Neural membrane protein 35 (NMP35): a novel member of a gene family which is highly expressed in the adult nervous system

Epigenome-Wide Analysis Reveals DNA Methylation Alteration in ZFP57 and Its Target RASGFR2 in a Mexican Population Cohort with Autism

Autism Spectrum Disorders (ASD) comprise a group of heterogeneous and complex neurodevelopmental disorders. Genetic and environmental factors contribute to ASD etiology. DNA methylation is particularly relevant for ASD due to its mediating role in the complex interaction between genotype and environment and has been implicated in ASD pathophysiology. The lack of diversity in DNA methylation studies in ASD individuals is remarkable. Since genetic and environmental factors are likely to vary across populations, the study of underrepresented populations is necessary to understand the molecular alterations involved in ASD and the risk factors underlying these changes. This study explored genome-wide differences in DNA methylation patterns in buccal epithelium cells between Mexican ASD patients (n = 27) and age-matched typically developing (TD: n = 15) children. DNA methylation profiles were evaluated with the Illumina 450k array. We evaluated the interaction between sex and ASD and found a differentially methylated region (DMR) over the 5′UTR region of ZFP57 and one of its targets, RASGRF2. These results match previous findings in brain tissue, which may indicate that ZFP57 could be used as a proxy for DNA methylation in different tissues. This is the first study performed in a Mexican, and subsequently, Latin American, population that evaluates DNA methylation in ASD patients.

Landscape of Bone Marrow Metastasis in Human Neuroblastoma Unraveled by Transcriptomics and Deep Multiplex Imaging

While the bone marrow attracts tumor cells in many solid cancers leading to poor outcome in affected patients, comprehensive analyses of bone marrow metastases have not been performed on a single-cell level. We here set out to capture tumor heterogeneity and unravel microenvironmental changes in neuroblastoma, a solid cancer with bone marrow involvement. To this end, we employed a multi-omics data mining approach to define a multiplex imaging panel and developed DeepFLEX, a pipeline for subsequent multiplex image analysis, whereby we constructed a single-cell atlas of over 35,000 disseminated tumor cells (DTCs) and cells of their microenvironment in the metastatic bone marrow niche. Further, we independently profiled the transcriptome of a cohort of 38 patients with and without bone marrow metastasis. Our results revealed vast diversity among DTCs and suggest that FAIM2 can act as a complementary marker to capture DTC heterogeneity. Importantly, we demonstrate that malignant bone marrow infiltration is associated with an inflammatory response and at the same time the presence of immuno-suppressive cell types, most prominently an immature neutrophil/granulocytic myeloid-derived suppressor-like cell type. The presented findings indicate that metastatic tumor cells shape the bone marrow microenvironment, warranting deeper investigations of spatio-temporal dynamics at the single-cell level and their clinical relevance.

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.

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.

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.

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.

Faim2 contributes to neuroprotection by erythropoietin in transient brain ischemia

Delayed cell death in the penumbra region of acute ischemic stroke occurs through apoptotic mechanisms, making it amenable to therapeutic interventions. Fas/CD95 mediates apoptotic cell death in response to external stimuli. In mature neurons, Fas/CD95 signaling is modulated by Fas-apoptotic inhibitory molecule 2 (Faim2), which reduces cell death in animal models of stroke, meningitis, and Parkinson disease. Erythropoietin (EPO) has been studied as a therapeutic strategy in ischemic stroke. Erythropoietin stimulates the phosphatidylinositol-3 kinase/Akt (PI3K/Akt) pathway, which regulates Faim2 expression. Therefore, up-regulation of Faim2 may contribute to neuroprotection by EPO. Male Faim2-deficient mice (Faim2^-/- ) and wild-type littermates (WT) were subjected to 30 min of middle cerebral artery occlusion (MCAo) followed by 72 h of reperfusion. EPO was applied before (30 min) and after (24 and 48 h) MCAo. In WT mice application of EPO at a low dose (5000 U/kg) significantly reduced stroke volume, whereas treatment with high dose (90 000 U/kg) did not. In Faim2^-/- animals administration of low-dose EPO did not result in a significant reduction in stroke volume. Faim2 expression as measured by quantitative reverse transcription polymerase chain reaction (qRT-PCR) increased after low-dose EPO but not with high dose. An extensive phenotyping including analysis of cerebral vessel architecture did not reveal confounding differences between the genotypes. In human post-mortem brain Faim2 displayed a differential expression in areas of penumbral ischemia. Faim2 up-regulation may contribute to the neuroprotective effects of low-dose erythropoietin in transient brain ischemia. The dose-dependency may explain mixed effects of erythropoietin observed in clinical stroke trials.

Inhibition of Apoptosis by Expression of Antiapoptotic Proteins in Recombinant Human Keratinocytes

The Fas ligand/Fas interaction plays an important role in the regulation of immune responses. Allografted cells undergo Fas-mediated apoptosis induced by CD8+ T cells. Our objective was to prevent human keratinocytes from immunologically induced apoptosis. We focused on three proteins with inhibitory function on Fas-mediated apoptosis. Human keratinocytes were transfected with either Flip, Faim, or Lifeguard (LFG). The treatment proved to be practicable and efficient. The recombinant keratinocytes with expression of our target proteins were cocultured with CD8+ T cells and the apoptotic activity was then evaluated. Activation of caspase-8 was detectable in control but not in the recombinant cells. Quantitative analysis revealed significant induction of T-cell-induced apoptosis in nontransfected keratinocytes (p = 0.04, n = 12) but not in Flip (p = 0.66), Faim (p = 0.42), or LFG (p = 0.44) expressing cells. Our results suggest that heterotopic expression of antiapoptotic proteins can induce the resistance of keratinocytes to a major mechanism of rejection.

Mice lacking Faim2 show increased cell death in the MPTP mouse model of Parkinson disease

The death receptor Fas/CD95 mediates apoptotic cell death in response to external stimuli. In neurons, Fas-induced apoptosis is prevented by Fas-apoptotic inhibitory molecule 2 (Faim2). Mice lacking Faim2 showed increased neurodegeneration in animal models of stroke and bacterial meningitis. We therefore tested the relevance of Faim2 in a classical animal model of Parkinson disease and determined the toxicity of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) in Faim2-deficient mice. Without MPTP treatment, there was no difference in the dopaminergic system between Faim2-deficient mice and control mice. MPTP was applied i.p. in doses of 30 mg per kg on five consecutive days. Fourteen days after the last MPTP injection, the number of dopaminergic neurons in the lateral substantia nigra, assayed by stereological counting, was reduced by 39% in control mice and 53% in Faim2-deficient mice. The density of dopaminergic fibers in the dorsal striatum was reduced by 36% in control mice and 69% in Faim2-deficient mice, in the ventral striatum 44% in control mice and 76% in Faim2-deficient mice. Fiber density recovered at 90 days after MPTP with similar density in both groups. Striatal catecholamine levels were reduced by 81-84% in both groups and recovered at 90 days. Faim2 expression was documented in mouse midbrain using quantitative reverse transcription-PCR (qRT-PCR) and found decreased after MPTP administration. Taken together, our findings demonstrate increased degeneration of dopaminergic neurons with Faim2 deficiency, indicating that Fas-induced apoptosis contributes to cell death in the MPTP mouse model. Along with the decreased expression of Faim2 after MPTP, this finding indicates that boosting Faim2 function might represent a therapeutic strategy for Parkinson disease.

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.

TRIM21, a negative modulator of LFG in breast carcinoma MDA-MB-231 cells in vitro

Lifeguard (LFG) is a transmembrane protein which is highly expressed in tissues of the hippocampus and the cerebellum, especially during postnatal development. This protein is responsible for the protection of neurons against Fas-induced apoptosis, and the same effect can be seen in tumor cells derived from mastocarcinoma. However, the molecular function of LFG and its regulation in the carcinogenesis of human breast cells remains to be elucidated. In the present study, we investigated the connection of the interaction of LFG within an array analysis of over 9,000 different proteins. Results showed an interaction between the proteins tripartite motif-containing 21 (TRIM21) and LFG and a negative regulatory effect of TRIM21 towards LFG on the protein level. Furthermore, Fas-induced apoptosis decreased upon the addition of TRIM21 to the cultured cells. These results revealed TRIM21 to be a negative modulator of LFG in cells of mastocarcinoma in vitro. For all analyses, MDA-MB-231 cells were used. The interaction of TRIM21 and LFG was analyzed by co-immunoprecipitation. To examine changes in regulatory processes, western blot analyses, real-time PCR, activity of apoptotic process and flow cytometric analyses were carried out.

The transmembrane Bax inhibitor motif (TMBIM) containing protein family: Tissue expression, intracellular localization and effects on the ER CA²⁺-filling state

Bax inhibitor-1 (BI-1) is an evolutionarily conserved pH-dependent Ca²⁺ leak channel in the endoplasmic reticulum and the founding member of a family of six highly hydrophobic mammalian proteins named transmembrane BAX inhibitor motif containing (TMBIM) 1-6 with BI-1 being TMBIM6. Here we compared the structure, subcellular localization, tissue expression and the effect on the cellular Ca²⁺ homeostasis of all family members side by side. We found that all TMBIM proteins possess the di-aspartyl pH sensor responsible for pH sensing identified in TMBIM6 and its bacterial homologue BsYetJ. TMBIM1-3 and TMBIM4-6 represent two phylogenetically distinct groups that are localized in the Golgi apparatus (TMBIM1-3), endoplasmic reticulum (TMBIM4-6) or mitochondria (TMBIM5) but share a common structure of at least seven transmembrane domains with the last domain being semi-hydrophobic. TMBIM1 is mainly expressed in muscle, TMBIM2 and 3 in the nervous system, TMBIM4 and 5 are ubiquitously expressed and TMBIM6 in skeletal muscle, kidney, liver and spleen. All TMBIM proteins reduce the Ca²⁺ content of the endoplasmic reticulum, and all but TMBIM5 also reduce the cytosolic resting Ca²⁺ concentration. These results suggest that the TMBIM family has comparable functions in the maintenance of intracellular Ca²⁺ homeostasis in a wide variety of tissues. This article is part of a Special Issue entitled: 13th European Symposium on Calcium.

MYCN repression of Lifeguard/FAIM2 enhances neuroblastoma aggressiveness

Neuroblastoma (NBL) is the most common solid tumor in infants and accounts for 15% of all pediatric cancer deaths. Several risk factors predict NBL outcome: age at the time of diagnosis, stage, chromosome alterations and MYCN (V-Myc Avian Myelocytomatosis Viral Oncogene Neuroblastoma-Derived Homolog) amplification, which characterizes the subset of the most aggressive NBLs with an overall survival below 30%. MYCN-amplified tumors develop exceptional chemoresistance and metastatic capacity. These properties have been linked to defects in the apoptotic machinery, either by silencing components of the extrinsic apoptotic pathway (e.g. caspase-8) or by overexpression of antiapoptotic regulators (e.g. Bcl-2, Mcl-1 or FLIP). Very little is known on the implication of death receptors and their antagonists in NBL. In this work, the expression levels of several death receptor antagonists were analyzed in multiple human NBL data sets. We report that Lifeguard (LFG/FAIM2 (Fas apoptosis inhibitory molecule 2)/NMP35) is downregulated in the most aggressive and undifferentiated tumors. Intringuingly, although LFG has been initially characterized as an antiapoptotic protein, we have found a new association with NBL differentiation. Moreover, LFG repression resulted in reduced cell adhesion, increased sphere growth and enhanced migration, thus conferring a higher metastatic capacity to NBL cells. Furthermore, LFG expression was found to be directly repressed by MYCN at the transcriptional level. Our data, which support a new functional role for a hitherto undiscovered MYCN target, provide a new link between MYCN overexpression and increased NBL metastatic properties.

Axonal transport of neural membrane protein 35 mRNA increases axon growth

Many neuronal mRNAs are transported from cell bodies into axons and dendrites. Localized translation of the mRNAs brings autonomy to these processes that can be vast distances from the cell body. For axons, these translational responses have been linked to growth and injury signaling, but there has been little information about local function of individual axonally synthesized proteins. In the present study, we show that axonal injury increases levels of the mRNA encoding neural membrane protein 35 (NMP35) in axons, with a commensurate decrease in the cell body levels of NMP35 mRNA. The 3' untranslated region (3'UTR) of NMP35 is responsible for this localization into axons. Previous studies have shown that NMP35 protein supports cell survival by inhibiting Fas-ligand-mediated apoptosis; however, these investigations did not distinguish functions of the locally generated NMP35 protein. Using axonally targeted versus cell-body-restricted NMP35 constructs, we show that NMP35 supports axonal growth, and overexpression of an axonally targeted NMP35 mRNA is sufficient to increase axonal outgrowth.

Antiapoptotic protein Lifeguard is required for survival and maintenance of Purkinje and granular cells

Lifeguard (LFG) is an inhibitor of Fas-mediated cell death and is highly expressed in the cerebellum. We investigated the biological role of LFG in the cerebellum in vivo, using mice with reduced LFG expression generated by shRNA lentiviral transgenesis (shLFG mice) as well as LFG null mice. We found that LFG plays a role in cerebellar development by affecting cerebellar size, internal granular layer (IGL) thickness, and Purkinje cell (PC) development. All these features are more severe in early developmental stages and show substantial recovery overtime, providing a remarkable example of cerebellar plasticity. In adult mice, LFG plays a role in PC maintenance shown by reduced cellular density and abnormal morphology with increased active caspase 8 and caspase 3 immunostaining in shLFG and knockout (KO) PCs. We studied the mechanism of action of LFG as an inhibitor of the Fas pathway and provided evidence of the neuroprotective role of LFG in cerebellar granule neurons (CGNs) and PCs in an organotypic cerebellar culture system. Biochemical analysis of the Fas pathway revealed that LFG inhibits Fas-mediated cell death by interfering with caspase 8 activation. This result is supported by the increased number of active caspase 8-positive PCs in adult mice lacking LFG. These data demonstrate that LFG is required for proper development and survival of granular and Purkinje cells and suggest LFG may play a role in cerebellar disorders.

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.

The ancient cell death suppressor BAX inhibitor-1

Bax inhibitor-1 (BI-1) was initially identified for its ability to inhibit BAX-induced apoptosis in yeast cells and is the founding member of a family of highly hydrophobic proteins localized in diverse cellular membranes. It is evolutionarily conserved and orthologues from plants can substitute for mammalian BI-1 in regard to its anti-apoptotic function suggesting a high degree of functional conservation. BI-1 interacts with BCL-2 and BCL-XL and, similar to these two anti-apoptotic proteins, the effect of BI-1 on cell death involves changes in the amount of Ca(2+) releasable from intracellular stores. However, BI-1 is also a negative regulator of the endoplasmic reticulum stress sensor IRE1 α, it interacts with G-actin and increases actin polymerization, enhances cancer metastasis by altering glucose metabolism and activating the sodium-hydrogen exchanger, and reduces the production of reactive oxygen species through direct interaction with NADPH-P450 reductase. In this contribution, we summarize what is known about the expression, intracellular localization and structure of BI-1 and specifically illuminate its effects on the intracellular Ca(2+) homeostasis and how this might relate to its other functions. We also present a thorough phylogenetic analysis of BI-1 proteins from major phyla together with paralogues from all BI-1 family members.

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.

The anti-apoptotic protein lifeguard is expressed in breast cancer cells and tissues

Lifeguard (LFG) is an anti-apoptotic protein that inhibits Fas-mediated death in tumour cells. However, the molecular function of human LFG in the carcinogenesis of human breast cells is uncertain. We studied the expression and function of endogenous LFG in four breast cancer cell lines (MCF-7, MDA-MB-231, T-47D and HS 578T), a human breast epithelial cell line (HS 578Bst), and in healthy and cancerous breast tissues. Molecular (Western blot and RT-PCR) and immunohistochemical techniques were used to investigate the LFG expression. To investigate the breast cancer cell proliferation in the presence of Fas, we performed fluorescent cell viability assays. The possible association of Fas with LFG was analyzed by immunofluorescence microscopy. In this paper, we provide convincing evidence that LFG is overexpressed in several human breast cancer cell lines. More importantly, we found that the LFG expression correlates with high tumour grades in primary breast tumours. Finally, we demonstrated that Fas sensitivity is reduced in breast cancer cell lines expressing LFG. Our results indicated that LFG is strongly expressed in breast cancer epithelial cells. Moreover, the overexpression of LFG correlated with tumour grade and reduced Fas sensitivity. Our findings support the idea that LFG may have a role in the downregulation of apoptosis in breast cancer cells.

A functional equivalent of endoplasmic reticulum and Golgi in axons for secretion of locally synthesized proteins

Subcellular localization of protein synthesis provides a means to regulate the protein composition in far reaches of a cell. This localized protein synthesis gives neuronal processes autonomy to rapidly respond to extracellular stimuli. Locally synthesized axonal proteins enable neurons to respond to guidance cues and can help to initiate regeneration after injury. Most studies of axonal mRNA translation have concentrated on cytoplasmic proteins. While ultrastructural studies suggest that axons do not have rough endoplasmic reticulum or Golgi apparatus, mRNAs for transmembrane and secreted proteins localize to axons. Here, we show that growing axons with protein synthetic activity contain ER and Golgi components needed for classical protein synthesis and secretion. Isolated axons have the capacity to traffic locally synthesized proteins into secretory pathways and inhibition of Golgi function attenuates translation-dependent axonal growth responses. Finally, the capacity for secreting locally synthesized proteins in axons appears to be increased by injury.

RECS1 deficiency in mice induces susceptibility to cystic medial degeneration

RECS1 is a novel shear stress-responsive gene that encodes a protein putatively forming seven-span transmembrane domains. We reports here that mouse RECS1 (mRECS1) transcripts is detected in most tissues except for thymus, spleen and testis. The putative cytoplasmic N-terminus of mRECS1 has a high content of proline (23%) and glycine (12%) residues, contains one PPXY motif, multiple PXXP motifs and one overlapping P(T/S)AP and PPXY motif (P(T/S)APPXY). The PPXY motif lies within one potential PEST sequence (PEST score: +7.65). We prepared anti-RECS1 polyclonal antibody and found by western blot analysis that the mRECS1 protein in the lung and aorta was detected as a 34.4 kDa band. However, one shifted 58 kDa band or three shifted bands (48, 69, 82 kDa) were detected in the heart or the liver, respectively. Since northern blot detected only one species of mRECS1 mRNA in heart and liver tissues, as well as other tissues (approximately 2.2 kb), these differences in molecular weight seem to be due to posttranslational modification. Biochemical fractionation and RECS1-GFP fusion protein revealed that RECS1 localizes at the endosomal/lysosomal membranes in the cytoplasm. To understand the function of RECS1 in the body, we made RECS1 knockout (KO) mice and found that RECS1 KO mice (older than 14 months) are prone to cystic medial degeneration (CMD). Taken together, we conclude that RECS1 is an endosomal/lysosomal membrane protein which plays protective roles in vascular remodeling.

Lifeguard/neuronal membrane protein 35 regulates Fas ligand-mediated apoptosis in neurons via microdomain recruitment

Fas ligand (FasL)-receptor system plays an essential role in regulating cell death in the developing nervous system, and it has been implicated in neurodegenerative and inflammatory responses in the CNS. Lifeguard (LFG) is a protein highly expressed in the hippocampus and the cerebellum, and it shows a particularly interesting regulation by being up-regulated during postnatal development and in the adult. We show that over-expression of LFG protected cortical neurons from FasL-induced apoptosis and decreased caspase-activation. Reduction of endogenous LFG expression by small interfering RNA sensitized cerebellar granular neurons to FasL-induced cell death and caspase-8 activation, and also increased sensitivity of cortical neurons. In differentiated cerebellar granular neurons, protection from FasL-induced cell death could be attributed exclusively to LFG and appears to be independent of FLICE inhibitor protein. Thus, LFG is an endogenous inhibitor of FasL-mediated neuronal death and it mediates the FasL resistance of CNS differentiated neurons. Finally, we also demonstrate that LFG is detected in lipid rafts microdomains, where it may interact with Fas receptor and regulate FasL-activated signaling pathways.

FasL (CD95L/APO-1L) resistance of neurons mediated by phosphatidylinositol 3-kinase-Akt/protein kinase B-dependent expression of lifeguard/neuronal membrane protein 35

The contribution of Fas (CD95/APO-1) to cell death mechanisms of differentiated neurons is controversially discussed. Rat cerebellar granule neurons (CGNs) express high levels of Fas in vitro but are resistant to FasL (CD95L/APO-1L/CD178)-induced apoptosis. We here show that this resistance was mediated by a phosphatidylinositol 3-kinase (PI 3-kinase)-Akt/protein kinase B (PKB)-dependent expression of lifeguard (LFG)/neuronal membrane protein 35. Reduction of endogenous LFG expression by antisense oligonucleotides or small interfering RNA lead to increased sensitivity of CGNs to FasL-induced cell death and caspase-8 cleavage. The inhibition of PI 3-kinase activity sensitized CGNs to FasL-induced caspase-8 and caspase-3 processing and caspase-dependent fodrin cleavage. Pharmacological inhibition of PI 3-kinase, overexpression of the inhibitory protein IkappaB, or cotransfection of an LFG reporter plasmid with dominant-negative Akt/PKB inhibited LFG reporter activity, whereas overexpression of constitutively active Akt/PKB increased LFG reporter activity. Overexpression of LFG in CGNs interfered with the sensitization to FasL by PI 3-kinase inhibitors. In contrast to CGNs, 12 glioma cell lines, which are sensitive to FasL, did not express LFG. Gene transfer of LFG into these FasL-susceptible glioma cells protected against FasL-induced apoptosis. These results demonstrate that LFG mediated the FasL resistance of CGNs and that, under certain circumstances, e.g., inhibition of the PI 3-kinase-Akt/PKB pathway, CGNs were sensitized to FasL.

Congruence of tissue expression profiles from Gene Expression Atlas, SAGEmap and TissueInfo databases

BACKGROUND

Extracting biological knowledge from large amounts of gene expression information deposited in public databases is a major challenge of the postgenomic era. Additional insights may be derived by data integration and cross-platform comparisons of expression profiles. However, database meta-analysis is complicated by differences in experimental technologies, data post-processing, database formats, and inconsistent gene and sample annotation.

RESULTS

We have analysed expression profiles from three public databases: Gene Expression Atlas, SAGEmap and TissueInfo. These are repositories of oligonucleotide microarray, Serial Analysis of Gene Expression and Expressed Sequence Tag human gene expression data respectively. We devised a method, Preferential Expression Measure, to identify genes that are significantly over- or under-expressed in any given tissue. We examined intra- and inter-database consistency of Preferential Expression Measures. There was good correlation between replicate experiments of oligonucleotide microarray data, but there was less coherence in expression profiles as measured by Serial Analysis of Gene Expression and Expressed Sequence Tag counts. We investigated inter-database correlations for six tissue categories, for which data were present in the three databases. Significant positive correlations were found for brain, prostate and vascular endothelium but not for ovary, kidney, and pancreas.

CONCLUSION

We show that data from Gene Expression Atlas, SAGEmap and TissueInfo can be integrated using the UniGene gene index, and that expression profiles correlate relatively well when large numbers of tags are available or when tissue cellular composition is simple. Finally, in the case of brain, we demonstrate that when PEM values show good correlation, predictions of tissue-specific expression based on integrated data are very accurate.

Neural membrane protein 35/Lifeguard is localized at postsynaptic sites and in dendrites

We have previously identified and characterized a cDNA coding for neural membrane protein 35 (NMP35). We showed that NMP35 mRNA is predominantly expressed in the adult CNS with a neuronal expression pattern. Functional analysis indicates that the human homologue of NMP35, Lifeguard, plays a role in Fas-mediated cell death. In this study we used affinity-purified antibodies raised against the putative cytoplasmic N-terminal domain of NMP35 to determine its precise subcellular localization in the adult CNS. NMP35 protein is widely expressed throughout the brain and spinal cord, most prominently in dendrites of several neuronal cell types and in the surrounding neuropil. Immunofluorescence confocal microscopy reveals colocalization of NMP35 with the glutamate receptor GluR2 and adjacent localization to the presynaptic vesicle protein synaptophysin. These data suggest that NMP35 may be localized to the postsynaptic membrane. Immunoelectron microscopy with NMP35 antibodies confirms the expression of the protein in dendritic processes and in a subset of synapses at the postsynaptic membrane and density. These findings suggest a role for NMP35 in synapses of the adult central nervous system.

Large scale isolation of non-uniform shear stress-responsive genes from cultured human endothelial cells through the preparation of a subtracted cDNA library

To investigate the molecular mechanisms responsible for the regional selectivity of early atherogenesis, we have applied a non-uniform shear stress to cultured human umbilical vein endothelial cells (HUVEC). We used a microcarrier culture system and a combination of subtraction and reverse-subtraction methods to isolate a number of genes upregulated by shear stress. The resultant subtracted library includes several known genes (e.g. MCP-1, TM) whose responsiveness to shear stress has been previously reported, indicating that the library is enriched for genes upregulated by shear stress. Also included are atherosclerosis-related genes (e.g. CTGF, IL-8) whose responsiveness to shear stress had not been demonstrated, other known genes whose relationship to atherosclerosis had not been reported, and novel genes. Some responsive to centrifugal force and shear stress (RECS) genes are also upregulated following stimulation by steady laminar shear stress in a parallel plate chamber. Interestingly, the library includes ET-1 and PAI, which are well known atherogenic factors that are downregulated by laminar shear stress. This implies that turbulent shear stress has effects on HUVEC that are different from those elicited by laminar shear stress. Importantly, analysis of specimens taken from human aorta showed that several RECS genes are transcriptionally upregulated in atherosclerotic lesions, suggesting that the subtracted library includes novel therapeutic targets for the treatment of atherosclerosis.

Superoxide modification and inactivation of a neuronal receptor-like complex

Excessive superoxide (O(-)(2)) formation is toxic to cells and organisms. O(-)(2) reacts with either iron-sulfur centers or cysteines (Cys) of cytoplasmic proteins. Reactions with membrane proteins, however, have not been fully characterized. In the present studies, the reaction of O(-)(2) with a protein complex that has glutamate/N-methyl-D-aspartate (NMDA) receptor characteristics and with one of the subunits of this complex was examined. Exposure of the complex purified from neuronal membranes and the recombinant glutamate-binding protein (GBP) subunit of this complex to the O(-)(2)-generating system of xanthine (X) plus xanthine oxidase (XO) caused strong inhibition of L-[3H]glutamate binding. Inhibition of glutamate binding to the complex and GBP by O(-)(2) was greater than that produced by H(2)O(2), another product of the X plus XO reaction. Mutation of two cysteine (Cys) residues in recombinant GBP (Cys(190,191)) eliminated the effect of O(-)(2) on L-[3H]glutamate binding. Both S-thiolation reaction of GBP in synaptic membranes with [35S]cystine and reaction of Cys residues in GBP with [3H]NEM were significantly decreased after exposure of membranes to O(-)(2). Inhibition of cysteylation of membrane GBP by O(-)(2) was still observed after iron chelation by desferrioxamine, albeit diminished, and was not altered by the presence of catalase. Overall, the results indicated that GBP exposure to O(-)(2) modified Cys residues in this protein. The modification was not characterized but it was probably that of disulfide formation.

Cloning and identification of differentially expressed transcripts in primary culture of GABAergic neurons

A RNA based arbitrarily primed polymerase chain reaction (RAP-PCR) was used to identify differentially expressed transcripts in primary cultures of cerebral cortical neurons prepared from E16 mouse cerebral cortex. The majority of neurons found in this culture preparation are known to be GABAergic. Different primer combinations were used, and the PCR products were separated on PAGE. Visualization by silver staining revealed a high resolution RNA fingerprint pattern with a total of about 200 transcripts. Six differentially expressed cDNA fragments were recovered, cloned and sequenced. The results of a NCBI database search showed that 6 clones were highly homologous to known genes and expressed sequence tags (ESTs), and that they were either up-regulated or down-regulated during development. Among these clones, Clone 3.1.7 shared 99% sequence homology to mouse Reelin, a neuronal migration and positioning related protein. Clone 4.6.2 shared 91% homology to Rat prepro bone morphogenetic protein-3 mRNA. Clone 6.10.2 had 90% homology to a novel orphan gene of calcium-independent alpha-latrotoxin receptor, which stimulates presynaptic neurotransmitter release. Northern blot analysis confirmed the up-regulated expression profile of Clone 6.10.2 in neuron from Day 2 to 7 during stages of differentiation and development.

Oligodendrocyte Transmembrane Protein: A Novel Member of the Glutamate-Binding Protein Subfamily

Oligodendrocytes (OLGs) are cells from the central nervous system that synthesize, assemble, and maintain myelin, the multilamellar membrane that surrounds axons and facilitates the fast conduction of nerve impulses. We have shown that OLGs initiate their myelinogenic phenotype upon adhesion to GRASP, a heparin-binding glycoprotein that we purified from horse serum. In an attempt to identify the genes implicated in establishing this phenotype, we isolated a novel 3500 bp cDNA related to, but distinct from, a subfamily of glutamate-binding proteins (GBP). The cDNA encodes a protein of 511 amino acids, whose predicted sequence can be modeled as a tetrahelical integral protein with a large external loop and with the N- and C-termini located inside the cell. We have named this protein oligodendrocyte transmembrane protein (OTMP). Transcription of the message is induced upon OLG acquiring a myelinogenic phenotype (i.e., upon adhesion). The temporal expression in conjunction with the structural and biochemical features of OTMP is suggestive of a signaling receptor with a role in myelinogenesis.

Cascade of caspase activation in potassium-deprived cerebellar granule neurons: targets for treatment with peptide and protein inhibitors of apoptosis

Cerebellar granule neurons (CGN) cultured in the presence of serum and depolarizing potassium concentrations undergo apoptosis when switched to serum-free medium containing physiological potassium concentrations. Here we show that processing of the key protease, caspase-3, depends on the activation of caspase-9, but not of caspase-8. Selective peptide inhibitors of caspase-9 block processing of caspase-3 and caspase-8 and inhibit apoptosis, whereas a selective inhibitor of caspase-8 blocks neither processing of caspase-3 nor cell death. The data obtained with peptide inhibitors were confirmed by adenovirally mediated ectopic expression of the cytokine response modifier A (crmA), the baculovirus protein p35, and the X chromosome-linked inhibitor of apoptosis (XIAP). Further, caspase-8-activating death receptors do not mediate apoptosis in CGN and potassium withdrawal-induced apoptosis evolves unaltered in gld or lpr mice, which harbor mutations in the CD95/CD95 ligand system. Thus, neuronal apoptosis triggered by potassium deprivation is death receptor-independent but involves the mitochondrial pathway of caspase activation.

Identification by RNA-based arbitrarily primed PCR of the involvement of cytochrome c oxidase in the development of resistance to methotrexate

RNA-based arbitrarily primed PCR (RAP-PCR) was used to identify sequences in CHO K1 cells that were differentially expressed upon methotrexate incubation during the development of resistance to this drug. Ten different RAP products were isolated, cloned and sequenced. Among these, we identified one sequence that showed 84% identity with the nucleotide sequence of rat cytochrome c oxidase subunit II, and 90% identity with the amino acid sequence of this protein. This RAP fragment was up-regulated in a dose- and time-dependent manner. The overexpression of cytochrome c oxidase subunit II mRNA as a result of methotrexate incubation was corroborated by quantitative RT-PCR and Northern blot analysis. Incubation of cells with sodium azide, a specific cytochrome c oxidase inhibitor, decreased the number of resistant colonies after methotrexate treatment. Thus, overexpression of cytochrome c oxidase is involved in the development of resistance to methotrexate. These results suggest that sodium azide may be used as a modulator in chemotherapy with methotrexate.

Immunocytochemical and in situ hybridization studies of the expression and distribution of three subunits of a complex with N-methyl-D-aspartate receptor-like properties

A group of four proteins with recognition sites for L-glutamate, N-methyl-D-aspartate, glycine, and competitive and non-competitive inhibitors of N-methyl-D-aspartate receptors was previously purified from rat brain synaptic membranes. The biochemical and immunochemical characteristics of this complex, as well as the sequences of the complementary DNAs of three subunits, are distinct from those of other glutamate receptors, transporters, or enzymes. The function of this complex has not yet been defined, but it appears to be involved in glutamate-induced neuronal excitation and toxicity. It is not known whether all protein components of the complex are expressed in the same populations of brain cells. In the present study, immunohistochemical and in situ hybridization were used to map the distribution of the glutamate-binding, glycine/thienylcyclohexylpiperidine-binding, and carboxypiperazinyl-propylphosphonate-binding protein subunits of the complex. These proteins were abundantly expressed in pyramidal neurons of the hippocampus and cerebral cortex, and in granule cells of the dentate gyrus, cerebellum, and olfactory tubercle. Based on these results, it was concluded that the three subunits of the complex have similar patterns of expression in rat brain. The distribution of one subunit of the complex, glutamate-binding protein, was traced throughout the rat brain, thus providing a potential map of the expression of the complex in rodent brain. In addition, probes were developed in the present study that should be useful in future explorations of the role of these proteins in brain function and of the possible co-localization of the protein subunits in single cells or cell processes.

LFG: an anti-apoptotic gene that provides protection from Fas-mediated cell death

Programmed cell death regulates a number of biological phenomena, and the apoptotic signal must itself be tightly controlled to avoid inappropriate cell death. We established a genetic screen to search for molecules that inhibit the apoptotic signal from the Fas receptor. Here we report the isolation of a gene, LFG, that protects cells uniquely from Fas but not from the mechanistically related tumor necrosis factor alpha death signal. LFG is widely distributed, but remarkably is highly expressed in the hippocampus. LFG can bind to the Fas receptor, but does not regulate Fas expression or interfere with binding of an agonist antibody. Furthermore LFG does not inhibit binding of FADD to Fas.

Embryonic expression of epithelial membrane protein 1 in early neurons

Epithelial membrane protein 1 (EMP1) is a member of the peripheral myelin protein 22 (PMP22) family. This family is best known for the crucial contribution of PMP22 to the development and maintenance of the peripheral nervous system (PNS). PMP22 is widely expressed, with highest levels in myelinating Schwann cells, and mutations affecting the PMP22 gene lead to PNS-restricted neuropathies. We have investigated the spatio-temporal distribution of EMP1 and compared it to that of PMP22. We found that EMP1 and PMP22 mRNA are most conspicuously expressed in the prenatal mouse brain during neurogenesis. In the developing forebrain, we localized EMP1 mRNA and protein to the first set of neurons that are generated and leave the ventricular zone to form the preplate. Later in development, EMP1 was found in derivatives of the preplate, the marginal zone and the subplate. Reduced expression was observed in the newly generated cortical plate neurons. In other parts of the developing CNS and PNS, EMP1 was also detected in early neurons and along the initial fiber tracts. Furthermore, EMP1 was highly expressed by immature neurons in embryonal dorsal root ganglia-explant cultures and in neuroectodermal differentiated P19 cells. While PMP22 functions mainly in Schwann cell growth and differentiation, the spatio-temporal localization of EMP1 suggests a role in neuronal differentiation and neurite outgrowth.

Identification of genes induced by neuregulin in cultured myotubes

The formation of the neuromuscular junction (NMJ) involves a series of inductive interactions between motor neurons and muscle fibers. The neural signals proposed to induce the mRNA expression of acetylcholine receptors in muscle include neuregulin (NRG). In the present study, we have employed RNA fingerprinting by arbitrarily primed PCR analysis to identify the differentially expressed transcripts following NRG treatment in cultured myotubes. Nine partial cDNA fragments were isolated; the mRNA expression of eight of these genes was found to be up-regulated by NRG. The spatial and temporal expression profiles of these NRG-regulated genes in rat tissues during development suggest potential functional roles during the formation of NMJ in vivo. Our findings not only allowed the identification of novel genes, but also suggested possible functions for some known genes that are consistent with their potential roles at the NMJ. Furthermore, the identification of G-protein beta1 subunit and G-protein-coupled receptor as NRG-regulated genes has provided the first demonstration that activation of the NRG signaling pathway can induce the expression of components in the G-protein signaling cascade.