Diosmetin inhibits cell proliferation and promotes apoptosis through STAT3/c-Myc signaling pathway in human osteosarcoma cells

BACKGROUND: Diosmetin is a bioflavonoid compound naturally abundant in citrus fruits. It is found to perform a variety of activities, while its antitumor property in osteosarcoma, a malignant tumor with unmet clinical treatment, remained unknown. METHODS: Colony formation assay, cell cycle analysis and apoptosis analysis were conducted respectively to observe the effect of diosmetin on cell proliferation and apoptosis in human osteosarcoma cells. Western blot and immunoprecipitation were used to detect the expression of apoptotic molecules and activation of STAT3/c-Myc pathway in Saos-2 and U2SO cells. RESULTS: Diosmetin significantly inhibited cell proliferation, induced cell cycle arrest at G2/M phase and promoted cell apoptosis in both Saos-2 and U2SO cells. Moreover, Diosmetin downregulated the expression of anti-apoptotic protein Bcl-xL while upregulated the levels of pro-apoptotic proteins including cleaved Caspase-3, cleaved-PARP and Bax. Furthermore, diosmetin dose-dependently inhibited STAT3 phosphorylation, reduced the expression of its downstream protein c-Myc and impeded the interaction between STAT3 molecules. CONCLUSIONS: These results suggest that diosmetin exerts anti-osteosarcoma effects by suppressing cell proliferation and inducing apoptosis via inhibiting the activation of STAT3/c-Myc signaling pathway, which provide the possibility for diosmetin to be a chemotherapeutic candidate for osteosarcoma.

Staphylococcus aureus regulates secretion of interleukin-6 and monocyte chemoattractant protein-1 through activation of nuclear factor kappaB signaling pathway in human osteoblasts

OBJECTIVE: Activation of nuclear factor kappaB by diverse bacteria regulates the secretion of chemokines and cytokines. Staphylococcus aureus (S. aureus)-infected osteoblasts can significantly increase the secretion of interleukin-6 and monocyte chemoattractant protein-1. The aim of this study was to investigate whether S. aureus can activate nuclear factor kappaB in human osteoblasts, and whether the activation of nuclear factor kappaB by S. aureus regulates the secretion of interleukin-6 and monocyte chemoattractant protein-1. METHODS: Immunoblot and electrophoretic mobility shift assay were used to detect the degradation of IκBa and activation of nuclear factor kappaB in human osteoblasts in response to S. aureus, respectively. Enzyme-linked immunosorbent assay was used to measure the secretion of interleukin-6 and monocyte chemoattractant protein-1 in the supernatants. Lastly, carbobenzoxyl-l-leucinyl-l-leucinyl-l-leucinal, an inhibitor of the nuclear factor kappaB, was used to determine if activation of nuclear factor kappaB by S. aureus in human osteoblasts regulates the secretions of interleukin-6 and monocyte chemoattractant protein-1. RESULTS: Our results for the first time demonstrated that S. aureus can induce the degradation of IκBa and activation of nuclear factor kappaB in human osteoblasts in a time and dose-dependent manner. In addition, inhibition of nuclear factor kappaB by carbobenzoxyl-l-leucinyl-l-leucinyl-l-leucinal suppressed the secretion of interleukin-6 and monocyte chemoattractant protein-1 in the supernatants of S. aureus-infected human osteoblasts in a dose-dependent manner. CONCLUSION: These findings suggest that S. aureus can activate nuclear factor kappaB in human osteoblasts, and subsequently regulate the secretion of interleukin-6 and monocyte chemoattractant protein-1. The nuclear factor kappaB transcription factor regulates a number of genes involved in a wide variety of biological processes. Further study of the effects of nuclear factor kappaB activation on S. aureus-infected human osteoblast may provide us new insights into discovery of the immune mechanisms in osteomyelitis.