and phorbolesters influence the regulation of HLA-class II expression in a contrary direction.

Topics: Antibodies; Calcimycin; Cell Transformation, Neoplastic; Gene Expression Regulation, Neoplastic; Histocompatibility Antigens Class II; Humans; Immunoglobulin M; Interleukin-4; Lymphoma, B-Cell; Protein Kinase C; Receptors, Fc; Receptors, IgE; Signal Transduction; Tetradecanoylphorbol Acetate; Tumor Cells, Cultured; Up-Regulation