MUC1 expression prevents and MUC1-galectin-3 interaction promotes homotypic aggregation of human colon cancer cells. A: Cell surface staining with B27.29 anti-MUC1 antibody followed by analysis with flow cytometry shows higher cell surface MUC1 expression in HT29-5F7 than in HT29 cells. B: Representative flow cytometry plots from the aggregation assessment of human colon cancer HT29-5F7 and HT29 cells in the presence or absence of 1 μg/ml recombinant galectin-3. The top right (blue) in the bivariate correlation plot are the cell population containing both DiO- and Dil-labelled cells that are defined in this study as cell aggregates. C: The more strongly MUC1-expressing HT29-5F7 cells show less spontaneous cell aggregation than the parental HT29 cells. Data are expressed as mean ± SEM of triplicate determinations from three independent experiments. D: galectin-3 treatment induces a dose-dependent increase of HT29-5F7 but not HT29 cell aggregation. Data are expressed as mean ± SEM of triplicate determinations from four independent experiments. **p < 0.01, ***p < 0.001.