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Background: Mitochondria are dynamic organelles that undergo fission and fusion. During cell stress, mitochondrial dynamics shift to fission, leading to mitochondrial fragmentation, membrane leakage, and apoptosis. Mitochondrial fragmentation requires the cleavage of both outer and inner membranes, but the mechanism of inner membrane cleavage is unclear. Bif-1 and prohibitin-2 may regulate mitochondrial dynamics., Methods: We used azide-induced ATP depletion to incite cell stress in mouse embryonic fibroblasts and renal proximal tubular cells, and renal ischemia-reperfusion to induce stress in mice. We also used knockout cells and mice to determine the role of Bif-1, and used multiple techniques to analyze the molecular interaction between Bif-1 and prohibitin-2., Results: Upon cell stress, Bif-1 translocated to mitochondria to bind prohibitin-2, resulting in the disruption of prohibitin complex and proteolytic inactivation of the inner membrane fusion protein OPA1. Bif-1-deficiency inhibited prohibitin complex disruption, OPA1 proteolysis, mitochondrial fragmentation, and apoptosis. Domain deletion analysis indicated that Bif-1 interacted with prohibitin-2 via its C-terminus. Notably, mutation of Bif-1 at its C-terminal tryptophan-344 not only prevented Bif-1/prohibitin-2 interaction but also reduced prohibitin complex disruption, OPA1 proteolysis, mitochondrial fragmentation, and apoptosis, supporting a pathogenic role of Bif-1/prohibitin-2 interaction. In mice, Bif-1 bound prohibitin-2 during renal ischemia/reperfusion injury, and Bif-1-deficiency protected against OPA1 proteolysis, mitochondrial fragmentation, apoptosis and kidney injury., Conclusions: These findings suggest that during cell stress, Bif-1 regulates mitochondrial inner membrane by interacting with prohibitin-2 to disrupt prohibitin complexes and induce OPA1 proteolysis and inactivation., (Copyright © 2019 by the American Society of Nephrology.)

As the first member of glycylcycline bacteriostatic agents, tigecycline is approved as a novel expanded-spectrum antibiotic, which is clinically available. However, accumulating evidence indicated that tigecycline was provided with the potential application in cancer therapy. In this paper, tigecycline was shown to exert an anti-proliferative effect on neuroblastoma cell lines. Furthermore, it was found that tigecycline induced G1-phase cell cycle arrest instead of apoptosis by means of Akt pathway inhibition. In neuroblastoma cell lines, the Akt activator insulin-like growth factor-1 (hereafter referred to as IGF-1) reversed tigecycline-induced cell cycle arrest. Besides, tigecycline inhibited colony formation and suppressed neuroblastoma cells xenograft formation and growth. After tigecycline treatment in vivo, the Akt pathway inhibition was confirmed as well. Collectively, our data provided strong evidences that tigecycline inhibited neuroblastoma cells growth and proliferation through the Akt pathway inhibition in vitro and in vivo. In addition, these results were supported by previous studies concerning the application of tigecycline in human tumors treatment, suggesting that tigecycline might act as a potential candidate agent for neuroblastoma treatment.

The response to UV irradiation is important for a cell to maintain its genetic integrity when challenged by environmental genotoxins. An immediate early response to UV irradiation is the rapid induction of activating transcription factor 3 (ATF3) expression. Although emerging evidence has linked ATF3 to stress pathways regulated by the tumor suppressor p53 and the histone acetyltransferase Tip60, the role of ATF3 in the UV response remains largely unclear. Here, we report that ATF3 mediated dichotomous UV responses. Although UV irradiation enhanced the binding of ATF3 to Tip60, knockdown of ATF3 expression decreased Tip60 stability, thereby impairing Tip60 induction by UV irradiation. In line with the role of Tip60 in mediating UV-induced apoptosis, ATF3 promoted the death of p53-defective cells in response to UV irradiation. However, ATF3 could also activate p53 and promote p53-mediated DNA repair, mainly through altering histone modifications that could facilitate recruitment of DNA repair proteins (such as DDB2) to damaged DNA sites. As a result, ATF3 rather protected the p53 wild-type cells from UV-induced apoptosis. Our results thus indicate that ATF3 regulates cell fates upon UV irradiation in a p53-dependent manner., (© 2016 by The American Society for Biochemistry and Molecular Biology, Inc.)

ER stress has been implicated in the pathogenesis of both acute and chronic kidney diseases. However, the molecular regulation of ER stress in kidney cells and tissues remains poorly understood. In this study, we examined tunicamycin-induced ER stress in renal proximal tubular cells (RPTC). Tunicamycin induced the phosphorylation and activation of PERK and eIF2α within 2 h in RPTC, which was followed by the induction of GRP78 and CHOP. Consistently, tunicamycin also induced apoptosis in RPTC. Interestingly, mTOR was activated rapidly during tunicamycin treatment, as indicated by phosphorylation of both mTOR and p70S6K. Inhibition of mTOR with rapamycin partially suppressed the phosphorylation of PERK and eIF2a and the induction of CHOP and GRP78 induction during tunicamycin treatment. Rapamycin also inhibited apoptosis during tunicamycin treatment and increased cell survival. Collectively, the results suggest that mTOR plays a regulatory role in ER stress, and inhibition of mTOR may have potential therapeutic effects in ER stress-related renal diseases.

Leflunomide as an immunosuppressive drug is generally used in the treatment of rheumatoid arthritis. It inhibits DHODH (dihydroorotate dehydrogenase ), which is one of the essential enzymes in the de novo pyrimidine biosynthetic pathway. Here we showed that leflunomide significantly reduced cell proliferation and self-renewal activity. Annexin V-FITC/PI staining assay revealed that leflunomide induced S-phase cell cycle arrest, and promoted cell apoptosis. In vivo xenograft study in SCID mice showed that leflunomide inhibited tumor growth and development. We also observed that DHODH was commonly expressed in neuroblastoma. When treated with leflunomide, the neuroblastoma cell lines BE(2)-C, SK-N-DZ, and SK-N-F1 showed dramatic inhibition of DHODH at mRNA and protein levels. Considering the favorable toxicity profile and the successful clinical experience with leflunomide in rheumatoid arthritis, this drug represents a potential new candidate for targeted therapy in neuroblastoma.

Adeno-associated virus (AAV) is a nonpathogenic parvovirus that efficiently replicates in the presence of adenovirus (Ad). Exogenous expression of the AAV replication proteins induces caspase-dependent apoptosis, but determining if AAV infection causes apoptosis during viral infection is complicated by Ad-mediated programmed cell death. To eliminate Ad-induced cytolysis, we used an E3 adenoviral death protein (ADP) mutant, pm534. AAV and pm534-coinfected cells exhibited increased cell killing compared to pm534 alone. Relative to cells infected with Ad alone, AAV and wild-type Ad-infected cells displayed decreased ADP expression, increased cytolysis until the third day of the infection, and decreased cytolysis thereafter. Biochemical and morphological characteristics of apoptosis were observed during coinfections with AAV and pm534 or Ad, including a moderate degree of caspase activation that was not present during infections with pm534 or Ad alone. AAV coinfection also increased extracellular pH. These studies suggest that AAV induces caspase-dependent and caspase-independent apoptosis.

Nuclear factor-kappa B (NF-kappa B) promotes cell survival by upregulating expression of anti-apoptotic genes, a process that is antagonized by inhibitors of kappa B (I kappa B) factors. The only NF-kappa B family member known to be mutated in human cancer is NF-kappa B2 p100 (ref. 2), a factor with I kappa B activity. Here, we report the isolation from irradiated mouse tumour cells of a complex that induces caspase-8 activity in cell-free assays and identify p100 as an essential component of this complex. Expression of p100 profoundly sensitizes cells to death-receptor-mediated apoptosis through a pathway that is independent of I kappa B-like activity. The carboxyl terminus of p100 contains a death domain that is absent from all known tumour-derived mutants. This death domain mediates recruitment of p100 into death machinery complexes after ligand stimulation and is essential for p100's pro-apoptotic activity. p100 also sensitizes NIH3T3 cells to apoptosis triggered by oncogenic Ras, resulting in a marked inhibition of transformation that is rescued by suppression of endogenous caspase-8. These observations thus identify an I kappa B-independent apoptotic activity of NF-kappa B2 p100 and help explain its unique tumour suppressor role.

The signaling pathway for DNA damaging drug-triggered apoptosis was examined in a chemosensitive human neuroblastoma cell line, SH-SY5Y. Doxorubicin and etoposide induce rapid and extensive apoptosis in SH-SY5Y cells. After the drug treatment, p53 protein levels increase in the nucleus, leading to the induction of its transcription targets p21(Waf1/Cip1) and MDM2. Inactivation of p53, either by the human papillomavirus type 16 E6 protein or by a dominant-negative mutant p53 (R175H), completely protects SH-SY5Y cells from drug-triggered apoptosis. Cytochrome c and caspase-9 function downstream of p53 in mediating the drug-triggered apoptosis in SH-SY5Y cells. In drug-treated cells, cytochrome c is released, and caspase-9 becomes activated. Inactivation of p53 blocks cytochrome c release and caspase-9 activation. Furthermore, drug-induced cell death can be prevented by expression of a dominant-negative mutant of caspase-9. These findings define a molecular pathway for mediating DNA damaging drug-induced apoptosis in the human neuroblastoma SH-SY5Y cells and suggest that inactivation of essential components of this apoptotic pathway may confer drug resistance on neuroblastoma cells.

Autonomous cell proliferation is one of the hallmarks of cancer cells, driven by activated growth-promoting oncogenes. However, deregulated activation of these oncogenes also triggers apoptosis via multiple pathways. Among them, the ARF-p53 pathway appears to play a major role in mediating oncogene-induced apoptosis. Consequently, suppression of apoptosis by inactivation of p53 and other tumor suppressors is central to tumor development. These findings have broad implications in understanding cancer genetics and therapy. They help define the roles for oncogenes and tumor suppressor genes in tumorigenesis. Furthermore, the notion that cancer cells often carry specific defects in apoptotic pathways but are inherently sensitive to apoptosis as a result of deregulated proliferation, offers numerous opportunities for manipulating apoptosis in directions of clinical application.

Leflunomide as an immunosuppressive drug is generally used in the treatment of rheumatoid arthritis. It inhibits DHODH (dihydroorotate dehydrogenase ), which is one of the essential enzymes in the de novo pyrimidine biosynthetic pathway. Here we showed that leflunomide significantly reduced cell proliferation and self-renewal activity. Annexin V-FITC/PI staining assay revealed that leflunomide induced S-phase cell cycle arrest, and promoted cell apoptosis. In vivo xenograft study in SCID mice showed that leflunomide inhibited tumor growth and development. We also observed that DHODH was commonly expressed in neuroblastoma. When treated with leflunomide, the neuroblastoma cell lines BE(2)-C, SK-N-DZ, and SK-N-F1 showed dramatic inhibition of DHODH at mRNA and protein levels. Considering the favorable toxicity profile and the successful clinical experience with leflunomide in rheumatoid arthritis, this drug represents a potential new candidate for targeted therapy in neuroblastoma. [ABSTRACT FROM AUTHOR]

Nuclear factor-κB (NF-κB) promotes cell survival by upregulating expression of anti-apoptotic genes, a process that is antagonized by inhibitors of κB (IκB) factors. The only NF-κB family member known to be mutated in human cancer is NF-κB2 p100 (ref. 2), a factor with IκB activity. Here, we report the isolation from irradiated mouse tumour cells of a complex that induces caspase-8 activity in cell-free assays and identify p100 as an essential component of this complex. Expression of p100 profoundly sensitizes cells to death-receptor-mediated apoptosis through a pathway that is independent of IκB-Iike activity. The carboxyl terminus of p100 contains a death domain that is absent from all known tumour-derived mutants. This death domain mediates recruitment of p100 into death machinery complexes after ligand stimulation and is essential for p100's pro-apoptotic activity. p100 also sensitizes NIH3T3 cells to apoptosis triggered by oncogenic Ras, resulting in a marked inhibition of transformation that is rescued by suppression of endogenous caspase-8. These observations thus identify an IκBindependent apoptotic activity of NF-κB2 pl00 and help explain its unique tumour suppressor role. [ABSTRACT FROM AUTHOR]

Leflunomide as an immunosuppressive drug is generally used in the treatment of rheumatoid arthritis. It inhibits DHODH (dihydroorotate dehydrogenase ), which is one of the essential enzymes in the de novo pyrimidine biosynthetic pathway. Here we showed that leflunomide significantly reduced cell proliferation and self-renewal activity. Annexin V-FITC/PI staining assay revealed that leflunomide induced S-phase cell cycle arrest, and promoted cell apoptosis. In vivo xenograft study in SCID mice showed that leflunomide inhibited tumor growth and development. We also observed that DHODH was commonly expressed in neuroblastoma. When treated with leflunomide, the neuroblastoma cell lines BE(2)-C, SK-N-DZ, and SK-N-F1 showed dramatic inhibition of DHODH at mRNA and protein levels. Considering the favorable toxicity profile and the successful clinical experience with leflunomide in rheumatoid arthritis, this drug represents a potential new candidate for targeted therapy in neuroblastoma. [ABSTRACT FROM AUTHOR]