Engineering of a heparin-binding growth factor with heparan sulfate sugar chains

Fibroblast growth factor (FGF) family members cannot exert their biological activity in the absence of their interaction with heparan sulfate or heparin in the vicinity of their receptors. Cell surface proteoglycans are thought to serve such heparan sulfate sugar chains in physiological conditions. In an attempt to utilize this interaction for engineering FGFs, our aim was to construct an FGF neoglycoprotein with heparan sulfate sugar chains. A novel chimeric protein was designed in which part of syndecan-4 containing glycosaminoglycan (GAG) attachment sites was ligated to the N-terminus of FGF-1. When the cDNA encoding the protein was transfected into CHO-K1 cells, the chimeric protein was secreted into the conditioned medium with GAG modifications. One fraction of the resultant chimeric protein had acquired the ability to stimulate DNA synthesis of the target cells in the absence of exogenous or cellular heparin/heparan sulfate, indicating that the biological function of FGF-1 was successfully modified by this approach. Furthermore in artificial wound fluid which mimics inflammation, the activity of this protein was highly augmented due to the generation of small HS fragments which act as activators. These results suggest that engineering heparin-binding proteins with heparan sulfate sugar chains is highly effective.