Induction of apoptosis by the N-acetyl-galactosamine-specific toxic lectin from Viscum album L. is associated with a decrease of nuclear p53 and Bcl-2 proteins and induction of telomeric associations.
The ribosome-inhibiting proteins from Viscum album L., i.e. the mistletoe lectins (ML), were recognized to induce apoptosis in various tumour cell lines and human lymphocytes. However, several aspects of ML-induced cell death are unclear. We report that the galNAc-binding ML III incubated with human lymphocytes mediates a very effective death signal resulting in the binding of Annexin-V and expression of mitochondrial membrane proteins Apo2.7, but also in an influx of the DNA intercalating dye propidium iodide. The addition of the ribosome-inhibiting protein Volkensin also induced Apo2.7 molecules, while Momordin, lacking a carbohydrate-binding chain, did not enter the cell membrane and thus did not affect the cells. However, we observed ML III to preferentially affect CD8+ cells with a memory phenotype (CD62L(lo)) as compared to their CD8+ CD62L(hi) counterparts, CD4+ T cells and CD19+ B cells. Furthermore, ML III did not induce sister chromatid exchange-inducing DNA lesions but reduced the intensity of telomeric signals, increased the frequencies of telomeric associations and C-anaphases and reduced nuclear Bcl-2 and p53 proteins. Whatever the exact mechanisms are, our results provide strong evidence that the ML III-mediated cytotoxicity involves distinct killing pathways, i.e. (1) primary cell death via an induction of apoptosis which may not be dependent on protein and/or RNA synthesis and may not involve p53 and Bcl-2 proteins and (2) a loss of telomeres resulting in chromosomal instability in the surviving cells which is incompatible with life. However, we cannot exclude the possibility that this effect is due to a decrease in nuclear p53 proteins.
Büssing
A
A
Krebsforschung Herdecke, Department of Applied Immunology, Communal Hospital Herdecke, University Witten/Herdecke, Germany. ArBuess@t-online.de
Multani
A S
AS
Pathak
S
S
Pfüller
U
U
Schietzel
M
M
D017209:Apoptosis; D018414:CD8-Positive T-Lymphocytes / Q000187:drug effects*; D006023:Glycoproteins; D015658:HIV Infections / Q000097:blood*; D006801:Humans; D037102:Lectins / Q000494:pharmacology*; D009000:Monocytes / Q000187:drug effects; D009699:N-Glycosyl Hydrolases; D009363:Neoplasm Proteins / Q000187:drug effects* / Q000378:metabolism; D037121:Plant Lectins; D028321:Plant Preparations; D010940:Plant Proteins / Q000494:pharmacology*; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000187:drug effects* / Q000378:metabolism; D054788:Ribosome Inactivating Proteins; D054790:Ribosome Inactivating Proteins, Type 2; D012854:Sister Chromatid Exchange / Q000187:drug effects*; D014118:Toxins, Biological / Q000494:pharmacology*; D016159:Tumor Suppressor Protein p53 / Q000187:drug effects* / Q000378:metabolism
D006023:Glycoproteins; D037102:Lectins; D009363:Neoplasm Proteins; D037121:Plant Lectins; D028321:Plant Preparations; D010940:Plant Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D054790:Ribosome Inactivating Proteins, Type 2; D014118:Toxins, Biological; D016159:Tumor Suppressor Protein p53; C488864:mistletoe lectin III; C009674:ribosome inactivating protein, Viscum; C049134:volkensin; D009699:N-Glycosyl Hydrolases; D054788:Ribosome Inactivating Proteins