Carcinoembryonic antigen is a sialyl Lewis x/a carrier and an E­selectin ligand in non­small cell lung cancer.

The formation of distant metastasis resulting from vascular dissemination is one of the leading causes of mortality in non­small cell lung cancer (NSCLC). This metastatic dissemination initiates with the adhesion of circulating cancer cells to the endothelium. The minimal requirement for the binding of leukocytes to endothelial E­selectins and subsequent transmigration is the epitope of the fucosylated glycan, sialyl Lewis x (sLex), attached to specific cell surface glycoproteins. sLex and its isomer sialyl Lewis a (sLea) have been described in NSCLC, but their functional role in cancer cell adhesion to endothelium is still poorly understood. In this study, it was hypothesised that, similarly to leukocytes, sLe glycans play a role in NSCLC cell adhesion to E­selectins. To assess this, paired tumour and normal lung tissue samples from 18 NSCLC patients were analyzed. Immunoblotting and immunohistochemistry assays demonstrated that tumour tissues exhibited significantly stronger reactivity with anti­sLex/sLea antibody and E­selectin chimera than normal tissues (2.2­ and 1.8­fold higher, respectively), as well as a higher immunoreactive score. High sLex/sLea expression was associated with bone metastasis. The overall α1,3­fucosyltransferase (FUT) activity was increased in tumour tissues, along with the mRNA levels of FUT3, FUT6 and FUT7, whereas FUT4 mRNA expression was decreased. The expression of E­selectin ligands exhibited a weak but significant correlation with the FUT3/FUT4 and FUT7/FUT4 ratios. Additionally, carcinoembryonic antigen (CEA) was identified in only 8 of the 18 tumour tissues; CEA­positive tissues exhibited significantly increased sLex/sLea expression. Tumour tissue areas expressing CEA also expressed sLex/sLea and showed reactivity to E­selectin. Blot rolling assays further demonstrated that CEA immunoprecipitates exhibited sustained adhesive interactions with E­selectin­expressing cells, suggesting CEA acts as a functional protein scaffold for E­selectin ligands in NSCLC. In conclusion, this work provides the first demonstration that sLex/sLea are increased in primary NSCLC due to increased α1,3­FUT activity. sLex/sLea is carried by CEA and confers the ability for NSCLC cells to bind E­selectins, and is potentially associated with bone metastasis. This study contributes to identifying potential future diagnostic/prognostic biomarkers and therapeutic targets for lung cancer.

Glycosylation as a Main Regulator of Growth and Death Factor Receptors Signaling.

Glycosylation is a very frequent and functionally important post-translational protein modification that undergoes profound changes in cancer. Growth and death factor receptors and plasma membrane glycoproteins, which upon activation by extracellular ligands trigger a signal transduction cascade, are targets of several molecular anti-cancer drugs. In this review, we provide a thorough picture of the mechanisms bywhich glycosylation affects the activity of growth and death factor receptors in normal and pathological conditions. Glycosylation affects receptor activity through three non-mutually exclusive basic mechanisms: (1) by directly regulating intracellular transport, ligand binding, oligomerization and signaling of receptors; (2) through the binding of receptor carbohydrate structures to galectins, forming a lattice thatregulates receptor turnover on the plasma membrane; and (3) by receptor interaction with gangliosides inside membrane microdomains. Some carbohydrate chains, for example core fucose and ß1,6-branching, exert a stimulatory effect on all receptors, while other structures exert opposite effects on different receptors or in different cellular contexts. In light of the crucial role played by glycosylation in the regulation of receptor activity, the development of next-generation drugs targeting glyco-epitopes of growth factor receptors should be considered a therapeutically interesting goal.