GRIM-19 is essential for maintenance of mitochondrial membrane potential

Mitochondrial GRIM19 Loss Induces Liver Fibrosis through NLRP3/IL33 Activation via Reactive Oxygen Species/NF-кB Signaling

Background and Aims

Hepatic fibrosis (HF) is a critical step in the progression of hepatocellular carcinoma (HCC). Gene associated with retinoid-IFN-induced mortality 19 (GRIM19), an essential component of mitochondrial respiratory chain complex I, is frequently attenuated in various human cancers, including HCC. Here, we aimed to investigate the potential relationship and underlying mechanism between GRIM19 loss and HF pathogenesis.

Methods

GRIM19 expression was evaluated in normal liver tissues, hepatitis, hepatic cirrhosis, and HCC using human liver disease spectrum tissue microarrays. We studied hepatocyte-specific GRIM19 knockout mice and clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein-9 (Cas9) lentivirus-mediated GRIM19 gene-editing in murine hepatocyte AML12 cells in vitro and in vivo. We performed flow cytometry, immunofluorescence, immunohistochemistry, western blotting, and pharmacological intervention to uncover the potential mechanisms underlying GRIM19 loss-induced HF.

Results

Mitochondrial GRIM19 was progressively downregulated in chronic liver disease tissues, including hepatitis, cirrhosis, and HCC tissues. Hepatocyte-specific GRIM19 heterozygous deletion induced spontaneous hepatitis and subsequent liver fibrogenesis in mice. In addition, GRIM19 loss caused chronic liver injury through reactive oxygen species (ROS)-mediated oxidative stress, resulting in aberrant NF-кB activation via an IKK/IкB partner in hepatocytes. Furthermore, GRIM19 loss activated NLRP3-mediated IL33 signaling via the ROS/NF-кB pathway in hepatocytes. Intraperitoneal administration of the NLRP3 inhibitor MCC950 dramatically alleviated GRIM19 loss-driven HF in vivo.

Conclusions

The mitochondrial GRIM19 loss facilitates liver fibrosis through NLRP3/IL33 activation via ROS/NF-кB signaling, providing potential therapeutic approaches for earlier HF prevention.

GRIM-19 deficiency promotes macrophage polarization to the M1 phenotype partly through glycolysis in unexplained recurrent spontaneous abortion†

The occurrence of unexplained recurrent spontaneous abortion (URSA) is closely related to immune system disorders, however, the underlying mechanisms remain unclear. The purpose of this study was to investigate the expression of GRIM-19 in URSA and the possible pathogenesis of URSA according to macrophage polarization. Here, we showed that GRIM-19 was downregulated in the uterine decidual macrophages of patients with URSA and that GRIM-19 downregulation was accompanied by increased M1 macrophage polarization. Furthermore, the expression levels of glycolytic enzymes were substantially enhanced in the uterine decidual macrophages of URSA patients, and glycolysis in THP-1-derived macrophages was further enhanced by the downregulation of GRIM-19. Additionally, the increase of M1 macrophages resulting from the loss of GRIM-19 was significantly reversed in cells treated with 2-deoxy-D-glucose (2-DG, an inhibitor of glycolysis). To provide more direct evidence, GRIM-19 deficiency was shown to promote macrophage polarization to the M1 phenotype in GRIM-19+/- mouse uteri. Overall, our study provides evidence that GRIM-19 deficiency may play a role in regulating macrophage polarization in URSA, and that glycolysis may participate in this process.

GRIM19 deficiency aggravates metabolic disorder and ovarian dysfunction in PCOS

CONTEXT

Polycystic ovary syndrome (PCOS) is one of the most common endocrine disorders in women. Retinoid-interferon-induced mortality 19 (GRIM19) is a functional component of mitochondrial complex I that plays a role in cellular energy metabolism. However, the role of GRIM19 in the pathogenesis of PCOS is still unclear.

OBJECTIVE

To investigate the role of GRIM19 in the pathogenesis of PCOS.

DESIGN

We first measured the expression of GRIM19 in human granulosa cells (hGCs) from patients with and without PCOS (n = 16 per group), and then established a PCOS mouse model with WT and Grim19+/- mice for in vivo experiments. Glucose uptake-related genes RAC1 and GLUT4 and energy metabolism levels in KGN cells were examined in vitro by knocking down GRIM19 in the cell lines. Additionally, ovulation-related genes such as p-ERK1/2, HAS2, and PTX3 were also studied to determine their expression levels.

RESULTS

GRIM19 expression was reduced in hGCs of PCOS patients, which was negatively correlated with BMI and serum testosterone level. Grim19+/- mice with PCOS exhibited a markedly anovulatory phenotype and disturbed glycolipid metabolism. In vitro experiments, GRIM19 deficiency inhibited the RAC1/GLUT4 pathway, reducing insulin-stimulated glucose uptake in KGN cells. Moreover, GRIM19 deficiency induced mitochondrial dysfunction, defective glucose metabolism, and apoptosis. In addition, GRIM19 deficiency suppressed the expression of ovulation-related genes in KGN cells, which was regulated by dihydrotestosterone mediated androgen receptor.

CONCLUSIONS

GRIM19 deficiency may mediate ovulation and glucose metabolism disorders in PCOS patients. Our results suggest that GRIM19 may be a new target for diagnosis and treatment.

Mitochondrial GRIM-19 loss in parietal cells promotes spasmolytic polypeptide-expressing metaplasia through NLR family pyrin domain-containing 3 (NLRP3)-mediated IL-33 activation via a reactive oxygen species (ROS) -NRF2- Heme oxygenase-1(HO-1)-NF-кB axis

Spasmolytic polypeptide-expressing metaplasia (SPEM), as a pre-neoplastic precursor of intestinal metaplasia (IM), plays critical roles in the development of chronic atrophic gastritis (CAG) and gastric cancer (GC). However, the pathogenetic targets responsible for the SPEM pathogenesis remain poorly understood. Gene associated with retinoid-IFN-induced mortality 19 (GRIM-19), an essential subunit of the mitochondrial respiratory chain complex I, was progressively lost along with malignant transformation of human CAG, little is known about the potential link between GRIM-19 loss and CAG pathogenesis. Here, we show that lower GRIM-19 is associated with higher NF-кB RelA/p65 and NLR family pyrin domain-containing 3 (NLRP3) levels in CAG lesions. Functionally, GRIM-19 deficiency fails to drive direct differentiation of human GES-1 cells into IM or SPEM-like cell lineages in vitro, whereas parietal cells (PCs)-specific GRIM-19 knockout disturbs gastric glandular differentiation and promotes spontaneous gastritis and SPEM pathogenesis without intestinal characteristics in mice. Mechanistically, GRIM-19 loss causes chronic mucosal injury and aberrant NRF2 (Nuclear factor erythroid 2-related factor 2)- HO-1 (Heme oxygenase-1) activation via reactive oxygen species (ROS)-mediated oxidative stress, resulting in aberrant NF-кB activation by inducing p65 nuclear translocation via an IKK/IкB partner, while NRF2-HO-1 activation contributes to GRIM-19 loss-driven NF-кB activation via a positive feedback NRF2-HO-1 loop. Furthermore, GRIM-19 loss did not cause obvious PCs loss but triggers NLRP3 inflammasome activation in PCs via a ROS-NRF2-HO-1-NF-кB axis, leading to NLRP3-dependent IL-33 expression, a key mediator for SPEM formation. Moreover, intraperitoneal administration of NLRP3 inhibitor MCC950 drastically attenuates GRIM-19 loss-driven gastritis and SPEM in vivo. Our study suggests that mitochondrial GRIM-19 maybe a potential pathogenetic target for the SPEM pathogenesis, and its deficiency promotes SPEM through NLRP3/IL-33 pathway via a ROS-NRF2-HO-1-NF-кB axis. This finding not only provides a causal link between GRIM-19 loss and SPEM pathogenesis, but offers potential therapeutic strategies for the early prevention of intestinal GC.

Grim-19 plays a key role in mitochondrial steroidogenic acute regulatory protein stability and ligand-binding properties in Leydig cells

Grim-19 (gene associated with retinoid-IFN-induced mortality 19), the essential component of complex I of mitochondrial respiratory chain, functions as a noncanonical tumor suppressor by controlling apoptosis and energy metabolism. However, additional biological actions of Grim-19 have been recently suggested in male reproduction. We investigated here the expression and functional role of Grim-19 in murine testis. Testicular Grim-19 expression was detected from mouse puberty and increased progressively thereafter, and GRIM-19 protein was observed to be expressed exclusively in interstitial Leydig cells (LCs), with a prominent mitochondrial localization. In vivo lentiviral vector-mediated knockdown of Grim-19 resulted in a significant decrease in testosterone production and triggered aberrant oxidative stress in testis, thus impairing male fertility by inducing germ cell apoptosis and oligozoospermia. The control of testicular steroidogenesis by GRIM-19 was validated using the in vivo knockdown model with isolated primary LCs and in vitro experiments with MA-10 mouse Leydig tumor cells. Mechanistically, we suggest that the negative regulation exerted by GRIM-19 deficiency-induced oxidative stress on steroidogenesis may be the result of two phenomena: a direct effect through inhibition of phosphorylation of steroidogenic acute regulatory protein (StAR) and subsequent impediment to StAR localization in mitochondria and an indirect pathway that is to facilitate the inhibiting role exerted by the extracellular matrix on the steroidogenic capacity of LCs via promotion of integrin activation. Altogether, our observations suggest that Grim-19 plays a potent role in testicular steroidogenesis and that its alterations may contribute to testosterone deficiency-related disorders linked to metabolic stress and male infertility.

CIGB-300-Regulated Proteome Reveals Common and Tailored Response Patterns of AML Cells to CK2 Inhibition

Protein kinase CK2 is a highly pleiotropic and ubiquitously expressed Ser/Thr kinase with instrumental roles in normal and pathological states, including neoplastic phenotype in solid tumor and hematological malignancies. In line with previous reports, CK2 has been suggested as an attractive prognostic marker and molecular target in acute myeloid leukemia (AML), a blood malignant disorder that remains as an unmet medical need. Accordingly, this work investigates the complex landscape of molecular and cellular perturbations supporting the antileukemic effect exerted by CK2 inhibition in AML cells. To identify and functionally characterize the proteomic profile differentially modulated by the CK2 peptide-based inhibitor CIGB-300, we carried out LC-MS/MS and bioinformatic analysis in human cell lines representing two differentiation stages and major AML subtypes. Using this approach, 109 and 129 proteins were identified as significantly modulated in HL-60 and OCI-AML3 cells, respectively. In both proteomic profiles, proteins related to apoptotic cell death, cell cycle progression, and transcriptional/translational processes appeared represented, in agreement with previous results showing the impact of CIGB-300 in AML cell proliferation and viability. Of note, a group of proteins involved in intracellular redox homeostasis was specifically identified in HL-60 cell-regulated proteome, and flow cytometric analysis also confirmed a differential effect of CIGB-300 over reactive oxygen species (ROS) production in AML cells. Thus, oxidative stress might play a relevant role on CIGB-300-induced apoptosis in HL-60 but not in OCI-AML3 cells. Importantly, these findings provide first-hand insights concerning the CIGB-300 antileukemic effect and draw attention to the existence of both common and tailored response patterns triggered by CK2 inhibition in different AML backgrounds, a phenomenon of particular relevance with regard to the pharmacologic blockade of CK2 and personalized medicine.

Grim-19 deficiency promotes decidual macrophage autophagy in recurrent spontaneous abortion

Dysregulation of decidual macrophages leads to the occurrence of recurrent spontaneous abortion (RSA). However, the role of macrophages in RSA occurrence remains unclear. In this study, we found that the expression of Grim-19 was decreased, and the expression of autophagy related proteins Beclin1, LC3B II/I and BNIP3 was markedly upregulated in decidual macrophages of RSA patients compared with the normal pregnancy group. Furthermore, we demonstrated that downregulation of GRIM-19 increased the expression of autophagy related proteins Beclin1, LC3B II/I, BNIP3 and the proinflammatory cytokines IL1B, IL6 and TNFa in uterine mononuclear cells of GRIM-19^+/- mice. The proportion of CD45+CD11b+F4/80+LC3B+ cells in GRIM-19^+/- mouse uteri was significantly higher than that in WT mouse uteri. In addition, we confirmed that inhibition of Grim-19 by siRNA enhanced the expression of autophagy related proteins in RAW264.7 cells and THP-1 cells. More importantly, downregulation of Grim-19 in RAW264.7 cells promoted the release of proinflammatory cytokines and promoted phagocytic activity, which could be reversed by autophagy blockade. For THP-1-derived macrophages, the results of RNA-seq suggested that Grim-19 mainly modulates immune and inflammatory-related pathways, leading to cytokine production, and thus contributing to inflammation. Therefore, our data reveal that Grim-19 deficiency influences macrophage function, characterized by enhanced proinflammatory cytokines and phagocytic activity, and this might be regulated by autophagy. This may represent a novel mechanism for the occurrence of RSA.

GRIM-19 is a target of mycobacterial Zn2+ metalloprotease 1 and indispensable for NLRP3 inflammasome activation

Tuberculosis is a communicable disease caused by Mycobacterium tuberculosis which primarily infects macrophages and establishes intracellular parasitism. A mycobacterial virulence factor Zn²⁺ metalloprotease 1 (Zmp1) is known to suppress interleukin (IL)-1β production by inhibiting caspase-1 resulting in phagosome maturation arrest. However, the molecular mechanism of caspase-1 inhibition by Zmp1 is still elusive. Here, we identified GRIM-19 (also known as NDUFA13), an essential subunit of mitochondrial respiratory chain complex I, as a novel Zmp1-binding protein. Using the CRISPR/Cas9 system, we generated GRIM-19 knockout murine macrophage cell line J774.1 and found that GRIM-19 is essential for IL-1β production during mycobacterial infection as well as in response to NLRP3 inflammasome-activating stimuli such as extracellular ATP or nigericin. We also found that GRIM-19 is required for the generation of mitochondrial reactive oxygen species and NLRP3-dependent activation of caspase-1. Loss of GRIM-19 or forced expression of Zmp1 resulted in a decrease in mitochondrial membrane potential. Our study revealed a previously unrecognized role of GRIM-19 as an essential regulator of NLRP3 inflammasome and a molecular mechanism underlying Zmp1-mediated suppression of IL-1β production during mycobacterial infection.

Structural exploration with AlphaFold2-generated STAT3α structure reveals selective elements in STAT3α-GRIM-19 interactions involved in negative regulation

STAT3, an important transcription factor constitutively activated in cancers, is bound specifically by GRIM-19 and this interaction inhibits STAT3-dependent gene expression. GRIM-19 is therefore, considered as an inhibitor of STAT3 and may be an effective anti-cancer therapeutic target. While STAT3 exists in a dimeric form in the cytoplasm and nucleus, it is mostly present in a monomeric form in the mitochondria. Although GRIM-19-binding domains of STAT3 have been identified in independent experiments, yet the identified domains are not the same, and hence, discrepancies exist. Human STAT3-GRIM-19 complex has not been crystallised yet. Dictated by fundamental biophysical principles, the binding region, interactions and effects of hotspot mutations can provide us a clue to the negative regulatory mechanisms of GRIM-19. Prompted by the very nature of STAT3 being a challenging molecule, and to understand the structural basis of binding and interactions in STAT3α-GRIM-19 complex, we performed homology modelling and ab-initio modelling with evolutionary information using I-TASSER and avant-garde AlphaFold2, respectively, to generate monomeric, and subsequently, dimeric STAT3α structures. The dimeric form of STAT3α structure was observed to potentially exist in an anti-parallel orientation of monomers. We demonstrate that during the interactions with both unphosphorylated and phosphorylated STAT3α, the NTD of GRIM-19 binds most strongly to the NTD of STAT3α, in direct contrast to the earlier works. Key arginine residues at positions 57, 58 and 68 of GRIM-19 are mainly involved in the hydrogen-bonded interactions. An intriguing feature of these arginine residues is that these display a consistent interaction pattern across unphosphorylated and phosphorylated monomers as well as unphosphorylated dimers in STAT3α-GRIM-19 complexes. MD studies verified the stability of these complexes. Analysing the binding affinity and stability through free energy changes upon mutation, we found GRIM-19 mutations Y33P and Q61L and among GRIM-19 arginines, R68P and R57M, to be one of the top-most major and minor disruptors of binding, respectively. The proportionate increase in average change in binding affinity upon mutation was inclined more towards GRIM-19 mutants, leading to the surmise that GRIM-19 may play a greater role in the complex formation. These studies propound a novel structural perspective of STAT3α-GRIM-19 binding and inhibitory mechanisms in both the monomeric and dimeric forms of STAT3α as compared to that observed from the earlier experiments, these experimental observations being inconsistent among each other.

Age-Dependent Decline in Neuron Growth Potential and Mitochondria Functions in Cortical Neurons

The age of incidence of spinal cord injury (SCI) and the average age of people living with SCI is continuously increasing. However, SCI is extensively modeled in young adult animals, hampering translation of research to clinical applications. While there has been significant progress in manipulating axon growth after injury, the impact of aging is still unknown. Mitochondria are essential to successful neurite and axon growth, while aging is associated with a decline in mitochondrial functions. Using isolation and culture of adult cortical neurons, we analyzed mitochondrial changes in 2-, 6-, 12- and 18-month-old mice. We observed reduced neurite growth in older neurons. Older neurons also showed dysfunctional respiration, reduced membrane potential, and altered mitochondrial membrane transport proteins; however, mitochondrial DNA (mtDNA) abundance and cellular ATP were increased. Taken together, these data suggest that dysfunctional mitochondria in older neurons may be associated with the age-dependent reduction in neurite growth. Both normal aging and traumatic injury are associated with mitochondrial dysfunction, posing a challenge for an aging SCI population as the two elements can combine to worsen injury outcomes. The results of this study highlight this as an area of great interest in CNS trauma.

Elucidating the role of GRIM-19 as a substrate and allosteric activator of pro-apoptotic serine protease HtrA2

HtrA2 (high-temperature requirement A2) and GRIM-19 (gene associated with retinoic and interferon-induced mortality 19 protein) are involved in various biological functions with their deregulation leading to multiple diseases. Although it is known that the interaction between GRIM-19 with HtrA2 promotes the pro-apoptotic activity of the latter, the mechanistic details remained elusive till date. Moreover, designing allosteric modulators of HtrA2 remains obscure due to lack of adequate information on the mode of interaction with its natural substrates cum binding partners. Therefore, in this study, we have unfolded the interaction between HtrA2 and GRIM-19 so as to understand its subsequent functional repercussions. Using in silico analyses and biochemical assays, we identified the region in GRIM-19 that is involved in protein-protein interaction with HtrA2. Furthermore, we have presented a comprehensive illustration of HtrA2's cleavage site specificity. Quantitative analysis using enzyme kinetics underscored the role of GRIM-19 in significant allosteric activation of HtrA2. Overall, this is an extensive study that not only defines HtrA2-GRIM-19 interaction, but also creates a framework for developing strategies toward allosteric regulation of HtrA2 for future therapeutic interventions.

Gene Expression and Resistance to Glucocorticoid-Induced Apoptosis in Acute Lymphoblastic Leukemia: A Brief Review and Update

BACKGROUND

Resistance to glucocorticoid (GC)-induced apoptosis in Acute Lymphoblastic Leukemia (ALL), is considered one of the major prognostic factors for the disease. Prednisolone is a corticosteroid and one of the most important agents in the treatment of acute lymphoblastic leukemia. The mechanics of GC resistance are largely unknown and intense ongoing research focuses on this topic.

AIM

The aim of the present study is to review some aspects of GC resistance in ALL, and in particular of Prednisolone, with emphasis on previous and present knowledge on gene expression and signaling pathways playing a role in the phenomenon.

METHODS

An electronic literature search was conducted by the authors from 1994 to June 2019. Original articles and systematic reviews selected, and the titles and abstracts of papers screened to determine whether they met the eligibility criteria, and full texts of the selected articles were retrieved.

RESULTS

Identification of gene targets responsible for glucocorticoid resistance may allow discovery of drugs, which in combination with glucocorticoids may increase the effectiveness of anti-leukemia therapies. The inherent plasticity of clinically evolving cancer justifies approaches to characterize and prevent undesirable activation of early oncogenic pathways.

CONCLUSION

Study of the pattern of intracellular signal pathway activation by anticancer drugs can lead to development of efficient treatment strategies by reducing detrimental secondary effects.

Role of Transportome in the Gills of Chinese Mitten Crabs in Response to Salinity Change: A Meta-Analysis of RNA-Seq Datasets

Chinese mitten crab (CMC) or Eriocheir sinensis is a strong osmoregulator that can keep rigorous cellular homeostasis. CMC can flourish in freshwater, as well as seawater, habitats and represents the most important species for freshwater aquaculture. Salt stress can have direct effects on several stages (e.g., reproduction, molting, growth, etc.) of the CMC life cycle. To get a better overview of the genes involved in the gills of CMC under different salinity conditions, we conducted an RNA-Seq meta-analysis on the transcriptomes of four publicly available datasets. The meta-analysis identified 405 differentially expressed transcripts (DETs), of which 40% were classified into various transporter classes, including accessory factors and primary active transporters as the major transport classes. A network analysis of the DETs revealed that adaptation to salinity is a highly regulated mechanism in which different functional modules play essential roles. To the best of our knowledge, this study is the first to conduct a transcriptome meta-analysis of gills from crab RNA-Seq datasets under salinity. Additionally, this study is also the first to focus on the differential expression of diverse transporters and channels (transportome) in CMC. Our meta-analysis opens new avenues for a better understanding of the osmoregulation mechanism and the selection of potential transporters associated with salinity change.

Mitochondrial GRIM-19 deficiency facilitates gastric cancer metastasis through oncogenic ROS-NRF2-HO-1 axis via a NRF2-HO-1 loop

BACKGROUND

NRF2, a prime target of cellular defense against oxidative stress, has shown a dark side profile in cancer progression. GRIM-19, an essential subunit of the mitochondrial MRC complex I, was recently identified as a suppressive role in tumorigenesis of human gastric cancer (GC). However, little information is available on the role of GRIM-19 and its cross-talk with NRF2 in GC metastasis.

METHODS

Online GC database was used to investigate DNA methylation and survival outcomes of GRIM-19. CRISPR/Cas9 lentivirus-mediated gene editing, metastasis mice models and pharmacological intervention were applied to investigate the role of GRIM-19 deficiency in GC metastasis. Quantitative RT-PCR, FACS, Western blot, IHC, IF and reporter gene assay were performed to explore underlying mechanisms.

RESULTS

Low GRIM-19 is correlated with poor survival outcome of GC patients while DNA hypermethylation is associated with GRIM-19 downregulation. GRIM-19 deficiency facilitates GC metastasis and triggers aberrant oxidative stress as well as ROS-dependent NRF2-HO-1 activation. Experimental interventions of specific ROS, NRF2 or HO-1 inhibitor significantly abrogate GRIM-19 deficiency-driven GC metastasis in vitro and in vivo. Moreover, HO-1 inhibition not only reverses GRIM-19 deficiency-driven NRF2 activation, but also feedback blocks NRF2 activator-induced NRF2 signaling, resulting in decreased metastasis-associated genes.

CONCLUSIONS

Our data suggest that GRIM-19 deficiency accelerates GC metastasis through the oncogenic ROS-NRF2-HO-1 axis via a positive-feedback NRF2-HO-1 loop. Therefore, this study not only offers novel insights into the role of oncogenic NRF2 in tumor progression, but also provides new strategies to alleviate the dark side of NRF2 by targeting HO-1.

GRIM-19 Ameliorates Multiple Sclerosis in a Mouse Model of Experimental Autoimmune Encephalomyelitis with Reciprocal Regulation of IFNγ/Th1 and IL-17A/Th17 Cells

The protein encoded by the Gene Associated with Retinoid-Interferon-Induced Mortality-19 (GRIM-19) is located in the mitochondrial inner membrane and is homologous to the NADH dehydrogenase 1-alpha subcomplex subunit 13 of the electron transport chain. Multiple sclerosis (MS) is a demyelinating disease that damages the brain and spinal cord. Although both the cause and mechanism of MS progression remain unclear, it is accepted that an immune disorder is involved. We explored whether GRIM-19 ameliorated MS by increasing the levels of inflammatory cytokines and immune cells; we used a mouse model of experimental autoimmune encephalomyelitis (EAE) to this end. Six-to-eight-week-old male C57BL/6, IFNγ-knockout (KO), and GRIM-19 transgenic mice were used; EAE was induced in all strains. A GRIM-19 overexpression vector (GRIM19 OVN) was electrophoretically injected intravenously. The levels of Th1 and Th17 cells were measured via flow cytometry, immunofluorescence, and immunohistochemical analysis. IL-17A and IFNγ expression levels were assessed via ELISA and quantitative PCR. IL-17A expression decreased and IFNγ expression increased in EAE mice that received injections of the GRIM19 OVN. GRIM-19 transgenic mice expressed more IFNγ than did wild-type mice; this inhibited EAE development. However, the effect of GRIM-19 overexpression on the EAE of IFNγ-KO mice did not differ from that of the empty vector. GRIM-19 expression was therapeutic for EAE mice, elevating the IFNγ level. GRIM-19 regulated the Th17/Treg cell balance.

Helicobacter pylori infection induces STAT3 phosphorylation on Ser727 and autophagy in human gastric epithelial cells and mouse stomach

Helicobacter pylori (H. pylori) infection is considered as one of the principal risk factors of gastric cancer. Constitutive activation of the signal transducer and activator of transcription 3 (STAT3) plays an important role in inflammation-associated gastric carcinogenesis. In the canonical STAT3 pathway, phosphorylation of STAT3 on Tyr705 is a major event of STAT3 activation. However, recent studies have demonstrated that STAT3 phosphorylated on Ser727 has an independent function in mitochondria. In the present study, we found that human gastric epithelial AGS cells infected with H. pylori resulted in localization of STAT3 phosphorylated on Ser727 (P-STAT3^Ser727), predominantly in the mitochondria. Notably, H. pylori-infected AGS cells exhibited the loss of mitochondrial integrity and increased expression of the microtubule-associated protein light chain 3 (LC3), the autophagosomal membrane-associated protein. Treatment of AGS cells with a mitophagy inducer, carbonyl cyanide 3-chlorophenylhydrazone (CCCP), resulted in accumulation of P-STAT3^Ser727 in mitochondria. In addition, the elevated expression and mitochondrial localization of LC3 induced by H. pylori infection were attenuated in AGS cells harboring STAT3 mutation defective in Ser727 phosphorylation (S727A). We also observed that both P-STAT3^Ser727 expression and LC3 accumulation were increased in the mitochondria of H. pylori-inoculated mouse stomach.

Chemiosmotic misunderstandings

Recent publications have questioned the appropriateness of the chemiosmotic theory, a key tenet of modern bioenergetics originally described by Mitchell and since widely improved upon and applied. In one of them, application of Gauss' law to a model charge distribution in mitochondria was argued to refute the possibility of ATP generation through H⁺ movement in the absence of a counterion, whereas a different author advocated, for other reasons, the impossibility of chemiosmosis and proposed that a novel energy-generation scheme (referred to as "murburn") relying on superoxide-catalyzed (or superoxide-promoted) ADP phosphorylation would operate instead. In this letter, those proposals are critically examined and found to be inconsistent with established experimental data and new theoretical calculations.

GRIM-19 deficiency promotes clear cell renal cell carcinoma progression and is associated with high TNM stage and Fuhrman grade

Clear cell renal cell carcinoma (ccRCC) exhibits the highest mortality among all urological malignancies. The investigation of the potential disease progression markers can improve ccRCC diagnosis and treatment. Gene associated with retinoid-interferon-induced mortality-19 (GRIM-19) is involved in carcinogenesis and cancer progression in a variety of cancer types including RCC. While, its role in ccRCC remains unclear, this cancer type is considered the most aggressive RCC subtype. In the present study, RT-qPCR, western blotting and immunohistochemical (IHC) assays demonstrated that GRIM-19 protein and mRNA levels were downregulated in ccRCC tumor tissues compared with the corresponding levels noted in paracancerous non-tumor tissues. The deficiency of this protein contributed in relaxed and/or collapsed structures of the kidney tubules and collecting duct noted in tumor tissues. Moreover, the reduction in GRIM-19 expression was associated with high tumor, lymph nodes and metastasis (TNM) stage and Fuhrman grade of ccRCC tumors. The data suggested that GRIM-19 acted as a tumor suppressor and that its deficiency promoted ccRCC development and progression. GRIM-19 can be considered a potential tumor marker for ccRCC.

Alteration of Gene Associated with Retinoid-interferon-induced Mortality-19-expressing Cell Types in the Mouse Hippocampus Following Pilocarpine-induced Status Epilepticus

The gene associated with retinoid-interferon-induced mortality-19 (GRIM-19) plays several significant roles in cellular processes, including ATP synthesis, reactive oxygen species formation, and the regulation of glycolytic enzyme activity, which are closely related to the pathophysiological mechanisms of epilepsy. Therefore, we investigated the expression pattern of GRIM-19 in the CA1 area of the hippocampus in 8-week-old male C57BL/6 mice following pilocarpine-induced status epilepticus (SE). Neuronal death in the hippocampal CA1 area was prominently observed at 4 and 7 days after SE, and astrocytes and microglia became progressively activated beginning at 1 day after SE. GRIM-19 immunoreactivity was decreased in the damaged pyramidal cell layer but markedly increased in the stratum radiatum and stratum lacunosum-moleculare of the hippocampus at 4 and 7 days after SE. In addition, the cell types of GRIM-19-expressing cells in the epileptic hippocampus were identified. GRIM-19 was mainly co-localized in neurons but only slightly expressed in glia in the normal hippocampus. Most of the GRIM-19-positive cells induced by SE in the stratum radiatum and stratum lacunosum-moleculare were glial fibrillary acidic protein-expressing reactive astrocytes. Moreover, we observed that both GRIM-19 and pyruvate kinase isozyme M2, a glycolytic enzyme, were highly expressed in reactive astrocytes after SE. These results indicate that expression of GRIM-19 in the hippocampus is mainly observed in neurons under normal conditions but is altered in the SE mouse model as evidenced by its increased expression in reactive astrocytes. The possible role of GRIM-19 in the glycolytic activity of reactive astrocytes is also discussed.

Expression of GRIM-19 in unexplained recurrent spontaneous abortion and possible pathogenesis

STUDY QUESTION

Is aberrant expression of gene associated with retinoid-interferon-induced mortality-19 (GRIM-19) associated with unexplained recurrent spontaneous abortion (URSA)?

SUMMARY ANSWER

GRIM-19 deficiency may regulate regulatory T cell/T helper 17 cell (Treg/Th17) balance partly through reactive oxygen species (ROS)-mammalian target of rapamycin (mTOR) signaling axis in URSA.

WHAT IS KNOWN ALREADY

Immunological disorders may cause impaired maternal immune tolerance to the fetus and result in fetal rejection. The differentiation of Treg and Th17 cells is controlled by phosphoinositide 3-kinase (PI3K)/Akt/mTOR signaling pathway. GRIM-19 participates in the immune response, but its role in URSA is largely unknown.

STUDY DESIGN, SIZE, DURATION

The current study included 28 URSA patients and 30 non-pregnant healthy women.

PARTICIPANTS/MATERIALS, SETTING, METHODS

The proportion of Treg and Th17 cells in peripheral blood of URSA patients and control subjects were assessed with flow cytometry. The expression of GRIM-19 in peripheral blood lymphocytes (PBLs) was measured with quantitative real-time PCR and western blot analysis. Furthermore, the ROS level in the PBLs of URSA patients and control subjects were assessed by 2',7'-dichlorodihydrofluorescein diacetate (DCFH-DA) staining. Then, Akt/mTOR expression in the PBLs was measured. Downregulation of GRIM-19 in Jurkat cells was performed by specific siRNA. Then, intracellular ROS production and the expression of p-mTOR, which is known to enhance Th17 differentiation and decrease Treg cell differentiation, were detected. Finally, N-acetylcysteine (NAC) was used to decrease the intracellular ROS level, and the expression of p-mTOR was measured.

MAIN RESULTS AND THE ROLE OF CHANCE

The proportion of Treg cells was reduced in URSA patients, whereas the proportion of Th17 cells was increased. The expression of GRIM-19 was significantly lower in PBLs of URSA patients. Furthermore, there is a considerable increase in intracellular ROS production and a high level of p-Akt and p-mTOR expression in the PBLs of URSA patients compared with the control subjects. In parallel to this, downregulation of GRIM-19 in the Jurkat cells by siRNA results in an increased ROS production and an increased expression of p-mTOR. Importantly, the upregulation of p-mTOR resulting from GRIM-19 loss was significantly reversed in the cells treatment with ROS inhibitor N-acetyl-l-cysteine (NAC), indicating that ROS was indeed required for GRIM-19 depletion induced p-mTOR expression.

LARGE SCALE DATA

None.

LIMITATIONS, REASONS FOR CAUTION

A large number of researches have confirmed that the differentiation of Treg and Th17 cells is controlled by PI3K/Akt/mTOR signaling pathway. We have not shown the regulatory role of ROS and PI3K/Akt/mTOR in Treg and Th17 differentiation in this study.

WIDER IMPLICATIONS OF THE FINDINGS

Our study has demonstrated that GRIM-19 deficiency may play a role in regulating Treg/Th17 balance partly through ROS-mTOR signaling axis in URSA. The present study offers a new perspective to the roles of GRIM-19 in immunoregulation.

STUDY FUNDING AND COMPETING INTEREST(S)

This work was supported by the National Natural Science Foundation of China (Grant numbers 81571511, 81701528, 81370711 and 30901603), the Shandong Provincial Natural Science Foundation (Grant numbers ZR2017PH052 and ZR2013HM090) and the Science Foundation of Qilu Hospital of Shandong University, Fundamental Research Funds of Shandong University (Grant numbers 2015QLQN50 and 2015QLMS24). The authors declare that there is no conflict of interest that could prejudice the impartiality of the present research.

Heterogeneity of GRIM-19 Expression in the Adult Mouse Brain

Gene associated with retinoid-interferon-induced mortality-19 (GRIM-19) is a subunit of the mitochondrial respiratory chain complex I that has a significant effect on ATP production. The brain is particularly susceptible to ATP deficiency due to its limited energy storage capability and its high rate of oxygen consumption. Thus, GRIM-19 might be involved in regulating ATP level in the brain or cell death caused by several neurological disorders. To understand the physiological and pathophysiological roles of GRIM-19 in the brain, a thorough investigation of the neuroanatomic distribution of GRIM-19 in the normal brain is necessary. Therefore, the present study examined the distribution patterns of GRIM-19 in the adult C57BL/6 mouse brain using immunohistochemistry and identified cell types expressing GRIM-19 using double immunofluorescence staining. We found that GRIM-19 was ubiquitously but not homogenously expressed throughout the brain. GRIM-19 immunoreactivity was predominantly observed in neurons, but not in astrocytes, microglia, or oligodendrocytes under normal physiological conditions. Following transient global cerebral ischemia, GRIM-19-positive immunoreactivity was, however, observed in neurons as well as glial cells including astrocytes in the hippocampus. Furthermore, GRIM-19 was weakly expressed in the hippocampal subgranular zone, in which neural stem and progenitor cells are abundant, but highly expressed in the immature and mature neuronal cells in the granular cell layer of the normal brain, suggesting an inverse correlation between expression of GRIM-19 and stemness activity. Collectively, our study demonstrating widespread and differential distribution of GRIM-19 in the adult mouse brain contributes to investigating the functional and pathophysiological roles of this protein.

Cerebral mitochondrial electron transport chain dysfunction in multiple system atrophy and Parkinson's disease

Multiple system atrophy (MSA) is a neurodegenerative disease characterised by glial cytoplasmic inclusions (GCIs), containing α-synuclein. Mutated COQ2, encoding an enzyme essential for co-enzyme Q10 (CoQ10) biosynthesis, has been associated with MSA. CoQ10 is an electron carrier in the mitochondrial electron transport chain (ETC) and antioxidant. It has been shown to be deficient in MSA brain tissue, thus implicating mitochondrial dysfunction in MSA. To investigate mitochondrial dysfunction in MSA further we examined ETC activity in MSA and control brain tissue, compared with Parkinson's disease (PD) where mitochondrial dysfunction is known to be important. Using cerebellar and occipital white matter ETC complex I, II/III and IV activities were measured spectrophotometrically, selected individual components of the ETC were assessed by immunoblotting and cellular complex IV activity was analysed by enzyme histochemistry. We show decreased complex II/III activity with increased complex I and IV activity in MSA cerebellar white matter. This corresponds with the deficit in CoQ10 previously described in MSA and reflects the high regional pathological burden of GCIs. This study highlights mitochondrial dysfunction in MSA pathogenesis, suggests an influence on selective regional vulnerability to disease and points to shared disease mechanisms in α-synucleinopathies.

Mitochondrial GRIM-19 as a potential therapeutic target for STAT3-dependent carcinogenesis of gastric cancer

Aberrant STAT3 activation occurs in most human gastric cancers (GCs) and contributes to the malignant progression of GC, but mechanism(s) underlying aberrant STAT3 remain largely unknown. Here we demonstrated that the gene associated with retinoid interferon-induced mortality 19 (GRIM-19) was severely depressed or lost in GC and chronic atrophic gastritis (CAG) tissues and its loss contributed to GC tumorigenesis partly by activating STAT3 signaling. In primary human GC tissues, GRIM-19 was frequently depressed or lost and this loss correlated with advanced clinical stage, lymph node metastasis, H. pylori infection and poor overall survival of GC patients. In CAG tissues, GRIM-19 was progressively decreased along with its malignant transformation. Functionally, we indentified an oncogenic role of GRIM-19 loss in promoting GC tumorigenesis. Ectopic GRIM-19 expression suppressed GC tumor formation in vitro and in vivo by inducing cell cycle arrest and apoptosis. Moreover, we revealed that GRIM-19 inhibited STAT3 transcriptional activation and its downstream targets by reducing STAT3 nuclear distribution. Conversely, knockdown of GRIM-19 induced aberrant STAT3 activation and accelerated GC cell growth in vitro and in vivo, and this could be partly attenuated by the blockage of STAT3 activation. In addition, we observed subcellular redistributions of GRIM-19 characterized by peri-nuclear aggregates, non-mitochondria cytoplasmic distribution and nuclear invasion, which should be responsible for reduced STAT3 nuclear distribution. Our studies suggest that mitochondrial GRIM-19 could not only serve as an valuable prognostic biomarker for GC development, but also as a potential therapeutic target for STAT3-dependent carcinogenesis of GC.

Insulin upregulates GRIM-19 and protects cardiac mitochondrial morphology in type 1 diabetic rats partly through PI3K/AKT signaling pathway

Insulin is involved in the development of diabetic heart disease and is important in the activities of mitochondrial complex I. However, the effect of insulin on cardiac mitochondrial nicotinamide adenine dinucleotide dehydrogenase (ubiquinone) 1 subunit of retinoic-interferon-induced mortality 19 (GRIM-19) has not been characterized. The aim of this study was to investigate the effect of insulin on the mitochondrial GRIM-19 in the hearts of rats with streptozotocin (STZ)-induced type 1 diabetes. Protein changes of GRIM-19 were evaluated by western blotting and reverse transcription-quantitative polymerase chain reaction. Furthermore, the effects of insulin on mitochondrial complex I were detected in HeLa cells and H9C2 cardiac myocytes. During the development of diabetic heart disease, the cardiac function did not change within the 8 weeks, but the mitochondrial morphology was altered. The hearts from the rats with STZ-induced diabetes exhibited reduced expression of GRIM-19. Prior to the overt cardiac dilatation, mitochondrial alterations were already present. Following subcutaneous insulin injection, it was demonstrated that GRIM-19 protein was altered, as well as the mitochondrial morphology. The phosphoinositide 3-kinase inhibitor LY294002 had an effect on insulin signaling in H9C2 cardiacmyocytes, and decreased the level of GRIM-19 by half compared with that in the insulin group. The results indicate that insulin is essential for the control of cardiac mitochondrial morphology and the GRIM-19 expression partly via PI3K/AKT signaling pathways.

Die Another Day: Inhibition of Cell Death Pathways by Cytomegalovirus

Multicellular organisms have evolved multiple genetically programmed cell death pathways that are essential for homeostasis. The finding that many viruses encode cell death inhibitors suggested that cellular suicide also functions as a first line of defence against invading pathogens. This theory was confirmed by studying viral mutants that lack certain cell death inhibitors. Cytomegaloviruses, a family of species-specific viruses, have proved particularly useful in this respect. Cytomegaloviruses are known to encode multiple death inhibitors that are required for efficient viral replication. Here, we outline the mechanisms used by the host cell to detect cytomegalovirus infection and discuss the methods employed by the cytomegalovirus family to prevent death of the host cell. In addition to enhancing our understanding of cytomegalovirus pathogenesis we detail how this research has provided significant insights into the cross-talk that exists between the various cell death pathways.

The Mitochondrial Complex(I)ty of Cancer

Recent evidence highlights that the cancer cell energy requirements vary greatly from normal cells and that cancer cells exhibit different metabolic phenotypes with variable participation of both glycolysis and oxidative phosphorylation. NADH-ubiquinone oxidoreductase (Complex I) is the largest complex of the mitochondrial electron transport chain and contributes about 40% of the proton motive force required for mitochondrial ATP synthesis. In addition, Complex I plays an essential role in biosynthesis and redox control during proliferation, resistance to cell death, and metastasis of cancer cells. Although knowledge about the structure and assembly of Complex I is increasing, information about the role of Complex I subunits in tumorigenesis is scarce and contradictory. Several small molecule inhibitors of Complex I have been described as selective anticancer agents; however, pharmacologic and genetic interventions on Complex I have also shown pro-tumorigenic actions, involving different cellular signaling. Here, we discuss the role of Complex I in tumorigenesis, focusing on the specific participation of Complex I subunits in proliferation and metastasis of cancer cells.

GRIM-19, a gene associated with retinoid-interferon-induced mortality, affects endometrial receptivity and embryo implantation

GRIM-19 is associated with apoptosis, abnormal proliferation, immune tolerance and malignant transformation, and it also plays an important role in early embryonic development. Although the homologous deletion of GRIM-19 causes embryonic lethality in mice, the precise role of GRIM-19 in embryo implantation has not been elucidated. Here we show that GRIM-19 plays an important role in endometrial receptivity and embryo implantation. Day 1 to Day 6 pregnant mouse uteri were collected. Immunohistochemistry studies revealed the presence of GRIM-19 on the luminal epithelium and glandular epithelium throughout the implantation period in pregnant mice. The protein and mRNA levels of GRIM-19 were markedly decreased on Day 4 of pregnancy in pregnant mice, but there was no change in GRIM-19 levels in a group of pseudopregnant mice. Overexpression of GRIM-19 decreased the adhesion rate of RL95–2–BeWo co-cultured spheroids and increased apoptosis. Furthermore, STAT3 and IL-11 mRNA and protein levels were reduced by overexpressing GRIM-19, but protein and mRNA levels of TNF-α were increased. These findings indicate the involvement of GRIM-19 in the embryo implantation process by regulating adhesion, apoptosis and immune tolerance.

Expression of NDUFA13 in asthenozoospermia and possible pathogenesis

Asthenozoospermia is a common cause of male infertility, which is characterized by reduced forward motility of spermatozoa. The cause and pathogenesis of asthenozoospermia are not fully understood. The purpose of this study was to investigate the expression of nicotinamide adenine dinucleotide (NADH) dehydrogenase (ubiquinone) 1 alpha subcomplex, 13 (NDUFA13) in the spermatozoa of men with asthenozoospermia and its possible pathogenesis. Protein content of NDUFA13 in spermatozoa was measured by Western blot analysis. The results showed that NDUFA13 expression in spermatozoa was significantly lower in men with asthenozoospermic than in men with normozoospermia (P < 0.01). Immunofluorescence experiments showed that NDUFA13 was expressed predominantly in the sperm mid-piece. A lower mitochondrial membrane potential, a higher intracellular reactive oxygen species (ROS) level and more apoptotic cells were also detected in men with asthenozoospermia. NDUFA13-specific small interfering RNA was used in the mouse spermatocyte GC2-spd cell line to down-regulate the expression of NDUFA13. The knockdown of NDUFA13 in the GC2-spd cells caused a collapse of mitochondrial membrane potential, an increase in ROS level and more apoptotic cells. Our study showed that NDUFA13 deficiency may be associated with asthenozoospermia through the disturbance of spermatozoa mitochondrial membrane potential and by increasing apoptosis and intracellular ROS.

GhMCS1, the Cotton Orthologue of Human GRIM-19, Is a Subunit of Mitochondrial Complex I and Associated with Cotton Fibre Growth

GRIM-19 (Gene associated with Retinoid-Interferon-induced Mortality 19) is a subunit of mitochondrial respiratory complex I in mammalian systems, and it has been demonstrated to be a multifunctional protein involved in the cell cycle, cell motility and innate immunity. However, little is known about the molecular functions of its homologues in plants. Here, we characterised GhMCS1, an orthologue of human GRIM-19 from cotton (Gossypium hirsutum L.), and found that it was essential for maintaining complex integrity and mitochondrial function in cotton. GhMCS1 was detected in various cotton tissues, with high levels expressed in developing fibres and flowers and lower levels in leaves, roots and ovules. In fibres at different developmental stages, GhMCS1 expression peaked at 5-15 days post anthesis (dpa) and then decreased at 20 dpa and diminished at 25 dpa. By Western blot analysis, GhMCS1 was observed to be localised to the mitochondria of cotton leaves and to colocalise with complex I. In Arabidopsis, GhMCS1 overexpression enhanced the assembly of complex I and thus respiratory activity, whereas the GhMCS1 homologue (At1g04630) knockdown mutants showed significantly decreased respiratory activities. Furthermore, the mutants presented with some phenotypic changes, such as smaller whole-plant architecture, poorly developed seeds and fewer trichomes. More importantly, in the cotton fibres, both the GhMCS1 transcript and protein levels were correlated with respiratory activity and fibre developmental phase. Our results suggest that GhMCS1, a functional ortholog of the human GRIM-19, is an essential subunit of mitochondrial complex I and is involved in cotton fibre development. The present data may deepen our knowledge on the potential roles of mitochondria in fibre morphogenesis.

Screening and identification of proteins interacting with IL-24 by the yeast two-hybrid screen, Co-IP, and FRET assays

Interleukin-24 (IL-24) is an ideal tumor-suppressor gene, but the mechanisms underlying its antitumor specificity remain to be elucidated. The best way to investigate these problems is to begin from the initiation of corresponding signaling cascades activated by IL-24 with screening and identifying those proteins that interacted with IL-24. With the aim of identifying these initial interactions, a yeast two-hybrid screening was performed by transforming AH109 cells containing PGBKT7-IL-24 with a liver cDNA plasmid library. These cells were then plated on synthetic nutrient medium (SD/-Trp/-Leu/-His) for the first screening and on quadruple dropout medium containing X-α-gal for the second screening. Positive colonies were further verified by repeating the MATE experiments, co-immunoprecipitation (Co-IP) analysis, and fluorescence resonance energy transfer (FRET) assays in vitro. Following the yeast two-hybrid screening, 15 genes were selected for sequencing, with two genes, HLA-C and NDUFA13, further verified using Co-IP assays and FRET assays. Both HLA-C and NDUFA13 were found to interact with IL-24. We found that HLA-C and NDUFA13 could interact with IL-24 and it may be involved in the signal induced by IL-24. Overall, this study contributes further insight into the cancer-specific apoptosis-inducing abilities of IL-24 to potentially enhance its therapeutic potential, and it also provides outlets for other biological functions of IL-24.

The Effect of Aging on Mitochondrial Complex I and the Extent of Oxidative Stress in the Rat Brain Cortex

One of the characteristic features of the aging is dysfunction of mitochondria. Its role in the regulation of metabolism and apoptosis suggests a possible link between these cellular processes. This study investigates the relationship of respiratory complex I with aging-related oxidative stress in the cerebral mitochondria. Deterioration of complex I seen in senescent (26-months old) mitochondria was accompanied by decline in total thiol group content, increase of HNE and HNE-protein adducts as well as decreased content of complex I subunits, GRIM-19 and NDUFV2. On the other hand, decline of complex I might be related with the mitochondrial apoptosis through increased Bax/Bcl-2 cascade in 15-month old animal brains. Higher amount of Bcl-2, Bcl-xL with the lower content of GRIM-19 could maintain to some extent elevated oxidative stress in mitochondria as seen in the senescent group. In the cortical M1 region increased presence of TUNEL+ cells and more than 20-times higher density of Fluoro-Jade C+ cells in 26-months old was observed, suggesting significant neurodegenerative effect of aging in the neuronal cells. Our study supports a scenario in which the age-related decline of complex I might sensitize neurons to the action of death agonists, such as Bax through lipid and protein oxidative stimuli in mitochondria. Although aging is associated with oxidative stress, these changes did not increase progressively with age, as similar extent of lesions was observed in oxidative stress markers of the both aged groups.

Pivotal Importance of STAT3 in Protecting the Heart from Acute and Chronic Stress: New Advancement and Unresolved Issues

The transcription factor, signal transducer and activator of transcription 3 (STAT3), has been implicated in protecting the heart from acute ischemic injury under both basal conditions and as a crucial component of pre- and post-conditioning protocols. A number of anti-oxidant and antiapoptotic genes are upregulated by STAT3 via canonical means involving phosphorylation on Y705 and S727, although other incompletely defined posttranslational modifications are involved. In addition, STAT3 is now known to be present in cardiac mitochondria and to exert actions that regulate the electron transport chain, reactive oxygen species production, and mitochondrial permeability transition pore opening. These non-canonical actions of STAT3 are enhanced by S727 phosphorylation. The molecular basis for the mitochondrial actions of STAT3 is poorly understood, but STAT3 is known to interact with a critical subunit of complex I and to regulate complex I function. Dysfunctional complex I has been implicated in ischemic injury, heart failure, and the aging process. Evidence also indicates that STAT3 is protective to the heart under chronic stress conditions, including hypertension, pregnancy, and advanced age. Paradoxically, the accumulation of unphosphorylated STAT3 (U-STAT3) in the nucleus has been suggested to drive pathological cardiac hypertrophy and inflammation via non-canonical gene expression, perhaps involving a distinct acetylation profile. U-STAT3 may also regulate chromatin stability. Our understanding of how the non-canonical genomic and mitochondrial actions of STAT3 in the heart are regulated and coordinated with the canonical actions of STAT3 is rudimentary. Here, we present an overview of what is currently known about the pleotropic actions of STAT3 in the heart in order to highlight controversies and unresolved issues.

The Non-structural Protein of Crimean-Congo Hemorrhagic Fever Virus Disrupts the Mitochondrial Membrane Potential and Induces Apoptosis

Viruses have developed distinct strategies to overcome the host defense system. Regulation of apoptosis in response to viral infection is important for virus survival and dissemination. Like other viruses, Crimean-Congo hemorrhagic fever virus (CCHFV) is known to regulate apoptosis. This study, for the first time, suggests that the non-structural protein NSs of CCHFV, a member of the genus Nairovirus, induces apoptosis. In this report, we demonstrated the expression of CCHFV NSs, which contains 150 amino acid residues, in CCHFV-infected cells. CCHFV NSs undergoes active degradation during infection. We further demonstrated that ectopic expression of CCHFV NSs induces apoptosis, as reflected by caspase-3/7 activity and cleaved poly(ADP-ribose) polymerase, in different cell lines that support CCHFV replication. Using specific inhibitors, we showed that CCHFV NSs induces apoptosis via both intrinsic and extrinsic pathways. The minimal active region of the CCHFV NSs protein was determined to be 93-140 amino acid residues. Using alanine scanning, we demonstrated that Leu-127 and Leu-135 are the key residues for NSs-induced apoptosis. Interestingly, CCHFV NSs co-localizes in mitochondria and also disrupts the mitochondrial membrane potential. We also demonstrated that Leu-127 and Leu-135 are important residues for disruption of the mitochondrial membrane potential by NSs. Therefore, these results indicate that the C terminus of CCHFV NSs triggers mitochondrial membrane permeabilization, leading to activation of caspases, which, ultimately, leads to apoptosis. Given that multiple factors contribute to apoptosis during CCHFV infection, further studies are needed to define the involvement of CCHFV NSs in regulating apoptosis in infected cells.

Identification of a Mitochondrial DNA Polymerase Affecting Cardiotoxicity of Sunitinib Using a Genome-Wide Screening on S. pombe Deletion Library

Drug toxicity is a key issue for drug R&D, a fundamental challenge of which is to screen for the targets genome-wide. The anticancer tyrosine kinase inhibitor sunitinib is known to induce cardiotoxicity. Here, to understand the molecular insights of cardiotoxicity by sunitinib at the genome level, we used a genome-wide drug target screening technology (GPScreen) that measures drug-induced haploinsufficiency (DIH) in the fission yeast Schizosaccharomyces pombe genome-wide deletion library and found a mitochondrial DNA polymerase (POG1). In the results, sunitinib induced more severe cytotoxicity and mitochondrial damage in POG1-deleted heterozygous mutants compared to wild type (WT) of S. pombe. Furthermore, knockdown of the human ortholog POLG of S. pombe POG1 in human cells significantly increased the cytotoxicity of sunitinib. Notably, sunitinib dramatically decreased the levels of POLG mRNAs and proteins, of which downregulation was already known to induce mitochondrial damage of cardiomyocytes, causing cardiotoxicity. These results indicate that POLG might play a crucial role in mitochondrial damage as a gene of which expressional pathway is targeted by sunitinib for cardiotoxicity, and that genome-wide drug target screening with GPScreen can be applied to drug toxicity target discovery to understand the molecular insights regarding drug toxicity.

Constraining the Lateral Helix of Respiratory Complex I by Cross-linking Does Not Impair Enzyme Activity or Proton Translocation

Complex I (NADH:ubiquinone oxidoreductase) is a multisubunit, membrane-bound enzyme of the respiratory chain. The energy from NADH oxidation in the peripheral region of the enzyme is used to drive proton translocation across the membrane. One of the integral membrane subunits, nuoL in Escherichia coli, has an unusual lateral helix of ∼75 residues that lies parallel to the membrane surface and has been proposed to play a mechanical role as a piston during proton translocation (Efremov, R. G., Baradaran, R., and Sazanov, L. A. (2010) Nature 465, 441-445). To test this hypothesis we have introduced 11 pairs of cysteine residues into Complex I; in each pair one is in the lateral helix, and the other is in a nearby region of subunit N, M, or L. The double mutants were treated with Cu(2+) ions or with bi-functional methanethiosulfonate reagents to catalyze cross-link formation in membrane vesicles. The yields of cross-linked products were typically 50-90%, as judged by immunoblotting, but in no case did the activity of Complex I decrease by >10-20%, as indicated by deamino-NADH oxidase activity or rates of proton translocation. In contrast, several pairs of cysteine residues introduced at other interfaces of N:M and M:L subunits led to significant loss of activity, in particular, in the region of residue Glu-144 of subunit M. The results do not support the hypothesis that the lateral helix of subunit L functions like a piston, but rather, they suggest that conformational changes might be transmitted more directly through the functional residues of the proton translocation apparatus.

A New Semantic Functional Similarity over Gene Ontology

Identifying functionally similar or closely related genes and gene products has significant impacts on biological and clinical studies as well as drug discovery. In this paper, we propose an effective and practically useful method measuring both gene and gene product similarity by integrating the topology of gene ontology, known functional domains and their functional annotations. The proposed method is comprehensively evaluated through statistical analysis of the similarities derived from sequence, structure and phylogenetic profiles, and clustering analysis of disease genes clusters. Our results show that the proposed method clearly outperforms other conventional methods. Furthermore, literature analysis also reveals that the proposed method is both statistically and biologically promising for identifying functionally similar genes or gene products. In particular, we demonstrate that the proposed functional similarity metric is capable of discoverying new disease related genes or gene products.

Overexpression of GRIM-19, a mitochondrial respiratory chain complex I protein, suppresses hepatocellular carcinoma growth

GRIM-19 has been demonstrated as an important regulator for the normal tissue development. Recently, more evidences regarded GRIM-19 as the new tumor suppressor. However, the possible mechanisms underlying GRIM-19 suppressing cancer growth are unclear. In the present study, Paired hepatocellular carcinoma (HCC) and adjacent non-tumor liver tissues were obtained from 54 patients who underwent primary surgical HCC tissue resection. GRIM-19 protein expression in HCC tissues was performed by immunohistochemistry. Cells were transfected by lentiviruses plasmid expressing GRIM-19. RT-PCR and Western blot analyses were performed to confirm the expression of GRIM-19 mRNA or protein. Cell proliferation was assessed by MTT and FCM analyses. Mitochondrial membrane potential and apoptosis were respectively determined by using fluorescence microscopy and FCM analyses. AKT1, pAKT1, cyclinD1, CDK4, PCNA, Bax, Bcl-2, cleaved caspase-9, cleaved caspase-3, and cytochrome C were detected by Western blot and immunofluorescence. GRIM-19 protein expression was markedly lower in HCC than in paired adjacent non-tumor liver tissues. GRIM-19 overexpression in HCC cells significantly induced cell cycle arrest and enhanced apoptosis. We also found that AKT1 expression and phosphorylation were regulated by the expression of GRIM-19. Collectively, our study demonstrated that GRIM-19 overexpression suppressed HCC growth and downregulated AKT1 expression, suggesting that GRIM-19 might play a crucial role in hepatocarcinogenesis through negatively regulating the PI3K/AKT signaling pathway.

STAT3 signaling in pulmonary arterial hypertension

Pulmonary artery hypertension (PAH) is a proliferative disorder associated with enhanced pulmonary artery smooth muscle cell proliferation and suppressed apoptosis. The sustainability of this phenotype requires the activation of pro-survival transcription factor like the signal transducers and activators of transcription-3 (STAT3). Using multidisciplinary and translational approaches, we and others have demonstrated that STAT3 activation in both human and experimental models of PAH accounts for the modulation of the expression of several proteins already known as implicated in PAH pathogenesis, as well as for signal transduction to other transcription factors. Furthermore, recent data demonstrated that STAT3 could be therapeutically targeted in different animal models and some molecules are actually in clinical trials for cancer or PAH treatment.

Induction of intrinsic apoptosis pathway in colon cancer HCT-116 cells by novel 2-substituted-5,6,7,8-tetrahydronaphthalene derivatives

2-Acetyl tetralin (1) reacted with N,N-dimethylformamide dimethylacetal (DMF-DMA) to afford the enaminone 3. The reaction of 3 with piperidine and morpholine afforded the trans enaminone 5a,b, respectively. Compound 3 was treated with primary aromatic amines to give secondary enaminones 6a-e. The enaminone 3 reacted with acetylglycine and hippuric acid to yield pyranones 10a, b, respectively. The reaction of enaminone 3 with 1,4-benzoquinone and 1,4-naphthoquinone gave benzofuranyl tetralin derivatives 14a,b, respectively. Also, when 3 reacted with 5-amino-3-phenyl-1H-pyrazole 15a and 5-amino-1,2,3-triazole 15b, it afforded the new pyrazolo[1,5-a]pyrimidine 17a and 1,2,3-triazolo[1,5-a]pyrimidine 17b, respectively. While the reaction of 3 with pyrimidines 18a, b resulted in the formation of pyrido[2,3-d]pyrimidine derivatives 20a, b, respectively. Investigations of the cytotoxic effect of those compounds against different human cell lines indicated that some compounds showed high selective cytotoxicity against colon cancer HCT-116 cells. Some of these compounds led to DNA damaging and fragmentation that was associated with the induction of apoptosis via mitochondrial pathway. This pathway is initiated by the impairment of mitochondrial transmembrane potential (Δψm) and in response to that the mitochondria released cytochrome c increased, that in turn activated caspase-9 and caspase-3 and induced apoptosis. Compounds 17b and 20b were promising anti-cancer agents that induced intrinsic apoptosis pathway in colon cancer cells.

Molecular cloning and multifunctional characterization of GRIM-19 (gene associated with retinoid-interferon-induced mortality 19) homologue from turbot (Scophthalmus maximus)

GRIM-19 (gene associated with retinoid-interferon-induced mortality 19), a novel cell death regulatory gene, plays important roles in cell apoptosis, embryogenesis, mitochondrial respiratory chain and immune response. To date, little information is known about fish GRIM-19 characteristics except orange-spotted grouper (Epinephelus coioides). Here a new GRIM-19 gene is identified and characterized from turbot (Scophthalmus maximus), an economic marine fish in China and Europe. Briefly, turbot GRIM-19 is a 595-bp gene encoding a 144 amino acids protein, which shares the closest relationship with Atlantic halibut (Hippoglossus hippoglossus). The expression of turbot grim-19 in liver, spleen and kidney is up-regulated by the infection of Vibrio anguillarum and LCDV (lymphocystis disease virus). Subsequently, a recombinant protein of turbot GRIM-19 is acquired and the anti-bacterial function is proved by liquid culture inhibition experiment. The subcellular location indicates that turbot GRIM-19 is co-localized with STAT3 in the cytoplasm, which is mainly determined by GRIM-19 41-84 amino acids and STAT3 1-321 amino acids. Finally, the involvements of turbot GRIM-19 in cell apoptosis and NF-κB pathway are investigated. All these data help to understand GRIM-19 function in fish, as well as provide the application possibility of GRIM-19 in fish disease resistance breeding.

Differentially expressed proteins in malignant and benign adrenocortical tumors

We have compared the microsomal protein composition of eight malignant and six benign adrenocortical tumors with proteomic methods. IGF2 had increased level in the malignant tumors, confirming previous microarray studies on the same material. Aldolase A, a glycolytic enzyme, also showed increased levels in the malignant tissue compared to the benign. Additionally, several proteins belonging to complex I in the mitochondrial respiration chain showed decreased levels in the malignant tissue. Taken together, this may indicate a shift in energy metabolism where glycolysis may be favored over tight coupling of glycolysis and mitochondrial respiration, a phenomenon known as the Warburg effect. One of the complex I proteins that showed decreased levels in the malignant tissue was GRIM-19. This protein has been suggested as a tumor suppressive protein by being a negative regulator of STAT3. In summary, an analysis of the microsomal proteome in adrenocortical tumors identifies groups of proteins as well as specific proteins differentially expressed in the benign and malignant forms. These proteins shed light on the biology behind malignancy and could delineate future drug targets.

Loss of STAT3 in mouse embryonic fibroblasts reveals its Janus-like actions on mitochondrial function and cell viability

STAT3 has been implicated in mitochondrial function; however, the physiological relevance of this action is not established. Here we studied the importance of STAT3 to the cellular response to stimuli, TNFα and serum deprivation, which increase mitochondrial reactive oxygen species (ROS) formation. Experiments were performed using wild type (WT) and STAT3 knockout (KO) mouse embryonic fibroblasts (MEF). Both WT and STAT3 KO MEF expressed similar levels of tumor necrosis factor receptor 1 (TNFR1) and exhibited comparable IκBα degradation with TNFα. However, in the absence of STAT3 nuclear accumulation of NFκB p65 with TNFα was attenuated and induction of the survival protein c-FLIPL was eliminated. Nonetheless, WT MEF were more sensitive to TNFα-induced death which was attributed to necrosis. Deletion of STAT3 decreased ROS formation induced by TNFα and serum deprivation. STAT3 deletion was associated with lower levels of complex I and rates of respiration. Relative to WT cells, mitochondria of STAT3 KO cells released significantly more cytochrome c in response to oxidative stress and had greater caspase 3 cleavage due to serum deprivation. Our findings are consistent with STAT3 being important for mitochondrial function and cell viability by ensuring mitochondrial integrity and the expression of pro-survival genes.

Mitoneet mediates TNFα-induced necroptosis promoted by exposure to fructose and ethanol

Fructose and ethanol are metabolized principally in the liver and are both known to contribute to the development of hepatic steatosis that can progress to hepatic steatohepatitis. The present study indentifies a synergistic interaction between fructose and ethanol in promoting hepatocyte sensitivity to TNFα-induced necroptosis. Concurrent exposure to fructose and ethanol induces the overexpression of the CDGSH iron-sulfur domain-containing protein 1 (CISD1 or mitoneet), which is localized to the outer mitochondrial membrane. The increased expression of mitoneet primes the hepatocyte for TNFα-induced cytotoxicity. Treatment with TNFα induces the translocation of a Stat3-Grim-19 complex to the mitochondria, which binds to mitoneet and promotes the rapid release of its 2Fe-2S cluster, causing an accumulation of mitochondrial iron. The dramatic increase of mitochondrial iron provokes a surge in formation of reactive oxygen species, resulting in mitochondrial injury and cell death. Additionally, mitoneet is constitutively expressed at high levels in L929 fibrosarcoma cells and is required for L929 cells to undergo TNFα-induced necroptosis in the presence of caspase inhibition, indicating the importance of mitoneet to the necroptotic form of cell death.

Accessory subunits of mitochondrial complex I

Mitochondrial complex I has a molecular mass of almost 1 MDa and comprises more than 40 polypeptides. Fourteen central subunits harbour the bioenergetic core functions. We are only beginning to understand the significance of the numerous accessory subunits. The present review addresses the role of accessory subunits for assembly, stability and regulation of complex I and for cellular functions not directly associated with redox-linked proton translocation.

Suppression of mitochondrial complex I influences cell metastatic properties

Despite the fact that mitochondrial dysfunction has an important role in tumorigenesis and metastasis, the underlying mechanism remains to be elucidated. Mitochondrial Complex I (NADH:ubiquinone oxidoreductase) is the first and the largest protein complex of the mitochondrial electron-transport chain (ETC),which has an essential role in maintaining mitochondrial function and integrity. In this study, we separately knocked down two subunits of mitochondrial complex I, GRIM-19 or NDUFS3, and investigated their effects on metastatic behaviors and explored the possible mechanisms. Our data showed that stable down-modulation of GRIM-19 or NDUFS3 decreased complex I activity and reactive oxygen species (ROS) production; led to enhanced cell adhesion, migration, invasion, and spheroid formation; and influenced the expressions of extracellular matrix (ECM) molecules and its related proteins. We also observed that the expressions of GRIM-19, NDUFS3, and ECM elements were correlated with invasive capabilities of breast cancer cell lines. These results suggest that inhibition of complex I affects metastatic properties of cancer cells, and mitochondrial ROS might play a crucial role in these processes by regulating ECM.