IκΒα inhibits apoptosis at the outer mitochondrial membrane independently of NF-κB retention

MiR-34a promotes mitochondrial pathway of apoptosis in human salivary gland epithelial cells by activating NF-κB signaling

To investigate the potential molecular mechanism of miR-34a in Sjögren's syndrome (SS). Transmission electron microscopy was used to observe the salivary gland tissues of mild and severe SS patients. SS mouse model was constructed and injected with miR-34a antagonist. HSGE cells were transfected with miR-34a mimic. Starbase predicted miR-34a binding sites and validated them with dual-luciferase reporter assays. Immunohistochemistry, HE staining, CCK-8, TUNEL assay, flow cytometry, immunofluorescence and Western Blot were used to investigate the effects of miR-34a on NF-κB signaling and mitochondrial pathway of apoptosis in HSGE cells. Severe SS patients showed obvious mitochondrial damage and apoptosis in salivary glands. MiR-34a was overexpressed and NF-κB signaling is activated in salivary glands of severe SS patients. Inhibition of miR-34a alleviated salivary gland injury in SS mice, as well as inhibited the activation of NF-κB signaling and mitochondrial pathway of apoptosis. In conclusion, miR-34a promoted NF-κB signaling by targeting IκBα, thereby causing mitochondrial pathway apoptosis and aggravating SS-induced salivary gland damage.

Gene coexpression network analysis reveals the genes and pathways in pectoralis major muscle and liver associated with wooden breast in broilers

Wooden breast (WB) is a myopathy mainly affecting pectoralis major (PM) muscle in modern commercial broiler chickens, causing enormous economic losses in the poultry industry. Recent studies have observed hepatic and PM muscle injury in broilers affected by WB, but the relationships between WB and the 2 tissues are mostly unclear. In the current study, the RNA-seq raw data of PM muscle and liver were downloaded from GSE144000, and we constructed the gene coexpression networks of PM muscle and liver to explore the relationships between WB and the 2 tissues using the weighted gene coexpression network analysis (WGCNA) method. Six and 2 gene coexpression modules were significantly correlated with WB in the PM muscle and liver networks, respectively. TGF-beta signaling, Toll-like receptor signaling and mTOR signaling pathways were significantly enriched in the genes within the 6 gene modules of PM muscle network. Meanwhile, mTOR signaling pathway was significantly enriched in the genes within the 2 gene modules of liver network. In the consensus gene coexpression network across the 2 tissues, salmon module (r = -0.5 and p = 0.05) was significantly negatively correlated with WB, in which Toll-like receptor signaling, apoptosis, and autophagy pathways were significantly enriched. The genes related with the 3 pathways, myeloid differentiation primary response 88 (MYD88), interferon regulatory factor 7 (IRF7), mitogen-activated protein kinase 14 (MAPK14), FBJ murine osteosarcoma viral oncogene homolog (FOS), jun proto-oncogene (JUN), caspase-10, unc-51 like autophagy activating kinase 2 (ULK2) and serine/threonine kinase 11 (LKB1), were identified in salmon module. In this current study, we found that the signaling pathways related with cell inflammation, apoptosis and autophagy might influence WB across 2 tissues in broilers.

Biological role of mitochondrial TLR4-mediated NF-κB signaling pathway in central nervous system injury

Previous studies suggested that central nervous system injury is often accompanied by the activation of Toll-like receptor 4/NF-κB pathway, which leads to the upregulation of proapoptotic gene expression, causes mitochondrial oxidative stress, and further aggravates the inflammatory response to induce cell apoptosis. Subsequent studies have shown that NF-κB and IκBα can directly act on mitochondria. Therefore, elucidation of the specific mechanisms of NF-κB and IκBα in mitochondria may help to discover new therapeutic targets for central nervous system injury. Recent studies have suggested that NF-κB (especially RelA) in mitochondria can inhibit mitochondrial respiration or DNA expression, leading to mitochondrial dysfunction. IκBα silencing will cause reactive oxygen species storm and initiate the mitochondrial apoptosis pathway. Other research results suggest that RelA can regulate mitochondrial respiration and energy metabolism balance by interacting with p53 and STAT3, thus initiating the mitochondrial protection mechanism. IκBα can also inhibit apoptosis in mitochondria by interacting with VDAC1 and other molecules. Regulating the biological role of NF-κB signaling pathway in mitochondria by targeting key proteins such as p53, STAT3, and VDAC1 may help maintain the balance of mitochondrial respiration and energy metabolism, thereby protecting nerve cells and reducing inflammatory storms and death caused by ischemia and hypoxia.

Inhibition of NF-κB-Mediated Proinflammatory Transcription by Ru(II) Complexes of Anti-Angiogenic Ligands in Triple-Negative Breast Cancer

Nuclear factor kappa beta (NF-κB) plays a pivotal role in breast cancer, particularly triple-negative breast cancer, by promoting inflammation, proliferation, epithelial-mesenchymal transition, metastasis, and drug resistance. Upregulation of NF-κB boosts vascular endothelial growth factor (VEGF) expression, assisting angiogenesis. The Ru(II) complexes of methyl- and dimethylpyrazolyl-benzimidazole N,N donors inhibit phosphorylation of ser536 in p65 and translocation of the NF-κB heterodimer (p50/p65) to the nucleus, disabling transcription to upregulate inflammatory signaling. The methyl- and dimethylpyrazolyl-benzimidazole inhibit VEGFR2 phosphorylation at Y1175, disrupting downstream signaling through PLC-γ and ERK1/2, ultimately suppressing Ca(II)-signaling. Partial release of the antiangiogenic ligand in a reactive oxygen species-rich environment is possible as per our observation to inhibit both NF-κB and VEGFR2 by the complexes. The complexes are nontoxic to zebrafish embryos up to 50 μM, but the ligands show strong in vivo antiangiogenic activity at 3 μM during embryonic growth in Tg(fli1:GFP) zebrafish but no visible effect on the adult phase.

G6PD maintains the VSMC synthetic phenotype and accelerates vascular neointimal hyperplasia by inhibiting the VDAC1-Bax-mediated mitochondrial apoptosis pathway

BACKGROUND

Glucose-6-phosphate dehydrogenase (G6PD) plays an important role in vascular smooth muscle cell (VSMC) phenotypic switching, which is an early pathogenic event in various vascular remodeling diseases (VRDs). However, the underlying mechanism is not fully understood.

METHODS

An IP‒LC‒MS/MS assay was conducted to identify new binding partners of G6PD involved in the regulation of VSMC phenotypic switching under platelet-derived growth factor-BB (PDGF-BB) stimulation. Co-IP, GST pull-down, and immunofluorescence colocalization were employed to clarify the interaction between G6PD and voltage-dependent anion-selective channel protein 1 (VDAC1). The molecular mechanisms involved were elucidated by examining the interaction between VDAC1 and apoptosis-related biomarkers, as well as the oligomerization state of VDAC1.

RESULTS

The G6PD level was significantly elevated and positively correlated with the synthetic characteristics of VSMCs induced by PDGF-BB. We identified VDAC1 as a novel G6PD-interacting molecule essential for apoptosis. Specifically, the G6PD-NTD region was found to predominantly contribute to this interaction. G6PD promotes VSMC survival and accelerates vascular neointimal hyperplasia by inhibiting VSMC apoptosis. Mechanistically, G6PD interacts with VDAC1 upon stimulation with PDGF-BB. By competing with Bax for VDAC1 binding, G6PD reduces VDAC1 oligomerization and counteracts VDAC1-Bax-mediated apoptosis, thereby accelerating neointimal hyperplasia.

CONCLUSION

Our study showed that the G6PD-VDAC1-Bax axis is a vital switch in VSMC apoptosis and is essential for VSMC phenotypic switching and neointimal hyperplasia, providing mechanistic insight into early VRDs.

A novel triptolide analog downregulates NF-κB and induces mitochondrial apoptosis pathways in human pancreatic cancer

Pancreatic cancer is the seventh leading cause of cancer-related death worldwide, and despite advancements in disease management, the 5 -year survival rate stands at only 12%. Triptolides have potent anti-tumor activity against different types of cancers, including pancreatic cancer, however poor solubility and toxicity limit their translation into clinical use. We synthesized a novel pro-drug of triptolide, (E)-19-[(1'-benzoyloxy-1'-phenyl)-methylidene]-Triptolide (CK21), which was formulated into an emulsion for in vitro and in vivo testing in rats and mice, and used human pancreatic cancer cell lines and patient-derived pancreatic tumor organoids. A time-course transcriptomic profiling of tumor organoids treated with CK21 in vitro was conducted to define its mechanism of action, as well as transcriptomic profiling at a single time point post-CK21 administration in vivo. Intravenous administration of emulsified CK21 resulted in the stable release of triptolide, and potent anti-proliferative effects on human pancreatic cancer cell lines and patient-derived pancreatic tumor organoids in vitro, and with minimal toxicity in vivo. Time course transcriptomic profiling of tumor organoids treated with CK21 in vitro revealed <10 differentially expressed genes (DEGs) at 3 hr and ~8,000 DEGs at 12 hr. Overall inhibition of general RNA transcription was observed, and Ingenuity pathway analysis together with functional cellular assays confirmed inhibition of the NF-κB pathway, increased oxidative phosphorylation and mitochondrial dysfunction, leading ultimately to increased reactive oxygen species (ROS) production, reduced B-cell-lymphoma protein 2 (BCL2) expression, and mitochondrial-mediated tumor cell apoptosis. Thus, CK21 is a novel pro-drug of triptolide that exerts potent anti-proliferative effects on human pancreatic tumors by inhibiting the NF-κB pathway, leading ultimately to mitochondrial-mediated tumor cell apoptosis.

Repairing gastric ulcer with hyaluronic acid/extracellular matrix composite through promoting M2-type polarization of macrophages

The treatment of gastric ulcer and perforation using synthetic and biomaterials has been a clinical challenge. In this work, a drug-carrying layer of hyaluronic acid was combined with a gastric submucosal decellularized extracellular matrix called gHECM. The regulation of macrophage polarization by the extracellular matrix's components was then investigated. This work proclaims how gHECM responds to inflammation and aids in the regeneration of the gastric lining by altering the phenotype of surrounding macrophages and stimulating the body's whole immune response. In a nutshell, gHECM promotes tissue regeneration by changing the phenotype of macrophages around the site of injury. In particular, gHECM reduces the production of pro-inflammatory cytokines, decreases the percentage of M1 macrophages, and further encourages differentiation of macrophage subpopulation to the M2 phenotype and the release of anti-inflammatory cytokines, which could block the NF-κB pathway. Activated macrophages are capable of immediately delivering through spatial barriers, modulating the peripheral immune system, influencing the inflammatory microenvironment, and ultimately promoting the recovery of inflammation and healing of ulcers. They contribute to the secreted cytokines that act on local tissues or enhance the chemotactic ability of macrophages through paracrine secretion. In this study, we focused on the immunological regulatory network of macrophage polarization to further develop the mechanisms behind this process. Nevertheless, the signaling pathways involved in this process need to be further explored and identified. We think that our research will encourage more investigation into how the decellularized matrix affects immune modulation and will help the decellularized matrix perform better as a new class of natural biomaterials for tissue engineering.

MicroRNA Regulation in Infectious Diseases and Its Potential as a Biosensor in Future Aquaculture Industry: A Review

An infectious disease is the most apprehensive problem in aquaculture as it can lead to high mortality in aquatic organisms and massive economic loss. Even though significant progress has been accomplished in therapeutic, prevention, and diagnostic using several potential technologies, more robust inventions and breakthroughs should be achieved to control the spread of infectious diseases. MicroRNA (miRNA) is an endogenous small non-coding RNA that post-transcriptionally regulates the protein-coding genes. It involves various biological regulatory mechanisms in organisms such as cell differentiation, proliferation, immune responses, development, apoptosis, and others. Furthermore, an miRNA also acts as a mediator to either regulate host responses or enhance the replication of diseases during infection. Therefore, the emergence of miRNAs could be potential candidates for the establishment of diagnostic tools for numerous infectious diseases. Interestingly, studies have revealed that miRNAs can be used as biomarkers and biosensors to detect diseases, and can also be used to design vaccines to attenuate pathogens. This review provides an overview of miRNA biogenesis and specifically focuses on its regulation during infection in aquatic organisms, especially on the host immune responses and how miRNAs enhance the replication of pathogens in the organism. In addition to that, we explored the potential applications, including diagnostic methods and treatments, that can be employed in the aquaculture industry.

Multiple Actions of Telomerase Reverse Transcriptase in Cell Death Regulation

Telomerase reverse transcriptase (TERT), a core part of telomerase, has been known for a long time only for its telomere lengthening function by reverse transcription of RNA template. Currently, TERT is considered as an intriguing link between multiple signaling pathways. The diverse intracellular localization of TERT corresponds to a wide range of functional activities. In addition to the canonical function of protecting chromosome ends, TERT by itself or as a part of the telomerase complex participates in cell stress responses, gene regulation and mitochondria functioning. Upregulation of TERT expression and increased telomerase activity in cancer and somatic cells relate to improved survival and persistence of such cells. In this review, we summarize the data for a comprehensive understanding of the role of TERT in cell death regulation, with a focus on the interaction of TERT with signaling pathways involved in cell survival and stress response.

IKBA phosphorylation governs human sperm motility through ACC-mediated fatty acid beta-oxidation

The nuclear factor-κB (NF-κB) signaling pathway regulates specific immunological responses and controls a wide range of physiological processes. NF-κB inhibitor alpha (IKBA) is an NF-κB inhibitory mediator in the cytoplasm that modulates the nuclear translocation and DNA binding activities of NF-κB proteins. However, whether the upstream cascade of the canonical NF-κB signaling pathway has physiological roles independent of IKBA-mediated transcriptional activation remains unclear. Herein we investigated the function of IKBA in mature sperm in which transcriptional and translational events do not occur. IKBA was highly expressed in human sperm. The repression of IKBA phosphorylation by its inhibitor Bay117082 markedly enhanced sperm motility. On the contrary, lipopolysaccharide-stimulated IKBA phosphorylation significantly decreased sperm motility. Nevertheless, Bay117082 treatment did not affect the motility of IKBA-knockout sperm. Further, untargeted metabolomic analysis and pharmacological blocking assays revealed that the Bay117082-induced increase in sperm motility was attributable to fatty acid β-oxidation (FAO) enhancement. In addition, we found that IKBA phosphorylation inhibition resulted in a significant reduction of acetyl-CoA carboxylase levels in the FAO metabolic pathway. Our findings indicate that IKBA-mediated signaling orchestrates sperm motility program and improves our understanding of transcription-independent NF-κB signaling pathway in cells.

Akt-mediated mitochondrial metabolism regulates proplatelet formation and platelet shedding post vasopressin exposure

BACKGROUND

Platelet shedding from mature megakaryocytes (MKs) in thrombopoiesis is the critical step for elevating circulating platelets fast and efficiently, however, the underlying mechanism is still not well-illustrated, and the therapeutic targets and candidates are even less.

OBJECTIVES

In order to investigate the mechanisms for platelet shedding after vasopressin treatment and find new therapeutic targets for thrombocytopenia.

METHODS

Platelet production was evaluated both in vivo and in vitro after arginine vasopressin (AVP) administration. The underlying biological mechanism of AVP-triggered thrombopoiesis were then investigated by a series of molecular and bioinformatics techniques.

RESULTS

it is observed that proplatelet formation and platelet shedding in the final stages of thrombopoiesis promoted by AVP, an endogenous hormone, can quickly increases peripheral platelets. This rapid elevation is thus able to speed up platelet recovery after radiation as expected. The mechanism analysis reveal that proplatelet formation and platelet release from mature MKs facilitated by AVP is mainly mediated by Akt-regulated mitochondrial metabolism. In particular, phosphorylated Akt regulates mitochondrial metabolism through driving the association of hexokinase-2 with mitochondrial voltage dependent anion channel-1 in AVP-mediated thrombopoiesis. Further studies suggest that this interaction is stabilized by IκBα, the expression of which is controlled by insulin-regulated membrane aminopeptidase.

CONCLUSION

these data demonstrate that phosphorylated Akt-mediated mitochondrial metabolism regulates platelet shedding from MKs in response to AVP, which will provide new therapeutic targets and further drug discovery clues for thrombocytopenia treatment.

Mitochondrial Contribution to Inflammation in Diabetic Kidney Disease

Diabetes is the leading cause of chronic kidney disease worldwide. Despite the burden, the factors contributing to the development and progression of diabetic kidney disease (DKD) remain to be fully elucidated. In recent years, increasing evidence suggests that mitochondrial dysfunction is a pathological mediator in DKD as the kidney is a highly metabolic organ rich in mitochondria. Furthermore, low grade chronic inflammation also contributes to the progression of DKD, and several inflammatory biomarkers have been reported as prognostic markers to risk-stratify patients for disease progression and all-cause mortality. Interestingly, the term "sterile inflammation" appears to be used in the context of DKD describing the development of intracellular inflammation in the absence of bacterial or viral pathogens. Therefore, a link between mitochondrial dysfunction and inflammation in DKD exists and is a hot topic in both basic research and clinical investigations. This review summarizes how mitochondria contribute to sterile inflammation in renal cells in DKD.

Shedding Light on NF-κB Functions in Cellular Organelles

NF-κB is diffusely recognized as a transcriptional factor able to modulate the expression of various genes involved in a broad spectrum of cellular functions, including proliferation, survival and migration. NF-κB is, however, also acting outside the nucleus and beyond its ability to binds to DNA. NF-κB is indeed found to localize inside different cellular organelles, such as mitochondria, endoplasmic reticulum, Golgi and nucleoli, where it acts through different partners in mediating various biological functions. Here, we discuss the relationship linking NF-κB to the cellular organelles, and how this crosstalk between cellular organelles and NF-κB signalling may be evaluated for anticancer therapies.

Cell demise inhibited: Unexpected liaisons between mitochondria and IκΒα

IκΒα (the protein product of NFKBIA gene) has widely been considered a pro- apoptotic factor due to its ability to inhibit the anti-apoptotic transcription factor NFκB. Our findings indicate that IκΒα also exerts a strong anti-apoptotic activity at the outer mitochondria membrane (OMM). This function we uncovered is distinct from its ability to sequester and inhibit NFκB. IκΒα instead binds to voltage dependent anion channel 1 (VDAC1) and Hexokinase 2 (HK2), stabilizes this complex and prevents mitochondria outer membrane permeabilisation (MOMP) and apoptosis.

Post-translational Modifications of IκBα: The State of the Art

The nuclear factor-kappa B (NF-κB) signaling pathway regulates a variety of biological functions in the body, and its abnormal activation contributes to the pathogenesis of many diseases, such as cardiovascular and respiratory diseases and cancers. Therefore, to ensure physiological homeostasis of body systems, this pathway is strictly regulated by IκBα transcription, IκBα synthesis, and the IκBα-dependent nuclear transport of NF-κB. Particularly, the post-translational modifications of IκBα including phosphorylation, ubiquitination, SUMOylation, glutathionylation and hydroxylation are crucial in the abovementioned regulatory process. Because of the importance of the NF-κB pathway in maintaining body homeostasis, understanding the post-translational modifications of IκBα can not only provide deeper insights into the regulation of NF-κB pathway but also contribute to the development of new drug targets and biomarkers for the diseases.

Serum deprivation initiates adaptation and survival to oxidative stress in prostate cancer cells

Inadequate nutrient intake leads to oxidative stress disrupting homeostasis, activating signaling, and altering metabolism. Oxidative stress serves as a hallmark in developing prostate lesions, and an aggressive cancer phenotype activating mechanisms allowing cancer cells to adapt and survive. It is unclear how adaptation and survival are facilitated; however, literature across several organisms demonstrates that a reversible cellular growth arrest and the transcription factor, nuclear factor-kappaB (NF-κB), contribute to cancer cell survival and therapeutic resistance under oxidative stress. We examined adaptability and survival to oxidative stress following nutrient deprivation in three prostate cancer models displaying varying degrees of tumorigenicity. We observed that reducing serum (starved) induced reactive oxygen species which provided an early oxidative stress environment and allowed cells to confer adaptability to increased oxidative stress (H₂O₂). Measurement of cell viability demonstrated a low death profile in stressed cells (starved + H₂O₂), while cell proliferation was stagnant. Quantitative measurement of apoptosis showed no significant cell death in stressed cells suggesting an adaptive mechanism to tolerate oxidative stress. Stressed cells also presented a quiescent phenotype, correlating with NF-κB nuclear translocation, suggesting a mechanism of tolerance. Our data suggests that nutrient deprivation primes prostate cancer cells for adaptability to oxidative stress and/or a general survival mechanism to anti-tumorigenic agents.

Mitochondrial Fission Mediates Endothelial Inflammation

Endothelial inflammation and mitochondrial dysfunction have been implicated in cardiovascular diseases, yet, a unifying mechanism tying them together remains limited. Mitochondrial dysfunction is frequently associated with mitochondrial fission/fragmentation mediated by the GTPase Drp1 (dynamin-related protein 1). Nuclear factor (NF)-κB, a master regulator of inflammation, is implicated in endothelial dysfunction and resultant complications. Here, we explore a causal relationship between mitochondrial fission and NF-κB activation in endothelial inflammatory responses. In cultured endothelial cells, TNF-α (tumor necrosis factor-α) or lipopolysaccharide induces mitochondrial fragmentation. Inhibition of Drp1 activity or expression suppresses mitochondrial fission, NF-κB activation, vascular cell adhesion molecule-1 induction, and leukocyte adhesion induced by these proinflammatory factors. Moreover, attenuations of inflammatory leukocyte adhesion were observed in Drp1 heterodeficient mice as well as endothelial Drp1 silenced mice. Intriguingly, inhibition of the canonical NF-κB signaling suppresses endothelial mitochondrial fission. Mechanistically, NF-κB p65/RelA seems to mediate inflammatory mitochondrial fission in endothelial cells. In addition, the classical anti-inflammatory drug, salicylate, seems to maintain mitochondrial fission/fusion balance against TNF-α via inhibition of NF-κB. In conclusion, our results suggest a previously unknown mechanism whereby the canonical NF-κB cascade and a mitochondrial fission pathway interdependently regulate endothelial inflammation.

Overexpression of ubiquitin-conjugating enzyme E2 L3 in hepatocellular carcinoma potentiates apoptosis evasion by inhibiting the GSK3β/p65 pathway

UBE2L3 is a ubiquitin-conjugating protein belonging to the E2 family that consists of 153 amino acid residues. In this study, we found that UBE2L3 was generally upregulated in clinical HCC samples compared to non-tumour samples and that there was a strong association between high UBE2L3 expression and tumour size, clinical grade and prognosis in HCC patients. UBE2L3 depletion inhibited the proliferation and induced the apoptosis of HCC cells. At the molecular level, we observed that UBE2L3 depletion enhanced the protein stability of GSK3β, thus promoting the expression and activation of GSK3β. Subsequently, activated GSK3β phosphorylated p65 and promoted its nuclear translocation to increase the expression of target genes, including PUMA, Bax, Bim, Bad, and Bid. In vivo, knockout of UBE2L3 in HCC cells inhibited tumour growth in orthotopic liver injection nude mouse models. Moreover, inhibition of p65 or GSK3β significantly restored the effects induced by UBE2L3 knockout in HCC. Together, this study reveals the stimulatory effect of UBE2L3 on HCC cell proliferation, suggesting that UBE2L3 may be an important pro-tumorigenic factor in liver carcinogenesis and a potential therapeutic target of HCC.

Hypoxia induces rapid, STAT3 and ROS dependent, mitochondrial translocation of RelA(p65) and IκBα

The nuclear factor-κB (NF-κB) family of transcription factors can directly or indirectly regulate many important areas of biology, including immunity, inflammation and cell survival. One intriguing aspect of NF-κB crosstalk with other cell signalling pathways is its regulation of mitochondrial biology, including biogenesis, metabolism and apoptosis. In addition to regulating the expression of mitochondrial genes encoded in the nucleus, NF-κB signalling components are also found within mitochondria themselves and associated with mitochondrial DNA. However, complete biochemical analysis of mitochondrial and sub-mitochondrial localisation of all NF-κB subunits has not been undertaken. Here, we show that only the RelA NF-κB subunit and its inhibitor IκBα reside within mitochondria, whilst p50 is found in the endoplasmic reticulum (ER). Fractionation of mitochondria revealed that only RelA was found in the mitoplast, the location of the mtDNA. We demonstrate that hypoxia leads to a very rapid but transient accumulation of RelA and IκBα in mitochondria. This effect required reactive oxygen species (ROS) but was not dependent on the hypoxia sensing transcription factor subunit HIF1α or intracellular Ca2+ release. We also observed rapid mitochondrial localisation of transcription factor STAT3 following hypoxia. Inhibition of STAT3 blocked RelA and IκBα mitochondrial localisation revealing a previously unknown aspect of crosstalk between these key cellular regulators.

What Is Nuclear Factor Kappa B (NF-κB) Doing in and to the Mitochondrion?

A large body of literature supports the idea that nuclear factor kappa B (NF-κB) signaling contributes to not only immunity, but also inflammation, cancer, and nervous system function. However, studies on NF-κB activity in mitochondrial function are much more limited and scattered throughout the literature. For example, in 2001 it was first published that NF-κB subunits were found in the mitochondria, including not only IkBα and NF-κB p65 subunits, but also NF-κB pathway proteins such as IKKα, IKKβ, and IKKγ, but not much follow-up work has been done to date. Upon further thought the lack of studies on NF-κB activity in mitochondrial function is surprising given the importance and the evolutionary history of both NF-κB and the mitochondrion. Both are ancient in their appearance in our biological record where both contribute substantially to cell survival, cell death, and the regulation of function and/or disease. Studies also show NF-κB can influence mitochondrial function from outside the mitochondria. Therefore, it is essential to understand the complexity of these roles both inside and out of this organelle. In this review, an attempt is made to understand how NF-κB activity contributes to overall mitochondrial function – both inside and out. The discussion at times is speculative and perhaps even provocative to some, since NF-κB does not yet have defined mitochondrial targeting sequences for some nuclear-encoded mitochondrial genes and mechanisms of mitochondrial import for NF-κB are not yet entirely understood. Also, the data associated with the mitochondrial localization of proteins must be yet further proved with additional experiments.

Persistent IKKα phosphorylation induced apoptosis in UVB and Poly I:C co-treated HaCaT cells plausibly through pro-apoptotic p73 and abrogation of IκBα

Toll-like receptor 3 (TLR3), a member of pattern recognition receptors, is reported to initiate skin inflammation by recognizing double-strand RNA (dsRNA) released from UVB-irradiated cells. Recently, we have discovered the NF-κB pathway activated by TLR3 is involved in apoptosis of UVB-Poly I:C-treated HaCaT cells. The real culprit for apoptosis has not been precisely identified since the system of NF-κB pathway is complex. In this study, we silenced main transcriptional factors in NF-κB family, RelA, RelB and c-Rel, but to our surprise the results show that none of them participate in apoptosis induction in UVB-Poly I:C-treated HaCaT cells. Therefore, we moved to investigate the apoptosis-associated molecules in the upstream of NF-κB pathway. We firstly checked the expression of IκBα, an NF-κB inhibitor. UVB (4.8 mJ/cm²) and Poly I:C (0.3 μg/mL) co-treatment decreased IκBα expression level in a time-dependent manner. Silencing IκBα with siRNA further enhanced UVB-Poly I:C-induced cell death. We then investigated IκB kinase (IKK) complex that contributes to the degradation of IκBα. IKK is composed of IKKα, IKKβ and NEMO. Treatment with IKK-16, an IKKα/β inhibitor, significantly diminished UVB-Poly I:C-induced IκBα degradation and thus apoptosis. Silencing either IKKα or NEMO but not IKKβ with corresponding siRNA inhibited apoptosis. Tumor repressor p73, a homologue of p53, is reported to mediate IKKα-induced apoptosis in DNA damage response. Silencing p73 reduced cell apoptosis in UVB-Poly I:C-treated HaCaT cells. In summary, UVB and Poly I:C co-treatment activates IKKα and NEMO, which diminishes anti-apoptotic IκBα, resulting in enhancement of apoptosis through p73. The findings partially clarify the possible molecular mechanism of pro-apoptotic NF-κB pathway activated by TLR3 in the fate of UVB-irradiated epidermis.

Sub-lethal ultraviolet B irradiation and Poly I:C treatment synergistically induced apoptosis of HaCaT cells through NF-κB pathway

Ultraviolet B (UVB) irradiation exerts multiple effects on skin cells, inducing apoptosis, senescence and carcinogenesis. Toll-like receptor 3, a member of pattern recognition receptors, is reported to initiate inflammation by recognizing double-strand RNA (dsRNA) released from UVB-irradiated cells. It has not been studied, however, whether apoptosis induction in UVB irradiation is attributed to TLR3 activation. Here, we report on the pro-apoptotic role of TLR3 in UVB-irradiated epidermal cells. Poly I:C, an analogue of dsRNA that activates TLR3, was used in combination with sub-lethal UVB (4.8 mJ/cm²) irradiation for investigating the effects of TLR3 activation on human immortalized keratinocyte HaCaT cells. Although sub-lethal dose of either Poly I:C or UVB alone did not induce cell death, UVB-Poly I:C co-treatment synergistically induced cell death by activation of caspase-3 and cleavages of ICAD and PARP, with apoptotic features when stained with Annexin V/PI or Hoechst 33342. Treatment with pan-caspase inhibitor, Z-VAD, attenuated UVB-Poly I:C-induced cell death. Silencing TLR3 by siRNA rescued HaCaT cells from UVB-Poly I:C-induced apoptosis. NF-κB, a major downstream component of TLR3 pathway, that usually negatively regulates the classical TLR3 apoptotic pathway, was analyzed by western blotting and immunofluorescence confocal microscopy. The results indicate to our surprise that NF-κB is translocated to nucleus in the cells co-treated with UVB-Poly I:C. The nuclear translocation of NF-κB is attenuated by TLR3 silencing. Treatment with BAY, an inhibitor of NF-κB pathway, blocked UVB-Poly I:C-induced apoptosis. Therefore, we conclude that NF-κB pathway plays a cytotoxic role in UVB-Poly I:C-treated HaCaT cells, mediating TLR3-related apoptosis.

Regulation of breast cancer induced bone disease by cancer-specific IKKβ

NFκB is implicated in breast cancer bone metastasis and skeletal remodelling. However, the role of IKKβ, a key component of the canonical NFκB pathway, in the regulation of breast cancer osteolytic metastasis has not been investigated. Here, we describe the cancer-specific contribution of IKKβ to bone metastasis, skeletal tumour growth and osteolysis associated with breast cancer. IKKβ is highly expressed in invasive breast tumours and its level of expression was higher in patients with bone metastasis. IKKβ overexpression in parental MDA-MD-231 breast cancer cells, promoted mammary tumour growth but failed to convey osteolytic potential to these cells in mice. In contrast, IKKβ overexpression in osteotropic sub-clones of MDA-MB-231 cells with differing osteolytic phenotypes increased incidence of bone metastasis, exacerbated osteolysis and enhanced skeletal tumour growth, whereas its knockdown was inhibitory. Functional and mechanistic studies revealed that IKKβ enhanced the ability of osteotropic MDA-MB-231 cells to migrate, increase osteoclastogenesis, and to inhibit osteoblast differentiation via a mechanism mediated, at least in part, by cytoplasmic sequestering of FoxO3a and VEGFA production. Thus, tumour-selective manipulation of IKKβ and its interaction with FoxO3a may represent a novel strategy to reduce the development of secondary breast cancer in the skeleton.

Aberrant control of NF-κB in cancer permits transcriptional and phenotypic plasticity, to curtail dependence on host tissue: molecular mode

The role of the transcription factor NF-κB in shaping the cancer microenvironment is becoming increasingly clear. Inflammation alters the activity of enzymes that modulate NF-κB function, and causes extensive changes in genomic chromatin that ultimately drastically alter cell-specific gene expression. NF-κB regulates the expression of cytokines and adhesion factors that control interactions among adjacent cells. As such, NF-κB fine tunes tissue cellular composition, as well as tissues' interactions with the immune system. Therefore, NF-κB changes the cell response to hormones and to contact with neighboring cells. Activating NF-κB confers transcriptional and phenotypic plasticity to a cell and thereby enables profound local changes in tissue function and composition. Research suggests that the regulation of NF-κB target genes is specifically altered in cancer. Such alterations occur not only due to mutations of NF-κB regulatory proteins, but also because of changes in the activity of specific proteostatic modules and metabolic pathways. This article describes the molecular mode of NF-κB regulation with a few characteristic examples of target genes.

Expanding the Interactome of the Noncanonical NF-κB Signaling Pathway

NF-κB signaling is a central pathway of immunity and integrates signal transduction upon a wide array of inflammatory stimuli. Noncanonical NF-κB signaling is activated by a small subset of TNF family receptors and characterized by NF-κB2/p52 transcriptional activity. The medical relevance of this pathway has recently re-emerged from the discovery of primary immunodeficiency patients that have loss-of-function mutations in the MAP3K14 gene encoding NIK. Nevertheless, knowledge of protein interactions that regulate noncanonical NF-κB signaling is sparse. Here we report a detailed state-of-the-art mass spectrometry-based protein-protein interaction network including the noncanonical NF-κB signaling nodes TRAF2, TRAF3, IKKα, NIK, and NF-κB2/p100. The value of the data set was confirmed by the identification of interactions already known to regulate this pathway. In addition, a remarkable number of novel interactors were identified. We provide validation of the novel NIK and IKKα interactor FKBP8, which may regulate processes downstream of noncanonical NF-κB signaling. To understand perturbed noncanonical NF-κB signaling in the context of misregulated NIK in disease, we also provide a differential interactome of NIK mutants that cause immunodeficiency. Altogether, this data set not only provides critical insight into how protein-protein interactions can regulate immune signaling but also offers a novel resource on noncanonical NF-κB signaling.

MicroRNA-7 Regulates the Function of Mitochondrial Permeability Transition Pore by Targeting VDAC1 Expression

Mitochondrial dysfunction is one of the major contributors to neurodegenerative disorders including Parkinson disease. The mitochondrial permeability transition pore is a protein complex located on the mitochondrial membrane. Under cellular stress, the pore opens, increasing the release of pro-apoptotic proteins, and ultimately resulting in cell death. MicroRNA-7 (miR-7) is a small non-coding RNA that has been found to exhibit a protective role in the cellular models of Parkinson disease. In the present study, miR-7 was predicted to regulate the function of mitochondria, according to gene ontology analysis of proteins that are down-regulated by miR-7. Indeed, miR-7 overexpression inhibited mitochondrial fragmentation, mitochondrial depolarization, cytochrome c release, reactive oxygen species generation, and release of mitochondrial calcium in response to 1-methyl-4-phenylpyridinium (MPP(+)) in human neuroblastoma SH-SY5Y cells. In addition, several of these findings were confirmed in mouse primary neurons. Among the mitochondrial proteins identified by gene ontology analysis, the expression of voltage-dependent anion channel 1 (VDAC1), a constituent of the mitochondrial permeability transition pore, was down-regulated by miR-7 through targeting 3'-untranslated region of VDAC1 mRNA. Similar to miR-7 overexpression, knockdown of VDAC1 also led to a decrease in intracellular reactive oxygen species generation and subsequent cellular protection against MPP(+). Notably, overexpression of VDAC1 without the 3'-UTR significantly abolished the protective effects of miR-7 against MPP(+)-induced cytotoxicity and mitochondrial dysfunction, suggesting that the protective effect of miR-7 is partly exerted through promoting mitochondrial function by targeting VDAC1 expression. These findings point to a novel mechanism by which miR-7 accomplishes neuroprotection by improving mitochondrial health.