ABSTRACT
Fucoidans inhibit tumour cell adhesion to various substrata, but their mechanisms of action are not fully understood. Using 3H-fucoidan, we observed that fucoidan binds to fibronectin, this binding being saturable and sensitive to ionic strength and pH. The interaction occurred on at least four different sites along the polypeptide chain, two of them being the heparin-binding sequences. Moreover, when MDA-MB-231 tumour cells were exposed to DTAF-fucoidan, internalization occurred and punctuated vesicles were observed in the perinuclear region. The treated cells also showed a different morphology with a cytoskeleton devoid of vinculin and a reorganiztion of the repartition of the integrin-alpha5 subunit on the cell surface. Based on these data, we hypothesize that fucoidan inhibits the adhesion of MDA-MB-231 cells to fibronectin i) by blocking the protein's heparin- and cell-binding domains, ii) by modulating the reorganization of the integrin alpha5 subunit and iii) by down-regulating the expression of vinculin.
Subject(s)
Adenocarcinoma/pathology , Antineoplastic Agents/pharmacology , Breast Neoplasms/pathology , Fibronectins/metabolism , Polysaccharides/pharmacology , Actins/metabolism , Adenocarcinoma/metabolism , Antineoplastic Agents/metabolism , Breast Neoplasms/metabolism , Cell Adhesion/drug effects , Cell Line, Tumor , Cell Membrane/metabolism , Cell Membrane/pathology , Dose-Response Relationship, Drug , Extracellular Matrix/metabolism , Extracellular Matrix/pathology , Humans , Integrin alpha5/biosynthesis , Integrin beta1/biosynthesis , Polysaccharides/metabolismABSTRACT
Fucans are sulphated polysaccharides extracted from brown seaweed, which display a wide scale of activities including inhibition of tumour cell invasion. Like several sulphated polysaccharides, they have been shown to be potent inhibitors of experimental metastasis. However, their mechanism of action is not fully understood Using standard adhesion and chemoinvasion assays, we demonstrated that fucans can inhibit MDA-MB231 cell invasion through matrigel. This effect is correlated with a direct interaction of the fucans with laminin that leads to an inhibition of cell adhesion. It depends upon the sulphate content and the molecular weight of the fucans. Moreover, chromogenic assays allowed us to bring to the fore an increase of u-PA activity in the MDA-MB231 culture medium when tests were performed in the presence of fucans. Since tumour cell adhesion is a prerequisite step in the invasion process, our results suggest that the inhibitory effect of fucans on MDA-MB231 cell invasion is caused, at least in part, by the blockage of tumour cell adhesion to the extracellular matrix and by the increase of the proteolysis of the extracellular membrane.
