Tiam1 is involved in the regulation of bufalin-induced apoptosis in human leukemia cells

Abstract

Bufalin, a component of the Chinese medicine chan'su, induces apoptosis in various lines of human tumor cells, such as leukemia HL60 and U937 cells, by altering the expression of apoptosis-related genes, for example, bcl-2 and c-myc. In this study, we characterized a gene that is involved in bufalin-induced apoptosis by the di erential display (DD) technique. The partial nucleotide sequence of one of the di erentially expressed clones obtained after treatment with bufalin was identical to that of the human gene for Tiam1. When U937 cells were treated with 10 77 M bufalin, expression of both Tiam1 mRNA and the protein was induced 1 h after the start of the treatment. The increase of Tiam1 mRNA was transient but the level of Tiam1 protein continued to increase at least for 6 h. In addition, the activities of Rac1 and p21-activated kinase (PAK) were also stimulated by bufalin treatment. To evaluate the role of Tiam1 in the apoptotic process, we examined the e ects of the expression of sense and antisense RNA for Tiam1 in U937 cells. Apoptosis was strongly induced by bufalin in cells that expressed sense RNA for Tiam1 as compared to apoptosis in control cells treated with bufalin only. Cells expressing antisense RNA for Tiam1 were signi®cantly more resistant than the control bufalin-treated cells to induction of DNA fragmentation in response to bufalin. Moreover, sense transformants had elevated activities of PAK and c-Jun NH 2 -terminal kinase (JNK). These results suggest that Tiam1 might play a critical role in bufalin-induced apoptosis through the activation of Rac1, PAK, and JNK pathway.

Bufalin, a Traditional Oriental Medicine, Induces Apoptosis in Human Cancer Cells

“…Treatment of K562 cells with other cardiotonic steroids, such as cinobufagin, ouabain and digitoxigenin, at the concentration of 10 nM for four days resulted in weak or no effect on the cells. These findings suggest that bufalin might have potentiality as a new agent in the differentiation therapy for human myelogenous leukemia (Zhang et al, 1991;Masuda et al, 1995;Watabe et al, 1998;Kawazoe et al, 1999).…”

Rac1 regulates heat shock responses by reorganization of vimentin filaments: Identification using MALDI-TOF MS

“…This finding indicates that Rac1 is involved in the activation of SAPK/JNK by heat shock as well as by fas ligand, TNFa, etc. 8,17 The activation of SAPK/JNK has been recently shown to be an essential component of the signal transduction pathway which leads to programmed cell death in response to certain stimuli. 20 Resistance to stress-induced cell death was examined in thermotolerant cells and in hsp70 overexpressing cells, which prevent the activation of SAPK/JNK.…”

“…15 A few reports imply that Rac1 is involved in the apoptosis induced by death ligands such as fas ligand 16 and TNFa. 17 Almost nothing is known about the correlation between Rac1 and environmental stresses, although many studies have shown that Rac1 controls the activity of SAPK/JNK which is strongly activated by environmental stresses. Recent reports showed that heat shock-induced cell death could be mediated by PAK2, a serine/threonine kinase that is activated by Rac1 and Cdc42 18 and Rac1 regulated stress-induced, redox-dependent HSF activation.…”

DNA Damage Induces the Accumulation of Tiam1 by Blocking β-TrCP-dependent Degradation

“…shown that Tiam1 is involved in apoptotic signaling in response to genotoxic stress (24,45). This prompted us to examine whether the level of Tiam1 ubiquitination was changed in response to genotoxic stress.…”