ABSTRACT
R-(-)-gossypol acetic acid (AT-101) is a natural cottonseed product that exhibits anticancer activity. However, the molecular mechanism behind the antileukemic activity of AT-101 has not been well characterized. In this study, we investigated how AT-101 induces apoptosis in human leukemia cells. Exposure to AT-101 significantly increased apoptosis in both human leukemia cell lines and primary human leukemia cells. This increase was accompanied by the activation of caspases, cytochrome c release, Bcl2-associated X protein (Bax) translocation, myeloid cell leukemia-1 (Mcl-1) downregulation, Bcl-2-associated death promoter (Bad) dephosphorylation, Akt inactivation, and RhoA/Rho-associated coiled-coil containing protein kinase 1/phosphatase and tensin homolog (RhoA/ROCK1/PTEN) activation. RhoA, rather than caspase-3 cleavage, mediated the cleavage/activation of ROCK1 that AT-101 induced. Inhibiting RhoA and ROCK1 activation by C3 exoenzyme (C3) and Y27632, respectively, attenuated the ROCK1 cleavage/activation, PTEN activity, Akt inactivation, Mcl-1 downregulation, Bad dephosphorylation, and apoptosis mediated by AT-101. Knocking down ROCK1 expression using a ROCK1-specific siRNA also significantly abrogated AT-101-mediated apoptosis. Constitutively active Akt prevented the AT-101-induced Mcl-1 downregulation, Bad dephosphorylation, and apoptosis. Conversely, AT-101 lethality was potentiated by the phosphatidylinositol 3-kinase inhibitor LY294002. In vivo, the tumor growth inhibition caused by AT-101 was also associated with RhoA/ROCK1/PTEN activation and Akt inactivation in a mouse leukemia xenograft model. Collectively, these findings suggest that AT-101 may preferentially induce apoptosis in leukemia cells by interrupting the RhoA/ROCK1/PTEN pathway, leading to Akt inactivation, Mcl-1 downregulation, Bad dephosphorylation, and Bax translocation, which culminate in mitochondrial injury and apoptosis.
Subject(s)
Apoptosis , Gossypol/analogs & derivatives , Leukemia/drug therapy , Leukemia/enzymology , PTEN Phosphohydrolase/metabolism , Signal Transduction , rho-Associated Kinases/metabolism , rhoA GTP-Binding Protein/metabolism , Animals , Caspase 3/metabolism , Cell Line, Tumor , Gossypol/administration & dosage , Humans , Leukemia/genetics , Leukemia/physiopathology , Mice , Mice, Inbred NOD , Mice, SCID , PTEN Phosphohydrolase/genetics , Proto-Oncogene Proteins c-akt/metabolism , Proto-Oncogene Proteins c-bcl-2/metabolism , bcl-2-Associated X Protein/metabolism , rho-Associated Kinases/genetics , rhoA GTP-Binding Protein/geneticsABSTRACT
Effects of phenethyl isothiocyanate (PEITC) have been investigated in human leukemia cells (U937, Jurkat, and HL-60) as well as in primary human acute myeloid leukemia (AML) cells in relation to apoptosis and cell signaling events. Exposure of cells to PEITC resulted in pronounced increase in the activation of caspase-3, -8, -9, cleavage/degradation of PARP, and apoptosis in dose- and time-dependent manners. These events were accompanied by the caspase-independent downregulation of Mcl-1, inactivation of Akt, as well as activation of Jun N-terminal kinase (JNK). Inhibition of PI3K/Akt by LY294002 significantly enhanced PEITC-induced apoptosis. Conversely, enforced activation of Akt by a constitutively active Akt construct markedly abrogated PEITC-mediated JNK activation, Mcl-1 downregulation, caspase activation, and apoptosis, and also interruption of the JNK pathway by pharmacological or genetically (e.g., siRNA) attenuated PEITC-induced apoptosis. Finally, administration of PEITC markedly inhibited tumor growth and induced apoptosis in U937 xenograft model in association with inactivation of Akt, activation of JNK, as well as downregulation of Mcl-1. Taken together, these findings represent a novel mechanism by which agents targeting Akt/JNK/Mcl-1 pathway potentiate PEITC lethality in transformed and primary human leukemia cells and inhibitory activity of tumor growth of U937 xenograft model.
Subject(s)
Antineoplastic Agents/pharmacology , Isothiocyanates/pharmacokinetics , JNK Mitogen-Activated Protein Kinases/metabolism , Leukemia/drug therapy , Proto-Oncogene Proteins c-akt/antagonists & inhibitors , Signal Transduction/drug effects , Animals , Antineoplastic Agents/administration & dosage , Apoptosis/drug effects , Female , Gene Expression Regulation, Leukemic/drug effects , HL-60 Cells , Humans , Isothiocyanates/administration & dosage , JNK Mitogen-Activated Protein Kinases/genetics , Jurkat Cells , Leukemia/genetics , Leukemia/metabolism , Leukemia/physiopathology , Male , Mice , Mice, SCID , Proto-Oncogene Proteins c-akt/genetics , Proto-Oncogene Proteins c-akt/metabolism , U937 Cells , Xenograft Model Antitumor AssaysABSTRACT
Two brothers born to same parents were diagnosed with inherited factor X deficiency of severe type. Clinical presentation in both the cases were haemarthrosis. The elder brother was diagnosed in the year 1991 when he was four and half years old. Recently the youngest child in the family also presented with haemarthrosis at age of one and half years. Diagnosis was made by abnormal results of Coagulation factors screening mainly Prothrombin time, Activated partial thromboplastin time, Russell's viper venom test, mixing tests factor X assay. Both the brothers had Factor X activity less than one percent.
