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

• Published in: Toxicology and applied pharmacology 2008-09, Vol.231 (3), p.401
• Main Authors: Jun, Do Youn, Park, Hae Sun, Kim, Jun Seok, Kim, Jong Sik, Park, Wan, Song, Bang Ho, Kim, Hee-Sook, Taub, Dennis, Kim, Young Ho
• Format: Article
• Language: English
• Subjects: Apoptosis - drug effects; Apoptosis - physiology; Caspases - genetics; Caspases - metabolism; Cell Death - drug effects; Cell Death - physiology; Cell Division - drug effects; Cell Division - physiology; Dose-Response Relationship, Drug; Estradiol - therapeutic use; Estradiol - toxicity; G2 Phase - drug effects; G2 Phase - physiology; Humans; Jurkat Cells; Leukemia-Lymphoma, Adult T-Cell - drug therapy; Leukemia-Lymphoma, Adult T-Cell - genetics; Leukemia-Lymphoma, Adult T-Cell - metabolism; U937 Cells
• ISSN: 1096-0333
• DOI: 10.1016/j.taap.2008.05.023

A pharmacological dose (2.5-10 microM) of 17alpha-estradiol (17alpha-E(2)) 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 17alpha-E(2) was not blocked by the anti-Fas neutralizing antibody ZB-4. While undergoing apoptosis, there was a remarkable accumulation of G(2)/M cells with the upregulatoin 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 17alpha-E(2)-induced apoptosis was completely abrogated by overexpression of Bcl-2 or by pretreatment with the pan-caspase inhibitor z-VAD-fmk, the accumulation of G(2)/M cells significantly increased. The caspase-8 inhibitor z-IETD-fmk failed to influence 17alpha-E(2)-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 G(1)/S boundary, 17alpha-E(2) failed to induce the G(2)/M arrest as well as apoptosis. These results demonstrate that the cytotoxicity of 17alpha-E(2) toward Jurkat T cells is attributable to apoptosis mainly induced in G(2)/M-arrested cells, in an ER-independent manner, via a mitochondria-dependent caspase pathway regulated by Bcl-2.