Phosphoinositide 3-Kinase/Akt and Nuclear Factor-κB Are Involved in Staphylococcus Aureus-induced Apoptosis in U937 Cells

Objective To explore the mechanisms involved in Staphylococcus aureus(S.aureus) invading human monocytic U937 cells.Methods S.aureus were added to U937 cells at multiplicity of infections(MOI) of 20:1 for 0,15,30,60,and 90 minutes,respectively.Cell apoptosis was analyzed with Hoechst 33258 staining and Annexin V-fluorescein isothiocyanate(FITC)/propidium iodide(PI) flow cytometry analysis.Akt and nuclear factor-κB(NF-κB) activities were detected by Western blotting.Results Infection of U937 cells with S.aureus induced rapid cell death in a time-dependent manner,and the cells displayed characteristic features of apoptosis.S.aureus-induced apoptosis was associated with a prominent downregulation of activated(phosphorylated) Akt and NF-κB.The inhibition of phosphorylated Akt by LY294002 led to the inhibition of NF-κB in a dose-dependent manner.Inhibition of Akt with LY294002 caused further increase in apoptosis of U937 cells.Conclusions S.aureus can stimulate the apoptosis of U937 cells.S.aureus induces apoptosis of U937 cells by inhibiting Akt-regulated NF-κB.

C-jun N-terminal Kinase-mediated Signaling Is Essential for Staphylococcus Aureus-induced U937 Apoptosis

Objective To investigate the effect of SP600125, a specific c-jun N-terminal protein kinase (JNK) inhibitor, on Staphylococcus aureus (S. aureus)-induced U937 cell death and the underlying mechanism. Methods The human monocytic U937 cells were treated with S. aureus at different time with or without SP600125. Cell apoptosis was analyzed by flow cytometry. JNK, Bax, and caspase-3 activities were detected by Western blotting. Results S. aureus induced apoptosis in cultured U937 cells in a time-dependent manner. Expression of Bax and phospho-JNK significantly increased in S. aureus-treated U937 cells, and the level of activated caspase-3 also increased in a time-dependent manner. Inhibition of JNK with SP600125 significantly inhibited S. aureus-induced apoptosis in U937 cells. Conclusions S. aureus can induce apoptosis in U937 cells by phosphorylation of JNK and activation of Bax and caspase-3. SP600125 protects U937 cells from apoptosis induced by S. aureus via inhibiting the activity of JNK.

HEPATOCYTE GROWTH FACTOR PROTECTS AGAINST APOPTOSIS INDUCED BY ADVANCED GLYCATION END PRODUCTS IN ENDOTHELIAL CELLS

Objective To investigate the effects of hepatocyte growth factor(HGF)on vascular endothelial cells apoptosis induced by advanced glycation end products(AGEs)and its possible mechanism. Methods Human umbilical vein endothelial cells(HUVECs)were cultured in vitro and intervened by different concentrations of AGEs and HGF.The cell inhibitory rates of each group with different culture time(12, 24, 48, and 72 hours)were measured by methyl thiazolyl tetrazolium(MTT)assay. The early stage apoptosis was detected by flow cytometry with Annexin V-FITC/PI double staining, morphology of cell apoptosis was observed by hoechst 33258 fluorescence staining, and the expression of apoptosis-associated genes Bax and Bcl-2 were determined by Western blotting.The activity of caspase-3 was detected by enzyme-linked immunosorbent assay (ELISA).Results Morphological observation indicated that high concentration of AGEs induced characteristic apoptotic changes in HUVECs.Within a certain concentration range, HUVECs apoptosis inducing rates by AGEs were in both dose- and time-dependent manners.HGF significantly inhibited the apoptosis of HUVECs induced by AGEs (P< 0.05).AGEs significantly promoted expression of Bax protein, but not Bcl-2.Whereas HGF significantly promoted the expression of Bcl-2(P<0.01)and decreased the activity of caspase-3(P<0.05)without affecting Bax level.Conclusions AGEs can induce the apoptosis of endothelial cells in vitro.HGF may effectively attenuate AGEs-induced endothelial cells apoptosis through upregulating Bcl-2 gene expression and inhibiting caspase-3 activation.

INVOLVEMENT OF p38 MITOGEN-ACTIVATED PROTEIN KINASE IN E.coli-INDUCED U937 APOPTOSIS

Objective To investigate whether the effect of E.coli on U937 cell lines apoptosis is mediated via p38 mitogen-activated protein kinase (MAPK) activation. Methods The U937 cell lines were treated with E.coli at different time or together with SB203580, an inhibitor for p38. Cell apoptosis was analyzed by flow cytometry. p38 activities were detected by Western blotting. Results E.coli induced apoptosis in cultured U937 cell lines in a time-dependent manner. The phosphorylation of p38 was induced after 10 minutes infection, reached the peak after 20 minutes, and started to decline after 30 minutes. In contrast, the level of total p38 protein was not changed in whole experimental period. Inhibition of p38 with SB203580 significantly inhibited E.coli induced apoptosis in U937 cells. Conclusion The activation of the p38 MAPK in U937 cell lines by E.coli is a major pathway to mediate the apoptosis.

Propensity score analyses of long-term outcomes of perivascular hepatocellular carcinoma: Radiofrequency ablation vs. surgery

We read with great interest the article by Dr.Lee et al.[1],which compared the long-term outcomes of patients with perivascular hepatocellular carcinoma(HCC)after radiofrequency ablation(RFA)and surgical resection(SR)as first-line treatment.By using propensity score matching(PSM)analyses,the authors concluded that SR provided better long-term tumor control and overall survival than RFA for patients with small periportal tumors.Herein,we would like to raise the following comments.