β-Hydroxyisovalerylshikonin induces apoptosis in human leukemia cells by inhibiting the activity of a polo-like kinase 1 (PLK1)

Abstract

b-Hydroxyisovalerylshikonin (b-HIVS), which was isolated from the plant, Lithospermum radix, induces apoptosis in various lines of human tumor cells. To identify genes involved in b-HIVS-induced apoptotic process, we performed cDNA array analysis and found that b-HIVS suppresses the expression of the gene for a polo-like kinase 1 (PLK1) that is involved in control of the cell cycle. When U937 and HL60 cells were treated with 10 À6 m b-HIVS for 0.5 h, both the amount of PLK1 itself and the kinase activity of this enzyme were decreased. By contrast, Bcr-Abl-positive K562 cells were resistant to the induction of apoptosis by b-HIVS and this compound did not suppress the kinase activity of PLK1 in these cells. However, simultaneous treatment of K562 cells with both b-HIVS and STI571, which selectively inhibits the protein tyrosine kinase (PTK) activity of Bcr-Abl, strongly induced apoptosis. Moreover, b-HIVS increased the inhibitory effect of STI571 on PTK activity. Treatment of K562 cells with antisense oligodeoxynucleotides (ODNs) specific for PLK1 sensitized these cells to the b-HIVS-induced fragmentation of DNA. These results suggest that suppression of the activity of PLK1 via inhibition of tyrosine kinase activity by b-HIVS might play a critical role in the induction of apoptosis.

Involvement of Tumor Necrosis Factor Receptor-associated Protein 1 (TRAP1) in Apoptosis Induced by β-Hydroxyisovalerylshikonin

“…9A (left panel), the extent of the tyrosine phosphorylation of proteins in DMS114 cells was clearly reduced after treatment of the cells with ␤-HIVS and the expression of both TRAP1 and PLK1 was suppressed in a dose-dependent manner. These results were consistent with our previous finding that the expression of PLK1 is suppressed, via inhibition of tyrosine kinase activity, by ␤-HIVS (14). The results in Fig.…”

“…We also showed that the effect of ␤-HIVS on PLK1 activity occurs upstream of mitochondria (14). Mitochondria play an important role in the regulation of apoptosis by releasing apoptogenic molecules that include cytochrome c (50 -52).…”

“…In the present study, we tried to clarify the involvement of mitochondria in ␤-HIVS-induced apoptosis. To identify genes that might be involved in mitochondrial functions during ␤-HIVS-induced apoptosis, we performed cDNA array analysis using HL60 cells, as described previously (14). We found that the expression of several genes was affected by treatment of cells with ␤-HIVS (data not shown).…”

“…This feature of ␤-HIVS is very useful for the inhibition of PTK activity in vivo because ␤-HIVS does not need to compete with ATP in the intracellular environment. In a previous study, we demonstrated that apoptosis is induced via suppression of the kinase activity of polo-like kinase 1 (PLK1) after inhibition of PTK activity by ␤-HIVS (14). Polo-like kinase 1 and its homologs are involved in several aspects of mitosis, including activation of the anaphase-promoting complex (15), maturation of the centrosome (16) and formation of bipolar spindles (17,18).…”

Polo-like kinases (Plks) and cancer

“…Expression of the Plk1 gene was significantly suppressed by b-hydroxyisovalerylshikonin (b-HIVS) in U937 and HL60 cells (Masuda et al, 2003). Treatment with Plk1-specific antisense ODNs sensitized K562 cells to b-HIVS-induced apoptosis, indicating that suppression of the expression and activity of Plk1 by b-HIVS is involved in apoptosis (Masuda et al, 2003).…”