thymosin and Leukemia--Myeloid

Our previous works have shown that bone marrow stromal cells secrete thymosin beta4 (Tbeta4) and AcSDKP. Tbeta4 and AcSDKP are existed in the conditioned medium of bone marrow endothelial cells. They exerted inhibitory effects on hematopoietic cells and then had protective effect on the early hematopoietic cells, which were cultured in the presence of hematopoietic stimulators. Thymosin beta4 consists of 43 peptides with a molecular weight of 4963. It contains at its N-terminal end the sequence of the acetylated tetrapeptide Ac-N-Ser-Asp-Lys-Pro (AcSDKP). This study was performed to evaluate the effect of Tbeta4 and AcSDKP on the growth of HL-60 cells. It was showed that Tbeta4 (10(-11)-10(-7)mol/L) and AcSDKP (10(-11)-10(-7)mol/L) had the dose-dependent inhibitory effect on the proliferation of HL-60 cells. Based on cell morphology and NBT reduction, Tbeta4 and AcSDKP induced differentiation of HL-60 cells. Morphologic and DNA fragment analysis proved that Tbeta4 and AcSDKP induced apoptosis of HL-60 cells. In order to analyze the mechanism of the effects of Tbeta4 and AcSDKP, intracellular free Ca(2+) concentration ([Ca(2+)](i)) of HL-60 leukemic cells was tested and Atlas cDNA Expression Array was performed. The results showed that Tbeta4 and AcSDKP could increased [Ca(2+)](i) by stimulating the release of Ca(2+) from intracellular Ca(2+) pool. Moreover, AcSDKP could also elicit a potent extracelluar calcium influx in HL-60 cells. Tbeta4 could also change apoptotic-related gene expression in leukemic cells, and resulted in the inhibition of proliferation and induction of differentiation and apoptosis of leukemic cells.

Topics: Animals; Apoptosis; Calcium; Cattle; DNA Fragmentation; HL-60 Cells; Humans; Leukemia, Myeloid; Oligonucleotide Array Sequence Analysis; Oligopeptides; Thymosin; Up-Regulation

Prothymosin alpha (ProT alpha) is a nuclear protein related to cell proliferation. Its gene is highly activated during postnatal development at stages containing many proliferating but also differentiating cells. In this report, a study on ProT alpha gene expression during differentiation of human myeloid leukemic (HL-60) cells was undertaken to analyze the possible association of ProT alpha to cell differentiation. When HL-60 cells were induced to differentiate to granulocytes (using retinoic acid) or monocyte/macrophages (using 12-O-tetradecanoylphorbol-13-acetate), a marked down-regulation in the levels of ProT alpha transcript was found. When cell division of immature HL-60 cells was interrupted by either treatment with hydroxyurea or serum starvation, ProT alpha gene expression was not significantly altered. These findings suggest that loss of ProT alpha mRNA in induced HL-60 cells is a differentiation-related event. Examination of the stability of ProT alpha mRNA showed that the stabilization of the ProT alpha transcript is differentially regulated in the two HL-60 lineages. Nuclear run-on experiments revealed that during HL-60 differentiation, the transcriptional activity of the ProT alpha gene does not experience significant variations.

Topics: Cell Differentiation; Down-Regulation; Humans; Hydroxyurea; Leukemia, Myeloid; Protein Precursors; RNA, Messenger; Tetradecanoylphorbol Acetate; Thymosin; Tretinoin; Tumor Cells, Cultured; Up-Regulation