Characterization of mouse brain-specific angiogenesis inhibitor 1 (BAI1) and phytanoyl-CoA alpha-hydroxylase-associated protein 1, a novel BAI1-binding protein

High placental expression of FLT1, LEP, PHYHIP and IL3RA - In persons of African ancestry with severe preeclampsia

INTRODUCTION

Mortality from preeclampsia (PE) and PE-associated morbidities are 3-to 5-fold higher in persons of African ancestry than in those of Asian and European ancestries.

METHODS

To elucidate placental contribution to worse PE outcomes in African ancestry pregnancies, we performed bulk RNA sequencing on 50 placentas from persons with severe PE (sPE) of African (n = 9), Asian (n = 18) and European (n = 23) ancestries and 73 normotensive controls of African (n = 10), Asian (n = 15) and European (n = 48) ancestries.

RESULTS

Previously described canonical preeclampsia genes, involved in metabolism and hypoxia/angiogenesis including: LEP, HK2, FSTL3, FLT1, ENG, TMEM45A, ARHGEF4 and HTRA1 were upregulated sPE versus normotensive placentas across ancestries. LTF, NPR3 and PHYHIP were higher in African vs. Asian ancestry sPE placentas. Allograft rejection/adaptive immune response genes were upregulated in placentas from African but not in Asian or European ancestry sPE patients; IL3RA was of particular interest because the patient with the highest placental IL3RA expression, a person of African ancestry with sPE, developed postpartum cardiomyopathy, and was the only patient out of 123, that developed this condition. Interestingly, the sPE patients with the highest IL3RA expression among persons of Asian and European ancestries developed unexplained tachycardia peripartum, necessitating echocardiography in the European ancestry patient. The association between elevated placental IL3RA levels and unexplained tachycardia or peripartum cardiomyopathy was found to be significant in the 50 sPE patients (p = .0005).

DISCUSSION

High placental upregulation of both canonical preeclampsia and allograft rejection/adaptive immune response genes may contribute to worse PE outcomes in African ancestry sPE patients.

Emerging roles of adhesion G protein-coupled receptors

Adhesion G protein-coupled receptors (aGPCRs) form a sub-group within the GPCR superfamily. Their distinctive structure contains an abnormally large N-terminal, extracellular region with a GPCR autoproteolysis-inducing (GAIN) domain. In most aGPCRs, the GAIN domain constitutively cleaves the receptor into two fragments. This process is often required for aGPCR signalling. Over the last two decades, much research has focussed on aGPCR-ligand interactions, in an attempt to deorphanize the family. Most ligands have been found to bind to regions N-terminal to the GAIN domain. These receptors may bind a variety of ligands, ranging across membrane-bound proteins and extracellular matrix components. Recent advancements have revealed a conserved method of aGPCR activation involving a tethered ligand within the GAIN domain. Evidence for this comes from increased activity in receptor mutants exposing the tethered ligand. As a result, G protein-coupling partners of aGPCRs have been more extensively characterised, making use of their tethered ligand to create constitutively active mutants. This has led to demonstrations of aGPCR function in, for example, neurodevelopment and tumour growth. However, questions remain around the ligands that may bind many aGPCRs, how this binding is translated into changes in the GAIN domain, and the exact mechanism of aGPCR activation following GAIN domain conformational changes. This review aims to examine the current knowledge around aGPCR activation, including ligand binding sites, the mechanism of GAIN domain-mediated receptor activation and how aGPCR transmembrane domains may relate to activation. Other aspects of aGPCR signalling will be touched upon, such as downstream effectors and physiological roles.

The Ser19Stop single nucleotide polymorphism (SNP) of human PHYHIPL affects the cerebellum in mice

The HapMap Project is a major international research effort to construct a resource to facilitate the discovery of relationships between human genetic variations and health and disease. The Ser19Stop single nucleotide polymorphism (SNP) of human phytanoyl-CoA hydroxylase-interacting protein-like (PHYHIPL) gene was detected in HapMap project and registered in the dbSNP. PHYHIPL gene expression is altered in global ischemia and glioblastoma multiforme. However, the function of PHYHIPL is unknown. We generated PHYHIPL Ser19Stop knock-in mice and found that PHYHIPL impacts the morphology of cerebellar Purkinje cells (PCs), the innervation of climbing fibers to PCs, the inhibitory inputs to PCs from molecular layer interneurons, and motor learning ability. Thus, the Ser19Stop SNP of the PHYHIPL gene may be associated with cerebellum-related diseases.

Mechanisms of adhesion G protein-coupled receptor activation

Adhesion G protein-coupled receptors (AGPCRs) are a thirty-three-member subfamily of Class B GPCRs that control a wide array of physiological processes and are implicated in disease. AGPCRs uniquely contain large, self-proteolyzing extracellular regions that range from hundreds to thousands of residues in length. AGPCR autoproteolysis occurs within the extracellular GPCR autoproteolysis-inducing (GAIN) domain that is proximal to the N terminus of the G protein-coupling seven-transmembrane-spanning bundle. GAIN domain-mediated self-cleavage is constitutive and produces two-fragment holoreceptors that remain bound at the cell surface. It has been of recent interest to understand how AGPCRs are activated in relation to their two-fragment topologies. Dissociation of the AGPCR fragments stimulates G protein signaling through the action of the tethered-peptide agonist stalk that is occluded within the GAIN domain in the holoreceptor form. AGPCRs can also signal independently of fragment dissociation, and a few receptors possess GAIN domains incapable of self-proteolysis. This has resulted in complex theories as to how these receptors are activated in vivo, complicating pharmacological advances. Currently, there is no existing structure of an activated AGPCR to support any of the theories. Further confounding AGPCR research is that many of the receptors remain orphans and lack identified activating ligands. In this review, we provide a detailed layout of the current theorized modes of AGPCR activation with discussion of potential parallels to mechanisms used by other GPCR classes. We provide a classification means for the ligands that have been identified and discuss how these ligands may activate AGPCRs in physiological contexts.

Brain-specific angiogenesis inhibitor 1 is expressed in the Myo/Nog cell lineage

The Myo/Nog cell lineage was discovered in the chick embryo and is also present in adult mammalian tissues. The cells are named for their expression of mRNA for the skeletal muscle specific transcription factor MyoD and bone morphogenetic protein inhibitor Noggin. A third marker for Myo/Nog cells is the cell surface molecule recognized by the G8 monoclonal antibody (mAb). G8 has been used to detect, track, isolate and kill Myo/Nog cells. In this study, we screened a membrane proteome array for the target of the G8 mAb. The array consisted of >5,000 molecules, each synthesized in their native confirmation with appropriate post-translational modifications in a single clone of HEK-293T cells. G8 mAb binding to the clone expressing brain-specific angiogenesis inhibitor 1 (BAI1) was detected by flow cytometry, re-verified by sequencing and validated by transfection with the plasmid construct for BAI1. Further validation of the G8 target was provided by enzyme-linked immunosorbent assay. The G8 epitope was identified by screening a high-throughput, site directed mutagenesis library designed to cover 95–100% of the 954 amino acids of the extracellular domain of the BAI1 protein. The G8 mAb binds within the third thrombospondin repeat of the extracellular domain of human BAI1. Immunofluorescence localization experiments revealed that G8 and a commercially available BAI1 mAb co-localize to the subpopulation of Myo/Nog cells in the skin, eyes and brain. Expression of the multi-functional BAI1 protein in Myo/Nog cells introduces new possibilities for the roles of Myo/Nog cells in normal and diseased tissues.

Understanding the Role of the BAI Subfamily of Adhesion G Protein-Coupled Receptors (GPCRs) in Pathological and Physiological Conditions

Brain-specific angiogenesis inhibitors (BAIs) 1, 2, and 3 are members of the adhesion G protein-coupled receptors, subfamily B, which share a conserved seven-transmembrane structure and an N-terminal extracellular domain. In cell- and animal-based studies, these receptors have been shown to play diverse roles under physiological and pathological conditions. BAI1 is an engulfment receptor and performs major functions in apoptotic-cell clearance and interacts (as a pattern recognition receptor) with pathogen components. BAI1 and -3 also participate in myoblast fusion. Furthermore, BAI1–3 have been linked to tumor progression and neurological diseases. In this review, we summarize the current understanding of the functions of BAI1–3 in pathological and physiological conditions and discuss future directions in terms of the importance of BAIs as pharmacological targets in diseases.

The Adhesion-GPCR BAI1 Promotes Excitatory Synaptogenesis by Coordinating Bidirectional Trans-synaptic Signaling

Excitatory synapses are specialized cell-cell contacts located on actin-rich dendritic spines that mediate information flow and storage in the brain. The postsynaptic adhesion-G protein-coupled receptor (A-GPCR) BAI1 is a critical regulator of excitatory synaptogenesis, which functions in part by recruiting the Par3-Tiam1 polarity complex to spines, inducing local Rac1 GTPase activation and actin cytoskeletal remodeling. However, a detailed mechanistic understanding of how BAI1 controls synapse and spine development remains elusive. Here, we confirm that BAI1 is required in vivo for hippocampal spine development, and we identify three distinct signaling mechanisms mediating BAI1's prosynaptogenic functions. Using in utero electroporation to sparsely knock down BAI1 expression in hippocampal pyramidal neurons, we show that BAI1 cell-autonomously promotes spinogenesis in the developing mouse brain. BAI1 appears to function as a receptor at synapses, as its extracellular N-terminal segment is required for both its prospinogenic and prosynaptogenic functions. Moreover, BAI1 activation with a Stachel-derived peptide, which mimics a tethered agonist motif found in A-GPCRs, drives synaptic Rac1 activation and subsequent spine and synapse development. We also reveal, for the first time, a trans-synaptic function for BAI1, demonstrating in a mixed-culture assay that BAI1 induces the clustering of presynaptic vesicular glutamate transporter 1 (vGluT1) in contacting axons, indicative of presynaptic differentiation. Finally, we show that BAI1 forms a receptor complex with the synaptogenic cell-adhesion molecule Neuroligin-1 (NRLN1) and mediates NRLN1-dependent spine growth and synapse development. Together, these findings establish BAI1 as an essential postsynaptic A-GPCR that regulates excitatory synaptogenesis by coordinating bidirectional trans-synaptic signaling in cooperation with NRLN1.SIGNIFICANCE STATEMENT Adhesion-G protein-coupled receptors are cell-adhesion receptors with important roles in nervous system development, function, and neuropsychiatric disorders. The postsynaptic adhesion-G protein-coupled receptor BAI1 is a critical regulator of dendritic spine and excitatory synapse development. However, the mechanism by which BAI1 controls these functions remains unclear. Our study identifies three distinct signaling paradigms for BAI1, demonstrating that it mediates forward, reverse, and lateral signaling in spines. Activation of BAI1 by a Stachel-dependent mechanism induces local Rac1 activation and subsequent spinogenesis/synaptogenesis. BAI1 also signals trans-synaptically to promote presynaptic differentiation. Furthermore, BAI1 interacts with the postsynaptic cell-adhesion molecule Neuroligin-1 (NRLN1) and facilitates NRLN1-dependent spine growth and excitatory synaptogenesis. Thus, our findings establish BAI1 as a functional synaptogenic receptor that promotes presynaptic and postsynaptic development in cooperation with synaptic organizer NRLN1.

New Targets for Parkinson's Disease: Adhesion G Protein-Coupled Receptor B1 is Downregulated by AMP-Activated Protein Kinase Activation

While progressive dopaminergic neurodegeneration is responsible for the cardinal motor defects in Parkinson's disease (PD), new diagnostics and therapeutic targets are necessary to effectively address this major global health burden. We evaluated whether the adhesion G protein-coupled receptor B1 (ADGRB1, formerly BAI1, brain-specific angiogenesis inhibitor 1) might contribute to dopaminergic neuronal loss. We used bioinformatic analyses, as well as in vitro and in vivo PD models. We report in this study that ADGRB1 is decreased in PD and that the ADGRB1 level is specifically decreased in dopaminergic neurons in the substantia nigra of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-intoxicated mice. In primary mouse mesencephalic neurons and human neuroblastoma cell lines, 1-methyl-4-phenylpyridinium (MPP⁺), a toxic metabolite of MPTP, suppressed the expression of ADGRB1. Moreover, we applied a network generation tool, Ingenuity Pathway Analysis^®, with the transcriptomics dataset to extend the upstream regulatory pathway of ADGRB1 expression. AMP-activated protein kinase (AMPK) was predicted as a regulator, and consequently, 5-aminoimidazole-4-carboxamide ribonucleotide, a specific activator of AMPK, reduced the ADGRB1 protein level. Finally, ADGRB1 overexpression decreased nuclear condensation induced by MPP⁺ treatment. Taken together, we observed that decreased ADGRB1 by activation of AMPK induced neuronal cell death in MPTP/MPP⁺-mediated PD models, suggesting that ADGRB1 might potentially play a survival role in the neurodegenerative pathway of PD. These data offer new insights into dopaminergic cell death with therapeutic implications for neurodegenerative disorders.

An investigation into the potential role of brain angiogenesis inhibitor protein 3 (BAI3) in the tumorigenesis of small-cell carcinoma: a review of the surrounding literature

Brain angiogenesis inhibitor protein 3 (BAI3) is from the adhesion group of seven-transmembrane spanning G protein-coupled receptors (GPCRs) and has been identified via gene expression profiling as being upregulated in small-cell lung cancer (SCLC) tumors. It has subsequently been validated as a sensitive and specific immunohistochemical marker for SCLC, helping to differentiate these tumors from morphologically similar large-cell neuroendocrine (LCNEC) malignancies. It is, however, still unclear as to the role BAI3 proteins might play in SCLC and indeed how they might contribute to tumorigenesis. Interestingly, the pattern of staining observed on immunohistochemistry was in fact nuclear as opposed to the membranous staining pattern expected of transmembrane-bound molecules. This fact has lead the authors to believe that the protein receptor is structurally altered in SCLC and that this modification may confer different behavioral properties that contribute toward tumorigenesis. Nuclear localization is not unique to BAI3 and has been reported in a number of GPCRs and frequently correlates with survival outcomes. BAI3 has the potential to act as target for pharmaceutical intervention inline with developing trends in molecular pathology aiming to provide personalized, treatment regimes based on tumor-specific mutation profiles. The adhesion group of the GPCR superfamily is still poorly understood. We present a review of the existing literature regarding the role they play in both physiological and disease states and the mechanisms by which they influence a range of cellular processes.

Context Specific and Differential Gene Co-expression Networks via Bayesian Biclustering

Identifying latent structure in high-dimensional genomic data is essential for exploring biological processes. Here, we consider recovering gene co-expression networks from gene expression data, where each network encodes relationships between genes that are co-regulated by shared biological mechanisms. To do this, we develop a Bayesian statistical model for biclustering to infer subsets of co-regulated genes that covary in all of the samples or in only a subset of the samples. Our biclustering method, BicMix, allows overcomplete representations of the data, computational tractability, and joint modeling of unknown confounders and biological signals. Compared with related biclustering methods, BicMix recovers latent structure with higher precision across diverse simulation scenarios as compared to state-of-the-art biclustering methods. Further, we develop a principled method to recover context specific gene co-expression networks from the estimated sparse biclustering matrices. We apply BicMix to breast cancer gene expression data and to gene expression data from a cardiovascular study cohort, and we recover gene co-expression networks that are differential across ER+ and ER- samples and across male and female samples. We apply BicMix to the Genotype-Tissue Expression (GTEx) pilot data, and we find tissue specific gene networks. We validate these findings by using our tissue specific networks to identify trans-eQTLs specific to one of four primary tissues.

Intragenic Locus in Human PIWIL2 Gene Shares Promoter and Enhancer Functions

Recently, more evidence supporting common nature of promoters and enhancers has been accumulated. In this work, we present data on chromatin modifications and non-polyadenylated transcription characteristic for enhancers as well as results of in vitro luciferase reporter assays suggesting that PIWIL2 alternative promoter in exon 7 also functions as an enhancer for gene PHYHIP located 60Kb upstream. This finding of an intragenic enhancer serving as a promoter for a shorter protein isoform implies broader impact on understanding enhancer-promoter networks in regulation of gene expression.

Adhesion GPCRs as Novel Actors in Neural and Glial Cell Functions: From Synaptogenesis to Myelination

Adhesion G-protein-coupled receptors (aGPCRs) are emerging as key regulators of nervous system development and health. aGPCRs can regulate many aspects of neural development, including cell signaling, cell-cell and cell-matrix interactions, and, potentially, mechanosensation. Here, we specifically focus on the roles of several aGPCRs in synapse biology, dendritogenesis, and myelinating glial cell development. The lessons learned from these examples may be extrapolated to other contexts in the nervous system and beyond.

Adhesion GPCR-Related Protein Networks

Adhesion G protein-coupled receptors (aGPCRs/ADGRs) are unique receptors that combine cell adhesion and signaling functions. Protein networks related to ADGRs exert diverse functions, e.g., in tissue polarity, cell migration, nerve cell function, or immune response, and are regulated via different mechanisms. The large extracellular domain of ADGRs is capable of mediating cell-cell or cell-matrix protein interactions. Their intracellular surface and domains are coupled to downstream signaling pathways and often bind to scaffold proteins, organizing membrane-associated protein complexes. The cohesive interplay between ADGR-related network components is essential to prevent severe disease-causing damage in numerous cell types. Consequently, in recent years, attention has focused on the decipherment of the precise molecular composition of ADGR protein complexes and interactomes in various cellular modules. In this chapter, we discuss the affiliation of ADGR networks to cellular modules and how they can be regulated, pinpointing common features in the networks related to the diverse ADGRs. Detailed decipherment of the composition of protein networks should provide novel targets for the development of novel therapies with the aim to cure human diseases related to ADGRs.

International Union of Basic and Clinical Pharmacology. XCIV. Adhesion G protein-coupled receptors

The Adhesion family forms a large branch of the pharmacologically important superfamily of G protein-coupled receptors (GPCRs). As Adhesion GPCRs increasingly receive attention from a wide spectrum of biomedical fields, the Adhesion GPCR Consortium, together with the International Union of Basic and Clinical Pharmacology Committee on Receptor Nomenclature and Drug Classification, proposes a unified nomenclature for Adhesion GPCRs. The new names have ADGR as common dominator followed by a letter and a number to denote each subfamily and subtype, respectively. The new names, with old and alternative names within parentheses, are: ADGRA1 (GPR123), ADGRA2 (GPR124), ADGRA3 (GPR125), ADGRB1 (BAI1), ADGRB2 (BAI2), ADGRB3 (BAI3), ADGRC1 (CELSR1), ADGRC2 (CELSR2), ADGRC3 (CELSR3), ADGRD1 (GPR133), ADGRD2 (GPR144), ADGRE1 (EMR1, F4/80), ADGRE2 (EMR2), ADGRE3 (EMR3), ADGRE4 (EMR4), ADGRE5 (CD97), ADGRF1 (GPR110), ADGRF2 (GPR111), ADGRF3 (GPR113), ADGRF4 (GPR115), ADGRF5 (GPR116, Ig-Hepta), ADGRG1 (GPR56), ADGRG2 (GPR64, HE6), ADGRG3 (GPR97), ADGRG4 (GPR112), ADGRG5 (GPR114), ADGRG6 (GPR126), ADGRG7 (GPR128), ADGRL1 (latrophilin-1, CIRL-1, CL1), ADGRL2 (latrophilin-2, CIRL-2, CL2), ADGRL3 (latrophilin-3, CIRL-3, CL3), ADGRL4 (ELTD1, ETL), and ADGRV1 (VLGR1, GPR98). This review covers all major biologic aspects of Adhesion GPCRs, including evolutionary origins, interaction partners, signaling, expression, physiologic functions, and therapeutic potential.

The BAI subfamily of adhesion GPCRs: synaptic regulation and beyond

The brain-specific angiogenesis inhibitors 1-3 (BAI1-3) comprise a subfamily of adhesion G-protein-coupled receptors (GPCRs). These receptors are highly expressed in the brain and were first studied for their ability to inhibit angiogenesis and tumor formation. Subsequently, BAI1 was found to play roles in apoptotic cell phagocytosis and myoblast fusion. Until recently, however, little was known about the physiological importance of the BAI subfamily in the context of normal brain function. Recent work has provided evidence for key roles of BAI1-3 in the regulation of synaptogenesis and dendritic spine formation. In this review, we summarize the current understanding of the BAI subfamily with regard to downstream signaling pathways, physiological actions, and potential importance as novel drug targets in the treatment of psychiatric and neurological diseases.

Role of phosphatidylserine receptors in enveloped virus infection

We recently demonstrated that a soluble protein, Gas6, can facilitate viral entry by bridging viral envelope phosphatidylserine to Axl, a receptor tyrosine kinase expressed on target cells. The interaction between phosphatidylserine, Gas6, and Axl was originally shown to be a molecular mechanism through which phagocytes recognize phosphatidylserine exposed on dead cells. Since our initial report, several groups have confirmed that Axl/Gas6, as well as other phosphatidylserine receptors, facilitate entry of dengue, West Nile, and Ebola viruses. Virus binding by viral envelope phosphatidylserine is now a viral entry mechanism generalized to many families of viruses. In addition to Axl/Gas6, various molecules are known to recognize phosphatidylserine; however, the effects of these molecules on virus binding and entry have not been comprehensively evaluated and compared. In this study, we examined most of the known human phosphatidylserine-recognizing molecules, including MFG-E8, TIM-1, -3, and -4, CD300a, BAI1, and stabilin-1 and -2, for their abilities to facilitate virus binding and infection. Using pseudotyped lentiviral vectors, we found that a soluble phosphatidylserine-binding protein, MFG-E8, enhances transduction. Cell surface receptors TIM-1 and -4 also enhance virus binding/transduction. The extent of enhancement by these molecules varies, depending on the type of pseudotyping envelope proteins. Mutated MFG-E8, which binds viral envelope phosphatidylserine without bridging virus to cells, but, surprisingly, not annexin V, which has been used to block phagocytosis of dead cells by concealing phosphatidylserine, efficiently blocks these phosphatidylserine-dependent viral entry mechanisms. These results provide insight into understanding the role of viral envelope phosphatidylserine in viral infection.

IMPORTANCE

Envelope phosphatidylserine has previously been shown to be important for replication of various envelope viruses, but details of this mechanism(s) were unclear. We were the first to report that a bifunctional serum protein, Gas6, bridges envelope phosphatidylserine to a cell surface receptor, Axl. Recent studies demonstrated that many envelope viruses, including vaccinia, dengue, West Nile, and Ebola viruses, utilize Axl/Gas6 to facilitate their entry, suggesting that the phosphatidylserine-mediated viral entry mechanism can be shared by various enveloped viruses. In addition to Axl/Gas6, various molecules are known to recognize phosphatidylserine; however, the effects of these molecules on virus binding and entry have not been comprehensively evaluated and compared. In this study, we examined most human phosphatidylserine-recognizing molecules for their abilities to facilitate viral infection. The results provide insights into the role(s) of envelope phosphatidylserine in viral infection, which can be applicable to the development of novel antiviral reagents that block phosphatidylserine-mediated viral entry.

miRNA expression is modulated over time after focal ischaemia: up-regulation of miR-347 promotes neuronal apoptosis

Despite the large number of molecules reported as being over-expressed after ischaemia, little is known regarding their regulation. miRNAs are potent post-transcriptional regulators of gene expression, and reports have shown differentially miRNA expression in response to focal cerebral ischaemia. The present study analysed miRNA expression from acute to late phases of ischaemia to identify specific ischaemia-related miRNAs, elucidate their role, and identify potential targets involved in stroke pathophysiology. Of 112 miRNAs, 32 showed significant changes and different expression profiles. In addition to the previously reported differentially expressed miRNAs, new ischaemia-regulated miRNAs have been found, including miR-347. Forty-seven genes involved in brain functions or related to ischaemia are predicted to be potential targets of the differentially expressed miRNAs after middle cerebral artery occlusion. Analysis of four of these targets (Acsl4, Arf3, Btg2 and Dpysl5) showed them to be differentially regulated by ischaemia at the transcriptional or post-transcriptional level. Acsl4, Bnip3l and Phyhip, potential targets of miR-347, were up-regulated after miR-347 over-expression, inducing neuronal apoptotic death. Our findings suggest that miR-347 plays an important role in regulating neuronal cell death, identify Acsl4 as a new protein requiring study in ischaemia, and provide an important resource for future functional studies of miRNAs after ischaemia.

Brain-specific angiogenesis inhibitor-1 signaling, regulation, and enrichment in the postsynaptic density

Brain-specific angiogenesis inhibitor-1 (BAI1) is an adhesion G protein-coupled receptor that has been studied primarily for its anti-angiogenic and anti-tumorigenic properties. We found that overexpression of BAI1 results in activation of the Rho pathway via a Gα(12/13)-dependent mechanism, with truncation of the BAI1 N terminus resulting in a dramatic enhancement in receptor signaling. This constitutive activity of the truncated BAI1 mutant also resulted in enhanced downstream phosphorylation of ERK as well as increased receptor association with β-arrestin2 and increased ubiquitination of the receptor. To gain insights into the regulation of BAI1 signaling, we screened the C terminus of BAI1 against a proteomic array of PDZ domains to identify novel interacting partners. These screens revealed that the BAI1 C terminus interacts with a variety of PDZ domains from synaptic proteins, including MAGI-3. Removal of the BAI1 PDZ-binding motif resulted in attenuation of receptor signaling to Rho but had no effect on ERK activation. Conversely, co-expression with MAGI-3 was found to potentiate signaling to ERK by constitutively active BAI1 in a manner that was dependent on the PDZ-binding motif of the receptor. Biochemical fractionation studies revealed that BAI1 is highly enriched in post-synaptic density fractions, a finding consistent with our observations that BAI1 can interact with PDZ proteins known to be concentrated in the post-synaptic density. These findings demonstrate that BAI1 is a synaptic receptor that can activate both the Rho and ERK pathways, with the N-terminal and C-terminal regions of the receptor playing key roles in the regulation of BAI1 signaling activity.

Expression of brain-specific angiogenesis inhibitor 1 is inversely correlated with pathological grade, angiogenesis and peritumoral brain edema in human astrocytomas

As the most common intracranial malignant neoplasms, astrocytomas are characterized by high neovascularization and severe peritumoral brain edema (PTBE). Angiogenesis is a prerequisite for the growth of solid tumors, including astrocytoma, and brain-specific angiogenesis inhibitor 1 (BAI1) is a novel angiogenesis inhibitor. In the present study, the expression levels of BAI1, vascular endothelial growth factor (VEGF) and basic fibroblast growth factor (bFGF) were investigated using immunohistochemical methods in 90 human brain astrocytoma specimens of various pathological grades and in 11 normal human brain tissues. Vascular endothelial cells were stained for CD105 and the microvessel density (MVD) was assessed. The volume of astrocytoma and PTBE in each case was evaluated by magnetic resonance imaging (MRI). The results showed that BAI1 was highly expressed in the normal brain tissues, but that the expression decreased with the rising pathological grades of astrocytoma, MVD number and PTBE, indicating that BAI1 expression was inversely correlated with these factors. Furthermore, it was observed that the expression of VEGF and bFGF were inversely correlated with BAI1 expression in the human brain astrocytomas. These results indicate that the BAI1 gene may be used as a marker of decreased tumor progression and tumoral neovascularization, as well as PTBE.

Temporal expression analysis of angiogenesis-related genes in brain development

Background

The current knowledge on molecular pathogenesis of cerebral vascular malformations (CVM), which are believed to arise during development, is very limited. To unravel the molecular mechanisms involved in CVMs, a detailed understanding of the brain vascular development at molecular level is crucial. In this study, we aimed to explore the temporal and comparative expression profile of angiogenesis-related genes in the establishment of brain vasculature.

Methods

Expression of a total of 113 angiogenesis-related genes during murine brain development has been analyzed using low-density array systems designed for angiogenesis-related genes. Bai1 (brain specific angiogenesis inhibitor-1), a recently identified novel anti-angiogenic gene, has been selected for further characterization.

Results

We found that 62 out of 113 analyzed genes have expression in brain development at varying levels. Nineteen of these were differentially expressed between embryonic and postnatal stages (>1.5 fold). Bai1 is strongly expressed on growing blood vessels of cerebral cortex and hippocampus, partially expressed in the lateral regions of striatum, but mostly absent on the thalamus.

Conclusion

By showing the comparative expression analysis of angiogenesis-related genes throughout brain development, the data presented here will be a crucial addition to further functional studies on cerebrovascular research.

Emerging roles for the BAI1 protein family in the regulation of phagocytosis, synaptogenesis, neurovasculature, and tumor development

While G-protein-coupled receptors (GPCRs) have received considerable attention for their biological activity in a diversity of physiological functions and have become targets for therapeutic intervention in many diseases, the function of the cell adhesion subfamily of GPCRs remains poorly understood. Within this group, the family of brain angiogenesis inhibitor molecules (BAI1-3) has become increasingly appreciated for their diverse roles in biology and disease. In particular, recent findings suggest emerging roles for BAI1 in the regulation of phenomena including phagocytosis, synaptogenesis, and the inhibition of tumor growth and angiogenesis via the processing of its extracellular domain into secreted vasculostatins. Here we summarize the known biological features of the BAI proteins, including their structure, proteolysis events, and interacting partners, and their recently identified ability to regulate certain signaling pathways. Finally, we discuss the potential of the BAIs as therapeutics or targets for diseases as varied as cancer, stroke, and schizophrenia.

The cell-adhesion G protein-coupled receptor BAI3 is a high-affinity receptor for C1q-like proteins

C1q-like genes (C1ql1-C1ql4) encode small, secreted proteins that are expressed in differential patterns in the brain but whose receptors and functions remain unknown. BAI3 protein, in contrast, is a member of the cell-adhesion class of G protein-coupled receptors that are expressed at high levels in the brain but whose ligands have thus far escaped identification. Using a biochemical approach, we show that all four C1ql proteins bind to the extracellular thrombospondin-repeat domain of BAI3 with high affinity, and that this binding is mediated by the globular C1q domains of the C1ql proteins. Moreover, we demonstrate that addition of submicromolar concentrations of C1ql proteins to cultured neurons causes a significant decrease in synapse density, and that this decrease was prevented by simultaneous addition of the thrombospondin-repeat fragment of BAI3, which binds to C1ql proteins. Our data suggest that C1ql proteins are secreted signaling molecules that bind to BAI3 and act, at least in part, to regulate synapse formation and/or maintenance.

Adhesion-GPCRs in the CNS

There are a total of 33 members of adhesion G protein-coupled receptors (GPCRs) in humans and 30 members in mice and rats. More than half of these receptors are expressed in the central nervous system (CNS), indicating their possible roles in the development and function of the CNS. Indeed, it has been shown that adhesion-GPCRs are involved in the regulation of neurulation, cortical development and neurite growth. Among the few adhesion-GPCRs being studied, GPR56 is so far the only member associated with a human brain malformation called bilateral frontoparietal polymicrogyria (BFPP). The histopathology of BFPP is a cobblestone-like brain malformation characterized by neuronal overmigration through a breached pial basement membrane (BM). Further studies in the Gpr56 knockout mouse model revealed that GPR56 is expressed in radial glial cells and regulates the integrity of the pial BM by binding a putative ligand in the extracellular matrix of the developing brain.

Emerging roles of brain-specific angiogenesis inhibitor 1

Brain-specific angiogenesis inhibitor 1 (BAI1) encodes a seven-transmembrane protein that belongs to the adhesion-GPCR family. Although BAI1 was named for the ability of its extracellular region to inhibit angiogenesis in tumor models, its function in physiological contexts was elusive and remained an orphan receptor until recently. BAI1 is now considered a phagocytic receptor that can recognize phosphatidylserine exposed on apoptotic cells. Moreover, BAI1 has been shown to function upstream of the signaling module comprised of ELMO/Dock180/Rac proteins, thereby facilitating the cytoskeletal reorganization necessary to mediate the phagocytic clearance of apoptotic cells. Here, we review the phylogeny, structure, associating proteins, as well as the known and proposed functions of BAI1.

Adhesion-GPCRs: emerging roles for novel receptors

The G protein-coupled receptor (GPCR) family comprises the largest class of cell surface receptors found in metazoan proteomes. Within the novel GPCR subfamily of adhesion-GPCRs, approximately 150 distinct orthologues, from invertebrates to mammals, have been identified to date. All members of this family contain a large extracellular region, often containing common protein modules, coupled to a seven-transmembrane domain via a stalk region that seems to be crucial for functionality. Owing to their unique structure, restricted expression profile and involvement in several human diseases, adhesion-GPCRs have long been proposed to have vital dual roles in cellular adhesion and signalling. More recent studies have provided structural, evolutionary, developmental and immunological insights in relation to the adhesion-GPCR family.

Non-manifesting Refsum heterozygotes carrying the c.135-2A>G PAHX gene transition

So far, subjects heterozygous for PAHX mutations are regarded as non-symptomatic. In the 24-year-old, HIV-negative daughter and the 26-year-old, HIV-negative son of a patient with Refsum disease due to the homozygous c.135-2A>G transition at the splice site before exon 3 of the PAHX gene, slight abnormalities suggestive of the disease became apparent. The daughter reported a single fever cramp in childhood, recurrent, short-lived amaurotic episodes after getting up from supine, short-sightedness, hypoacusis, and restless legs. The son complained about restless legs, hyperhidrosis, hypoacusis, and bulbar oscillations. Though both children carried the same mutation as their mother in the heterozygous form, clinical neurologic examination, nerve conduction studies and serum phytanic acid concentration were normal in both of them, implying that the described abnormalities were not causally related to the PAHX mutation. In the absence of elevated phytanic acid concentrations, clinical neurologic abnormalities in heterozygous relatives of Refsum patients are not attributable to heterozygosity for PAHX mutations.

MicroRNA expression profile in murine central nervous system development

MicroRNAs (miRNAs) regulate gene expression in a post-transcriptional sequence-specific manner. In order to better understand the possible roles of miRNAs in central nervous system (CNS) development, we examined the expression profile of 104 miRNAs during murine brain development. We obtained brain samples from animals at embryonic days (E) E15, E17, and postnatal days (P) P1 and P7. Total RNA was isolated from tissue and used to obtain mature miRNAs by reverse transcription. Our results indicate that there is a group of 12 miRNAs that show a distinct expression profile, with the highest expression during embryonic stages and decreasing significantly during development. This profile suggests key roles in processes occurring during early CNS development.

Structural and mechanistic studies on the peroxisomal oxygenase phytanoyl-CoA 2-hydroxylase (PhyH)

Phytanic acid (PA) is an epimeric metabolite of the isoprenoid side chain of chlorophyll. Owing to the presence of its epimeric β-methyl group, PA cannot be metabolized by β-oxidation. Instead, it is metabolized in peroxisomes via α-oxidation to give pristanic acid, which is then oxidized by β-oxidation. PhyH (phytanoyl-CoA 2-hydroxylase, also known as PAHX), an Fe(II) and 2OG (2-oxoglutarate) oxygenase, catalyses hydroxylation of phytanoyl-CoA. Mutations of PhyH ablate its role in α-oxidation, resulting in PA accumulation and ARD (adult Refsum's disease). The structure and function of PhyH is discussed in terms of its clinical importance and unusual selectivity. Most point mutations of PhyH causing ARD cluster in two distinct groups around the Fe(II)- and 2OG-binding sites. Therapaeutic possibilities for the treatment of Refsum's disease involving PhyH are discussed.

The evolutionary history and tissue mapping of GPR123: specific CNS expression pattern predominantly in thalamic nuclei and regions containing large pyramidal cells

The Adhesion family of G protein-coupled receptors (GPCRs) includes 33 receptors and is the second largest GPCR family. Most of these proteins are still orphans and fairly little is known of their tissue distribution and evolutionary context. We report the evolutionary history of the Adhesion family protein GPR123 as well as mapping of GPR123 mRNA expression in mouse and rat using in situ hybridization and real-time PCR, respectively. GPR123 was found to be well conserved within the vertebrate lineage, especially within the transmembrane regions and in the distal part of the cytoplasmic tail, containing a potential PDZ binding domain. The real-time PCR data indicates that GPR123 is predominantly expressed in CNS. The in situ data show high expression in thalamic nuclei and regions containing large pyramidal cells like cortex layers 5 and 6 and subiculum. Moreover, we found distinct expression in amygdala, hypothalamus, inferior olive and spinal cord. The CNS specific expression, together with the high sequence conservation between the vertebrate sequences investigated, indicate that GPR123 may have an important role in the regulation of neuronal signal transduction.

A repressor complex, AP4 transcription factor and geminin, negatively regulates expression of target genes in nonneuronal cells

The transcription of neuron-specific genes must be repressed in nonneuronal cells. REST/NRSF is a transcription factor that restricts the expression of many neuronal genes through interaction with the neuron-restrictive silencer element at the promoter level. PAHX-AP1 is a neuronal gene that is developmentally up-regulated in the adult mouse brain but that has no functional NRSE motif in its 5' upstream sequence. Here, we report that the transcription factor AP4 and the corepressor geminin form a functional complex in which SMRT and histone deacetylase 3 are recruited. The functional complex represses PAHX-AP1 expression in nonneuronal cells and participates in regulating the developmental expression of PAHX-AP1 in the brain. This complex also serves as a transcriptional repressor of DYRK1A, a candidate gene for Down's syndrome. Furthermore, compared with that in normal fetal brain, the expression of AP4 and geminin is reduced in Down's syndrome fetal brain at 20 weeks of gestation age, at which time premature overexpression of dual-specificity tyrosine-phosphorylated and regulated kinase 1A (DYRK1A) is observed. Our findings indicate that AP4 and geminin act as a previously undescribed repressor complex distinct from REST/NRSF to negatively regulate the expression of target genes in nonneuronal cells and suggest that the AP4-geminin complex may contribute to suppressing the precocious expression of target genes in fetal brain.

Brain-specific angiogenesis inhibitor 2 regulates VEGF through GABP that acts as a transcriptional repressor

Previously, we reported that decreased brain-specific angiogenesis inhibitor 2 (BAI2) induced increased VEGF expression. The regulatory mechanisms for this process are not understood. Here we show that GA-binding protein gamma (GABPgamma) associates with the cytoplasmic domain of BAI2, and GABPalpha/gamma or GABPalpha/beta works as a transcriptional repressor of VEGF in SHSY5Y cells. Transcriptional activity of wild-type VEGF promoter was significantly increased in anti-sense BAI2-transfected cells, but not that of VEGF promoter harboring mutated GABP sites. In in vivo focal cerebral ischemia model, the decrease in BAI2 accompanied by decreased GABPalpha and GABPgamma elicited increased VEGF expression before the onset of HIF-1alpha. Our results point out that BAI2 controls VEGF transcription through GABP under normal conditions and cerebral ischemia.

Structure of human phytanoyl-CoA 2-hydroxylase identifies molecular mechanisms of Refsum disease

Refsum disease (RD), a neurological syndrome characterized by adult onset retinitis pigmentosa, anosmia, sensory neuropathy, and phytanic acidaemia, is caused by elevated levels of phytanic acid. Many cases of RD are associated with mutations in phytanoyl-CoA 2-hydroxylase (PAHX), an Fe(II) and 2-oxoglutarate (2OG)-dependent oxygenase that catalyzes the initial alpha-oxidation step in the degradation of phytenic acid in peroxisomes. We describe the x-ray crystallographic structure of PAHX to 2.5 A resolution complexed with Fe(II) and 2OG and predict the molecular consequences of mutations causing RD. Like other 2OG oxygenases, PAHX possesses a double-stranded beta-helix core, which supports three iron binding ligands (His(175), Asp(177), and His(264)); the 2-oxoacid group of 2OG binds to the Fe(II) in a bidentate manner. The manner in which PAHX binds to Fe(II) and 2OG together with the presence of a cysteine residue (Cys(191)) 6.7 A from the Fe(II) and two further histidine residues (His(155) and His(281)) at its active site distinguishes it from that of the other human 2OG oxygenase for which structures are available, factor inhibiting hypoxia-inducible factor. Of the 15 PAHX residues observed to be mutated in RD patients, 11 cluster in two distinct groups around the Fe(II) (Pro(173), His(175), Gln(176), Asp(177), and His(220)) and 2OG binding sites (Trp(193), Glu(197), Ile(199), Gly(204), Asn(269), and Arg(275)). PAHX may be the first of a new subfamily of coenzyme A-binding 2OG oxygenases.

Lipid-mediated delivery of brain-specific angiogenesis inhibitor 1 gene reduces corneal neovascularization in an in vivo rabbit model

Corneal neovascularization, which occurs in many pathologic states of the cornea, reduces the visual acuity. Recently, we found that the extracellular region of brain-specific angiogenesis inhibitor 1 (BAI1-ECR) has antiproliferative activity through functional blocking of alpha(v)beta(5) integrin in endothelial cells. In this study, we investigated the effects of lipid-mediated subconjunctival injection of the BAI1-ECR gene on corneal angiogenesis induced by epithelial debridement by heptanol in the rabbit. When a pEGFP-BAI1-ECR plasmid was given subconjunctivally 1 week after epithelial debridement, green fluorescence was detected in the corneal stroma with expression persisting for 7 days. To test the effect of BAI1-ECR on neovascularization, rabbits were injected with the BAI1-ECR gene or empty vector two or three times at 1-week intervals beginning 1 week after debridement. When measured with biomicroscopy at 1 or 2 weeks after two weekly injections, BAI1-delivered eyes had significantly less neovascularized corneal area than vector-injected ones in both time periods. Similar microscopic results were obtained after three weekly injections of BAI1-ECR. In quantitative histological examination, the BAI1-receiving eyes showed significantly less neovascular area and number of vessels than vector-injected ones. Also, after two weekly injections, BAI1-delivered eyes had decreased neovascularized corneal area equivalent to that of anti-VEGF antibody-injected ones. These results indicate that BAI1-ECR gene delivery effectively reduces experimental corneal neovascularization and suggest that the BAI1-ECR protein can be used as an angiogenesis suppressor in the eye.

Expression of brain-specific angiogenesis inhibitor 3 (BAI3) in normal brain and implications for BAI3 in ischemia-induced brain angiogenesis and malignant glioma

Murine brain-specific angiogenesis inhibitor 1 and 2 (mBAI1, mBAI2) are involved in angiogenesis after cerebral ischemia. In this study, mBAI3 was cloned and characterized. Northern and Western blot analyses demonstrated a unique developmental expression pattern in the brain. The level of mBAI3 in brain peaked 1 day after birth, unlike mBAI1 and mBAI2, which peaked 10 days after birth. In situ hybridization analyses of the brain showed the same localization of BAI3 as BAI1 and BAI2, which includes most neurons of cerebral cortex and hippocampus. In the in vivo focal cerebral ischemia model, BAI3 expression decreased from 0.5 h after hypoxia until 8 h, but returned to control level after 24 h. The expression of vascular endothelial growth factor following ischemia showed an inverse pattern. The decreased expressions of BAIs in high-grade gliomas were observed, but BAI3 expression was generally lower in malignant gliomas than in normal brain. Our results indicate that the expression and distribution of BAI3 in normal brain, but not its developmental expression, are very similar to those of BAI1 and BAI2, and that BAI3 may participate in the early phases of ischemia-induced brain angiogenesis and in brain tumor progression.

The promoter of brain-specific angiogenesis inhibitor 1-associated protein 4 drives developmentally targeted transgene expression mainly in adult cerebral cortex and hippocampus

Restricting transgene expression to specific cell types and maintaining long-term expression are major goals for gene therapy. Previously, we cloned brain-specific angiogenesis inhibitor 1-associated protein 4 (BAI1-AP4), a novel brain-specific protein that interacts with BAI1, and found that it was developmentally upregulated in the adult brain. In this report, we isolated 5 kb of the 5' upstream sequence of the mouse BAI1-AP4 gene and analyzed its promoter activity. Functional analyses demonstrated that an Sp1 site was the enhancer, and the region containing the transcription initiation site and an AP2-binding site was the basal promoter. We examined the ability of the BAI1-AP4 promoter to drive adult brain-specific expression by using it to drive lacZ expression in transgenic (TG) mice. Northern blot analyses showed a unique pattern of beta-galactosidase expression in TG brain, peaking at 1 month after birth, like endogenous BAI1-AP4. Histological analyses demonstrated the same localization and developmental expression of beta-galactosidase and BAI1-AP4 in most neurons of the cerebral cortex and hippocampus. Our data indicate that TG mice carrying the BAI1-AP4 promoter could be a valuable model system for region-specific brain diseases.

KAI1 COOH-Terminal Interacting Tetraspanin (KITENIN), a Member of the Tetraspanin Family, Interacts with KAI1, a Tumor Metastasis Suppressor, and Enhances Metastasis of Cancer

We cloned recently an alternatively spliced variant of KAI1 mRNA that lacked exon 7 at the COOH-terminal region and showed differences in metastasis suppression when compared with the wild-type KAI1. These findings indicated that the COOH-terminal region of KAI1 is critical for its metastasis suppressor function. In this study, we isolated a cDNA clone of VANGL1, a member of the tetraspanin protein family, which interacted specifically with the COOH-terminal cytoplasmic domain of KAI1 in the yeast two-hybrid system. We renamed it KAI1 COOH-terminal interacting tetraspanin (KITENIN). We found that KITENIN-overexpressing CT-26 mouse colon cancer cells showed increased tumorigenicity and early hepatic metastasis in vivo, as well as increased invasiveness and adhesion to fibronectin in vitro compared with parental cells. Moreover, increased levels of KITENIN were observed in a human gastric tumor and its metastatic tissues, compared with the normal adjacent mucosa. Our results indicate that KITENIN promotes adhesion and invasion of cancer cells in vitro and in vivo, and suggest that KITENIN participates in the regulation of the tumor formation and metastasis by interacting with KAI1, a metastasis suppressor and antisense KITENIN strategy that can be used to inhibit metastasis in various cancers.

Molecular basis of Refsum disease: sequence variations in phytanoyl-CoA hydroxylase (PHYH) and the PTS2 receptor (PEX7)

Refsum disease has long been known to be an inherited disorder of lipid metabolism characterized by the accumulation of phytanic acid (3,7,11,15-tetramethylhexadecanoic acid) caused by an alpha-oxidation deficiency of this branched chain fatty acid in peroxisomes. The mechanism of phytanic acid alpha-oxidation and the enzymes involved had long remained mysterious, but they have been resolved in recent years. This has led to the resolution of the molecular basis of Refsum disease. Interestingly, Refsum disease is genetically heterogeneous; two genes, PHYH (also named PAHX) and PEX7, have been identified to cause Refsum disease, as reviewed in this work.

Extracellular fragment of brain-specific angiogenesis inhibitor 1 suppresses endothelial cell proliferation by blocking αvβ5 integrin

Brain-specific angiogenesis inhibitor 1 (BAI1) is a transmembrane protein with anti-angiogenic activity. The mechanisms underlying BAI1 activity are unknown. In this study, we found that overexpression of BAI1 increased cell death in human umbilical vein endothelial cells (HUVECs) and, to a lesser degree, in SHSY5Y and U343 cells. Conditioned medium from BAI1-transfected U343 cells inhibited proliferation of HUVECs, and this effect was neutralized by addition of anti-BAI1 serum. The conditioned medium contained four cleavage products of the BAI1 extracellular domain. BAI1's middle extracellular region containing five thrombospondin type 1 repeats (BAI1-TSR) was sufficient for BAI1's antiproliferative effect on HUVECs. BAI1's action on HUVECs was blocked by anti-alpha(v) integrin, but not by anti-CD36 antibody treatment. Introduction of alpha(v)beta(5) integrin into HEK293 cells rendered them susceptible to cell death by BAI1, and BAI1-TSR bound with alpha(v)beta(5) integrin, but not to alpha(v)beta(3) integrin in brain tissue. Fluorescent BAI1-TSR colocalized with alpha(v)beta(5) integrin in HUVECs. Together, our results indicate that BAI1 has antiproliferative action on surrounding endothelial cells by blocking alpha(v)beta(5) integrin, and its active region is BAI1-TSR. BAI1-TSR could be valuable for regulating brain angiogenesis.

Expression of brain-specific angiogenesis inhibitor 2 (BAI2) in normal and ischemic brain: involvement of BAI2 in the ischemia-induced brain angiogenesis

Previously, the authors cloned and characterized murine brain-specific angiogenesis inhibitor 1 (mBAI1). In this study, the authors cloned mBAI2 and analyzed its functional characteristics. Northern and Western blot analyses demonstrated a unique developmental expression pattern of mBAI2 in the brain. The expression level of mBAI2 appeared to increase as the development of the brain progressed. Reverse transcription-polymerase chain reaction (RT-PCR) analyses demonstrated the existence of alternative splice variants of mBAI2, which were defective in parts of type I repeat of thrombospondin or the third cytoplasmic loop of the seven-span transmembrane domain that were considered essential to the functions of mBAI2. The expressions of spliced variants in the brain were differently regulated compared with wild-type mBAI2 during development and ischemic conditions. In situ hybridization analyses of the brain showed the same localization of BAI2 as BAI1, such as in most neurons of cerebral cortex. In the in vivo focal cerebral ischemia model and the in vitro hypoxic cell culture model with cobalt, BAI2 expression decreased after hypoxia and preceded the increased expression of vascular endothelial growth factor (VEGF). RT-PCR analysis of antisense BAI2 cDNA-transfected SHSY5Y cells showed an increased VEGF expression as well as a decreased BAI2 expression. Immunohistochemical study of focal ischemic cortex showed that the regional localization of decreased BAI2 was related to the formation of new vessels. These results suggest that the brain-specific developmental expression pattern of angiostatic BAI2 is correlated with the decreased neovascularization in the adult brain, and that angiostatic BAI2 participates in the ischemia-induced brain angiogenesis in concert with angiogenic VEGF.

Selectivity and promiscuity of the first and second PDZ domains of PSD-95 and synapse-associated protein 102

PDZ domains typically interact with the very carboxyl terminus of their binding partners. Type 1 PDZ domains usually require valine, leucine, or isoleucine at the very COOH-terminal (P(0)) position, and serine or threonine 2 residues upstream at P(-2). We quantitatively defined the contributions of carboxyl-terminal residues to binding selectivity of the prototypic interactions of the PDZ domains of postsynaptic density protein 95 (PSD-95) and its homolog synapse-associated protein 90 (SAP102) with the NR2b subunit of the N-methyl-d-aspartate-type glutamate receptor. Our studies indicate that all of the last five residues of NR2b contribute to the binding selectivity. Prominent were a requirement for glutamate or glutamine at P(-3) and for valine at P(0) for high affinity binding and a preference for threonine over serine at P(-2), in the context of the last 11 residues of the NR2b COOH terminus. This analysis predicts a COOH-terminal (E/Q)(S/T)XV consensus sequence for the strongest binding to the first two PDZ domains of PSD-95 and SAP102. A search of the human genome sequences for proteins with a COOH-terminal (E/Q)(S/T)XV motif yielded 50 proteins, many of which have not been previously identified as PSD-95 or SAP102 binding partners. Two of these proteins, brain-specific angiogenesis inhibitor 1 and protein kinase Calpha, co-immunoprecipitated with PSD-95 and SAP102 from rat brain extracts.

Brain-specific angiogenesis inhibitor 1 (BAI1) is expressed in human cerebral neuronal cells

Brain-specific angiogenesis inhibitor 1 (BAI1) is a p53-target gene specifically expressed in the brain. We examined the distribution of the endogenous BAI1 protein in normal human brain tissue using a polyclonal antibody against the extracellular region of BAI1. Immunohistochemical study demonstrated that BAI1 was expressed in neuronal cells of the cerebral cortex but not in astrocytes. BAI1 protein was localized in the cellular cytoplasm and membrane. It was predominantly localized in the cellular membrane when expressed in cultured cells by means of gene transfection. BAI1 protein may play an important role in neuronal functions such as synapse formation and signal transduction.