Abstract
Wheat germ lectin (WGA) is a cytotoxic lectin for many cell lines [Wang et al., 2000], but its underlying mechanism is not clear. In this report, we found that incubation of synchronized mouse L929 fibroblasts with WGA resulted in a dose‐dependent reduction of intracellular incorporation of ^3^H‐thymidine and MTT (3‐[4,5‐dimethylthiazol‐2‐yl]‐2,5 diphenyl tetrazolium bromide)‐conversion activity (IC~50~ ≅ 0.4 μM). Fluorescein‐conjugated WGA was demonstrated to transport from the cell surface into the paranuclear region of cultured L929 cells within 30 min, and subsequently evoked lipid peroxidation of plasma membrane and vacuolation in the cytoplasm of these cells. Studies with tritiated thymidine incorporation, immunofluorescence microscopy, immunoblotting analysis and flow cytometry revealed that WGA inhibited cell cycle progression after one replication, resulting in G~2~/M arrest and alteration of cell cycle regulatory proteins, particularly activation of p21^Cip1/WAF1^ and suppression of cyclin B and cdc 2. Although there was an increase of cytosolic caspase 3 and bax protein expression, no apoptotic bodies were observed by both fluorescence and transmission electron microscopy. These results suggest that WGA arrested L929 proliferation after one cell cycle in the G~2~/M phase through activation of the p21^Cip1/WAF1^ and suppression of Cyclin B–Cdc2. © 2004 Wiley‐Liss, Inc.