Enhancement of artificial juxtacrine stimulation of insulin by co-immobilization with adhesion factors

Insulin was co-immobilized with a cell adhesion factor--fibronectin or polyallylamine--on a surface-hydrolyzed poly(methyl methacrylate) film. Chinese hamster ovary cells overexpressing human insulin receptors were cultured on the film in the absence of serum or soluble proteins. While insulin immobilization did not affect cell adhesion, insulin immobilized on fibronectin-immobilized film reduced the adhesion. Addition of the tetrapeptide Arg-Gly-Asp-Ser (RGDS) inhibited cell adhesion onto fibronectin-immobilized films while cell adhesion onto polyallylamine-immobilized films was not inhibited by RGDS. Small amounts of immobilized insulin (1 to 10% of the amount of free insulin required to achieve cell growth acceleration) were sufficient to stimulate cell proliferation. The maximal mitogenic effect of immobilized insulin was greater than that of free insulin. In addition, co-immobilization with the adhesion factor remarkably enhanced the mitogenic effect. The phosphorylation of the receptor with free insulin attained the maximum degree very rapidly but ceased quickly. On the other hand, the receptor phosphorylation with immobilized insulin was accompanied by a longer induction period and lasted a longer period of time than that with free insulin. Insulin co-immobilization on fibronectin or polyallylamineimmobilized films reduced the induction period by enhancement of cell adhesion. The early and long-lasting receptor activation might have been caused by the greater mitogenic effect of co-immobilized biosignaling polypeptides.