Effects of Celastrol on growth inhibition of U937 leukemia cells through the regulation of the Notch1/NF-kappaB signaling pathway in vitro / 癌症

ABSTRACT

<p><b>BACKGROUND AND OBJECTIVE</b>Leukemia is a malignant tumor highly dependent on nuclear factor kappa-light-chain-enhancer of activated B cells (NF-kappaB), which is relevant for the occurrence, metastasis, proliferation, apoptosis, and drug resistance of tumor cells. Research has confirmed that the NF-kappaB family is one of the target genes in the Notch signaling pathway. This study investigated the effects of Celastrol on the apoptosis of U937 cells and the expression levels of Notch1 and NF-kappaB in these cells.</p><p><b>METHODS</b>U937 cells were treated with various concentrations Celastrol (0.5-16.0) micromol/L for 12-60 h. MTT assay was performed to examine the effect of Celastrol on growth inhibition of U937 cells. Cell apoptosis was detected through both Annexin-V FITC/PI double-labeled cytometry and transmission electron microscopy (TEM). Cell cycle regulation was studied by propidium iodide. Western blot analysis and reverse transcription-polymerase chain reaction (RT-PCR) technologies were applied to assess the expression level of Notch1 in U937 cells. Subcellular distributions of NF-kappaB/p65 were detected through confocal microscopy.</p><p><b>RESULTS</b>Celastrol presented striking growth inhibition and apoptosis induction potency on U937 cells in vitro in a time- and dose-dependent manner. The IC50 value of Celastrol for 24 h was (6.21 +/- 0.242) micromol/L. Moreover, Celastrol induced apoptosis in U937 cells in a cell-cycle dependent manner, which means that Celastrol could arrest U937 cells in the G0/G1 phase. Through TEM, apoptotic bodies containing nuclear fragments were found in Celastrol-treated U937 cells. Overexpression of Notch1 was found in U937 cells, while Celastrol could downregulate it at both the protein and mRNA level in a dose-dependent manner, and expression of NF-kappaB decreased in nuclei and increased in the cytoplasm (P < 0.05).</p><p><b>CONCLUSIONS</b>Celastrol inhibited cell proliferation and induced apoptosis in U937 cells in a concentration-dependent manner. The possible mechanism might be involved in the regulation of a survival signaling pathway, such as Notch or NF-kappaB.</p>