Heat shock treatment protects human HL-60 cells from apoptosis induced by lectin II isolated from Korean mistletoe, Viscum album var. Coloratum

Mistletoe lectin II (ML II) isolated from Korean mistletoe (Viscum album va r. Coloratum), an effective therapeutic agent for cancers, is known to indu ce cell death via apoptosis. In the present study, we found the protective effect of heat shock treatment of human leukemia HL-60 cells against ML II- induced apoptosis. Exposure of HL-60 cells to ML II for 4 h resulted in apo ptosis of the cells, which was evaluated by examining "DNA ladder" formatio n and DNA fragmentation assay. The DNA fragmentation was significantly redu ced in the cells subjected to heat shock treatment by incubation at 42 degr ees C for 1 h and subsequently allowed to recover for 2-16 h at 37 degrees C, prior to exposure to ML II. HL-60 cells transfected with heat shock prot ein (hsp) 70 gene exhibited resistance to ML II-induced apoptosis very simi lar to that seen when untransfected cells were heat-shocked. These results indicate that ML II-induced apoptosis in HL-60 cells is inhibited by heat s hock treatment, at least in part, via a hsp 70-mediated mechanism.