Endoplasmic reticulum membrane-sorting protein of lymphocytes (BAP31) is highly expressed in neurons and discrete endocrine cells

ER-organelle contacts: A signaling hub for neurological diseases

Neuronal health is closely linked to the homeostasis of intracellular organelles, and organelle dysfunction affects the pathological progression of neurological diseases. In contrast to isolated cellular compartments, a growing number of studies have found that organelles are largely interdependent structures capable of communicating through membrane contact sites (MCSs). MCSs have been identified as key pathways mediating inter-organelle communication crosstalk in neurons, and their alterations have been linked to neurological disease pathology. The endoplasmic reticulum (ER) is a membrane-bound organelle capable of forming an extensive network of pools and tubules with important physiological functions within neurons. There are multiple MCSs between the ER and other organelles and the plasma membrane (PM), which regulate a variety of cellular processes. In this review, we focus on ER-organelle MCSs and their role in a variety of neurological diseases. We compared the biological effects between different tethering proteins and the effects of their respective disease counterparts. We also discuss how altered ER-organelle contacts may affect disease pathogenesis. Therefore, understanding the molecular mechanisms of ER-organelle MCSs in neuronal homeostasis will lay the foundation for the development of new therapies targeting ER-organelle contacts.

BAP31 Promotes Angiogenesis via Galectin-3 Upregulation in Neuroblastoma

Neuroblastoma (NB) is one of the highly vascularized childhood solid tumors, and understanding the molecular mechanisms underlying angiogenesis in NB is crucial for developing effective therapeutic strategies. B-cell receptor-associated protein 31 (BAP31) has been implicated in tumor progression, but its role in angiogenesis remains unexplored. This study investigated BAP31 modulation of pro-angiogenic factors in SH-SY5Y NB cells. Through protein overexpression, knockdown, antibody blocking, and quantification experiments, we demonstrated that overexpression of BAP31 led to increased levels of vascular endothelial growth factor A (VEGFA) and Galectin-3 (GAL-3), which are known to promote angiogenesis. Conditioned medium derived from BAP31-overexpressing neuroblastoma cells stimulated migration and tube formation in endothelial cells, indicating its pro-angiogenic properties. Also, we demonstrated that BAP31 enhances capillary tube formation by regulating hypoxia-inducible factor 1 alpha (HIF-1α) and its downstream target, GAL-3. Furthermore, GAL-3 downstream proteins, Jagged 1 and VEGF receptor 2 (VEGFR2), were up-regulated, and blocking GAL-3 partially inhibited the BAP31-induced tube formation. These findings suggest that BAP31 promotes angiogenesis in NB by modulating GAL-3 and VEGF signaling, thereby shaping the tumor microenvironment. This study provides novel insights into the pro-angiogenic role of BAP31 in NB.

HNF4A-BAP31-VDAC1 axis synchronously regulates cell proliferation and ferroptosis in gastric cancer

B cell receptor associated protein 31 (BAP31) is closely associated with tumor progression, while the role and mechanism of BAP31 in gastric cancer (GC) remains unknown. This study explored that BAP31 was upregulated in GC tissues and high expression indicated poor survival of GC patients. BAP31 knockdown inhibited cell growth and induced G1/S arrest. Moreover, BAP31 attenuation increased the lipid peroxidation level of the membrane and facilitated cellular ferroptosis. Mechanistically, BAP31 regulated cell proliferation and ferroptosis by directly binding to VDAC1 and affected VDAC1 oligomerization and polyubiquitination. HNF4A was bound to BAP31 at the promoter and increased its transcription. Furthermore, knockdown of BAP31 inclined to make GC cells vulnerable to 5-FU and ferroptosis inducer, erastin, in vivo and in vitro. Our work suggests that BAP31 may serve as prognostic factor for gastric cancer and act as potential therapeutic strategy for gastric cancer.

Mitochondria-associated membranes: A hub for neurodegenerative diseases

In eukaryotic cells, organelles could coordinate complex mechanisms of signaling transduction metabolism and gene expression through their functional interactions. The functional domain between ER and mitochondria, called mitochondria-associated membranes (MAM), is closely associated with various physiological functions including intracellular lipid transport, Ca²⁺ transfer, mitochondria function maintenance, and autophagosome formation. In addition, more evidence suggests that MAM modulate cellular functions in health and disease. Studies have also demonstrated the association of MAM with numerous diseases, including neurodegenerative diseases, cancer, viral infection, obesity, and diabetes. In fact, recent evidence revealed a close relationship of MAM with Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's disease (HD), amyotrophic lateral sclerosis (ALS), and other neurodegenerative diseases. In this view, elucidating the role of MAM in neurodegenerative diseases is particularly important. This review will focus the main tethering protein complexes of MAM and functions of MAM. Besides, the role of MAM in the regulation of neurodegenerative diseases and the potential molecular mechanisms is introduced to provide a new understanding of the pathogenesis of these diseases.

BAP31: Physiological functions and roles in disease

B-cell receptor-associated protein 31 (BAP31 or BCAP31) is a ubiquitously expressed transmembrane protein found mainly in the endoplasmic reticulum (ER), including in mitochondria-associated membranes (MAMs). It acts as a broad-specificity membrane protein chaperone and quality control factor, which can promote different fates for its clients, including ER retention, ER export, ER-associated degradation (ERAD), or evasion of degradation, and it also acts as a MAM tetherer and regulatory protein. It is involved in several cellular processes - it supports ER and mitochondrial homeostasis, promotes proliferation and migration, plays several roles in metabolism and the immune system, and regulates autophagy and apoptosis. Full-length BAP31 can be anti-apoptotic, but can also mediate activation of caspase-8, and itself be cleaved by caspase-8 into p20-BAP31, which promotes apoptosis by mobilizing ER calcium stores at MAMs. BAP31 loss-of-function mutations is the cause of 'deafness, dystonia, and central hypomyelination' (DDCH) syndrome, characterized by severe neurological symptoms and early death. BAP31 is furthermore implicated in a growing number of cancers and other diseases, and several viruses have been found to target it to promote their survival or life cycle progression. The purpose of this review is to provide an overview and examination of the basic properties, functions, mechanisms, and roles in disease of BAP31.

Further delineation of BCAP31-linked intellectual disability: description of 17 new families with LoF and missense variants

The BCAP31 gene, located at Xq28, encodes BAP31, which plays a role in ER-to-Golgi anterograde transport. To date, BCAP31 pathogenic variants have been reported in 12 male cases from seven families (six loss of function (LoF) and one missense). Patients had severe intellectual disability (ID), dystonia, deafness, and central hypomyelination, delineating a so-called deafness, dystonia and cerebral hypomyelination syndrome (DDCH). Female carriers are mostly asymptomatic but may present with deafness. BCAP31 is flanked by the SLC6A8 and ABCD1 genes. Contiguous deletions of BCAP31 and ABCD1 and/or SLC6A8 have been described in 12 patients. Patients with deletions including BCAP31 and SLC6A8 have the same phenotype as BCAP31 patients. Patients with deletions of BCAP31 and ABCD1 have contiguous ABCD1 and DXS1375E/BCAP31 deletion syndrome (CADDS), and demonstrate a more severe neurological phenotype with cholestatic liver disease and early death. We report 17 novel families, 14 with intragenic BCAP31 variants (LoF and missense) and three with a deletion of BCAP31 and adjacent genes (comprising two CADDS patients, one male and one symptomatic female). Our study confirms the phenotype reported in males with intragenic LoF variants and shows that males with missense variants exhibit a milder phenotype. Most patients with a LoF pathogenic BCAP31 variant have permanent or transient liver enzyme elevation. We further demonstrate that carrier females (n = 10) may have a phenotype comprising LD, ID, and/or deafness. The male with CADDS had a severe neurological phenotype, but no cholestatic liver disease, and the symptomatic female had moderate ID and cholestatic liver disease.

Biological roles of the B cell receptor-associated protein 31: Functional Implication in Cancer

BAP31 is a ubiquitously expressed integral membrane protein of the endoplasmic reticulum. BAP31 is involved in various biological and molecular processes, including protein transport, viral processing, apoptosis signaling, MHC 1 antigen processing and presentation, mitochondria and ER calcium regulation, and proteasomal protein degradation. We employed a BAP31 interaction search using STRING and inBioMap™ protein-protein interaction networks, and the Metabolic Atlas, which revealed molecular and metabolic interactors involved in various pathways essential for cell growth, cell survival, and disease development. BAP31, as a chaperone and resident protein of the ER, was reported in the development of some central nervous system disorders and metabolic diseases about AD, ALS, and Liver disease. In addition, BAP31 is overexpressed in many cancers. Furthermore, research around BAP31 involvement in cancer has taken up a shape, focusing on its roles in cancer cell survival, disease prognosis, and targeted treatment. Here, we address published data on the Biological roles of BAP31 in both health and disease. We present an analytical description of BAP31 expression and functional implication in some human cancers and the impact of its expression and regulation while it models as a potential target in cancer therapy. Besides, a profound understanding of BAP31 is insightful of the gap between cancer development and neurodegeneration, thus generating novel ideas surrounding the link between the two different cell phenomena.

B-Cell Receptor-Associated Protein 31 Negatively Regulates the Expression of Monoamine Oxidase A Via R1

B-cell receptor-associated protein 31 (Bap31) is a three trans-membrane protein of the endoplasmic reticulum (ER). Patients who have loss of function of Bap31 suffered from X-linked syndrome, such as motor and intellectual disabilities, dystonia, and sensorineural deafness. However, the underlying mechanism of Bap31 on X-linked syndrome remains unclear. Here, we found that a total of 21 proteins (9 up-regulated and 12 down-regulated proteins) related with X-linked syndrome were screened from shRNA-Bap31 transfected cells with the isobaric tags for relative and absolute quantification (iTRAQ) technique. One gene with the greatest change trend, monoamine oxidase A (MAOA), was identified. MAOA expression was up-regulated by Bap31 knockdown. However, Bap31 did not affect the ubiquitination degradation of MAOA protein. Of note, Bap31 selectively regulated the expression of cell division cycle associated 7-like (R1/RAM2/CDCA7L/JPO2, a transcriptional repressor of MAOA) and the binding activity of R1 with MAOA promoter, thereby affecting MAOA expression. This study demonstrates the molecular mechanisms of Bap31 in MAOA via R1 and supports the potential function of Bap31 on X-linked syndrome.

Epitope Mapping of Antibodies Suggests the Novel Membrane Topology of B-Cell Receptor Associated Protein 31 on the Cell Surface of Embryonic Stem Cells: The Novel Membrane Topology of BAP31

When located in the endoplasmic reticulum (ER) membrane, B-cell receptor associated protein 31 (BAP31) is involved in the export of secreted proteins from the ER to the plasma membrane. In a previous study, we generated two monoclonal antibodies (mAbs), 297-D4 and 144-A8, that bound to surface molecules on human embryonic stem cells (hESCs), but not to surface molecules on mouse embryonic stem cells (mESCs). Subsequent studies revealed that the mAbs recognized BAP31 on the surface of hESCs. To investigate the membrane topology of BAP31 on the cell surface, we first examined the epitope specificity of 297-D4 and 144-A8, as well as a polyclonal anti-BAP31 antibody (α-BAP31). We generated a series of GST-fused BAP31 mutant proteins in which BAP31 was serially deleted at the C- terminus. GST-fused BAP31 mutant proteins were then screened to identify the epitopes targeted by the antibodies. Both 297-D4 and 144-A8 recognized C-terminal residues 208-217, while α-BAP31 recognized C-terminal residues 165-246, of BAP31 on hESCs, suggesting that the C-terminal domain of BAP31 is exposed on the cell surface. The polyclonal antibody α-BAP31 bound to mESCs, which confirmed that the C-terminal domain of BAP31 is also exposed on the surface of these cells. Our results show for the first time the novel membrane topology of cell surface-expressed BAP31 as the extracellular exposure of the BAP31 C-terminal domain was not predicted from previous studies.

BAP31, a promising target for the immunotherapy of malignant melanomas

PURPOSE

Malignant melanoma's (MM) incidence is rising faster than that of any other cancer in the US and the overall survival at 5 years is less than 10%. B cell associated protein 31 (BAP31) is overexpressed in most MMs and might be a promising target for immunotherapy of this disease.

EXPERIMENTAL DESIGN

Firstly, we investigated the expression profiles of human BAP31 (hBAP31) and mouse BAP31 (mBAP31) in human and mouse normal tissues, respectively. The expression level of hBAP31 in human MMs and mBAP31 in B16 melanoma cells was also analyzed. Then we constructed novel mBAP31 DNA vaccines and tested there ability to stimulate mBAP31-specific immune responses and antitumor immunity in B16 melanoma-bearing mice.

RESULTS

For the first time, we found that protein expression of hBAP31 were dramatically upregulated in human MMs when compared with human normal tissues. Predominant protein expression of mBAP31 was found in mouse B16 melanoma cells but not in mouse important organs. When mice were immunized with mBAP31 DNA vaccines, strong cellular response to mBAP31 was observed in the vaccinated mice. CTLs isolated from immunized mice could effectively kill mBAP31-positive target mouse B16 melanoma tumor cells in vitro and vaccination with mBAP31 DNA vaccines had potent anti-tumor activity in therapeutic model using B16 melanoma cells.

CONCLUSIONS

These are the first data supporting a vaccine targeting BAP31 that is capable of inducing effective immunity against BAP31-expressing MMs and will be applicable to human MMs and hBAP31 DNA vaccine warrants investigation in human clinical trials.

High-resolution genetic mapping of allelic variants associated with cell wall chemistry in Populus

Background

QTL cloning for the discovery of genes underlying polygenic traits has historically been cumbersome in long-lived perennial plants like Populus. Linkage disequilibrium-based association mapping has been proposed as a cloning tool, and recent advances in high-throughput genotyping and whole-genome resequencing enable marker saturation to levels sufficient for association mapping with no a priori candidate gene selection. Here, multiyear and multienvironment evaluation of cell wall phenotypes was conducted in an interspecific P. trichocarpa x P. deltoides pseudo-backcross mapping pedigree and two partially overlapping populations of unrelated P. trichocarpa genotypes using pyrolysis molecular beam mass spectrometry, saccharification, and/ or traditional wet chemistry. QTL mapping was conducted using a high-density genetic map with 3,568 SNP markers. As a fine-mapping approach, chromosome-wide association mapping targeting a QTL hot-spot on linkage group XIV was performed in the two P. trichocarpa populations. Both populations were genotyped using the 34 K Populus Infinium SNP array and whole-genome resequencing of one of the populations facilitated marker-saturation of candidate intervals for gene identification.

Results

Five QTLs ranging in size from 0.6 to 1.8 Mb were mapped on linkage group XIV for lignin content, syringyl to guaiacyl (S/G) ratio, 5- and 6-carbon sugars using the mapping pedigree. Six candidate loci exhibiting significant associations with phenotypes were identified within QTL intervals. These associations were reproducible across multiple environments, two independent genotyping platforms, and different plant growth stages. cDNA sequencing for allelic variants of three of the six loci identified polymorphisms leading to variable length poly glutamine (PolyQ) stretch in a transcription factor annotated as an ANGUSTIFOLIA C-terminus Binding Protein (CtBP) and premature stop codons in a KANADI transcription factor as well as a protein kinase. Results from protoplast transient expression assays suggested that each of the polymorphisms conferred allelic differences in the activation of cellulose, hemicelluloses, and lignin pathway marker genes.

Conclusion

This study illustrates the utility of complementary QTL and association mapping as tools for gene discovery with no a priori candidate gene selection. This proof of concept in a perennial organism opens up opportunities for discovery of novel genetic determinants of economically important but complex traits in plants.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-1215-z) contains supplementary material, which is available to authorized users.

Mutations in BCAP31 cause a severe X-linked phenotype with deafness, dystonia, and central hypomyelination and disorganize the Golgi apparatus

BAP31 is one of the most abundant endoplasmic reticulum (ER) membrane proteins. It is a chaperone protein involved in several pathways, including ER-associated degradation, export of ER proteins to the Golgi apparatus, and programmed cell death. BAP31 is encoded by BCAP31, located in human Xq28 and highly expressed in neurons. We identified loss-of-function mutations in BCAP31 in seven individuals from three families. These persons suffered from motor and intellectual disabilities, dystonia, sensorineural deafness, and white-matter changes, which together define an X-linked syndrome. In the primary fibroblasts of affected individuals, we found that BCAP31 deficiency altered ER morphology and caused a disorganization of the Golgi apparatus in a significant proportion of cells. Contrary to what has been described with transient-RNA-interference experiments, we demonstrate that constitutive BCAP31 deficiency does not activate the unfolded protein response or cell-death effectors. Rather, our data demonstrate that the lack of BAP31 disturbs ER metabolism and impacts the Golgi apparatus, highlighting an important role for BAP31 in ER-to-Golgi crosstalk. These findings provide a molecular basis for a Mendelian syndrome and link intracellular protein trafficking to severe congenital brain dysfunction and deafness.

Interaction of Bap31 and MHC class I molecules and their traffic out of the endoplasmic reticulum

The endoplasmic reticulum (ER) protein Bap31 associates with nascent class I MHC molecules. It appears to mediate the export of class I MHC molecules from the ER and may also be involved in their quality control. In this study, we use Förster resonance energy transfer and quantitative fluorescence imaging to show that in human, HeLa cells, Bap31 clusters with MHC class I (HLA-A2) molecules in the ER, and traffics via export vesicles to the ER/Golgi intermediate compartment. Förster resonance energy transfer between Bap31 and HLA-A2 and forward traffic increases when MHC class I molecules are loaded with a pulse of peptide. The increased forward traffic is blocked by overexpression of Bap29, a partner protein for Bap31, which localizes to the ER. Thus, in HeLa cells, Bap31 is involved in the exit of peptide-loaded MHC class I from the ER, and its function is regulated by its interaction with its homologue, Bap29.

Bap31 enhances the endoplasmic reticulum export and quality control of human class I MHC molecules

The assembly of class I MHC molecules and their export from the endoplasmic reticulum (ER) is governed by chaperones and accessory proteins. We present evidence that the putative cargo receptor protein Bap31 participates in the transport and the quality control of human class I molecules. Transfection of the human adenocarcinoma cell line HeLa with yellow fluorescent protein-Bap31 chimeras increased surface levels of class I in a dose-dependent manner, by as much as 3.7-fold. The increase in surface class I resulted from an increase in the rate of export of newly synthesized class I molecules to the cell surface and from an increase in the stability of the exported molecules. We propose that Bap31 performs quality control on class I molecules in two distinct phases: first, by exporting peptide-loaded class I molecules to the ER/Golgi intermediate compartment, and second, by retrieving class I molecules that have lost peptides in the acidic post-ER environment. This function of Bap31 is conditional or redundant, because we find that Bap31 deficiency does not reduce surface class I levels. Overexpression of the Bap31 homolog, Bap29, decreases surface class levels in HeLa, indicating that it does not substitute for Bap31.

BAP31 Is Involved in the Retention of Cytochrome P450 2C2 in the Endoplasmic Reticulum

Microsomal cytochrome P450 2C2 is an integral endoplasmic reticulum (ER) membrane protein that is directly retained in the ER and excluded from transport vesicles. We have used bimolecular fluorescence complementation and co-immunoprecipitation to show that a ubiquitous ER membrane protein (BAP31) interacts with P450 2C2 in transfected COS-1 cells. A chimera containing only the N-terminal signal anchor of P450 2C1 (P450 2C1-(1-29)) also interacted with BAP31, which is consistent with interaction of the two proteins via their transmembrane domains. Down-regulation of BAP31 expression with small interfering RNA resulted in redistribution of green fluorescent protein-tagged P450 2C2 or P450 2C1-(1-29) from the ER into the nuclear membrane and compact perinuclear compartment structures as well as the cell surface in a small fraction of the cells. In Bap31-null embryonic stem cells, a significant fraction of P450 2C2 or P450 2C1-(1-29) was detected at the cell surface and nuclear envelope, but was redistributed to the ER by expression of BAP31. The expression level of P450 2C2 was significantly increased in COS-1 cells with repressed levels of BAP31. Formation of the pro-apoptotic p20 fragment of BAP31 was detected in transfected COS-1 cells expressing P450 2C2, and annexin V staining was consistent with the activation of an apoptotic pathway in these cells. Down-regulation of BAP31 with small interfering RNA partially reversed the apoptosis. These results suggest that interaction of P450 2C2 with BAP31 is important for its ER retention and expression level and that BAP31 may be involved in the regulation of apoptosis induced by the ER overload response to increased expression of P450.

Increase of AMPA receptor glutamate receptor 1 subunit and B-cell receptor-associated protein 31 gene expression in hippocampus of fatigued mice

Central fatigue is an indispensable biosignal for maintaining life, but the neuronal and molecular mechanisms involved remain unclear. In this study, we searched for genes differentially expressed in the hippocampus of fatigued mice to elucidate the mechanisms underlying fatigue. Mice were forced to swim in an adjustable-current water pool, and the maximum swimming time (endurance) until fatigue was measured thrice. Fatigued and nonfatigued mice with equal swimming capacity and body weight were compared. We found that the genes of GluR1 and B-cell receptor-associated protein 31 (Bap31), which acts as a transport molecule in the secretory pathway or as a mediator of apoptosis, were upregulated in the hippocampus of fatigued mice, and increases of GluR1 and Bap31 were confirmed by Northern blotting and real-time PCR. No change of gene expression of AMPA receptor subunits other than GluR1 was observed. These results suggest that a compositional change of AMPA receptor (increase of GluR1) and upregulation of the Bap31 gene may be implicated in fatigue in mice.

Tula hantavirus triggers pro-apoptotic signals of ER stress in Vero E6 cells

Tula virus is a member of the Hantavirus genus of the family Bunyaviridae. Viruses of this family have an unusual pattern of intracellular maturation at the ER–Golgi compartment. We recently found that Tula virus, similar to several other hantaviruses, is able to induce apoptosis in cultured cells [Li, X.D., Kukkonen, S., Vapalahti, O., Plyusnin, A., Lankinen, H., Vaheri, A., 2004. Tula hantavirus infection of Vero E6 cells induces apoptosis involving caspase 8 activation. J. Gen. Virol. 85, 3261–3268.]. However, the cellular mechanisms remain to be clarified. In this study, we demonstrate that the progressive replication of Tula virus in Vero E6 cells initiates several death programs that are intimately associated with ER stress: (1) early activation of ER-resident caspase-12; (2) phosphorylation of Jun NH₂-terminal kinase (JNK) and its downstream target transcriptional factor, c-jun; (3) induction of the pro-apoptotic transcriptional factor, growth arrest- and DNA damage-inducible gene 153, or C/EBP homologous protein (Gadd153/chop); and (4) changes in the ER-membrane protein BAP31 implying cross-talk with the mitochondrial apoptosis pathway. Furthermore, we confirmed that a sustained ER stress was induced marked by an increased expression of an ER chaperone Grp78/BiP. Taken together, we have identified involvement of ER stress-mediated death program in Tula virus-infected Vero E6 cells which provides a new approach to understand the mechanisms in hantavirus-induced apoptosis.

Association of BAP31 with CD11b/CD18

The beta2 integrin CD11b/CD18 is an integral membrane protein that is present in the plasma membrane and secondary granules of neutrophils and functions as a major adhesion molecule. Upon cellular activation, there is translocation of intracellular pools of CD11b/CD18 to the plasma membrane in concert with enhanced cellular adhesion. Although much is known about the function of CD11b/CD18, how this protein is transported within the cell is less well defined. Here we report that CD11b/CD18 specifically binds to BAP31, a member of a novel class of sorting proteins regulating cellular anterograde transport. Through experiments aimed at identifying CD11b/CD18-binding proteins, we produced a monoclonal antibody termed E1B2 that recognizes a 28-kDa membrane protein that co-precipitates with CD11b/CD18. Microsequence analysis of the E1B2 antigen revealed that it is BAP31. Co-association of CD11b/CD18 and BAP31 was confirmed in co-immunoprecipitation and protein binding assays. Additional experiments revealed that the binding of BAP31 to CD11b/CD18 was not dependent on divalent cations nor mediated by the I-domain of CD11b. Using glutathione S-transferase fusion chimeras, we determined that binding of CD11b/CD18 to BAP31 is mediated through interactions with the cytoplasmic tail of BAP31. Immunolocalization studies revealed colocalization of BAP31 and CD11b/CD18 within neutrophil secondary granules. Subcellular fractionation studies in polymorphonuclear leukocytes (PMN) revealed similar patterns of redistribution of BAP31 and CD11b/CD18 from fractions enriched in secondary granules to the plasma membrane following stimulation with formylmethionylleucylphenylalanine (fMLP). Given the known sorting properties of BAP31, these findings suggest that BAP31 may play a role in regulating intracellular trafficking of CD11b/CD18 in neutrophils.

ERp29, a general endoplasmic reticulum marker, is highly expressed throughout the brain

ERp29 is a recently discovered resident of the endoplasmic reticulum (ER) that is abundant in brain and most other mammalian tissues. Investigations of nonneural secretory tissues have implicated ERp29 in a major role producing export proteins, but a molecular activity remains wanting for this functional orphan. Intriguingly, ERp29 appears to be heavily utilized in the cerebellum, a brain region not conventionally regarded as neurosecretory. To elucidate this functional quandary, we used immunochemical approaches to characterize the regional, cellular, and subcellular distributions of ERp29 in rat brain. Immunohistochemistry revealed ubiquitous expression in neuronal and nonneuronal cells, with a distinctive variation in somatic ERp29 levels. Highly expressing cells were found in diverse locations, implying that ERp29 is not biased towards the cerebellum functionally. Using immunolocalization data mined from the literature, a proteomic profile was developed to assess the functional significance of ERp29's characteristic expression pattern. Surprisingly, ERp29 correlated poorly with classical markers of neurosecretion, but strongly with a variety of major membrane proteins. Together with immunogold localization of ERp29 to somatic ER, these observations led to a novel hypothesis that ERp29 is involved primarily in production of endomembrane proteins rather than proteins destined for export. This study establishes ERp29 as a general ER marker for brain cells and provides a stimulating clue about ERp29's enigmatic function. ERp29 appears to have broad significance for neural pathophysiology, given its ubiquitous distribution and prominence in brain over classical ER residents like BiP and protein disulfide isomerase.

Adult neuron survival strategies--slamming on the brakes

Developing neurons are programmed to die by an apoptotic pathway unless they are rescued by extrinsic growth factors that generate an anti-apoptotic response. By contrast, adult neurons need to survive for the lifetime of the organism, and their premature death can cause irreversible functional deficits. The default apoptotic pathway is shut down when development is complete, and consequently growth factors are no longer required to prevent death. To protect against accidental apoptotic cell death, anti-apoptotic mechanisms are activated in mature neurons in response to stress. Loss or reduced activity of these intrinsic anti-apoptotic 'brakes' might contribute to or accelerate neurodegeneration, whereas their activation might rescue neurons from injury or genetic abnormalities.

Bifunctional apoptosis inhibitor (BAR) protects neurons from diverse cell death pathways

The bifunctional apoptosis regulator (BAR) is a multidomain protein that was originally identified as an inhibitor of Bax-induced apoptosis. Immunoblot analysis of normal human tissues demonstrated high BAR expression in the brain, compared to low or absent expression in other organs. Immunohistochemical staining of human adult tissues revealed that the BAR protein is predominantly expressed by neurons in the central nervous system. Immunofluorescence microscopy indicated that BAR localizes mainly to the endoplasmic reticulum (ER) of cells. Overexpression of BAR in CSM 14.1 neuronal cells resulted in significant protection from a broad range of cell death stimuli, including agents that activate apoptotic pathways involving mitochondria, TNF-family death receptors, and ER stress. Downregulation of BAR by antisense oligonucleotides sensitized neuronal cells to induction of apoptosis. Moreover, the search for novel interaction partners of BAR identified several candidate proteins that might contribute to the regulation of neuronal apoptosis (HIP1, Hippi, and Bap31). Taken together, the expression pattern and functional data suggest that the BAR protein is involved in the regulation of neuronal survival.

A pox on thee! Manipulation of the host immune system by myxoma virus and implications for viral–host co-adaptation

The poxviruses have evolved a diverse array of proteins which serve to subvert innate and adaptive host responses that abort or at least limit viral infections. Myxoma virus and its rabbit host are considered to represent an ideal poxvirus-host system in which to study the effects of these immunomodulatory proteins. Studies of laboratory rabbits (Oryctolagus cuniculus) infected with gene knockout variants of myxoma virus have provided compelling evidence that several myxoma virus gene products contribute to the pathogenic condition known as myxomatosis. However, myxomatosis, which is characterized by skin lesions, systemic immunosuppression, and a high mortality rate, does not occur in the virus' natural South American host, Sylvilogus brasiliensis. Moreover, in Australia where myxoma virus was willfully introduced to control populations of O. cuniculus, myxomatosis-resistant rabbits emerged within a year of myxoma virus introduction into the field. In this review I discuss the characterized immunomodulatory proteins of myxoma virus, their biochemical properties, their pathogenic effects in laboratory rabbits, the role of the host immune system in the susceptibility or resistance to myxomatosis, and the evidence that immunomodulatory genes may have been attenuated during the co-adaptation of myxoma virus and O. cuniculus in Australia.