Paris Polyphylla Monomer PP-26 Induces Mitochondrial Pathway-Mediated Cell Apoptosis by Inhibiting the PI3K/Akt Pathway in Human Gastric Cancer Cells

Background: Paris polyphylla is a traditional Chinese medicinal herb that has been used as a haemostatic, antimicrobial and anticancer agent. Gastric cancer (GC) is a global health problem, with more than 1 million people newly diagnosed with gastric cancer worldwide each year.Methods: The MTT and colony formation assay were used to test the anti-proliferative effects of PP-26 on MGC-803 and BGC-823 cells. Flow cytometry assays, Hoechst 33258 staining assay and Caspase inhibitor Z-VAD-FMK were used to test apoptosis. JC-1 staining used to measure changes in mitochondrial membrane potential and western blot analysis were used to test apoptotic and PI3K/Akt pathway related proteins.Results: PP-26 had a dose-dependent inhibitory effect on the proliferation of MGC-803 and BGC-823 cells, but had no obvious anti-proliferative effect on normal liver LO2 cells and normal embryonic kidney HEK-293 cells. Additionally, PP-26 induced typical apoptotic morphological changes, such as nuclear pyknosis, nuclear cracking and apoptotic bodies. Moreover, PP-26 induced a decrease in mitochondrial membrane potential. And PP-26 modulated the expression of Bcl-xL, Mcl-1, Bax, caspase-9/-3 and PARP proteins and induced cell apoptosis through the mitochondrial apoptotic pathway. Next, using an irreversible general caspase inhibitor (Z-VAD-FMK), we confirmed the activation of the mitochondrial apoptotic pathway induced by PP-26. Furthermore, PP-26 inhibited the phosphorylation of Akt and GSK-3β. The inhibition of Akt protein activated the mitochondrial apoptotic pathway.Conclusion: Collectively, these results indicated that PP-26 inhibited the proliferation of MGC-803 and BGC-823 cells by inhibiting the Akt signalling pathway and activating the mitochondrial apoptotic pathway.

Effects and Related Mechanisms of the Senolytic Agent ABT-263 on the Survival of Irradiated A549 and Ca9-22 Cancer Cells

Senolytic agents eliminate senescent cells and are expected to reduce senescent cell-mediated adverse effects in cancer therapy. However, the effects of senolytic agents on the survival of irradiated cancer cells remain unknown. Here, the effects of the senolytic agent ABT-263 on the survival of irradiated A549 and Ca9-22 cancer cells were investigated. ABT-263 was added to the culture medium after irradiation. SA-β-gal activity and cell size, which are hallmarks of cell senescence, were evaluated using a flow cytometer. The colony-forming assay and annexin V staining were performed to test cell survival. We first confirmed that radiation increased the proportion of cells with high SA-β-gal activity and that ABT-263 decreased it. Of note, ABT-263 decreased the survival of irradiated cancer cells and increased the proportion of radiation-induced annexin V+ cells. Furthermore, the caspase inhibitor suppressed the ABT-263-induced decrease in the survival of irradiated cells. Intriguingly, ABT-263 decreased the proportion of SA-β-gal low-activity/large cells in the irradiated A549 cells, which was recovered by the caspase inhibitor. Together, these findings suggest that populations maintaining the ability to proliferate existed among the irradiated cancer cells showing senescence-related features and that ABT-263 eliminated the population, which led to decreased survival of irradiated cancer cells.

Nuclear Opening and Histone Release Are Essential for Nuclear but Not Chromatin Condensation during Terminal Erythropoiesis

Nuclear condensation and enucleation are characteristic processes in mammalian terminal erythropoiesis. These processes are associated with the transient nuclear opening formation that mediates partial histone release to the cytoplasm. Our previous report showed that caspases are involved in the cleavage of nuclear lamina to enable histone release. However, it remains unclear whether nuclear opening formation and histone release regulate the genomic three-dimensional organization during nuclear condensation. To answer this question, we cultured E13.5 mouse fetal liver Ter119 negative erythroid progenitor cells in erythropoietin (EPO) containing medium for 48 h with or without the presence of caspase inhibitor. As expected, caspase inhibitor blocked nuclear opening formation and histone release, and significantly reduced nuclear condensation and enucleation. We next performed a Hi-C sequencing to investigate chromatin structural change during terminal differentiation and nuclear condensation. To this end, the cultured fetal liver erythroid cells with or without caspase inhibitor were harvested at 30 h right before enucleation for Hi-C sequencing. The sequencing results showed that cells at 30 h contain significantly more interactions than freshly isolated erythroid progenitors, which is consistent with chromatin condensation during terminal erythropoiesis. Further analysis showed that increased interactions mainly accumulate as inter-chromosomal interactions, suggesting inter-chromosome interaction is the dominant structural force driving erythrocyte chromatin condensation. Surprisingly, there were no significant chromatin structural changes between caspase inhibitor treated and mock-treated cells when compared at 30 h. We also performed ATAC-seq and RNA-seq with the same experiment settings, both corresponded to Hi-C sequencing and showed little difference under caspase inhibitor treatment. These results indicate that although histone release and nuclear condensation are compromised with the inhibition of caspases, chromatin stays condensed with well-organized three-dimensional structure and appropriate gene expression regulations. To further confirm this phenomenon, we generated caspase-3 and -7 double knock out (cas3cas7-/-) mice. Cas3cas7-/- mice are embryonically lethal due to defective cardiac development. The hematopoietic tissues in these mice have not been well studied. We harvested fetal liver Ter119 negative erythroid progenitor cells from E13.5 cas3cas7-/- mice and the cells from the littermate (cas7-/-, cas3+/-cas7-/-) mice were used as controls. We first cultured Ter119 negative fetal liver erythroid progenitors in EPO containing medium for 48 h. Immunofluorescence analysis showed that the nuclear opening was significantly inhibited, and the nuclear size significantly increased in the erythroid cells from cas3cas7-/- mice due to failure of histone release into cytoplasm. Flow cytometry analysis showed that enucleation was significantly impaired in cas3cas7-/- cells, but the cells could still differentiate although with lower efficiency. We further performed an in vivo assay in which E13.5 cas3cas7-/- fetal liver cells were transplanted into wild type lethally irradiated recipient mice. EPO medium cultured bone marrow lineage negative cells from these transplanted mice showed significant reduction in nuclear opening and histone release, and enlargement of nuclear size. However, these mice survived well despite anemia. These results indicate a portion of orthochromatic erythroblasts managed to enucleate even with the less condensed nuclei. Overall, our study demonstrates that nuclear opening and histone release are essential for nuclear condensation but have minimal effects on chromatin condensation or the regulation of gene expression in terminal erythropoiesis. Appropriate nuclear condensation is important for efficient enucleation. However, orthochromatic erythroblasts could still manage to enucleate although with low efficacies. Disclosures No relevant conflicts of interest to declare.

Apoptosis Enhances the Replication of Human Coronavirus OC43

Human coronavirus OC43 (HCoV-OC43) is one of the coronaviruses causing a mild common cold, but few studies have been made on this strain. Here, we identified the molecular mechanisms involved in HCoV-OC43-induced apoptosis and its implications for viral reproduction in Vero cells and MRC-5 cells. HCoV-OC43 infection induced apoptosis that was accompanied by cleavage of caspase-3 and PARP, degradation of cyclin D1, and cell cycle arrest at S and G2M phases. Dephosphorylation of STAT1 and STAT3, induced by HCoV-OC43 infection, was also associated with HCoV-OC43-mediated apoptosis. The pan-caspase inhibitor effectively prevented HCoV-OC43-induced apoptosis and reduced viral replication, suggesting that apoptosis contributes to viral replication. Collectively our results indicate that HCoV-OC43 induces caspase-dependent apoptosis to promote viral replication in Vero cells and MRC-5 cells.

Impact of FasL Stimulation on Sclerostin Expression and Osteogenic Profile in IDG-SW3 Osteocytes

The Fas ligand (FasL) is known from programmed cell death, the immune system, and recently also from bone homeostasis. As such, Fas signalling is a potential target of anti-osteoporotic treatment based on the induction of osteoclastic cell death. Less attention has been paid to osteocytes, although they represent the majority of cells within the mature bone and are the key regulators. To determine the impact of FasL stimulation on osteocytes, differentiated IDG-SW3 cells were challenged by FasL, and their osteogenic expression profiles were evaluated by a pre-designed PCR array. Notably, the most downregulated gene was the one for sclerostin, which is the major marker of osteocytes and a negative regulator of bone formation. FasL stimulation also led to significant changes (over 10-fold) in the expression of other osteogenic markers: Gdf10, Gli1, Ihh, Mmp10, and Phex. To determine whether these alterations involved caspase-dependent or caspase-independent mechanisms, the IDG-SW3 cells were stimulated by FasL with and without a caspase inhibitor: Q-VD-OPh. The alterations were also detected in the samples treated by FasL along with Q-VD-OPh, pointing to the caspase-independent impact of FasL stimulation. These results contribute to an understanding of the recently emerging pleiotropic effects of Fas/FasL signalling and specify its functions in bone cells.

MCPIP1 Enhances TNF-α-Mediated Apoptosis through Downregulation of the NF-κB/cFLIP Axis

Monocyte chemoattractant protein-1-induced protein 1 (MCPIP1) is rapidly produced under proinflammatory stimuli, thereby feeding back to downregulate excessive inflammation. In this study, we used the stable, inducible expressions of wild-type (WT) MCPIP1 and an MCPIP1-D141N mutant in T-REx-293 cells by means of a tetracycline on (Tet-on) system. We found that WT MCPIP1 but not MCPIP1-D141N mutant expression dramatically increased apoptosis, caspase-3, -7, -8, and -9 activation, and c-Jun N-terminal kinase (JNK) phosphorylation in TNF-α-treated cells. The pan-caspase inhibitor, z-VAD-fmk, and the caspase-1 inhibitor, z-YVAD-fmk, but not the JNK inhibitor, SP600125, significantly reversed apoptosis and caspase activation in TNF-α/MCPIP1-treated cells. Surprisingly, MCPIP1 itself was also cleaved, and the cleavage was suppressed by treatment with the pan-caspase inhibitor and caspase-1 inhibitor. Moreover, MCPIP1 was found to contain a caspase-1/-4 consensus recognition sequence located in residues 234~238. As expected, the WT MCPIP1 but not the MCPIP1-D141N mutant suppressed NF-κB activation, as evidenced by inhibition of IκB kinase (IKK) phosphorylation and IκB degradation using Western blotting, IKK activity using in vitro kinase activity, and NF-κB translocation to nuclei using an immunofluorescence assay. Interestingly, MCPIP1 also significantly inhibited importin α3 and importin α4 expressions, which are major nuclear transporter receptors for NF-κB. Inhibition of NF-κB activation further downregulated expression of the caspase-8 inhibitor, cFLIP. In summary, the results suggest that MCPIP1 could enhance the TNF-α-induced apoptotic pathway through decreasing NF-κB activation and cFLIP expression.

Exocyst Inactivation in Urothelial Cells Disrupts Autophagy and Activates non-canonical NF-κB

Ureter obstruction is a highly prevalent event during embryonic development and is a major cause of pediatric kidney disease. We have reported that ureteric bud specific ablation of the exocyst Exoc5 subunit in late murine gestation results in failure of urothelial stratification, cell death, and complete ureter obstruction. However, the mechanistic connection between disrupted exocyst activity, urothelial cell death, and subsequent ureter obstruction was unclear. Here, we report that inhibited urothelial stratification does not drive cell death during ureter development. Instead, we demonstrate that the exocyst plays a critical role in autophagy in urothelial cells, and that disruption of autophagy activates a urothelial NF-κB stress response. Impaired autophagy first provokes canonical NF κB activity which is progressively followed by increasing non-canonical NF-κB activity and cell death if the stress remains unresolved. Furthermore, we demonstrate that ureter obstructions can be completely rescued in Exoc5 conditional knockout mice by administering a single dose of pan-caspase inhibitor z VAD-FMK at E16.5 prior to urothelial cell death. Taken together, ablation of Exoc5 disrupts autophagic stress response and activates progressive NF-κB signaling which promotes obstructive uropathy.