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

Tumor intrinsic immunity related proteins may be novel tumor suppressors in some types of cancer

Immune checkpoint blockade therapy (ICBT) can unleash T-cell responses against cancer. However, only a small fraction of patients exhibited responses to ICBT. The role of immune checkpoints in cancer cells is not well understood. In this study, we analyzed T-cell coinhibitory/costimulatory genes across more than 1100 samples of the Cancer Cell Line Encyclopedia (CCLE). Nearly 90% of such genes were not expressed or had low expression across the CCLE cancer cell lines. Cell line screening showed the enrichment of cancer cells deprived of the expression of CD27, CEACAM1, CTLA4, LRIG1, PDCD1LG2, or TNFRSF18, suggesting their role as tumor suppressor. The metagene expression signature derived from these six genes - Immu6Metagene was associated with prolonged survival phenotypes. A common set of five oncogenic pathways were significantly inhibited in different types of tumors of the cancer patients with good survival outcome and high Immu6Metagene signature expression. These pathways were TGF-β signaling, angiogenesis, EMT, hypoxia and mitotic process. Our study showed that oncoimmunology related molecules especially the six genes of the Immu6Metagene signature may play the tumor suppressor role in certain cancers. Therefore, the ICBT targeting them should be considered in such context to improve the efficacy.

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.

Inhibition of cell invasion and migration by CEACAM1-4S in breast cancer

Carcinoembryonic antigen-related cell adhesion molecule 1 (CEACAM1), a cell-cell adhesion molecule, has been revealed to perform an important role in tumor progression. Although there are a number of studies on CEACAM1 in patients with breast cancer, there is limited information on the roles of CEACAM1 in breast cancer metastasis. The present study aimed to identify whether CEACAM1 is involved in breast cancer development and to investigate the underlying mechanisms. First, the expression of CEACAM1 was observed in patients with breast cancer, and the association between CEACAM1 expression levels and migration and invasion of breast cancer cells was analyzed. As there are 12 isoforms of CEACAM1, of which CEACAM1-4S dominates in the human breast epithelium, subsequent study focused on CEACAM1-4S as a representative of all the isoforms. Results of the present study demonstrated that CEACAM1-4S suppresses breast cancer cell invasion and migration in a manner that is dependent on the balance between matrix metalloproteinase 2/tissue inhibitor of metalloproteinase 2 and E-/N-cadherin expression. In addition, CEACAM1-4S was likely to cause reversal of epithelial-mesenchymal transition of breast cancer cells through repressing Smad2 and signal transducer and phosphorylation of activator of transcription 3. In conclusion, the present study demonstrated that CEACAM1-4S performs an inhibitory role in breast cancer metastasis, and restoring CEACAM1-4S expression may provide a novel strategy for therapy of patients with metastatic breast cancer.

The role of CEA-related cell adhesion molecule-1 (CEACAM1) in vascular homeostasis

Carcinoembryonic antigen (CEA)-related cell adhesion molecules belong to the immunoglobulin superfamily, are expressed in a broad spectrum of tissues and cell types and exert context-dependent activating as well as inhibitory effects. Among these molecules, the CEA-related cell adhesion molecule-1 (CEACAM1) is a transmembrane molecule with an extracellular, a transmembrane and a cytoplasmic domain. The latter contains immunoreceptor tyrosine-based inhibitory motifs and functions as a signaling molecule. CEACAM1 can form homo- and heterodimers which is relevant for its signaling activities. CEACAM1 acts as co-receptor that modulates the activity of different receptor types including VEGFR-2, and B and T cell receptors. CEACAM1 is expressed in endothelial cells, in pericytes of developing and newly formed immature blood vessels and in angiogenically activated adult vessels, e.g., tumor blood vessels. However, it is either undetectable or only weakly expressed in quiescent blood vessels. Recent studies indicated that CEACAM1 is involved in the regulation of the endothelial barrier function. In CEACAM1 ^-/- mice, increased vascular permeability and development of small atherosclerotic lesions was observed in the aortae. CEACAM1 is also detectable in activated lymphatic endothelial cells and plays a role in tumor lymphangiogenesis. This review summarizes the vascular effects of CEACAM1 and focuses on its role in vascular morphogenesis and endothelial barrier regulation.

High-fat diet amplifies renal renin angiotensin system expression, blood pressure elevation, and renal dysfunction caused by Ceacam1 null deletion

Carcinoembryonic antigen-related cell adhesion molecule 1 (CEACAMl), a substrate of the insulin receptor tyrosine kinase, regulates insulin action by promoting insulin clearance. Global null mutation of Ceacam1 gene (Cc1(-/-)) results in features of the metabolic syndrome, including insulin resistance, hyperinsulinemia, visceral adiposity, elevated blood pressure, and albuminuria. It also causes activation of the renal renin-angiotensin system (RAS). In the current study, we tested the hypothesis that high-fat diet enhances the expression of RAS components. Three-month-old wild-type (Cc1(+/+)) and Cc1(-/-) mice were fed either a regular or a high-fat diet for 8 wk. At baseline under regular feeding conditions, Cc1(-/-) mice exhibited higher blood pressure, urine albumin-to-creatinine ratio (UACR), and renal expression of angiotensinogen, renin/prorenin, angiotensin-converting enzyme, (pro)renin receptor, angiotensin subtype AT1 receptor, angiotensin II, and elevated PI3K phosphorylation, as detected by p85α (Tyr(508)) immunostaining, inflammatory response, and the expression of collagen I and collagen III. In Cc1(+/+) mice, high-fat diet increased blood pressure, UACR, the expression of angiotensin-converting enzyme and angiotensin II, PI3K phosphorylation, inflammatory response, and the expression of collagen I and collagen III. In Cc1(-/-) mice, high-fat intake further amplified these parameters. Immunohistochemical staining showed increased p-PI3K p85α (Tyr(508)) expression in renal glomeruli, proximal, distal, and collecting tubules of Cc1(-/-) mice fed a high-fat diet. Together, this demonstrates that high-fat diet amplifies the permissive effect of Ceacam1 deletion on renal expression of all RAS components, PI3K phosphorylation, inflammation, and fibrosis.

Down-regulation of CEACAM1 in breast cancer

Carcinoembryonic antigen-related adhesion molecule 1 (CEACAM1) is a type 1 transmembrane glycoprotein belonging to the CEA family, which has been found to exist as either soluble forms in body fluids or membrane-bound forms on the cell surface. Aberrant CEACAM1 expression is associated with tumor progression and has been found in a variety of human malignancies. Increasing interest has been devoted to the expression of CEACAM1 in breast cancer, but most of these findings are contradictory. The aim of this study was to investigate CEACAM1 expression in breast cancer in greater detail. Using immunohistochemical staining, we found that CEACAM1 expression was reduced or lost in breast cancer tissues compared with noncancerous breast tissues. In addition, soluble CEACAM1 levels in the culture medium of breast cancer cell lines were significantly lower than those in a nontumorigenic breast epithelial cell line. Immunofluorescence analysis consistently showed that breast cancer cell lines have relatively low expression of membrane-bound CEACAM1. Furthermore, CEACAM1 mRNA and protein expression levels were down-regulated in breast cancer cell lines as measured using real-time reverse transcriptase-polymerase chain reaction and western blot analysis, respectively. Taken together, our results demonstrate a systematic down-regulation of CEACAM1 in breast cancer and suggest that a strategy to restore CEACAM1 expression may be helpful for the treatment of breast cancer.

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

The carcinoembryonic antigen (CEA) gene family belongs to the immunoglobulin (Ig) superfamily and codes for a vast number of glycoproteins that differ greatly both in amino acid composition and function. The CEA family is divided into two groups, the carcinoembryonic antigen-related cell adhesion molecules (CEACAMs) and the pregnancy-specific glycoproteins. The CEA family members are implicated in pleiotropic (patho)physiological functions including cell-cell adhesion, pregnancy, immunity, neovascularization, regulation of insulin homeostasis, and carcinogenesis. In general, the CEA-encoded proteins are composed of an extracellular region with Ig variable and constant-like domains and a cytoplasmic region containing signaling motifs. Of particular interest, the well-studied human and mouse CEA genes are arranged in clusters in a single chromosome. Taking into account this characteristic, we made an effort to reconstruct the evolutionary history of the CEA gene family. Toward this end, the publicly available genomes were searched extensively for CEA homologs. The domain organization of the retrieved protein sequences was analyzed, and, subsequently, comprehensive phylogenetic analyses of the entire length CEA homologous proteins were performed. A series of evolutionarily conserved amino acid residues, functionally important, were identified. The relative positioning of these residues on the modeled tertiary structure of novel CEA protein domains revealed that they are, also, spatially conserved. Furthermore, the chromosomal arrangement of CEA genes was examined, and it was found that the CEA genes are preserved in terms of position, transcriptional orientation, and number in all species under investigation.

CEA-Related CAMs

The carcinoembryonic antigen (CEA) family comprises a large number of cellular surface molecules, the CEA-related cell adhesion molecules (CEACAMs), which belong to the Ig superfamily. CEACAMs exhibit a complex expression pattern in normal and malignant tissues. The majority of the CEACAMs are cellular adhesion molecules that are involved in a great variety of distinct cellular processes, for example in the integration of cellular responses through homo- and heterophilic adhesion and interaction with a broad selection of signal regulatory proteins, i.e., integrins or cytoskeletal components and tyrosine kinases. Moreover, expression of CEACAMs affects tumor growth, angiogenesis, cellular differentiation, immune responses, and they serve as receptors for commensal and pathogenic microbes. Recently, new insights into CEACAM structure and function became available, providing further elucidation of their kaleidoscopic functions.

The transmembrane domain of CEACAM1-4S is a determinant of anchorage independent growth and tumorigenicity

CEACAM1 is a multifunctional Ig-like cell adhesion molecule expressed by epithelial cells in many organs. CEACAM1-4L and CEACAM1-4S, two isoforms produced by differential splicing, are predominant in rat liver. Previous work has shown that downregulation of both isoforms occurs in rat hepatocellular carcinomas. Here, we have isolated an anchorage dependent clone, designated 253T-NT that does not express detectable levels of CEACAM1. Stable transfection of 253-NT cells with a wild type CEACAM1-4S expression vector induced an anchorage independent growth in vitro and a tumorigenic phenotype in vivo. These phenotypes were used as quantifiable end points to examine the functionality of the CEACAM1-4S transmembrane domain. Examination of the CEACAM1 transmembrane domain showed N-terminal GXXXG dimerization sequences and C-terminal tyrosine residues shown in related studies to stabilize transmembrane domain helix-helix interactions. To examine the effects of transmembrane domain mutations, 253-NT cells were transfected with transmembrane domain mutants carrying glycine to leucine or tyrosine to valine substitutions. Results showed that mutation of transmembrane tyrosine residues greatly enhanced growth in vitro and in vivo. Mutation of transmembrane dimerization motifs, in contrast, significantly reduced anchorage independent growth and tumorigenicity. 253-NT cells expressing CEACAM1-4S with both glycine to leucine and tyrosine to valine mutations displayed the growth-enhanced phenotype of tyrosine mutants. The dramatic effect of transmembrane domain mutations constitutes strong evidence that the transmembrane domain is an important determinant of CEACAM1-4S functionality and most likely by other proteins with transmembrane domains containing dimerization sequences and/or C-terminal tyrosine residues.

Membrane trafficking of AQP5 and cAMP dependent phosphorylation in bronchial epithelium

Phosphorylation pathway has been identified as an important step in membrane trafficking for AQP5. We generated stably transfected BEAS-2B human bronchial epithelial cells with various over-expression constructs on permeable support. In stable cells with wild-type AQP5 and S156A (AQP5 mutant targeting PKA consensus sequence), AQP5 expression was predominantly polarized to the apical membrane, whereas stable cells with N185D (AQP5 mutant targeting second NPA motif), mainly localized to the cytoplasm. Treatment with H89 and/or chlorophenylthio-cAMP (cpt-cAMP) did not affect membrane expression of AQP5 in any of three stable cells. In cells with wild-type AQP5 and N185D, AQP5s were phosphorylated by PKA, while phosphorylation of AQP5 was not detected in cells with S156A. These results indicate that, in AQP5, serine156 may be phosphorylated by PKA, but membrane expression of AQP5 may not be regulated by PKA phosphorylation. We conclude that AQP5 membrane targeting can include more than one mechanism besides cAMP dependent phosphorylation.

hCEACAM1-4L downregulates hDAF-associated signalling after being recognized by the Dr adhesin of diffusely adhering Escherichia coli

Human decay accelerating factor (hDAF, CD55) and members of the carcinoembryonic-antigen-related cell-adhesion molecules (hCEACAMs) family are recognized as receptors by Gram-negative, diffusely adhering Escherichia coli (DAEC) strains expressing Afa/Dr adhesins. We report here that hCEACAM1-4L has a key function in downregulating the protein tyrosine Src kinase associated with hDAF signalling. After infecting HeLa epithelial cells stably transfected with hCEACAM1-4L cDNA with Dr adhesin-positive E. coli, the amount of the pTyr(416)-active form of the Src protein decreased, whereas that of the pTyr(527)-inactive form of Src protein did not increase. This downregulation of the Src protein implies that part of the hCEACAM1-4L protein had been translocated into lipid rafts, the protein was phosphorylated at Tyr residues in the cytoplasmic domain, and it was physically associated with the protein tyrosine phosphatase, SHP-2. Finally, we found that the hCEACAM1-4L-associated SHP-2 was not phosphorylated and lacked phosphatase activity, suggesting that the downregulation of Src protein associated with hDAF signalling results from the absence of dephosphorylation of the pTyr(527)-inactive form necessary for Src kinase activation.

CEACAM1 impedes thyroid cancer growth but promotes invasiveness: a putative mechanism for early metastases

CEACAM1, also known as biliary glycoprotein (BGP), CD66a, pp120 and C-CAM1, is a member of the CEA immunoglobulin superfamily. CEACAM1 is a putative tumor suppressor based on diminished expression in some solid neoplasms such as colorectal carcinoma. However, CEACAM1 is overexpressed in some tumors such as non-small cell lung cancer. To clarify the mechanism of action of this cell adhesion molecule, we studied thyroid carcinoma that has a spectrum of morphologies and variable behavior allowing separation of proliferation from invasion and metastasis. CEACAM1 is expressed in thyroid carcinoma cell lines derived from tumors that exhibit aggressive behavior. Introduction of CEACAM1 into endogenously deficient WRO cells resulted in reduced cell cycle progression associated with p21 upregulation and diminished Rb phosphorylation. Forced CEACAM1 expression enhanced cell-matrix adhesion and migration and promoted tumor invasiveness. Conversely, small interfering RNA (siRNA)-mediated downregulation of CEACAM1 expression in MRO cells accelerated cell cycle progression and significantly enhanced tumor size in xenografted mice. CEACAM1 is not appreciably expressed in normal thyroid tissue or benign thyroid tumors. In a human thyroid tissue array, CEACAM1 reactivity was associated with metastatic spread but not with increased tumor size. These findings identify CEACAM1 as a unique mediator that restricts tumor growth whereas increasing metastatic potential. Our data highlight a complex repertoire of actions providing a putative mechanism underlying the spectrum of biologic behaviors associated with thyroid cancer.

CEACAM1 in cervical cancer and precursor lesions: association with human papillomavirus infection

Carcinoembryonic antigen-related cell adhesion molecule 1 (CEACAM1) is an adhesion molecule expressed in a wide variety of tissues including epithelial cells, leukocytes, and tumors that may establish both homotypic and heterotypic interactions. The aim of this work was to study the protein expression pattern of CEACAM1 in cervical cancer and precursor lesions in the context of human papillomavirus (HPV) infection. We used immunohistochemistry to analyze CEACAM1 expression in formalin-fixed, paraffin-embedded cervical tissues from 15 healthy women, 15 patients with low-grade squamous intraepithelial lesions (SIL), 15 patients with high-grade SIL, and 15 patients with squamous carcinomas. HPV types were identified by PCR. CEACAM1 was either undetectable (13/15) or low (2/15) in normal cervical tissues. By contrast, CEACAM1 expression was increased in high-grade SIL (10 samples staining intermediate/high and 4 samples staining low) as compared with low-grade SIL with undetectable (n=3) or low (n=12) expression. CEACAM1 expression was undetectable or low in cervical carcinoma. Our results suggest that CEACAM1 may be an interesting progression marker in SIL and cervical cancer, in particular due to reported immunoregulatory properties.

Deletion of the carcinoembryonic antigen-related cell adhesion molecule 1 (Ceacam1) gene contributes to colon tumor progression in a murine model of carcinogenesis

Carcinoembryonic antigen-related cell adhesion molecule 1 (CEACAM1) is a glycoprotein that is part of the carcinoembryonic antigen and the immunoglobulin superfamilies. We have shown that it functions as a tumor suppressor and that this function depends upon the presence of the longer CEACAM1 cytoplasmic domain. In this report, we describe the generation of a Ceacam1-/- mouse. The Ceacam1-/- colon exhibits increased in vivo proliferation relative to the wild-type counterpart with a corresponding decreased expression of the p21(Cip1) and p27(Kip1) Cyclin D kinase inhibitors. The colonic villi undergo decreased apoptosis. Out of 35 litters of mice, no spontaneous tumors in any tissues normally expressing CEACAM1 were found over the lifespan of the animals, suggesting that CEACAM1 may not be involved in initiation of tumor development. However, when mice are treated with azoxymethane to induce colonic tumors, we find that Ceacam1-/- mice developed a significantly greater number of tumors than their littermate controls. Moreover, the tumor size was greater in the knockout mice relative to that in the wild-type mice. These results indicate that deletion of CEACAM1 favors progression of colon tumorigenesis.

Carcinoembryonic Antigen–Related Cell Adhesion Molecule 1a-4L Suppression of Rat Hepatocellular Carcinomas

Carcinoembryonic antigen (CEA)–related cell adhesion molecule 1 (CEACAM1) is a member of the CEA family of immunoglobulin-like adhesion molecules with two major splice variants, CEACAM1a-4L and CEACAM1b-4S, differing in the length of their COOH-terminal cytoplasmic tail. Both forms are down-regulated in prostate and liver carcinomas relative to normal tissues. We have previously shown in a nude mouse xenograft model that restoration of CEACAM1a-4L expression in human prostate carcinoma cells (PC-3) suppresses tumorigenicity, an effect observed with carcinomas from several other tissues but never established for hepatocellular carcinomas. In this report, we have examined the effect of CEACAM1a-4L on tumorigenicity of 1682A, a rat hepatocellular carcinoma that grows on the omentum when injected into the peritoneal cavity. Results show that restoration of CEACAM1a-4L expression at levels 13- and 0.45-fold compared with negative controls or normal hepatocytes, respectively, completely suppressed the formation of 1682A tumor nodules on the omentum at 3 weeks after injection. In contrast, 1682A cells infected with CEACAM1b-4S or an empty retroviral vector formed multiple clusters of tumor nodules. Although tumor nodules of 1682A cells positive and negative for CEACAM1a-4L did not display significant differences in histologic organization, aggregates formed in vitro by 1682A-L were smaller in size and displayed enlarged intercellular spaces relative to their 1682A-V counterparts. Restoration of CEACAM1a-4L expression did not elevate levels of apoptosis but seemed to cause an increase in the length of G1. This is the first demonstration of CEACAM1a-4L–induced tumor suppression in liver carcinomas using a quantifiable i.p. syngeneic transplantation model.

Identification of a novel group of evolutionarily conserved members within the rapidly diverging murine Cea family

The carcinoembryonic antigen (CEA) family comprises a still actively evolving populous group of proteins that are involved in controlling tissue homeostasis, immune responses, and host/pathogen interactions. The genes identified to date in rodents and primates exhibit low sequence similarity and an extremely variable domain composition. Among the 22 murine Cea-related genes, only for Ceacam1 has an ortholog been assigned. To identify all CEA-related genes in mouse, rat, and human we undertook genome-wide analyses. Eight of 9 new expressible genes (Ceacam12-Ceacam20) could be located within the approximately 6.5-Mb murine Cea locus. Five of the genes were rodent-specific (Ceacam12-Ceacam15 and Ceacam17). Surprisingly, for the remaining 4 (Ceacam16 and Ceacam18-Ceacam20) orthologs could be detected in all three genomes at syntenic locations. Gene-specific reverse transcription/PCR analyses of total RNA from 31 murine adult, placental, and embryonic tissues as well as tumors revealed very distinct expression patterns, suggesting diversified functions within the CEA family.

Pathogenesis of Afa/Dr diffusely adhering Escherichia coli

Over the last few years, dramatic increases in our knowledge about diffusely adhering Escherichia coli (DAEC) pathogenesis have taken place. The typical class of DAEC includes E. coli strains harboring AfaE-I, AfaE-II, AfaE-III, AfaE-V, Dr, Dr-II, F1845, and NFA-I adhesins (Afa/Dr DAEC); these strains (i) have an identical genetic organization and (ii) allow binding to human decay-accelerating factor (DAF) (Afa/Dr(DAF) subclass) or carcinoembryonic antigen (CEA) (Afa/Dr(CEA) subclass). The atypical class of DAEC includes two subclasses of strains; the atypical subclass 1 includes E. coli strains that express AfaE-VII, AfaE-VIII, AAF-I, AAF-II, and AAF-III adhesins, which (i) have an identical genetic organization and (ii) do not bind to human DAF, and the atypical subclass 2 includes E. coli strains that harbor Afa/Dr adhesins or others adhesins promoting diffuse adhesion, together with pathogenicity islands such as the LEE pathogenicity island (DA-EPEC). In this review, the focus is on Afa/Dr DAEC strains that have been found to be associated with urinary tract infections and with enteric infection. The review aims to provide a broad overview and update of the virulence aspects of these intriguing pathogens. Epidemiological studies, diagnostic techniques, characteristic molecular features of Afa/Dr operons, and the respective role of Afa/Dr adhesins and invasins in pathogenesis are described. Following the recognition of membrane-bound receptors, including type IV collagen, DAF, CEACAM1, CEA, and CEACAM6, by Afa/Dr adhesins, activation of signal transduction pathways leads to structural and functional injuries at brush border and junctional domains and to proinflammatory responses in polarized intestinal cells. In addition, uropathogenic Afa/Dr DAEC strains, following recognition of beta(1) integrin as a receptor, enter epithelial cells by a zipper-like, raft- and microtubule-dependent mechanism. Finally, the presence of other, unknown virulence factors and the way that an Afa/Dr DAEC strain emerges from the human intestinal microbiota as a "silent pathogen" are discussed.

CEACAM1 modulates epidermal growth factor receptor--mediated cell proliferation

Phosphorylation of the cell adhesion protein CEACAM1 increases insulin sensitivity and decreases insulin-dependent mitogenesis in vivo. Here we show that CEACAM1 is a substrate of the EGFR and that upon being phosphorylated, CEACAM1 reduces EGFR-mediated growth of transfected Cos-7 and MCF-7 cells in response to EGF. Using transgenic mice overexpressing a phosphorylation-defective CEACAM1 mutant in liver (L-SACC1), we show that the effect of CEACAM1 on EGF-dependent cell proliferation is mediated by its ability to bind to and sequester Shc, thus uncoupling EGFR signaling from the ras/MAPK pathway. In L-SACC1 mice, we also show that impaired CEACAM1 phosphorylation leads to ligand-independent increase of EGFR-mediated cell proliferation. This appears to be secondary to visceral obesity and the metabolic syndrome, with increased levels of output of free fatty acids and heparin-binding EGF-like growth factor from the adipose tissue of the mice. Thus, L-SACC1 mice provide a model for the mechanistic link between increased cell proliferation in states of impaired metabolism and visceral obesity.

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.

Inhibition of prostate tumor growth by overexpression of NudC, a microtubule motor-associated protein

Microtubules play a central role in coordinating various cellular functions that are orchestrated by their interaction with molecular motors. Anticancer drugs that target microtubule dynamics have been shown to be effective in cancer treatment. However, the effect of microtubule motor-associated molecules on cancer cell proliferation is not clear. Here, we investigated the role of NudC, a nuclear movement protein associated with the microtubule motor dynein, on prostate tumorigenesis. Recombinant adenovirus expressing NudC (Ad-NudC) was used to examine the effects of NudC on the tumorigenicity of prostate cancer cells. Expression of NudC in LNCaP cells inhibited their anchorage-independent growth in a soft agar colony assay. Expression of NudC in DU145 or PC-3 cells inhibited tumor growth in a subcutaneous xenograft model. At the cellular level, expression of NudC in DU145 and PC-3 cells inhibited cell proliferation at 48 h after Ad-NudC infection. FACS analysis of cell cycle distribution showed that 50-60% of Ad-NudC-infected PC-3 cells have a G2/M-phase DNA content compared to about 16-19% in Ad-Luciferase (Ad-Luc)-infected control cells, suggesting that NudC overexpression resulted in aberrant cell cycle progression. Immunofluorescence microscopy revealed a significant increase in cells with a single enlarged nucleus and cells exhibiting multiple nuclei, along with a concomitant increase in cell size in Ad-NudC-infected cells. These results suggest that NudC overexpression led to a block in cell division of prostate cancer cells, and that Ad-NudC may provide a new anticancer drug approach targeting the function of a microtubule motor-associated protein.

Role for NudC, a dynein-associated nuclear movement protein, in mitosis and cytokinesis

NudC, a nuclear movement protein that associates with dynein, was originally cloned as a mitogen-inducible early growth response gene. NudC forms a biochemical complex with components of the dynein/dynactin complex and is suggested to play a role in translocation of nuclei in proliferating neuronal progenitors as well as in migrating neurons in culture. Here, we show that NudC plays multiple roles in mitosis and cytokinesis in cultured mammalian cells. Altering NudC levels by either small interfering RNA-mediated gene silencing or adenovirus-mediated overexpression resulted in multinucleated cells and cells with persistent intercellular connections and disorganized midzone and midbody matrix. These phenotypes suggest a failure in cytokinesis in NudC altered cells. Further, a key mitotic enzyme, polo-like kinase, is mislocalized from the centrosomes and the midbody in NudC altered cells. Gene silencing of nud-1, the Caenorhabditis elegans ortholog of NudC, led to a loss of midzone microtubules and the rapid regression of the cleavage furrow, which resulted in one-celled embryos containing two nuclei. The loss of midzone microtubule organization owing to silencing of the NudC/nud-1 gene in two systems, coupled with the loss of Plk1 from mitotic structures in mammalian cells, provide clues to the cytokinesis defect and the multinucleation phenotype. Our findings suggest that NudC functions in mitosis and cytokinesis, in part by regulating microtubule organization at the midzone and midbody.

The role of putative phosphorylation sites in the targeting and shuttling of the aquaporin-2 water channel

In renal collecting ducts, a vasopressin-induced cAMP increase results in the phosphorylation of aquaporin-2 (AQP2) water channels at Ser-256 and its redistribution from intracellular vesicles to the apical membrane. Hormones that activate protein kinase C (PKC) proteins counteract this process. To determine the role of the putative kinase sites in the trafficking and hormonal regulation of human AQP2, three putative casein kinase II (Ser-148, Ser-229, Thr-244), one PKC (Ser-231), and one protein kinase A (Ser-256) site were altered to mimic a constitutively non-phosphorylated/phosphorylated state and were expressed in Madin-Darby canine kidney cells. Except for Ser-256 mutants, seven correctly folded AQP2 kinase mutants trafficked as wild-type AQP2 to the apical membrane via forskolin-sensitive intracellular vesicles. With or without forskolin, AQP2-Ser-256A was localized in intracellular vesicles, whereas AQP2-S256D was localized in the apical membrane. Phorbol 12-myristate 13-acetate-induced PKC activation following forskolin treatment resulted in vesicular distribution of all AQP2 kinase mutants, while all were still phosphorylated at Ser-256. Our data indicate that in collecting duct cells, AQP2 trafficking to vasopressin-sensitive vesicles is phosphorylation-independent, that phosphorylation of Ser-256 is necessary and sufficient for expression of AQP2 in the apical membrane, and that PMA-induced PKC-mediated endocytosis of AQP2 is independent of the AQP2 phosphorylation state.

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.

Regulation of insulin action by CEACAM1

Activation of the tyrosine kinase of the insulin receptor by insulin binding initiates a cascade of signaling pathways that mediates the metabolic and growth-promoting effects of insulin. Insulin action is regulated by the amount of circulating insulin, which is, in turn, partially regulated by insulin clearance in liver. Receptor-mediated insulin endocytosis followed by degradation mediates insulin clearance. Earlier studies in transfected cells suggested that the carcinoembryonic antigen-related cell adhesion molecule 1 (CEACAM1), a substrate of the insulin receptor in liver, upregulates receptor-mediated insulin endocytosis and degradation in a phosphorylation-dependent manner. To test this hypothesis, a transgenic mouse, L-SACC1, overexpressing a dominant-negative phosphorylation-defective S503A CEACAM1 mutant in liver was established. The transgenic mouse demonstrated that CEACAM1 increases insulin clearance to maintain insulin sensitivity. Because insulin resistance is the hallmark of type 2 diabetes, understanding the mechanism of CEACAM1 regulation of insulin clearance and action might lead to novel therapeutic strategies against this disease.