ObjectiveTo establish whether the prevalence of positive reverse transcriptase-polymerase chain reaction (RT-PCR) results decreased during the first 3 months after colorectal cancer excision, and to assess whether persistence of RT-PCR positivity after primary colorectal cancer excision was related to tumor stage or locally advanced and metastatic disease. MethodsSystemic venous blood was collected from patients with colorectal cancer before and at intervals up to 12 weeks after surgery. RNA was extracted from the mononuclear cell fraction of the blood samples and subjected to RT-PCR using specific primers for carcinoembryonic antigen mRNA and cytokeratin-20 mRNA. Healthy individuals with no history of cancer were used as controls. ResultsThe results of RT-PCR were positive in 81 of 116 patients with colorectal cancer before surgery, with no significant differences in preoperative prevalence by Dukes stage or presence of locally advanced or metastatic disease. There was a significant decrease in the prevalence of RT-PCR positivity at 24 hours after surgery compared with before surgery. On subgroup analysis by Dukes stage, only the decrease in Dukes A and B patients reached significance. Seven of the 143 controls were RT-PCR positive.

Galectin-3 is a Mr 30,000 protein with carbohydrate-binding specificity for type I and II ABH blood group epitopes and polylactosamine glycans expressed on cell surface and extracellular matrix glycoproteins such as laminin. Cell lines propagated from human normal mammary epithelia and from benign or infiltrating components of primary breast tumours express low levels of galectin-3 in the cytoplasm. However, galectin-3 when added exogenously in solution or when bound within a three-dimensional matrix markedly enhanced the migration of the primary tumour cell lines through a Matrigel barrier. Galectin-3 expression in the cytoplasm and intercellularly on surface membranes was greatly increased in cell lines propagated from malignant ascites and pleural effusions of late stage breast cancer. These cell lines were non-invasive in the Matrigel assay and exogenous galectin-3 had no enhancing effect on invasiveness. These results suggest that galectin-3 could play multiple roles in cell metastasis at an early invasive stage by acting in a paracrine manner to stimulate cell migration through an extracellular matrix, and in later stage cancers in synergy with other mediators of cell-cell aggregation. However, endogenous galectin-3 expression in human breast cancers is not correlated directly with their invasive potential in vitro.

Alteration in cell surface carbohydrates, and in particular cell surface sialylation, have been known to occur during oncogenic transformation. To examine the basis for such changes, we have transformed the rat fibroblast cell line FR3T3 with the oncogenes c-Ha-ras EJ, v-mycOK10, v-src, polyoma virus middle T or the transforming bovine papilloma virus 1 (BPV1), and measured the sialytransferase activities of cellular lysates. We found that, in contrast to all other oncogenes examined, c-Ha-ras induced a striking increase in beta-galactoside alpha-2,6-sialytransferase (Gal alpha-2,6-ST) activity in FR3T3 cells. This increase in Gal alpha-2,6-ST activity resulted in the increased expression of cell surface alpha-2,6-linked sialic acid on cell surface glycoconjugates, as determined by cell staining with fluorescein-labelled Sambucus nigra agglutinin. Immunoprecipitation and immunofluorescence experiments revealed that the increase in Gal alpha-2,6-ST activity was due to an elevation of expression of the enzyme. Moreover, Northern analysis suggested that the increased expression of this enzyme was the result of an increase in the steady-state mRNA level of the Gal alpha-2,6-ST gene. These results support the notion that alterations seen in cell surface glycoconjugates during oncogenic transformation can be the result of altered expression of glycosyltransferases.

Through cloning experiments with the FRras EJ4 cell line, previously described to exhibit a Sambucus nigra agglutinin (SNA)+ phenotype, three clones with a SNA- phenotype were isolated. All the selected SNA+ and SNA- clones expressed the ras oncoprotein and cloned in soft agar with the same efficiency. We were interested in studying the adhesion and invasion properties of the FRras cells presenting a SNA + or - phenotype. They were first compared in their biochemical properties and we found that FRras SNA- were characterized by a low alpha-2,6-sialylation of their cell surface glycoproteins and a low beta-galactoside alpha-2,6 sialytransferase activity. Using in vitro invasion assays, FRras cells exhibiting a low alpha-2,6-sialylation on their surface were found to have a low invasive potential compared to their counterpart SNA+. FRras SNA-clones exhibit a different morphology from that of FRras SNA+ clones. Moreover, homotypic aggregation assays indicated that FRras SNA- were more cohesive with each other and adhesion assays showed that they were more adhesive to fibronectin.