LFG: a candidate apoptosis regulatory gene family

Heterologous VvDREB2c Expression Improves Heat Tolerance in Arabidopsis by Inducing Photoprotective Responses

Extreme temperatures limit grape production and sustainability. Dehydration-responsive element-binding (DREB) transcription factors affect plant responses to temperature related stresses. Therefore, we investigated the role of VvDREB2c, a DREB-coding gene, found in grapes (Vitis vinifera L.). Protein characterization revealed that VvDREB2c is localized to the nucleus and that its AP2/ERF domain contains three β-sheets and one α-helix sheet. Analysis of the VvDREB2c promoter region revealed the presence of light-, hormone-, and stress-related cis-acting elements. Furthermore, we observed that the heterologous expression of VvDREB2c in Arabidopsis improved growth, drought tolerance, and heat tolerance. Furthermore, it improved the leaf quantum yield of regulated energy dissipation [Y(NPQ)], elevated the activities of RuBisCO, and phosphoenolpyruvate carboxylase and reduced the quantum yield of non-regulated energy dissipation [Y(NO)] in plants exposed to high temperatures. VvDREB2c-overexpressing lines also specifically upregulated several photosynthesis-related genes (CSD2, HSP21, and MYB102). In addition, VvDREB2c-overexpressing lines reduced light damage and enhanced photoprotective ability by dissipating excess light energy and converting it into heat, which eventually improves tolerance to high temperature. The contents of abscisic acid, jasmonic acid, and salicylic acid and differentially expressed genes (DEGs) in the mitogen-activated protein kinase (MAPK) signaling pathway were affected by heat stress in VvDREB2c-overexpressing lines, which indicated that VvDREB2c positively regulates heat tolerance via a hormonal pathway in Arabidopsis. VvDREB2c promotes heat tolerance in Arabidopsis by exerting effects on photosynthesis, hormones, and growth conditions. This study may provide useful insights into the enrichment of the heat-tolerance pathways in plants.

TMBIM1 promotes proliferation and attenuates apoptosis in glioblastoma cells by targeting the p38 MAPK signalling pathway

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Our research firstly identified that TMBIM1 promotes proliferation and attenuates apoptosis via the p38/MAPK pathway in GBM.

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We also revealed that TMBIM1 regulates the sensitivity of GBM cells to TMZ. Our research will provide an important basis for future intensive molecular mechanism research in GBM and TMBIM1 might be a potential therapeutic target for treating GBM.

Glioblastoma multiforme (GBM) is the most common and most fatal primary malignant brain tumour in adults. The average survival time of patients after diagnosis is only 12–15 months. And its characteristics of excessive proliferation and apoptosis evasion play a crucial role in the poor prognosis of patients. Therefore, it is worth investigating the molecular mechanism of GBM to find an effective therapeutic target to overcome the dilemma. In the current study, Transmembrane BAX inhibitor motif containing 1 (TMBIM1) was highly expressed in GBM tissues and high TMBIM1 expression in GBM cell lines (U87 and U251) could promote cell proliferation and inhibit cell cycle arrest. In addition, TMBIM1 could significantly attenuate GBM cell apoptosis and decrease the sensitivity of GBM cells to temozolomide (TMZ). In terms of the molecular mechanism, we revealed that TMBIM1 interferes with the p38/MAPK pathway by inhibiting p38 phosphorylation to promote cell proliferation and attenuate cell apoptosis. In vivo experiments showed that the survival time of mice in TMBIM1 knockdown group was significantly prolonged. Our discovery provided an important basis for future intensive molecular mechanism research in GBM and presented a potential target for the treatment of GBM.

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.

HbLFG1, a Rubber Tree (Hevea brasiliensis) Lifeguard Protein, Can Facilitate Powdery Mildew Infection by Suppressing Plant Immunity

Powdery mildew causes substantial losses in crop and economic plant yields worldwide. Although powdery mildew infection of rubber trees (Hevea brasiliensis), caused by the biotrophic fungus Erysiphe quercicola, severely threatens natural rubber production, little is known about the mechanism by which E. quercicola adapts to H. brasiliensis to invade the host plant. In barley and Arabidopsis thaliana, lifeguard (LFG) proteins, which have topological similarity to BAX INHIBITOR-1, are involved in host plant susceptibility to powdery mildew infection. In this study, we characterized an H. brasiliensis LFG protein (HbLFG1) with a focus on its function in regulating defense against powdery mildew. HbLFG1 gene expression was found to be upregulated during E. quercicola infection. HbLFG1 showed conserved functions in cell death inhibition and membrane localization. Expression of HbLFG1 in Nicotiana benthamiana leaves and A. thaliana Col-0 was demonstrated to significantly suppress callose deposition induced by conserved pathogen-associated molecular patterns chitin and flg22. Furthermore, we found that overexpression of HbLFG1 in H. brasiliensis mesophyll protoplasts significantly suppressed the chitin-induced burst of reactive oxygen species. Although A. thaliana Col-0 and E. quercicola displayed an incompatible interaction, Col-0 transformants overexpressing HbLFG1 were shown to be susceptible to E. quercicola. Collectively, the findings of this study provide evidence that HbLFG1 acts as a negative regulator of plant immunity that facilitates E. quercicola infection in H. brasiliensis.

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.

Modulation of voltage-gated CaV2.2 Ca2+ channels by newly identified interaction partners

Voltage-gated Ca²⁺ channels are typically integrated in a complex network of protein-protein-interactions, also referred to as Ca²⁺ channel nanodomains. Amongst the neuronal Ca_V2 channel family, Ca_V2.2 is of particular importance due to its general role for signal transmission from the periphery to the central nervous system, but also due to its significance for pain perception. Thus, Ca_V2.2 is an ideal target candidate to search for pharmacological inhibitors but also for novel modulatory interactors. In this review we summarize the last years findings of our intense screenings and characterization of the six Ca_V2.2 interaction partners, tetraspanin-13 (TSPAN-13), reticulon 1 (RTN1), member 1 of solute carrier family 38 (SLC38), prostaglandin D2 synthase (PTGDS), transmembrane protein 223 (TMEM223), and transmembrane BAX inhibitor motif 3 (Grina/TMBIM3) containing protein. Each protein shows a unique way of channel modulation as shown by extensive electrophysiological studies. Amongst the newly identified interactors, Grina/TMBIM3 is most striking due to its modulatory effect which is rather comparable to G-protein regulation.

Integrating RNA-Seq with GWAS reveals novel insights into the molecular mechanism underpinning ketosis in cattle

Background

Ketosis is a common metabolic disease during the transition period in dairy cattle, resulting in long-term economic loss to the dairy industry worldwide. While genetic selection of resistance to ketosis has been adopted by many countries, the genetic and biological basis underlying ketosis is poorly understood.

Results

We collected a total of 24 blood samples from 12 Holstein cows, including 4 healthy and 8 ketosis-diagnosed ones, before (2 weeks) and after (5 days) calving, respectively. We then generated RNA-Sequencing (RNA-Seq) data and seven blood biochemical indicators (bio-indicators) from leukocytes and plasma in each of these samples, respectively. By employing a weighted gene co-expression network analysis (WGCNA), we detected that 4 out of 16 gene-modules, which were significantly engaged in lipid metabolism and immune responses, were transcriptionally (FDR < 0.05) correlated with postpartum ketosis and several bio-indicators (e.g., high-density lipoprotein and low-density lipoprotein). By conducting genome-wide association signal (GWAS) enrichment analysis among six common health traits (ketosis, mastitis, displaced abomasum, metritis, hypocalcemia and livability), we found that 4 out of 16 modules were genetically (FDR < 0.05) associated with ketosis, among which three were correlated with postpartum ketosis based on WGCNA. We further identified five candidate genes for ketosis, including GRINA, MAF1, MAFA, C14H8orf82 and RECQL4. Our phenome-wide association analysis (Phe-WAS) demonstrated that human orthologues of these candidate genes were also significantly associated with many metabolic, endocrine, and immune traits in humans. For instance, MAFA, which is involved in insulin secretion, glucose response, and transcriptional regulation, showed a significantly higher association with metabolic and endocrine traits compared to other types of traits in humans.

Conclusions

In summary, our study provides novel insights into the molecular mechanism underlying ketosis in cattle, and highlights that an integrative analysis of omics data and cross-species mapping are promising for illustrating the genetic architecture underpinning complex traits.

Inhibition of miR-193a-3p protects human umbilical vein endothelial cells against intermittent hypoxia-induced endothelial injury by targeting FAIM2

OBJECTIVE

The functions and molecular regulatory mechanisms of miR-193a-3p in cardiac injury induced by obstructive sleep apnea (OSA) are poorly understood. This study aimed to explore the role of miR-193a-3p in intermittent hypoxia(IH)-induced human umbilical vein endothelial cells (HUVECs) injury.

RESULTS

In this study, we found that IH significantly decreased viability but enhanced cell apoptosis. Concurrently, the miR-193a-3p expression level was increased in HUVECs after IH. Subsequent experiments showed that IH-induced injury was ameliorated through miR-193a-3p silence. Fas apoptotic inhibitory molecule 2 (FAIM2) was predicted by bioinformatics analysis and further identified as a direct target gene of miR-193a-3p. Interestingly, the effect of miR-193a-3p inhibition under IH could be reversed by down-regulating FAIM2 expression.

CONCLUSION

In conclusion, our study first revealed that miR-193a-3p inhibition could protect HUVECs against intermittent hypoxia-induced damage by negatively regulating FAIM2. These findings could advance our understanding of the underlying mechanisms for OSA-related cardiac injury.

METHODS

We exposed HUVECs to IH condition; the expression levels of miR-193a-3p were detected by RT-qPCR. Cell viability, and the expressions of apoptosis-associated proteins were examined via CCK-8, and western blotting, respectively. Target genes of miR-193a-3p were confirmed by dual-luciferase reporter assay.

SNHG7: A novel vital oncogenic lncRNA in human cancers

Long noncoding RNAs (lncRNAs) are a group of RNAs that lack protein-coding ability, with lengths greater than 200 nucleotides. Increasing evidence has indicated that they mediate multiple physiological and pathological processes by regulating gene expression at the epigenetic, transcriptional, post-transcriptional, and translational levels. The deregulation of lncRNAs was demonstrated to have tumor suppressive or oncogenic effects, and thus, these molecules play vital regulatory roles in tumor initiation and progression. Small nucleolar RNA hostgene 7 (SNHG7) is a lncRNA located on chromosome 9q34.3. Different studies have explored the potential role of SNHG7 in the development and progression of multiple human malignancies such as bladder, breast, colorectal, esophageal, gastric, and prostate cancer, as well as osteosarcoma, among others, and high expression predicts poor prognosis and poor survival for such patients. Moreover, this molecule can promote proliferation and metastasis, while inhibiting apoptosis in cancer cells. The present review highlights the latest insights into the expression, functional roles, and molecular mechanisms of SNHG7 in different human malignancies.

What a Difference a Gene Makes: Identification of Virulence Factors of Cowpox Virus

Cowpox virus (CPXV) is a zoonotic orthopoxvirus (OPV) that causes spillover infections from its animal hosts to humans. In 2009, several human CPXV cases occurred through transmission from pet rats. An isolate from a diseased rat, RatPox09, exhibited significantly increased virulence in Wistar rats and caused high mortality compared to that caused by the mildly virulent laboratory strain Brighton Red (BR). The RatPox09 genome encodes four genes which are absent in the BR genome. We hypothesized that their gene products could be major factors influencing the high virulence of RatPox09. To address this hypothesis, we employed several BR-RatPox09 chimeric viruses. Using Red-mediated mutagenesis, we generated BR-based knock-in mutants with single or multiple insertions of the respective RatPox09 genes. High-throughput sequencing was used to verify the genomic integrity of all recombinant viruses, and transcriptomic analyses confirmed that the expression profiles of the genes that were adjacent to the modified ones were unaltered. While the in vitro growth kinetics were comparable to those of BR and RatPox09, we discovered that a knock-in BR mutant containing the four RatPox09-specific genes was as virulent as the RatPox09 isolate, causing death in over 75% of infected Wistar rats. Unexpectedly, the insertion of gCPXV0030 (g7tGP) alone into the BR genome resulted in significantly higher clinical scores and lower survival rates matching the rate for rats infected with RatPox09. The insertion of gCPXV0284, encoding the BTB (broad-complex, tramtrack, and bric-à-brac) domain protein D7L, also increased the virulence of BR, while the other two open reading frames failed to rescue virulence independently. In summary, our results confirmed our hypothesis that a relatively small set of four genes can contribute significantly to CPXV virulence in the natural rat animal model.IMPORTANCE With the cessation of vaccination against smallpox and its assumed cross-protectivity against other OPV infections, waning immunity could open up new niches for related poxviruses. Therefore, the identification of virulence mechanisms in CPXV is of general interest. Here, we aimed to identify virulence markers in an experimental rodent CPXV infection model using bacterial artificial chromosome (BAC)-based virus recombineering. We focused our work on the recent zoonotic CPXV isolate RatPox09, which is highly pathogenic in Wistar rats, unlike the avirulent BR reference strain. In several animal studies, we were able to identify a novel set of CPXV virulence genes. Two of the identified virulence genes, encoding a putative BTB/POZ protein (CPXVD7L) and a B22R-family protein (CPXV7tGP), respectively, have not yet been described to be involved in CPXV virulence. Our results also show that single genes can significantly affect virulence, thus facilitating adaptation to other hosts.

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.

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.

Grina/TMBIM3 modulates voltage-gated CaV2.2 Ca2+ channels in a G-protein-like manner

Grina/TMBIM3 is a poorly characterized transmembrane protein with a broad expression pattern in mammals and with a very ancient origin within eukaryotes. Although initially characterized as an NMDA-receptor associated subunit, there is increasing evidence that Grina/TMBIM3 is involved in the unfolded protein response and controls apoptosis via regulation of Ca²⁺ homeostasis. Here, we investigate a putative direct interaction of Grina/TMBIM3 with voltage gated Ca²⁺ channels, in particular with the Ca_V2.2 α1-subunit and describe its modulatory effects on the current through Ca_V2.2 N-type channels. Direct interaction was confirmed by co-immunoprecipitation studies and membrane localization was proven. Co-expression of Grina/TMBIM3 with Ca_V2.2 channels resulted in a significant decrease of the current amplitude and in a slowing of the kinetics of current activation. This effect was accompanied by a significant shift of the voltage dependencies of activation time constants towards more depolarized voltages. Application of a stimulus protocol including a strong depolarizing pulse relieved inhibition of current amplitude by Grina/TMBIM3. When Grina/TMBIM3 was present, inactivation by an action potential-like train of pulses was diminished. Both observations resemble mechanisms that are well-studied modulatory effects of G-protein βγ subunits on Ca_V2 channels. The impact of Grina/TMBIM3 and G-protein βγ subunits are rather comparable with respect to suppression of current amplitude and slowing of activation kinetics. Furthermore, both modulators had the same effect on current inactivation when evoked by an action potential-like train of pulses.

New insights into the phylogeny of the TMBIM superfamily across the tree of life: Comparative genomics and synteny networks reveal independent evolution of the BI and LFG families in plants

The Transmembrane BAX Inhibitor Motif containing (TMBIM) superfamily, divided into BAX Inhibitor (BI) and Lifeguard (LFG) families, comprises a group of cytoprotective cell death regulators conserved in prokaryotes and eukaryotes. However, no research has focused on the evolution of this superfamily in plants. We identified 685 TMBIM proteins in 171 organisms from Archaea, Bacteria, and Eukarya, and provided a phylogenetic overview of the whole TMBIM superfamily. Then, we used orthology and synteny network analyses to further investigate the evolution and expansion of the BI and LFG families in 48 plants from diverse taxa. Plant BI family forms a single monophyletic group; however, monocot BI sequences transposed to another genomic context during evolution. Plant LFG family, which expanded trough whole genome and tandem duplications, is subdivided in LFG I, LFG IIA, and LFG IIB major phylogenetic groups, and retains synteny in angiosperms. Moreover, two orthologous groups (OGs) are shared between bryophytes and seed plants. Other several lineage-specific OGs are present in plants. This work clarifies the phylogenetic classification of the TMBIM superfamily across the three domains of life. Furthermore, it sheds new light on the evolution of the BI and LFG families in plants providing a benchmark for future research.

Golgi anti-apoptotic protein: a tale of camels, calcium, channels and cancer

Golgi anti-apoptotic protein (GAAP), also known as transmembrane Bax inhibitor-1 motif-containing 4 (TMBIM4) or Lifeguard 4 (Lfg4), shares remarkable amino acid conservation with orthologues throughout eukaryotes, prokaryotes and some orthopoxviruses, suggesting a highly conserved function. GAAPs regulate Ca²⁺ levels and fluxes from the Golgi and endoplasmic reticulum, confer resistance to a broad range of apoptotic stimuli, promote cell adhesion and migration via the activation of store-operated Ca²⁺ entry, are essential for the viability of human cells, and affect orthopoxvirus virulence. GAAPs are oligomeric, multi-transmembrane proteins that are resident in Golgi membranes and form cation-selective ion channels that may explain the multiple functions of these proteins. Residues contributing to the ion-conducting pore have been defined and provide the first clues about the mechanistic link between these very different functions of GAAP. Although GAAPs are naturally oligomeric, they can also function as monomers, a feature that distinguishes them from other virus-encoded ion channels that must oligomerize for function. This review summarizes the known functions of GAAPs and discusses their potential importance in disease.

Arabidopsis GAAP1 and GAAP3 Modulate the Unfolded Protein Response and the Onset of Cell Death in Response to ER Stress

The function of human Golgi antiapoptotic proteins (GAAPs) resembles that of BAX inhibitor-1, with apoptosis inhibition triggered by intrinsic and extrinsic stimuli. However, little is known about the function of GAAP-related proteins in plants. Here, we studied Arabidopsis GAAP1 and GAAP3 and found that they were localized on the cellular membrane, including the endoplasmic reticulum (ER) membrane. The function of GAAP1/GAAP3 in ER-stress response was tested, and results showed that single or double mutation in GAAP1 and GAAP3 reduced plant survival and enhanced cell death under ER stress. The expression of both genes was induced by various abiotic stress signals. Quantitative real-time polymerase chain reaction analysis showed that GAAP1/GAAP3 level affected the expression pattern of the unfolded-protein response (UPR) signaling pathway genes upon prolonged ER stress. The mutation in both GAAP1 and GAAP3 genes promoted and enhanced UPR signaling when confronted with mild ER stress. Moreover, GAAP1/GAAP3 inhibited cell death caused by ER stress and promoted plant-growth recovery by turning down inositol-requiring enzyme 1 (IRE1) signaling after ER stress had been relieved. Co-immunoprecipitation (Co-Ip) and BiFC assays showed that GAAP1/GAAP3 interacted with IRE1. These data suggested that GAAP1/GAAP3 played dual roles in the negative regulation of IRE1 activity and anti-programmed cell death.

Identification and characterization of new isoforms of human fas apoptotic inhibitory molecule (FAIM)

Fas Apoptosis Inhibitory Molecule (FAIM) is an evolutionarily highly conserved death receptor antagonist, widely expressed and known to participate in physiological and pathological processes. Two FAIM transcript variants have been characterized to date, namely FAIM short (FAIM-S) and FAIM long (FAIM-L). FAIM-S is ubiquitously expressed and serves as an anti-apoptotic protein in the immune system. Furthermore, in neurons, this isoform promotes NGF-induced neurite outgrowth through NF-кB and ERK signaling. In contrast FAIM-L is found only in neurons, where it exerts anti-apoptotic activity against several stimuli. In addition to these two variants, in silico studies point to the existence of two additional isoforms, neither of which have been characterized to date. In this regard, here we confirm the presence of these two additional FAIM isoforms in human fetal brain, fetal and adult testes, and placenta tissues. We named them FAIM-S_2a and FAIM-L_2a since they have the same sequence as FAIM-S and FAIM-L, but include exon 2a. PCR and western blot revealed that FAIM-S_2a shows ubiquitous expression in all the tissues and cellular models tested, while FAIM-L_2a is expressed exclusively in tissues of the nervous system. In addition, we found that, when overexpressed in non-neuronal cells, the splicing factor nSR100 induces the expression of the neuronal isoforms, thus identifying it as responsible for the generation of FAIM-L and FAIM-L_2a. Functionally, FAIM-S_2a and FAIM-L_2a increased neurite outgrowth in response to NGF stimulation in a neuronal model. This observation thus, supports the notion that these two isoforms are involved in neuronal differentiation. Furthermore, subcellular fractionation experiments revealed that, in contrast to FAIM-S and FAIM-L, FAIM-S_2a and FAIM-L_2a are able to localize to the nucleus, where they may have additional functions. In summary, here we report on two novel FAIM isoforms that may have relevant roles in the physiology and pathology of the nervous system.

European contribution to the study of ROS: A summary of the findings and prospects for the future from the COST action BM1203 (EU-ROS)

The European Cooperation in Science and Technology (COST) provides an ideal framework to establish multi-disciplinary research networks. COST Action BM1203 (EU-ROS) represents a consortium of researchers from different disciplines who are dedicated to providing new insights and tools for better understanding redox biology and medicine and, in the long run, to finding new therapeutic strategies to target dysregulated redox processes in various diseases. This report highlights the major achievements of EU-ROS as well as research updates and new perspectives arising from its members. The EU-ROS consortium comprised more than 140 active members who worked together for four years on the topics briefly described below. The formation of reactive oxygen and nitrogen species (RONS) is an established hallmark of our aerobic environment and metabolism but RONS also act as messengers via redox regulation of essential cellular processes. The fact that many diseases have been found to be associated with oxidative stress established the theory of oxidative stress as a trigger of diseases that can be corrected by antioxidant therapy. However, while experimental studies support this thesis, clinical studies still generate controversial results, due to complex pathophysiology of oxidative stress in humans. For future improvement of antioxidant therapy and better understanding of redox-associated disease progression detailed knowledge on the sources and targets of RONS formation and discrimination of their detrimental or beneficial roles is required. In order to advance this important area of biology and medicine, highly synergistic approaches combining a variety of diverse and contrasting disciplines are needed.

FAS apoptotic inhibitory molecule 2 is a stress-induced intrinsic neuroprotective factor in the retina

We report the neuroprotective role of FAS apoptotic inhibitory molecule 2 (FAIM2), an inhibitor of the FAS signaling pathway, during stress-induced photoreceptor apoptosis. Retinal detachment resulted in increased FAIM2 levels in photoreceptors with higher amounts detected at the tips of outer segments. Activation of FAS death receptor via FAS-ligand led to JNK-mediated FAIM2 phosphorylation, decreased proteasome-mediated degradation and increased association with the FAS receptor. Photoreceptor apoptosis was accelerated in Faim2 knockout mice following experimental retinal detachment. We show that FAIM2 is primarily involved in reducing stress-induced photoreceptor cell death but this effect was transient. FAIM2 was found to interact with both p53 and HSP90 following the activation of the FAS death pathway and FAIM2/HSP90 interaction was dependent on the phosphorylation of FAIM2. Lack of FAIM2 led to increased expression of proadeath genes Fas and Ripk1 in the retina under physiologic conditions. These results demonstrate that FAIM2 is an intrinsic neuroprotective factor activated by stress in photoreceptors and delays FAS-mediated photoreceptor apoptosis. Modulation of this pathway to increase FAIM2 expression may be a potential therapeutic option to prevent photoreceptor death.

BCL-2 family: integrating stress responses at the ER to control cell demise

In the last decade, the endoplasmic reticulum (ER) has emerged as a central organelle regulating the core mitochondrial apoptosis pathway. At the ER membrane, a variety of stress signals are integrated toward determining cell fate, involving a complex cross talk between key homeostatic pathways including the unfolded protein response, autophagy, calcium signaling and mitochondrial bioenergetics. In this context, key regulators of cell death of the BCL-2 and TMBIM/BI-1 family of proteins have relevant functions as stress rheostats mediated by the formation of distinct protein complexes that regulate the switch between adaptive and proapoptotic phases under stress. Here, we overview recent advances on our molecular understanding of how the apoptotic machinery integrates stress signals toward cell fate decisions upstream of the mitochondrial gateway of death.

Bax-inhibitor-1 knockdown phenotypes are suppressed by Buffy and exacerbate degeneration in a Drosophila model of Parkinson disease

BACKGROUND

Bax inhibitor-1 (BI-1) is an evolutionarily conserved cytoprotective transmembrane protein that acts as a suppressor of Bax-induced apoptosis by regulation of endoplasmic reticulum stress-induced cell death. We knocked down BI-1 in the sensitive dopa decarboxylase (Ddc) expressing neurons of Drosophila melanogaster to investigate its neuroprotective functions. We additionally sought to rescue the BI-1-induced phenotypes by co-expression with the pro-survival Buffy and determined the effect of BI-1 knockdown on the neurodegenerative α-synuclein-induced Parkinson disease (PD) model.

METHODS

We used organismal assays to assess longevity of the flies to determine the effect of the altered expression of BI-1 in the Ddc-Gal4-expressing neurons by employing two RNAi transgenic fly lines. We measured the locomotor ability of these RNAi lines by computing the climbing indices of the climbing ability and compared them to a control line that expresses the lacZ transgene. Finally, we performed biometric analysis of the developing eye, where we counted the number of ommatidia and calculated the area of ommatidial disruption.

RESULTS

The knockdown of BI-1 in these neurons was achieved under the direction of the Ddc-Gal4 transgene and resulted in shortened lifespan and precocious loss of locomotor ability. The co-expression of Buffy, the Drosophila anti-apoptotic Bcl-2 homologue, with BI-1-RNAi resulted in suppression of the reduced lifespan and impaired climbing ability. Expression of human α-synuclein in Drosophila dopaminergic neurons results in neuronal degeneration, accompanied by the age-dependent loss in climbing ability. We exploited this neurotoxic system to investigate possible BI-1 neuroprotective function. The co-expression of α-synuclein with BI-1-RNAi results in a slight decrease in lifespan coupled with an impairment in climbing ability. In supportive experiments, we employed the neuron-rich Drosophila compound eye to investigate subtle phenotypes that result from altered gene expression. The knockdown of BI-1 in the Drosophila developing eye under the direction of the GMR-Gal4 transgene results in reduced ommatidia number and increased disruption of the ommatidial array. Similarly, the co-expression of BI-1-RNAi with Buffy results in the suppression of the eye phenotypes. The expression of α-synuclein along with the knockdown of BI-1 resulted in reduction of ommatidia number and more disruption of the ommatidial array.

CONCLUSION

Knockdown of BI-1 in the dopaminergic neurons of Drosophila results in a shortened lifespan and premature loss in climbing ability, phenotypes that appear to be strongly associated with models of PD in Drosophila, and which are suppressed upon overexpression of Buffy and worsened by co-expression with α-synuclein. This suggests that BI-1 is neuroprotective and its knockdown can be counteracted by the overexpression of the pro-survival Bcl-2 homologue.

TMBIM-mediated Ca2+ homeostasis and cell death

Ca²⁺ is a ubiquitous intracellular messenger that regulates numerous physiological activities in humans, animals, plants, and bacteria. Cytosolic Ca²⁺ is kept at a low level, but subcellular organelles such as the endoplasmic reticulum (ER) and Golgi apparatus maintain high-concentration Ca²⁺ stores. Under resting conditions, store Ca²⁺ homeostasis is dynamically regulated to equilibrate between active Ca²⁺ uptake and passive Ca²⁺ leak processes. The evolutionarily conserved Transmembrane BAX Inhibitor-1 Motif-containing (TMBIM) proteins mediate Ca²⁺ homeostasis and cell death. This review focuses on recent advances in functional and structural analysis of TMBIM proteins in regulation of the two related functions. The roles of TMBIM proteins in pathogen infection and cancer are also discussed with prospects for treatment. This article is part of a Special Issue entitled: ECS Meeting edited by Claus Heizmann, Joachim Krebs and Jacques Haiech.

lncRNA-SNHG7 promotes the proliferation, migration and invasion and inhibits apoptosis of lung cancer cells by enhancing the FAIM2 expression

There is growing evidence that long non-coding RNAs (lncRNAs) are related to cancer development. In the present study, we found that the expression levels of lncRNA-SNHG7 mRNA and protein obviously increased in lung cancer tissues compared to adjacent non-cancerous tissues. Simultaneously, the expression levels of Fas apoptotic inhibitory molecule 2 (FAIM2) also increased in lung cancer tissues. In addition, lncRNA-SNHG7 was of positive relevance with FAIM2 in human lung cancer tissues. Silence of lncRNA‑SNHG7 by siRNA repressed the level of FAIM2 protein and suppressed cell proliferation, migration and invasion and accelerated apoptosis of A594 cells in vitro. Furthermore, silence of FAIM2 by siRNA generated a phenotype similar to silence of lncRNA-SNHG7 by siRNA. Therefore, our research showed that lncRNA-SNHG7 promotes the proliferation, migration and invasion, and inhibits apoptosis of lung cancer cells by enhancing the FAIM2 expression, suggesting that lncRNA-SNHG7 as a key regulator of gene expression, may be a promising therapeutic strategy for the treatment of lung cancer. It may improve the understanding of their biogenesis and function of lung cancer and further provide the theoretical fundamental basis for cancer pathogenesis and treatment.

Lifeguard inhibition of Fas-mediated apoptosis: A possible mechanism for explaining the cisplatin resistance of triple-negative breast cancer cells

Triple-negative breast cancer does not express estrogen receptor-α, progesterone or the HER2 receptor making hormone or antibody therapy ineffective. Cisplatin may initiate p73-dependent apoptosis in p53 mutant cell lines through Fas trimerization and Caspase-8 activation and Bax up regulation and subsequent Caspase-9 activation. The triple-negative breast cancer, MDA-MB-231, overexpresses the protein Lifeguard, which inhibits Fas-mediated apoptosis by inhibiting Caspase-8 activation after Fas trimerization. The relationship between Fas, Lifeguard and cisplatin is investigated by down regulating Lifeguard via shRNA. Results demonstrate that cisplatin's efficacy increases when Lifeguard is down regulated. Lifeguard Knockdown MDA-MB-231 continue to decrease in cell viability from 24 to 48h after cisplatin treatment while no additional decrease in viability is observed in the Wild-Type MDA over the same period. Higher Caspase-8 activity in the Lifeguard knockdown MDA after cisplatin administration could explain the significant decrease in cell viability from 24 to 48h. This cell type is also more sensitive to Fas ligand-mediated reductions in cell viability, confirming Lifeguard's anti-apoptotic function through the Fas receptor. This research suggests that the efficacy of chemotherapy acting through the Fas pathway would increase if Lifeguard were not overexpressed to inhibit Fas-mediated apoptosis.

Lifeguard Inhibits Fas Ligand-mediated Endoplasmic Reticulum-Calcium Release Mandatory for Apoptosis in Type II Apoptotic Cells

Death receptors are members of the tumor necrosis factor receptor superfamily involved in the extrinsic apoptotic pathway. Lifeguard (LFG) is a death receptor antagonist mainly expressed in the nervous system that specifically blocks Fas ligand (FasL)-induced apoptosis. To investigate its mechanism of action, we studied its subcellular localization and its interaction with members of the Bcl-2 family proteins. We performed an analysis of LFG subcellular localization in murine cortical neurons and found that LFG localizes mainly to the ER and Golgi. We confirmed these results with subcellular fractionation experiments. Moreover, we show by co-immunoprecipitation experiments that LFG interacts with Bcl-XL and Bcl-2, but not with Bax or Bak, and this interaction likely occurs in the endoplasmic reticulum. We further investigated the relationship between LFG and Bcl-XL in the inhibition of apoptosis and found that LFG protects only type II apoptotic cells from FasL-induced death in a Bcl-XL dependent manner. The observation that LFG itself is not located in mitochondria raises the question as to whether LFG in the ER participates in FasL-induced death. Indeed, we investigated the degree of calcium mobilization after FasL stimulation and found that LFG inhibits calcium release from the ER, a process that correlates with LFG blockage of cytochrome c release to the cytosol and caspase activation. On the basis of our observations, we propose that there is a required step in the induction of type II apoptotic cell death that involves calcium mobilization from the ER and that this step is modulated by LFG.

Golgi anti-apoptotic proteins are highly conserved ion channels that affect apoptosis and cell migration

Golgi anti-apoptotic proteins (GAAPs) are multitransmembrane proteins that are expressed in the Golgi apparatus and are able to homo-oligomerize. They are highly conserved throughout eukaryotes and are present in some prokaryotes and orthopoxviruses. Within eukaryotes, GAAPs regulate the Ca²⁺ content of intracellular stores, inhibit apoptosis, and promote cell adhesion and migration. Data presented here demonstrate that purified viral GAAPs (vGAAPs) and human Bax inhibitor 1 form ion channels and that vGAAP from camelpox virus is selective for cations. Mutagenesis of vGAAP, including some residues conserved in the recently solved structure of a related bacterial protein, BsYetJ, altered the conductance (E207Q and D219N) and ion selectivity (E207Q) of the channel. Mutation of residue Glu-207 or -178 reduced the effects of GAAP on cell migration and adhesion without affecting protection from apoptosis. In contrast, mutation of Asp-219 abrogated the anti-apoptotic activity of GAAP but not its effects on cell migration and adhesion. These results demonstrate that GAAPs are ion channels and define residues that contribute to the ion-conducting pore and affect apoptosis, cell adhesion, and migration independently.

Genome-wide RNAi screen reveals a role for multipass membrane proteins in endosome-to-golgi retrieval

Endosome-to-Golgi retrieval is an essential membrane trafficking pathway required for many important physiological processes and linked to neurodegenerative disease and infection by bacterial and viral pathogens. The prototypical cargo protein for this pathway is the cation-independent mannose 6-phosphate receptor (CIMPR), which delivers lysosomal hydrolases to endosomes. Efficient retrieval of CIMPR to the Golgi requires the retromer complex, but other aspects of the endosome-to-Golgi retrieval pathway are poorly understood. Employing an image-based antibody-uptake assay, we conducted a genome-wide RNAi loss-of-function screen for novel regulators of this trafficking pathway and report ∼90 genes that are required for endosome-to-Golgi retrieval of a CD8-CIMPR reporter protein. Among these regulators of endosome-to-Golgi retrieval are a number of multipass membrane-spanning proteins, a class of proteins often overlooked with respect to a role in membrane trafficking. We further demonstrate a role for three multipass membrane proteins, SFT2D2, ZDHHC5, and GRINA, in endosome-to-Golgi retrieval.

Role of lifeguard β-isoform in the development of breast cancer

In the last century there has been great progress in the treatment of breast cancer by improving drug and radiation therapy as well as surgical techniques. Despite this development, breast cancer remains a major cause of death among women in Europe and the US. The cause of breast cancer at the cellular level is still not fully understood. In the present study, we investigated the expression of the Lifeguard β-isoform in breast cancer tissues. In contrast to Lifeguard, the β-isoform has one transmembrane domain less, which is the last of seven (99 bp), and due to this we suspect that the Lifeguard β-isoform exhibits a different function. We determined the expression and function of the β-isoform of Lifeguard in breast cancer cell lines (MCF-7 and MDA-MB-231), a human breast epithelial cell line (MCF10A) and in breast tumour tissue sections. Western blotting, PCR arrays and immunofluorescence were used to investigate the expression of Lifeguard and its β-isoform. Moreover, we investigated the ability of Lifeguard β-isoform expression to inhibit apoptosis induced by Fas. Our results indicated that Lifeguard β-isoform is strongly expressed in breast tumour tissues. More notably, we demonstrated that Fas sensitivity was reduced in the MCF10A breast cells expressing the Lifeguard β-isoform. Taken together, our findings indicate the role of the Lifeguard β-isoform as an anti-apoptotic protein and provide further evidence of the potential of the Lifeguard β-isoform as a target for the development of novel therapeutic strategies.

Pseudogenization of testis-specific Lfg5 predates human/Neanderthal divergence

Recent reviews discussed the critical roles of apoptosis in human spermatogenesis and infertility. These reviews highlight the FasL-induced caspase cascade in apoptosis lending importance to our discovery of the pseudogene status of the Lfg5 gene in modern humans, Neanderthal and the Denisovan. This gene is a member of the ancient and highly conserved apoptosis Lifeguard family. This pseudogenization is the result of a premature stop codon at the 3'-end of exon 8 not found in any other ortholog. With the current exception of the domesticated bovine and buffalo, Lfg5's expression in mammals is testis-specific. A full analysis of this gene, its phylogenetic context and its recent hominin changes suggest its inactivation was likely under selection in human evolution.

Modulation of hippocampal neuroplasticity by Fas/CD95 regulatory protein 2 (Faim2) in the course of bacterial meningitis

Supplemental digital content is available in the text.

Fas-apoptotic inhibitory molecule 2 (Faim2) is a neuron-specific membrane protein and a member of the evolutionary conserved lifeguard apoptosis regulatory gene family. Its neuroprotective effect in acute neurological diseases has been demonstrated in an in vivo model of focal cerebral ischemia. Here we show that Faim2 is physiologically expressed in the human brain with a changing pattern in cases of infectious meningoencephalitis.In Faim2-deficient mice, there was increased caspase-associated hippocampal apoptotic cell death and an increased extracellular signal-regulated kinase pattern during acute bacterial meningitis induced by subarachnoid infection with Streptococcus pneumoniae type 3 strain. However, after rescuing the animals by antibiotic treatment, Faim2 deficiency led to increased hippocampal neurogenesis at 7 weeks after infection. This was associated with improved performance of Faim2-deficient mice compared to wild-type littermates in the Morris water maze, a paradigm for hippocampal spatial learning and memory. Thus, Faim2 deficiency aggravated degenerative processes in the acute phase but induced regenerative processes in the repair phase of a mouse model of pneumococcal meningitis. Hence, time-dependent modulation of neuroplasticity by Faim2 may offer a new therapeutic approach for reducing hippocampal neuronal cell death and improving cognitive deficits after bacterial meningitis.

Susceptibility genes 101: how to be a good host

To confer resistance against pathogens and pests in plants, typically dominant resistance genes are deployed. However, because resistance is based on recognition of a single pathogen-derived molecular pattern, these narrow-spectrum genes are usually readily overcome. Disease arises from a compatible interaction between plant and pathogen. Hence, altering a plant gene that critically facilitates compatibility could provide a more broad-spectrum and durable type of resistance. Here, such susceptibility (S) genes are reviewed with a focus on the mechanisms underlying loss of compatibility. We distinguish three groups of S genes acting during different stages of infection: early pathogen establishment, modulation of host defenses, and pathogen sustenance. The many examples reviewed here show that S genes have the potential to be used in resistance breeding. However, because S genes have a function other than being a compatibility factor for the pathogen, the side effects caused by their mutation demands a one-by-one assessment of their usefulness for application.

The characteristics of Bax inhibitor-1 and its related diseases

Bax inhibitor-1 (BI-1) is an evolutionarily-conserved endoplasmic reticulum protein. The expression of BI-1 in mammalian cells suppresses apoptosis induced by Bax, a pro-apoptotic member of the Bcl-2 family. BI-1 has been shown to be associated with calcium (Ca(2+)) levels, reactive oxygen species (ROS) production, cytosolic acidification, and autophagy as well as endoplasmic reticulum stress signaling pathways. According to both in vitro and clinical studies, BI-1 promotes the characteristics of cancers. In other diseases, BI-1 has also been shown to regulate insulin resistance, adipocyte differentiation, hepatic dysfunction and depression. However, the roles of BI-1 in these disease conditions are not fully consistent among studies. Until now, the molecular mechanisms of BI-1 have not directly explained with regard to how these conditions can be regulated. Therefore, this review investigates the physiological role of BI-1 through molecular mechanism studies and its application in various diseases.

LIFEGUARD proteins support plant colonization by biotrophic powdery mildew fungi

Pathogenic microbes manipulate eukaryotic cells during invasion and target plant proteins to achieve host susceptibility. BAX INHIBITOR-1 (BI-1) is an endoplasmic reticulum-resident cell death suppressor in plants and animals and is required for full susceptibility of barley to the barley powdery mildew fungus Blumeria graminis f.sp. hordei. LIFEGUARD (LFG) proteins resemble BI-1 proteins in terms of predicted membrane topology and cell-death-inhibiting function in metazoans, but display clear sequence-specific distinctions. This work shows that barley (Hordeum vulgare L.) and Arabidopsis thaliana genomes harbour five LFG genes, HvLFGa-HvLFGe and AtLFG1-AtLFG5, whose functions are largely uncharacterized. As observed for HvBI-1, single-cell overexpression of HvLFGa supports penetration success of B. graminis f.sp. hordei into barley epidermal cells, while transient-induced gene silencing restricts it. In penetrated barley epidermal cells, a green fluorescent protein-tagged HvLFGa protein accumulates at the site of fungal entry, around fungal haustoria and in endosomal or vacuolar membranes. The data further suggest a role of LFG proteins in plant-powdery mildew interactions in both monocot and dicot plants, because stable overexpression or knockdown of AtLFG1 or AtLFG2 also support or delay development of the powdery mildew fungus Erysiphe cruciferarum on the respective Arabidopsis mutants. Together, this work has identified new modulators of plant-powdery mildew interactions, and the data further support functional similarities between BI-1 and LFG proteins beyond cell death regulation.

hGAAP promotes cell adhesion and migration via the stimulation of store-operated Ca2+ entry and calpain 2

Golgi antiapoptotic proteins (GAAPs) are highly conserved Golgi membrane proteins that inhibit apoptosis and promote Ca(2+) release from intracellular stores. Given the role of Ca(2+) in controlling cell adhesion and motility, we hypothesized that human GAAP (hGAAP) might influence these events. In this paper, we present evidence that hGAAP increased cell adhesion, spreading, and migration in a manner that depended on the C-terminal domain of hGAAP. We show that hGAAP increased store-operated Ca(2+) entry and thereby the activity of calpain at newly forming protrusions. These hGAAP-dependent effects regulated focal adhesion dynamics and cell migration. Indeed, inhibition or knockdown of calpain 2 abrogated the effects of hGAAP on cell spreading and migration. Our data reveal that hGAAP is a novel regulator of focal adhesion dynamics, cell adhesion, and migration by controlling localized Ca(2+)-dependent activation of calpain.

Gene expression analysis of novel genes in the prefrontal cortex of major depressive disorder subjects

Dysregulation of the glutamatergic system has been implicated not only in the treatment of major depressive disorder (MDD), but also in the excitotoxic effects of stress and anxiety on the prefrontal cortex, which may precede the onset of a depressive episode. Our previous studies demonstrate marked deficits in prominent postsynaptic proteins involved in glutamate neurotransmission in the prefrontal cortex (PFC), Brodmann's area 10 (BA 10) from subjects diagnosed with major depressive disorder (MDD). In the same group of subjects we have identified deficits in expression and phosphorylation level of key components of the mammalian target of rapamycin (mTOR) signaling pathway, known to regulate translation initiation. Based on our previous findings, we have postulated that glutamate-dependent dysregulation of mTOR-initiated protein synthesis in the PFC may underlie the pathology of MDD. The aim of this study was to use the NanoString nCounter System to perform analysis of genes coding for glutamate transporters, glutamate metabolizing enzymes, neurotrophic factors and other intracellular signaling markers involved in glutamate signaling that were not previously investigated by our group in the PFC BA 10 from subjects with MDD. We have analyzed a total of 200 genes from 16 subjects with MDD and 16 healthy controls. These are part of the same cohort used in our previous studies. Setting our cutoff p-value≤0.01, marked upregulation of genes coding for mitochondrial glutamate carrier (GC1; p=0.0015), neuropilin 1 (NRP-1; p=0.0019), glutamate receptor ionotropic N-methyl-d-aspartate-associated protein 1 (GRINA; p=0.0060), and fibroblast growth factor receptor 1 (FGFR-1; p=0.010) was identified. No significant differences in expression of the remaining 196 genes were observed between MDD subjects and controls. While upregulation of FGFR-1 has been previously shown in MDD; abnormalities in GC-1, GRINA, and NRP-1 have not been reported. Therefore, this postmortem study identifies GC1, GRINA, and NRP-1 as novel factors associated with MDD; however, future studies will be needed to address the significance of these genes in the pathophysiology of depression and antidepressant activity.

Human and viral Golgi anti-apoptotic proteins (GAAPs) oligomerize via different mechanisms and monomeric GAAP inhibits apoptosis and modulates calcium

Golgi anti-apoptotic proteins (GAAPs) are hydrophobic proteins resident in membranes of the Golgi complex. They protect cells from a range of apoptotic stimuli, reduce the Ca²⁺ content of intracellular stores, and regulate Ca²⁺ fluxes. GAAP was discovered in camelpox virus, but it is highly conserved throughout evolution and encoded by all eukaryote genomes examined. GAAPs are part of the transmembrane Bax inhibitor-containing motif (TMBIM) family that also includes other anti-apoptotic and Ca²⁺-modulating membrane proteins. Most TMBIM members show multiple bands when analyzed by SDS-PAGE, suggesting that they may be oligomeric. However, the molecular mechanisms of oligomerization, the native state of GAAPs in living cells and the functional significance of oligomerization have not been addressed. TMBIM members are thought to have evolved from an ancestral GAAP. Two different GAAPs, human (h) and viral (v)GAAP were therefore selected as models to examine oligomerization of TMBIM family members. We show that both hGAAP and vGAAP in their native states form oligomers and that oligomerization is pH-dependent. Surprisingly, hGAAP and vGAAP do not share the same oligomerization mechanism. Oligomerization of hGAAP is independent of cysteines, but oligomerization of vGAAP depends on cysteines 9 and 60. A mutant vGAAP that is unable to oligomerize revealed that monomeric vGAAP retains both its anti-apoptotic function and its effect on intracellular Ca²⁺ stores. In conclusion, GAAP can oligomerize in a pH-regulated manner, and monomeric GAAP is functional.

ERK-mediated activation of Fas apoptotic inhibitory molecule 2 (Faim2) prevents apoptosis of 661W cells in a model of detachment-induced photoreceptor cell death

In this study, we examined the role of Fas apoptotic inhibitory molecule 2 (Faim2), an inhibitor of the Fas signaling pathway, and its regulation by stress kinase signaling during Fas-mediated apoptosis of 661W cells, an immortalized photoreceptor-like cell line Treatment of 661W cells with a Fas-activating antibody led to increased levels of Faim2. Both ERK and JNK stress kinase pathways were activated in Fas-treated 661W cells, but only the inhibition of the ERK pathway reduced the levels of Faim2. Blocking the ERK pathway using a pharmacological inhibitor increased the susceptibility of 661W cells to Fas-induced caspase activation and apoptosis. When the levels of Faim2 were reduced in 661W cells by siRNA knockdown, Fas activating antibody treatment resulted in earlier and more robust caspase activation, and increased cell death. These results demonstrate that Faim2 acts as a neuroprotectant during Fas-mediated apoptosis of 661W cells. The expression of Faim2 is triggered, at least in part, by Fas-receptor activation and subsequent ERK signaling. Our findings identify a novel protective pathway that auto-regulates Fas-induced photoreceptor apoptosis in vitro. Modulation of this pathway to increase Faim2 expression may be a potential therapeutic option to prevent photoreceptor death.

Six-transmembrane topology for Golgi anti-apoptotic protein (GAAP) and Bax inhibitor 1 (BI-1) provides model for the transmembrane Bax inhibitor-containing motif (TMBIM) family

The Golgi anti-apoptotic protein (GAAP) is a hydrophobic Golgi protein that regulates intracellular calcium fluxes and apoptosis. GAAP is highly conserved throughout eukaryotes and some strains of vaccinia virus (VACV) and camelpox virus. Based on sequence, phylogeny, and hydrophobicity, GAAPs were classified within the transmembrane Bax inhibitor-containing motif (TMBIM) family. TMBIM members are anti-apoptotic and were predicted to have seven-transmembrane domains (TMDs). However, topology prediction programs are inconsistent and predicted that GAAP and other TMBIM members have six or seven TMDs. To address this discrepancy, we mapped the transmembrane topology of viral (vGAAP) and human (hGAAP), as well as Bax inhibitor (BI-1). Data presented show a six-, not seven-, transmembrane topology for vGAAP with a putative reentrant loop at the C terminus and both termini located in the cytosol. We find that this topology is also conserved in hGAAP and BI-1. This places the charged C terminus in the cytosol, and mutation of these charged residues in hGAAP ablated its anti-apoptotic function. Given the highly conserved hydrophobicity profile within the TMBIM family and recent phylogenetic data indicating that a GAAP-like protein may have been the ancestral progenitor of a subset of the TMBIM family, we propose that this vGAAP topology may be used as a model for the remainder of the TMBIM family of proteins. The topology described provides valuable information on the structure and function of an important but poorly understood family of proteins.

TMBIM3/GRINA is a novel unfolded protein response (UPR) target gene that controls apoptosis through the modulation of ER calcium homeostasis

Transmembrane BAX inhibitor motif-containing (TMBIM)-6, also known as BAX-inhibitor 1 (BI-1), is an anti-apoptotic protein that belongs to a putative family of highly conserved and poorly characterized genes. Here we report the function of TMBIM3/GRINA in the control of cell death by endoplasmic reticulum (ER) stress. Tmbim3 mRNA levels are strongly upregulated in cellular and animal models of ER stress, controlled by the PERK signaling branch of the unfolded protein response. TMBIM3/GRINA synergies with TMBIM6/BI-1 in the modulation of ER calcium homeostasis and apoptosis, associated with physical interactions with inositol trisphosphate receptors. Loss-of-function studies in D. melanogaster demonstrated that TMBIM3/GRINA and TMBIM6/BI-1 have synergistic activities against ER stress in vivo. Similarly, manipulation of TMBIM3/GRINA levels in zebrafish embryos revealed an essential role in the control of apoptosis during neuronal development and in experimental models of ER stress. These findings suggest the existence of a conserved group of functionally related cell death regulators across species beyond the BCL-2 family of proteins operating at the ER membrane.

A shear stress responsive gene product PP1201 protects against Fas-mediated apoptosis by reducing Fas expression on the cell surface

Cells that form vascular system employ different mechanisms to offset deleterious consequences of exposure to cytokines and cells present in blood. Vascular homeostasis is sustained in part by genes, whose expression increases in response to hemodynamic forces in these cells. PP1201 (also known as RECS1) is one such gene whose expression level increases in response to laminar shear stress. Aged mice deficient in PP1201 are prone to develop cystic medial degeneration (CMD), a form of aortic aneurism manifested with loss of smooth muscle cells and accumulation of basophilic substances. Here we found that higher levels of PP1201 can protect against Fas ligand (FasL)-induced apoptosis. PP1201 interacted with the Fas receptor (CD95/Apo1) and colocalized with it in the Golgi compartment. Unlike its homolog lifeguard (LFG), PP1201 overexpression in several types of cells including primary human aortic smooth muscle cells (AoSMC) decreased the expression of Fas on the plasma membrane without changing the total Fas levels. Only high but not constitutive level of PP1201 controls Fas signaling. Our data suggest that PP1201 functions as an anti-apoptotic protein and its increased expression in vascular cells can contribute to homeostasis by reducing Fas trafficking to the cell membrane.

A yeast BH3-only protein mediates the mitochondrial pathway of apoptosis

Mitochondrial outer membrane permeabilization is a watershed event in the process of apoptosis, which is tightly regulated by a series of pro- and anti-apoptotic proteins belonging to the BCL-2 family, each characteristically possessing a BCL-2 homology domain 3 (BH3). Here, we identify a yeast protein (Ybh3p) that interacts with BCL-X(L) and harbours a functional BH3 domain. Upon lethal insult, Ybh3p translocates to mitochondria and triggers BH3 domain-dependent apoptosis. Ybh3p induces cell death and disruption of the mitochondrial transmembrane potential via the mitochondrial phosphate carrier Mir1p. Deletion of Mir1p and depletion of its human orthologue (SLC25A3/PHC) abolish stress-induced mitochondrial targeting of Ybh3p in yeast and that of BAX in human cells, respectively. Yeast cells lacking YBH3 display prolonged chronological and replicative lifespans and resistance to apoptosis induction. Thus, the yeast genome encodes a functional BH3 domain that induces cell death through phylogenetically conserved mechanisms.

Silencing of anti-apoptotic transmembrane protein lifeguard sensitizes solid tumor cell lines MCF-7 and SW872 to perifosine-induced cell death activation

Lifeguard (LFG), an anti-apoptotic protein with high expression rates in breast cancer cells, has been identified as a molecule that inhibits death mediated by Fas. The molecular function of LFG and its regulation in the carcinogenesis of human breast and sarcoma cells, however, remains to be elucidated. In the present study, we investigated the ability of LFG expression to inhibit apoptosis induced by the alkyl-phospholipid perifosine. Results showed that LFG was able to be downregulated in selected sarcoma and breast cancer cell lines characterized by high endogenous LFG expression. A decreased LFG expression led to enhanced sensitivity to treatment with an agonistic Fas antibody or treatment with perifosine. Taken together, our findings indicate the role of LFG as an anti-apoptotic protein and provide further evidence of the potential of LFG as a target for the development of novel therapeutic strategies.

Fas/CD95 regulatory protein Faim2 is neuroprotective after transient brain ischemia

Death receptor (DR) signaling has a major impact on the outcome of numerous neurological diseases, including ischemic stroke. DRs mediate not only cell death signals, but also proinflammatory responses and cell proliferation. Identification of regulatory proteins that control the switch between apoptotic and alternative DR signaling opens new therapeutic opportunities. Fas apoptotic inhibitory molecule 2 (Faim2) is an evolutionary conserved, neuron-specific inhibitor of Fas/CD95-mediated apoptosis. To investigate its role during development and in disease models, we generated Faim2-deficient mice. The ubiquitous null mutation displayed a viable and fertile phenotype without overt deficiencies. However, lack of Faim2 caused an increase in susceptibility to combined oxygen-glucose deprivation in primary neurons in vitro as well as in caspase-associated cell death, stroke volume, and neurological impairment after cerebral ischemia in vivo. These processes were rescued by lentiviral Faim2 gene transfer. In summary, we provide evidence that Faim2 is a novel neuroprotective molecule in the context of cerebral ischemia.

Transmembrane BAX inhibitor motif containing (TMBIM) family proteins perturbs a trans-Golgi network enzyme, Gb3 synthase, and reduces Gb3 biosynthesis

Globotriaosylceramide (Gb3) is a well known receptor for Shiga toxin (Stx), produced by enterohemorrhagic Escherichia coli and Shigella dysenteriae. The expression of Gb3 also affects several diseases, including cancer metastasis and Fabry disease, which prompted us to look for factors involved in its metabolism. In the present study, we isolated two cDNAs that conferred resistance to Stx-induced cell death in HeLa cells by expression cloning: ganglioside GM3 synthase and the COOH terminus region of glutamate receptor, ionotropic, N-methyl-D-asparate-associated protein 1 (GRINA), a member of the transmembrane BAX inhibitor motif containing (TMBIM) family. Overexpression of the truncated form, named GRINA-C, and some members of the full-length TMBIM family, including FAS inhibitory molecule 2 (FAIM2), reduced Gb3, and lactosylceramide was accumulated instead. The change of glycolipid composition was restored by overexpression of Gb3 synthase, suggesting that the synthase is affected by GRINA-C and FAIM2. Interestingly, the mRNA level of Gb3 synthase was unchanged. Rather, localization of the synthase as well as TGN46, a trans-Golgi network marker, was perturbed to form punctate structures, and degradation of the synthase in lysosomes was enhanced. Furthermore, GRINA-C was associated with Gb3 synthase. These observations may demonstrate a new type of posttranscriptional regulation of glycosyltransferases.

Transactivation of lifeguard (LFG) by Akt-/LEF-1 pathway in MCF-7 and MDA-MB 231 human breast cancer cells

Lifeguard (LFG) has been identified as a molecule that uniquely inhibits death mediated by Fas. The molecular function of human LFG and its regulation in carcinogenesis is uncertain. In our study, we investigated the potential regulation of LFG expression by Akt/LEF-1 pathway. The Glycogen synthase kinase-3 (GSK3) can be regulated by different signaling pathways including those mediated by protein kinase Akt. Inhibition of GSK3beta subunits activity results in the stabilisation of the beta-catenin protein and its accumulation in the nucleus, where it associates with members of the TCF/LEF-1 family of transcription factors to mediate gene transcription. In Western blots, RT-PCR and by small interfering RNA directed against LEF-1, we demonstrated that LFG expression correlates with GSK3beta and LEF-1 activation. Moreover, we showed that LFG mRNA was down-regulated after transfection with siRNA against LEF-1 in MDA-MB-231 cells. Our results therefore identify LFG as a target of the Akt/LEF-1 pathway in MDA-MB-231 breast tumour cells, a regulation which could play a key role in breast tumour progression.