Targeted disruption of carcinoembryonic antigen-related cell adhesion molecule 1 promotes diet-induced hepatic steatosis and insulin resistance.

Carcinoembryonic antigen-related cell adhesion molecule 1 (CC1) is a cell adhesion molecule within the Ig superfamily. The Tyr-phosphorylated isoform of CC1 (CC1-L) plays an important metabolic role in the regulation of hepatic insulin clearance. In this report, we show that CC1-deficient (Cc1(-/-)) mice are prone to hepatic steatosis, as revealed by significantly elevated hepatic triglyceride and both total and esterified cholesterol levels compared with age-matched wild-type controls. Cc1(-/-) mice were also predisposed to lipid-induced hepatic steatosis and dysfunction as indicated by their greater susceptibility to store lipids and express elevated levels of enzymatic markers of liver damage after chronic feeding of a high-fat diet. Hepatic steatosis in the Cc1(-/-) mice was linked to a significant increase in the expression of key lipogenic (fatty acid synthase, acetyl CoA carboxylase) and cholesterol synthetic (3-hydroxy-3-methylglutaryl-coenzyme A reductase) enzymes under the control of sterol regulatory element binding proteins-1c and -2 transcription factors. Cc1(-/-) mice also exhibited impaired insulin clearance, glucose intolerance, liver insulin resistance, and elevated hepatic expression of the key gluconeogenic transcriptional activators peroxisome proliferator-activated receptor-gamma coactivator-1 and Forkhead box O1. Lack of CC1 also exacerbated both glucose intolerance and hepatic insulin resistance induced by high-fat feeding, but insulin clearance was not further deteriorated in the high-fat-fed Cc1(-/-) mice. In conclusion, our data indicate that CC1 is a key regulator of hepatic lipogenesis and that Cc1(-/-) mice are predisposed to liver steatosis, leading to hepatic insulin resistance and liver damage, particularly when chronically exposed to dietary fat.

GPI-anchored CEA family glycoproteins CEA and CEACAM6 mediate their biological effects through enhanced integrin alpha5beta1-fibronectin interaction.

Carcinoembryonic antigen (CEA) and CEA family member CEACAM6 are glycophosphatidyl inositol (GPI)-anchored, intercellular adhesion molecules that are up-regulated in a wide variety of human cancers, including colon, breast, and lung. When over-expressed in a number of cellular systems, these molecules are capable of inhibiting cellular differentiation and anoikis, as well as disrupting cell polarization and tissue architecture, thus increasing tumorigenicity. The present study shows that perturbation of the major fibronectin receptor, integrin alpha5beta1, underlies some of these biological effects. Using confocal microscopy and specific antibodies, CEA and CEACAM6 were demonstrated to co-cluster with integrin alpha5beta1 on the cell surface. The presence of CEA and CEACAM6 was shown to lead to an increase in the binding of the integrin alpha5beta1 receptor to its ligand fibronectin, without changing its cell surface levels, resulting in increased adhesion of CEA/CEACAM6-expressing cells to fibronectin. More tenacious binding of free fibronectin to cells led to enhanced fibronectin matrix assembly and the formation of a polymerized fibronectin "cocoon" around the cells. Disruption of this process with specific monoclonal antibodies against either fibronectin or integrin alpha5beta1 led to the restoration of cellular differentiation and anoikis in CEA/CEACAM6 producing cells.

Carcinoembryonic antigen-immunoglobulin Fc fusion protein (CEA-Fc) for identification and activation of anti-CEA immunoglobulin-T-cell receptor-modified T cells, representative of a new class of Ig fusion proteins.

Chimeric immunoglobulin-T-cell receptor (IgTCR)-modified T cells ("designer T cells") kill tumor cells based on antibody-redirected recognition of tumor-associated antigen. Anti-carcinoembryonic antigen (CEA) designer T cells have been prepared and applied in adoptive cellular immunotherapy regimens for CEA-positive cancers. A CEA-immunoglobulin Fc (CEA-Fc) fusion protein was created from the A3B3 region of CEA and the Fc portion of human IgG for the purposes of activation and detection of anti-CEA designer T cells. CEA-Fc was expressed at high yield in CHO cells and purified to homogeneity in a single step on a protein A affinity column. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis revealed that CEA-Fc formed disulfide-linked dimers with a molecular weight of about 170 kDa and a monomer size of 85kDa. The A3B3 CEA component of the CEA-Fc bound to anti-CEA monoclonal antibody MN-14, as well as to the single-chain Fv (sFv) derived from this antibody that was expressed in the IgTCR on the surface of designer T cells. The Fc portion of CEA-Fc was recognized by anti-human IgG Fc antibody and bound by human monocyte Fc receptors. CEA-Fc activated the anti-CEA designer T cells as plate-bound or monocyte-bound form but not as soluble form, as measured by CD69 expression and T-cell proliferation. Our results indicate that the CEA-Fc fusion protein can be used to detect the expression of the anti-CEA IgTCR chimeric receptors on the modified T cells, as well as to serve as an antigen to activate the anti-CEA IgTCR modified T cells. CEA-Fc is the prototype for a new class of antigen-Fc molecules that may significantly augment the analytic and therapeutic goals of adoptive designer T-cell immunotherapies.

Deregulated expression of the human tumor marker CEA and CEA family member CEACAM6 disrupts tissue architecture and blocks colonocyte differentiation.

Human carcinoembryonic antigen (CEA) and the CEA family member CEACAM6 (formerly nonspecific cross-reacting antigen [NCA]) function in vitro, at least, as homotypic intercellular adhesion molecules and, in model systems, can block the terminal differentiation and anoikis of several different cell types. We have recently demonstrated that the increased cell surface levels of CEA and CEACAM6 in purified human colonocytes from freshly excised, well to poorly differentiated colon carcinomas are inversely correlated with the degree of cellular differentiation. Thus, deregulated expression of CEA/CEACAM6 could directly contribute to colon tumorigenesis by the inhibition of terminal differentiation and anoikis. Evidence against this view includes the common observation of increased CEA/CEACAM6 expression as normal colonocytes differentiate in their migration up colonic crypt walls. We report here the direct effects of deregulated overexpression of CEA/CEACAM6, at levels observed in colorectal carcinomas, on the differentiation of two human colonic cell lines, SW-1222 and Caco-2. Stable transfectants of both of these cell lines that constitutively express 10- to 30-fold higher cell surface levels of CEA/CEACAM6 than endogenous levels failed to polarize and differentiate into glandular structures in monolayer or 3D culture or to form colonic crypts in a tissue architecture assay in nude mice. In addition, these transfectants were found to exhibit increased tumorigenicity in nude mice. These results thus support the contention that deregulated overexpression of CEA and CEACAM6 could provide a tumorigenic contribution to colon carcinogenesis.