Biosynthesis and glycosylation of the carcinoembryonic antigen

Site-Specific N-Linked Glycosylation Analysis of Human Carcinoembryonic Antigen by Sheathless Capillary Electrophoresis-Tandem Mass Spectrometry

With 28 potential N-glycosylation sites, human carcinoembryonic antigen (CEA) bears an extreme amount of N-linked glycosylation, and approximately 60% of its molecular mass can be attributed to its carbohydrates. CEA is often overexpressed and released by many solid tumors, including colorectal carcinomas. CEA displays an impressive heterogeneity and variability in sugar content; however, site-specific distribution of carbohydrate structures has not been reported so far. The present study investigated CEA samples purified from human colon carcinoma and human liver metastases and enabled the characterization of 21 out of 28 potential N-glycosylation sites with respect to their occupancy. The coverage was achieved by a multienzymatic digestion approach with specific enzymes, such as trypsin, endoproteinase Glu-C, and the nonspecific enzyme, Pronase, followed by analysis using sheathless CE-MS/MS. In total, 893 different N-glycopeptides and 128 unique N-glycan compositions were identified. Overall, a great heterogeneity was found both within (micro) and in between (macro) individual N-glycosylation sites. Moreover, notable differences were found on certain N-glycosylation sites between primary adenocarcinoma and metastatic tumor in regard to branching, bisection, sialylation, and fucosylation. Those features, if further investigated in a targeted manner, may pave the way toward improved diagnostics and monitoring of colorectal cancer progression and recurrence. Raw mass spectrometric data and Skyline processed data files that support the findings of this study are available in the MassIVE repository with the identifier MSV000086774 [DOI: 10.25345/C5Z50X].

The influence of metastatic site on the expression of CEA and cellular localization of β-catenin in colorectal cancer

BACKGROUND AND AIM

The usefulness of carcinoembryonic antigen (CEA) in the diagnosis and prognosis of colorectal cancer (CRC) is unclear. The aim was to analyze changes in the expression of CEA during CRC progression and metastasis, so as to determine the influence of tumor metastatic organ on the CEA expression by CRC cells.

METHODS

The human biopsies of adenocarcinomas in colon and CRC liver and lung metastases were analyzed by immunohistochemistry for the expression of CEA. Expression of E-cadherin and β-catenin was also analyzed to localize the CRC neoplastic glands in metastatic tissues.

RESULTS

The CRC neoplastic glands in colon and liver expressed significantly higher amount of CEA compared with crypts in normal colon. In contrast, CRC neoplastic glands formed in lung expressed low CEA level. However, CEA expression was high in areas of tumor necrosis in lung. E-cadherin and β-catenin were cell membrane-bound in normal crypts and CRC neoplastic glands in colon and liver. Although these two proteins were also cell membrane-bound in a majority of CRC neoplastic glands in lungs, a significant proportion of these expressed β-catenin in the nucleus, which lacked either E-cadherin or β-catenin at the cell membrane.

CONCLUSION

Our findings indicate that lung microenvironment is unique in that it suppresses the expression of CEA by CRC cells forming neoplastic glands. In addition, lung microenvironment promotes nuclear localization of β-catenin, suggesting that the Wnt signaling pathway is relatively active highly in CRC metastasized to lung, when compared with liver or colon.

Xenotransplantation in immunosuppressed nude mice of human solid tumors and acute leukemias directly from patients or in vitro cell lines

Athymic nude (nu/nu) mice are widely employed for the heterotransplantation of human tumor cell lines established in vitro and tumor cells directly grafted from patients. By contrast, hemopoietic malignancies have consistently proved difficult to transplant and well-characterized human leukemias suitable for studies in nude mice are scarce. We report here our experience with subcutaneous xenotransplantation of human neoplastic cells into nu/nu mice immunosuppressed through sublethal irradiation and splenectomy (SI-nu/nu) and with an additional injection of anti-Asialo-GM1 antibodies (SIA-nu/nu) in order to eliminate natural killer activity. Thirteen out of 16 continuous cell lines established in vitro from solid tumors and 7 out of 14 human tumors obtained from fragments of surgical specimens formed a progressively growing tumor in SI-nu/nu mice. Six out of 8 in vitro established human leukemic cell lines and 5 out of 18 neoplastic hematopoietic cells directly xenotransplanted from the patient grew SIA-nu/nu mice. When the membrane and chromosome markers of neoplastic cells that grew into the mice were evaluated, only marginal differences with those of the original tumors were found. In addition, when interfering factors alter the histological aspect of the primary tumor, xenotransplantation may also be of some help in histological diagnosis. By using SI- and SIA-nu/nu mice, it is thus possible to build up several new in vivo experimental systems with fresh human tumors that may be of value in studying the efficacy of differentiation factors and immunological maneuvers on the in vivo growth of human tumors.