Fibronectin facilitates adhesion of K562 leukemic cells normally growing in suspension to cationic surfaces

The role of protein adsorption in the forced adhesive growth of K562 leukemic cells onto a cationic surface composed of polylysine was investigated. Numerous studies have demonstrated that adhesion in anchorage-dependent cells is mediated in vitro by adsorption of serum proteins [particularly proteins of the extracellular matrix (ECM) such as fibronectin and vitronectin] present in the growth medium. Specifically, adhesion has been shown to occur when ECM proteins attach to the substratum and act as ligands for specific receptors located on the surface of cells. K562 cells are human erythroleukemic cells that normally grow in suspension. These cells are not involved in the same cell adhesion processes as anchorage-dependent cells and do not need to be attached to ECM proteins in order to survive and grow. Thus, with these systems, it is possible to better determine the role of protein adsorption in the adhesion of cells, growing in suspension such as blood cells, onto charged surfaces. The results presented show that adhesion of K562 cells onto the positively charged polylysine surface in the presence of serum is mediated through specific interactions between fibronectin receptors present on K562 cells and fibronectin adsorbed onto that cationic surface. Specifically, determination of cell adhesion under different experimental conditions indicates that nonspecific charge interactions do not take place directly between the cells and polylysine, but rather take place between polylysine and fibronectin, which adsorbs onto the cationic polymer. In addition, flow cytometric analyses reveal that only fibronectin receptors are present on these cells and, consequently, only fibronectin can be responsible for the actual adhesion of these cells onto the cationic surface. In view of the data presented, the possibility should be considered that ECM components adsorbed onto surfaces with specific charges and/or belonging to certain functional groups are involved in structural and functional modifications in cells. These cells grow in suspension and are normally not involved in adhesion phenomena, though these components should be considered. These considerations should be made especially when designing biomaterials that can modulate the response of cells growing in suspension, such as blood cells, and also in tissue engineering of blood substitutes.