Bulky glycocalyx drives cancer invasiveness by modulating substrate-specific adhesion.

The majority of the eukaryotic cell surface is decorated with a layer of membrane-attached polysaccharides and glycoproteins collectively referred to as the glycocalyx. While the formation of a bulky glycocalyx has been associated with the cancer progression, the mechanisms by which the glycocalyx regulates cancer invasiveness are incompletely understood. We address this question by first documenting subtype-specific expression of the major glycocalyx glycoprotein Mucin-1 (MUC1) in breast cancer patient samples and breast cancer cell lines. Strikingly, glycocalyx disruption led to inhibition of 2D motility, loss of 3D invasion, and reduction of clonal scattering in breast cancer cells at the population level. Tracking of 2D cell motility and 3D invasiveness of MUC1-based sorted subpopulations revealed the fastest motility and invasiveness in intermediate MUC1-expressing cells, with glycocalyx disruption abolishing these effects. While differential sensitivity in 2D motility is attributed to a nonmonotonic dependence of focal adhesion size on MUC1 levels, higher MUC1 levels enhance 3D invasiveness via increased traction generation. In contrast to inducing cell rounding on collagen-coated substrates, high MUC1 level promotes cell adhesion and confers resistance to shear flow on substrates coated with the endothelial surface protein E-selectin. Collectively, our findings illustrate how MUC1 drives cancer invasiveness by differentially regulating cell-substrate adhesion in a substrate-dependent manner.