okadaic-acid and Leukemia--Myeloid--Acute

In order to investigate the effect of PP2A activator and PP2A inhibitor on proliferation of HL-60 cells and analyze the changes of PP2A activity in patients with acute myeloid leukemia (AML), HL-60 cells were treated with FTY720 alone or in combination with okadaic acid (OA) for 24 hours in culture. Cell proliferation was assayed with CCK8 kit. In addition, 20 AML patients including de novo AML and relapsed AML were enrolled in this study. The activity of PP2A in the peripheral blood mononuclear cells of patients was assayed with a PP2A Immunoprecipitation Phosphatase Assay Kit, the data were analyzed by software SPSS 16.0. The results indicated that as compared with control group, the proliferation of cells in FTY720 group was obviously inhibited (p < 0.05). The proliferation of cells in FTY720 + OA group was slightly inhibited as compared with the control group, there was no statistical difference (p > 0.05), but there was significant difference between the FTY720 + OA and FTY720 groups (p < 0.05). The activity of PP2A in AML patients (453.67 ± 102.52 pmol phosphate) was obviously lower than that in the normal controls (673.29 ± 96.32 pmol phosphate), there was significant difference between them (p < 0.01). It is concluded that the activation or inhibition of PP2A can affect the proliferation of HL-60 cells in vitro. Compared with healthy individuals, the activity of PP2A in AML patients is obviously lower. PP2A protein playing a key role in the occurrence and development of AML may be valuable for the diagnosis and treatment of AML.

Topics: Adult; Aged; Apoptosis; Case-Control Studies; Cell Proliferation; Enzyme Activators; Enzyme Inhibitors; Female; Fingolimod Hydrochloride; HL-60 Cells; Humans; Leukemia, Myeloid, Acute; Male; Middle Aged; Okadaic Acid; Propylene Glycols; Protein Phosphatase 2; Sphingosine; Young Adult

The association between the phosphorylation status of the retinoblastoma protein, pRb and changes in cell cycle control caused by either protein kinase C (PKC) or protein kinase A (PKA) stimulation was evaluated in human myeloblastic leukaemia ML-1 cells. TPA-induced PKC activation resulted in dephosphorylation of pRb and subsequently induced ML-1 differentiation based on morphological changes and CD14 expression. In the present study, we showed that inhibition of protein phosphatases (PP-1 and PP-2a) prevented the TPA-induced differentiation in ML-1 cells. Preinhibition of PP-1 and PP-2a activities with 1-100 nM okadaic acid dose-dependently blunted the decrease in the phosphorylation status of pRb obtained with TPA and overrode cell cycle arrest. PKA stimulation with 8-chlorophenylthio-cAMP (100 microM) decreased cell proliferation by 65% and the distribution of cells in the G1 phase significantly increased from 38% to 83% concomitant with a 34% decline in the number of cells present in the S phase. In addition, PKA stimulation significantly decreased the pRb phosphorylation status but did not elicit CD14 expression, indicating that cAMP-induced dephosphorylation of pRb cannot by itself trigger differentiation in ML-1 cells.

Topics: Cell Differentiation; Cyclic AMP-Dependent Protein Kinases; Enzyme Inhibitors; G1 Phase; Humans; Leukemia, Myeloid, Acute; Lipopolysaccharide Receptors; Okadaic Acid; Phosphoprotein Phosphatases; Phosphorylation; Retinoblastoma Protein; S Phase; Tetradecanoylphorbol Acetate; Tumor Cells, Cultured

Okadaic acid is a polyether compound of a C38 fatty acid, isolated from a black sponge, Halichondria okadai. Previous studies showed that okadaic acid is a skin irritant and induces ornithine decarboxylase (OrnDCase; 3-hydroxyl-L-glutamate 1-carboxy-lyase, EC 4.1.1.17) in mouse skin 4 hr after its application to the skin. This induction was strongly inhibited by pretreatment of the skin with 13-cis-retinoic acid. A two-stage carcinogenesis experiment in mouse skin initiated by a single application of 100 micrograms of 7,12-dimethylbenz[a]anthracene (DMBA) and followed by application of 10 micrograms of okadaic acid twice a week revealed that okadaic acid is a potent additional tumor promoter: tumors developed in 93% of the mice treated with DMBA and okadaic acid by week 16. In contrast, tumors were found in only one mouse each in the groups treated with DMBA alone or okadaic acid alone. An average of 2.6 tumors per mouse was found in week 30 in the group treated with DMBA and okadaic acid. Unlike phorbol 12-tetradecanoate 13-acetate (TPA), teleocidin, and aplysiatoxin, okadaic acid did not inhibit the specific binding of [3H]TPA to a mouse skin particulate fraction when added up to 100 microM or activate calcium-activated, phospholipid-dependent protein kinase (protein kinase C) in vitro when added up to 1.2 microM. Therefore, the actions of okadaic acid and phorbol ester may be mediated in different ways. These results show that okadaic acid is a non-TPA-type tumor promoter in mouse skin carcinogenesis.

Topics: 9,10-Dimethyl-1,2-benzanthracene; Animals; Enzyme Induction; Ethers, Cyclic; Humans; Leukemia, Myeloid, Acute; Lyngbya Toxins; Mice; Okadaic Acid; Ornithine Decarboxylase; Porifera; Protein Kinase C; Skin; Skin Neoplasms; Tetradecanoylphorbol Acetate; Tumor Cells, Cultured