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 leukem ic cells onto a cationic surface composed of polylysine was investigated. N umerous studies have demonstrated that adhesion in anchorage-dependent cell s is mediated in vitro by adsorption of serum proteins [particularly protei ns of the extracellular matrix (ECM) such as fibronectin and vitronectin] p resent in the growth medium. Specifically, adhesion has been shown to occur hen ECM proteins attach to the substratum and act as ligands for specific receptors located on the surface of cells. K562 cells are human erythroleuk emic cells that normally grow in suspension. These cells are not involved i n 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, wit h these systems, it is possible to better determine the role of protein ads orption in the adhesion of cells, growing in suspension such as blood cells , onto charged surfaces. The results presented show that adhesion of K562 c ells onto the positively charged polylysine surface in the presence of seru m is mediated through specific interactions between fibronectin receptors p resent on K562 cells and fibronectin adsorbed onto that cationic surface. S pecifically, determination of cell adhesion under different experimental co nditions indicates that nonspecific charge interactions do not take place d irectly between the cells and polylysine, but rather take place between pol ylysine and fibronectin, which adsorbs onto the cationic polymer. In additi on, flow cytometric analyses reveal that only fibronectin receptors are pre sent on these cells and, consequently, only fibronectin can be responsible for the actual adhesion of these cells onto the cationic surface. In view o f the data presented, the possibility should be considered that ECM compone nts adsorbed onto surfaces with specific charges and/or belonging to certai n 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 con siderations 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. (C) 2001 John Wiley & Sons, inc.