Carcinoembryonic antigen gene family: molecular cloning of cDNA for a PS beta G/FL-NCA glycoprotein with a novel domain arrangement

Pregnancy-specific glycoprotein (PSG) in baboon (Papio hamadryas): family size, domain structure, and prediction of a functional region in primate PSGs

Pregnancy-specific glycoprotein (PSG) constitutes a major component of serum of pregnant women and appears to be essential for a successful pregnancy. Its function is, however, still unknown. Because of the evolutionary divergence between human and rodent PSG, functional studies may require a primate animal model. We have characterized PSG transcripts in a baboon placenta cDNA library and analyzed baboon genomic DNA. The main PSG isoform had the domain structure N-A1-B2-C similar to the human type IIa isoform. The type I isoform (N-A1-A2-B2-C) was also expressed. Fifteen similar PSG genes were identified of which at least nine were simultaneously expressed in third trimester baboon placenta. Thus, the baboon PSG family was as complex as that of humans. Recombinant baboon PSG (isoform IIa) had a molecular weight of 38 kDa and reacted with antibodies against human PSG. Comparative analysis of 43 N-domain amino acid sequences of PSG from four species and nine primate carcinoembryonic antigen subgroup N domain sequences identified a number of residues in the GFCC'C" ss-sheet and FG loop that are probable candidates for PSG binding to its putative ligand.

Revealing some oncofetal antigens in peripheral blood mononuclear cells of donors and patients with B-chronic lymphocytic leukemia

Eidelman et al. showed that the expression of functional carcinoembryonic antigen (CEA) on the surface of cells can block terminal differentiation and maintain their proliferative capabilities. This led us to analyze the expression of CEA, trophoblast-specific beta-1-glycoprotein (TSG) and embryonic prealbumin-1 (EPA) in peripheral blood mononuclear cells (PBMs) isolated from healthy donors and patients with B-chronic lymphocytic leukemia (B-CLL). We demonstrated that the PBMs of patients with B-CLL differed from PBMs of healthy donors by having greater numbers of CEA-, EPA- and TSG-positive cells.

Expression of pregnancy-specific beta 1-glycoprotein genes in hematopoietic cells

The presence of PSG in blood cells has been demonstrated by immunohistochemical staining. However, the origin of those proteins is not known. This report examines the expression of the PSG genes in different types of freshly isolated blood cells. RNA isolated from bone marrow and peripheral blood cells of healthy individuals was analyzed for PSG transcripts by reverse transcriptase-polymerase chain reaction using synthetic oligonucleotide primers specific for the PSG genes. The level of expression of the PSG genes in different types of cells exhibited significant individual variation. Trace amounts of PSG transcripts could be detected in polymorphonuclear cells (PMN), monocytes and B lymphocytes while T lymphocytes always contained the highest level of transcript. The expression of PSG genes in the blood cells apparently was not affected by the method of isolation nor by overnight culturing of these cells except in the case when lymphocytes were separated by rosetting with sheep red blood cells. All reported PSG transcripts were detected in blood cells. Both type I and type II transcripts of the PSG genes were detected in blood cells with the exception of type II transcript of PSG5 and PSG11 which were only found in the placenta. Tissue specificity in the expression or alternative splicing of some of the PSG family members was implicated.

Pregnancy specific beta 1-glycoprotein in human intestine

Pregnancy-specific beta 1-glycoprotein (PSG) transcripts have been identified in a number of placental and non-placental tissues. Using a placental PSG cDNA probe to screen a normal human intestinal cDNA library we have isolated 22 hybridizing clones. These clones could be divided into four groups. Nucleotide sequence analysis showed that one group of clones correspond to functional and another group correspond to non-functional PSG cDNAs. The other two groups are homologous to the nonspecific cross-reacting antigen (NCA) and biliary glycoprotein (BGP), both of which are members of the carcinoembryonic antigen (CEA) family. Thus, PSG, NCA and BGP are co-expressed in normal human intestine. RNA and immunoblot analysis, along with polymerase chain reaction amplification further confirm the expression of PSG in human intestinal tissue.

Identification of three new genes and estimation of the size of the carcinoembryonic antigen family

Using carcinoembryonic antigen (CEA) subgroup-specific degenerate PCR primers, we have identified three new CEA gene family member L/N exons (CGM9, CGM10, and CGM11) and all previously reported L/N exons of the CEA subgroup (CEA, BGP, NCA, CGM1, CGM2, CGM6, CGM7, and CGM8). This suggests that the CEA subgroup contains 11 genes. CGM9, CGM10, and CGM11 seem to be pseudogenes. A deletion of an asparagine in CGM9 results in loss of a glycosylation site, which is conserved throughout the CEA gene family. We have previously suggested the number of genes in the pregnancy-specific glycoprotein (PSG) subgroup to be 11, which together with this study indicates that the CEA gene family contains 22 genes in all. Parsimony analysis of the CEA subgroup interrelationships suggests that CGM7 occupies the most primitive position within the CEA subgroup, being a sister group to the rest. CEA, BGP, NCA, and CGM1 form a fairly well-supported group within the CEA subgroup.

Nucleotide sequence of a pregnancy-specific beta 1 glycoprotein gene family member. Identification of a functional promoter region and several putative regulatory sequences

The pregnancy-specific beta 1 glycoprotein (PSG) genes encode a group of heterogeneous proteins produced in large amounts by the human syncytiotrophoblast. Their expression seems to be regulated at the transcriptional level during normal pregnancy. In the present work, we isolated from a human placental library a 17 kb genomic fragment corresponding to a member of the PSG multigene family. DNA sequence analysis of 1190 nucleotides upstream of the translational start and of the first intron, revealed the presence of several putative regulatory sequences. In a transient chloramphenicol acetyltransferase expression assay, 5' flanking sequences within 123 nucleotides upstream to the first major transcription initiation site, functioned as a strong promoter in COS-7 cells. Meanwhile, sequences 5' further upstream had the ability to abolish this promoter activity. The sequence analyzed did not contain any obvious TATA-like boxes or G+C-rich regions, suggesting the existence of unique promoter elements implicated in transcription initiation and regulation of this PSG gene family member.

The pregnancy-specific glycoprotein family of the immunoglobulin superfamily: identification of new members and estimation of family size

The members of the carcinoembryonic antigen (CEA)/pregnancy-specific glycoprotein (PSG) gene family have a characteristic N-terminal domain that is homologous to the immunoglobulin variable region. We have estimated the size of the PSG subfamily by identification of N-domain exons from isolated genomic clones and from total genomic DNA through PCR amplification and DNA sequence determination. The PSG subfamily contains at least 11 different genes. For 7 of these, two DNA sequences differing from each other in 1 to 4 nucleotides were detected. Most likely, they represent different alleles. They are PSG1, PSG2, PSG3, PSG4, PSG5, PSG6, PSG7, PSG8, PSG11, PSG12, and PSG13. Six of the N-domain sequences described here are new. All of the PSGs except PSG1, PSG4, and PSG8 contained the arginine-glycine-aspartic acid sequence at position 93-95 corresponding to the complementarity determining region 3 of immunoglobulin. Parsimony analysis of 24 CEA and PSG sequences using 12 members of the immunoglobulin gene superfamily as outgroups to root the family tree shows that the N-domain of the CEA group genes evolved in one major branch and the PSG group genes in the other.

Characterization of new members of the pregnancy-specific beta 1-glycoprotein family

Three cDNAs encoding members of the pregnancy-specific beta 1-glycoprotein (PSG) family were isolated from human term placental cDNA library. All three cDNAs encode proteins with similar domain structure. There is a leader sequence of 34 amino acids followed by an N-domain of 109 amino acids. Immediately after the N-domain are one or two copies of a repeating A-domain of 93 amino acids, a B-domain of 85 amino acids and a C-domain of variable size. The proteins are highly hydrophilic. However, one of them has an 81-amino acid C-domain which is very hydrophobic and could potentially serve as a membrane attachment site. The putative cell-cell recognition tripeptide, Arg-Gly-Asp, is present in the N-domain of two of the proteins. Partial sequence of one of the cDNAs has been found in HeLa cells while cDNAs highly homologous to two of the cDNAs have been found in the fetal liver. Functional roles of the PSG proteins basing on their structure are proposed.

Cloning and expression of a new pregnancy-specific beta 1-glycoprotein member

Human pregnancy-specific beta 1-glycoproteins (PSGs) are a group of closely related placental glycoproteins and members of the immunoglobulin superfamily. To study possible functional roles of PSG, three type 1 cDNA clones which encode PSG in a N-A1-A2-B2-C domain arrangement have been characterized in this laboratory. Now, we report the cloning of a type II cDNA (PSG9) which is 1512 bp and encodes a PSG of 332 amino acids in a N-A1-B2-C domain arrangement. In vitro expression experiments demonstrate that PSG9 encodes a 36 kDa nonglycosylated protein which is processed to a glycosylated protein of 46 kDa. Ribonuclease protection analyses show that PSG mRNAs that share sequence similarity with the PSG9 transcript are expressed in both human placenta and placental fibroblasts.

Carcinoembryonic antigen gene family: molecular biology and clinical perspectives

The carcinoembryonic antigen (CEA) gene family belongs to the immunoglobulin super-gene family and can be divided into two main subgroups based on sequence comparisons. In humans it is clustered on the long arm of chromosome 19 and consists of approximately 20 genes. The CEA subgroup genes code for CEA and its classical crossreacting antigens, which are mainly membrane-bound, whereas the other subgroup genes encode the pregnancy-specific glycoproteins (PSG), which are secreted. Splice variants of individual genes and differential post-translational modifications of the resulting proteins, e.g., by glycosylation, indicate a high complexity in the number of putative CEA-related molecules. So far, only a limited number of CEA-related antigens in humans have been unequivocally assigned to a specific gene. Rodent CEA-related genes reveal a high sequence divergence and, in part, a completely different domain organization than the human CEA gene family, making it difficult to determine individual gene counterparts. However, rodent CEA-related genes can be assigned to human subgroups based on similarity of expression patterns, which is characteristic for the subgroups. Various functions have been determined for members of the CEA subgroup in vitro, including cell adhesion, bacterial binding, an accessory role for collagen binding or ecto-ATPases activity. Based on all that is known so far on its biology, the clinical outlook for the CEA family has been reassessed.

Characterization of the genomic organization of human carcinoembryonic antigen (CEA): comparison with other family members and sequence analysis of 5' controlling region

A cosmid containing the entire coding region for human carcinoembryonic antigen has been isolated. Detailed analysis and sequencing have determined an organization comprising nine exons encoding amino acids and one for a 3' untranslated fragment. Comparison with other family members reveals a complex pattern of homology at the 3' end of the gene. The 5' noncoding region is rich in purine-rich motifs and possible enhancer elements and has a region with properties similar to those of HTF islands.

Linkage of two human pregnancy-specific beta 1-glycoprotein genes: one is associated with hydatidiform mole

A genomic clone containing two linked human pregnancy-specific beta 1-glycoprotein (PS beta G) genes has been isolated and characterized. The two genes are arranged in the same 5'----3' orientation; the 3' region (including the A2 and B-C exons) of the upstream gene, PSGGA, is linked to the 5' region (including the 5'/L and L/N exons) of PSGGB, the downstream gene. Depending upon the domains compared, PSGGA and PSGGB share 92-98% nucleotide and 86-95% amino acid sequence identity with PSG93, the most abundant PS beta G transcript. The 3' exon (B-C) of PSGGA contains four alternative splice sites and three polyadenylylation sites, which account for the 3' heterogeneity previously reported in the PS beta G family. Each of the predicted PSGGA-encoded proteins would have a different carboxyl terminus. PSGGB corresponds to the previously identified cDNA PSG6, which encodes proteins containing a 34-amino acid leader peptide and a 108-amino acid N domain, which is one amino acid shorter than the majority of PS beta G N domains. Additionally, the PSGGB-encoded proteins contain the cell-surface recognition tripeptide Arg-Gly-Asp, shared by several previously reported PS beta Gs as deduced from cDNA sequences. Northern blot hybridization performed with a PSGGB-specific oligonucleotide probe to the N domain revealed that PSGGB or a PSGGB-like gene encodes a major 1.7-kilobase mRNA in hydatidiform mole tissues and a major 2.0-kilobase mRNA in term placenta tissues. Moreover, the PSGGB-specific probe hybridized most strongly with mRNA from molar trophoblastic tissue, suggesting that the PSGGB-like species may be the gene preferentially expressed in gestational trophoblastic disease. Additionally, the sequence of a 2315-base-pair PS beta G cDNA (PSG95) that contains an N-A1-A2-B2-C domain arrangement is reported. The coding region of PSG95 is identical to the previously reported cDNA clones PSG1d and FL-NCA, but PSG95 contains an additional 518 and 523 base pairs in the 3' end as compared with PSG1d and FL-NCA, respectively.

Expression of the CD15 differentiation antigen (3-fucosyl-N-acetyl-lactosamine, LeX) on putative neutrophil adhesion molecules CR3 and NCA-160

The expression of the carbohydrate antigen 3-fucosyl-N-acetyl-lactosamine (CD15, LeX) on human neutrophil glycoproteins has been studied by immunoprecipitation and immunoblotting by using monoclonal antibody MC2. The antigen is expressed on membrane glycoproteins of approximate molecular mass 165 and 105 kDa. These glycoproteins include the complement receptor and adhesion molecule, CR3, in which the beta-chain (CD18, 105 kDa) shows much greater expression than the alpha-chain (CD11b, 165 kDa). Most of the 165 kDa CD15 antigen is accounted for by expression on the carcinoembryonic antigen (CEA)-related molecule NCA160. Other members of this family, NCA95, NCA90 and NCA55, which are also found in neutrophils, do not express the CD15 antigen. There is a marked increase in the surface expression of CD15, CR3 and the antigen recognized by anti-CEA antibodies upon activation of neutrophils by the chemotactic peptide N-formylmethionyl-leucylphenylalanine.

Carcinoembryonic antigen gene family members in submandibular salivary gland: demonstration of pregnancy-specific glycoproteins by cDNA cloning

We have recently shown that human submandibular salivary gland and saliva contain a number of glycoproteins belonging to the carcinoembryonic antigen (CEA) gene family. The members of the CEA family can be divided into the CEA subgroup and the pregnancy specific beta 1 glycoprotein (PSG) subgroup. The latter glycoproteins are abundant in placenta and fetal liver. Here we report that PSG's are expressed in normal adult submandibular salivary gland. Thus, cDNA cloning and sequencing gave two clones (SG5 and SG9) which coded for glycoproteins with a domain arrangement of N-A1-A2-B2-C and a third clone (SG8) which coded for a glycoprotein with a domain arrangement of N-A1-B2-C. SG5 is identical to PSG3, and SG9 to PSG1d, while SG8 most probably corresponds to PSG2. The 3' untranslated regions of the different members of the PSG subgroup contain highly homologous segments, suggesting a common evolutionary origin.

Identification of a new carcinoembryonic antigen (CEA) family member in human fetal liver--cloning and sequence determination of pregnancy-specific glycoprotein 7

The carcinoembryonic antigen gene family consists of the CEA- and the Pregnancy-Specific Glycoprotein- (PSG) subfamilies. Human fetal liver express several PSGs. Here we report cloning and sequencing of a new PSG subfamily member, PSG7. It is the fifth type of PSG found in fetal liver. PSG7 has the N-A1-A2-B2-C domain arrangement. Unlike other PSGs the N-terminal of PSG7 is unblocked. PSG7 has a cysteine in the C-terminal domain, which may allow dimerization. Variability analysis according to Wu and Kabat reveals that the region in the N-domain corresponding to complementarity determining region 3 of immunoglobulin is different between PSG subfamily members. Many members, including PSG7, contain the RGD sequence in this region. The CD2 region as well as two other short sequences (in N and A1 domains respectively) also show some variability. The function of PSGs is probably linked to the N-domain and the CDR2- and CD3-like regions are most likely responsible for ligand binding.

The nucleotide and deduced amino acid sequences of a cDNA encoding a new species of pregnancy-specific beta 1-glycoprotein (PS beta G)

We screened a cDNA library of a human placenta with cDNA for nonspecific cross-reacting antigen, a member of the carcinoembryonic antigen gene family. One of the positive clones, PS34, was found to encode a 426 amino acid protein belonging to pregnancy-specific beta 1-glycoprotein (PS beta G). The mature PS34 protein consisted of domains, N, A1, A2, B2 and C. The domain-N of PS34 showed sequence similarities of 79.8-83.5% to those of the PS beta G members so far reported, indicating PS34 is a new member of PS beta G and also of the carcinoembryonic antigen gene family.

The human pregnancy-specific glycoprotein genes are tightly linked on the long arm of chromosome 19 and are coordinately expressed

The pregnancy-specific glycoprotein (PSG) genes encode a group of proteins which are found in large amounts in placenta and maternal serum. In situ hybridization analyses of metaphase chromosomes reveal that all the human pregnancy-specific glycoprotein (PSG) genes are located on the long arm of chromosome 19 (19q13.2-13.3), overlapping the region containing the closely-related carcinoembryonic antigen (CEA) gene subgroup. Higher resolution analyses indicate that the PSG genes are closely linked within an 800kb SacII restriction endonuclease fragment. This has been confirmed through restriction endonuclease mapping and DNA sequence analyses of isolated genomic clones, which show that at least some of these genes are located in very close proximity. Further, these studies have helped to identify a new member of the PSG gene subfamily (PSG7). DNA/RNA hybridization analyses, using gene-specific oligonucleotide probes based on published sequences, showed that five from six PSG genes tested are coordinately transcribed in the placenta. Due to the close proximity of these genes and their coordinated expression pattern, common transcriptional regulatory elements may exist.

Characterization of a cDNA clone encoding a new species of the nonspecific cross-reacting antigen (NCA), a member of the CEA gene family

To clarify the molecular structures of the nonspecific cross-reacting antigens (NCAs) produced by human granulocytes, we cloned cDNAs from libraries of normal white blood cells. A clone, NCA-W272, was found to code a protein similar to NCA of tumor cells. The protein consisted of a signal peptide (34 aa), domain-N (108 aa), -A1 (92 aa), -B1 (86 aa) and -M (29 aa). Similarity of the amino acid sequence of each domain to that of the tumor NCA was 72, 92, 76 and 79%, respectively. COS-1 cells transfected with an expression vector carrying the cDNA synthesized a 70 kDa glycoprotein, which was reactive with anti-NCA antibody and released from cell surface by phosphatidylinositol-specific phospholipase C. Thus the clone NCA-W272 was indicated to encode a new species of NCA distinct from the tumor NCA.

Expression of human pregnancy specific beta 1 glycoprotein (PSG) genes during placental development

Using gene-specific oligonucleotide probes, the expression of four pregnancy specific beta 1 glycoprotein (PSG) genes termed A, B, C-D and E (Streydio et al., 1988 and in press) and of some of their splice variants Ci, C and D were analysed during human placental development. Except for a stronger hybridization signal obtained at 9 weeks of gestation, which might be correlated to the development of the placenta, the relative amounts of the different PSG mRNAs showed little variation throughout pregnancy as revealed by Northern blots performed at 6, 13, 18 and 40 weeks of gestation. The expression of the different PSG genes does not seem to be developmentally regulated, in contrast to placental lactogen, used as a control, the expression of which is clearly correlated with the age of gestation. PSG D, A, E transcripts seem equally abundant, while PSG B expression was much lower. Moreover, the proportion of the PSG C-D variants resulting from alternative splicing remained constant during gestation.

Expression of the pregnancy-specific beta 1-glycoprotein genes in human testis

Northern blot analysis with placental pregnancy-specific beta 1-glycoprotein (SP1) cDNA probe showed the presence of SP1 mRNAs in human testis. Presence of translational products of the mRNAs was demonstrated by Western blot analysis with anti-human SP1 antibodies albeit difference in mobilities between the testis and placental proteins was apparent. Screening of human testis cDNA library with placental SP1 probe yielded 4 groups of positive clones. Two groups were identical to human placental SP1 cDNAs previously reported. The other 2 groups consisted of cDNA of incompletely processed mRNAs. These 2 groups were present in high abundance. Sequence analysis suggested that the cDNAs were products of different genes.

Cell adhesion activity of non-specific cross-reacting antigen (NCA) and carcinoembryonic antigen (CEA) expressed on CHO cell surface: homophilic and heterophilic adhesion

Cell adhesion activity of carcinoembryonic antigen (CEA) and non-specific cross-reacting antigen (NCA) has been analysed by using CHO cells which had been transfected with cDNAs and are ectopically expressing each antigen on their surface. CEA expressing CHO tended to aggregate easily within 30 min after being suspended by trypsinization. Cell adhesion assay between 51Cr labelled cells and monolayered cells showed both homophilic and heterophilic interaction, the extent of which was CEA-CEA much greater than CEA-NCA greater than NCA-NCA. These reactions were completely inhibited by Fab' fragment of anti-CEA antibody. The results strongly suggested that CEA and NCA function as Ca++ independent cell adhesion molecules by homophilic and heterophilic interactions.

cDNA cloning demonstrates the expression of pregnancy-specific glycoprotein genes, a subgroup of the carcinoembryonic antigen gene family, in fetal liver

The pregnancy-specific glycoprotein (PSG) genes constitute a subgroup of the carcinoembryonic antigen (CEA) gene family. Here we report the cloning of four cDNAs coding for different members of the PSG family from a human fetal liver cDNA library. They are derived from three closely related genes (PSG1, PSG4 and PSG6). Two of the cDNA clones represent splice variants of PSG1 (PSG1a, PSG1d) differing in their C-terminal domain and 3'-untranslated regions. All encoded proteins show the same domain arrangement (N-RA1-RA2-RB2-C). Transcripts of the genes PSG1 and PSG4 could be detected in placenta by hybridization with gene-specific oligonucleotides. Expression of cDNA in a mouse and monkey cell line shows that the glycosylated PSG1a protein has a Mr of 65-66 kD and is released from the transfected cells. Sequence comparisons in the C-terminal domain and the 3'-untranslated regions of CEA/PSG-like genes suggests a complex splicing pattern to exist for various gene family members and a common evolutionary origin of these regions.