Cloning and Expression of a cDNA Coding for a Rat Liver Plasma Membrane Ecto-ATPase

Hepatic Insulin Clearance: Mechanism and Physiology

Upon its secretion from pancreatic β-cells, insulin reaches the liver through the portal circulation to exert its action and eventually undergo clearance in the hepatocytes. In addition to insulin secretion, hepatic insulin clearance regulates the homeostatic level of insulin that is required to reach peripheral insulin target tissues to elicit proper insulin action. Receptor-mediated insulin uptake followed by its degradation constitutes the basic mechanism of insulin clearance. Upon its phosphorylation by the insulin receptor tyrosine kinase, carcinoembryonic antigen-related cell adhesion molecule 1 (CEACAM1) takes part in the insulin-insulin receptor complex to increase the rate of its endocytosis and targeting to the degradation pathways. This review summarizes how this process is regulated and how it is associated with insulin-degrading enzyme in the liver. It also discusses the physiological implications of impaired hepatic insulin clearance: Whereas reduced insulin clearance cooperates with increased insulin secretion to compensate for insulin resistance, it can also cause hepatic insulin resistance. Because chronic hyperinsulinemia stimulates hepatic de novo lipogenesis, impaired insulin clearance also causes hepatic steatosis. Thus impaired insulin clearance can underlie the link between hepatic insulin resistance and hepatic steatosis. Delineating these regulatory pathways should lead to building more effective therapeutic strategies against metabolic syndrome.

CEACAM1 in Liver Injury, Metabolic and Immune Regulation

Carcinoembryonic antigen-related cell adhesion molecule 1 (CEACAM1) is a transmembrane glycoprotein that is expressed on epithelial, endothelial and immune cells. CEACAM1 is a differentiation antigen involved in the maintenance of epithelial polarity that is induced during hepatocyte differentiation and liver regeneration. CEACAM1 regulates insulin sensitivity by promoting hepatic insulin clearance, and controls liver tolerance and mucosal immunity. Obese insulin-resistant humans with non-alcoholic fatty liver disease manifest loss of hepatic CEACAM1. In mice, deletion or functional inactivation of CEACAM1 impairs insulin clearance and compromises metabolic homeostasis which initiates the development of obesity and hepatic steatosis and fibrosis with other features of non-alcoholic steatohepatitis, and adipogenesis in white adipose depot. This is followed by inflammation and endothelial and cardiovascular dysfunctions. In obstructive and inflammatory liver diseases, soluble CEACAM1 is shed into human bile where it can serve as an indicator of liver disease. On immune cells, CEACAM1 acts as an immune checkpoint regulator, and deletion of Ceacam1 gene in mice causes exacerbation of inflammation and hyperactivation of myeloid cells and lymphocytes. Hence, hepatic CEACAM1 resides at the central hub of immune and metabolic homeostasis in both humans and mice. This review focuses on the regulatory role of CEACAM1 in liver and biliary tract architecture in health and disease, and on its metabolic role and function as an immune checkpoint regulator of hepatic inflammation.

The CEA Family: A System in Transitional Evolution?

The CEA family consists of two structurally and functionally distinct subgroups; the group including CEA, NCA and CGM-6 which are cell surface-bound by phosphatidylinositol (PI) linkages, and the group of BGP splice variants which have transmembrane and cytoplasmic domains. Although all CEA family members mediate intercellular adhesion in vitro, the PI-linked group show Ca++ and temperature independent adhesion whereas the BGP group show rapidly reversible Ca++ and temperature dependent adhesion. From the close alignment in cDNA nucleotide sequences between family members and between repeated domains in one family member, it is apparent that the CEA family is now rapidly evolving; in fact, analogs of only the transmembrane BGP group have been found so far in the mouse. The addition of a new group of potent adhesion molecules to complex species at some time after the rodent radiation has strong evolutional implications, which are discussed.

The GDA1_CD39 superfamily: NTPDases with diverse functions

The first comprehensive review of the ubiquitous "ecto-ATPases" by Plesner was published in 1995. A year later, a lymphoid cell activation antigen, CD39, that had been cloned previously, was shown to be an ecto-ATPase. A family of proteins, related to CD39 and a yeast GDPase, all containing the canonical apyrase conserved regions in their polypeptides, soon started to expand. They are now recognized as members of the GDA1_CD39 protein family. Because proteins in this family hydrolyze nucleoside triphosphates and diphosphates, a unifying nomenclature, nucleoside triphosphate diphopshohydrolases (NTPDases), was established in 2000. Membrane-bound NTPDases are either located on the cell surface or membranes of intracellular organelles. Soluble NTPDases exist in the cytosol and may be secreted. In the last 15 years, molecular cloning and functional expression have facilitated biochemical characterization of NTPDases of many organisms, culminating in the recent structural determination of the ecto-domain of a mammalian cell surface NTPDase and a bacterial NTPDase. The first goal of this review is to summarize the biochemical, mutagenesis, and structural studies of the NTPDases. Because of their ability in hydrolyzing extracellular nucleotides, the mammalian cell surface NTPDases (the ecto-NTPDases) which regulate purinergic signaling have received the most attention. Less appreciated are the functions of intracellular NTPDases and NTPDases of other organisms, e.g., bacteria, parasites, Drosophila, plants, etc. The second goal of this review is to summarize recent findings which demonstrate the involvement of the NTPDases in multiple and diverse physiological processes: pathogen-host interaction, plant growth, eukaryote cell protein and lipid glycosylation, eye development, and oncogenesis.

ATP as a co-transmitter with noradrenaline in sympathetic nerves--function and fate

ATP and noradrenaline are co-stored in synaptic vesicles in sympathetic nerves and when co-released act postjunctionally to evoke contraction of visceral and vascular smooth muscle. In the original purinergic nerve hypothesis it was proposed that ATP would then be sequentially broken down to ADP, AMP and adenosine. Although such breakdown can be measured, it is not clear how the time-scale of breakdown compares with the time-course of the postjunctional actions of ATP. We have investigated the role of ectoATPase in modulating purinergic neurotransmission in the guinea-pig vas deferens using ARL67156 (formerly FPL67516), a recently developed inhibitor of ectoATPase. ARL67156 (1-100 microM) potentiated neurogenic contractions in a concentration-dependent manner. Onset of potentiation was rapid and the effect reversed rapidly on washout of the drug. The effect was also frequency dependent, being greater at lower frequencies. The purinergic component of the neurogenic contraction was isolated using the alpha 1 antagonist prazosin (100 nM) and ARL67156 caused a similar potentiation. ARL67156 also potentiated contractions evoked by exogenous ATP (100 microM), but had no effect on those of the stable analogue alpha, beta-methylene ATP (500 nM). In the presence of the P2 purinoceptor antagonist PPADS (100 microM), ARL67156 also had no effect on contractions evoked by noradrenaline (10 microM) or KCI (40 mM). These results are consistent with an inhibitory action of ARL67156 on ectoATPase and suggest that ectoATPase modulates purinergic transmission in the guinea-pig vas deferens. When released from sympathetic nerves, ATP acts at the P2X purinoceptor, a ligand-gated cation channel, to evoke depolarization and contraction. In single acutely dissociated smooth muscle cells of the rat tail artery, studied under voltage-clamp conditions, ATP and its analogues evoke an inward current, with a rank order potency of 2-methylthioATP = ATP > alpha, beta-methylene ATP. This is very different from the order of potency for evoking contraction in whole vessel rings, which is alpha, beta-methylene ATP > > 2-methylthioATP > or = ATP. This discrepancy can be explained by a previously unrecognized attenuation of the action of ATP and 2-methylthioATP, but not alpha, beta-methylene ATP, by ectoATPase in whole tissues.

P2X receptors: a third major class of ligand-gated ion channels

Three classes of ligand-gated ion channels are defined by their molecular architecture. The first embraces nicotinic, 5-HT3, glycine and GABA receptors. The second class contains the glutamate receptors-AMPA, kainate and NMDA types. The third class is the P2X receptors for ATP. Current knowledge of the structure of these channels is reviewed, and set beside what is known of their basic functional properties. The aim of this paper is to consider how our more complete understanding of the first two classes of channels might be helpful in forming a molecular picture of P2X receptor function.

Cloning, purification, and identification of the liver canalicular ecto-ATPase as NTPDase8

Extracellular nucleotides regulate critical liver functions via the activation of specific transmembrane receptors. The hepatic levels of extracellular nucleotides, and therefore the related downstream signaling cascades, are modulated by cell-surface enzymes called ectonucleotidases, including nucleoside triphosphate diphosphohydrolase-1 (NTPDase1/CD39), NTPDase2/CD39L1, and ecto-5'-nucleotidase/CD73. The goal of this study was to determine the molecular identity of the canalicular ecto-ATPase/ATPDase that we hypothesized to correspond to the recently cloned NTPDase8. Human and rat NTPDase8 cDNAs were cloned, and the genes were located on chromosome loci 9q34 and 3p13, respectively. The recombinant proteins, expressed in COS-7 and HEK293T cells, were biochemically characterized. NTPDase8 was also purified from rat liver by Triton X-100 solubilization, followed by DEAE, Affigel Blue, and concanavalin A chromatographies. Importantly, NTPDase8 was responsible for the major ectonucleotidase activity in liver. The ion requirement, apparent K(m) values, nucleotide hydrolysis profile, and preference as well as the resistance to azide were similar for recombinant NTPDase8s and both purified rat NTPDase8 and porcine canalicular ecto-ATPase/ATPDase. The partial NH(2)-terminal amino acid sequences of all NTPDase8s share high identity with the purified liver canalicular ecto-ATPase/ATPDase. Histochemical analysis showed high ectonucleotidase activities in bile canaliculi and large blood vessels of rat liver, in agreement with the immunolocalization of NTPDase1, 2, and 8 with antibodies developed for this study. No NTPDase3 expression could be detected in liver. In conclusion, NTPDase8 is the canalicular ecto-ATPase/ATPDase and is responsible for the main hepatic NTPDase activity. The canalicular localization of this enzyme suggests its involvement in the regulation of bile secretion and/or nucleoside salvage.

The E-NTPDase family of ectonucleotidases: Structure function relationships and pathophysiological significance

Ectonucleotidases are ectoenzymes that hydrolyze extracellular nucleotides to the respective nucleosides. Within the past decade, ectonucleotidases belonging to several enzyme families have been discovered, cloned and characterized. In this article, we specifically address the cell surface-located members of the ecto-nucleoside triphosphate diphosphohydrolase (E-NTPDase/CD39) family (NTPDase1,2,3, and 8). The molecular identification of individual NTPDase subtypes, genetic engineering, mutational analyses, and the generation of subtype-specific antibodies have resulted in considerable insights into enzyme structure and function. These advances also allow definition of physiological and patho-physiological implications of NTPDases in a considerable variety of tissues. Biological actions of NTPDases are a consequence (at least in part) of the regulated phosphohydrolytic activity on extracellular nucleotides and consequent effects on P2-receptor signaling. It further appears that the spatial and temporal expression of NTPDases by various cell types within the vasculature, the nervous tissues and other tissues impacts on several patho-physiological processes. Examples include acute effects on cellular metabolism, adhesion, activation and migration with other protracted impacts upon developmental responses, inclusive of cellular proliferation, differentiation and apoptosis, as seen with atherosclerosis, degenerative neurological diseases and immune rejection of transplanted organs and cells. Future clinical applications are expected to involve the development of new therapeutic strategies for transplantation and various inflammatory cardiovascular, gastrointestinal and neurological diseases.

Expression Pattern of Osteopontin in Endometrial Carcinoma: Correlation With Expression of the Adhesion Molecule CEACAM1

Osteopontin (OPN) and CEACAM1 have diverse biological functions in the uterus and placenta throughout the estrous cycle and pregnancy and have been shown to interact with integrin beta3. OPN is a glycoprotein of the extracellular matrix, which has been shown to mediate cellular migration and invasion and to contribute to tumorigenesis in several types of cancers. Recently we showed the expression pattern of OPN in gestational trophoblastic tumors. CEACAM1 is an adhesion molecule of the carcinoembryonic antigen family that we have recently found to be expressed in endometrial cancer and that has been shown to be down-regulated in colorectal, prostate, and breast cancer. In this study, immunohistochemistry and immunofluorescence with specific antibodies were performed on a series of 20 normal endometrial samples, 17 endometrial hyperplasias, and 43 endometrial carcinomas (28 endometrioid, 10 serous, and 5 clear cell carcinomas) to investigate the expression pattern and cell-type specific localization of OPN and to correlate it with the expression of CEACAM1. In addition, Western blot was performed on normal human endometrium and endometrial neoplasia. Strong OPN expression with a consistent cytoplasmic localization in epithelial glandular cells was observed in the normal human endometrium in 80% of the samples of the proliferative and secretory phase (score 8-12). Similar results could be found in endometrial hyperplasias. Strong expression of OPN could be observed in 29 (67.4%) of the 43 analyzed endometrial carcinomas. Of the 43 analyzed tumors, 18 (41.8%) were in the high score (8-12) category with a strong OPN expression level; 11 of 43 (25.5%) showed a moderate score (4-7) category. In endometrioid carcinoma with increasing malignancy grade, increasing areas with low OPN expression level or complete loss of OPN expression could be observed. In contrast, serous tumors showed a strong OPN expression level. Similar results could be found in Western blot analysis. CEACAM1 showed similar results and could be found to be coexpressed with OPN in normal human endometrium and in endometrial neoplasia as we showed using immunofluorescence. In this study, the different expression patterns of OPN in endometrial tumors could additionally support the biological diversity of endometrioid and serous carcinomas together with other markers. We suggest that OPN might play a different role in the pathogenesis of endometrial cancer (possibly as a functional complex with CEACAM1) and could be relevant for invasive growth of such lesions.

Expression of recombinant MDA-BF-1 with a kinase recognition site and a 7-histidine tag for receptor binding and purification

Prostate cancer metastasizes predominantly to bone, where it induces osteoblastic lesions. Paracrine factors secreted by the metastatic cancer cells are thought to mediate these events. We previously isolated a novel bone metastasis-related factor (MDA-BF-1) from bone marrow aspirate samples from patients with prostate cancer and bone metastasis, and found that this factor stimulated osteoblast differentiation, possibly by interacting with a receptor on the osteoblasts. Identifying this putative MDA-BF-1 receptor biochemically requires the expression of MDA-BF-1 for receptor binding assays and for the preparation of a ligand-affinity column. We tagged MDA-BF-1 with a peptide containing a protein kinase A phosphorylation site plus a 7-histidine sequence to facilitate the labeling of MDA-BF-1 for receptor binding assay and the binding of MDA-BF-1 to an immobilized metal affinity column. The recombinant MDA-BF-1 protein (MDA-BF1-kinase-his) was expressed in Sf9 cells using a baculovirus expression system. About 0.8 mg of purified MDA-BF1-kinase-his protein was obtained from 4 x 10(8) Sf9 cells. MDA-BF1-kinase-his can be phosphorylated by PKA with a specific activity around 10(5)cpm/mug protein. Receptor binding assays using this (32)P-labeled MDA-BF-1 showed that MDA-BF-1 bound to membranes prepared from Saos-2, an osteosarcoma cell line, and C2C12, a mouse pluripotent mesenchymal precursor cell line that can be induced to become osteoblast by BMP-2. In contrast, MDA-BF-1 did not bind to membranes from PC-3 human prostate cancer cells or HEK293 human embryonic kidney cells. These observations suggest that the MDA-BF-1 receptor is expressed in cells of osteoblastic lineage. In addition to its use as a ligand for receptor binding assays, a ligand affinity column can be prepared by binding MDA-BF1-kinase-his to an IMAC for the purification of MDA-BF-1 receptor.

Characterization of an ecto-ATPase activity in Cryptococcus neoformans

Cryptococcus neoformans is the causative agent of pulmonary cryptococcosis and cryptococcal meningoencephalitis, which are major clinical manifestations in immunosuppressed patients. In the present study, a surface ATPase (ecto-ATPase) was identified in C. neoformans yeast cells. Intact yeasts hydrolyzed adenosine-5'-triphosphate (ATP) at a rate of 29.36+/-3.36nmol Pi/hx10(8) cells. In the presence of 5 mM MgCl(2), this activity was enhanced around 70 times, and an apparent K(m) for Mg-ATP corresponding to 0.61mM was determined. Inhibitors of phosphatases, mitochondrial Mg(2+)-ATPases, V-ATPases, Na(+)-ATPases or P-ATPases had no effect on the cryptococcal ATPase, but extracellular impermeant compounds reduced enzyme activity in living cells. ATP was the best substrate for the cryptococcal ecto-enzyme, but it also efficiently hydrolyzed inosine 5'-triphosphate (ITP), cytidine 5'-triphosphate (CTP), guanosine 5'-triphosphate (GTP) and uridine-5'-triphosphate (UTP). In the presence of ATP, C. neoformans became less susceptible to the antifungal action of fluconazole. Our results are indicative of the occurrence of a C. neoformans ecto-ATPase that may have a role in fungal physiology.

Developmental profile of NTPDase activity in synaptic plasma membranes isolated from rat cerebral cortex

In the present study the developmental profile of ATP-hydrolyzing activity promoted by NTPDase 1, its kinetic properties and the enzyme protein abundance associated with synaptic plasma membrane from rat cerebral cortex were characterized. NTPDase 1 activity increased from birth to day 30; afterwards it decreased and remained unchanged from adulthood (90 days) to senescence (365 days). Kinetic analysis revealed that enzyme exhibited the highest specific activity at day 30 and highest apparent affinity for ATP at day 365; however, V(max)/K(m) values remained unchanged for each age studied. Immunoblot analysis demonstrated that relative abundance of NTPDase 1 is highest at day 15 during ontogeny. The discrepancy between maximum enzyme activity and maximum enzyme protein abundance indicates that NTPDase 1 may have an additional role during development.

Two Variable Regions in Carcinoembryonic Antigen-related Cell Adhesion Molecule1 N-terminal Domains Located in or Next to Monoclonal Antibody and Adhesion Epitopes Show Evidence of Recombination in Rat but Not in Human

In this paper, we have characterized the structure, evolutionary origin, and function of rat and human carcinoembryonic antigen-related cell adhesion molecule1 (CEACAM1) multifunctional Ig-like cell adhesion proteins that are expressed by many epithelial tissues. Restriction enzyme digestion reverse transcriptase-PCR analysis identified three cDNAs encoding novel CEACAM1 N-domains. Comparative sequence analysis showed that human and rat CEACAM1 N-domains segregated into two groups differing in similarity to rat CEACAM1(a)-4L and human CEACAM1. Sequence variability analysis indicated that both human and rat N-domains possessed two variable regions, and one contained a major adhesive epitope. Recombination analysis showed that the group of rat but not human N-domains with high sequence similarity was derived at least in part by recombination. Binding assays revealed that three monoclonal antibodies with strong reactivity for the CEACAM1(a)-4L N-domain showed no reactivity with CEACAM1(b)-4S, an allele with a different N-domain sequence. CEACAM1(b)-4S displayed adhesive activity efficiently blocked by a synthetic peptide corresponding to the adhesive epitope in CEACAM1(a)-4L. Blocking analysis also showed that the adhesive epitope for rat CEACAM1 was located downstream from the equivalent human and mouse epitopes. Glycosylation analysis demonstrated O-linked sugars on rat CEACAM1(b)-4S from COS-1 cells. However, this was not the alteration responsible for the lack of monoclonal antibody reactivity. When considered together with previous studies, our findings suggest an inverse relationship between functionality and amino acid sequence similarity to CEACAM1. Like IgG, the N-domain of CEACAM1 appears to tolerate 10-15% sequence diversification without loss of function but begins to show either altered specificity or diminished functionality at higher levels.

Regulation of E-kinase mediated cell-adhesion molecule(s) function by E-NTPase(s): imminent regulatory inter-dependency for cell adhesion

E-NTPase is a cell membrane bound enzyme, suggested to play a role in maintaining the [NTP](o) and cell adhesion. Attempts to purify this enzyme resulted identification of many proteins co-purifying with E-NTPase. The amino acid sequence of chicken gizzard smooth muscle E-NTPase has been shown to have considerable amino acid sequence homology with mammalian CD39. On the other hand, the purified rat cardiac sarcolemmal E-NTPase showed identical sequence homology with platelet CD36. In this communication, an effort was made to provide rationale for the functional relevance of E-NTPase with reference to cell-adhesion process.

Identification of Sp2 as a transcriptional repressor of carcinoembryonic antigen-related cell adhesion molecule 1 in tumorigenesis

Down-regulation of carcinoembryonic antigen-related cell adhesion molecule 1 (CEACAM1) tumor suppressor gene expression is common in several malignancies including prostate, colon, and breast cancer. The mechanism that mediates this down-regulation is not known. Here, we report that down-regulation of CEACAM1 expression in prostate cancer cells occurs primarily at the transcriptional level and is mediated by Sp2, a member of the Sp family of transcription factors. Sp2 binds to the CEACAM1 promoter in vitro and in vivo, and transient overexpression of Sp2 down-regulates endogenous CEACAM1 expression in normal prostate epithelial cells. Sp2 appears to repress CEACAM1 gene expression by recruiting histone deacetylase activity to the CEACAM1 promoter. In human prostate cancer specimens, Sp2 expression is high in prostate cancer cells but low in normal prostate epithelial cells and is inversely correlated with CEACAM1 expression. Our studies show that transcriptional repression by Sp2 represents one mechanism by which CEACAM1 tumor suppressor gene is down-regulated in prostate cancer.

Inhibition of prostate tumor angiogenesis by the tumor suppressor CEACAM1

We have previously shown that CEACAM1, a cell-adhesion molecule, acts as a tumor suppressor in prostate carcinoma. Expression of CEACAM1 in prostate cancer cells suppresses their growth in vivo. However, CEACAM1 has no effect on the growth of prostate cancer cells in vitro. This difference suggests that the antitumor effect of CEACAM1 may be due to inhibition of tumor angiogenesis, perhaps by increased secretion of antiangiogenic molecules from the cells. In this study, we have demonstrated that expression of CEACAM1 in DU145 prostate cancer cells induced the production of a factor or factors that specifically blocked the growth of endothelial but not epithelial cells. Conditioned medium from the CEACAM1-expressing cells but not control luciferase-expressing cells inhibited endothelial cell migration up a gradient of stimulatory vascular endothelial growth factor in vitro and inhibited corneal neovascularization induced by basic fibroblast growth factor in vivo. Moreover, conditioned medium from CEACAM1-expressing cells induced endothelial cell apoptosis in vitro. Only medium conditioned by CEACAM1 mutants that were able to suppress tumor growth in vivo could cause endothelial cell apoptosis. These observations suggest that CEACAM1-mediated tumor suppression in vivo is, at least in part, due to the ability of CEACAM1 to inhibit tumor angiogenesis.

Carcinoembryonic antigen-related cell adhesion molecule 1 expression and signaling in human, mouse, and rat leukocytes: evidence for replacement of the short cytoplasmic domain isoform by glycosylphosphatidylinositol-linked proteins in human leukocytes

Carcinoembryonic Ag-related cell adhesion molecule 1 (CEACAM1), the primordial carcinoembryonic Ag gene family member, is a transmembrane cell adhesion molecule expressed in leukocytes, epithelia, and blood vessel endothelia in humans and rodents. As a result of differential splicing, CEACAM1 occurs as several isoforms, the two major ones being CEACAM1-L and CEACAM1-S, that have long (L) or short (S) cytoplasmic domains, respectively. The L:S expression ratios vary in different cells and tissues. In addition to CEACAM1, human but not rodent cells express GPI-linked CEACAM members (CEACAM5-CEACAM8). We compared the expression patterns of CEACAM1-L, CEACAM1-S, CEACAM6, and CEACAM8 in purified populations of neutrophilic granulocytes, B lymphocytes, and T lymphocytes from rats, mice, and humans. Human granulocytes expressed CEACAM1, CEACAM6, and CEACAM8, whereas human B lymphocytes and T lymphocytes expressed only CEACAM1 and CEACAM6. Whereas granulocytes, B cells, and T cells from mice and rats expressed both CEACAM1-L and CEACAM1-S in ratios of 2.2-2.9:1, CEACAM1-S expression was totally lacking in human granulocytes, B cells, and T cells. Human leukocytes only expressed the L isoforms of CEACAM1. This suggests that the GPI-linked CEACAM members have functionally replaced CEACAM1-S in human leukocytes. Support for the replacement hypothesis was obtained from experiments in which the extracellular signal-regulated kinases (Erk)1/2 were activated by anti-CEACAM Abs. Thus, Abs against CEACAM1 activated Erk1/2 in rat granulocytes, but not in human granulocytes. Erk1/2 in human granulocytes could, however, be activated by Abs against CEACAM8. We demonstrated that CEACAM1 and CEACAM8 are physically associated in human granulocytes. The CEACAM1/CEACAM8 complex in human cells might accordingly play a similar role as CEACAM1-L/CEACAM1-S dimers known to occur in rat cells.

Secreted CEACAM1 splice variants in rat cell lines and in vivo in rat serum

The widely expressed adhesion receptor CEACAM1 is a member of the carcinoembryonic antigen (CEA) family within the immunoglobulin (Ig) superfamily of glycoproteins. While the expression of transmembrane isoforms has been described in detail, only little is known about soluble isoforms. By RT-PCR characterization of rat pheochromocytoma PC12 and mammary adenocarcinoma MTC cell lines, two novel splice variants, designated CEACAM1-4C1 and CEACAM1-4C2, lacking the transmembrane region, were identified. In addition, we demonstrate the expression of transmembrane CEACAM1-4L and CEACAM1-4S with a truncated cytoplasmic domain. The C-termini of CEACAM1-4C2 and CEACAM1-L are identical, which allowed the specific in vitro and in vivo detection of the soluble CEACAM1-4C2 protein by an antiserum generated against the CEACAM1-L cytoplasmic part. Functionally, soluble CEACAM1 could inhibit CEACAM1-mediated aggregation of CHO cells. In conclusion, our data define a new mechanism for the appearance of functionally active rat CEACAM1 protein in body fluids.

Androgen regulation of the cell-cell adhesion molecule-1 (Ceacam1) gene

Previous studies have established that the cell-cell adhesion molecule-1 (CEACAM1, previously known as C-CAM1) functions as a tumor suppressor in prostate cancer and is involved in the regulation of prostate growth and differentiation. However, the molecular mechanism that modulates CEACAM1 expression in the prostate is not well defined. Since the growth of prostate epithelial cells is androgen-regulated, we investigated the effects of androgen and the androgen receptor (AR) on CEACAM1 expression. Transient transfection experiments showed that the AR can enhance the Ceacam1 promoter activity in a ligand-dependent manner and that the regulatory element resides within a relatively short (-249 to -194 bp) segment of the 5'-flanking region of the Ceacam1 gene. This androgen regulation is likely through direct AR-promoter binding because a mutant AR defective in DNA binding failed to upregulate reporter gene expression. Furthermore, electrophoretic mobility shift assays demonstrated that the AR specifically binds to this sequence, and mutation analysis of the potential ARE sequences revealed a region within the sequence that was required for the AR to activate the Ceacam1 gene. Therefore, the regulation of Ceacam1 gene expression by androgen may be one of the mechanisms by which androgen regulates prostatic function.

cis Interaction of the cell adhesion molecule CEACAM1 with integrin beta(3)

CEACAM1 is a cell adhesion molecule that has been implicated in a number of physiological processes (eg, tumor suppressor in epithelial tissues, potent angiogenic factor in microvessel formation, microbial receptor in human granulocytes and epithelial cells). The mechanism of CEACAM1 action is still largely unresolved but recent findings demonstrated that the cytoplasmic CEACAM1 domain is linked indirectly to the actin-based cytoskeleton. We have isolated integrin beta(3) as an associated protein using CEACAM1 tail affinity purification. This association depends on phosphorylation of Tyr-488 in the CEACAM1 cytoplasmic domain. Confocal laser scanning microscopy confirmed in vivo colocalization of both molecules in human granulocytes and epithelial cells. Furthermore, the concentrated colocalization at the tumor-stroma interface of invading melanoma masses suggests a functional role of CEACAM1-integrin beta(3) interaction in melanoma invasion. Moreover, colocalization of the two adhesion molecules is also found at the apical surface of glandular cells of pregnancy endometrium. Colocalization of CEACAM1 and integrin beta(3) at the transitional zone from proliferative to invasive extravillous trophoblast of the maternal-fetal interface supports a role for CEACAM1/integrin beta(3) complexes in cell invasion.

Signal transduction by the CEACAM1 tumor suppressor. Phosphorylation of serine 503 is required for growth-inhibitory activity

CEACAM1 is a cell-cell adhesion molecule that mediates homophilic cell adhesion. In addition, CEACAM1 was also shown to suppress the growth of prostate, breast, and colon tumors. Structural and functional analyses showed that the adhesion activity of CEACAM1 is mediated by its extracellular domain while its cytoplasmic domain is necessary and sufficient for growth-inhibitory activity. The signal pathways leading to CEACAM1-mediated growth suppression are not known. We studied the importance of phosphorylation of serine 503 in this growth-inhibitory signaling pathway. Full-length CEACAM1 was found to be phosphorylated in vivo in both tyrosine and serine residues. Mutation of tyrosine 488 to phenylalanine did not abolish the tumor-suppressive activity of CEACAM1, suggesting that phosphorylation at tyrosine 488 is not critical for CEACAM1's tumor-suppressive activity. Although expression of CEACAM1's cytoplasmic domain inhibited the growth of DU145 prostate cancer cells in vivo, mutation of serine 503 to alanine abolished the growth-inhibitory activity. In addition, the change of serine 503 to aspartic acid produced tumor-suppressive activity similar to that of the wild-type CEACAM1. These results suggested that phosphorylation at serine 503 is essential for CEACAM1's growth-inhibitory function in vivo.

Expression pattern of the adhesion molecule CEACAM1 (C-CAM, CD66a, BGP) in gestational trophoblastic lesions

CEACAM1 (CD66a, BGP, C-CAM) is an adhesion molecule of the carcinoembryonic antigen (CEA) family which has been shown to be normally expressed at the apical pole of epithelial cells and to show a dysregulated expression pattern in tumors derived from the latter. The purpose of the present study was to investigate the expression pattern of CEACAM1 in gestational trophoblastic lesions and to compare this expression with the one observed in the normal trophoblast. For this purpose, we performed immunohistochemistry using the 4D1/C2 monoclonal antibody which specifically recognizes CEACAM1 and does not interact with other members of the CEA family. Immunohistochemistry was performed on a total of 20 cases of gestational trophoblastic lesions including complete hydatidiform moles, one placental site trophoblastic nodule (PSN), one placental site trophoblastic tumor (PSTT), and three choriocarcinomas. Immunostaining for cytokeratin, hPL, hCG, and Ki-67 was also performed. Normal placental samples served as a control. CEACAM1 was absent from villous cyto- and syncytiotrophoblast in both normal placenta and hydatidiform molar samples. It was present in the benign extravillous trophoblast, with stronger expression in the proximal extravillous trophoblast of anchoring villi, but was also observed in interstitial and endovascular intermediate trophoblast and chorionic intermediate-like trophoblast. Partial expression was observed in the trophoblast proliferating from the surface of molar villi. In choriocarcinomas, areas of weak expression could be observed along with large areas without CEACAM1 expression. In the PSN and especially in the PSTT, CEACAM1 expression was stronger and more diffuse. The specific localization to extravillous trophoblast and its expression pattern in gestational trophoblastic lesions indicate that CEACAM1 can potentially be a helpful additional diagnostic marker in the differential diagnosis of such lesions.

The CEACAM1-L Ser503 residue is crucial for inhibition of colon cancer cell tumorigenicity

CEACAM1 (also known as biliary glycoprotein, C-CAM or CD66a) is a cell adhesion molecule of the immunoglobulin family behaving as a tumor inhibitory protein in colon, prostate, liver, endometrial and breast cancers. Inhibition of tumor development is dependent upon the presence of the long 71-73 amino acid cytoplasmic domain of the CEACAM1 protein (CEACAM1-L). We have recently defined a number of cis-acting motifs within the long cytoplasmic domain participating in tumor cell growth inhibition. These are Tyr488, corresponding to an Immunoreceptor Tyrosine-based Inhibition Motif, as well as the three terminal lysine residues of the protein. In this study, we provide evidence that treatment with phorbol esters leads to increased phosphorylation of in vivo (32)P-labeled CEACAM1-L in mouse CT51 carcinoma cells, in the mouse 1MEA 7R.1 liver carcinoma cells and in 293 human embryonic kidney cells transfected with the Ceacam1-L cDNA. Basal level Ser phosphorylation was abrogated by treatment with the staurosporine inhibitor, but not by the protein kinase C-specific inhibitor calphostin C or other inhibitors such as H7 or sphingosine. Specific inhibitors of protein kinase A or calmodulin kinase had only minimal effects on the levels of basal or PMA-induced Ser phosphorylation. Furthermore, PMA treatment of the CT51 cells induced cell spreading and cellular relocalization of the CEACAM1-L protein. Since Ser503 has been described as a PMA-induced phosphorylation site in other cell systems, we investigated whether Ser503 was involved in these responses in mouse intestinal cells. No differences were noticed in the basal or the PMA-induced phosphorylation levels, kinase inhibitor sensitivity or the PMA-induced relocalization of the protein between the wild-type and the Ser503Ala mutant CEACAM1-L. However, we provide evidence that Ser503 participates in CEACAM1-L-mediated tumor inhibition as its mutation to an Ala led to in vivo tumor development, contrary to the tumor inhibitory phenotype observed with the wild-type CEACAM1-L protein.

Soluble isoforms of CEACAM1 containing the A2 domain: increased serum levels in patients with obstructive jaundice and differences in 3-fucosyl-N-acetyl-lactosamine moiety

CEACAM1 (biliary glycoprotein or CD66a) is a member of the carcinoembryonic antigen (CEA) subgroup of the CEA family. Eleven RNA isoforms derived from the splicing of a single CEACAM1 gene have been described. Some of the CEACAM1 isoforms have been recognized by the CD66 antibodies in T and B lymphocytes, natural killer cells, granulocytes and epithelial cells in several human tissues. Although it is also present in soluble form in bile and serum, and elevated levels have been found in the serum of patients with liver diseases, it is not known which isoforms are primarily involved. In order to learn more about the distribution and properties of particular CEACAM1 isoforms, we have prepared a monoclonal antibody specific for the A2 domain of CEACAM1, designated TEC-11. This antibody does not cross-react with other members of the CEA family. Immunoblotting analysis revealed that the TEC-11 epitope was present in all cell types expressing CEACAM1 containing the A2 domain [CEACAM1(A2)], including granulocytes (160 000 MW isoform) and sperm cells (140 000 MW isoform). A 115 000 MW isoform of CEACAM1(A2) was present in human serum, bile, saliva and seminal fluid. Human bile, saliva and seminal fluid also contained the 160 000 MW CEACAM1(A2) isoform. Significantly higher serum levels of the 115 000 MW CEACAM1(A2) isoform were detected in patients with obstructive jaundice. The 160 000 MW isoform of CEACAM1(A2) in bile, but not a 115 000 MW isoform in serum and bile, carried the 3-fucosyl-N-acetyl-lactosamine moiety. The combined data indicate that various isoforms of CEACAM1(A2) are present in different body fluids where they could take part in different CEACAM1-mediated functions.

Down-regulation of Bgp1(a) viral receptor by interferon-gamma is related to the antiviral state and resistance to mouse hepatitis virus 3 infection

Together with the evidence that the reduced virus growth and the antiviral state induced by interferon (IFN)-gamma, occurring only in macrophages from resistant animals, correlated with the decrease of MHV3 binding to macrophage membrane proteins, we show here the expression of cellular and viral genes in resistant (A/J) and susceptible (BALB/c) mouse macrophages after IFN-gamma activation/infection. The expression of interferon response gene 47 and interferon regulatory factor 1 genes takes place after IFN-gamma activation in both macrophages, indicating their activation. The expression of the biliary glycoprotein 1(a) (Bgp1(a), the main virus receptor) decreased only in IFN-gamma-activated A/J mouse macrophages, in contrast to the expression of the Bgp2 (alternative receptor), which was not influenced by IFN-gamma activation. The synthesis of both viral mRNA and virus particles was delayed only in IFN-gamma-activated A/J mouse macrophages compared with susceptible BALB/c macrophages. Besides the evidence that IFN-gamma may modulate the expression of the Bgp1(a) isoform of carcinoembryonic antigen family, these data show that IFN-gamma, which induces resistance against MHV3 infection, may be involved in the down-regulation of the main viral receptor expression, a key step forward in our understanding of the molecular basis of resistance against virus infection.

Purification, characterization, and localization of an ATP diphosphohydrolase in porcine kidney

Membranes of pig kidney cortex tissue were solubilized in the presence of Triton X-100. Partial purification of ATP diphosphohydrolase (ATPDase) was achieved by successive chromatography on concanavalin A-Sepharose, Q-Sepharose Fast Flow, and 5'-AMP-Sepharose 4B. Monoclonal antibodies against ATPDase were generated. Further purification of the ATPDase was obtained by immunoaffinity chromatography with these monoclonal antibodies. NH(2)-terminal amino acid sequencing of the 78-kDa protein showed a sequence very homologous to mammalian CD39. The protein is highly glycosylated, with a nominal molecular mass of approximately 57 kDa. The purified enzyme hydrolyzed di- and triphosphates of adenosine, guanosine, cytidine, uridine, inosine, and thymidine, but AMP and diadenosine polyphosphates could not serve as substrates. All enzyme activities were dependent on divalent cations and were partially inhibited by 10 mM sodium azide. The distribution of the enzyme in pig kidney cortex was examined immunohistochemically. The enzyme was found to be present in blood vessel walls of glomerular and peritubular capillaries.

The differential effects of pp120 (Ceacam 1) on the mitogenic action of insulin and insulin-like growth factor 1 are regulated by the nonconserved tyrosine 1316 in the insulin receptor

pp120 (Ceacam 1) undergoes ligand-stimulated phosphorylation by the insulin receptor, but not by the insulin-like growth factor 1 receptor (IGF-1R). This differential phosphorylation is regulated by the C terminus of the beta-subunit of the insulin receptor, the least conserved domain of the two receptors. In the present studies, deletion and site-directed mutagenesis in stably transfected hepatocytes derived from insulin receptor knockout mice (IR(-/-)) revealed that Tyr(1316), which is replaced by the nonphosphorylatable phenylalanine in IGF-1R, regulated the differential phosphorylation of pp120 by the insulin receptor. Similarly, the nonconserved Tyr(1316) residue also regulated the differential effect of pp120 on IGF-1 and insulin mitogenesis, with pp120 downregulating the growth-promoting action of insulin, but not that of IGF-1. Thus, it appears that pp120 phosphorylation by the insulin receptor is required and sufficient to mediate its downregulatory effect on the mitogenic action of insulin. Furthermore, the current studies revealed that the C terminus of the beta-subunit of the insulin receptor contains elements that suppress the mitogenic action of insulin. Because IR(-/-) hepatocytes are derived from liver, an insulin-targeted tissue, our observations have finally resolved the controversy about the role of the least-conserved domain of insulin and IGF-1Rs in mediating the difference in the mitogenic action of their ligands, with IGF-1 being more mitogenic than insulin.

The adhesion molecule CEACAM1 (CD66a, C-CAM, BGP) is specifically expressed by the extravillous intermediate trophoblast

CEACAM1 (CD66a, C-CAM, BGP) is an adhesion molecule of the carcinoembryonic antigen family which has been shown to be normally expressed at the apical pole of epithelial cells, including the apical pole of endometrial surface and glandular epithelia. The purpose of the present study was to investigate its expression pattern at the maternal-fetal interface, and thus to determine whether CEACAM1 could be implicated in the human implantation process. For this purpose, we performed immunohistochemistry using the 4D1/C2 monoclonal antibody (mAb) as well as flow cytometry and Western blot on isolated trophoblast populations. On the maternal side of the maternal-fetal interface, CEACAM1 was present in epithelial cells of pregnancy endometrium as well as in small endometrial vessels, whereas it was absent from decidual cells. On the fetal side, CEACAM1 was strongly expressed by the extravillous (intermediate) trophoblast at the implantation site, as well as by extravillous trophoblast cells with invasive phenotype in primary culture, as shown by flow cytometry and Western blot. Expression was also observed in placental villous core vessels but was absent from both villous cyto- and syncytiotrophoblasts throughout the pregnancy. We conclude that, given its specific expression pattern, CEACAM1 can be a useful marker for extravillous intermediate trophoblast and might be functionally implicated in mediating trophoblast/endometrial and/or trophoblast/endothelial interactions during the trophoblastic invasion of the endometrium.

Identification and characterization of a novel hepatic canalicular ATP diphosphohydrolase

We have identified and characterized a novel ATP diphosphohydrolase (ATPDase) with features of E-type ATPases from porcine liver. Immunoblotting with a specific monoclonal antibody to this ectoenzyme revealed high expression in liver with lesser amounts in kidney and duodenum. This ATPDase was localized by immunohistochemistry to the bile canalicular domain of hepatocytes and to the luminal side of the renal ductular epithelium. In contrast, ATPDase/cd39 was detected in vascular endothelium and smooth muscle in these organs. We purified the putative ATPDase from liver by immunoaffinity techniques and obtained a heavily glycosylated protein with a molecular mass estimated at 75 kDa. This enzyme hydrolyzed all tri- and diphosphonucleosides but not AMP or diadenosine polyphosphates. There was an absolute requirement for divalent cations (Ca(2+) > Mg(2+)). Biochemical activity was unaffected by sodium azide or other inhibitors of ATPases. Kinetic parameters derived from purified preparations of hepatic ATPDase indicated V(max) of 8.5 units/mg of protein with apparent K(m) of 100 microM for both ATP or ADP as substrates. NH(2)-terminal amino acid sequencing revealed near 50% identity with rat liver lysosomal (Ca(2+)-Mg(2+))-ATPase. The different biochemical properties and localization of the hepatic ATPDase suggest pathophysiological functions that are distinct from the vascular ATPDase/cd39.

Essential role of biliary glycoprotein (CD66a) in morphogenesis of the human mammary epithelial cell line MCF10F

Normal mammary epithelial cells express the cell surface protein biliary glycoprotein (BGP or CD66a) in a polarized manner, suggesting that this protein may play a role in the formation of mammary acini. In order to test this hypothesis, we interrupted the expression of BGP in the mammary epithelial line MCF10F when cultured in or on Matrigel, a source of extracellular matrix (ECM). When analyzed by immunofluorescence confocal microscopy, the BGP staining is confined to the lumenal surface and colocalizes with actin. Sequential scanning electron microscopy demonstrates that the MCF10F cells migrate to form clusters, followed by apoptotic cell death within the center, resulting in lumen formation. Transmission electron micrographs reveal the presence of tight junctions and desmosomes between the cells, microvilli along the lumenal surface, and typical apoptotic bodies within the lumen. When the MCF10F cells are transfected with the BGP antisense gene and grown in Matrigel, they exhibit reduced acini formation (12% and 20%) compared to untransfected cells (52%) or to cells transfected with vector only (62%). Acini formation is also significantly reduced when MCF10F cells grown in Matrigel are treated with anti-BGP antibody (18% at 100 microgram/ml), or recombinant soluble BGP (18% at 0.4 microM). In contrast, the BGP-negative MCF7 breast tumor cell line, which does not form acini when grown in matrigel, exhibits >60% cell death with the occasional formation of acini, when transfected with the BGP sense gene and grown in Matrigel. These results support the hypothesis that BGP plays a role in the normal differentiation program of mammary epithelial cells, indicating that its expression is essential to the formation of the lumen. Furthermore, and as shown by others, the differentiation program depends on the presence of ECM. The lack of expression of BGP in the MCF7 breast cancer cell line suggests that the downregulation of BGP expression confers a growth advantage to these cells in ECM. In addition, we found that the MCF10F cells could be separated into a BGP-positive epithelial fraction (MCF10F-e), and a BGP-negative myoepithelial fraction (MCF10F-m). When the myoepithelial cell-enriched fraction is grown on Matrigel, web-like structures are formed. These cells have a typical spindle shape cell morphology and express keratin, alpha-smooth muscle actin and vimentin, markers of the myoepithelial cell phenotype. When MCF10F-m cells are treated with IFNgamma, they express CEA (carcinoembryonic antigen) but not BGP. Since breast carcinomas, especially in situ carcinomas, express CEA, this finding may suggest a heretofore unappreciated relationship between myoepithelial cells and breast cancer.

Inhibition of rat parotid ecto-ATPase activity

The inhibitory profile of several known and suspected ecto-ATPase inhibitors was compared on ecto-ATPase activity in rat parotid plasma membranes. Those chemicals with high IC50 (above 130 microM) were the nucleotides alpha,beta-methylene ATP, beta,gamma-methylene ATP, 2-methylthio ATP, inosine triphosphate, 5'-p-fluorosulphonylbenzoyladenosine, the sulphonates, 1-amino-2-naphthol-4-sulphonic acid, Coomassie brilliant blue G, and the stilbene disulphonates, DIDS and SITS. Those agents with low IC50 were: Coomassie brilliant blue R (114 microM), ATPgammaS (49 microM), suramin (72 microM) and Reactive blue 2 (28 microM). The last three inhibitors have similar potencies as inhibitors of ATP hydrolysis by whole parotid acinar cells. ARL67156, a selective inhibitor of ecto-ATPase, had an IC50 of approx. 120 microM. Suramin displayed non-competitive inhibition of ecto-ATPase whereas the inhibitory effects of ATPgammaS and Reactive blue 2 were curvilinear on Dixon plots. These results define the effects of various agents on ecto-ATPase in an exocrine tissue that has been shown to respond to extracellular ATP.

The cytoplasmic domain of C-CAM1 tumor suppressor is necessary and sufficient for suppressing the tumorigenicity of prostate cancer cells

We have previously shown that C-CAM1 cell adhesion molecule can suppress the growth of prostate cancer cells in vivo. In this study, we determined the minimal domain of C-CAM1 that is required for its tumor-suppressive activity. DU145 prostate cancer cells were infected with recombinant adenoviruses containing various C-CAM1 mutant genes, and the effects of the mutant C-CAM1 proteins on the growth of DU145 cells were assessed in a nude-mice xenograft model. Deletion of C-CAM1's cytoplasmic domain, which is not required for its adhesion activity, abolished the growth-suppressive activity, whereas deletion of the adhesion domain did not. This observation suggests that C-CAM1's extracellular domain may be not essential for its tumor suppressive activity. Indeed, we found that expression of the C-CAM1 cytoplasmic domain alone led to growth suppression of DU145 cells. These results suggest that the cytoplasmic domain of C-CAM1 is necessary and sufficient for its growth-suppressive function.

cis-Determinants in the cytoplasmic domain of CEACAM1 responsible for its tumor inhibitory function

CEACAM1, also known as C-CAM, BGP and CD66a, is a member of the carcinoembryonic antigen (CEA) family which is itself part of the immunoglobulin supergene family. CEACAM1 is involved in intercellular adhesion, signal transduction and tumor cell growth regulation. CEACAM1 is down-regulated in colon and prostate carcinomas, as well as in endometrial, bladder and hepatic tumors, and 30% of breast cancers. We have shown in a mouse colon tumor model that CEACAM1 with a long cytoplasmic domain inhibited the development of tumors whereas a splice variant lacking the cytoplasmic domain did not. In this study, we define the subregions of the long cytoplasmic domain participating in the tumor inhibition phenotype of CEACAM1. We show that a single point mutation of Tyr488, conforming to an Immunoreceptor Tyrosine Inhibition Motif (ITIM), was sufficient to reverse the in vivo tumor cell growth inhibition. Substitution or deletion of residues in the C-terminal region of the CEACAM1 cytoplasmic domain also led to reversal of tumor cell growth inhibition. This result is in agreement with our previous studies demonstrating the C-terminal region of the cytoplasmic domain influences the levels of CEACAM1 Tyr phosphorylation and its association with the protein Tyr phosphatases SHP-1 and SHP-2. Furthermore, removal of the N-terminal domain of CEACAM1, essential for intercellular adhesion, did not impair the tumor inhibitory effect. These results suggest that Tyr phosphorylation or dephosphorylation of the CEACAM1 cytoplasmic domain represents a crucial step in the control of epithelial cell proliferation.

N-glycosylation of the carcinoembryonic antigen related cell adhesion molecule, C-CAM, from rat liver: detection of oversialylated bi- and triantennary structures

Rat C-CAM is a ubiquitous, transmembrane and carcinoembryonic antigen related cell adhesion molecule. The human counterpart is known as biliary glycoprotein (BGP) or CD66a. It is involved in different cellular functions ranging from intercellular adhesion, microbial receptor activity, signaling and tumor suppression. In the present study N-glycosylation of C-CAM immunopurified from rat liver was analyzed in detail. The primary sequence of rat C-CAM contains 15 potential N-glycosylation sites. The N-glycans were enzymatically released from glycopeptides, fluorescently labeled with 2-aminobenzamide, and separated by two-dimensional HPLC. Oligosaccharide structures were characterized by enzymatic sequencing and MALDI-TOF-MS. Mainly bi- and triantennary complex structures were identified. The presence of type I and type II chains in the antennae of these glycans results in heterogeneous glycosylation of C-CAM. Sialylation of the sugars was found to be unusual; bi- and triantennary glycans contained three and four sialic acid residues, respectively, and this linkage seemed to be restricted to the type I chain in the antennae. Approximately 20% of the detected sugars contain these unusual numbers of sialic acids. C-CAM is the first transmembrane protein found to be oversialylated.

Regulation of Human Intestinal Intraepithelial Lymphocyte Cytolytic Function by Biliary Glycoprotein (CD66a)

Human small intestinal intraepithelial lymphocytes (iIEL) are a unique population of CD8αβ+ TCR-αβ+ but CD28− T lymphocytes that may function in intestinal epithelial cell immunosurveillance. In an attempt to define novel cell surface molecules involved in iIEL function, we raised several mAbs against activated iIELs derived from the small intestine that recognized an Ag on activated, but not resting, iIELs. Using expression cloning and binding studies with Fc fusion proteins and transfectants, the cognate Ag of these mAbs was identified as the N domain of biliary glycoprotein (CD66a), a carcinoembryonic Ag-related molecule that contains an immune receptor tyrosine-based inhibitory motif. Functionally, these mAbs inhibited the anti-CD3-directed and lymphokine-activated killer activity of the P815 cell line by iIELs derived from the human small intestine. These studies indicate that the expression of biliary glycoprotein on activated human iIELs and, potentially, other mucosal T lymphocytes is involved in the down-regulation of cytolytic function.

The cDNA cloning of human placental ecto-ATP diphosphohydrolases I and II

The cDNA clones of two isoforms (enzymes I and II) of human placental ecto-ATP diphosphohydrolases have been isolated based on the N-terminal amino acid (aa) sequence of the immunopurified 82 kDa protein and characterized. The cDNA clone encoding enzyme I consists of 2081 nucleotides and the predicted enzyme I consists of 517 aa residues. Enzyme I has a 5'-UTR and an N-terminal 11 aa sequence that differ from CD39, but the rest of the sequence is the same as CD39. The hydropathy plot indicated that enzyme I has two hydrophobic regions near the N- and C-termini of the molecule. In contrast, enzyme II consists of 1814 nucleotides and the predicted protein consists of 306 aa residues. The sequence of 1-1018 nucleotides of enzyme II is identical to that of enzyme I, but the 1019-1814 nucleotide sequence is different from both enzyme I and CD39. The hydropathy plot indicated that enzyme II has one hydrophobic region near the N-terminus, suggesting that enzyme II is also anchored to the cell membrane. It is, however, likely that some of enzyme II exists as a soluble form in plasma, possibly after proteolytic processing.

C-CAM-mediated adhesion leads to an outside-in dephosphorylation signal

The rat cell-cell adhesion molecule C-CAM, a member of the carcinoembryonic antigen family, was shown to be expressed in various isoforms, differing in the length of the cytoplasmic domain. The long isoform C-CAML inhibits the growth of different malignant cells. Several studies suggest that it is involved in the mechanism of signal transduction. So far no direct correlation between C-CAM function and C-CAM phosphorylation has been reported. In the present study we addressed the question of whether C-CAM-mediated adhesion is accompanied by changes in phosphorylation of the cytoplasmic domain of C-CAM. It was demonstrated that C-CAML is constitutively phosphorylated in adherent growing cells as well as in cells growing in suspension. In contrast, C-CAML-mediated cell aggregation is accompanied by a 40% reduction in C-CAML phosphorylation compared with nonaggregated cells. The same dephosphorylation was achieved by antibody-induced clustering of C-CAML in the plasma membrane. Phosphorylation and dephosphorylation indicate a C-CAM-mediated outside-in signalling induced by cell-cell adhesion.

C-CAM1 expression: differential effects on morphology, differentiation state and suppression of human PC-3 prostate carcinoma cells

Studies in rat prostate and liver have suggested that C-CAM1 is involved in the formation and maintenance of histotypic associations in tissues and possibly tumors. Most recently, C-CAM1 has been shown to suppress tumorigenicity of prostate and colon carcinoma cells. However, the mechanisms whereby C-CAM1 suppresses growth and the relationship of this activity to its proposed role in histotypic interactions remain largely unknown. In the present study, we have analysed the growth, phenotypic, morphological and ultrastructural characteristics of four human PC-3 prostate carcinoma cell lines transduced with C-CAM1 retrovirus. We report that three of four lines regained their tumorigenic phenotype in vivo while maintaining high levels of C-CAM1 expression and a growth retarded phenotype in vitro. These findings suggested that high levels of C-CAM1 expression were negatively influencing recovery during reconstitution after freezing or during the latency period after subcutaneous injection and that loss of suppression resulted from changes in expression of other molecules required for full disclosure of C-CAM1 mediated growth inhibition. Results from Northern blot and immunofluorescence analyses of tumor nodules demonstrated that C-CAM1 decreased rather than enhanced phenotypic differentiation and induced ultrastructural and morphological changes that occurred independently of tumor suppression.

Cell adhesion properties and effects on receptor-mediated insulin endocytosis are independent properties of pp120, a substrate of the insulin receptor tyrosine kinase

pp120 undergoes phosphorylation by the tyrosine kinase of the insulin, not the insulin-like growth factor 1 (IGF-1), receptor. Moreover, pp120 stimulates receptor-mediated insulin, but not IGF-1, endocytosis, suggesting that pp120 phosphorylation underlies its effect on insulin endocytosis. pp120 phosphorylation also underlies its bile acid transport and tumor suppression functions. In addition to depending on the intracellular tail, the cell adhesion property of pp120 depends on Arg98 in the N-terminal IgV-like ectoplasmic domain. To investigate whether this domain mediates the effect of pp120 on insulin endocytosis, we mutated Arg98 to Ala and examined whether this mutation altered pp120 phosphorylation and its effect on ligand endocytosis in transfected NIH 3T3 cells. This mutation did not modify either pp120 phosphorylation or its effect on receptor-mediated ligand endocytosis. These findings support the hypothesis that stimulation of insulin endocytosis by pp120 is not mediated by Arg98 in the N-terminal IgV-like ectoplasmic domain of pp120.

Carcinoembryonic antigen-related cell-cell adhesion molecule C-CAM is greatly increased in serum and urine of rats with liver diseases

C-CAM (rat cell CAM/human CD66a) is ubiquitous and multifunctional. It is involved in intercellular adhesion, signal transduction and cell growth inhibition. Structurally, it is related to the carcinoembryonic antigen. In the present study serum, bile and urine of rats with liver diseases were analyzed for the presence of cell CAM. After bile duct ligation and during galactosamine (GalN) hepatitis we found that large amounts of liver membrane-bound C-CAM are secreted or shed into blood. The serum level of another liver membrane-bound protein, LI-cadherin, is not increased. It was shown that C-CAM is also present in bile fluid, and for the first time that C-CAM is present in the urine of rats with liver diseases. A particularly high concentration was measured in the urine of rats suffering from GalN hepatitis.

Demonstration of adhesion activity of the soluble Ig-domain protein C-CAM4 by attachment to the plasma membrane

The carcinoembryonic antigen (CEA) family is a large group of proteins with immunoglobulin (Ig)-like structures. The membrane-associated CEA-family proteins have been shown to mediate intercellular adhesion. In addition to these membrane-associated proteins, several secreted CEA-like proteins, such as C-CAM4, PSG1b, and PSG11s, have also been identified. The functions of these soluble proteins are not clear because they cannot support intercellular adhesion like the membrane-associated proteins can. A fundamental question important for understanding the functions of these soluble proteins is whether they can interact in a homophilic fashion as do many of their membrane-associated homologues. We found that the homophilic interactions between these soluble proteins were too weak to be detected by solution binding assays. This is not unexpected because interactions between adhesion molecules are usually transient and weak to allow for control of association and dissociation. By expressing these soluble CEA-family proteins, C-CAM4, PSG1b, and PSG11s, as membrane-anchored forms, we showed that C-CAM4 could mediate intercellular adhesion, whereas PSG1b and PSG11s, despite their 52% identity to C-CAM4, could not. These results suggest that C-CAM4, but not PSG1b and PSG11s, can probably form homodimers. Thus, these secretory CEA-family members most likely have different interaction mechanisms, i.e., C-CAM4 might function as dimers, while PSGs might function as monomers.

Extracellular nucleotide signaling in the inner ear

Extracellular nucleotides, particularly adenosine 5'-triphosphate (ATP), act as signaling molecules in the inner ear. Roles as neurotransmitters, neuromodulators, and as autocrine or paracrine humoral factors are evident. The diversity of the signaling pathways for nucleotides, which include a variety of ATP-gated ion channels (assembled from different subtypes of P2X-receptor subunit) and also different subtypes of G protein-coupled nucleotide receptors (P2Y receptors) supports a major physiological role for ATP in the regulation of hearing and balance. Almost invariably both P2X and P2Y receptor expression is apparent in the complex tissue structures associated with the inner-ear labyrinth. However P2X-receptor expression, commonly associated with fast neurotransmission, is apparent not only with the cochlear and vestibular primary afferent neurons, but also appears to mediate humoral signaling via ATP-gated ion channel localization to the endolymphatic surface of the cochlear sensory epithelium (organ of Corti). This is the site of the sound-transduction process and recent data, including both electrophysiological, imaging, and immunocytochemistry, has shown that the ATP-gated ion channels are colocalized here with the mechano-electrical transduction channels of the cochlear hair cells. In contrast to this direct action of extracellular ATP on the sound-transduction process, an indirect effect is apparent via P2Y-receptor expression, prevalent on the marginal cells of the stria vascularis, a tissue that generates the standing ionic and electrical gradients across the cochlear partition. The site of generation of these gradients, including the dark-cell epithelium of the vestibular labyrinth, may be under autocrine or paracrine regulation mediated by P2Y receptors sensitive to both purines (ATP) and pyrimidines such as UTP. There is also emerging evidence that the nucleoside adenosine, formed as a breakdown product of ATP by the action of ectonucleotidases and acting via P1 receptors, is also physiologically significant in the inner ear. P1-receptor expression (including A1, A2, and A3 subtypes) appear to have roles associated with stress, acting alongside P2Y receptors to enhance cochlear blood flow and to protect against the action of free radicals and to modulate the activity of membrane conductances. Given the positioning of a diverse range of purinergic-signaling pathways within the inner ear, elevations of nucleotides and nucleosides are clearly positioned to affect hearing and balance. Recent data clearly supports endogenous ATP- and adenosine-mediated changes in sensory transduction via a regulation of the electrochemical gradients in the cochlea, alterations in the active and passive mechanical properties of the cells of the sensory epithelium, effects on primary afferent neurons, and control of the blood supply. The field now awaits conclusive evidence linking a physiologically-induced modulation of extracellular nucleotide and nucleoside levels to altered inner ear function.

cea5, a structurally divergent member of the murine carcinoembryonic antigen gene family, is exclusively expressed during early placental development in trophoblast giant cells

The carcinoembryonic antigen (CEA) gene family encodes a large family of glycoproteins. Some are probably involved in the homeostasis/development of epithelial cells and granulocyte activation, while others e.g. the pregnancy-specific glycoproteins, are expressed in the placenta and are essential for a positive outcome of pregnancy. In this paper, we have characterized cea5, a member of the murine CEA gene family. RNase protection and in situ hybridization analyses revealed that Cea5 mRNA is exclusively synthesized in primary and secondary trophoblast giant cells of the placenta only during early stages of development. Full-length Cea5 cDNA was obtained by a reverse transcription-polymerase chain reaction using day 10.5 post-coitum placental RNA. The 1.6-kilobase pair (kb) Cea5 mRNA encodes a secreted glycoprotein with a predicted size of 30 kDa. It is composed of a leader peptide (L), one immunoglobulin (Ig) variable or N, and one Ig constant-like or A domain. This domain organization is unique within the human and murine CEA families. Two overlapping cosmid clones covering 54 kb of the cea5 gene locus were mapped. cea5 consists of three exons (L, N, A/3'-untranslated region exon) located within a 4-kb region. rnCGM2, the rat cea5 counterpart, exhibits the same restricted expression pattern. This together with their exceptional conservation within the rat and murine CEA families and their absence from the human CEA family suggests that cea5 and rnCGM2 are of functional importance for rodent placental development.