Inhibition of human glioma cell proliferation by altered Bax/Bcl-2-p53 expression and apoptosis induction by Rhaponticum carthamoides extracts from transformed and normal roots.

OBJECTIVE: The objective of this study was to determine the cytotoxic effect and apoptotic activity of Rhaponticum carthamoides transformed root (TR) and root of soil-grown plant (NR) extracts in a human glioma primary cells. The effect of these root extracts on cell cycle arrest, mitochondrial membrane potential (ΔΨm) and expression levels of apoptosis-related genes (Bcl-2, Bax and p53) were also examined. METHODS: Cytotoxic activity of root extracts was evaluated by MTT assay. Apoptosis and cell cycle were determined by flow cytometry. Expression levels of apoptosis-related gene were analysed by RT-PCR and Western blotting. ΔΨm was examined by the use of JC-1 reagent. KEY FINDINGS: Rhaponticum carthamoides root extracts inhibit cell growth and induce apoptosis in a dose-dependent manner in human glioma cells. The root extracts were found to up-regulate the pro-apoptotic Bax protein and down-regulate the anti-apoptotic Bcl-2 protein, consequently increasing the ratios of Bax/Bcl-2 protein levels. Moreover, an increase of the p53 protein level and reduction of ΔΨm in glioma cells were observed after treatment with NR and TR extracts. CONCLUSION: The results of this study may offer a new insight into the potential anticancer activity of R. carthamoides root extracts.

A preliminary study of apoptosis induction in glioma cells via alteration of the Bax/Bcl-2-p53 axis by transformed and non-transformed root extracts of Leonurus sibiricus L.

Leonurus sibiricus L. is a traditional medicinal plant which occurs in southern Siberia, China, Korea, Japan, and Vietnam. The plant shows several pharmacological effects, but the most interesting is its anti-cancer activity. The aim of our study was to examine the induction of apoptosis in malignant glioma cells, the most aggressive primary brain tumors of the central nervous system, following treatment with transformed root (TR) or non-transformed root (NR) L. sibiricus extracts. Both the NR and TR extracts were found to have cytotoxic activity in the glioma primary cells. The human glioblastoma cell lines obtained from patients were confirmed to be tumorogenic by the following three markers: D10S1709, D10S1172, and D22S283. HPLC and MS analysis revealed the presence of polyphenolic compounds (chlorogenic acid, ferulic acid, caffeic acid, p-coumaric acid, ellagic acid, and verbascoside) in both sets of root extracts. In summary, our findings demonstrate that treatment of the glioma cells with NR and TR extracts resulted (a) in significant cell growth inhibition, (b) S- and G2/M-phase cell cycle arrest, and (c) apoptosis in a dose-dependent fashion by changing Bax/Bcl-2 ratio (about 4-fold increase) and p53 (5-fold increase) activation. These findings indicate that NR and TR extracts exhibit anti-cancer activity through the regulation of genes involved in apoptosis. This is the first report to demonstrate the cytotoxic effect of polyphenolic extracts from L. sibiricus roots against glioma cells, but further studies are required to understand the complete mechanism of its apoptosic activity.

The Src family kinase Hck couples BCR/ABL to STAT5 activation in myeloid leukemia cells.

Signal transducer and activator of transcription 5 (STAT5) is constitutively activated by BCR/ABL, the oncogenic tyrosine kinase responsible for chronic myelogenous leukemia. The mechanism of BCR/ABL-mediated STAT5 activation is unknown. We show here that the BCR/ABL SH3 and SH2 domains interact with hematopoietic cell kinase (Hck), leading to the stimulation of Hck catalytic activity. Active Hck phosphorylated STAT5B on Tyr699, which represents an essential step in STAT5B stimulation. Moreover, a kinase-dead Hck mutant and Hck inhibitor PP2 abrogated BCR/ABL-dependent activation of STAT5 and elevation of expression of STAT5 downstream effectors A1 and pim-1. These data identify a novel BCR/ABL-Hck-STAT5 signaling pathway, which plays an important role in BCR/ABL-mediated transformation of myeloid cells.

Complementary functions of the antiapoptotic protein A1 and serine/threonine kinase pim-1 in the BCR/ABL-mediated leukemogenesis.

BCR/ABL oncogenic tyrosine kinase activates STAT5, which plays an important role in leukemogenesis. The downstream effectors of the BCR/ABL-->STAT5 pathway remain poorly defined. We show here that expression of the antiapoptotic protein A1, a member of the Bcl-2 family, and the serine/threonine kinase pim-1 are enhanced by BCR/ABL. This up-regulation requires activation of STAT5 by the signaling from SH3+SH2 domains of BCR/ABL. Enhanced expression of A1 and pim-1 played a key role in the BCR/ABL-mediated cell protection from apoptosis. In addition, pim-1 promoted proliferation of the BCR/ABL-transformed cells. Both A1 and pim-1 were required to induce interleukin 3-independent cell growth, inhibit activation of caspase 3, and stimulate cell cycle progression. Moreover, simultaneous up-regulation of both A1 and pim-1 was essential for in vitro transformation and in vivo leukemogenesis mediated by BCR/ABL. These data indicate that induction of A1 and pim-1 expression may play a critical role in the BCR/ABL-dependent transformation.