TMBIM protein family: ancestral regulators of cell death

TMBIM6/BI-1 is an intracellular environmental regulator that induces paraptosis in cancer via ROS and Calcium-activated ERAD II pathways

Transmembrane B cell lymphoma 2-associated X protein inhibitor motif-containing (TMBIM) 6, also known as Bax Inhibitor-1 (BI-1), has been heavily researched for its cytoprotective functions. TMBIM6 functional diversity includes modulating cell survival, stress, metabolism, cytoskeletal dynamics, organelle function, regulating cytosolic acidification, calcium, and reactive oxygen species (ROS). Clinical research shows TMBIM6 plays a key role in many of the world's top diseases/injuries (i.e., Alzheimer's, Parkinson's, diabetes, obesity, brain injury, liver disease, heart disease, aging, etc.), including cancer, where TMBIM6 expression impacts patient survival, chemoresistance, cancer progression, and metastasis. We show TMBIM6 is activated by, and undergoes, different conformational changes that dictate its function following a significant change in the cell's IntraCellular Environment (ICE). TMBIM6 agonism, following ICE change, can help the cell overcome multiple stresses including toxin exposure, viral infection, wound healing, and excitotoxicity. However, in cancer cells TMBIM6 agonism results in rapid paraptotic induction irrespective of the cancer type, sub-type, genotype or phenotype. Furthermore, the level of TMBIM6 expression in cancer did not dictate the level of paraptotic induction; however, it did dictate the rate at which paraptosis occurred. TMBIM6 agonism did not induce paraptosis in cancer via canonical routes involving p38 MAPK, JNK, ERK, UPR, autophagy, proteasomes, or Caspase-9. Instead, TMBIM6 agonism in cancer upregulates cytosolic Ca2+ and ROS, activates lysosome biogenesis, and induces paraptosis via ERAD II mechanisms. In xenograft models, we show TMBIM6 agonism induces rapid cancer cell death with no toxicity, even at high doses of TMBIM6 agonist (>450 mg/kg). In summary, this study shows TMBIM6's functional diversity is only activated by severe ICE change in diseased/injured cells, highlighting its transformative potential as a therapeutic target across various diseases and injuries, including cancer.

Impact of ambient air pollution on colorectal cancer risk and survival: insights from a prospective cohort and epigenetic Mendelian randomization study

BACKGROUND

This study investigates the associations between air pollution and colorectal cancer (CRC) risk and survival from an epigenomic perspective.

METHODS

Using a newly developed Air Pollutants Exposure Score (APES), we utilized a prospective cohort study (UK Biobank) to investigate the associations of individual and combined air pollution exposures with CRC incidence and survival, followed by an up-to-date systematic review with meta-analysis to verify the associations. In epigenetic two-sample Mendelian randomization analyses, we examine the associations between genetically predicted DNA methylation related to air pollution and CRC risk. Further genetic colocalization and gene-environment interaction analyses provided different insights to disentangle pathogenic effects of air pollution via epigenetic modification.

FINDINGS

During a median 12.97-year follow-up, 5767 incident CRC cases among 428,632 participants free of baseline CRC and 533 deaths in 2401 patients with CRC were documented in the UK Biobank. A higher APES score was associated with an increased CRC risk (HR, 1.03, 95% CI = 1.01-1.06; P = 0.016) and poorer survival (HR, 1.13, 95% CI = 1.03-1.23; P = 0.010), particularly among participants with insufficient physical activity and ever smokers (Pinteraction > 0.05). A subsequent meta-analysis of seven observational studies, including UK Biobank data, corroborated the association between PM2.5 exposure (per 10 μg/m3 increment) and elevated CRC risk (RR,1.42, 95% CI = 1.12-1.79; P = 0.004; I2 = 90.8%). Genetically predicted methylation at PM2.5-related CpG site cg13835894 near TMBIM1/PNKD and cg16235962 near CXCR5, and NO2-related cg16947394 near TMEM110 were associated with an increased CRC risk. Gene-environment interaction analysis confirmed the epigenetic modification of aforementioned CpG sites with CRC risk and survival.

INTERPRETATION

Our study suggests the association between air pollution and CRC incidence and survival, underscoring the possible modifying roles of epigenomic factors. Methylation may partly mediate pathogenic effects of air pollution on CRC, with annotation to epigenetic alterations in protein-coding genes TMBIM1/PNKD, CXCR5 and TMEM110.

FUNDING

Xue Li is supported by the Natural Science Fund for Distinguished Young Scholars of Zhejiang Province (LR22H260001), the National Nature Science Foundation of China (No. 82204019) and Healthy Zhejiang One Million People Cohort (K-20230085). ET is supported by a Cancer Research UK Career Development Fellowship (C31250/A22804). MGD is supported by the MRC Human Genetics Unit Centre Grant (U127527198).

A chromosome-level genome assembly of the soybean pod borer: insights into larval transcriptional response to transgenic soybean expressing the pesticidal Cry1Ac protein

BACKGROUND

Genetically modified (GM) crop plants with transgenic expression of Bacillus thuringiensis (Bt) pesticidal proteins are used to manage feeding damage by pest insects. The durability of this technology is threatened by the selection for resistance in pest populations. The molecular mechanism(s) involved in insect physiological response or evolution of resistance to Bt is not fully understood.

RESULTS

To investigate the response of a susceptible target insect to Bt, the soybean pod borer, Leguminivora glycinivorella (Lepidoptera: Tortricidae), was exposed to soybean, Glycine max, expressing Cry1Ac pesticidal protein or the non-transgenic parental cultivar. Assessment of larval changes in gene expression was facilitated by a third-generation sequenced and scaffolded chromosome-level assembly of the L. glycinivorella genome (657.4 Mb; 27 autosomes + Z chromosome), and subsequent structural annotation of 18,197 RefSeq gene models encoding 23,735 putative mRNA transcripts. Exposure of L. glycinivorella larvae to transgenic Cry1Ac G. max resulted in prediction of significant differential gene expression for 204 gene models (64 up- and 140 down-regulated) and differential splicing among isoforms for 10 genes compared to unexposed cohorts. Differentially expressed genes (DEGs) included putative peritrophic membrane constituents, orthologs of Bt receptor-encoding genes previously linked or associated with Bt resistance, and those involved in stress responses. Putative functional Gene Ontology (GO) annotations assigned to DEGs were significantly enriched for 36 categories at GO level 2, respectively. Most significantly enriched cellular component (CC), biological process (BP), and molecular function (MF) categories corresponded to vacuolar and microbody, transport and metabolic processes, and binding and reductase activities. The DEGs in enriched GO categories were biased for those that were down-regulated (≥ 0.783), with only MF categories GTPase and iron binding activities were bias for up-regulation genes.

CONCLUSIONS

This study provides insights into pathways and processes involved larval response to Bt intoxication, which may inform future unbiased investigations into mechanisms of resistance that show no evidence of alteration in midgut receptors.

Regulation of BCR-mediated Ca2+ mobilization by MIZ1-TMBIM4 safeguards IgG1+ GC B cell-positive selection

The transition from immunoglobulin M (IgM) to affinity-matured IgG antibodies is vital for effective humoral immunity. This is facilitated by germinal centers (GCs) through affinity maturation and preferential maintenance of IgG+ B cells over IgM+ B cells. However, it is not known whether the positive selection of the different Ig isotypes within GCs is dependent on specific transcriptional mechanisms. Here, we explored IgG1+ GC B cell transcription factor dependency using a CRISPR-Cas9 screen and conditional mouse genetics. We found that MIZ1 was specifically required for IgG1+ GC B cell survival during positive selection, whereas IgM+ GC B cells were largely independent. Mechanistically, MIZ1 induced TMBIM4, an ancestral anti-apoptotic protein that regulated inositol trisphosphate receptor (IP3R)-mediated calcium (Ca2+) mobilization downstream of B cell receptor (BCR) signaling in IgG1+ B cells. The MIZ1-TMBIM4 axis prevented mitochondrial dysfunction-induced IgG1+ GC cell death caused by excessive Ca2+ accumulation. This study uncovers a unique Ig isotype-specific dependency on a hitherto unidentified mechanism in GC-positive selection.

The US21 viroporin of human cytomegalovirus stimulates cell migration and adhesion

The human cytomegalovirus (HCMV) US12 gene family contributes to virus-host interactions by regulating the virus' cell tropism and its evasion of host innate immune responses. US21, one of the 10 US12 genes (US12-US21), is a descendant of a captured cellular transmembrane BAX inhibitor motif-containing gene. It encodes a 7TMD endoplasmic reticulum (ER)-resident viroporin (pUS21) capable of reducing the Ca2+ content of ER stores, which, in turn, protects cells against apoptosis. Since regulation of Ca2+ homeostasis affects a broad range of cellular responses, including cell motility, we investigated whether pUS21 might also interfere with this cytobiological consequence of Ca2+ signaling. Indeed, deletion of the US21 gene impaired the ability of HCMV-infected cells to migrate, whereas expression of US21 protein stimulated cell migration and adhesion, as well as focal adhesion (FA) dynamics, in a way that depended on its ability to manipulate ER Ca2+ content. Mechanistic studies revealed pUS21-mediated cell migration to involve calpain 2 activation since its inhibition prevented the viroporin's effects on cell motility. Pertinently, pUS21 expression stimulated a store-operated Ca2+ entry (SOCE) mechanism that may determine the activation of calpain 2 by promoting Ca2+ entry. Furthermore, pUS21 was observed to interact with talin-1, a calpain 2 substrate, and crucial protein component of FA complexes. A functional consequence of this interaction was confirmed by talin-1 knockdown, which abrogated the pUS21-mediated increase in cell migration. Together, these results indicate the US21-encoded viroporin to be a viral regulator of cell adhesion and migration in the context of HCMV infection. IMPORTANCE Human cytomegalovirus (HCMV) is an opportunistic pathogen that owes part of its success to the capture, duplication, and tuning of cellular genes to generate modern viral proteins which promote infection and persistence in the host by interfering with many cell biochemical and physiological pathways. The US21 viral protein provides an example of this evolutionary strategy: it is a cellular-derived calcium channel that manipulates intracellular calcium homeostasis to confer edges to HCMV replication. Here, we report on the characterization of a novel function of the US21 protein as a viral regulator of cell migration and adhesion through mechanisms involving its calcium channel activity. Characterization of HCMV multifunctional regulatory proteins, like US21, supports the better understanding of viral pathogenesis and may open avenues for the design of new antiviral strategies that exploit their functions.

TMBIM6 deficiency leads to bone loss by accelerating osteoclastogenesis

TMBIM6 is an endoplasmic reticulum (ER) protein that modulates various physiological and pathological processes, including metabolism and cancer. However, its involvement in bone remodeling has not been investigated. In this study, we demonstrate that TMBIM6 serves as a crucial negative regulator of osteoclast differentiation, a process essential for bone remodeling. Our investigation of Tmbim6-knockout mice revealed an osteoporotic phenotype, and knockdown of Tmbim6 inhibited the formation of multinucleated tartrate-resistant acid phosphatase-positive cells, which are characteristic of osteoclasts. Transcriptome and immunoblot analyses uncovered that TMBIM6 exerts its inhibitory effect on osteoclastogenesis by scavenging reactive oxygen species and preventing p65 nuclear localization. Additionally, TMBIM6 depletion was found to promote p65 localization to osteoclast-related gene promoters. Notably, treatment with N-acetyl cysteine, an antioxidant, impeded the osteoclastogenesis induced by TMBIM6-depleted cells, supporting the role of TMBIM6 in redox regulation. Furthermore, we discovered that TMBIM6 controls redox regulation via NRF2 signaling pathways. Our findings establish TMBIM6 as a critical regulator of osteoclastogenesis and suggest its potential as a therapeutic target for the treatment of osteoporosis.

Yeast Bax Inhibitor (Bxi1p/Ybh3p) Is Not Required for the Action of Bcl-2 Family Proteins on Cell Viability

Permeabilization of mitochondrial membrane by proteins of the BCL-2 family is a key decisive event in the induction of apoptosis in mammalian cells. Although yeast does not have homologs of the BCL-2 family, when these are expressed in yeast, they modulate the survival of cells in a way that corresponds to their activity in mammalian cells. The yeast gene, alternatively referred to as BXI1 or YBH3, encodes for membrane protein in the endoplasmic reticulum that was, contradictorily, shown to either inhibit Bax or to be required for Bax activity. We have tested the effect of the deletion of this gene on the pro-apoptotic activity of Bax and Bak and the anti-apoptotic activity of Bcl-XL and Bcl-2, as well on survival after treatment with inducers of regulated cell death in yeast, hydrogen peroxide and acetic acid. While deletion resulted in increased sensitivity to acetic acid, it did not affect the sensitivity to hydrogen peroxide nor to BCL-2 family members. Thus, our results do not support any model in which the activity of BCL-2 family members is directly affected by BXI1 but rather indicate that it may participate in modulating survival in response to some specific forms of stress.

Calcium signaling in lysosome-dependent cell death

Calcium is a crucial messenger of intracellular and extracellular signals, regulating a great variety of cellular processes such as cell death, proliferation, and metabolism. Inside the cell, calcium signaling is one of the main interorganelle communication mediators, with central functional roles at the endoplasmic reticulum (ER), mitochondria, Golgi complex, and lysosomes. Lysosomal function is highly dependent on lumenal calcium and most of the lysosomal membrane-localised ion channels regulate several lysosomal functions and properties such as lumenal pH. One of these functions configures a specific type of cell death involving lysosomes, named lysosome-dependent cell death (LDCD), which contributes to maintenance of tissue homeostasis, development and pathology when deregulated. Here, we cover the fundamental aspects of LDCD with a special focus on recent advances in calcium signaling in LDCD.

A gating mechanism of the BsYetJ calcium channel revealed in an endoplasmic reticulum lipid environment

The transmembrane BAX inhibitor-1-containing motif 6 (TMBIM6) is suggested to modulate apoptosis by regulating calcium homeostasis in the endoplasmic reticulum (ER). However, the precise molecular mechanism underlying this calcium regulation remains poorly understood. To shed light on this issue, we investigated all negatively charged residues in BsYetJ, a bacterial homolog of TMBIM6, using mutagenesis and fluorescence-based functional assays. We reconstituted BsYetJ in membrane vesicles with a lipid composition similar to that of the ER. Our results show that the charged residues E49 and R205 work together as a major gate, regulating calcium conductance in these ER-like lipid vesicles. However, these residues become largely inactive when reconstituted in other lipid environments. In addition, we found that D195 acts as a minor filter compared to the E49-R205 dyad. Our study uncovers a previously unknown function of BsYetJ/TMBIM6 in the calcium-dependent inactivation of BsYetJ, providing a framework for the development of a lipid-dependent mechanistic model of BsYetJ that will facilitate our understanding of calcium-dependent apoptosis.

TMBIM5 is the Ca2+ /H+ antiporter of mammalian mitochondria

Mitochondrial Ca2+ ions are crucial regulators of bioenergetics and cell death pathways. Mitochondrial Ca2+ content and cytosolic Ca2+ homeostasis strictly depend on Ca2+ transporters. In recent decades, the major players responsible for mitochondrial Ca2+ uptake and release have been identified, except the mitochondrial Ca2+ /H+ exchanger (CHE). Originally identified as the mitochondrial K+ /H+ exchanger, LETM1 was also considered as a candidate for the mitochondrial CHE. Defining the mitochondrial interactome of LETM1, we identify TMBIM5/MICS1, the only mitochondrial member of the TMBIM family, and validate the physical interaction of TMBIM5 and LETM1. Cell-based and cell-free biochemical assays demonstrate the absence or greatly reduced Na+ -independent mitochondrial Ca2+ release in TMBIM5 knockout or pH-sensing site mutants, respectively, and pH-dependent Ca2+ transport by recombinant TMBIM5. Taken together, we demonstrate that TMBIM5, but not LETM1, is the long-sought mitochondrial CHE, involved in setting and regulating the mitochondrial proton gradient. This finding provides the final piece of the puzzle of mitochondrial Ca2+ transporters and opens the door to exploring its importance in health and disease, and to developing drugs modulating Ca2+ exchange.

In vitroSodium Fluoride Treatment Significantly Affects Apoptosis and Proliferation in the Liver of Embryonic Chickens

Sodium fluoride (NaF), although helpful in preventing dental decay, may negatively affect the body. The aim of this study was to examine the effects of a 6-h in vitro treatment of livers isolated from 14-day-old chicken embryos with NaF at doses of 1.7 (D1), 3.5 (D2), 7.1 (D3) and 14.2 mM (D4), with regard to apoptosis, cell proliferation and tissue structure. The mRNA expression of the apoptosis regulators CYCS, APAF1, BCL2, CASP3, CASP9 and TMBIM1 was analysed by the qPCR method. Apoptotic cells were detected by a TUNEL assay. The tissue and DNA structure were also analysed by histological staining (H&E, Feulgen). The number of proliferating cells was determined and the apoptosis regulatory proteins were localised by the immunohistochemical staining of PCNA, CASP3 and APAF1. The results showed that the mRNA expression of CYCS, BCL2, CASP3, CASP9 and APAF1 increased significantly in the D1 group, as did that of CASP9 in the D3 group and of BCL2 and APAF1 in the D4 group. The number of apoptotic cells increased significantly in the D4 group, where they increased from 18% to 49%. On the other hand, the number of proliferating cells decreased gradually, in a dose-dependent manner, from 84% in the control group to 5.5% in the D4 group. The expression of apoptosis-regulating factors also increased: in the D3 and D4 groups, the CASP3 immunopositive reaction was more intensive in single cells in the embryonic livers, whereas that of APAF1 increased in the hepatocytes as well as in the hepatic blood vessel walls. The mechanism of the effect of NaF on apoptosis in the embryonic liver is very complex. In the groups exposed to higher doses of NaF, apoptosis was significantly stimulated, while proliferation was inhibited and the tissue structure was damaged. The expression of apoptosis regulators at the mRNA and protein levels increased, but the mRNA expression did not depend on the NaF dose. These results reveal that NaF, by changing the balance between apoptosis and the proliferation of hepatocytes, may disturb the development and function of the liver in embryonic chickens. Therefore, the risk of exposure to NaF should be considered when determining the standards for human and animal exposure to this compound.

Mitochondria-associated niches in health and disease

The appreciation of the importance of interorganelle contacts has steadily increased over the past decades. Advances in imaging, molecular biology and bioinformatic techniques allowed the discovery of new mechanisms involved in the interaction and communication between organelles, providing novel insights into the inner works of a cell. In this Review, with the mitochondria under the spotlight, we discuss the most recent findings on the mechanisms mediating the communication between organelles, focusing on Ca2+ signaling, lipid exchange, cell death and stress responses. Notably, we introduce a new integrative perspective to signaling networks that is regulated by interorganelle interactions – the mitochondria-associated niches – focusing on the link between the molecular determinants of contact sites and their functional outputs, rather than simply physical and structural communication. In addition, we highlight the neuropathological and metabolic implications of alterations in mitochondria-associated niches and outline how this concept might improve our understanding of multi-organelle interactions.

Plastid methylerythritol phosphate pathway participates in the hypersensitive response-related cell death in Nicotiana benthamiana

Programmed cell death (PCD), a characteristic feature of hypersensitive response (HR) in plants, is an important cellular process often associated with the defense response against pathogens. Here, the involvement of LytB, a gene encoding 4-hydroxy-3-methylbut-2-enyl diphosphate reductase that participates in the final step of the plastid methylerythritol phosphate (MEP) pathway, in plant HR cell death was studied. In Nicotiana benthmiana plants, silencing of the NbLytB gene using virus-induced gene silencing (VIGS) caused plant growth retardation and albino leaves with severely malformed chloroplasts. In NbLytB-silenced plants, HR-related cell death mediated by the expression of either the human proapoptotic protein gene Bax or an R gene with its cognate Avr effector gene was inhibited, whereas that induced by the nonhost pathogen Pseudomonas syringae pv. syringae 61 was enhanced. To dissect the isoprenoid pathway and avoid the pleiotropic effects of VIGS, chemical inhibitors that specifically inhibit isoprenoid biosynthesis in plants were employed. Treatment of N. benthamiana plants with fosmidomycin, a specific inhibitor of the plastid MEP pathway, effectively inhibited HR-related PCD, whereas treatment with mevinolin (a cytoplasmic mevalonate pathway inhibitor) and fluridone (a carotenoid biosynthesis inhibitor) did not. Together, these results suggest that the MEP pathway as well as reactive oxygen species (ROS) generation in the chloroplast play an important role in HR-related PCD, which is not displaced by the cytosolic isoprenoid biosynthesis pathway.

miR-125a-3p regulates apoptosis by suppressing TMBIM4 in lens epithelial cells

PURPOSE

To explore the regulatory effect of miR-125a-3p on lens epithelial cells (LECs) under ultraviolet radiation B (UVB) irradiation.

METHODS

The expression of miR-125a-3p in age-related cataract (ARC) specimens and cell models was detected by qRT-PCR. UVB was utilized to establish DNA damage model of LECs. Cell count kit-8 was applied in detecting cell viability. Cell apoptosis ratio was analyzed by flow cytometry. Dual luciferase reports were applied to analyze the mechanism between miRNA and target genes. Nanoparticle tracking analysis, and Western blot were used to identify whether the exosomes were typical exosomes.

RESULTS

miR-125a-3p was upregulated in ARC tissues and LECs treated with UVB. Knockdown of miR-125a-3p in LECs significantly decreased apoptosis and increased viability of UVB-irradiated LECs. We predicted that miR-125a-3p could regulate transmembrane Bax inhibitor motif containing 4 (TMBIM4) by the bioinformatics databases TargetScan, miRBase, and miRWalk. Luciferase reporter assays demonstrated that miR-125a-3p may suppress TMBIM4 protein translation by binding to 3'UTR of TMBIM4 mRNA. Overexpression of miR-125a-3p decreased TMBIM4, which suggested that miR-125a-3p could inhibit TMBIM4. Moreover, knockdown of TMBIM4 decreased cell viability and enhanced cell apoptosis during UVB irradiation. In addition, the exosome secretion of LECs irradiated by UVB was enhanced, and the expression of miR-125a-3p was high. Cell viability was significantly decreased, and cell apoptosis was increased during UVB-exos treatment.

CONCLUSION

This study indicated that miR-125a-3p regulated apoptosis by suppressing TMBIM4 in LECs under oxidative damage, providing a new idea for clinical therapeutic target of cataract.

FAIM2 is a potential pan-cancer biomarker for prognosis and immune infiltration

Fas apoptosis inhibitory molecule 2 (FAIM2) is an important member of the transmembrane BAX inhibitor motif containing (TMBIM) family. However, the role of FAIM2 in tumor prognosis and immune infiltration has rarely been studied. Here, we conducted a pan-cancer analysis to explore the role of FAIM2 in various tumors and further verified the results in glioma through molecular biology experiment. FAIM2 expression and clinical stages in tumor samples and para-cancerous samples were analyzed by TIMER2 database, GEPIA database, and the TISIDB database. The role of FAIM2 on prognosis was analyzed via GEPIA2. We utilized the ESTIMATE algorithm to evaluate the ImmuneScore and StromalScore of various tumors. In addition, we explored the correlation between FAIM2 expression and tumor immune cell infiltration by the TIMER2 database. The immune checkpoint genes, tumor mutation burden (TMB), microsatellite instability (MSI), mismatch repair (MMR), and DNA methylation related to FAIM2 were analyzed based on the TCGA database. The correlation between FAIM2 expression with Copy number variations (CNV) and methylation is explored by GSCA database. Protein-Protein Interaction (PPI) analysis was obtained from the STRING database and the CellMiner database was used to explore the association between FAIM2 expression and drug response. FAIM2 co-expression genes were studied by the LinkedOmics database. Immunohistochemistry, Western Blotting Analysis, Cell Viability Assay, Colony Formation Assay, and Edu staining assay were used in the molecular biology experiments section. The FAIM2 expression was down-regulated in most tumors and highly expressed FAIM2 was associated with a better prognosis in several cancers. FAIM2 plays an essential role in the tumor microenvironment and is closely associated with immune Infiltration in various tumors. The expression of FAIM2 was closely correlated to TMB, MSI, MMR, CNV, and DNA methylation. Furthermore, FAIM2 related genes in the PPI network and its co-expression genes in glioma are involved in a large number of immune-related pathways. Molecular biology experiments verified a cancer suppressor role for FAIM2 in glioma. FAIM2 may serve as a potential pan-cancer biomarker for prognosis and immune infiltration, especially in glioma. Moreover, this study might provide a potential target for tumor immunotherapy.

High-throughput sequencing unravels the cell heterogeneity of cerebrospinal fluid in the bacterial meningitis of children

Bacterial meningitis (BM) is a common life-threatening infection in children that occurs in the central nervous system (CNS). The cytologic examination of cerebrospinal fluid (CSF) is a key parameter in the diagnosis of BM, but the heterogeneity of cells in the CSF has not been elucidated, which limits the current understanding of BM neuroinflammation. In this study, CSF samples were collected from a number of BM patients who were in different stages of disease progression. Single-cell RNA-sequencing (scRNA-seq), with additional bulk transcriptome sequencing, was conducted to decipher the characteristics of CSF cells in BM progression. A total of 18 immune cell clusters in CSF were identified, including two neutrophils, two monocytes, one macrophage, four myeloid dendritic cells, five T cells, one natural killer cell, one B cell, one plasmacytoid dendritic cell, and one plasma cell subtype. Their population profiles and dynamics in the initial onset, remission, and recovery stages during BM progression were also characterized, which showed decreased proportions of myeloid cells and increased proportions of lymphoid cells with disease progression. One novel neutrophil subtype, FFAR2+TNFAIP6+ neutrophils, and one novel monocyte subtype, THBS1+IL1B+ monocytes, were discovered, and their quantity changes positively correlated with the intensity of the inflammatory response in the CSF during BM. In addition, the CSF of BM patients with unsatisfactory therapeutic responses presented with different cell heterogeneity compared to the CSF of BM patients with satisfactory therapeutic responses, and their CSF featured altered intercellular communications and increased proportions of type II myeloid dendritic cells and plasmacytoid dendritic cells. Moreover, the bulk transcriptome profiles of autologous CSF cells and peripheral blood leukocytes of BM patients showed that the immune cells in these two physiological compartments exhibited distinct immune responses under different onset conditions. In particular, the CSF cells showed a high expression of macrophage characteristic genes and a low expression of platelet characteristic genes compared with peripheral blood leukocytes. Our study conducted an in-depth exploration of the characteristics of CSF cells in BM progression, which provided novel insights into immune cell engagement in acute CNS infection.

Regulation of mitochondrial proteostasis by the proton gradient

Mitochondria adapt to different energetic demands reshaping their proteome. Mitochondrial proteases are emerging as key regulators of these adaptive processes. Here, we use a multiproteomic approach to demonstrate the regulation of the m‐AAA protease AFG3L2 by the mitochondrial proton gradient, coupling mitochondrial protein turnover to the energetic status of mitochondria. We identify TMBIM5 (previously also known as GHITM or MICS1) as a Ca²⁺/H⁺ exchanger in the mitochondrial inner membrane, which binds to and inhibits the m‐AAA protease. TMBIM5 ensures cell survival and respiration, allowing Ca²⁺ efflux from mitochondria and limiting mitochondrial hyperpolarization. Persistent hyperpolarization, however, triggers degradation of TMBIM5 and activation of the m‐AAA protease. The m‐AAA protease broadly remodels the mitochondrial proteome and mediates the proteolytic breakdown of respiratory complex I to confine ROS production and oxidative damage in hyperpolarized mitochondria. TMBIM5 thus integrates mitochondrial Ca²⁺ signaling and the energetic status of mitochondria with protein turnover rates to reshape the mitochondrial proteome and adjust the cellular metabolism.

Traditional Chinese Medicine Ginseng Dingzhi Decoction Ameliorates Myocardial Fibrosis and High Glucose-Induced Cardiomyocyte Injury by Regulating Intestinal Flora and Mitochondrial Dysfunction

Myocardial fibrosis refers to the pathological changes of heart structure and morphology caused by various reasons of myocardial damage. It has become an important challenge in the later clinical treatment of acute myocardial infarction/ischemic cardiomyopathy or diabetes complicated with heart failure. Ginseng Dingzhi Decoction (GN), a Chinese herbal medicine, can reduce heart failure and protect cardiomyocytes. We infer that this may be related to the interaction with intestinal microbiota and mitochondrial homeostasis. The regulatory mechanism of GN on gut microbiota and mitochondria has not yet been elucidated. The intestinal microbiota was analyzed by the 16S rRNA gene; the fecal samples were sequenced and statistically analyzed to determine the changes of microbiota in the phenotype of heart failure rats. In addition, GN can regulate the microbial population that increases the proportion of short-chain fatty acids and anti-inflammatory bacteria and reduces the proportion of conditional pathogens to diabetic phenotype. The results suggest that GN may improve myocardial injury by regulating intestinal flora. Our data also show that stress-type heart failure caused by TAC (transverse aortic constriction) is accompanied by severe cardiac hypertrophy, reduced cardiac function, redox imbalance, and mitochondrial dysfunction. However, the use of GN intervention can significantly reduce heart failure and myocardial hypertrophy, improve heart function and improve myocardial damage, and maintain the mitochondrial homeostasis and redox of myocardial cells under high glucose stimulation. Interestingly, through in vitro experiments after TMBIM6 siRNA treatment, the improvement effect of GN on cell damage and the regulation of mitochondrial homeostasis were eliminated. TMBIM6 can indirectly regulate mitophagy and mitochondrial homeostasis to attenuate myocardial damage and confirms the regulatory effect of GN on mitophagy and mitochondrial homeostasis. We further intervened cardiomyocytes in high glucose through metformin (MET) and GN combination therapy. Research data show that MET and GN combination therapy can improve the level of mitophagy and protect cardiomyocytes. Our findings provide novel mechanistic insights for the treatment of diabetes combined with myocardial injury (myocardial fibrosis) and provide a pharmacological basis for the study of the combination of Chinese medicine and conventional diabetes treatment drugs.

Expression, purification and microscopic characterization of transmembrane BAX Inhibitor-1 motif containing protein 5

Transmembrane bax inhibitor-1 motif containing protein 5 (TMBIM5) is located on the inner membrane of mitochondria and is widely expressed in tissues but less frequently in the intestine and thymus. TMBIM5 affects mitochondrial cristae organization and is associated with Parkinson's disease. Here, we present the first report about expression, purification and the 2D classification projections derived from negatively stained electron micrographs of recombinant H. sapiens TMBIM5 (hTMBIM5). The described methods and results will support further structural and functional study of hTMBIM5.

Antioxidant supplements promote tumor formation and growth and confer drug resistance in hepatocellular carcinoma by reducing intracellular ROS and induction of TMBIM1

Background

Controversy over the benefits of antioxidants supplements in cancers persists for long. Using hepatocellular carcinoma (HCC) as a model, we investigated the effects of exogenous antioxidants N-acetylcysteine (NAC) and glutathione (GSH) on tumor formation and growth.

Methods

Multiple mouse models, including diethylnitrosamine (DEN)-induced and Trp53KO/C-MycOE-induced HCC models, mouse hepatoma cell and human HCC cell xenograft models with subcutaneous or orthotopic injection were used. In vitro assays including ROS assay, colony formation, sphere formation, proliferation, migration and invasion, apoptosis, cell cycle assays were conducted. Western blot was performed for protein expression and RNA-sequencing to identify potential gene targets.

Results

In these multiple different mouse and cell line models, we observed that NAC and GSH promoted HCC tumor formation and growth, accompanied with significant reduction of intracellular reactive oxygen species (ROS) levels. Moreover, NAC and GSH promoted cancer stemness, and abrogated the tumor-suppressive effects of Sorafenib both in vitro and in vivo. Exogenous supplementation of NAC or GSH reduced the expression of NRF2 and GCLC, suggesting the NRF2/GCLC-related antioxidant production pathway might be desensitized. Using transcriptomic analysis to identify potential gene targets, we found that TMBIM1 was significantly upregulated upon NAC and GSH treatment. Both TCGA and in-house RNA-sequence databases showed that TMBIM1 was overexpressed in HCC tumors. Stable knockdown of TMBIM1 increased the intracellular ROS; it also abolished the promoting effects of the antioxidants in HCC cells. On the other hand, BSO and SSA, inhibitors targeting NAC and GSH metabolism respectively, partially abrogated the pro-oncogenic effects induced by NAC and GSH in vitro and in vivo.

Conclusions

Our data implicate that exogenous antioxidants NAC and GSH, by reducing the intracellular ROS levels and inducing TMBIM expression, promoted HCC formation and tumor growth, and counteracted the therapeutic effect of Sorafenib. Our study provides scientific insight regarding the use of exogenous antioxidant supplements in cancers.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13578-021-00731-0.

Control of lysosomal-mediated cell death by the pH-dependent calcium channel RECS1

Programmed cell death is regulated by the balance between activating and inhibitory signals. Here, we have identified RECS1 (responsive to centrifugal force and shear stress 1) [also known as TMBIM1 (transmembrane BAX inhibitor motif containing 1)] as a proapoptotic member of the TMBIM family. In contrast to other proteins of the TMBIM family, RECS1 expression induces cell death through the canonical mitochondrial apoptosis pathway. Unbiased screening indicated that RECS1 sensitizes cells to lysosomal perturbations. RECS1 localizes to lysosomes, where it regulates their acidification and calcium content, triggering lysosomal membrane permeabilization. Structural modeling and electrophysiological studies indicated that RECS1 is a pH-regulated calcium channel, an activity that is essential to trigger cell death. RECS1 also sensitizes whole animals to stress in vivo in Drosophila melanogaster and zebrafish models. Our results unveil an unanticipated function for RECS1 as a proapoptotic component of the TMBIM family that ignites cell death programs at lysosomes.

Up-regulation of apoptotic- and cell survival-related gene pathways following exposures of western corn rootworm to B. thuringiensis crystalline pesticidal proteins in transgenic maize roots

BACKGROUND

Resistance of pest insect species to insecticides, including B. thuringiensis (Bt) pesticidal proteins expressed by transgenic plants, is a threat to global food security. Despite the western corn rootworm, Diabrotica virgifera virgifera, being a major pest of maize and having populations showing increasing levels of resistance to hybrids expressing Bt pesticidal proteins, the cell mechanisms leading to mortality are not fully understood.

RESULTS

Twenty unique RNA-seq libraries from the Bt susceptible D. v. virgifera inbred line Ped12, representing all growth stages and a range of different adult and larval exposures, were assembled into a reference transcriptome. Ten-day exposures of Ped12 larvae to transgenic Bt Cry3Bb1 and Gpp34/Tpp35Ab1 maize roots showed significant differential expression of 1055 and 1374 transcripts, respectively, compared to cohorts on non-Bt maize. Among these, 696 were differentially expressed in both Cry3Bb1 and Gpp34/Tpp35Ab1 maize exposures. Differentially-expressed transcripts encoded protein domains putatively involved in detoxification, metabolism, binding, and transport, were, in part, shared among transcripts that changed significantly following exposures to the entomopathogens Heterorhabditis bacteriophora and Metarhizium anisopliae. Differentially expressed transcripts in common between Bt and entomopathogen treatments encode proteins in general stress response pathways, including putative Bt binding receptors from the ATP binding cassette transporter superfamily. Putative caspases, pro- and anti-apoptotic factors, as well as endoplasmic reticulum (ER) stress-response factors were identified among transcripts uniquely up-regulated following exposure to either Bt protein.

CONCLUSIONS

Our study suggests that the up-regulation of genes involved in ER stress management and apoptotic progression may be important in determining cell fate following exposure of susceptible D. v. virgifera larvae to Bt maize roots. This study provides novel insights into insect response to Bt intoxication, and a possible framework for future investigations of resistance mechanisms.

[Bax inhibitor-1 inhibits calcification of vascular smooth muscle cells in vitro]

OBJECTIVE

To investigate the effect of Bax inhibitor-1(BI-1)on calcification of vascular smooth muscle cells(VSMCs).

METHODS

VSMCs were isolated from the thoracic aorta of SD rats.VSMCs or BI-1-overexpressing VSMCs(transfected with a BI-1-overexpressing plasmid) were cultured in normal medium or calcified medium containing β-glycerophosphate and calcium chloride, and the cell calcification was examined with Alizarin red staining.Enzyme-linked immunosorbent assay was used to determine the intracellular calcium content and alkaline phosphatase activity.The expression levels of Runt-related transcription factor 2 (RUNX2), bone morphogenetic protein 2 (BMP-2) and caspase-3 were detected with Western blotting.

RESULTS

After 14 days of culture in the calcified medium, the VSMCs showed significantly reduced expression of BI-1 protein(P=0.001).BI-1 overexpression in the VSMCs caused a significant reduction of calcium level and alkaline phosphatase activities(P=0.0006) and lowered the expression levels of RUNX2 and BMP-2 (P=0.0001) in the cells.The VSMCs with induced calcification exhibited a significantly increased apoptosis rate, but BI-1 overexpression obviously inhibited VSMC apoptosis in the calcified medium (P=0.0003).

CONCLUSION

BI-1 may attenuate vascular calcification by inhibiting calcium deposition, osteogenic differentiation and apoptosis.

tmbim4 protects against triclocarban-induced embryonic toxicity in zebrafish by regulating autophagy and apoptosis

Triclocarban (TCC), an antibacterial agent widely used in personal care products, can affect embryonic development. However, the specific molecular mechanism of TCC-induced embryonic developmental damage remains unclear. In this study, TCC exposure was found to increase the expression of tmbim4 gene in zebrafish embryos. The tmbim4 mutant embryos are more susceptible to TCC exposure than wild-type (WT) embryos, with tmbim4 overexpression reducing TCC-induced embryonic death in the former. Exposure of tmbim4 mutant larvae to 400 μg/L TCC substantially increased apoptosis in the hindbrain and eyes. RNA-sequencing of WT and tmbim4 mutant larvae indicated that knockout of the tmbim4 gene in zebrafish affects the autophagy pathway. Abnormalities in autophagy can increase apoptosis and TCC exposure caused abnormal accumulation of autophagosomes in the hindbrain of tmbim4 mutant zebrafish embryos. Pretreatment of TCC-exposed tmbim4 mutant zebrafish embryos with autophagosome formation inhibitors, substantially reduced the mortality of embryos and apoptosis levels. These results indicate that defects in the tmbim4 gene can reduce zebrafish embryo resistance to TCC. Additionally, apoptosis induced by abnormal accumulation of autophagosomes is involved in this process.

A comprehensive overview of the complex world of the endo- and sarcoplasmic reticulum Ca2+-leak channels

Inside cells, the endoplasmic reticulum (ER) forms the largest Ca²⁺ store. Ca²⁺ is actively pumped by the SERCA pumps in the ER, where intraluminal Ca²⁺-binding proteins enable the accumulation of large amount of Ca²⁺. IP₃ receptors and the ryanodine receptors mediate the release of Ca²⁺ in a controlled way, thereby evoking complex spatio-temporal signals in the cell. The steady state Ca²⁺ concentration in the ER of about 500 μM results from the balance between SERCA-mediated Ca²⁺ uptake and the passive leakage of Ca²⁺. The passive Ca²⁺ leak from the ER is often ignored, but can play an important physiological role, depending on the cellular context. Moreover, excessive Ca²⁺ leakage significantly lowers the amount of Ca²⁺ stored in the ER compared to normal conditions, thereby limiting the possibility to evoke Ca²⁺ signals and/or causing ER stress, leading to pathological consequences. The so-called Ca²⁺-leak channels responsible for Ca²⁺ leakage from the ER are however still not well understood, despite over 20 different proteins have been proposed to contribute to it. This review has the aim to critically evaluate the available evidence about the various channels potentially involved and to draw conclusions about their relative importance.

Structure and regulation of the BsYetJ calcium channel in lipid nanodiscs

BsYetJ is a bacterial homolog of transmembrane BAX inhibitor-1 motif-containing 6 (TMBIM6) membrane protein that plays a key role in the control of calcium homeostasis. However, the BsYetJ (or TMBIM6) structure embedded in a lipid bilayer is uncharacterized, let alone the molecular mechanism of the calcium transport activity. Herein, we report structures of BsYetJ in lipid nanodiscs identified by double electron-electron resonance spectroscopy. Our results reveal that BsYetJ in lipid nanodiscs is structurally different from those crystallized in detergents. We show that BsYetJ conformation is pH-sensitive in apo state (lacking calcium), whereas in a calcium-containing solution it is stuck in an intermediate, inert to pH changes. Only when the transmembrane calcium gradient is established can the calcium-release activity of holo-BsYetJ occur and be mediated by pH-dependent conformational changes, suggesting a dual gating mechanism. Conformational substates involved in the process and a key residue D171 relevant to the gating of calcium are identified. Our study suggests that BsYetJ/TMBIM6 is a pH-dependent, voltage-gated calcium channel.

Development on Citrus medica infected with 'Candidatus Liberibacter asiaticus' has sex-specific and -nonspecific impacts on adult Diaphorina citri and its endosymbionts

Huanglongbing (HLB) is a deadly, incurable citrus disease putatively caused by the unculturable bacterium, 'Candidatus Liberibacter asiaticus' (CLas), and transmitted by Diaphorina citri. Prior studies suggest D. citri transmits CLas in a circulative and propagative manner; however, the precise interactions necessary for CLas transmission remain unknown, and the impact of insect sex on D. citri-CLas interactions is poorly understood despite reports of sex-dependent susceptibilities to CLas. We analyzed the transcriptome, proteome, metabolome, and microbiome of male and female adult D. citri reared on healthy or CLas-infected Citrus medica to determine shared and sex-specific responses of D. citri and its endosymbionts to CLas exposure. More sex-specific than shared D. citri responses to CLas were observed, despite there being no difference between males and females in CLas density or relative abundance. CLas exposure altered the abundance of proteins involved in immunity and cellular and oxidative stress in a sex-dependent manner. CLas exposure impacted cuticular proteins and enzymes involved in chitin degradation, as well as energy metabolism and abundance of the endosymbiont 'Candidatus Profftella armatura' in both sexes similarly. Notably, diaphorin, a toxic Profftella-derived metabolite, was more abundant in both sexes with CLas exposure. The responses reported here resulted from a combination of CLas colonization of D. citri as well as the effect of CLas infection on C. medica. Elucidating these impacts on D. citri and their endosymbionts contributes to our understanding of the HLB pathosystem and identifies the responses potentially critical to limiting or promoting CLas acquisition and propagation in both sexes.

Transmembrane BAX Inhibitor-1 Motif Containing Protein 5 (TMBIM5) Sustains Mitochondrial Structure, Shape, and Function by Impacting the Mitochondrial Protein Synthesis Machinery

The Transmembrane Bax Inhibitor-1 motif (TMBIM)-containing protein family is evolutionarily conserved and has been implicated in cell death susceptibility. The only member with a mitochondrial localization is TMBIM5 (also known as GHITM or MICS1), which affects cristae organization and associates with the Parkinson's disease-associated protein CHCHD2 in the inner mitochondrial membrane. We here used CRISPR-Cas9-mediated knockout HAP1 cells to shed further light on the function of TMBIM5 in physiology and cell death susceptibility. We found that compared to wild type, TMBIM5-knockout cells were smaller and had a slower proliferation rate. In these cells, mitochondria were more fragmented with a vacuolar cristae structure. In addition, the mitochondrial membrane potential was reduced and respiration was attenuated, leading to a reduced mitochondrial ATP generation. TMBIM5 did not associate with Mic10 and Mic60, which are proteins of the mitochondrial contact site and cristae organizing system (MICOS), nor did TMBIM5 knockout affect their expression levels. TMBIM5-knockout cells were more sensitive to apoptosis elicited by staurosporine and BH3 mimetic inhibitors of Bcl-2 and Bcl-XL. An unbiased proteomic comparison identified a dramatic downregulation of proteins involved in the mitochondrial protein synthesis machinery in TMBIM5-knockout cells. We conclude that TMBIM5 is important to maintain the mitochondrial structure and function possibly through the control of mitochondrial biogenesis.

Getting intimate: Lysosomes and ER rendezvous to control autophagy

The endoplasmic reticulum (ER) is the source of lysosomal calcium. The finding that the protein TMBIM6 -a putative ER calcium channel and cell death regulator -promotes calcium transfer from the ER to lysosomes to induce autophagy uncovers a missing piece in the puzzle of inter-organelle communication.

Mechanisms, regulation and functions of the unfolded protein response

Cellular stress induced by the abnormal accumulation of unfolded or misfolded proteins at the endoplasmic reticulum (ER) is emerging as a possible driver of human diseases, including cancer, diabetes, obesity and neurodegeneration. ER proteostasis surveillance is mediated by the unfolded protein response (UPR), a signal transduction pathway that senses the fidelity of protein folding in the ER lumen. The UPR transmits information about protein folding status to the nucleus and cytosol to adjust the protein folding capacity of the cell or, in the event of chronic damage, induce apoptotic cell death. Recent advances in the understanding of the regulation of UPR signalling and its implications in the pathophysiology of disease might open new therapeutic avenues.

Defective Sec61α1 underlies a novel cause of autosomal dominant severe congenital neutropenia

Background

The molecular cause of severe congenital neutropenia (SCN) is unknown in 30% to 50% of patients. SEC61A1 encodes the α-subunit of the Sec61 complex, which governs endoplasmic reticulum protein transport and passive calcium leakage. Recently, mutations in SEC61A1 were reported to be pathogenic in common variable immunodeficiency and glomerulocystic kidney disease.

Objective

Our aim was to expand the spectrum of SEC61A1-mediated disease to include autosomal dominant SCN.

Methods

Whole exome sequencing findings were validated, and reported mutations were compared by Western blotting, Ca2⁺ flux assays, differentiation of transduced HL-60 cells, in vitro differentiation of primary CD34 cells, quantitative PCR for unfolded protein response (UPR) genes, and single-cell RNA sequencing on whole bone marrow.

Results

We identified a novel de novo missense mutation in SEC61A1 (c.A275G;p.Q92R) in a patient with SCN who was born to nonconsanguineous Belgian parents. The mutation results in diminished protein expression, disturbed protein translocation, and an increase in calcium leakage from the endoplasmic reticulum. In vitro differentiation of CD34⁺ cells recapitulated the patient’s clinical arrest in granulopoiesis. The impact of Q92R-Sec61α1 on neutrophil maturation was validated by using HL-60 cells, in which transduction reduced differentiation into CD11b⁺CD16⁺ cells. A potential mechanism for this defect is the uncontrolled initiation of the unfolded protein stress response, with single-cell analysis of primary bone marrow revealing perturbed UPR in myeloid precursors and in vitro differentiation of primary CD34⁺ cells revealing upregulation of CCAAT/enhancer-binding protein homologous protein and immunoglobulin heavy chain binding protein UPR-response genes.

Conclusion

Specific mutations in SEC61A1 cause SCN through dysregulation of the UPR.

Bcl-2-Protein Family as Modulators of IP3 Receptors and Other Organellar Ca2+ Channels

The pro- and antiapoptotic proteins belonging to the B-cell lymphoma-2 (Bcl-2) family exert a critical control over cell-death processes by enabling or counteracting mitochondrial outer membrane permeabilization. Beyond this mitochondrial function, several Bcl-2 family members have emerged as critical modulators of intracellular Ca²⁺ homeostasis and dynamics, showing proapoptotic and antiapoptotic functions. Bcl-2 family proteins specifically target several intracellular Ca²⁺-transport systems, including organellar Ca²⁺ channels: inositol 1,4,5-trisphosphate receptors (IP₃Rs) and ryanodine receptors (RyRs), Ca²⁺-release channels mediating Ca²⁺ flux from the endoplasmic reticulum, as well as voltage-dependent anion channels (VDACs), which mediate Ca²⁺ flux across the mitochondrial outer membrane into the mitochondria. Although the formation of protein complexes between Bcl-2 proteins and these channels has been extensively studied, a major advance during recent years has been elucidating the complex interaction of Bcl-2 proteins with IP₃Rs. Distinct interaction sites for different Bcl-2 family members were identified in the primary structure of IP₃Rs. The unique molecular profiles of these Bcl-2 proteins may account for their distinct functional outcomes when bound to IP₃Rs. Furthermore, Bcl-2 inhibitors used in cancer therapy may affect IP₃R function as part of their proapoptotic effect and/or as an adverse effect in healthy cells.

BAX inhibitor-1: between stress and survival

Cellular gatekeepers are essential to maintain order within a cell and anticipate signals of stress to promote survival. BCL2 associated X, apoptosis regulator (BAX) inhibitor-1 (BI-1), also named transmembrane BAX inhibitor motif containing-6, is a highly conserved endoplasmic reticulum (ER) transmembrane protein. Originally identified as an inhibitor of BAX-induced apoptosis, its pro-survival properties have been expanded to include functions targeted against ER stress, calcium imbalance, reactive oxygen species accumulation, and metabolic dysregulation. Nevertheless, the structural biology and biochemical mechanism of action of BI-1 are still under debate. BI-1 has been implicated in several diseases, including chronic liver disease, diabetes, ischemia/reperfusion injury, neurodegeneration, and cancer. While most studies have demonstrated a beneficial role for BI-1 in the ubiquitous maintenance of cellular homeostasis, its expression in cancer cells seems most often to contribute to tumorigenesis and metastasis. Here, we summarize what is known about BI-1 and encourage future studies on BI-1's contribution to cellular life and death decisions to advocate its potential as a target for drug development and other therapeutic strategies.

Golgi pH and Ion Homeostasis in Health and Disease

Maintenance of the main Golgi functions, glycosylation and sorting, is dependent on the unique Golgi pH microenvironment that is thought to be set by the balance between the rates of V-ATPase-mediated proton pumping and its leakage back to the cytoplasm via an unknown pathway. The concentration of other ions, such as chloride, potassium, calcium, magnesium, and manganese, is also important for Golgi homeostasis and dependent on the transport activity of other ion transporters present in the Golgi membranes. During the last decade, several new disorders have been identified that are caused by, or are associated with, dysregulated Golgi pH and ion homeostasis. Here, we will provide an updated overview on these disorders and the proteins involved. We will also discuss other disorders for which the molecular defects remain currently uncertain but which potentially involve proteins that regulate Golgi pH or ion homeostasis.

Bax Inhibitor 1 (BI-1) as a conservative regulator of Programmed Cell Death

Programmed cell death (PCD) is a physiological process in which infected or unnecessary cells due to their suicidal death capability can be selectively eliminated. Pro- and antiapoptotic proteins play an important role in the induction or inhibition of this process. Presented article shows property of Bax-1 (BI-1) inhibitor which is one of the conservative protein associated with the endoplasmic reticulum (ER) as well as its cytoprotective role in the regulation of cellular processes. It was shown that: 1) BI-1 is a small protein consisting of 237 amino acids (human protein - 36 kDa) and has 6 (in animals) and 7 (in plants) α-helical transmembrane domains, 2) BI-1 is expressed in all organisms and in most tissues, moreover its level depends on the functional condition of cells and it is involved in the development or reaction to biotic and abiotic stresses, 3) BI-1 forms a pH-dependent Ca2+ channel enabling release of these ions from the ER, 4) cytoprotective effects of BI-1 requires a whole, unchanged C-terminus, 5) BI-1 can interact directly with numerous other proteins, BI-1 protein affects numerous cellular processes, including: counteracting ER stress, oxidative stress, loss of cellular Ca2+ homeostasis as well as this protein influences on sphingolipid metabolism, autophagy, actin polymerization, lysosomal activity and cell proliferation. Studies of BI-1 functions will allow understanding the mechanisms of anticancer therapy or increases the knowledge of crop tolerance to environmental stresses.

Calcium & ROS: Two orchestra directors for the requiem of death

Tumor necrosis factor alpha (TNF) triggers regulated necrosis of mycobacterium-infected macrophages through of mitochondrial reactive oxygen species (mitoROS) production in a RIPK1/3-dependent manner. To explain that, Roca and colleagues describe an inter-orgallenar circuit which involves the lysosomal ceramide production, mitoROS, BAX activation and RyR Ca²⁺ efflux from the endoplasmic reticulum into the mitochondrion.

Adenoviral TMBIM6 vector attenuates ER-stress-induced apoptosis in a neonatal hypoxic-ischemic rat model

Endoplasmic reticulum (ER) stress is a major pathology encountered after hypoxic-ischemic (HI) injury. Accumulation of unfolded proteins triggers the unfolded protein response (UPR), resulting in the activation of pro-apoptotic cascades that lead to cell death. Here, we identified Bax inhibitor 1 (BI-1), an evolutionarily conserved protein encoded by the transmembrane BAX inhibitor motif-containing 6 (TMBIM6) gene, as a novel modulator of ER-stress-induced apoptosis after HI brain injury in a neonatal rat pup. The main objective of our study was to overexpress BI-1, via viral-mediated gene delivery of human adenoviral-TMBIM6 (Ad-TMBIM6) vector, to investigate its anti-apoptotic effects as well as to elucidate its signaling pathways in an in vivo neonatal HI rat model and in vitro oxygen-glucose deprivation (OGD) model. Ten-day-old unsexed Sprague Dawley rat pups underwent right common carotid artery ligation followed by 1.5 h of hypoxia. Rat pups injected with Ad-TMBIM6 vector, 48 h pre-HI, showed a reduction in relative infarcted area size, attenuated neuronal degeneration and improved long-term neurological outcomes. Furthermore, silencing of BI-1 or further activating the IRE1α branch of the UPR, using a CRISPR activation plasmid, was shown to reverse the protective effects of BI-1. Based on our in vivo and in vitro data, the protective effects of BI-1 are mediated via inhibition of IRE1α signaling and in part via inhibition of the second stress sensor receptor, PERK. Overall, this study showed a novel role for BI-1 and ER stress in the pathophysiology of HI and could provide a basis for BI-1 as a potential therapeutic target.

EPO and TMBIM3/GRINA Promote the Activation of the Adaptive Arm and Counteract the Terminal Arm of the Unfolded Protein Response after Murine Transient Cerebral Ischemia

Ischemic stroke is known to cause the accumulation of misfolded proteins and loss of calcium homeostasis leading to impairment of endoplasmic reticulum (ER) function. The unfolded protein response (UPR) is an ER-located and cytoprotective pathway that aims to resolve ER stress. Transmembrane BAX inhibitor-1 motif-containing (TMBIM) protein family member TMBIM3/GRINA is highly expressed in the brain and mostly located at the ER membrane suppressing ER calcium release by inositol-1,4,5-trisphosphate receptors. GRINA confers neuroprotection and is regulated by erythropoietin (EPO) after murine cerebral ischemia. However, the role of GRINA and the impact of EPO treatment on the post-ischemic UPR have not been elucidated yet. We subjected GRINA-deficient (Grina^−/−) and wildtype mice to transient (30 min) middle cerebral artery occlusion (tMCAo) followed by 6 h or 72 h of reperfusion. We administered EPO or saline 0, 24 and 48 h after tMCAo/sham surgery. Oxygen–glucose deprivation (OGD) and pharmacological stimulation of the UPR using Tunicamycin and Thapsigargin were carried out in primary murine cortical mixed cell cultures. Treatment with the PERK-inhibitor GSK-2606414, IRE1a-RNase-inhibitor STF-083010 and EPO was performed 1 h prior to either 1 h, 2 h or 3 h of OGD. We found earlier and larger infarct demarcations in Grina^−/− mice compared to wildtype mice, which was accompanied by a worse neurological outcome and an abolishment of EPO-mediated neuroprotection after ischemic stroke. In addition, GRINA-deficiency increased apoptosis and the activation of the corresponding PERK arm of the UPR after stroke. EPO enhanced the post-ischemic activation of pro-survival IRE1a and counteracted the pro-apoptotic PERK branch of the UPR. Both EPO and the PERK-inhibitor GSK-2606414 reduced cell death and regulated Grina mRNA levels after OGD. In conclusion, GRINA plays a crucial role in post-ischemic UPR and the use of both GSK-2606414 and EPO might lead to neuroprotection.

EPO regulates neuroprotective Transmembrane BAX Inhibitor-1 Motif-containing (TMBIM) family members GRINA and FAIM2 after cerebral ischemia-reperfusion injury

BACKGROUND AND PURPOSE

Transmembrane BAX Inhibitor-1 Motif-containing (TMBIM) family members exert inhibitory activities in apoptosis and necroptosis. FAIM2 (TMBIM-2) is neuroprotective against murine focal ischemia and is regulated by erythropoietin (EPO). Similar to FAIM2, GRINA (TMBIM-3) is predominantly expressed in the brain. The role of GRINA in transient brain ischemia, its potential synergistic effects with FAIM2 and its regulation by EPO treatment were assessed.

METHODS

We performed transient (30 min) middle cerebral artery occlusion (tMCAo) followed by 72 h of reperfusion in GRINA-deficient (GRINA-/-), FAIM2-deficient (FAIM2-/-), double-deficient (GRINA-/-FAIM2-/-) and wildtype littermates (WT) mice. We administered EPO or saline 0, 24 and 48 h after tMCAo. We subjected primary murine cortical neurons (pMCN) of all mouse strains to oxygen-glucose deprivation (OGD) after GRINA and/or FAIM2 gene transfection.

RESULTS

Compared to wildtype controls GRINA deficiency led to a similar increase in infarct volumes as FAIM2 deficiency (p < .01). We observed the highest neurological deficits and largest infarct sizes in double-deficient mice. EPO administration upregulated GRINA and FAIM2 mRNA levels in wildtype littermates. EPO decreased infarct sizes and abrogated neurological impairments in wildtype controls. GRINA and/or FAIM2 deficient mice showed increased expression levels of cleaved-caspase 3 and of pro-apoptotic BAX mRNA. Further, caspase 8 was upregulated in FAIM2-/- and caspase 9 in GRINA-/- mice. Overexpression of GRINA and FAIM2 in wildtype and in double deficient pMCN decreased cell death rate after OGD.

CONCLUSIONS

GRINA and FAIM2 are highly expressed in the brain and convey EPO-mediated neuroprotection after ischemic stroke involving different caspases.

Deciphering GRINA/Lifeguard1: Nuclear Location, Ca2+ Homeostasis and Vesicle Transport

The Glutamate Receptor Ionotropic NMDA-Associated Protein 1 (GRINA) belongs to the Lifeguard family and is involved in calcium homeostasis, which governs key processes, such as cell survival or the release of neurotransmitters. GRINA is mainly associated with membranes of the endoplasmic reticulum, Golgi, endosome, and the cell surface, but its presence in the nucleus has not been explained yet. Here we dissect, with the help of different software tools, the potential roles of GRINA in the cell and how they may be altered in diseases, such as schizophrenia or celiac disease. We describe for the first time that the cytoplasmic N-terminal half of GRINA (which spans a Proline-rich domain) contains a potential DNA-binding sequence, in addition to cleavage target sites and probable PY-nuclear localization sequences, that may enable it to be released from the rest of the protein and enter the nucleus under suitable conditions, where it could participate in the transcription, alternative splicing, and mRNA export of a subset of genes likely involved in lipid and sterol synthesis, ribosome biogenesis, or cell cycle progression. To support these findings, we include additional evidence based on an exhaustive review of the literature and our preliminary data of the protein–protein interaction network of GRINA.

Golgi pH, Ion and Redox Homeostasis: How Much Do They Really Matter?

Exocytic and endocytic compartments each have their own unique luminal ion and pH environment that is important for their normal functioning. A failure to maintain this environment - the loss of homeostasis - is not uncommon. In the worst case, all the main Golgi functions, including glycosylation, membrane trafficking and protein sorting, can be perturbed. Several factors contribute to Golgi homeostasis. These include not only ions such as H⁺, Ca²⁺, Mg²⁺, Mn²⁺, but also Golgi redox state and nitric oxide (NO) levels, both of which are dependent on the oxygen levels in the cells. Changes to any one of these factors have consequences on Golgi functions, the nature of which can be dissimilar or similar depending upon the defects themselves. For example, altered Golgi pH homeostasis gives rise to Cutis laxa disease, in which glycosylation and membrane trafficking are both affected, while altered Ca²⁺ homeostasis due to the mutated SCPA1 gene in Hailey-Hailey disease, perturbs various protein sorting, proteolytic cleavage and membrane trafficking events in the Golgi. This review gives an overview of the molecular machineries involved in the maintenance of Golgi ion, pH and redox homeostasis, followed by a discussion of the organelle dysfunction and disease that frequently result from their breakdown. Congenital disorders of glycosylation (CDGs) are discussed only when they contribute directly to Golgi pH, ion or redox homeostasis. Current evidence emphasizes that, rather than being mere supporting factors, Golgi pH, ion and redox homeostasis are in fact key players that orchestrate and maintain all Golgi functions.

Deficiency in the membrane protein Tmbim3a/Grinaa initiates cold-induced ER stress and cell death by activating an intrinsic apoptotic pathway in zebrafish

Most members of the family of proteins containing a transmembrane BAX inhibitor motif (TMBIM) have anti-apoptotic activity, but their in vivo functions and intracellular mechanisms remain obscure. Here, we report that zebrafish Tmbim3a/Grinaa functions in the prevention of cold-induced endoplasmic reticulum (ER) stress and apoptosis. Using a gene-trapping approach, we obtained a mutant zebrafish line in which the expression of the tmbim3a/grinaa gene is disrupted by a Tol2 transposon insertion. Homozygous tmbim3a/grinaa mutant larvae exhibited time-dependently increased mortality and apoptosis under cold exposure (at 16 °C). Mechanistically, using immunofluorescence, fluorescence-based assessments of intracellular/mitochondrial Ca²⁺ levels, mitochondrial membrane potential measurements, and Ca²⁺-ATPase assays, we found that cold exposure suppresses sarcoplasmic/ER Ca²⁺-ATPase (SERCA) activity and induces the unfolded protein response (UPR) and ER stress. We also found that the cold-induced ER stress is increased in homozygous tmbim3a/grinaa mutant embryos. The cold-stress hypersensitivity of the tmbim3a/grinaa mutants was tightly associated with disrupted intracellular Ca²⁺ homeostasis, followed by mitochondrial Ca²⁺ overload and cytochrome c release, leading to the activation of caspase 9- and caspase-3-mediated intrinsic apoptotic pathways. Treatment of zebrafish larvae with the intracellular Ca²⁺ chelator 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetate-acetoxymethyl ester (BAPTA-AM) or with 2-aminoethoxydiphenyl borate (2-APB), an inhibitor of the calcium-releasing protein inositol 1,4,5-trisphosphate receptor (IP₃R), alleviated cold-induced cell death. Together, these findings unveil a key role of Tmbim3a/Grinaa in relieving cold-induced ER stress and in protecting cells against caspase 9- and caspase 3-mediated apoptosis during zebrafish development.

Ion and pH Sensitivity of a TMBIM Ca2+ Channel

The anti-apoptotic transmembrane Bax inhibitor motif (TMBIM) containing protein family regulates Ca2+ homeostasis, cell death, and the progression of diseases including cancers. The recent crystal structures of the TMBIM homolog BsYetJ reveal a conserved Asp171-Asp195 dyad that is proposed in regulating a pH-dependent Ca2+ translocation. Here we show that BsYetJ mediates Ca2+ fluxes in permeabilized mammalian cells, and its interaction with Ca2+ is sensitive to protons and other cations. We report crystal structures of BsYetJ in additional states, revealing the flexibility of the dyad in a closed state and a pore-opening mechanism. Functional studies show that the dyad is responsible for both Ca2+ affinity and pH dependence. Computational simulations suggest that protonation of Asp171 weakens its interaction with Arg60, leading to an open state. Our integrated analysis provides insights into the regulation of the BsYetJ Ca2+ channel that may inform understanding of human TMBIM proteins regarding their roles in cell death and diseases.

The characteristics of the ancient cell death suppressor, TMBIM6, and its related signaling pathways after endoplasmic reticulum stress

Activation of the unfolded protein response in combination with generation of reactive oxygen species, from cytochrome P450 members and NADPH-P450 reductases, are two major consequences of Endoplasmic Reticulum (ER) stress that cause oxidative damage and cell death. Herein, we reviewed the role of Bax Inhibitor-1 (BI-1), an evolutionarily conserved protein encoded by the Transmembrane Bax inhibitor Motif Containing 6 gene, in protection from ER stress. As BI-1 has multimodal properties that can target a wide array of pathophysiological consequences after injury, our main objective was to explore BI-1's protective role in ER stress and its potential signaling pathways.

Transcriptome and Proteome Response of Rhipicephalus annulatus Tick Vector to Babesia bigemina Infection

A system biology approach was used to gain insight into tick biology and interactions between vector and pathogen. Rhipicephalus annulatus is one of the main vectors of Babesia bigemina which has a massive impact on animal health. It is vital to obtain more information about this relationship, to better understand tick and pathogen biology, pathogen transmission dynamics, and new potential control approaches. In ticks, salivary glands (SGs) play a key role during pathogen infection and transmission. RNA sequencing obtained from uninfected and B. bigemina infected SGs obtained from fed female ticks resulted in 6823 and 6475 unigenes, respectively. From these, 360 unigenes were found to be differentially expressed (p < 0.05). Reversed phase liquid chromatography-mass spectrometry identified a total of 3679 tick proteins. Among them 406 were differently represented in response to Babesia infection. The omics data obtained suggested that Babesia infection lead to a reduction in the levels of mRNA and proteins (n = 237 transcripts, n = 212 proteins) when compared to uninfected controls. Integrated transcriptomics and proteomics datasets suggested a key role for stress response and apoptosis pathways in response to infection. Thus, six genes coding for GP80, death-associated protein kinase (DAPK-1), bax inhibitor-1 related (BI-1), heat shock protein (HSP), heat shock transcription factor (PHSTF), and queuine trna-ribosyltransferase (QtRibosyl) were selected and RNA interference (RNAi) performed. Gene silencing was obtained for all genes except phstf. Knockdown of gp80, dapk-1, and bi-1 led to a significant increase in Babesia infection levels while hsp and QtRibosyl knockdown resulted in a non-significant decrease of infection levels when compared to the respective controls. Gene knockdown did not affect tick survival, but engorged female weight and egg production were affected in the gp80, dapk-1, and QtRibosyl-silenced groups in comparison to controls. These results advanced our understanding of tick-Babesia molecular interactions, and suggested new tick antigens as putative targets for vaccination to control tick infestations and pathogen infection/transmission.

Hypoxia and Reactive Oxygen Species as Modulators of Endoplasmic Reticulum and Golgi Homeostasis

SIGNIFICANCE

Eukaryotic cells execute various functions in subcellular compartments or organelles for which cellular redox homeostasis is of importance. Apart from mitochondria, hypoxia and stress-mediated formation of reactive oxygen species (ROS) were shown to modulate endoplasmic reticulum (ER) and Golgi apparatus (GA) functions. Recent Advances: Research during the last decade has improved our understanding of disulfide bond formation, protein glycosylation and secretion, as well as pH and redox homeostasis in the ER and GA. Thus, oxygen (O₂) itself, NADPH oxidase (NOX) formed ROS, and pH changes appear to be of importance and indicate the intricate balance of intercompartmental communication.

CRITICAL ISSUES

Although the interplay between hypoxia, ER stress, and Golgi function is evident, the existence of more than 20 protein disulfide isomerase family members and the relative mild phenotypes of, for example, endoplasmic reticulum oxidoreductin 1 (ERO1)- and NOX4-knockout mice clearly suggest the existence of redundant and alternative pathways, which remain largely elusive.

FUTURE DIRECTIONS

The identification of these pathways and the key players involved in intercompartmental communication needs suitable animal models, genome-wide association, as well as proteomic studies in humans. The results of those studies will be beneficial for the understanding of the etiology of diseases such as type 2 diabetes, Alzheimer's disease, and cancer, which are associated with ROS, protein aggregation, and glycosylation defects.

Chemical biology suggests pleiotropic effects for a novel hexanuclear copper(ii) complex inducing apoptosis in hepatocellular carcinoma cells

A new hexanuclear copper(ii) complex proved potential chemotherapeutic applicability in inducing apoptosis in cancer calls by acting on multiple targets and signaling pathways.

Transmembrane protein GRINA modulates aerobic glycolysis and promotes tumor progression in gastric cancer

BACKGROUND

Recent observations indicate a decreased cancer risk in patients with Alzheimer's disease (AD). AD is a severe neurodegenerative disorder characterized by progressive cognitive decline. The 8q24 region has been shown to be involved in AD aetiology. We aimed to identify and explore the potential oncogenes or antioncogenes on chromosome 8q24.

METHODS

We compared expression of genes on Chromosome 8q24 in 32 pairs of samples from The Cancer Genome Atlas (TCGA) database. We conducted bioinformatics analysis of the commonly used gastric cancer databases and performed clinical verification of gastric cancer samples, combined with assessment of biological function both in vitro and in vivo to determine the relationship between upregulated expression of GRINA and gastric cancer progression. We also explored the molecular mechanism of GRINA upregulation and its function in gastric cancer development and progression.

RESULTS

The expression of GRINA in cancer tissues was significantly higher than that in normal tissues. GRINA indicated poor prognosis in gastric cancer. GRINA promoted the proliferation, migration and invasion capacity of gastric cancer cells. GRINA was transcriptionally mediated by c-Myc and promotes cell cycle transition. GRINA knockdown decreased PI3K/Akt/mTOR signaling and glycolytic metabolism in gastric cancer cells. The apoptosis rate was significantly increased in gastric cancer cell lines after knockdown of GRINA. The expression of pro-apoptotic protein Bax was significantly upregulated, whereas the anti-apoptotic protein Bcl-2 was significantly downregulated in GRINA silenced cells.

CONCLUSIONS

Human gastric cancers have increased levels of GRINA, which promotes growth of gastric cancer and inhibits tumor cells apoptosis.

Human cytomegalovirus US21 protein is a viroporin that modulates calcium homeostasis and protects cells against apoptosis

The human cytomegalovirus (HCMV) US12 gene family comprises a set of 10 contiguous genes (US12 to US21) with emerging roles in the regulation of virus cell tropism, virion composition, and immunoevasion. Of all of the US12 gene products, pUS21 shows the highest level of identity with two cellular transmembrane BAX inhibitor motif-containing (TMBIM) proteins: Bax inhibitor-1 and Golgi anti-apoptotic protein, both of which are involved in the regulation of cellular Ca²⁺ homeostasis and adaptive cell responses to stress conditions. Here, we report the US21 protein to be a viral-encoded ion channel that regulates intracellular Ca²⁺ homeostasis and protects cells against apoptosis. Indeed, we show pUS21 to be a 7TMD protein expressed with late kinetics that accumulates in ER-derived vesicles. Deletion or inactivation of the US21 gene resulted in reduced HCMV growth, even in fibroblasts, due to reduced gene expression. Ratiometric fluorescence imaging assays revealed that expression of pUS21 reduces the Ca²⁺ content of intracellular ER stores. An increase in cell resistance to intrinsic apoptosis was then observed as an important cytobiological consequence of the pUS21-mediated alteration of intracellular Ca²⁺ homeostasis. Moreover, a single point mutation in the putative pore of pUS21 impaired the reduction of ER Ca²⁺ concentration and attenuated the antiapoptotic activity of pUS21wt, supporting a functional link with its ability to manipulate Ca²⁺ homeostasis. Together, these results suggest pUS21 of HCMV constitutes a TMBIM-derived viroporin that may contribute to HCMV's overall strategy to counteract apoptosis in infected cells.