N-(1-pyrenyl) maleimide induces bak oligomerization and mitochondrial dysfunction in Jurkat Cells

Oxoglutarate Carrier Inhibition Reduced Melanoma Growth and Invasion by Reducing ATP Production

Recent findings indicate that (a) mitochondria in proliferating cancer cells are functional, (b) cancer cells use more oxygen than normal cells for oxidative phosphorylation, and (c) cancer cells critically rely on cytosolic NADH transported into mitochondria via the malate-aspartate shuttle (MAS) for ATP production. In a spontaneous lung cancer model, tumor growth was reduced by 50% in heterozygous oxoglutarate carrier (OGC) knock-out mice compared with wild-type counterparts. To determine the mechanism through which OGC promotes tumor growth, the effects of the OGC inhibitor N-phenylmaleimide (NPM) on mitochondrial activity, oxygen consumption, and ATP production were evaluated in melanoma cell lines. NPM suppressed oxygen consumption and decreased ATP production in melanoma cells in a dose-dependent manner. NPM also reduced the proliferation of melanoma cells. To test the effects of NPM on tumor growth and metastasis in vivo, NPM was administered in a human melanoma xenograft model. NPM reduced tumor growth by approximately 50% and reduced melanoma invasion by 70% at a dose of 20 mg/kg. Therefore, blocking OGC activity may be a useful approach for cancer therapy.

Linker Histone H1.2 Directly Activates BAK through the K/RVVKP Motif on the C-Terminal Domain

H1.2 is a key mediator of apoptosis following DNA double-strand breaks. The link between H1.2 and canonical apoptotic pathways is unclear. One study found that H1.2 stimulates cytochrome c (Cyt c) release; in contrast, apoptosis-inducing factor was found to be released in another study. The C-terminal domain (CTD) of H1.2 has been implicated in the latter pathway, but activation of the proapoptotic protein BCL-2 homologous antagonist/killer (BAK) is a common denominator in both pathways. This study aimed to determine whether the CTD of H1.2 is also responsible for mitochondrial Cyt c release and whether a previously identified K/RVVKP motif in the CTD mediates the response. This study investigated if H1.2 mediates apoptosis induction through direct interaction with BAK. We established that the CTD of H1.2 stimulates mitochondrial Cyt c release in vitro in a mitochondrial permeability transition-independent manner and that the substitution of a single valine with threonine in the K/RVVKP motif abolishes Cyt c release. Additionally, we showed that H1.2 directly interacts with BAK with weak affinity and that the CTD of H1.2 mediates this binding. Using two 20-amino acid peptides derived from the CTD of H1.2 and H1.1 (K/RVVKP motif inclusive), we determined the main residues involved in the direct interaction with BAK. We propose that H1.2 operates through the K/RVVKP motif by directly activating BAK through inter- and intramolecular interactions. These findings expand the view of H1.2 as a signal-transducing molecule that can activate apoptosis in a BAK-dependent manner.

NLRX1 modulates differentially NLRP3 inflammasome activation and NF-κB signaling during Fusobacterium nucleatum infection

NOD-like receptors (NLRs) play a large role in regulation of host innate immunity, yet their role in periodontitis remains to be defined. NLRX1, a member of the NLR family that localizes to mitochondria, enhances mitochondrial ROS (mROS) generation. mROS can activate the NLRP3 inflammasome, yet the role of NLRX1 in NLRP3 inflammasome activation has not been examined. In this study, we revealed the mechanism by which NLRX1 positively regulates ATP-induced NLRP3 inflammasome activation through mROS in gingival epithelial cells (GECs). We found that depletion of NLRX1 by shRNA attenuated ATP-induced mROS generation and redistribution of the NLRP3 inflammasome adaptor protein, ASC. Furthermore, depletion of NLRX1 inhibited Fusobacterium nucleatum infection-activated caspase-1, suggesting that it also inhibits the NLRP3 inflammasome. Conversely, NLRX1 also acted as a negative regulator of NF-κB signaling and IL-8 expression. Thus, NLRX1 stimulates detection of the pathogen F. nucleatum via the inflammasome, while dampening cytokine production. We expect that commensals should not activate the inflammasome, and NLRX1 should decrease their ability to stimulate expression of pro-inflammatory cytokines such as IL-8. Therefore, NLRX1 may act as a potential switch with regards to anti-microbial responses in healthy or diseased states in the oral cavity.

Exogenous spermine inhibits hypoxia/ischemia-induced myocardial apoptosis via regulation of mitochondrial permeability transition pore and associated pathways

Myocardial infarction (MI) is associated with a high mortality rate, which is attributed to the effects of myocyte loss that occurs as a result of ischemia-induced cell death. Very few therapies can effectively prevent or delay the effects of ischemia. Polyamines (PAs) are polycations required for cell growth and division, and their use may prevent cell loss. The aim of this study was to investigate the relationship between hypoxia/ischemia (H/I)-induced cell apoptosis and PA metabolism and to investigate the ability of spermine to limit H/I injury in cardiomyocytes by blocking the mitochondrial apoptotic pathway. Neonatal rat cardiomyocytes were placed under hypoxic conditions for 24 h after being subjected to 5 μM of spermine as a pretreatment therapy. H/I induced PA catabolism, which was indicated by a 1.3-fold up-regulation of spermidine/spermine N(1)-acetyltransferase expression. Exogenous spermine significantly reduced H/I-induced cell death rate (60 ± 2 to 36 ± 2%) and apoptosis rate (42 ± 2 to 21 ± 2%); it also attenuated lactate dehyodrogenase and creatine kinase leakage (440 ± 13 and 336 ± 16 U/L to 275 ± 15 and 235 ± 13 U/L). Furthermore, it decreases calcium overload (3.8 ± 0.2 to 2.2 ± 0.1 a.u.). Moreover, spermine pretreatment remarkably decreased cytochrome c release from the mitochondria to the cytosol, lowering the expression of cleaved caspase-3 and -9. With spermine pretreatment, there was an increase in Bcl-2 levels and phosphorylation of ERK1/2, phosphoinositide 3-kinase, Akt, and GSK-3β, preserving mitochondrial membrane potential and inducing an mitochondrial permeability transition pore opening. In conclusion, H/I decreased endogenous spermine concentrations in cardiomyocytes, which ultimately induced apoptosis. The addition of exogenous spermine effectively prevented myocyte cell death.

Fusobacterium nucleatum infection of gingival epithelial cells leads to NLRP3 inflammasome-dependent secretion of IL-1β and the danger signals ASC and HMGB1

Fusobacterium nucleatum is an invasive anaerobic bacterium that is associated with periodontal disease. Previous studies have focused on virulence factors produced by F. nucleatum, but early recognition of the pathogen by the immune system remains poorly understood. Although an inflammasome in gingival epithelial cells (GECs) can be stimulated by danger-associated molecular patterns (DAMPs) (also known as danger signals) such as ATP, inflammasome activation by this periodontal pathogen has yet to be described in these cells. This study therefore examines the effects of F. nucleatum infection on pro-inflammatory cytokine expression and inflammasome activation in GECs. Our results indicate that infection induces translocation of NF-κB into the nucleus, resulting in cytokine gene expression. In addition, infection activates the NLRP3 inflammasome, which in turn activates caspase-1 and stimulates secretion of mature IL-1β. Unlike other pathogens studied until now, F. nucleatum activates the inflammasome in GECs in the absence of exogenous DAMPs such as ATP. Finally, infection promotes release of other DAMPs that mediate inflammation, such as high-mobility group box 1 protein and apoptosis-associated speck-like protein, with a similar time-course as caspase-1 activation. Thus, F. nucleatum expresses the pathogen-associated molecular patterns necessary to activate NF-κB and also provides an endogenous DAMP to stimulate the inflammasome and further amplify inflammation through secretion of secondary DAMPs.