Biosynthesis of the cancer-related sialyl-alpha 2,6-lactosaminyl epitope in colon cancer cell lines expressing beta-galactoside alpha 2,6-sialyltransferase under a constitutive promoter.
An elevation of beta-galactoside alpha 2,6-sialyltransferase (ST6Gal.I) enzyme activity and an increased alpha 2,6-sialylation of cell membranes are among the most prominent glycosylation changes associated with colon cancer; both modifications correlate with a worse prognosis. In our previous studies, we have frequently observed a discrepancy between the ST6Gal.I level within a colon cancer sample or cell line and the respective level of reactivity with the alpha 2,6-sialyl-specific lectin from Sambucus nigra (SNA). In this study, we have investigated quantitatively the biosynthesis of the sialyl-alpha 2,6-lactosaminyl epitope in two colon cancer cell types expressing the ST6Gal.I cDNA under the control of a constitutive promoter. By measuring the amount of ST6Gal.I mRNA using competitive RT-PCR, the expression of alpha 2,6-sialylated lactosaminic structures with SNA and anti-CDw75 Ig, and the presence of unsubstituted lactosaminic termini by Erythrina cristagalli lectin, we reached the following conclusions: (a) a high proportion of the cell surface lactosaminic termini remains unsubstituted, even in the presence of a very high ST6Gal.I activity. This proportion is strongly dependent on the cell type; (b) ST6Gal.I-transfected colon cancer cells do not express the CDw75 epitope; (c) the level of ST6Gal.I enzyme activity only partially correlates with the mRNA level; (d) despite the control by a constitutive promoter, the ST6Gal.I mRNA is not constantly expressed over time; and (e) a very large portion of the enzyme molecules is secreted in the extracellular milieu. These results indicate that post-transcriptional and post-translational mechanisms play a pivotal role in the control of alpha 2,6-sialylation in colon cancer cells.
Dall'Olio
F
F
Dipartimento di Patologia Sperimentale, Università di Bologna, Italy. dallolio@alma.unibo.it
Chiricolo
M
M
Mariani
E
E
Facchini
A
A
D001483:Base Sequence; D015153:Blotting, Western; D002469:Cell Separation; D003110:Colonic Neoplasms / Q000201:enzymology / Q000276:immunology* / Q000473:pathology; D017931:DNA Primers; D000939:Epitopes / Q000096:biosynthesis* / Q000276:immunology; D005434:Flow Cytometry; D006801:Humans; D011401:Promoter Regions, Genetic; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D012799:Sialyltransferases / Q000235:genetics* / Q000378:metabolism; D014407:Tumor Cells, Cultured; D000094802:beta-D-Galactoside alpha 2-6-Sialyltransferase
D017931:DNA Primers; D000939:Epitopes; D012333:RNA, Messenger; D012799:Sialyltransferases; D000094802:beta-D-Galactoside alpha 2-6-Sialyltransferase