A comprehensive phylogenetic and structural analysis of the carcinoembryonic antigen (CEA) gene family

CT109-SN-38, a Novel Antibody-drug Conjugate with Dual Specificity for CEACAM5 and 6, Elicits Potent Killing of Pancreatic Cancer Cells

BACKGROUND

CEACAM5 and CEACAM6 are glycosylphosphatidylinositol (GPI)- linked members of the carcinoembryonic antigen-related cell adhesion molecule (CEACAM) family, which are frequently upregulated in epithelial cancers where they contribute to invasion, metastasis, immune evasion, and resistance to anoikis. CT109 is a novel antibody with dual specificity to both CEACAM5 and 6.

OBJECTIVES

In this study, we aimed to perform the preclinical characterization of CT109 and antibody- drug conjugate (ADCs) derivatives of CT109, focusing on CT109-SN-38.

METHODS

CT109's cognate epitope was characterized by scanning mutagenesis. CT109 specificity and internalization kinetics were assessed by immunoblot and flow cytometry, respectively. Cognate antigen expression prevalence in colorectal cancer and normal tissue arrays was determined by immunohistochemistry. CT109 conjugations were generated by the reaction of reduced CT109 cysteines with maleimide-functionalized payload linkers. In vitro cytotoxic activity of CT109 ADCs was characterized on antigen-positive and negative pancreatic ductal adenocarcinoma cell (PDAC) lines using a luminometric viability assay. In vivo efficacy of CT109-SN-38 was assessed on a PDAC tumor xenograft model at 10 and 25 mg/kg concentrations.

RESULTS

CT109 was shown to bind a glycoepitope centered on N309. CT109 is internalized in the CEACAM5+/CEACAM6+ double-positive PDAC line, BxPC-3, with a t1/2 of 2.3 hours. CT109 ADCs elicit a dose and antigen-dependent cytotoxic effect, with CT109-SN-38 exhibiting an IC50 value of 21 nM in BxPC-3 cells. In a BxPC-3 tumor xenograft model, CT109-SN-38 reduced tumor growth and induced regression in 3/10 mice at a concentration 25 mg/kg.

CONCLUSION

These data suggest that further preclinical and clinical development of CT109-SN-38 is warranted.

In Silico Identification and Analysis of Proteins Containing the Phox Homology Phosphoinositide-Binding Domain in Kinetoplastea Protists: Evolutionary Conservation and Uniqueness of Phox-Homology-Domain-Containing Protein Architectures

Kinetoplastea are free living and parasitic protists with unique features among Eukaryota. Pathogenic Kinetoplastea parasites (i.e., Trypanosoma and Leishmania spp.) undergo several developmental transitions essential for survival in their hosts. These transitions require membrane and cytoskeleton reorganizations that involve phosphoinositides (PIs). Phospholipids like PIs are key regulators of vital functions in all eukaryotes including signal transduction, protein transport and sorting, membrane trafficking, and cytoskeleton and membrane remodeling. A large repertoire of PI-metabolizing enzymes and PI-binding proteins/effectors carrying distinct PI-binding modules like the PX (phox homology) module could play significant roles in the life and virulence of pathogenic Kinetoplastea. The aim of this study was to retrieve the entire spectrum of Kinetoplastea protein sequences containing the PX module (PX-proteins), predict their structures, and identify in them evolutionary conserved and unique traits. Using a large array of bioinformatics tools, protein IDs from two searches (based on PFam's pHMM for PX domain (PF00787)) were combined, aligned, and utilized for the construction of a new Kinetoplastea_PX pHMM. This three-step search retrieved 170 PX-protein sequences. Structural domain configuration analysis identified PX, Pkinase, Lipocalin_5, and Vps5/BAR3-WASP domains and clustered them into five distinct subfamilies. Phylogenetic tree and domain architecture analysis showed that some domain architectures exist in proteomes of all Kinetoplastea spp., while others are genus-specific. Finally, amino acid conservation logos of the Kinetoplastea spp. and Homo sapiens PX domains revealed high evolutionary conservation in residues forming the critical structural motifs for PtdIns3P recognition. This study highlights the PX-Pkinase domain architecture as unique within Trypanosoma spp. and forms the basis for a targeted functional analysis of Kinetoplastea PX-proteins as putative targets for a rational design of anti-parasitic drugs.

"In the light of evolution:" keratins as exceptional tumor biomarkers

Keratins (KRTs) are the intermediate filament-forming proteins of epithelial cells, classified, according to their physicochemical properties, into "soft" and "hard" keratins. They have a key role in several aspects of cancer pathophysiology, including cancer cell invasion and metastasis, and several members of the KRT family serve as diagnostic or prognostic markers. The human genome contains both, functional KRT genes and non-functional KRT pseudogenes, arranged in two uninterrupted clusters on chromosomes 12 and 17. This characteristic renders KRTs ideal for evolutionary studies. Herein, comprehensive phylogenetic analyses of KRT homologous proteins in the genomes of major taxonomic divisions were performed, so as to fill a gap in knowledge regarding the functional implications of keratins in cancer biology among tumor-bearing species. The differential expression profiles of KRTs in diverse types of cancers were investigated by analyzing high-throughput data, as well. Several KRT genes, including the phylogenetically conserved ones, were found to be deregulated across several cancer types and to participate in a common protein-protein interaction network. This indicates that, at least in cancer-bearing species, these genes might have been under similar evolutionary pressure, perhaps to support the same important function(s). In addition, semantic relations between KRTs and cancer were detected through extensive text mining. Therefore, by applying an integrative in silico pipeline, the evolutionary history of KRTs was reconstructed in the context of cancer, and the potential of using non-mammalian species as model organisms in functional studies on human cancer-associated KRT genes was uncovered.

A novel missense variant in CEACAM16 gene causes autosomal dominant nonsyndromic hearing loss

Aim

Autosomal dominant non‐syndromic hearing loss is a common sensorineural disorder with extremely high genetic heterogeneity. CEA antigen‐related cell adhesion molecule 16(CEACAM16)is a secreted glycoprotein encoded by the CEACAM16 gene. Mutations in CEACAM16 lead to autosomal dominant non‐syndromic hearing loss in humans, due defects in the tectorial membrane of the inner ear. Here we reported a novel missense variant in CEACAM16 gene causes autosomal dominant non‐syndromic hearing loss.

Material and methods

A four‐generation Chinese family affected by late‐onset and progressive hearing loss was enrolled in this study. The proband was analyzed by targeted next‐generation sequencing and bioinformatic analysis. And in vitro experiments were performed in overexpressed transfected HEK293T cells to investigate the pathogenesis of the mutant protein.

Results

We identified a novel missense variant in the CEACAM16 gene c.763A>G; (p.Arg255Gly) as causing autosomal dominant non‐syndromic hearing loss in the Chinese family. Using Western blot analysis, ELISA, and immunofluorescence we found increased expression level of the secreted mutant CEACAM16 protein, both intracellularly and extracellularly, compared with wild type CEACAM16 protein.

Conclusion

Our study showed that the p.Arg255Gly variant leads to increased secretion of mutant CEACAM16 protein, with potential deleterious effect to the function of the protein. Our findings expand the mutation spectrum of CEACAM16, and further the understanding CEACAM16 function and implications in disease.

Targeted photoimmunotherapy for cancer

Photodynamic therapy (PDT) is a clinically approved procedure that can exert a curative action against malignant cells. The treatment implies the administration of a photoactive molecular species that, upon absorption of visible or near infrared light, sensitizes the formation of reactive oxygen species. These species are cytotoxic and lead to tumor cell death, damage vasculature, and induce inflammation. Clinical investigations demonstrated that PDT is curative and does not compromise other treatment options. One of the major limitations of the original method was the low selectivity of the photoactive compounds for malignant over healthy tissues. The development of conjugates with antibodies has endowed photosensitizing molecules with targeting capability, so that the compounds are delivered with unprecedented precision to the site of action. Given their fluorescence emission capability, these supramolecular species are intrinsically theranostic agents.

Evolution of host-microbe cell adherence by receptor domain shuffling

Stable adherence to epithelial surfaces is required for colonization by diverse host-associated microbes. Successful attachment of pathogenic microbes to host cells via adhesin molecules is also the first step in many devastating infections. Despite the primacy of epithelial adherence in establishing host-microbe associations, the evolutionary processes that shape this crucial interface remain enigmatic. Carcinoembryonic antigen-related cell adhesion molecules (CEACAMs) encompass a multifunctional family of vertebrate cell surface proteins which are recurrent targets of bacterial adhesins at epithelial barriers. Here, we show that multiple members of the primate CEACAM family exhibit evidence of repeated natural selection at protein surfaces targeted by bacteria, consistent with pathogen-driven evolution. Divergence of CEACAM proteins between even closely related great apes is sufficient to control molecular interactions with a range of bacterial adhesins. Phylogenetic analyses further reveal that repeated gene conversion of CEACAM extracellular domains during primate divergence plays a key role in limiting bacterial adhesin host tropism. Moreover, we demonstrate that gene conversion has continued to shape CEACAM diversity within human populations, with abundant human CEACAM1 variants mediating evasion of adhesins from pathogenic Neisseria. Together this work reveals a mechanism by which gene conversion shapes first contact between microbes and animal hosts.

Trillions of bacteria live in and on the human body. Most of them are harmless but some can cause serious infections. To grow in or on the body, bacteria often attach to proteins on the surface of cells that make up the lining of tissues like the gut or the throat. In some cases, bacteria use these proteins to invade the cells causing an infection. Genetic mutations in the genes encoding these proteins that protect against infection are more likely to be passed on to future generations. This may lead to rapid spread of these beneficial genes in a population.

A family of proteins called CEACAMs are frequent targets of infection-causing bacteria. These proteins have been shown to play a role in cancer progression. But they also play many helpful roles in the body, including helping transmit messages between cells, aiding cell growth, and helping the immune system recognize pathogens. Scientists are not sure if these multi-tasking CEACAM proteins can evolve to evade bacteria without affecting their other roles.

Baker et al. show that CEACAM proteins targeted by bacteria have undergone rapid evolution in primates. In the experiments, human genes encoding CEACAMs were compared with equivalent genes from 19 different primates. Baker et al. found the changes in human and primate CEACAMs often occur through a process called gene conversion. Gene conversion occurs when DNA sections are copied and pasted from one gene to another. Using laboratory experiments, they showed that some of these changes enabled CEACAM proteins to prevent certain harmful bacteria from binding.

The experiments suggest that some versions of CEACAM genes may protect humans or other primates against bacterial infections. Studies in natural populations are needed to test if this is the case. Learning more about how CEACAM proteins evolve and what they do may help scientists better understand the role they play in cancer and help improve cancer care. Studying CEACAM evolution may also help scientists understand how bacteria and other pathogens drive protein evolution in the body.

T cell-mediated elimination of cancer cells by blocking CEACAM6–CEACAM1 interaction

Carcinoembryonic antigen-related cell adhesion molecule 6 (CEACAM6), a cell surface receptor, is expressed on normal epithelial tissue and highly expressed in cancers of high unmet medical need, such as non-small cell lung, pancreatic, and colorectal cancer. CEACAM receptors undergo homo- and heterophilic interactions thereby regulating normal tissue homeostasis and angiogenesis, and in cancer, tumor invasion and metastasis. CEACAM6 expression on malignant plasma cells inhibits antitumor activity of T cells, and we hypothesize a similar function on epithelial cancer cells.

The interactions between CEACAM6 and its suggested partner CEACAM1 on T cells were studied. A humanized CEACAM6-blocking antibody, BAY 1834942, was developed and characterized for its immunomodulating effects in co-culture experiments with T cells and solid cancer cells and in comparison to antibodies targeting the immune checkpoints programmed cell death protein 1 (PD-1), programmed death-ligand 1 (PD-L1), and T cell immunoglobulin mucin-3 (TIM-3).

The immunosuppressive activity of CEACAM6 was mediated by binding to CEACAM1 expressed by activated tumor-specific T cells. BAY 1834942 increased cytokine secretion by T cells and T cell-mediated killing of cancer cells. The in vitro efficacy of BAY 1834942 correlated with the degree of CEACAM6 expression on cancer cells, suggesting potential in guiding patient selection. BAY 1834942 was equally or more efficacious compared to blockade of PD-L1, and at least an additive efficacy was observed in combination with anti-PD-1 or anti-TIM-3 antibodies, suggesting an efficacy independent of the PD-1/PD-L1 axis.

In summary, CEACAM6 blockade by BAY 1834942 reactivates the antitumor response of T cells. This warrants clinical evaluation.

Engagement of CEACAM1 by Helicobacterpylori HopQ Is Important for the Activation of Non-Canonical NF-κB in Gastric Epithelial Cells

The gastric pathogen Helicobacter pylori infects half of the world's population and is a major risk factor for gastric cancer development. In order to attach to human gastric epithelial cells and inject the oncoprotein CagA into host cells, H. pylori utilizes the outer membrane protein HopQ that binds to the cell surface protein CEACAM, which can be expressed on the gastric mucosa. Once bound, H. pylori activates a number of signaling pathways, including canonical and non-canonical NF-κB. We investigated whether HopQ-CEACAM interaction is involved in activating the non-canonical NF-κB signaling pathway. Different gastric cancer cells were infected with the H. pylori wild type, or HopQ mutant strains, and the activation of non-canonical NF-κB was related to CEACAM expression levels. The correlation between CEACAM levels and the activation of non-canonical NF-κB was confirmed in human gastric tissue samples. Taken together, our findings show that the HopQ-CEACAM interaction is important for activation of the non-canonical NF-κB pathway in gastric epithelial cells.

Characterization of a member of the CEACAM protein family as a novel marker of proton pump-rich ionocytes on the zebrafish epidermis

In humans, several members of the CEACAM receptor family have been shown to interact with intestinal pathogens in an inflammatory context. While CEACAMs have long been thought to be only present in mammals, recent studies have identified ceacam genes in other vertebrates, including teleosts. The function of these related genes remains however largely unknown. To gain insight into the function of CEACAM proteins in fish, we undertook the study of a putative member of the family, CEACAMz1, identified in Danio rerio. Sequence analysis of the ceacamz1 gene product predicted a GPI-anchored extracellular protein containing eleven immunoglobulin domains but revealed no evident orthology with human CEACAMs. Using a combination of RT-PCR analyses and in situ hybridization experiments, as well as a fluorescent reporter line, we showed that CEACAMz1 is first expressed in discrete cells on the ventral skin of zebrafish larvae and later on in the developing gills. This distribution remains constant until juvenile stage is reached, at which point CEACAMz1 is almost exclusively expressed in gills. We further observed that at late larval stages, CEACAMz1-expressing cells mostly localize on the afferent side of the branchial filaments and possibly in the inter-lamellar space. Using immunolabelling and 3D-reconstructions, we showed that CEACAMz1 is expressed in cells from the uppermost layer of skin epidermis. These cells are embedded within the keratinocytes pavement and we unambiguously identified them as proton-pump rich ionocytes (HR cells). As the expression of ceacamz1 is turned on concomitantly to that of other known markers of HR cells, we propose that ceacamz1 may serve as a novel marker of mature HR cells from the zebrafish epidermis.

Identification and expression analysis of novel splice variants of the human carcinoembryonic antigen-related cell adhesion molecule 19 (CEACAM19) gene using a high-throughput sequencing approach

Alternative splicing is commonly involved in carcinogenesis, being highly implicated in differential expression of cancer-related genes. Recent studies have shown that the human CEACAM19 gene is overexpressed in malignant breast and ovarian tumors, possessing significant biomarker attributes. In the present study, 3' rapid amplification of cDNA ends (3' RACE) and next-generation sequencing (NGS) were used for the detection and identification of novel CEACAM19 transcripts. Bioinformatical analysis of our NGS data revealed novel splice junctions between previously annotated exons and ultimately new exons. Next, fifteen novel CEACAM19 transcripts were identified with Sanger sequencing. Additionally, their expression profile was investigated in a wide panel of human cell lines, using nested PCR with variant-specific primers. The broad expression pattern of the CEACAM19 gene, along with the fact that its overexpression has previously been associated with ovarian and breast cancer progression, indicate the potential of novel CEACAM19 transcripts as putative diagnostic and/or prognostic biomarkers.

Natural selection supports escape from concerted evolution of a recently duplicated CEACAM1 paralog in the ruminant CEA gene family

Concerted evolution is often observed in multigene families such as the CEA gene family. As a result, sequence similarity of paralogous genes is significantly higher than expected from their evolutionary distance. Gene conversion, a “copy paste” DNA repair mechanism that transfers sequences from one gene to another and homologous recombination are drivers of concerted evolution. Nevertheless, some gene family members escape concerted evolution and acquire sufficient sequence differences that orthologous genes can be assigned in descendant species. Reasons why some gene family members can escape while others are captured by concerted evolution are poorly understood. By analyzing the entire CEA gene family in cattle (Bos taurus) we identified a member (CEACAM32) that was created by gene duplication and cooption of a unique transmembrane domain exon in the most recent ancestor of ruminants. CEACAM32 shows a unique, testis-specific expression pattern. Phylogenetic analysis indicated that CEACAM32 is not involved in concerted evolution of CEACAM1 paralogs in ruminants. However, analysis of gene conversion events revealed that CEACAM32 is subject to gene conversion but remarkably, these events are found in the leader exon and intron sequences but not in exons coding for the Ig-like domains. These findings suggest that natural selection hinders gene conversion affecting protein sequences of the mature protein and thereby support escape of CEACAM32 from concerted evolution.

Aberrant AFP expression characterizes a subset of hepatocellular carcinoma with distinct gene expression patterns and inferior prognosis

Background Serum tumor markers are ubiquitously used in the clinic for cancer screening. However, the mechanisms accounting for the elevated levels of the serum tumor markers remain to be explored.

Methods We performed a pan-cancer analysis of serum alpha-fetoprotein (AFP), carcinoembryonic antigen (CEA) and prostate-specific antigen (PSA). The relation between concentration of serum tumor markers and the expression of their coding genes was assessed. Then the expression of AFP and its genomic background in hepatocellular carcinoma (liver cancer) was studied.

Results High expression of AFP mRNA was found mainly in liver cancer. In gastric cancer, breast cancer and lung cancer, high AFP mRNA expression was also discovered occasionally. In liver cancer patients, serum AFP levels correlated significantly with AFP mRNA expression in cancer tissues (r = 0.72, p = 1.6e-45). Whole transcriptome analysis revealed that serum AFP levels clearly separated liver cancer into two classes with distinct expression profiles according to PCA analysis. Gene co-expression analysis revealed that AFP expression was connected to a module enriched with genes accounting for cell cycle and cell proliferation regulation. In addition, high AFP expression was associated with the molecular classification of liver cancer, including iCluster (Chi-square: 16.86, P = 0.0002). Methylation analysis revealed de-methylation of AFP promoter occurred in some liver cancer tissues, which was significantly related to AFP mRNA expression. Survival analysis indicated high serum AFP levels was prognostic of poorer survival of the liver cancer patients (Log-rank test: p = 0.046). This was confirmed by an independent dataset in which liver cancer patients with high serum AFP also had poorer survival (Log-rank test: p = 0.024).

Conclusion High expression of AFP defined a subtype of liver cancer with distinct gene expression profiles and clinical features. De-methylation of cytosine from CpG di-nucleotides in AFP promoter may be the cause of AFP re-expression in adult human liver cancer tissue.

Alternative splicing after gene duplication drives CEACAM1-paralog diversification in the horse

Background

The CEA gene family is one of the most rapidly evolving gene families in the human genome. The founder gene of the family is thought to be an ancestor of the inhibitory immune checkpoint molecule CEACAM1. Comprehensive analyses of mammalian genomes showed that the CEA gene family is subject to tremendous gene family expansion and contraction events in different mammalian species. While in some species (e.g. rabbits) less than three CEACAM1 related genes exist, were in others (certain microbat species) up to 100 CEACAM1 paralogs identified. We have recently reported that the horse has also an extended CEA gene family. Since mechanisms of gene family expansion and diversification are not well understood we aimed to analyze the equine CEA gene family in detail.

Results

We found that the equine CEA gene family contains 17 functional CEACAM1-related genes. Nine of them were secreted molecules and eight CEACAMs contain transmembrane and cytoplasmic domain exons, the latter being in the focus of the present report. Only one (CEACAM41) gene has exons coding for activating signaling motifs all other CEACAM1 paralogs contain cytoplasmic exons similar to that of the inhibitory receptor CEACAM1. However, cloning of cDNAs showed that only one CEACAM1 paralog contain functional immunoreceptor tyrosine-based inhibitory motifs in its cytoplasmic tail. Three receptors have acquired a stop codon in the transmembrane domain and two have lost their inhibitory motifs due to alternative splicing events. In addition, alternative splicing eliminated the transmembrane exon sequence of the putative activating receptor, rendering it to a secreted molecule. Transfection of eukaryotic cells with FLAG-tagged alternatively spliced CEACAMs indicates that they can be expressed in vivo. Thus detection of CEACAM41 mRNA in activated PBMC suggests that CEACAM41 is secreted by lymphoid cells upon activation.

Conclusions

The results of our study demonstrate that alternative splicing after gene duplication is a potent mechanism to accelerate functional diversification of the equine CEA gene family members. This potent mechanism has created novel CEACAM receptors with unique signaling capacities and secreted CEACAMs which potentially enables equine lymphoid cells to control distantly located immune cells.

Recent expansion and adaptive evolution of the carcinoembryonic antigen family in bats of the Yangochiroptera subgroup

BACKGROUND

Expansions of gene families are predictive for ongoing genetic adaptation to environmental cues. We describe such an expansion of the carcinoembryonic antigen (CEA) gene family in certain bat families. Members of the CEA family in humans and mice are exploited as cellular receptors by a number of pathogens, possibly due to their function in immunity and reproduction. The CEA family is composed of CEA-related cell adhesion molecules (CEACAMs) and secreted pregnancy-specific glycoproteins (PSGs). PSGs are almost exclusively expressed by trophoblast cells at the maternal-fetal interface. The reason why PSGs exist only in a minority of mammals is still unknown.

RESULTS

Analysis of the CEA gene family in bats revealed that in certain bat families, belonging to the subgroup Yangochiroptera but not the Yinpterochiroptera subgroup an expansion of the CEA gene family took place, resulting in approximately one hundred CEA family genes in some species of the Vespertilionidae. The majority of these genes encode secreted PSG-like proteins (further referred to as PSG). Remarkably, we found strong evidence that the ligand-binding domain (IgV-like domain) of PSG is under diversifying positive selection indicating that bat PSGs may interact with structurally highly variable ligands. Such ligands might represent bacterial or viral pathogen adhesins. We have identified two distinct clusters of PSGs in three Myotis species. The two PSG cluster differ in the amino acids under positive selection. One cluster was only expanded in members of the Vespertilionidae while the other was found to be expanded in addition in members of the Miniopteridae and Mormoopidae. Thus one round of PSG expansion may have occurred in an ancestry of all three families and a second only in Vespertilionidae. Although maternal ligands of PSGs may exist selective challenges by two distinct pathogens seem to be likely responsible for the expansion of PSGs in Vespertilionidae.

CONCLUSIONS

The rapid expansion of PSGs in certain bat species together with selection for diversification suggest that bat PSGs could be part of a pathogen defense system by serving as decoy receptors and/or regulators of feto-maternal interactions.

Factors Requiring Adjustment in the Interpretation of Serum Carcinoembryonic Antigen: A Cross-Sectional Study of 18,131 Healthy Nonsmokers

Serum carcinoembryonic antigen (CEA) is a well-known tumor marker for colorectal adenocarcinoma. However, CEA levels can be influenced by various nonmalignant conditions. A retrospective, cross-sectional study was performed including 18,131 healthy nonsmokers who underwent health check-ups with evaluation of the serum CEA level. In the training set, multivariate analysis revealed that the log-transformed CEA level had positive relationships with age (regression coefficient (r) = 0.005, P < 0.001), white blood cell (WBC) count (r = 0.007, P = 0.016), hemoglobin (HB, r = 0.016, P < 0.001), aspartate aminotransferase (AST, r = 0.002, P = 0.005), creatinine (r = 0.076, P = 0.038), and glycosylated hemoglobin (HbA1c, r = 0.052, P < 0.001); body mass index (BMI, r = -0.007, P < 0.001) showed a negative correlation. The results for age, BMI, WBC count, HB, AST, and HbA1c were validated in the test set. We were able to construct the following model to predict the log-transformed CEA level: log (CEA + 0.51) = -0.204 - 0.051 (gender) + 0.005 (age) - 0.006 (BMI) + 0.008 (WBC count) + 0.016 (HB) + 0.002 (AST) + 0.062 (creatinine) + 0.054 (HbA1c). For colorectal cancer prediction, the model with the observed CEA and adjusted CEA levels had significantly high predictive power (AUC 0.756, P < 0.001) than the model only including the observed CEA level (AUC 0.693, P < 0.001). Factors influencing serum CEA levels should be adjusted before clinical interpretation to increase the predictive value of CEA.

Coevolution of paired receptors in Xenopus carcinoembryonic antigen-related cell adhesion molecule families suggests appropriation as pathogen receptors

Background

In mammals, CEACAM1 and closely related members represent paired receptors with similar extracellular ligand-binding regions and cytoplasmic domains with opposing functions. Human CEACAM1 and CEACAM3 which have inhibitory ITIM/ITSM and activating ITAM-like motifs, respectively, in their cytoplasmic regions are such paired receptors. Various bacterial pathogens bind to CEACAM1 on epithelial and immune cells facilitating both entry into the host and down-regulation of the immune response whereas interaction with granulocyte-specific CEACAM3 leads to their uptake and destruction. It is unclear whether paired CEACAM receptors also exist in other vertebrate clades.

Results

We identified more than 80 ceacam genes in Xenopus tropicalis and X. laevis. They consist of two subgroups containing one or two putative paired receptor pairs each. Analysis of genomic sequences of paired receptors provide evidence that their highly similar ligand binding domains were adjusted by recent gene conversion events. In contrast, selection for diversification is observed among inhibitory receptor orthologs of the two frogs which split some 60 million years ago. The allotetraploid X. laevis arose later by hybridization of two closely related species. Interestingly, despite the conservation of the genomic landscape surrounding the homeologous ceacam loci only one locus resembles the one found in X. tropicalis. From the second X. laevis locus more than 80 % of the ceacam genes were lost including 5 of the 6 paired receptor genes. This suggests that once the gene for one of the paired receptors is lost the remaining gene cluster degrades rapidly probably due to lack of selection pressure exerted by pathogens.

Conclusions

The presence of paired receptors and selection for diversification suggests that also in amphibians CEACAM1-related inhibitory proteins are or were used as pathogen receptors.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-016-3279-9) contains supplementary material, which is available to authorized users.

The Genome-Wide Analysis of Carcinoembryonic Antigen Signaling by Colorectal Cancer Cells Using RNA Sequencing

Сarcinoembryonic antigen (CEA, CEACAM5, CD66) is a promoter of metastasis in epithelial cancers that is widely used as a prognostic clinical marker of metastasis. The aim of this study is to identify the network of genes that are associated with CEA-induced colorectal cancer liver metastasis. We compared the genome-wide transcriptomic profiles of CEA positive (MIP101 clone 8) and CEA negative (MIP 101) colorectal cancer cell lines with different metastatic potential in vivo. The CEA-producing cells displayed quantitative changes in the level of expression for 100 genes (over-expressed or down-regulated). They were confirmed by quantitative RT-PCR. The KEGG pathway analysis identified 4 significantly enriched pathways: cytokine-cytokine receptor interaction, MAPK signaling pathway, TGF-beta signaling pathway and pyrimidine metabolism. Our results suggest that CEA production by colorectal cancer cells triggers colorectal cancer progression by inducing the epithelial- mesenchymal transition, increasing tumor cell invasiveness into the surrounding tissues and suppressing stress and apoptotic signaling. The novel gene expression distinctions establish the relationships between the existing cancer markers and implicate new potential biomarkers for colorectal cancer hepatic metastasis.

Glycosylation Alters Dimerization Properties of a Cell-surface Signaling Protein, Carcinoembryonic Antigen-related Cell Adhesion Molecule 1 (CEACAM1)

Human carcinoembryonic antigen-related cell adhesion molecule 1 (C?/Au: EACAM1) is a cell-surface signaling molecule involved in cell adhesion, proliferation, and immune response. It is also implicated in cancer angiogenesis, progression, and metastasis. This diverse set of effects likely arises as a result of the numerous homophilic and heterophilic interactions that CEACAM1 can have with itself and other molecules. Its N-terminal Ig variable (IgV) domain has been suggested to be a principal player in these interactions. Previous crystal structures of the β-sandwich-like IgV domain have been produced using Escherichia coli-expressed material, which lacks native glycosylation. These have led to distinctly different proposals for dimer interfaces, one involving interactions of ABED β-strands and the other involving GFCC'C″ β-strands, with the former burying one prominent glycosylation site. These structures raise questions as to which form may exist in solution and what the effect of glycosylation may have on this form. Here, we use NMR cross-correlation measurements to examine the effect of glycosylation on CEACAM1-IgV dimerization and use residual dipolar coupling (RDC) measurements to characterize the solution structure of the non-glycosylated form. Our findings demonstrate that even addition of a single N-linked GlcNAc at potential glycosylation sites inhibits dimer formation. Surprisingly, RDC data collected on E. coli expressed material in solution indicate that a dimer using the non-glycosylated GFCC'C″ interface is preferred even in the absence of glycosylation. The results open new questions about what other factors may facilitate dimerization of CEACAM1 in vivo, and what roles glycosylation may play in heterophylic interactions.

Convergent evolution of pregnancy-specific glycoproteins in human and horse

Pregnancy-specific glycoproteins (PSGs) are members of the carcinoembryonic antigen cell adhesion molecule (CEACAM) family that are secreted by trophoblast cells. PSGs may modulate immune, angiogenic and platelet responses during pregnancy. Until now, PSGs are only found in species that have a highly invasive (hemochorial) placentation including humans, mice and rats. Surprisingly, analyzing the CEACAM gene family of the horse, which has a non-invasive epitheliochorial placenta, with the exception of the transient endometrial cups, we identified equine CEACAM family members that seem to be related to PSGs of rodents and primates. We identified seven genes that encode secreted PSG-like CEACAMs Phylogenetic analyses indicate that they evolved independently from an equine CEACAM1-like ancestor rather than from a common PSG-like ancestor with rodents and primates. Significantly, expression of PSG-like genes (CEACAM44, CEACAM48, CEACAM49 and CEACAM55) was found in non-invasive as well as invasive trophoblast cells such as purified chorionic girdle cells and endometrial cup cells. Chorionic girdle cells are highly invasive trophoblast cells that invade the endometrium of the mare where they form endometrial cups and are in close contact with maternal immune cells. Therefore, the microenvironment of invasive equine trophoblast cells has striking similarities to the microenvironment of trophoblast cells in hemochorial placentas, suggesting that equine PSG-like CEACAMs and rodent and primate PSGs have undergone convergent evolution. This is supported by our finding that equine PSG-like CEACAM49 exhibits similar activity to certain rodent and human PSGs in a functional assay of platelet-fibrinogen binding. Our results have implications for understanding the evolution of PSGs and their functions in maternal-fetal interactions.