Requirement of both mucins and proteoglycans in cell-cell dissociation and invasiveness of colon carcinoma HT-29 cells

Human colon carcinomas are characterized by an aberrant expression of mucins, which in some case leads to an abundant presence of mucus such as in mucinous and signet ring cell carcinomas. Cellular cloning of the human colon carcinoma cell line HT-29 (HT-29 STD), which is mainly composed of undifferentiated cells, yielded a highly mucin-secreting variant (HT-29 5M21). The latter cloned cells cultured on plastic display a polarized organization with an apical secretion of MUC5AC mucin (Lesuffleur et al., Int J Cancer 1998;76:383-92.). Our aim was to study these 2 cell-types as for the invasive and adhesive properties with regard to the function of E-cadherin. HT-29 STD cells were noninvasive in collagen type I, whereas HT-29 5M21 cells were invasive, and the latter behavior was connected to a loss of function of E-cadherin. Likewise, HT-29 5M21 cells were characterized by a cell-cell adhesion independent of E-cadherin, in contrast to the E-cadherin dependent cell-cell adhesion of HT-29 STD cells. Immunofluorescence of HT-29 5M21 cells cultured on collagen type I showed the disappearance of the polarized organization, with a redistribution of apical mucins to the entire cell surface. Treatment of HT-29 5M21 cells by 1-benzyl-2-acetamido-2-deoxy-alpha-D-galactopyranoside (GalNAcalpha-O-bn) or by beta-D-xyloside revealed that both mucins and proteoglycans were involved in the loss of E-cadherin function. The use of specific antibodies allowed to show that MUC5AC, MUC1 and heparan sulfate proteoglycans cooperated in the formation of a biological inhibitory complex towards the function of E-cadherin in this invasive HT-29 clone.