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    • Programmed cell death via apoptosis is associated with a ser

    2019-10-18

    Programmed cell death via apoptosis is associated with a series of morphological and biochemical characteristics, including cell shrinkage, the rapid increase of intracellular calcium, nuclear condensation, DNA fragmentation and the formation of apoptotic bodies. Known as a shared feature of most apoptotic cells, cell shrinkage or a decrease in cell volume is referred to as decreased apoptotic volume (apoptotic volume decrease, AVD). AVD is regarded as an early triggering factor for apoptosis as it emerges earlier than the release of cytochrome C, the activation of cysteine aspartic protease (cysteine-containing aspartate-specific proteases, caspase-3) and DNA fragmentation. Therefore, in the last decade, ion channels which contribute to cell volume regulation after osmotic cell swelling, have an important role in AVD. Cl− channels triggered with apoptosis inducers exhibit electrophysiological properties similar to those of VSOR Cl− channels. VSOR Cl− currents are activated in mitochondria and by death receptor-mediated apoptosis, while VSOR Cl− channel blockers (NPPB and DIDS) block these currents and can reverse apoptosis in tumor DPQ and T cells [34]. In accordance with previous data, we found that VSOR Cl− channels play a very important role in the proliferation of human NPCs, apoptosis in human lung adenocarcinoma cells [35]. These results suggest that VSOR Cl− channels are engaged in proliferation, metastasis and apoptosis in tumor cells. The ClC-3 chloride channel is a member of the voltage-dependent chloride channel family. When cell volume increases, the ClC-3 channel is activated, and Cl− efflux, which forms a chloride current, mediates the transport of substances, induces the release of intracellular organic matter and regulates cell volume. The ClC-3 channel protein is associated with cell proliferation, differentiation and apoptosis. However, the molecular mechanisms by which VSOR Cl− channels are regulated are not clear. The VSOR Cl− channel protein is thought to be a P-glycoprotein (P-glycoprotein, P-gP), like ClC-3 and ClC-2, and to influence cell apoptosis by taking part in the regulation of cell volume. The VSOR Cl− channel mediates the transmembrane transport of chloride ions to regulate AVD. Whereas it would be worthwhile to study whether this channel partakes in GNA-induced apoptosis of CNE-2Z cells, GNA was used to induce apoptosis in CNE-2Z cells in this study. The cells were treated with blocking agents (DIDS, DCPIB), and the survival rate, apoptosis and apoptosis rate were detected by MTT, DAPI staining and flow cytometry assays, respectively. We found that the chloride channel blockers (DIDS and DCPIB) effectively reduced CNE-2Z-induced apoptosis in GNA cells. Then, the CLC-3 gene was silenced by an siRNA in CNE-2Z cells. The results revealed that after the CLC-3 gene was silenced, cell apoptosis varied in a manner similar to that observed in blocker-treated CNE-2Z cells. Hence, in CNE-2Z cells induced by GNA, apoptosis may be related to the activation of VSOR Cl− channels, but the mechanism underlying this effect requires further exploration. Previous studies have found that GNA induces CNE-2Z cell apoptosis and that the activation of VSOR chloride channels may initiate GNA-induced apoptosis in CNE-2Z cells. On the basis of these data, in these experiments, we further explored the relationship between the activation of the VSOR Cl− channel and ER stress-mediated apoptosis in CNE-2Z cells. In recent years, the ER stress-mediated apoptosis pathway has been found to differ from the mitochondrial and death receptor pathways in that it can induce apoptosis independently via its own signal transduction pathway. In normal cells, GRP78, ATF6, IRE 1 and PERK form an integrated but inactive complex. Under ER stress, unfolded proteins accumulate, and GRP78 becomes separated from the complex, causing it to be activated. The signal is then transmitted to the nucleus to initiate the UPR. GRP78 is mainly present in the ER and significantly contributes to the activation of proto-oncogenes. Previous research has shown that GRP78 is expressed on the surfaces of tumor cells but not normal cells [36] Progress in research on the ER stress-related signaling pathway has revealed that the UPR can induce CHOP transcription by PERK, ATF6 and IRE1. Specifically, the PERK-eIF2a-ATF4 pathway has become a popular subject of research and the most important regulator of CHOP [37]. As the main molecular marker of ER stress, CHOP belongs to the C/EBP family of transcription factors. Under normal circumstances, CHOP levels are low in the cytoplasm. However, ER stress can induce the expression of CHOP by regulating nuclear target genes. CHOP is involved in the regulation of cell survival and ER stress-mediated apoptosis [38]. Its expression is increased in the nucleus when ER stress induces apoptosis, and its overexpression can induce cell apoptosis.