Hepatocyte adhesion on plastic. Different mechanisms for serum- and fibronectin-mediated adhesion

Hepatocytes adhere well on plastic in the presence of serum or fibronectin and subsequent spreading is not prevented when protein synthesis was blocked by cycloheximide. Protein synthesis-independent spreading was also observed in cultures containing serum depleted of fibronectin by affinity chromatography. This indicates that serum-mediated adhesion is independent of fibronectin and suggests the existence of an adhesion factor other than fibronectin in serum. The involvement of different membrane components for fibronectin- and serum-mediated adhesion was demonstrated by experiments where the different adhesion-inhibiting activities of antisera raised against plasma membranes of rat liver and Morris hepatoma 7777 (Neumeier et al., FEBS lett 168 (1984) 241-244) were used. Whereas anti-liver antibodies inhibited both types of adhesion, anti-hepatoma antibodies were only able to prevent fibronectin-mediated adhesion. This indicates again that two different mechanisms are responsible for fibronectin- and serum-mediated adhesion. Fractionation of fetal calf serum (FCS) by size exclusion HPLC revealed that proteins of molecular weights of 60-80 kD promoted attachment and spreading of hepatocytes. Spreading was not perturbated by anti-hepatoma antibodies, indicating that an adhesion factor of 60-80 kD is responsible for serum-mediated adhesion. 'Serum-spreading factor', also called vitronectin, from human plasma has been described as having a similar molecular weight. The purified factor was found to mediate hepatocyte adhesion which was not inhibited by anti-hepatoma antibodies. This suggests that serum-mediated adhesion depends on an adhesion factor present in FCS, which is similar to or identical with vitronectin.