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N Beauchemin

Publications and source records attributed to N Beauchemin.

At least 37 records · Page 2Linked to original sources
PubMed1995

Characterization and transcriptional activity of the mouse biliary glycoprotein 1 gene, a carcinoembryonic antigen-related gene.

The mouse biliary glycoprotein 1 gene (bgp1) encodes several multifunctional glycoprotein isoforms. These glycoproteins represent members of the carcinoembryonic antigen (CEA) family which belongs to the immunoglobulin superfamily. The Bgp1 glycoproteins function as cell adhesion molecules and receptors for the mouse hepatitis viruses. In contrast to CEA, whose overexpression has been correlated with cancer progression, the human and mouse Bgp proteins are generally down-regulated upon tumor formation. In this study, we report on the mouse bgp1 gene organization and transcriptional activation. We have isolated phage and cosmid clones encompassing the entire bgp1 coding region. This gene consists of nine exons, some of which are subjected to alternative splicing producing a minimum of four splice variants. A comparison of the murine bgp1 proximal promoter with the human BGP and mouse cea10/bgp3 genes revealed sequence conservation of 66% and 95%, respectively. RNase protection assays and primer extension analyses indicated that the mouse bgp1 transcriptional start site is positioned 240 nucleotides upstream of the ATG translational initiation codon, which is 140 nucleotides further upstream than in any other CEA family member. The bgp1 promoter is transcriptionally active in reporter gene activation in vitro transfection studies and in vivo using a bgp1-containing cosmid clone. We identified three putative AP-2 or AP-2-like sites and an upstream stimulatory factor (USF) recognition sequence within the proximal mouse bgp1 promoter region at positions similar to those used by the human BGP promoter region. These data suggest that the regulation of the mouse and human BGP genes may follow some common spatial and temporal expression. Interestingly, the bgp1 proximal promoter and coding region are also well conserved throughout evolution.

Animals↗
PubMed1995

The cea10 gene encodes a secreted member of the murine carcinoembryonic antigen family and is expressed in the placenta, gastrointestinal tract and bone marrow.

Although members of the carcinoembryonic antigen (CEA) family have been shown to convey cell adhesion in vitro, their location in some tissues contradicts such a function. As a basis for investigating their in vivo functions, we are characterizing the mouse CEA family. This paper describes the structure and expression of a new murine family member, cea10. Two full-length cDNA clones were isolated from a mouse colon library, whose deduced protein sequence comprises two immunoglobulin variable-like N-domains, directly followed by a short C-terminal domain indicating that this molecule is secreted. Although this domain organization suggests a closer relationship to the murine pregnancy-specific glycoproteins (PSG), which form a subgroup within the CEA family, sequence comparisons place Cea10 within the CEA subgroup. Overlapping cosmid clones containing the complete cea10 locus were mapped and the exons determined. No A2-like exon, characteristic for all other members of the murine CEA family, could be found. Sequences of the promoter and the first exon showed remarkably high similarity to the corresponding regions of bgp1 and bgp2, two other members of the murine CEA subgroup. Consensus sequences for two transcription factors (USF and an AP-2-like factor) that bind to the human BGP gene promoter were also present in the cea10 promoter and possibly convey expression of these genes in epithelial cells. RNase protection assays revealed transcriptional activity of cea10 in the colon and early placenta (10.5-12.5-day embryos) and to a lower extent in the small intestine, cecum, stomach, salivary glands and bone marrow. As some other CEA family members are deregulated in tumors, we quantified the expression levels of Cea10 transcripts in colonic mucosa and in adenomatous polyps of Min/+ mice. No differences in the steady-state levels of Cea10 mRNA could be found, suggesting that the Cea10 protein does not play a role in early tumor development. Taken together, Cea10 combines characteristic features of both CEA and PSG subgroup members in its structure and expression pattern.

Amino Acid Sequence↗
PubMed1995

Characterization of a new gene that encodes a functional MHV receptor and progress in the identification of the virus-binding site(s).

Several splice variants of the murine biliary glycoprotein 1 (Bgp 1) gene in the carcinoembryonic antigen gene superfamily serve as cellular receptors for mouse hepatitis virus. RNAPCR and immunoblot analysis of the receptor in inbred mouse strains showed that the glycoproteins expressed in SJL/J mice are encoded by an allelic variant of the Bgp 1 gene, named Bgp 1b. We recently cloned and characterized a second gene, Bgp 2, that encodes a functional MHV receptor glycoprotein which is not recognized by anti-MHVR MAb-CC1. A third gene related to Bgp 1 was cloned and expressed and shown to encode a soluble protein called Cea-10 that differs significantly in its N-terminal domain from Bgp 1 and Bgp 2. Chimeric proteins constructed between the different murine Bgps and point mutations in the prototype MHV receptor, Bgp 1a or MHVR, were analyzed to further characterize the MAb-CC1-binding and virus-binding domains within the N terminal domain of the receptor. Thus, the murine host for MHV expresses multiple splice variants of mRNAs encoded by several different Bgp-related genes which differ in their ability to serve as MHV receptors. The differential expression of these genes in different murine tissues may help to explain the tissue tropism of MHV strains.

Alternative Splicing↗
PubMed1994

Transcriptional control of the human biliary glycoprotein gene, a CEA gene family member down-regulated in colorectal carcinomas.

Biliary glycoprotein (BGP) isoantigens are derived by alternative splicing from a single gene and are the human homologs of rat C-CAM and the mouse Bgp species. These glycoproteins represent a family of cell-adhesion molecules. The mouse Bgp isoforms also act as receptors for the hepatitis viral capsid-protein. BGP is a member of the carcinoembryonic antigen (CEA) gene family, which belongs to the immunoglobulin supergene family, yet it displays restricted expression patterns and unique functions. Since the loss or reduced expression of BGP is associated with human colorectal carcinomas, the elements in its upstream regulatory region were analyzed. A cluster of transcriptional initiation sites and the minimal promoter, located within 150 bp upstream of the major transcriptional start site, were active in human colon carcinoma and hepatoma cells. Unlike the CEA gene, BGP gene transcription was not modulated by a silencer region; repetitive elements in the BGP upstream region were not involved in activation or repression. Footprinting experiments identified two cis-acting elements and mobility-shift assays demonstrated that these elements bound several transcription factors, among them, USF, HNF-4 and an AP-2-like factor. In cotransfection experiments, both the USF and HNF-4 transcription factors transactivate the BGP gene promoter and compete for the same regulatory element. The Sp1 transcription factor, shown to be involved in CEA gene transcriptional regulation, does not bind to the BGP gene promoter. We, therefore, propose that the relative distributions and interactions of these transcription factors mediate distinct transcriptional regulation of the BGP gene in colon and liver; this regulation could be distorted during the oncogenic process.

Animals↗
PubMed1994

Bgp2, a new member of the carcinoembryonic antigen-related gene family, encodes an alternative receptor for mouse hepatitis viruses.

Murine coronaviruses such as mouse hepatitis virus (MHV) infect mouse cells via cellular receptors that are isoforms of biliary glycoprotein (Bgp) of the carcinoembryonic antigen gene family (G. S. Dveksler, C. W. Dieffenbach, C. B. Cardellichio, K. McCuaig, M. N. Pensiero, G.-S. Jiang, N. Beauchemin, and K. V. Holmes, J. Virol. 67:1-8, 1993). The Bgp isoforms are generated through alternative splicing of the mouse Bgp1 gene that has two allelic forms called MHVR (or mmCGM1), expressed in MHV-susceptible mouse strains, and mmCGM2, expressed in SJL/J mice, which are resistant to MHV. We here report the cloning and characterization of a new Bgp-related gene designated Bgp2. The Bgp2 cDNA allowed the prediction of a 271-amino-acid glycoprotein with two immunoglobulin domains, a transmembrane, and a putative cytoplasmic tail. There is considerable divergence in the amino acid sequences of the N-terminal domains of the proteins coded by the Bgp1 gene from that of the Bgp2-encoded protein. RNase protection assays and RNA PCR showed that Bgp2 was expressed in BALB/c kidney, colon, and brain tissue, in SJL/J colon and liver tissue, in BALB/c and CD1 spleen tissue, in C3H macrophages, and in mouse rectal carcinoma CMT-93 cells. When Bgp2-transfected hamster cells were challenged with MHV-A59, MHV-JHM, or MHV-3, the Bgp2-encoded protein served as a functional MHV receptor, although with a lower efficiency than that of the MHVR glycoprotein. The Bgp2-mediated virus infection could not be inhibited by monoclonal antibody CC1 that is specific for the N-terminal domain of MHVR. Although CMT-93 cells express both MHVR and Bgp2, infection with the three strains of MHV was blocked by pretreatment with monoclonal antibody CC1, suggesting that MHVR was the only functional receptor in these cells. Thus, a novel murine Bgp gene has been identified that can be coexpressed in inbred mice with the Bgp1 glycoproteins and that can serve as a receptor for MHV strains when expressed in transfected hamster cells.

Amino Acid Sequence↗
PubMed1993

The expression of mouse biliary glycoprotein, a carcinoembryonic antigen-related gene, is down-regulated in malignant mouse tissues.

Mouse biliary glycoprotein (Bgp) is a member of the carcinoembryonic antigen gene family and is highly expressed in the epithelial cells of normal hepatic biliary ducts and intestine. Nine mouse Bgp isoforms have been identified through molecular cloning and shown to be splice and allelic variants of one Bgp gene. These glycoproteins function in vitro as intercellular adhesion molecules and serve as the mouse hepatitis virus receptors. Since human carcinoembryonic antigen is overexpressed in gastrointestinal tumors, we have investigated the expression of mouse Bgp in primary tumors and carcinoma cell lines. Our results demonstrate that the expression of the major mouse Bgp isoforms is down-regulated in tumors at the transcriptional and the posttranscriptional levels. This decrease in expression is corroborated by immunostaining of primary colonic tumors with anti-mouse Bgp antibodies. In addition, Bgp expression is influenced by transcriptional control mechanisms involving DNA methylation of the Bgp gene upstream regulatory region. Our results demonstrate that mouse Bgp protein expression is decreased upon malignant transformation and further suggest that Bgp proteins may be involved in the maintenance of the differentiated cellular phenotype.

3T3 Cells↗
PubMed1993

A polymerase-chain-reaction assay for the specific identification of transcripts encoded by individual carcinoembryonic antigen (CEA)-gene-family members.

Carcinoembryonic antigen (CEA) is a tumor marker that belongs to a family of closely related molecules with variable expression patterns. We have developed sets of oligonucleotide primers for the specific amplification of transcripts from individual CEA-family members using the reverse transcriptase/polymerase chain reaction (RT/PCR). Specific primer sets were designed for CEA, non-specific cross-reacting antigen (NCA), biliary glycoprotein (BGP), carcinoembryonic antigen gene-family members 1, 6 and 7 (CGM1, CGM6 and CGM7), and one set for all pregnancy-specific glycoprotein (PSG) transcripts. Primers were first tested for their specificity against individual cDNA clones and product-hybridization with internal, transcript-specific oligonucleotides. Total RNA from 12 brain and 63 gynecological tumors were then tested for expression of CEA-related transcripts. None were found in tumors located in the brain, including various mesenchymal and neuro-epithelial tumors. CEA and NCA transcripts were, however, present in an adenocarcinoma located in the nasal sinuses. In ovarian mucinous adenocarcinomas, we always found co-expression of CEA and NCA transcripts, and occasionally BGP mRNA. CEA-related transcripts were also found in some serous, endometrioid and clear-cell ovarian carcinomas. CEA, NCA and BGP transcripts were present in endometrial carcinomas of the uterus and cervical carcinomas, whereas uterine leiomyomas were completely negative. No transcripts were found from CGM1, CGM6, CGM7 or from PSG genes in any of the tumors tested. The PCR data were compared with immunohistochemical investigations of ovarian tumors at the protein level using CEA (26/3/13)-, NCA-50/90 (9A6FR) and NCA-95 (80H3)-specific monoclonal antibodies.

Antigens, Neoplasm↗
PubMed1993

Expression of the Bgp gene and characterization of mouse colon biliary glycoprotein isoforms.

The biliary glycoprotein (BGP)-encoding gene is a member of the human carcinoembryonic antigen (CEA) gene family. We have now cloned several mouse Bgp cDNAs from an outbred CDR-1 mouse colon cDNA library, as well as by reverse transcription-PCR amplification of colon RNA. The distinguishing features of the deduced Bgp protein isoforms are found in the two divergent N-terminal domains, the highly conserved internal C2-set immunoglobulin domains, and an intracytoplasmic domain of either 10 or 73 amino acids (aa). The cDNA structures suggest that these mRNAs are produced through alternative splicing of a Bgp gene and the usage of multiple transcriptional terminators. The Bgp deduced aa sequences are highly homologous to several well characterized rat hepatocyte proteins such as the cell CAM105/ecto-ATPase/pp120/HA4 proteins. Oligodeoxyribonucleotide probes representing the various cDNA isoform domains revealed predominant transcripts of 1.8, 3.1 and 4.0 kb on Northern analyses of mouse colon RNA; some of these bands are actually composed of several co-migrating transcripts. The transcripts encoding the long intracytoplasmic-tailed Bgp proteins are expressed at one-tenth the relative abundance of the shorter-tailed species. We have previously demonstrated that several mouse Bgp cDNAs, when transfected into eukaryotic cells, express BGP proteins at the cell surface and function in vitro as cell adhesion molecules, much like their human and rat counterparts. The expression of the many Bgp isoforms at the surface of epithelial cells, such as colon, suggests that these proteins play a determinant role, through self- or heterologous contact, in renewal and/or differentiation of their epithelia.

Amino Acid Sequence↗
PubMed1993

Several members of the mouse carcinoembryonic antigen-related glycoprotein family are functional receptors for the coronavirus mouse hepatitis virus-A59.

Mouse hepatitis virus-A59 (MHV-A59), a murine coronavirus, can utilize as a cellular receptor MHVR, a murine glycoprotein in the biliary glycoprotein (BGP) subfamily of the carcinoembryonic antigen (CEA) family in the immunoglobulin superfamily (G.S. Dveksler, M. N. Pensiero, C. B. Cardellichio, R. K. Williams, G.-S. Jiang, K. V. Holmes, and C. W. Dieffenbach, J. Virol. 65:6881-6891, 1991). Several different BGP isoforms are expressed in tissues of different mouse strains, and we have explored which of these glycoproteins can serve as functional receptors for MHV-A59. cDNA cloning, RNA-mediated polymerase chain reaction analysis, and Western immunoblotting with a monoclonal antibody, CC1, specific for the N-terminal domain of MHVR showed that the inbred mouse strains BALB/c, C3H, and C57BL/6 expressed transcripts and proteins of the MHVR isoform and/or its splice variants but not the mmCGM2 isoform. In contrast, adult SJL/J mice, which are resistant to infection with MHV-A59, express transcripts and proteins only of the mmCGM2-related isoforms, not MHVR. These data are compatible with the hypothesis that the MHVR and mmCGM2 glycoproteins may be encoded by different alleles of the same gene. We studied binding of anti-MHVR antibodies or MHV-A59 virions to proteins encoded by transcripts of MHVR and mmCGM2 and two splice variants of MHVR, one containing two immunoglobulin-like domains [MHVR(2d)] and the other with four domains as in MHVR but with a longer cytoplasmic domain [MHVR(4d)L]. We found that the three isoforms tested could serve as functional receptors for MHV-A59, although only isoforms that include the N-terminal domain of MHVR were recognized by monoclonal antibody CC1 in immunoblots or by MHV-A59 virions in virus overlay protein blot assays. Thus, in addition to MHVR, both the two-domain isoforms, mmCGM2 and MHVR(2d), and the MHVR(4d)L isoform served as functional virus receptors for MHV-A59. This is the first report of multiple related glycoprotein isoforms that can serve as functional receptors for a single enveloped virus.

3T3 Cells↗
PubMed1992

mmCGM1a: a mouse carcinoembryonic antigen gene family member, generated by alternative splicing, functions as an adhesion molecule.

Carcinoembryonic antigen is a human tumor marker and the prototype of a large family of immunoglobulin-like proteins. We have been developing a mouse model for this large protein family and have cloned a complementary DNA (cDNA) for a mouse carcinoembryonic antigen gene family member (mmCGM1a). Two transcripts expressed in several different adult mouse tissues hybridize to this cDNA, a 1.8-kilobase and a 4.6-kilobase mRNA. Sequences of many related cDNA clones indicate that they are most likely encoded by a single gene which undergoes alternative splicing. The protein encoded by the mmCGM1a cDNA shares 69% of the amino acid residues in the NH2-terminal domain with a rat liver ecto-ATPase and with the human biliary glycoprotein. Mouse fibroblast transfectant cells expressing the mmCGM1a protein on their cell surface exhibit calcium- and temperature-independent adhesion in vitro which can be specifically inhibited by an antibody raised against a carcinoembryonic antigen-related 120 kilodalton protein.

Amino Acid Sequence↗
PubMed1991

A mouse carcinoembryonic antigen gene family member is a calcium-dependent cell adhesion molecule.

Carcinoembryonic antigen (CEA) is a heavily glycosylated protein used clinically as a tumor marker to detect recurrences of many types of tumors. This glycoprotein belongs to the immunoglobulin superfamily and is the prototype of the large CEA family of proteins. In a concerted effort to determine the function(s) of this family, we have been investigating a similar family of proteins in the mouse. In this paper, we report the characterization of a new mouse family member named mmCGM2; this gene product is highly homologous to the human biliary glycoprotein of the CEA gene family and to a rat hepatocyte ecto-ATPase. In vitro transcription, translation, and glycosylation experiments have revealed that the mmCGM2 cDNA encodes a glycoprotein of 42 kDA with a putative extracellular N-terminal domain and a C2-set type immunoglobulin domain. We have used this cDNA as a probe to detect many different transcripts (1.5-4.6 kilobases) in mouse adult tissues, some of which are specific to particular tissues, while others are expressed ubiquitously. After transfection of a plasmid bearing the mmCGM2 cDNA into mouse fibroblasts known to lack CEA-related gene expression, transfectant cell clones were chosen and used to investigate the adhesion properties conferred onto the cells. Cells expressing the mmCGM2 cDNA in a sense orientation aggregated in a calcium- and temperature-dependent fashion. Together with human biliary glycoprotein, the mmCGM2 gene product is the first member of the immunoglobulin superfamily to exhibit calcium-dependent adhesion. The constant tissue reorganization necessary to the differentiation of precise structures in tissues which express these gene family members (colon, liver, and uterus) implies the necessity of a variety of specific cell-cell contacts which could utilize the cell adhesion properties that we have demonstrated.

Amino Acid Sequence↗
PubMed1990

The conformation of single-stranded nucleic acids tDNA versus tRNA.

Conformational analyses using the single-strand-specific nuclease from mung bean and restriction endonucleases have been performed on a series of DNA fragments related to the sequence of the yeast initiator tRNA(Met). Mung bean nuclease cleaves DNA fragments exclusively in some, but not all, single-stranded regions as predicted by RNA secondary structural rules. Comparison of cleavage patterns of yeast initiator tRNA(Met), tDNA(Met) (a DNA oligomer having the sequence of tRNA(Met] and the anti-tDNA(Met) (the complement of tDNA(Met] suggests that the conformation of the three molecules is very similar. Furthermore, both tDNA and anti-tDNA are cleaved by HhaI and CfoI restriction endonucleases at two GCG/C sites which would be in double-stranded regions (the acceptor and dihydrouridine stem), if the two molecules adopt the tRNA cloverleaf structure. On the other hand, minor cleavage products show that the core region, i.e. the extra loop area, is slightly more exposed in tDNA and in anti-tDNA than in tRNA. Therefore, we submit that the global conformation of nucleic acids is primarily dictated by the interaction of purine and pyrimidine bases with atoms and functional groups common to both RNA and DNA. In this view the 2'-hydroxyl group, in tRNA at least, is an auxiliary structural feature whose role is limited to fostering local interactions, which increase the stability of a given conformation.

Base Sequence↗
PubMed1990

Spatiotemporal expression of murine carcinoembryonic antigen (CEA) gene family members during mouse embryogenesis.

Carcinoembryonic antigen is a glycosylated protein used as a human tumor marker to assess recurrences of gastrointestinal, breast and lung cancers. This protein is a member of the immunoglobulin supergene family and has been shown to function as a homophilic and heterophilic cell adhesion molecule. We have studied the spatial and temporal expression of two cloned mouse CEA gene family members during development using Northern analyses and in situ hybridization. Transcripts detected by the mouse CEA probes are expressed from 10.5 days post coitum (p.c.) to birth in mouse embryos and fetuses and are present from 16.5 days p.c. to adulthood in intestine and colon as evaluated by Northern analyses. The RNA is also present in many other tissues including meninges, cartilage and bone, blood vessel walls, placenta, dermis, muscle layers of the stomach and intestine and bronchioles of developing mouse embryos and fetuses. This expression pattern is similar to that of proteins of the Transforming Growth Factor beta gene family. The role of mouse CEA gene family members is unclear; however, the localizations of these CEA family members in the mouse embryo and fetus suggest an important functional role during active morphogenesis, a complex process in which cell adhesion molecules are significantly involved.

Animals↗
PubMed1989

Carcinoembryonic antigen, a human tumor marker, functions as an intercellular adhesion molecule.

Carcinoembryonic antigen (CEA) is a member of a family of cell surface glycoproteins that are produced in excess in essentially all human colon carcinomas and in a high proportion of carcinomas at many other sites. The function of this widely used tumor marker and its relevance to malignant transformation is therefore of considerable interest. We demonstrate here that CEA mediates Ca2+-independent, homotypic aggregation of cultured human colon adenocarcinoma cells (LS-180) and rodent cells transfected with functional CEA cDNA. Furthermore, CEA can effect the homotypic sorting of cells in heterogeneous populations of aggregating cells. CEA can thus be considered a new addition to the family of intercellular adhesion molecules. We also show that, whereas CEA is localized mainly to epithelial cell membranes facing the lumen in normal adult intestine, it is found on adjacent cell membranes in both embryonic intestine and colonic tumors. A model for the role of CEA in the tissue architecture of adult, embryonic, and aberrant tumor intestinal epithelium is presented.

Biomarkers, Tumor↗
PubMed1989

A mouse analogue of the human carcinoembryonic antigen.

Functional human carcinoembryonic antigen (CEA)-like genes have been shown to be present in the mouse. Southern analyses of murine DNA using both human and murine CEA complementary DNA probes have revealed the presence of multiple CEA-like genes, while analyses of RNA from different mouse tissues showed CEA-like transcripts in adult colon and liver. Furthermore, a CEA-like protein, immunoprecipitable with a rabbit polyclonal serum raised against human CEA, has been detected in adult murine colon tissue. Several murine CEA complementary DNA clones have been isolated from a murine colon complementary DNA library, and characterization of one such clone demonstrates that both the N-terminal and the internal domains have been conserved between the two species. The existence of a murine counterpart of CEA strengthens the case for an essential function for this human tumor marker and provides an experimentally amenable system for elucidation of its biological properties.

Animals↗
PubMed1988

Transcription of genes of the carcinoembryonic antigen family in malignant and nonmalignant human tissues.

Normal and diseased human tissues were analyzed for the transcription of genes of the carcinoembryonic (CEA) family. Epithelial tissues of colonic origin, whether malignant or normal, all express two closely related mRNA species of 3.0- and 3.5-kilobase mRNA which code for CEA. Only tissues of colonic origin were found to express these CEA-specific transcripts. Colon carcinomas consistently express a 2.6-kilobase mRNA species as well which codes for nonspecific cross-reacting antigen. Nonneoplastic colon mucosas, on the other hand, express lower or nondetectable levels of this transcript. Most breast carcinomas produce only the nonspecific cross-reacting antigen mRNA, whereas leukocytes of chronic myelogeneous leukemia express both nonspecific cross-reacting antigen mRNA and a 2.3-kilobase mRNA corresponding to a yet undefined gene of the CEA family. Thus the multiple CEA-like products reported to be produced by these tissues correspond to only four different mRNA species coding for three different peptides. These data suggest a less complex organization of the CEA family than was previously suspected and point to posttranscriptional modifications, such as variable patterns of glycosylation, as the likely reason for much of the observed complexity in CEA-like glycoproteins.

Carcinoembryonic Antigen↗