Biliary Glycoprotein Research Articles

Biliary glycoprotein 1 expression during embryogenesis: Correlation with events of epithelial differentiation, mesenchymal‐epithelial interactions, absorption, and myogenesis

Biliary glycoprotein 1 expression during embryogenesis: Correlation with events of epithelial differentiation, mesenchymal‐epithelial interactions, absorption, and myogenesis

Characterization of the cholesterol crystallization-promoting low- density particle isolated from human bile

BACKGROUND & AIMS: Biliary concanavalin A-binding glycoprotein (CABG) contains cholesterol crystallization-promoting activity that is not accounted for by the pronucleators that have been characterized in this fraction. The aim of this study was to isolate and characterize the missing activity. METHODS: Biliary glycoprotein was isolated using concanavalin A-Sepharose. Promoting activity in CABG was purified using density gradient ultracentrifugation. RESULTS: Activity in CABG separated into two fractions at low (1.08) and high (1.29) density, which showed different crystallization kinetics in a model bile. The high-density fraction had a late onset time (49.2 +/- 17.8 hours) but a high crystal growth rate (13.4 +/- 5.2 micrograms. mL-1.h-1). The low- density fraction had a rapid onset time (33.9 +/- 20.9 hours) but a slower growth rate (6.5 +/- 3.8 micrograms.mL-1 .h-1). The high-density fraction was not further characterized in this study. The low-density fraction contained solid particles consisting of lipid and very little protein, and the activity was fully pronase resistant. Delipidation of the low-density fraction removed all activity. CONCLUSIONS: A potent pronase-resistant nucleation-promoting activity was activated from human bile and characterized. The low-density fraction may be responsible for the rapid nucleation in bile from typical patients with fast-nucleating gallstones. (Gastroenterology 1996 Jun;110(6):1936-44)

A CD66a-specific, activation-dependent epitope detected by recombinant human single chain fragments (scFvs) on CHO transfectants and activated granulocytes.

Antibodies to CD66 recognize at least five members (CD66a-e) of the carcinoembryonic antigen (CEA) family. Recombinant human single-chain Fv fragments (scFvs) that bind specifically to CD66a (biliary glycoprotein) were obtained from a naive human scFv library. The scFvs bound to the N-domain of CD66a on Chinese hamster ovary (CHO) transfectants but did not bind to freshly isolated peripheral granulocytes or to dimethylsulfoxide-treated HL-60 cells. In contrast, scFvs bound well to granulocytes that were short-term activated with N-formyl-Met-Leu-Phe or phorbol 12-myristate 13-acetate and to human HL-60 cells that were treated with all-trans-retinoic acid to induce granulocytic differentiation. Quantification of antigenic sites showed that the activation-dependent CD66a epitopes were expressed on nearly all of the CD66a molecules on CHO-biliary glycoprotein transfectants, but they were detected only on a portion of the molecules on activated polymorphonuclear neutrophils and differentiated HL-60 cells. Binding of CD66a scFvs to their neoepitopes on prestimulated PMNs induced respiratory burst, suggesting that CD66a is capable of delivering transmembrane signals in these cells.

Expression of a glycoprotein of the carcinoembryonic antigen family in normal and neoplastic sebaceous glands

Background: Carcinoembryonic antigen (CEA) is a well-known marker for sweat gland differentiation in adnexal neoplasms. Objective: The aim of this study was to examine the expression of glycoproteins of the CEA family, that is, CEA-180, nonspecific cross-reacting antigens (NCAs), and biliary glycoprotein (BGP), in sebaceous glands and in neoplasms with sebaceous differentiation. Methods: Normal adult and fetal skin, hyperplasias, hamartomas, and neoplasms with sebaceous or follicular differentiation were stained immunohistochemically with a panel of polyclonal and monoclonal antibodies highly specific for CEA-180, NCAs, and BGP. Double immunostaining was performed to correlate the CEA expression with that of epithelial membrane antigen (EMA), a glycoprotein consistently found in differentiating sebocytes. Results: Whereas sweat glands coexpressed CEA, NCAs, BGP, and EMA, sebaceous glands were exclusively labeled with the antibodies recognizing BGP or EMA. Staining of the sebaceous glands was restricted to mature sebocytes, sparing immature cells. At the ultrastructural level immunoreactivity for BGP and EMA was demonstrable in the golgi area, in small vesicles, and along the cell membranes. During fetal development BGP was not found until the sebaceous glands matured. The expression of BGP and EMA was highly conserved in reactive, hamartomatous, and neoplastic proliferations of adnexal structures with sebaceous differentiation. Conclusion: The expression of BGP, a CEA glycoprotein, in differentiating sebocytes accounts for the reactivity of many anti-CEA antibodies with sebaceous glands and thus disqualifies the CEA family as a monospecific marker for sweat gland differentiation.

Carcinoembryonic antigen and blood group-related carbohydrate antigens in glycoproteins in human bile in hepatolithiasis. Japanese Study Group of Hepatolithiasis.

We investigated whether carbohydrate antigens on biliary glycoproteins and carcinoembryonic antigen (CEA) are related to hepatolithiasis. CEA, ABO, and Lewis blood group-related antigens, as well as sialyl-Tn antigen in hepatic bile, were analyzed by Western blotting in samples from 12 patients with hepatolithiasis and 37 with other biliary diseases (choledocholithiasis, 13; cholecystolithiasis, 5; acute cholecystitis, 2; cholangiocarcinoma, 5; common bile duct carcinoma, 4; pancreatic carcinoma, 6; and metastatic carcinoma of liver, 2). CEA was positive on mucinous glycoprotein in six patients (50%) with hepatolithiasis and one case (17%) with pancreatic carcinoma. CEA was also positive on a glycoprotein of approximately 200 kd in eight patients (67%) with hepatolithiasis and two (33%) with pancreatic carcinoma. Lewis X was detected on the mucinous glycoprotein in almost all samples, as well as on glycoproteins of approximately 180 kd in all hepatolithiasis samples and approximately half of those from patients with other diseases. Sialyl-Tn antigen was detected on mucinous glycoprotein in four (80%) with cholangiocarcinoma, two (50%) with common bile duct carcinoma, and all pancreatic carcinoma samples. Mucinous glycoprotein and glycoproteins containing CEA and Lewis X antigens are enriched in hepatic bile of hepatolithiasis, and they may be closely related to the formation of intrahepatic calculi. Sialyl-Tn antigen in biliary mucinous glycoprotein will be a good marker of biliary and pancreatic carcinoma, and probably for cholangiocarcinoma complicated with hepatolithiasis.

Carcinoembryonic antigen and blood group-related carbohydrate antigens in glycoproteins in human bile in hepatolithiasi

We investigated whether carbohydrate antigens on biliary glycoproteins and carcinoembryonic antigen (CEA) are related to hepatolithiasis. CEA, ABO, and Lewis blood group-related antigens, as well as sialyl-Tn antigen in hepatic bile, were analyzed by Western blotting in samples from 12 patients with hepatolithiasis and 37 with other biliary diseases (choledocholithiasis,13; cholecystolithiasis, 5; acute cholecystitis, 2; cholangiocarcinoma, 5; common bile duct carcinoma, 4; pancreatic carcinoma, 6; and metastatic carcinoma of liver, 2). CEA was positive on mucinous glycoprotein in six patients (50%) with hepatolithiasis and one case (17%) with pancreatic carcinoma. CEA was also positive on a glycoprotein of approximately 200 kd in eight patients (67%) with hepatolithiasis and two (33%) with pancreatic carcinoma. Lewis X was detected on the mucinous glycoprotein in almost all samples, as well as on glycoproteins of approximately 180 kd in all hepatolithiasis samples and approximately half of those from patients with other diseases. Sialyl-Tn antigen was detected on mucinous glycoprotein in four (80%) with cholangiocarcinoma, two (50%) with common bile duct carcinoma, and all pancreatic carcinoma samples. Mucinous glycoprotein and glycoproteins containing CEA and Lewis X antigens are enriched in hepatic bile of hepatolithiasis, and they may be closely related to the formation of intrahepatic calculi. Sialyl-Tn antigen in biliary mucinous glycoprotein will be a good marker of biliary and pancreatic carcinoma, and probably for cholangiocarcinoma complicated with hepatolithiasis. (Hepatology 1996 Feb;23(2):258-63)

Neoplasms with sweat gland differentiation express various glycoproteins of the carcinoembryonic antigen (CEA) family.

Carcinoembryonic antigen (CEA) is a well-established marker for sweat gland differentiation in adnexal neoplasms. In contrast to previous assumptions, CEA does not represent a single oncofetal antigen but comprises a family of homologous glycoproteins, i.e. the classical CEA-180, biliary glycoprotein (BGP), and non-specific crossreacting antigens (NCA). The aim of the study was to evaluate the distribution of the respective glycoproteins of the CEA family in sweat gland neoplasms, as compared to normal sweat glands. A panel of mono-specific antibodies was applied to a total of 83 samples of hyperplastic and cystic alterations of sweat glands, sweat gland neoplasms, and cutaneous metastases of different origin. Within a single group of neoplasms the immunohistochemical profile was rather consistent. Staining for both CEA-180 and NCA-90 indicated ductal differentiation of both eccrine and apocrine glands. Co-expression of CEA-180, NCA-90, and BGP was consistent with differentiation towards the secretory part of eccrine glands or the transitional portion of proximal ducts. Neoplasms with signs of apocrine secretion showed a preferential immunoreactivity for NCA-90 and BGP. In conclusion, a specification of the members of the CEA family may be of some value in the differential diagnosis of adnexal neoplasms, but not in the discrimination of sweat gland carcinoma from metastatic carcinoma.

Glycoproteins of the Carcinoembryonic Antigen (CEA) Family Are Expressed in Sweat and Sebaceous Glands of Human Fetal and Adult Skin

The carcinoembryonic antigen (CEA) family comprises a group of glycoproteins including the classical CEA, nonspecific cross-reacting antigens (NCA), and biliary glycoprotein (BGP). CEA glycoproteins have been identified in many glandular and mucosal tissues. In view of their putative role in cell adhesion, protein sorting, and signal transduction, CEA glycoproteins are thought to be involved in embryogenesis, architectual integrity, and secretory mechanisms of glandular epithelia. Since there are few data available on the expression of CEA-like proteins in human skin, the aim of this study was to immunohistochemically specify and localize the CEA glycoproteins in cutaneous adult and fetal glands using a panel of well-characterized antibodies. The secretory parts of eccrine sweat glands expressed CEA, NCA-90, and BGP, whereas apocrine glands remained unreactive for CEA glycoproteins. The ductal epithelia of both eccrine and apocrine glands contained CEA and NCA-90. Sebaceous glands were stained for BGP only. Electron microscopy of sweat glands showed CEA glycoprotein expression in cytoplasmic organelles and on microvilli lining the ductal surface. In sebaceous glands, BGP were demonstrated in small vesicles and along the cell membranes of differentiating sebocytes. Fetal development of cutaneous glands was associated with early expression of CEA glycoproteins. Additionally, mice transgenic for human CEA were shown to express CEA in sweat glands. The overall distribution of CEA glycoproteins in cutaneous glands was consistent with that in epithelia of other glandular tissues.

CD66a (BGP), an adhesion molecule of the carcinoembryonic antigen family, is expressed in epithelium, endothelium, and myeloid cells in a wide range of normal human tissues.

CD66a, also called biliary glycoprotein (BGP), is a member of the carcinoembryonic antigen (CEA) family and of the immunoglobulin superfamily. CD66a is the human homologue of Cell-CAM, a well-defined cell adhesion molecule of the rat. In the present study a monoclonal antibody specific for CD66a was used to locate CD66a in human tissues. CD66a is expressed in epithelia, in certain endothelia, and in cells of the myeloid lineage. Hepatocytes were stained along the bile canaliculi. A characteristic apical membranous staining was observed in enterocytes, superficial absorptive cells of the colon, in the epithelia of esophageal and Brunner's glands, bile ducts and gallbladder, pancreatic ducts, proximal tubules of the kidney, prostate, endometrium, and mammary ducts. Selective staining of endothelia was present in glomeruli and vasa recta of the kidney, small placental vessels, adrenal sinusoids, endometrium, the prostate. Among the cells of the myeloid lineage, granulocytes and myelocytes were positive. The expression of CD66a by human cells and tissues is well comparable with the expression reported for Cell-CAM, the rat counterpart of CD66a. The wide tissue distribution of CD66a indicates that CD66a is a prominent human adhesion molecule.

Structure and function of C-CAM1: effects of the cytoplasmic domain on cell aggregation

C-CAMs are epithelial cell-adhesion molecules of the immunoglobulin supergene family with sequences highly homologous to carcinoembryonic antigen (CEA). C-CAMs and their human homologues, biliary glycoproteins, are unique among the CEA-family proteins in that they have cytoplasmic domains. Furthermore, alternative splicing generates C-CAM isoforms with different cytoplasmic domains, suggesting that the cytoplasmic domains of C-CAM may play important roles in regulating the function or functions of C-CAM. By using both sense and antisense approaches, we have shown that C-CAM1 is a tumour suppressor in prostate carcinogenesis. This observation raises the possibility that the cytoplasmic domain of C-CAM1 may be involved in signal transduction or interaction with cytoskeletal elements to elicit the tumour suppressor function. The cytoplasmic domain of C-CAM1 contains several potential phosphorylation sites, including putative consensus sequences for cyclic AMP-dependent kinase and tyrosine kinase. One of the potential tyrosine phosphorylation sites is located within the antigen-receptor homology (ARH) domain. The ARH domain of the membrane-bound IgM molecule is necessary for signal transduction in B-cells. These structural features suggest that the cytoplasmic domain of C-CAM1 may be important for signal transduction. To test this possibility, we generated several site-directed C-CAM1 mutants and tested their ability to support adhesion and their abilities to be phosphorylated in vivo. Results from these studies revealed that Tyr-488 is phosphorylated in vivo. However, replacing this tyrosine with phenylalanine did not significantly compromise its adhesion function. Similarly, Ser and Thr residues are phosphorylated in vivo, but deletion of the potential cyclic AMP-dependent kinase site did not significantly reduce the adhesion function. These results suggest that the kinase phosphorylation sites in the cytoplasmic domain of C-CAM1 are not required for the adhesion function. However, these phosphorylation sites are probably involved in the regulation of C-CAM-mediated signal transduction. Thus, there are probably distinct structural requirements for the adhesion and the signal transduction functions of C-CAM. Incidentally, a C-CAM1 deletion mutant containing a 10-amino-acid cytoplasmic domain was able to support adhesion activity. This is in contrast to our previous finding that a C-CAM isoform, C-CAM3, with a 6-amino-acid cytoplasmic domain could not support cell adhesion. This result indicates that the extra four amino acids, which are absent in C-CAM3 and contain a potential Ser/Thr phosphorylation site, are important for the adhesion function.

Biliary alpha 1-acid glycoprotein concentrations in gallstone-free controls and in patients with multiple or solitary cholesterol gallstones.

We recently identified a promoting glycoprotein in the concanavalin A-bound fraction of gallbladder bile as a biliary form of alpha 1-glycoprotein (AAG). The concentration of biliary AAG appears to exert an important promoting effect on the speed of cholesterol nucleation in many patients with cholesterol gallstone disease. In the current study, we provide information about the biliary concentration of AAG as well as the amount and comparative potency of its subfractions in patients with and without cholesterol gallstone disease. The amount of total biliary AAG and the amounts of its different isoforms separated by concanavalin A affinity chromatography were measured by ELISA. Estimates of absolute concentrations of AAG for each sample were normalized to the sample total protein content to give relative AAG values. The promoting activity (potency) of immunopurified biliary AAG from gallstone patients and gallstone-free controls on cholesterol crystallization was compared by a crystal growth assay. The mean absolute concentration of AAG in gallstone-free controls was not significantly different from multiple stone patients. The relative concentration of AAG (micrograms per milligram total protein) was significantly increased in patients with multiple stones when compared to controls (P < 0.05), and both the absolute and relative concentrations of AAG (micrograms per milligram bile), were three- and to five fold higher in a number of these patients. The functional activity and distribution of AAG in different subfractions was similar in gallstone patients and gallstone-free controls. The relative concentration of biliary AAG is significantly greater in cholesterol gallstone patients with multiple stones than in gallstone-free controls.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

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.

Biliary Nonmucin Glycoproteins in Patients with and without Gallstones

Total protein, mucin, and specific nonmucin glycoproteins are proposed pronucleating agents in cholesterol gallstone pathogenesis. However, characterization of specific nonmucin glycoproteins in patients with and without gallstones is unknown. Furthermore, nonmucin glycoproteins may be qualitatively different in patients with and without gallstones. Total protein and total and specific nonmucin glycoproteins were studied in gallbladder bile of 43 patients with cholesterol gallstones and 13 patients without gallstones. Patients with cholesterol gallstones had higher concentrations of both total protein and nonmucin glycoproteins than that observed in control patients (P < 0.05). SDS gel electrophoresis of nonmucin glycoproteins demonstrated an 84-kDa protein that was present significantly more often in patients with cholesterol gallstones (87% vs 8%, P < 0.05). Proposed 130- and 42-kDa pronucleating and 120-kDa anti-nucleating nonmucin glycoproteins were present in similar percentages in gallstone and control bile. Moreover, gallbladder bile of patients with the 84-kDa protein nucleated 50% faster than model bile and >100% faster than that of patients without this protein (P < 0.05). The currently described gallbladder pronucleating and anti-nucleating proteins are found with equal frequency in cholesterol gallstone and control patients. However, an 84-kDa protein is found more commonly in gallstone patients and was associated with a shortened crystal observation time. Thus, this glycoprotein may be important in cholesterol gallstone pathogenesis.

Opposite functions for two classes of genes of the human carcinoembryonic antigen family.

The human carcinoembryonic antigen (CEA) family can be divided into two subgroups according to the means of anchorage of member glycoproteins to the cell membrane: glycophosphatidyl inositol (GPI) linkage and transmembrane linkage. The GPI-linked members tend to be up-regulated in human tumours, whereas the transmembrane-linked members tend to be down-regulated. Thus the question as to whether the GPI members could be formally considered to function as oncogenes and the transmembrane members as tumour suppressors deserves consideration. Members of both subgroups function in vitro as intercellular adhesion molecules, but the characteristics of this adhesion, including temperature and divalent-cation dependence, differ markedly between the groups. Even the mechanism of intermolecular adhesion appears to differ fundamentally in that GPI-linked CEA-CEA binding involves a double reciprocal bonding between two domains, whereas transmembrane-linked biliary glycoprotein (BGP)-BGP binding requires only one domain. Finally, the ectopic expression of CEA in myoblasts can block myogenic differentiation leaving the cells with the ability to divide, while expression of BGP does not affect or may even accelerate myogenic differentiation. These differences in phenotypic effects in vitro thus mirror the differences observed in expression in tumours and support the view that the GPI and transmembrane groups have opposite effects on cells in relation to the malignant phenotype.

Mouse hepatitis virus receptor activities of an MHVR/mph chimera and MHVR mutants lacking N-linked glycosylation of the N-terminal domain

Mouse hepatitis virus binds to the N-terminal domain of its receptor, MHVR, a murine biliary glycoprotein with four immunoglobulin-like domains (G.S. Dveksler, M. N. Pensiero, C. W. Dieffenbach, C. B. Cardellichio, A.A. Basile, P.E. Elia, and K. V. Holmes, Proc. Natl. Acad. Sci. USA 90:1716-1720, 1993). A recombinant protein with only the anchored N-terminal domain was not a functional receptor, but a recombinant protein with the N-terminal domain of MHVR linked to the second and third immunoglobulin-like domains and anchor from the mouse poliovirus receptor homolog, mph, was a functional receptor for mouse hepatitis virus. The native four-domain MHVR has 16 potential N-linked glycosylation sites, including three on the N-terminal domain. Recombinant proteins lacking each one of these three sites or all three of them were functional receptors. Thus, glycosylation of the N-terminal domain is not required, but a glycoprotein longer than the N-terminal domain is required for virus receptor activity.

Fine needle aspiration of focal liver lesions.

Fourteen percutaneous fine needle aspirates (FNAs) of focal liver lesions performed under ultrasound guidance at the Sultan Qaboos University Hospital (SQUH), Oman, between January 1991 and October 1992, are presented. Ten of these were cytologically diagnosed as hepatocellular carcinomas (HCC). The patients' ages ranged from 50 to 70 years and eight of these were males. The important diagnostic cytological criteria of HCC were found to be increased nucleocytoplasmic (N/C) ratio, trabecular pattern, atypical naked nuclei, bile production by malignant hepatocytes and absence of bile duct epithelium. Carcinoembryonic antigen (CEA) positivity of bile canaliculi by cross-reaction with biliary glycoprotein I (BGP I) made possible the differentiation of HCC from metastases. We stress the importance of cell blocks as these often constitute microbiopsies. Ultrasound-guided FNA of focal liver lesions is recommended as a simple, easy and quick procedure.

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.

The N-Domain of the Biliary Glycoprotein (BGP) Adhesion Molecule Mediates Homotypic Binding: Domain Interactions and Epitope Analysis of BGPc

The biliary glycoproteins (BGPs) represent a group of at least eight differentially spliced molecules belonging to the carcinoembryonic antigen (CEA) subgroup of the CEA family. These molecules are recognized by the CD66 monoclonal antibodies (MoAbs) and function as homotypic and heterotypic adhesion molecules. The extracellular region of the BGPc splice variant comprises an N-terminal IgV-like domain and three IgC2-set domains (A1, B1, and A2). Using soluble recombinant BGP domain variants, we demonstrate in this report that the N-terminal domain mediates homotypic adhesion. Furthermore, this adhesion is both temperature- and cation-dependent. The soluble domain variants of BGP are ideal molecules for epitope mapping. Using these constructs, we have mapped 11 MoAbs that react with the CEA family to different domains of BGPc and have shown that the CD66 MoAbs, YTH71.3.2 and CLBgran 10 (M38), recognize epitopes in the N-terminal domain.

The N-domain of the biliary glycoprotein (BGP) adhesion molecule mediates homotypic binding: domain interactions and epitope analysis of BGPc

The biliary glycoproteins (BGPs) represent a group of at least eight differentially spliced molecules belonging to the carcinoembryonic antigen (CEA) subgroup of the CEA family. These molecules are recognized by the CD66 monoclonal antibodies (MoAbs) and function as homotypic and heterotypic adhesion molecules. The extracellular region of the BGPc splice variant comprises an N-terminal IgV-like domain and three IgC2-set domains (A1, B1, and A2). Using soluble recombinant BGP domain variants, we demonstrate in this report that the N-terminal domain mediates homotypic adhesion. Furthermore, this adhesion is both temperature- and cation-dependent. The soluble domain variants of BGP are ideal molecules for epitope mapping. Using these constructs, we have mapped 11 MoAbs that react with the CEA family to different domains of BGPc and have shown that the CD66 MoAbs, YTH71.3.2 and CLBgran 10 (M38), recognize epitopes in the N-terminal domain.