Glycosyl-moiety mediated apoptosis and signal regulation of cultured tumors by glycoprotein from hot water extract of hard clam, Meretrix lusoria

Zwe-Ling Kong, PhD, Chau-Chi Hwang, MS, Chen-Wei Lai, MS

Cellular Immunology Laboratory, Department of Food Science, National Taiwan Ocean University, Keelung, Taiwan.

Previous studies, we found that the hot water extract of hot clam (Meretrix lusoria) showed immune bioactivity remarkably. In this report, we showed the mechanism for antitumor effects of the principle S75II. Cell viability and cytotoxicity were quantified by MTT and LDH assay. Apoptosis was determined by DNA fragmentation, PI stain and FACScan cytometry. Tumor cells treated with S75II (10 ??g/ml for 24h) exhibited patterns of apoptotic cell death, such as membrane blebbing, chromatin condensation, DNA fragmentation and sub-G1 peak arrested in cell cycle. Histocytes U937 pretreated with swainsonine (1 ??g/ml), a lysosomal ??-mannosidase II inhibitor for five days, the cytotoxicity and apoptosis-inducing activities were blocked significantly. On the other hand, swainsonine was a reversible drug, the specific inhibitory effect was blocked when primed U937 cells cultured with the fresh medium for another 36h. Our results suggest that the principle of Meretrix lusoria may as a lectin-like component and its antitumor effect was may through cell membrane glycosyl-moiety interaction and triggered glycosylation-mediated apoptosis.

KEY WORDS: Antitumor, Lectin, Swainsonine, Flowcytometry.

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Paper presented at the International Symposium on Predictive Oncology and Intervention Strategies; Paris, France; February 9 - 12, 2002; in the section on Apoptosis - Molecular Mechanisms.