17α-Estradiol arrests cell cycle progression at G2/M and induces apoptotic cell death in human acute leukemia Jurkat T cells

Abstract

A pharmacological dose (2.5-10 μM) of 17α-estradiol (17α-E2) exerted a cytotoxic effect on human leukemias Jurkat T and U937 cells, which was not suppressed by the estrogen receptor (ER) antagonist ICI 182,780. Along with cytotoxicity in Jurkat T cells, several apoptotic events including mitochondrial cytochrome c release, activation of caspase-9, -3, and -8, PARP degradation, and DNA fragmentation were induced. The cytotoxicity of 17α-E2 was not blocked by the anti-Fas neutralizing antibody ZB-4. While undergoing apoptosis, there was a remarkable accumulation of G2/M cells with the upregulation of cdc2 kinase activity, which was reflected in the Thr56 phosphorylation of Bcl-2. Dephosphorylation at Tyr15 and phosphorylation at Thr161 of cdc2, and significant increase in the cyclin B1 level were underlying factors for the cdc2 kinase activation. Whereas the 17α-E2-induced apoptosis was completely abrogated by overexpression of Bcl-2 or by pretreatment with the pan-caspase inhibitor z-VAD-fmk, the accumulation of G2/M cells significantly increased. The caspase-8 inhibitor z-IETD-fmk failed to influence 17α-E2-mediated caspase-9 activation, but it markedly reduced caspase-3 activation and PARP degradation with the suppression of apoptosis, indicating the contribution of caspase-8; not as an upstream event of the mitochondrial cytochrome c release, but to caspase-3 activation. In the presence of hydroxyurea, which blocked the cell cycle progression at the G1/S boundary, 17α-E2 failed to induce the G2/M arrest as well as apoptosis. These results demonstrate that the cytotoxicity of 17α-E2 toward Jurkat T cells is attributable to apoptosis mainly induced in G2/M-arrested cells, in an ER-independent manner, via a mitochondriadependent caspase pathway regulated by Bcl-2.

Apoptosis of Human Jurkat T Cells Induced by the Methylene Chloride Extract from the Stems of Zanthoxylum schinifolium is Associated with Intrinsic Mitochondria-Dependent Activation of Caspase Pathway

“…5), excluding the involvement of Fas/FasL system in the SS-8-mediated apoptosis. Since it has [1,8,12] or as a downstream event of mitochondrial cytochrome c release [11], current data suggest that SS-8-mediated activation of caspase-8 might be down-stream event of mitochondrial cytochrome c release into cytosol or it occurs independently of mitochondria-dependent caspase cascade.…”

Tumor-suppressor Protein p53 Sensitizes Human Colorectal Carcinoma HCT116 Cells to 17α-estradiol-induced Apoptosis via Augmentation of Bak/Bax Activation

“…The cytotoxic effect of 17α-E2 on HCT116 cells was analyzed by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay as described previously [20]. Briefly, …”

“…Recently, we have shown that a pharmacological dose (5～10 μM) of 17α-E2, but not 17β-E2, can induce apoptosis in human acute leukemia Jurkat T cells, which are known to not express ERs [9], via a mitochondria-dependent caspase cascade activation [20]. The 17α-E2-induced apoptosis occurs mainly in G2/M-arrested cells and is accompanied by an increase in Bcl-2 phosphorylation at Thr-56 [20], a known site that can be phosphorylated by the Cdk1/cyclin B1 kinase during G2/M phase [14].…”

“…The 17α-E2-induced apoptosis occurs mainly in G2/M-arrested cells and is accompanied by an increase in Bcl-2 phosphorylation at Thr-56 [20], a known site that can be phosphorylated by the Cdk1/cyclin B1 kinase during G2/M phase [14]. More recently, we have reported that the apoptogenic activity of 17α-E2 was due to the impaired mitotic spindle assembly causing prometaphase arrest and prolonged Cdk1 activation, phosphorylation of the Bcl-2 family members (Bcl-2, Mcl-1 and Bim), Bak activation, and mitochondria-dependent caspase cascade activation [18].…”

Estrogen Reduces Caspase-3 Expression in the Inner Ear of Guinea Pigs Exposed to Simulated Microgravity and Inboard Noises of Spaceship

“…It has been reported that oestrogen protects pancreatic beta [11] , retina ganglion [12] , neuronal [13] , bone [14] , and heart [15] cells via inhibition of apoptosis. However, oestrogen also plays a role in increasing apoptosis in other cell types, such as osteoclasts [16] , breast cancer cells [17] , and leukaemia cells [18] . For human hearing, oestrogen seems to have protective effects [19] .…”