Cloning, structural analysis, and mapping of the B30 and B7 multigenic families to the major histocompatibility complex (MHC) and other chromosomal regions

Prognostic and Therapeutic Significance of BTN3A Proteins in Tumors

The Butyrophilin 3A (BTN3A) family is a type I transmembrane protein belonging to the immunoglobulin (Ig) superfamily. The family contains three members: BTN3A1, BTN3A2 and BTN3A3, which share 95% homology in the extracellular domain. The expression of BTN3A family members is different in different types of tumors, which plays an important role in tumor prognosis. Among them, there are many studies on tumor immunity of BTN3A1, which shows that it is essential for the activation of Vγ9Vδ2 T cells, while BTN3A3 is expected to become a potential therapeutic target for breast cancer. Recent studies have shown that the BTN3A family is closely related to the occurrence and development of tumors. Now the BTN3A family has become one of the research hotspots and is expected to become new tumor prediction and treatment targets.

RFPL3 and CBP synergistically upregulate hTERT activity and promote lung cancer growth

hTERT is the key component of telomerase and its overactivation contributes to maintaining telomere length and cell immortalization. Previously, we identified RFPL3 as a new transcription activator of hTERT in lung cancers. However, the exact mechanism of RFPL3 in mediating hTERT activation and its associated signal regulatory network remain unclear. In this study, we found that RFPL3 colocalized and interacted directly with CBP in the nucleus of lung cancer cells. Immunohistochemical analysis of tissue microarrays of lung cancers revealed the simultaneous overexpression of both RFPL3 and CBP predicted relatively poor prognosis. Furthermore, we confirmed their synergistic stimulation on hTERT expression and tumor cell growth. The binding of RFPL3 to hTERT promoter was reduced markedly when CBP was knocked down by its specific siRNA or suppressed by its inhibitor in lung cancer cells with stable overexpression of RFPL3. When one of the two proteins RFPL3 and CBP was upregulated or downregulated, whereas the another remains unchanged, hTERT expression and telomerase activity were activated or repressed accordingly. In the meantime, the growth of lung cancer cells was also promoted or attenuated accordingly. Furthermore, we also found that RFPL3 coordinated with CBP to upregulate hTERT through the CBP-induced acetylation of RFPL3 protein and their co-anchoring at hTERT promoter region. Collectively, our results reveal a new mechanism of hTERT regulation in lung cancer cells and suggest the RFPL3/CBP/hTERT signaling pathway may be a new targets for lung cancer treatment.

Structure and function of the SPRY/B30.2 domain proteins involved in innate immunity

The SPRY domain is a protein interaction module found in 77 murine and ~100 human proteins, and is implicated in important biological pathways, including those that regulate innate and adaptive immunity. The current definition of the SPRY domain is based on a sequence repeat discovered in the splA kinase and ryanodine receptors. The greater SPRY family is divided into the B30.2 (which contains a PRY extension at the N-terminus) and "SPRY-only" sub-families. In this brief review, we examine the current structural and biochemical literature on SPRY/B30.2 domain involvement in key immune processes and highlight a PRY-like 60 amino acid region in the N-terminus of "SPRY-only" proteins. Phylogenetic, structural, and functional analyses suggest that this N-terminal region is related to the PRY region of B30.2 and should be characterized as part of an extended SPRY domain. Greater understanding of the functional importance of the N-terminal region in "SPRY only" proteins will enhance our ability to interrogate SPRY interactions with their respective binding partners.

Exploring the diversity of SPRY/B30.2-mediated interactions

The SPla/Ryanodine receptor (SPRY)/B30.2 domain is one of the most common folds in higher eukaryotes. The human genome encodes 103 SPRY/B30.2 domains, several of which are involved in the immune response. Approximately 45% of human SPRY/B30.2-containing proteins are E3 ligases. The role and function of the majority of SPRY/B30.2 domains are still poorly understood, however, in several cases mutations in this domain have been linked to congenital disorders. The recent characterization of SPRY/B30.2-mediated protein interactions has provided evidence for a role of this domain as an adaptor module to assemble macromolecular complexes, analogous to Src homology (SH)2, SH3, and WW domains. However, functional and structural evidence suggests that SPRY/B30.2 is a more versatile fold, allowing a wide range of binding modes.

TRIM27 negatively regulates NOD2 by ubiquitination and proteasomal degradation

NOD2, the nucleotide-binding domain and leucine-rich repeat containing gene family (NLR) member 2 is involved in mediating antimicrobial responses. Dysfunctional NOD2 activity can lead to severe inflammatory disorders, but the regulation of NOD2 is still poorly understood. Recently, proteins of the tripartite motif (TRIM) protein family have emerged as regulators of innate immune responses by acting as E3 ubiquitin ligases. We identified TRIM27 as a new specific binding partner for NOD2. We show that NOD2 physically interacts with TRIM27 via the nucleotide-binding domain, and that NOD2 activation enhances this interaction. Dependent on functional TRIM27, ectopically expressed NOD2 is ubiquitinated with K48-linked ubiquitin chains followed by proteasomal degradation. Accordingly, TRIM27 affects NOD2-mediated pro-inflammatory responses. NOD2 mutations are linked to susceptibility to Crohn's disease. We found that TRIM27 expression is increased in Crohn's disease patients, underscoring a physiological role of TRIM27 in regulating NOD2 signaling. In HeLa cells, TRIM27 is partially localized in the nucleus. We revealed that ectopically expressed NOD2 can shuttle to the nucleus in a Walker A dependent manner, suggesting that NOD2 and TRIM27 might functionally cooperate in the nucleus.

We conclude that TRIM27 negatively regulates NOD2-mediated signaling by degradation of NOD2 and suggest that TRIM27 could be a new target for therapeutic intervention in NOD2-associated diseases.

Differential role for CD277 as a co-regulator of the immune signal in T and NK cells

The human butyrophilin (BTN) 3 or CD277 molecules belong to the B7 family members and are expressed in various immune cells such as T and NK cells. Here, we show that CD277 triggering considerably enhances TCR-induced cytokine production and cell proliferation, even when another co-stimulatory molecule, CD28, is engaged. These CD277-induced additive functional effects are in accordance with the detection of early T-cell activation events such as TCR-induced cell signaling being increased upon CD277 engagement. However, we found that CD277 triggering is not involved in CD16- or NKp46-induced NK cell activation. BTN3/CD277 comprises three structurally related members, BTN3A1, BTN3A2 and BTN3A3. CD277 antibodies recognize all isoforms and we describe a differential expression of BTN3 isoforms between T and NK cells that could explain differential CD277 functions between T and NK cells. Our results show that, while T cells express all BTN3/CD277 transcripts, NK cells express mostly BTN3A2, which lacks the B30.2 intracellular domain. Furthermore, NKp30-induced cytokine production is decreased by the specific engagement of BTN3A2, but not by BTN3A1 triggering. Thus, we provide new insights into the CD277 co-stimulatory pathway that may differentially participate in the regulation of various cell-mediated immune responses.

Yin-Yang of costimulation: crucial controls of immune tolerance and function

SUMMARY

In addition to signals from the T-cell receptor complex, it has been recognized for many years that a 'second' signal, most notably from CD28, is also important in T-cell activation. In the recent years, many new members of CD28 family as well as the molecules that share structural homology to CD28 ligands CD80 and CD86 have been discovered. Interestingly, some of these proteins function to dampen T-cell activation and regulate the induction of T-cell tolerance. Therefore, positive and negative costimulation are the two sides of the coin to fine tune T-cell receptor signaling to determine the outcome of T-cell receptor engagement-tolerance versus function.

Inhibitory costimulation and anti-tumor immunity

Costimulation was originally shown to be important in T-cell activation and effector differentiation. Recent characterization of B7/butyrophilin and members of the CD28 superfamily has revealed a large number of negative costimulatory molecules that dampen T-cell activation and regulate immune tolerance. Some of these molecules have been shown to be upregulated in the tumor microenvironment and may serve as potential targets for augmenting anti-tumor immunity. In this article, we summarize recent developments in the field of inhibitory costimulation and discuss the future direction of therapeutic manipulation of inhibitory costimulation in tumor immunotherapy.

BTNL2, a butyrophilin-like molecule that functions to inhibit T cell activation

B7 family members regulate T cell activation and tolerance. Although butyrophilin proteins share sequence homology with the B7 molecules, it is unclear whether they have any function in immune responses. In the present study, we characterize an MHC class II gene-linked butyrophilin family member, butyrophilin-like 2 (BTNL2), the mutation of which has been recently associated with the inflammatory autoimmune diseases sarcoidosis and myositis. Mouse BTNL2 is a type I transmembrane protein with two pairs of Ig-like domains separated by a heptad peptide sequence. BTNL2 mRNA is highly expressed in lymphoid tissues as well as in intestine. To characterize the function of BTNL2, we produced a BTNL2-Ig fusion protein. It recognized a putative receptor whose expression on B and T cells was significantly enhanced after activation. BTNL2-Ig inhibited T cell proliferation and TCR activation of NFAT, NF-kappaB, and AP-1 signaling pathways. BTNL2 is thus the first member of the butyrophilin family that regulates T cell activation, which has implications in immune diseases and immunotherapy.

Ohanin, a novel protein from king cobra venom: its cDNA and genomic organization

Ohanin, from king cobra venom, is a novel protein which induces hypolocomotion and hyperalgesia in mice [Pung, Y.F., Wong, P.T.H., Kumar, P.P., Hodgson W.C., Kini, R.M., 2005. Ohanin, a novel protein from king cobra venom induces hypolocomotion and hyperalgesia in mice. J. Biol. Chem. 280, 13137-13147.]. It is weakly similar to PRY-SPRY domains (B30.2-like domain). Here we report the complete cDNA and genomic organization of ohanin. Interestingly, cDNA sequence does not show significant sequence similarity to any known sequences, including those of B30.2-like domain-containing proteins. Its full-length cDNA sequence of 1558 bp encodes for prepro-ohanin with a propeptide segment at the C-terminal. Ohanin is the first member of a new subfamily of proteins containing B30.2-like domain with short N-terminal segment. We named this subfamily as vespryns. There are two mRNA subtypes differing in their 5'-untranslated regions. Southern hybridization study shows that ohanin is encoded by a single gene. Its genomic sequence is 7086 bp with five exons and four introns, and the two types of mRNAs are generated by alternative splicing of exon 2. Our results indicate that ohanin and vespryns may have evolved from the same ancestral gene as B30.2 domain.

Relationship between SPRY and B30.2 protein domains. Evolution of a component of immune defence?

SPRY and B30.2 are homologous domains which can be identified in 11 protein families encoded in the human genome. These include cell surface receptors of the immunoglobulin super-family (BTNs), negative regulators of the JAK/STAT pathway (SOCS-box SSB1-4) and proteins encoded by the numerous TRIM genes. Collectively, proteins containing SPRY and B30.2 domains cover a wide range of functions, including regulation of cytokine signalling (SOCS), RNA metabolism (DDX1, hnRNPs), intracellular calcium release (RyR receptors), immunity to retroviruses (TRIM5alpha) as well as regulatory and developmental processes (HERC1, Ash2L). In order to clarify the evolutionary relationship between the two domains, we compiled a curated database of SPRY and B30.2-domain sequences. We show that while SPRY domains are evolutionarily ancient, B30.2 domains, found in BTN and TRIM proteins, are a more recent evolutionary adaptation, comprising the combination of SPRY with an additional domain, PRY. The combination of SPRY and PRY to produce B30.2 domains may have been selected and maintained as a component of immune defence.

Structure of the PRYSPRY-domain: implications for autoinflammatory diseases

We determined the first structure of PRYSPRY, a domain found in over 500 different proteins, involved in innate immune signaling, cytokine signaling suppression, development, cell growth and retroviral restriction. The fold encompasses a 7-stranded and a 6-stranded antiparallel beta-sheet, arranged in a beta-sandwich. In the crystal, PRYSPRY forms a dimer where the C-terminus of an acceptor molecule binds to the concave surface of a donor molecule, which represents a putative interaction site. Mutations in the PRYSPRY domains of Pyrin, which are responsible for familial Mediterranean fever, map on the putative PRYSPRY interaction site.

Characterisation of a cluster of TRIM-B30.2 genes in the chicken MHC B locus

We have identified and characterised a cluster of six TRIM-B30.2 genes flanking the chicken BF/BL region of the B complex. The TRIM-B30.2 proteins are a subgroup of the TRIM protein family containing the tripartite motif (TRIM), consisting of a RING domain, a B-box and a coiled coil region, and a B30.2-like domain. In humans, a cluster of seven TRIM-B30.2 genes has been characterised within the MHC on Chromosome 6p21.33. Among the six chicken TRIM-B30.2 genes two are orthologous to those of the human MHC, and two (TRIM41 and TRIM7) are orthologous to human genes located on Chromosome 5. In humans, these last two genes are adjacent to GNB2L1, a guanine nucleotide-binding protein gene, the ortholog of the chicken c12.3 gene situated in the vicinity of the TRIM-B30.2 genes. This suggests that breakpoints specific to mammals have occurred and led to the remodelling of their MHC structure. In terms of structure, like their mammalian counterparts, each chicken gene consists of five coding exons; exon 1 encodes the RING domain and the B-box, exons 2, 3 and 4 form the coiled-coil region, and the last exon represents the B30.2-like domain. Phylogenetic analysis led us to assume that this extended BF/BL region may be similar to the human extended class I region, because it contains a cluster of BG genes sharing an Ig-V like domain with the BTN genes (Henry et al. 1997a) and six TRIM-B30.2 genes containing the B30.2-like domain, shared with the TRIM-B30.2 members and the BTN genes.

Applying proteomic methodologies to analyze the effect of hexamethylene bisacetamide (HMBA) on proliferation and differentiation of human gastric carcinoma BGC-823 cells

Human gastric carcinoma BGC-823 cells underwent morphological differentiation and cell cycle arrest in vitro when treated with 5mM hexamethylene bisacetamide (HMBA) for 48h. To further understand the mechanism of HMBA-induced differentiation, proteomic methodologies were applied to screen and identify altered proteins involved in the commitment of BGC-823 cells to differentiate. Five distinct altered proteins were acquired by two-dimensional (2-D) PAGE and were consequently identified as ras-related protein rab-35 (Rab-35), splice truncated isoform of transmembrane protease, serine 3 (serine TADG-12), regulator of G-protein signaling 1 (RGS1), ret finger protein-like 1 (RFPL1) and F-actin capping protein alpha-3 subunit (GSG3) by analysis of mass spectrograph. Of the five proteins, serine TADG-12 down-regulated under the detectable level after HMBA treatment, Rab-35, RGS1 and RFPL1 sharply up-regulated within the HMBA-induced BGC-823 cells, and GSG3, appearing in both treated and untreated cells, remarkably increased within BGC-823 cells after HMBA stimulation. Our results implicate that the molecular mechanism of BGC-823 cell differentiation in response to HMBA may involved in complex processes including a signaling network linking vesicle transport, actin cytoskeleton remodeling except for morphology differentiation, cell cycle G1 arrest.

Bioactive proteins from stonefish venom

1. Of all the venomous fish known, the stonefish is one of the most commonly encountered by man. Studies on its venom started in the 1950s, but little work was performed after that until several groups revived interest in the venom in the 1980s after easier accessibility to the fish. 2. Stonefish venom is a mixture of proteins, containing several enzymes, including hyaluronidase of high specific activity. A purified stonefish hyaluronidase has been characterized. 3. Several of the effects of the crude venom have been isolated to a protein lethal factor that has cytolytic, neurotoxic and hypotensive activity. This protein is stonustoxin from Synanceja horrida, trachynilysin from Synanceja trachynis and verrucotoxin from Synanceja verrucosa. 4. The biochemical properties and activities of these protein lethal factors are reviewed.

GNIP, a novel protein that binds and activates glycogenin, the self-glucosylating initiator of glycogen biosynthesis

Glycogenin is a self-glucosylating protein involved in the initiation of glycogen biosynthesis. Self-glucosylation leads to the formation of an oligosaccharide chain, which, when long enough, supports the action of glycogen synthase to elongate it and form a mature glycogen molecule. To identify possible regulators of glycogenin, the yeast two-hybrid strategy was employed. By using rabbit skeletal muscle glycogenin as a bait, cDNAs encoding three different proteins were isolated from the human skeletal muscle cDNA library. Two of the cDNAs encoded glycogenin and glycogen synthase, respectively, proteins known to be interactors. The third cDNA encoded a polypeptide of unknown function and was designated GNIP (glycogenin interacting protein). Northern blot analysis revealed that GNIP mRNA is highly expressed in skeletal muscle. The gene for GNIP generates at least four isoforms by alternative splicing. The largest isoform GNIP1 contains, from NH(2)- to COOH-terminal, a RING finger, a B box, a putative coiled-coil region, and a B30.2-like motif. The previously identified protein TRIM7 (tripartite motif containing protein 7) is also derived from the GNIP gene and is composed of the RING finger, B box, and coiled-coil regions. The GNIP2 and GNIP3 isoforms consist of the coiled-coil region and B30.2-like domain. Physical interaction between GNIP2 and glycogenin was confirmed by co-immunoprecipitation, and in addition GNIP2 was shown to stimulate glycogenin self-glucosylation 3-4-fold. GNIPs may represent a novel participant in the initiation of glycogen synthesis.

LIRF, a gene induced during hippocampal long-term potentiation as an immediate-early gene, encodes a novel RING finger protein

We describe here an LTP-induced gene, LIRF, which encodes a novel protein with RING finger and B30.2 domains in its N- and C-terminal portions, respectively. Each domain is encoded by one exon, suggesting that the organization of the gene was generated by exon shuffling. The amino acid sequences of the mouse, rat, and human LIRF proteins are highly conserved and contain a putative PEST sequence. LIRF is an immediate-early gene in hippocampal granule cells, and its expression is upregulated immediately after the induction of long-lasting long-term potentiation at perforant pathway-dentate gyrus synapses and returns to the basal level within 150 min. A heterologously expressed LIRF protein fused to EGFP localizes specifically to the cytoplasm in COS-7 cells. These findings suggest a possible involvement of LIRF in a limited, early phase of synaptic plasticity.

A novel gene on human chromosome 2p24 is differentially expressed between androgen-dependent and androgen-independent prostate cancer cells

Identification of genes involved in the transition from androgen-dependent to androgen-independent prostate cancer is important to extend our current knowledge of the disease. Using differential display RT-PCR analysis between androgen-dependent and androgen-independent prostate cancer cells, we have identified a novel gene, designated GC109. GC109 harbours a putative Cys-His cluster, a nuclear localisation signal, a leucine zipper and a ret finger protein (rfp)-like domain. GC109 mRNA expression in normal human tissues was found not to be restricted to the prostate. However, using a variety of 15 human cancer cell lines, GC109 mRNA was preferentially expressed in androgen-dependent LNCaP-FGC, compared with androgen-independent LNCaP-LNO, DU145 and PC3 human prostate cancer cells. Finally, the GC109 gene was mapped on human chromosome 2p24. Based on its protein domain structure and chromosomal localisation, we hypothesise that GC109 may be involved in chromosomal rearrangements in prostate cancer.

Enterophilins, a new family of leucine zipper proteins bearing a b30.2 domain and associated with enterocyte differentiation

Enterocyte terminal differentiation occurs at the crypt-villus junction through the transcriptional activation of cell-specific genes, many of which code for proteins of the brush border membrane such as intestinal alkaline phosphatase, sucrase-isomaltase, or the microvillar structural protein villin. Several studies have shown that this sharp increase in specific mRNA levels is intimately associated with arrest of cell proliferation. We isolated several clones from a guinea pig intestine cDNA library. They encode new proteins characterized by an original structure associating a carboxyl-terminal B30.2/RFP-like domain and a long leucine zipper at the amino terminus. The first member of this novel gene family codes for a 65-kDa protein termed enterophilin-1, which is specifically expressed in enterocytes before their final differentiation. Enterophilin-1 is the most abundant in the small intestine but is still present in significant amounts in colonic enterocytes. In Caco-2 cells, a similar 65-kDa protein was recognized by a specific anti-enterophilin-1 antibody, and its expression was positively correlated with cell differentiation status. In addition, transfection of HT-29 cells with enterophilin-1 full-length cDNA slightly inhibited cell growth and promoted an increase in alkaline phosphatase activity. Taken together, these data identify enterophilins as a new family of proteins associated with enterocyte differentiation.

B7-DC, a new dendritic cell molecule with potent costimulatory properties for T cells

Dendritic cells (DCs), unique antigen-presenting cells (APCs) with potent T cell stimulatory capacity, direct the activation and differentiation of T cells by providing costimulatory signals. As such, they are critical regulators of both natural and vaccine-induced immune responses. A new B7 family member, B7-DC, whose expression is highly restricted to DCs, was identified among a library of genes differentially expressed between DCs and activated macrophages. B7-DC fails to bind the B7.1/2 receptors CD28 and cytotoxic T lymphocyte-associated antigen (CTLA)-4, but does bind PD-1, a receptor for B7-H1/PD-L1. B7-DC costimulates T cell proliferation more efficiently than B7.1 and induces a distinct pattern of lymphokine secretion. In particular, B7-DC strongly costimulates interferon gamma but not interleukin (IL)-4 or IL-10 production from isolated naive T cells. These properties of B7-DC may account for some of the unique activity of DCs, such as their ability to initiate potent T helper cell type 1 responses.

The cluster of BTN genes in the extended major histocompatibility complex

We sequenced the 170-kb cluster of BTN genes in the extended major histocompatibility complex region, 4 Mb telomeric of human leukocyte antigen class I genes, at 6p22.1. The cluster consists of seven genes belonging to the expanding B7/butyrophilin-like group, a subset of the immunoglobulin gene superfamily. The main complex is composed of six genes, from two subfamilies, BTN2 and BTN3, arranged in pairs. This alternating pattern must have evolved by duplications of an original block of two genes, one from each subfamily. The sequences from the two subfamilies share approximately 50% amino acid identity. By analysis of repeat elements within each block, these duplications may be dated to approximately 100 million years ago, at about the time of the branching of the Rodentia and Primate lineages. The single BTN1A1 (butyrophilin) gene was positioned approximately 25 kb centromeric to the cluster. Each gene covers approximately 12 kb and consists of seven (BTN2 subfamily) or nine (BTN3 subfamily) coding exons. The predicted leader sequence, immunoglobulin-like IgV (variable)/IgC (constant) ectodomains, and the predicted transmembrane domain are encoded on separate exons and are separated from a B30.2 domain by a variable number of very short exons, 21 and 27 nucleotides in length. BTN transcripts were detected in all tissues examined. Alternative splicing, involving particularly the carboxyl-terminal B30.2 domain, was a notable feature. Most transcripts of BTN2 subfamily genes contained this domain, whereas BTN3 genes did not. Using immunofluorescence, we showed surface expression of BTN-green fluorescent protein fusions in mammalian cell transfectants.

The interferon-inducible Staf50 gene is downregulated during T cell costimulation by CD2 and CD28

It is well established that interferons (IFN) exert potent regulatory effects on the immune system. We have recently isolated a new IFN-induced human cDNA coding for a member of the Ring finger B-box/B30.2 subfamily that localizes to the chromosome band 11p15. We have named it Staf50. We show in this report that Staf50 is expressed in resting T cells in the absence of exogenous IFN treatment and is strongly repressed during T cell activation by anti-CD28 and anti-CD2 monoclonal antibodies (mAb) at both messenger and protein levels. In addition, we show that several members of the Ring finger B-box/B30.2 subfamily, including the 52-kDa SSA/Ro autoantigen, localize to the same chromosome band, 11p15, and are upregulated by IFN. These data led us to define a family of IFN-induced genes clustered on chromosome 11p15 that may be involved in T cell regulatory processes.

Molecular cloning of testis-abundant finger Protein/Ring finger protein 23 (RNF23), a novel RING-B box-coiled coil-B30.2 protein on the class I region of the human MHC

We have identified a genomic DNA fragment, using the PCR method with degenerate oligonucleotide primers which contain the conserved sequence of the RING finger domain. Using the DNA fragment as a probe, a novel cDNA was cloned from human and mouse testis. The cDNA had a domain structure of the typical RING-B box-coiled coil (RBCC)-B30.2 domain and therefore was named testis-abundant finger protein (tfp). Indeed, the transcript was highly expressed in the testis, although it was also found ubiquitously in various organs by Northern blot analysis. The tfp gene was mapped at the class I region of the human MHC (major histocompatibility complex), within which some known RBCC-B30.2 proteins such as RFP, RFB30/HERF1, AFP, and HZF had been localized. These findings demonstrate that several RBCC-B30.2 proteins including tfp, which are non-HLA proteins, are clustered within the class I region of the human MHC.

LICOS, a primordial costimulatory ligand?

In mammals, the classical B7 molecules expressed on antigen-presenting cells, B7-1 (CD80) and B7-2 (CD86), bind the structurally related glycoproteins CD28 and CTLA-4 (CD152), generating costimulatory signals that regulate the activation state of T cells. A recently identified human CD28-like protein, ICOS, also induces costimulatory signals in T cells when crosslinked with antibodies, but it is unclear whether ICOS is part of a B7-mediated regulatory pathway of previously unsuspected complexity, or whether it functions independently and in parallel. Here, we report that, rather than binding B7-1 or B7-2, ICOS binds a new B7-related molecule of previously unknown function that we call LICOS (for ligand of ICOS). At 37 degrees C, LICOS binds only to ICOS but, at lower, non-physiological temperatures, it also binds weakly to CD28 and CTLA-4. Sequence comparisons suggest that LICOS is the homologue of a molecule expressed by avian macrophages and of a murine protein whose expression is induced in non-lymphoid organs by tumour necrosis factor alpha (TNFalpha). Our results define the components of a distinct and novel costimulatory pathway and raise the possibility that LICOS, rather than B7-1 or B7-2, is the contemporary homologue of a primordial vertebrate costimulatory ligand.

A review and proposed nomenclature for major proteins of the milk-fat globule membrane

The characteristics and possible functions of the most abundant proteins associated with the bovine milk-fat globule membrane are reviewed. Under the auspices of the Milk Protein Nomenclature Committee of the ADSA, a revised nomenclature for the major membrane proteins is proposed and discussed in relation to earlier schemes. We recommend that proteins be assigned specific names as they are identified by molecular cloning and sequencing techniques. The practice of identifying proteins according to their Mr, electrophoretic mobility, or staining characteristics should be discontinued, except for uncharacterized proteins. The properties and amino acid sequences of the following proteins are discussed in detail: MUC1, xanthine dehydrogenase/oxidase, CD36, butyrophilin, adipophilin, periodic acid Schiff 6/7 (PAS 6/7), and fatty acid binding protein. In addition, a compilation of less abundant proteins associated with the bovine milk-fat globule membrane is presented.

Structure and dimerization of a soluble form of B7-1

B7-1 (CD80) and B7-2 (CD86) are glycoproteins expressed on antigen-presenting cells. The binding of these molecules to the T cell homodimers CD28 and CTLA-4 (CD152) generates costimulatory and inhibitory signals in T cells, respectively. The crystal structure of the extracellular region of B7-1 (sB7-1), solved to 3 A resolution, consists of a novel combination of two Ig-like domains, one characteristic of adhesion molecules and the other previously seen only in antigen receptors. In the crystal lattice, sB7-1 unexpectedly forms parallel, 2-fold rotationally symmetric homodimers. Analytical ultracentrifugation reveals that sB7-1 also dimerizes in solution. The structural data suggest a mechanism whereby the avidity-enhanced binding of B7-1 and CTLA-4 homodimers, along with the relatively high affinity of these interactions, favors the formation of very stable inhibitory signaling complexes.

Duplications on human chromosome 22 reveal a novel Ret Finger Protein-like gene family with sense and endogenous antisense transcripts

Analysis of 600 kb of sequence encompassing the beta-prime adaptin (BAM22) gene on human chromosome 22 revealed intrachromosomal duplications within 22q12-13 resulting in three active RFPL genes, two RFPL pseudogenes, and two pseudogenes of BAM22. The genomic sequence of BAM22vartheta1 shows a remarkable similarity to that of BAM22. The cDNA sequence comparison of RFPL1, RFPL2, and RFPL3 showed 95%-96% identity between the genes, which were most similar to the Ret Finger Protein gene from human chromosome 6. The sense RFPL transcripts encode proteins with the tripartite structure, composed of RING finger, coiled-coil, and B30-2 domains, which are characteristic of the RING-B30 family. Each of these domains are thought to mediate protein-protein interactions by promoting homo- or heterodimerization. The MID1 gene on Xp22 is also a member of the RING-B30 family and is mutated in Opitz syndrome (OS). The autosomal dominant form of OS shows linkage to 22q11-q12. We detected a polymorphic protein-truncating allele of RFPL1 in 8% of the population, which was not associated with the OS phenotype. We identified 6-kb and 1.2-kb noncoding antisense mRNAs of RFPL1S and RFPL3S antisense genes, respectively. The RFPL1S and RFPL3S genes cover substantial portions of their sense counterparts, which suggests that the function of RFPL1S and RFPL3S is a post-transcriptional regulation of the sense RFPL genes. We illustrate the role of intrachromosomal duplications in the generation of RFPL genes, which were created by a series of duplications and share an ancestor with the RING-B30 domain containing genes from the major histocompatibility complex region on human chromosome 6.

Characterization of DNA binding properties and sequence specificity of the human 52 kDa Ro/SS-A (Ro52) zinc finger protein

The Ro52 protein is an autoantigen in Sjögren's Syndrome and systemic lupus erythematosus. Although its function is not yet known, sequence similarities to other proteins suggest that it binds to DNA. In this study, the hypothesis that Ro52 recognizes particular nucleic acid sequences was tested. Ro52 bound to double stranded but not single stranded DNA. 1,10-Phenanthroline, a chelater of zinc, was found to inhibit this interaction, suggesting that the zinc fingers of Ro52 are functional. DNA sequences were selected from an oligonucleotide library by binding to Ro52 followed by amplification by Taq DNA polymerase in order to characterize the DNA sequence-binding motif for this protein. These studies support the hypothesis that Ro52 is functionally a member of a family of zinc finger proteins, many of which are known to bind to DNA or regulate gene expression. We speculate that Ro52 functions as a transcription factor, and that its disregulation may have important consequences in the expression or susceptibility of certain autoimmune diseases.

Structure and evolution of the extended B7 family

Here, Joëlle Henry and colleagues explore structural and evolutionary relationships between the B7 costimulator molecules and a growing number of molecules encoded within the major histocompatibility complex. They propose that B7 and MHC genes are derived from a common ancestor, with several members of this large gene family possibly having pivotal influences on T-cell activation.

HERF1, a novel hematopoiesis-specific RING finger protein, is required for terminal differentiation of erythroid cells

The AML1/core binding factor beta (CBFbeta) transcription factor is essential for definitive hematopoiesis; however, the downstream pathways through which it functions remain incompletely defined. Using a differential cloning approach to define components of this pathway, we have identified a novel gene designated HERF1 (for hematopoietic RING finger 1), whose expression during development is dependent on the presence of functional AML1/CBFbeta. HERF1 contains a tripartite RING finger-B box-alpha-helical coiled-coil domain and a C-terminal region homologous to the ret proto-oncogene-encoded finger protein. Expression of HERF1 during embryogenesis coincides with the appearance of definitive erythropoiesis and in adult mice is restricted to erythroid cells, increasing 30-fold during terminal differentiation. Importantly, inhibition of HERF1 expression blocked terminal erythroid differentiation of the murine erythroleukemia cell line MEL, whereas its overexpression induced erythroid maturation. These results suggest an important role for this protein in erythropoiesis.

The MHC big bang

The human Major Histocompatibility Complex (MHC) shares similarities with three other chromosome regions in human. This could be the vestige of ancestral large scale duplications. We discuss here the possibility i) that these duplications occurred during two rounds of tetraploidization supposed to have taken place during chordate evolution before the jawed vertebrate radiation, and ii) that one of the quadruplicate regions, relaxed of functional constraints, gave rise to the vertebrate MHC by a quick round of gene cis-duplication and cis-exon shuffling. These different rounds of cis-duplications and exon shufflings allowed the emergence of new genes participating in novel biological functions i.e. adaptive immune responses. Cis-duplications and cis-exon shufflings are ongoing processes in the evolution of some of these genes in this region as they have occurred and were fixed at different times and in different lineages during vertebrate evolution. In contrast, other genes within the MHC have remained stable since the emergence of jawed vertebrates.

The chromosomal duplication model of the major histocompatibility complex

The major histocompatibility complex (MHC) is a genetic region that has been extensively studied by immunologists, molecular biologists, and evolutionary biologists. Nevertheless, our knowledge of how the MHC acquired its present-day organization is quite limited. The recent discovery that the mammalian genome contains regions paralogous to the MHC has led us to the proposal that the MHC region of jawed vertebrates arose as a result of ancient chromosomal duplications. Here, I review the current status of this proposal.

The novel estrogen-responsive B-box protein (EBBP) gene is tamoxifen-regulated in cells expressing an estrogen receptor DNA-binding domain mutant

We have identified a 2.6-kb mRNA whose steady state levels are increased 2- to 4-fold by treatment of human mammary epithelial cells (HMEC) stably expressing an estrogen receptor (ER) transgene with either estrogen (E) or the antiestrogen, 4-hydroxy-tamoxifen (HT). The cDNA corresponding to this mRNA encodes a 564-amino acid protein, named estrogen-responsive B box protein (EBBP), that is a new member of a subfamily within the B box zinc finger protein family, which includes transcription factors (e.g. TIF1), tumor suppressor proteins (e.g. PML), and proteins implicated in development (e.g. ret finger protein, XNF7). The EBBP mRNA is detectable by Northern blot analysis in most tissues, with the exception of liver and peripheral blood lymphocytes, and the gene has been mapped to human chromosome 17p11.2. In contrast to most B box family members, EBBP has a predominantly cytoplasmic localization. Studies of the estrogenic regulation of EBBP expression demonstrated that the E-dependent increase in EBBP mRNA levels in the ER-transfected HMEC is an early, ER-mediated, and cycloheximide-insensitive process. In HMEC stably transfected with an ER mutant containing a deletion in the second zinc finger of the DNA-binding domain, E and HT had different effects on EBBP gene expression; EBBP regulation by E was dramatically reduced while the effects of HT were augmented. These data indicate that HT can modulate EBBP mRNA expression through a mutated ER, which has little activity when bound by E, and suggest that different molecular mechanisms control the E and HT responsiveness of the EBBP gene.