ABSTRACT
Objective: To investigate the involvement of Ca2+ in dengue virus (DENV)-infected human umbilical vein endothelial cells (HUVECs) and the disruption of endothelial integrity. Methods: HUVECs were infected with DENV-2 in the presence of intracellular Ca2+ or endoplasmic reticulum Ca2+ chelators. Virus infectivity was measured by focus-forming assay and quantitative RT-PCR. Intracellular Ca2+ was measured using Fluo-4-AM dye. VE-cadherin and focal adhesion kinase (FAK) expressions were investigated by immunofluorescence and immunoblotting assays, respectively. Results: DENV infection increased intracellular cytosolic Ca2+ levels and caused disassembly of the adherens junction protein, VEcadherin as evidenced by decreased VE-cadherin expression at the periphery of DENV-2 infected HUVECs. Depletion of intracellular Ca2+ stores, particularly those of the endoplasmic reticulum Ca2+, significantly decreased DENV yield in HUVECs. Decreased virus yield following the depletion of intracellular Ca2+ was caused by the inhibition of viral entry into HUVECs and not the inhibition of viral binding or attachment. DENV-2 infection also resulted in Ca2+- dependent activation of FAK. Conclusions: Intracellular Ca2+ is required for the early phases of DENV infection in endothelial cells. Increased cytosolic Ca2+ levels in endothelial cells during DENV infection activated FAK, disrupted adherens junctions and compromised barrier integrity. Thus, Ca2+ plays an important role in DENV infection in endothelial cells.
ABSTRACT
Objective: To systematically map the stepwise events leading to deoxyelephantopin-induced cell death of HCT116 human colorectal cancer cells and evaluate the effectiveness of deoxyelephantopin in vivo. Methods: HCT116 cells were treated with deoxyelephantopin at various concentrations and time points. Autophagy was confirmed by the detection of autophagosomes and autophagosomal proteins by electron microscopy and Western blotting assays, respectively, and then validated by siRNA knockdown. In addition, apoptosis was confirmed by the detection of apoptosis-related proteins. The intracellular reactive oxygen species (ROS) level was measured using flow cytometry. The growth inhibitory effect of deoxyelephantopin was further evaluated in vivo using a mouse xenograft model. Results: Deoxyelephantopin firstly elevated ROS production, which then triggered autophagic flux with the accumulation of autophagosomal proteins including LC3A/B, ATG5, and ATG7, followed by the induction of apoptosis via the intrinsic and extrinsic pathways. Pre-treatment with N-acetyl-L-cysteine, a ROS inhibitor, reversed both apoptosis and autophagy. The knockdown of LC3 prevented apoptosis induction which confirmed that deoxyelephantopin induced autophagy-dependent apoptosis in HCT116 cells. Accumulation of ROS also activated apoptosis via the mitogen-activated protein kinases signaling pathway. Furthermore, deoxyelephantopin also inhibited the PI3K/AKT/mTOR pathway, which then released the inhibition of autophagy. In vivo study further showed that deoxyelephantopin significantly suppressed the growth of HCT116 subcutaneous xenograft in nude mice. Conclusions: Our findings revealed that deoxyelephantopin elevates oxidative stress and induces ROS-dependent autophagy followed by apoptosis in HCT116 cells via the concerted modulation of multiple signaling pathways. These findings further support the development of deoxyelephantopin as a therapeutic agent for colorectal cancer.